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Philae
Illustration of Philae
Mission typeComet lander
OperatorEuropean Space Agency / DLR
COSPAR ID2004-006C Edit this at Wikidata
Websitewww.esa.int/rosetta
Mission durationPlanned: 1–6 weeks
Active: 12–14 November 2014
Hibernation: 15 November 2014 – 13 June 2015
Spacecraft properties
ManufacturerCNES
DLR
ASI
Launch mass100 kg (220 lb)[1]
Payload mass21 kg (46 lb)[1]
Dimensions1 × 1 × 0.8 m (3.3 × 3.3 × 2.6 ft)[1]
Power32 watts at 3 AU[2]
Start of mission
Launch date2 March 2004, 07:17 (2004-03-02UTC07:17) UTC
RocketAriane 5G+ V-158
Launch siteKourou ELA-3
ContractorArianespace
End of mission
Last contact9 July 2015, 18:07 (2015-07-09UTC18:08) UTC
67P/Churyumov–Gerasimenko lander
Landing date12 November 2014, 17:32 UTC[3]
Landing siteAbydos[4]

Philae (/ˈfaɪliː/[6] or /ˈfiːleɪ/[7]) was a robotic European Space Agency lander that accompanied the Rosetta spacecraft[8][9] until it separated to land on comet 67P/Churyumov–Gerasimenko, ten years and eight months after departing Earth.[10][11][12] On 12 November 2014, Philae touched down on the comet, but it bounced when its anchoring harpoons failed to deploy and a thruster designed to hold the probe to the surface did not fire.[13] After bouncing off the surface twice, Philae achieved the first-ever "soft" (nondestructive) landing on a comet nucleus,[14][15][16] although the lander's final, uncontrolled touchdown left it in a non-optimal location and orientation.[17]

Despite the landing problems, the probe's instruments obtained the first images from a comet's surface.[18] Several of the instruments on Philae made the first in-situ analysis of a comet nucleus, sending back data regarding the composition of the surface and outgassing from the subsurface.[19] In October 2020, scientific journal Nature published an article revealing what Philae had discovered while it was operational on the surface of 67P/Churyumov–Gerasimenko.[20]

On 15 November 2014 Philae entered safe mode, or hibernation, after its batteries ran down due to reduced sunlight and an off-nominal spacecraft orientation at the crash site. Mission controllers hoped that additional sunlight on the solar panels might be sufficient to reboot the lander.[21] Philae communicated sporadically with Rosetta from 13 June to 9 July 2015,[22][23][24] but contact was then lost. The lander's location was known to within a few tens of metres but it could not be seen. Its location was finally identified in photographs taken by Rosetta on 2 September 2016 as the orbiter was sent on orbits closer to the comet. The now-silent Philae was lying on its side in a deep crack in the shadow of a cliff. Knowledge of its location would help in interpretation of the images it had sent.[4][25] On 30 September 2016, the Rosetta spacecraft ended its mission by crashing in the comet's Ma'at region.[26]

The lander is named after the Philae obelisk, which bears a bilingual inscription and was used along with the Rosetta Stone to decipher Egyptian hieroglyphs. Philae was monitored and operated from DLR's Lander Control Center in Cologne, Germany, supported by the CNES's SONC in Toulouse, France.[27]

Mission

[edit]
Video report by the German Aerospace Centre about Philae's landing mission. (10 min, English, in 1080p HD)

Philae's mission was to land successfully on the surface of a comet, attach itself, and transmit data about the comet's composition. The Rosetta spacecraft and Philae lander were launched on an Ariane 5G+ rocket from French Guiana on 2 March 2004, 07:17 UTC, and travelled for 3,907 days (10.7 years) to Churyumov–Gerasimenko. Unlike the Deep Impact probe, which by design struck comet Tempel 1's nucleus on 4 July 2005, Philae is not an impactor. Some of the instruments on the lander were used for the first time as autonomous systems during the Mars flyby on 25 February 2007. CIVA, one of the camera systems, returned some images while the Rosetta instruments were powered down, while ROMAP took measurements of the Martian magnetosphere. Most of the other instruments needed contact with the surface for analysis and stayed offline during the flyby. An optimistic estimate of mission length following touchdown was "four to five months".[28]

Scientific goals

[edit]

The goals of the scientific mission have been summarised as follows:

"The scientific goals of its experiments focus on elemental, isotopic, molecular and mineralogical composition of the cometary material, the characterization of physical properties of the surface and subsurface material, the large-scale structure and the magnetic and plasma environment of the nucleus. In particular, surface and sub-surface samples will be acquired and sequentially analyzed by a suite of instruments. Measurements will be performed primarily during descent and along the first five days following touch-down. "[29]

Landing and surface operations

[edit]
Depiction of Philae on Churyumov-Gerasimenko

Philae remained attached to the Rosetta spacecraft after rendezvousing with Churyumov–Gerasimenko on 6 August 2014. On 15 September 2014, ESA announced "Site J" on the smaller lobe of the comet as the lander's destination.[30] Following an ESA public contest in October 2014, Site J was renamed Agilkia in honour of Agilkia Island.[31]

A series of four go/no-go checks were performed on 11–12 November 2014. One of the final tests before detachment from Rosetta showed that the lander's cold-gas thruster was not working correctly, but the "go" was given anyway, as it could not be repaired.[32][33] Philae detached from Rosetta on 12 November 2014 at 08:35 UTC SCET.[34][35]

Landing events

[edit]
Rosetta signal received at ESOC in Darmstadt, Germany (20 January 2014)

Philae's landing signal was received by Earth communication stations at 16:03 UTC after a 28-minute delay.[1][36] Unknown to mission scientists at that time, the lander had bounced. It began performing scientific measurements while slowly moving away from the comet and coming back down, confusing the science team.[37] Further analysis showed that it bounced twice.[38][3]

Philae's first contact with the comet occurred at 15:34:04 UTC SCET.[39] The probe rebounded off the comet's surface at 38 cm/s (15 in/s) and rose to an altitude of approximately 1 km (0.6 mi).[3] For perspective, had the lander exceeded about 44 cm/s (17 in/s), it would have escaped the comet's gravity.[40] After detecting the touchdown, Philae's reaction wheel was automatically powered off, resulting in its momentum being transferred back into the lander. This caused the vehicle to begin rotating every 13 seconds.[39] During this first bounce, at 16:20 UTC SCET, the lander is thought to have struck a surface prominence, which slowed its rotation to once every 24 seconds and sent the craft tumbling.[39][41] Philae touched down a second time at 17:25:26 UTC SCET and rebounded at 3 cm/s (1.2 in/s).[3][39] The lander came to a final stop on the surface at 17:31:17 UTC SCET.[39] It sits in rough terrain, apparently in the shadow of a nearby cliff or crater wall, and is canted at an angle of around 30 degrees, but is otherwise undamaged.[42] Its final location was determined initially by analysis of data from CONSERT in combination with the comet shape model based on images from the Rosetta orbiter,[43] and later precisely by direct imaging from Rosetta.[4]

An analysis of telemetry indicated that the initial impact was softer than expected,[44] that the harpoons had not deployed, and that the thruster had not fired.[45][13] The harpoon propulsion system contained 0.3 grams of nitrocellulose, which was shown by Copenhagen Suborbitals in 2013 to be unreliable in a vacuum.[46]

Operations and communication loss

[edit]
Philae's intended landing site Agilkia (Site J)

The primary battery was designed to power the instruments for about 60 hours.[17] ESA expected that a secondary rechargeable battery would be partially filled by the solar panels attached to the outside of the lander, but the limited sunlight (90 minutes per 12.4-hour comet day[47]) at the actual landing site was inadequate to maintain Philae's activities, at least in this phase of the comet's orbit.[48][49]

On the morning of 14 November 2014, the battery charge was estimated to be only enough for continuing operations for the remainder of the day. After first obtaining data from instruments whose operation did not require mechanical movement, comprising about 80% of the planned initial science observations, both the MUPUS soil penetrator and the SD2 drill were commanded to deploy. Subsequently, MUPUS data[50] as well as COSAC and Ptolemy data were returned. A final set of CONSERT data was also downlinked towards the end of operations. During the evening's transmission session, Philae was raised by 4 centimetres (1.6 in) and its body rotated 35 degrees to more favourably position the largest solar panel to capture the most sunlight in the future.[51][52] Shortly afterwards, electrical power dwindled rapidly and all instruments were forced to shut down. The downlink rate slowed to a trickle before coming to a stop.[47] Contact was lost on 15 November at 00:36 UTC.[53]

The German Aerospace Center's lander manager Stephan Ulamec stated:

Prior to falling silent, the lander was able to transmit all science data gathered during the First Science Sequence ... This machine performed magnificently under tough conditions, and we can be fully proud of the incredible scientific success Philae has delivered.[53]

Instrument results

[edit]

Data from the SESAME instrument determined that, rather than being "soft and fluffy" as expected, Philae's first touchdown site held a large amount of water ice under a layer of granular material about 25 cm (9.8 in) deep.[54] It found that the mechanical strength of the ice was high and that cometary activity in that region was low. At the final landing site, the MUPUS instrument was unable to hammer very far into the comet's surface, despite power being gradually increased. This area was determined to have the consistency of solid ice[55][56] or pumice.[57]

In the atmosphere of the comet, the COSAC instrument detected the presence of molecules containing carbon and hydrogen. Soil elements could not be assessed, because the lander was unable to drill into the comet surface, likely due to hard ice.[58] The SD2 drill went through the necessary steps to deliver a surface sample to the COSAC instrument,[55] but nothing entered the COSAC ovens.[59]

Upon Philae's first touchdown on the comet's surface, COSAC measured material at the bottom of the vehicle, which was disturbed by the landing, while the Ptolemy instrument measured material at the top of the vehicle. Sixteen organic compounds were detected, four of which were seen for the first time on a comet, including acetamide, acetone, methyl isocyanate and propionaldehyde.[60][61][62]

Reawakening and subsequent loss of communication

[edit]
Comet Churyumov–Gerasimenko in March 2015 as imaged by Rosetta in true colour

On 13 June 2015 at 20:28 UTC, ground controllers received an 85-second transmission from Philae, forwarded by Rosetta, indicating that the lander was in good health and had sufficiently recharged its batteries to come out of safe mode.[22][63] Philae sent historical data indicating that although it had been operating earlier than 13 June 2015, it had been unable to contact Rosetta before that date.[22] The lander reported that it was operating with 24 watts of electrical power at −35 °C (−31 °F).[63]

A new contact between Rosetta and Philae was confirmed on 19 June 2015.[64] The first signal was received on the ground from Rosetta at 13:37 UTC, while a second signal was received at 13:54 UTC. These contacts lasted about two minutes each and delivered additional status data.[64] By 26 June 2015, there had been a total of seven intermittent contacts between the lander and orbiter.[65] There were two opportunities for contact between the two spacecraft each Earth day, but their duration and quality depended on the orientation of the transmitting antenna on Philae and the location of Rosetta along its trajectory around the comet. Similarly, as the comet rotated, Philae was not always in sunlight and thus not always generating enough power via its solar panels to receive and transmit signals. ESA controllers continued to try to establish a stable contact duration of at least 50 minutes.[65]

Had Philae landed at the planned site of Agilkia in November 2014, its mission would probably have ended in March 2015 due to the higher temperatures of that location as solar heating increased.[66] As of June 2015, Philae's key remaining experiment was to drill into the comet's surface to determine its chemical composition.[67] Ground controllers sent commands to power up the CONSERT radar instrument on 5 July 2015, but received no immediate response from the lander. Confirmation was eventually received on 9 July, when the lander transmitted measurement data from the instrument.[68]

Immediately after its reawakening, housekeeping data suggested that the lander's systems were healthy, and mission control uploaded commands for Rosetta to establish a new orbit and nadir so as to optimize communications, diagnostics, and enable new science investigations with Philae.[66][69][70] However, controllers had difficulties establishing a stable communications connection with the lander. The situation was not helped by the need to keep Rosetta at a greater and safer distance from the comet as it became more active.[71] The last communication was on 9 July 2015,[24] and mission controllers were unable to instruct Philae to carry out new investigations.[72][73] Subsequently, Philae failed to respond to further commands, and by January 2016, controllers acknowledged no further communications were likely.[74]

On 27 July 2016, at 09:00 UTC, ESA switched off the Electrical Support System Processor Unit (ESS) onboard Rosetta, making further communications with Philae impossible.[75][76]

Location

[edit]

The lander was located on 2 September 2016 by the narrow-angle camera aboard Rosetta as it was slowly making its descent to the comet.[4] The search for the lander had been on-going during the Rosetta mission, using telemetry data and comparison of pictures taken before and after the lander's touchdown, looking for signs of the lander's specific reflectivity.[77]

The search area was narrowed down to the most promising candidate, which was confirmed by a picture taken at a distance of 2.7 km (1.7 mi), clearly showing the lander. The lander sits on its side wedged into a dark crevice of the comet, explaining the lack of electrical power and proper communication with the probe.[4] Knowing its exact location provides information needed to put Philae's two days of science into proper context.[4]

Design

[edit]
Rosetta and Philae

The lander was designed to deploy from the main spacecraft body and descend from an orbit of 22.5 kilometres (14 mi) along a ballistic trajectory.[78] It would touch down on the comet's surface at a velocity of around 1 metre per second (3.6 km/h; 2.2 mph).[79] The legs were designed to dampen the initial impact to avoid bouncing as the comet's escape velocity is only around 1 m/s (3.6 km/h; 2.2 mph),[80] and the impact energy was intended to drive ice screws into the surface.[81] Philae was to then fire a harpoon into the surface at 70 m/s (250 km/h; 160 mph) to anchor itself.[82][83] A thruster on top of Philae was to have fired to lessen the bounce upon impact and to reduce the recoil from harpoon firing.[32] During the landing, the harpoons did not fire and the thruster failed to operate, leading to a multiple-contact landing.[45][13]

Communications with Earth used the Rosetta orbiter as a relay station to reduce the electrical power needed. The mission duration on the surface was planned to be at least one week, but an extended mission lasting months was considered possible.[citation needed]

The main structure of the lander is made from carbon fiber, shaped into a plate maintaining mechanical stability, a platform for the science instruments, and a hexagonal "sandwich" to connect all the parts. The total mass is about 100 kilograms (220 lb). Its exterior is covered with solar cells for power generation.[11]

The Rosetta mission was originally planned to rendezvous with the comet 46P/Wirtanen. A failure in a previous Ariane 5 launch vehicle closed the launch window to reach the comet with the same rocket.[84] It resulted in a change in target to the comet 67P/Churyumov–Gerasimenko.[84] The larger mass of Churyumov–Gerasimenko and the resulting increased impact velocity required that the landing gear of the lander be strengthened.[85]

Spacecraft component Mass[29]: 208 
Structure 18.0 kg 39.7 lb
Thermal control system 3.9 kg 8.6 lb
Power system 12.2 kg 27 lb
Active descent system 4.1 kg 9.0 lb
Reaction wheel 2.9 kg 6.4 lb
Landing gear 10.0 kg 22 lb
Anchoring system 1.4 kg 3.1 lb
Central data management system 2.9 kg 6.4 lb
Telecommunications system 2.4 kg 5.3 lb
Common electronics box 9.8 kg 22 lb
Mechanical support system, harness, balancing mass 3.6 kg 7.9 lb
Scientific payload 26.7 kg 59 lb
Sum 97.9 kg 216 lb

Power management

[edit]

Philae's power management was planned for two phases. In the first phase, the lander operated solely on battery power. In the second phase, it was to run on backup batteries recharged by solar cells.[28]

The power subsystem comprises two batteries: a non-rechargeable primary 1000 watt-hour battery to provide power for the first 60 hours and a secondary 140 watt-hour battery recharged by the solar panels to be used after the primary is exhausted. The solar panels cover 2.2 square metres (24 sq ft) and were designed to deliver up to 32 watts at a distance of 3 AU from the Sun.[2]

Instruments

[edit]
Philae's instruments

The science payload of the lander consists of ten instruments totalling 26.7 kilograms (59 lb), making up just over one quarter of the mass of the lander.[29]

APXS
The Alpha Particle X-ray Spectrometer detects alpha particles and X-rays, which provide information on the elemental composition of the comet's surface.[86] The instrument is an improved version of the APXS on the Mars Pathfinder.
CIVA
The Comet Nucleus Infrared and Visible Analyser[87] (sometimes given as ÇIVA[88]) is a group of seven identical cameras used to take panoramic pictures of the surface plus a visible-light microscope and an infrared spectrometer. The panoramic cameras (CIVA-P) are arranged on the sides of the lander at 60° intervals: five mono imagers and two others making up a stereo imager. Each camera has a 1024×1024 pixel CCD detector.[89] The microscope and spectrometer (CIVA-M) are mounted on the base of the lander, and are used to analyse the composition, texture and albedo (reflectivity) of samples collected from the surface.[90]
CONSERT
The Comet Nucleus Sounding Experiment by Radiowave Transmission used electromagnetic wave propagation to determine the comet's internal structure. A radar on Rosetta transmitted a signal through the nucleus to be received by a detector on Philae.[91][92]
COSAC
The Cometary Sampling and Composition instrument is a combined gas chromatograph and time-of-flight mass spectrometer to perform analysis of soil samples and determine the content of volatile components.[93][94]
MUPUS
The Multi-Purpose Sensors for Surface and Sub-Surface Science instrument measured the density, thermal and mechanical properties of the comet's surface.[95]
Ptolemy
An instrument measuring stable isotope ratios of key volatiles on the comet's nucleus.[96][97] Parts of the instrument were manufactured by the Special Techniques Group at UKAEA.[98]
ROLIS
The Rosetta Lander Imaging System is a CCD camera used to obtain high-resolution images during descent and stereo panoramic images of areas sampled by other instruments.[99] The CCD detector consists of 1024×1024 pixels.[100]
ROMAP
The Rosetta Lander Magnetometer and Plasma Monitor is a magnetometer and plasma sensor to study the nucleus's magnetic field and its interactions with the solar wind.[101]
SD2
The Sampling, Drilling and Distribution system obtains soil samples from the comet and transfers them to the Ptolemy, COSAC, and CIVA instruments for in-situ analysis.[102] SD2 contains four primary subsystems: drill, ovens, carousel, and volume checker.[103][104] The drill system, made of steel and titanium, is capable of drilling to a depth of 230 mm (9.1 in), deploying a probe to collect samples, and delivering samples to the ovens.[105] There are a total of 26 platinum ovens to heat samples—10 medium temperature ovens at 180 °C (356 °F) and 16 high temperature ovens at 800 °C (1,470 °F)—and one oven to clear the drill bit for reuse.[106] The ovens are mounted on a rotating carousel that delivers the active oven to the appropriate instrument.[107] The electromechanical volume checker determines how much material was deposited into an oven, and may be used to evenly distribute material on CIVA's optical windows.[108] Development of SD2 was led by the Italian Space Agency with contributions by prime contractor Tecnospazio S.p.A. (now Selex ES S.p.A.) in charge of the system design and overall integration; the Italian company Tecnomare S.p.A., owned by Eni S.p.A., in charge of the design, development, and testing of the drilling/sampling tool and the volume checker; Media Lario; and Dallara.[104] The instrument's principal investigator is Amalia Ercoli-Finzi (Politecnico di Milano).[109]
SESAME
The Surface Electric Sounding and Acoustic Monitoring Experiments used three instruments to measure properties of the comet's outer layers. The Cometary Acoustic Sounding Surface Experiment (CASSE) measures the way in which sound travels through the surface. The Permittivity Probe (PP) investigates its electrical characteristics, and the Dust Impact Monitor (DIM) measures dust falling back to the surface.[110]

Analysis of comet

[edit]

On 28 October 2020, it was reported that Philae had discovered, among other things, "low-strength primitive ice inside cometary boulders."[20] This also included primitive water ice from the comet's estimated formation 4.5 billion years prior.[20] This occurred primarily at the site of Philae's second touchdown onto the 67P/Churyumov–Gerasimenko, where the spacecraft successfully produced four distinct surface contacts on two adjoining cometary boulders.[20] Philae was also able to drill 25 centimetres (9.8 in) into the comet's boulder ice.[20]

International contributions

[edit]
Austria
The Austrian Space Research Institute developed the lander's anchor and two sensors within MUPUS, which are integrated into the anchor tips.[111]
Belgium
The Belgian Institute for Space Aeronomy (BIRA) cooperated with different partners to build one of the sensors (DFMS) of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument.[112][113] The Belgian Institute for Space Aeronomy (BIRA) and Royal Observatory of Belgium (ROB) provided information about the space weather conditions at Rosetta to support the landing of Philae. The main concern was solar proton events.[114]
Canada
Two Canadian companies played a role in the mission. SED Systems, located on the University of Saskatchewan campus in Saskatoon, built three ground stations that were used to communicate with the Rosetta spacecraft.[115] ADGA-RHEA Group of Ottawa provided MOIS (Manufacturing and Operating Information Systems) software which supported the procedures and command sequences operations software.[116]
Finland
The Finnish Meteorological Institute provided the memory of the Command, Data and Management System (CDMS) and the Permittivity Probe (PP).[117]
France
The French Space Agency, in collaboration with various French scientific institutes (IAS, SA, LPG, LISA), provided the system's overall engineering, radiocommunications, battery assembly, CONSERT, CIVA and the ground segment (overall engineering and development/operation of the Scientific Operation & Navigation Centre).[2]
Germany
The German Space Agency (DLR) has provided the structure, thermal subsystem, flywheel, the Active Descent System (procured by DLR but made in Switzerland),[118] ROLIS, downward-looking camera, SESAME, acoustic sounding and seismic instrument for Philae. It has also managed the project and did the level product assurance. The University of Münster built MUPUS (it was designed and built in Space Research Centre of Polish Academy of Sciences[119]) and the Braunschweig University of Technology the ROMAP instrument. The Max Planck Institute for Solar System Research made the payload engineering, eject mechanism, landing gear, anchoring harpoon, central computer, COSAC, APXS and other subsystems. The institute has led development and construction of COSAC and DIM, a part of SESAME, as well as contributed to the deveplopment and construction of ROMAP.[120]
Hungary
The Command and Data Management Subsystem (CDMS) designed in the Wigner Research Centre for Physics of the Hungarian Academy of Sciences jointly with the Space and Ground Facilities Ltd. (a spin-off company of the Wigner Research Centre for Physics).[121][122] The Power Subsystem (PSS) designed in the Department of Broadband Infocommunications and Electromagnetic Theory at Budapest University of Technology and Economics.[123] CDMS is the fault tolerant central computer of the lander, while PSS assures that the power coming from the batteries and solar arrays are properly handled, controls battery charging and manages the onboard power distribution.
Ireland
Captec Ltd., based in Malahide, provided the independent validation of mission critical software (independent software validation facility or SVF)[124] and developed the software for the communications interface between the orbiter and the lander. Captec also provided engineering support to the prime contractor for the launch activities at Kourou.[125][126] Space Technology Ireland Ltd. at Maynooth University has designed, constructed and tested the Electrical Support System Processor Unit (ESS) for the Rosetta mission. ESS stores, transmits and provides decoding for the command streams passing from the spacecraft to the lander and handles the data streams coming back from the scientific experiments on the lander to the spacecraft.[127]
Italy
The Italian Space Agency (ASI) developed the SD2 instrument and the photovoltaic assembly. Italian Alenia Space was involved in the assembly, integration and testing of the probe, as well as several mechanical and electrical ground support equipment. The company also built the probe's S-band and X-band digital transponder, used for communications with Earth.[128]
Netherlands
Moog Bradford (Heerle, The Netherlands) provided the Active Descent System, which guided and propelled the lander down to its landing zone. To accomplish the ADS, a strategic industrial team was formed with Bleuler-Baumer Mechanik in Switzerland.[118]
Poland
The Space Research Centre of the Polish Academy of Sciences built the Multi-Purpose Sensors for Surface and Subsurface Science (MUPUS).[119]
Spain
The GMV Spanish division has been responsible for the maintenance of the calculation tools to calculate the criteria of lighting and visibility necessary to decide the point of landing on the comet, as well as the possible trajectories of decline of the Philae module. Other important Spanish companies or educational institutions that have been contributed are as follows: INTA, Airbus Defence and Space Spanish division, other small companies also participated in subcontracted packages in structural mechanics and thermal control like AASpace (former Space Contact),[129] and the Universidad Politécnica de Madrid.[130]
Switzerland
The Swiss Centre for Electronics and Microtechnology developed CIVA.[131]
United Kingdom
The Open University and the Rutherford Appleton Laboratory (RAL) developed PTOLEMY. RAL also constructed the blankets that kept the lander warm throughout its mission. Surrey Satellites Technology Ltd. (SSTL) constructed the momentum wheel for the lander. It stabilised the module during the descent and landing phases.[2] Manufacturer e2v supplied the CIVA and Rolis camera systems used to film the descent and take images of samples, as well as three other camera systems.[132]

Media coverage

[edit]

The landing was featured heavily in social media, with the lander having an official Twitter account portraying a personification of the spacecraft. The hashtag "#CometLanding" gained widespread traction. A Livestream of the control centres was set up, as were multiple official and unofficial events around the world to follow Philae's landing on Churyumov–Gerasimenko.[133][134] Various instruments on Philae were given their own Twitter accounts to announce news and science results.[135]

[edit]

Vangelis composed the music for the trio of music videos released by ESA to celebrate the first-ever attempted soft landing on a comet by ESA's Rosetta mission.[136][137][138]

On 12 November 2014, the search engine Google featured a Google Doodle of Philae on its home page.[139] On 31 December 2014, Google featured Philae again as part of its New Year's Eve 2014 Doodle.[140]

Online comic author Randall Munroe wrote a live updating strip on his website xkcd on the day of the landing.[141][142]

See also

[edit]

References

[edit]

Further reading

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Philae (spacecraft)

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from Grokipedia
Philae was a robotic lander that formed part of the European Space Agency's (ESA) Rosetta mission, designed to perform the first on a and conduct in-situ scientific analysis of its surface and subsurface. Launched aboard the orbiter on 2 March 2004 from the in , the lander traveled for a decade, including gravity assists from Earth and Mars, before arriving at Comet 67P/Churyumov–Gerasimenko in August 2014. On 12 November 2014, Philae separated from the orbiter and touched down on the comet's surface at the Agilkia site, marking humanity's first controlled landing on a cometary nucleus, though anchoring harpoons failed to deploy, causing the lander to bounce twice and settle in a less illuminated area called Abydos. Weighing 100 kilograms and roughly the size of a , Philae featured a compact, box-shaped with a carbon fiber structure, solar panels covering its sides, and a mechanical anchoring system intended to secure it against the comet's low gravity. It was developed by an international consortium led by the (DLR), with major contributions from the Institute for Solar System Research (MPS) in , the French space agency , and the (ASI), alongside instruments from 10 European countries and . The lander carried 10 scientific instruments, totaling about 21 kilograms, including cameras (CIVA and ROLIS), a gas analyzer (), a surface sampler and drill (SD2), and a multi-purpose sensor for subsurface probing (MUPUS), enabling studies of the comet's composition, structure, and environment. Despite limited restricting its battery life to about 60 hours initially, Philae completed approximately 80% of its planned first science sequence, transmitting panoramic images, spectral data on organic compounds, and measurements of the surface's and before entering on 15 November 2014. In June 2015, improved solar illumination allowed brief reactivation, during which it sent additional data packets to until communications ceased in July 2015 due to the comet's increasing distance from the Sun. The mission concluded on 30 September 2016 when was directed to impact the comet's surface, providing Philae's legacy as a pioneering effort that revealed key insights into cometary origins and the early Solar System.

Mission Background

Objectives and Scientific Goals

The Philae lander, as part of the European Space Agency's (ESA) mission, had the primary objective of performing the first in-situ analysis of a to investigate its surface composition, subsurface , and activity levels. This involved direct sampling and measurement at the surface of Comet 67P/Churyumov–Gerasimenko, providing ground-truth data on the physical properties such as , , and mechanical strength of the nucleus materials. Specific scientific goals included determining the elemental, isotopic, mineralogical, and molecular composition of the to trace its origins as primordial material from the early Solar System, approximately 4.6 billion years old. Measurements of isotopes, particularly of light elements like , carbon, , and oxygen, aimed to reveal the building blocks of planetary formation and potential delivery mechanisms for and organics to . Additionally, the mission sought to study organic molecules as precursors to , analyzing their abundance and through surface and subsurface sampling, while examining and gas emissions to understand cometary processes and the nucleus-coma interactions. Philae's objectives complemented the broader mission goals by offering a unique lander perspective, enabling close-range, anchored observations that the orbiter's could not achieve, such as direct drilling and sniffing of the nucleus environment. This integration allowed for a holistic study of the 's evolution as it approached the Sun, contrasting orbital data on global morphology and plasma interactions with localized in-situ insights. Historically, the mission advanced cometary science beyond flyby encounters like ESA's mission to Comet 1P/Halley in 1986, marking the first controlled on a and enabling long-term monitoring of surface changes.

Development and Launch

The development of the Philae lander originated within the broader framework of the European Space Agency's (ESA) mission, with conceptual studies dating back to the as part of early planning for comet exploration. In November 1993, was formally selected as the third cornerstone mission in ESA's Horizon 2000 long-term scientific program, which approved the project's outline and initiated detailed engineering phases. The Philae lander itself was developed by an international consortium led by the (DLR), in collaboration with the Max Planck Institute for Solar System Research (MPS), the French space agency , and the (ASI); assembly of the lander was completed by early 2003 at DLR facilities in , Germany, followed by rigorous integration testing with the orbiter. The mission, encompassing Philae, was primarily funded and managed by ESA, with contributions from 20 member states and international partners including , which supplied three key scientific instruments for the orbiter (Alice ultraviolet spectrometer, MIRO microwave spectrometer, and and Electron Sensor). The total mission cost reached approximately €1.4 billion, covering spacecraft development, launch, operations, and scientific , while Philae's specific development and integration expenses amounted to about €220 million. These resources supported a multinational effort involving over 50 contractors from 14 European countries and the , emphasizing collaborative to meet the mission's ambitious deep-space objectives. Key engineering challenges centered on mass constraints imposed by the launch vehicle, with Philae designed to a total mass of approximately 100 kg—including a 21 kg scientific payload—to ensure compatibility with the Rosetta orbiter's 3,000 kg fully fueled limit under Ariane 5 specifications. Integration with the orbiter demanded precise mechanical docking mechanisms, electrical interfaces, and data links to enable deployment after over a decade of cruise, while minimizing impacts on the orbiter's propulsion and attitude control systems. Additionally, Philae underwent extensive testing for deep-space survival, including thermal-vacuum simulations at facilities like DLR's Large Space Simulation Chamber to verify its ability to endure a multi-year hibernation phase with minimal power draw, relying on passive thermal insulation and battery preservation to protect electronics against extreme cold near -150°C. Philae launched with on March 2, 2004, from the in , , aboard an G+ rocket, which placed the composite spacecraft into an initial escape trajectory. To achieve the necessary and path to Comet 67P/Churyumov-Gerasimenko, the mission incorporated gravity assists from on March 4, 2005; November 13, 2007; and November 13, 2009, along with a Mars swingby on February 25, 2007, extending the outbound journey while conserving fuel.

Spacecraft Design

Lander Configuration

The Philae lander adopted a compact, box-shaped measuring approximately 1 m in each dimension prior to landing gear deployment, constructed from a carbon fibre polygonal sandwich structure comprising a baseplate and an instrument platform for robustness in and variable conditions. This configuration supported the integration of scientific payloads while maintaining a total mass of 100 kg, including margins for systems and contingencies. The three-legged , which unfolded during descent, was engineered to provide stability on uneven , damping upon impact to minimize bouncing in the comet's microgravity environment of about 10^{-4} m/s². For secure attachment to the surface, the lander incorporated anchors that fired automatically after , supplemented by screws embedded in each leg's foot for additional grip against potential rebounds or gas emissions. The MUPUS system's mechanism further aided surface penetration, driving a probe up to 23 cm deep to and enable subsurface probing. A provided for attitude stability during descent. The ROMAP instrument package monitored and plasma to determine orientation. The SD2 , with a reach of up to 56 cm, handled sample collection by drilling and distributing material to onboard ovens for analysis. , consisting of multi-layer blankets and coatings, protected internal components from temperature extremes between -180°C and +50°C. Power was supplied by a primary non-rechargeable Li-SOCl₂ battery with a capacity of 1518 Wh for the initial 60+ hours of operations, complemented by a secondary rechargeable Li-ion battery of 151 Wh for potential long-term use after recharging. Philae was mounted on the orbiter via a mechanical docking interface on the side opposite the high-gain antenna, with separation initiated by a pyrotechnic release sequence that ejected the lander at a of about 0.3 m/s toward the .

Instruments

Philae carried a suite of ten scientific instruments with a total mass of approximately 21 kilograms, designed to perform in-situ analyses of the comet's surface and subsurface. These instruments focused on imaging, composition, physical properties, and environmental monitoring, providing complementary close-up data to the capabilities of the orbiter. The payload emphasized high-resolution surface characterization and sample handling to address key questions about cometary origins and evolution. The instrument suite included optical and spectroscopic imagers for surface documentation, drills and samplers for material acquisition, probes for subsurface penetration, and sensors for gas, plasma, and seismic analysis. This configuration enabled a multifaceted investigation of the landing site's geology, chemistry, and interaction with the , with instruments often operating in tandem—for instance, samples collected by the drilling system were distributed to analytical devices for detailed examination. Key instruments and their primary functions are as follows:
  • CIVA (Comet Nucleus Infrared and Visible Analyser): A multispectral imaging system comprising seven panoramic cameras for 360-degree surface panoramas (60° field of view, 1024×1024 pixel CCD detectors), a microscopic imager (7 µm resolution), and a near-infrared spectrometer (1–4 µm wavelength range) to assess surface texture, mineralogy, and sample context.
  • ROLIS (ROsetta Lander Imaging System): A descent camera providing downward-facing images during touchdown (1024×1024 pixel CCD, 57° field of view, f/5 lens) and post-landing close-ups in visible and near-infrared for landing site mapping and spectroscopic surveys.
  • APXS (Alpha Proton X-ray Spectrometer): An elemental analyzer using a curium-244 radioactive source to induce particle scattering and X-ray fluorescence, identifying major and trace elements in surface materials to depths of about 10 mm.
  • MUPUS (MUlti-PUrpose Sensors for Surface and Sub-Surface Science): A thermal and mechanical probe with a hammer penetrator (up to 23 cm depth), radiometer (6–25 µm wavelengths), and temperature sensors to measure subsurface thermal conductivity, heat capacity, and strength.
  • SD2 (Sampling, Drilling, and Distribution): An automated drilling and sample handling system capable of extracting cores up to 23 cm deep and distributing material to 26 internal ovens for analysis by connected instruments like COSAC and Ptolemy.
  • COSAC (COmetary SAmpling and Composition experiment): A gas chromatograph and mass spectrometer for separating and identifying volatile and organic molecules in collected samples, with capabilities for enantiomer detection to study molecular chirality.
  • PTOLEMY: An evolved gas analyzer using pyrolysis (heating samples to ~1000°C) and mass spectrometry to determine isotopic ratios of light elements (e.g., ¹²C/¹³C, D/H) in refractory and volatile components.
  • SESAME (Surface Electrical, Seismic, and Acoustic Monitoring Experiment): A set of three sensors—a permittivity probe for dielectric properties, acoustic sounder (100 Hz–kHz frequency range) for mechanical waves, and dust impact analyzer (particle sizes 0.5 µm–3 mm)—to characterize surface electrical and elastic properties.
  • ROMAP (ROsetta MAGnetometer and Plasma monitor): A combined instrument with a triaxial magnetometer (±2000 nT range, 0.01 nT sensitivity), ion detector (40–8000 eV energy range), and pressure gauge to monitor the local magnetic field, plasma environment, and neutral gas density.
  • CONSERT (COmet Nucleus Sounding Experiment by Radiowave Transmission): A bistatic radar operating at 90 MHz, transmitting signals to the Rosetta orbiter to tomographically image the comet nucleus's internal structure and composition.
Prior to launch, the instruments underwent rigorous and testing, including ground-based simulations in facilities mimicking comet-like conditions such as low and analogs (e.g., soft soils at 7 kPa and hard at 2 MPa). The was used for operational rehearsals, while in-flight pre-delivery sequences during the cruise phase verified functionality, such as CIVA camera alignment and mass spectrometer background measurements. These efforts ensured reliability in the harsh, low-light environment of Comet 67P.

Power and Communication Systems

The Philae lander's primary power source consisted of non-rechargeable lithium-thionyl chloride (Li-SOCl₂) batteries, specifically Saft LSH20 cells arranged in a 8s4p configuration providing a capacity of 52 Ah (1518 Wh) at the beginning of , designed to support initial operations for approximately 60 hours including separation, descent, landing, and the first sequence. These batteries powered the lander autonomously during the primary mission phase, with solar panels—totaling about 2 m² of cells—intended to recharge a secondary 151 Wh for extended operations, though post-landing shadowing limited this capability as anticipated in shadowed sites. Due to (ESA) policies prohibiting sources for safety and political reasons, Philae relied entirely on chemical batteries and without radioisotope thermoelectric generators. Power management was handled by autonomous software, including the Mission Operations Scheduling Tool (MOST), a C++-based system that optimized instrument prioritization and sequencing under energy constraints to maximize scientific return within the limited battery life. This software simulated power consumption scenarios, enabling parallel instrument operations and adjustments to avoid pauses that could deplete resources prematurely. Thermal control integrated with power systems through two Thermal Control Units (TCUs) that monitored 31 sensors and managed heaters to maintain the warm compartment above -55°C during hibernation, while solar absorber foils (each 65,772 mm² with α/ε = 0.94/0.04 externally) and blankets facilitated passive heat dissipation via radiators to deep , consuming levels of 5-10 . Communication relied on an S-band transmitter operating at 2208 MHz for downlink and 2033.2 MHz for uplink to the orbiter, achieving a maximum data rate of 16 kbit/s for , with the Electrical Support System (ESS) on handling to Earth. The system featured redundant antennas pointed in the +z direction, but deployment challenges arose from the lander's non-nominal orientation after bouncing, affecting signal strength due to environmental obstructions and misalignment, limiting effective range to about 200 km. A direct-to-Earth capability was provisioned via a 22 GHz Ka-band link for high-rate transmission if needed, though primary operations prioritized the orbiter to conserve lander power. Low power margins ultimately constrained communication windows, leading to planned after the initial battery exhaustion.

Journey to Comet 67P

Launch and En Route Operations

Following its launch on 2 March 2004 aboard an Ariane 5 rocket from Kourou, French Guiana, the Rosetta spacecraft with the attached Philae lander embarked on a complex interplanetary trajectory to rendezvous with comet 67P/Churyumov-Gerasimenko. To achieve the required orbital energy without excessive propellant use, the mission relied on four gravity assist flybys: the first Earth swingby on 4 March 2005 at a minimum distance of 1,954 km, providing an initial velocity boost; a Mars flyby on 25 February 2007 at 250 km altitude, which adjusted the trajectory while allowing remote sensing of the planet's surface; a second Earth flyby on 13 November 2007 at 5,300 km; and a third Earth swingby on 13 November 2009 at 2,481 km. These maneuvers collectively altered Rosetta's heliocentric velocity by approximately 2.4 km/s in total delta-v, enabling the spacecraft to escape the inner solar system and pursue the comet's distant orbit. During the en route phase, Rosetta also conducted flybys of two asteroids: 2867 Šteins on 5 September 2008 at a distance of approximately 800 km, and on 10 July 2010 at about 3,000 km. These encounters provided opportunities for scientific observations and instrument testing. As Rosetta ventured beyond the , reaching distances up to 5.3 AU from the Sun by 2011, generation dropped to levels insufficient for full operations, prompting the spacecraft to enter deep-space mode on 8 June 2011. In this power-saving state, nearly all systems were shut down except for the main computer, receivers, and minimal heaters, allowing Rosetta—and by extension, the dormant Philae lander—to coast silently for 31 months while conserving the limited electrical output from its solar arrays. The hibernation concluded successfully with an onboard alarm triggering reactivation on 20 January 2014, after which ground controllers at ESA's ESOC confirmed nominal performance and began preparations for comet approach. This extended low-power phase was essential for the mission's longevity, as continued active operations would have depleted resources before arrival. Throughout the 10-year cruise phase, spanning approximately 6.4 billion kilometers, periodic health checks maintained the spacecraft's and lander's readiness. These included short activations during cruise phases for subsystem verifications, instrument calibrations, and mechanism tests. Synchronization efforts involved spin-up maneuvers to align Rosetta's rotation with Philae's orientation, facilitating stable communication and attitude control tests between the orbiter and lander. Such interventions, conducted roughly every few months post-hibernation exit, confirmed no degradation in critical components despite the harsh and environment of deep space.

Arrival and Orbiting Phase

On August 6, 2014, the Rosetta spacecraft achieved rendezvous with Comet 67P/Churyumov-Gerasimenko after a decade-long journey, entering an initial orbit approximately 100 km from the nucleus. This marked the beginning of the orbiting phase, during which Rosetta executed a series of seven thruster maneuvers between August and September 2014 to progressively reduce its distance to the comet, reaching as close as 29 km by early September. These closer approaches enabled detailed global mapping and characterization of the comet, providing essential data for planning the Philae lander's deployment. The Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) aboard Rosetta played a central role in surface mapping efforts, capturing high-resolution images that revealed the comet's irregular bilobate structure—resembling a rubber duck—with overall dimensions equivalent to about 4 km across its longest axis. OSIRIS imaging, combined with other instruments, facilitated the identification and evaluation of candidate landing sites, ultimately selecting Agilkia on the larger lobe as the primary target due to its relatively flat terrain and favorable illumination for solar power. Observations during this phase also determined the comet's rotation period to be 12.4 hours, influencing orbital planning to align with stable viewing windows. In preparation for deployment, mission teams conducted pre-deployment checks on the Philae lander, including system activations to verify functionality of its instruments and anchoring mechanisms, as well as trajectory simulations to model the descent path from Rosetta's orbit to the surface. These simulations incorporated comet rotation and gravitational data to ensure safe touchdown parameters, with final refinements performed about 30 days prior to separation. Such preparations confirmed Philae's readiness while minimizing risks associated with the comet's low gravity and uneven terrain.

Deployment from Rosetta

The deployment of the Philae lander from the Rosetta orbiter took place on November 12, 2014, at 08:35 UTC (09:35 CET), when Rosetta was positioned approximately 22.5 km above the surface of comet 67P/Churyumov-Gerasimenko. This altitude was chosen to ensure a controlled seven-hour ballistic descent, allowing Philae to reach the primary landing site, Agilkia (site J), with a planned touchdown velocity of about 1 m/s relative to the comet. The release was executed automatically via the lander's mechanical separation system (MSS), which utilized a belt-driven spindle drive for initial positioning and a spring mechanism to impart a gentle ejection velocity of 0.1874 m/s, ensuring the lander separated without imparting excessive momentum. Navigation and attitude control during the separation and initial descent relied on Philae's onboard systems, including the ROMAP instrument's sensors for monitoring rotation and magnetic fields to help assess orientation. An internal flywheel was activated to induce a slow rotation, stabilizing the lander and minimizing nutation caused by cometary outgassing, while Rosetta's prior trajectory adjustments using cold gas thrusters had precisely aligned the orbiter for the deployment. Shortly after undocking, radio signals from Philae confirmed successful separation, with the orbiter's instruments tracking the lander's departure in real time. Mission planners had prepared backup options in case the primary site proved unsuitable, selecting site C as an alternative based on 's mapping data from the orbiting phase. The entire sequence was monitored from the (ESOC) in , , with a one-way time of about 28 minutes between and Earth, enabling near-real-time confirmation of key events despite the communication delay.

Landing and Surface Operations

Descent and Touchdown Sequence

Philae's descent began immediately following its separation from the orbiter at 08:35 UTC on 12 November 2014, from an altitude of approximately 22.5 km above the surface of Comet 67P/Churyumov–Gerasimenko. The unpowered, unguided free-fall lasted about seven hours, during which the lander rotated slowly to maintain orientation toward the Sun for power generation and captured images of the approaching surface using the CIVA instrument, revealing rugged terrain with cliffs, boulders, and outcrops. First contact with the surface occurred at 15:34 UTC at the planned Agilkia site ( 12.04°, longitude 335.69°), where the three-legged made initial impact at a of around 1 m/s. However, the anchoring harpoons failed to deploy due to a malfunction in the system, which was intended to counteract and hold the lander in place; additionally, the surface proved unexpectedly soft and granular, with low friction, preventing secure footing. This led to an immediate , exacerbated by the comet's microgravity environment—estimated at about 10^{-4} m/s²—causing the lander to lift off to a height of approximately 1 km and travel horizontally for roughly two hours. During this first bounce, Philae collided with the rim of crater around 16:20 UTC, initiating a tumbling motion with a period of about 13 seconds, as detected by the ROMAP . A second brief touchdown followed at approximately 17:25 UTC, resulting in another low-altitude rebound to around 30 m before the lander rolled backward. The sequence culminated in a third and final at 17:31 UTC in the Abydos region (latitude -9.0°, longitude 357.8°), where Philae came to rest without anchoring, tilted at an angle of about 30 degrees in a shadowed crevice that limited solar exposure. CIVA images taken post-settlement confirmed the uneven, debris-strewn final site, highlighting the challenges of the low-gravity .

Initial Surface Activities

Upon final touchdown at the Abydos site on Comet 67P/Churyumov-Gerasimenko, Philae's was at full capacity, enabling the immediate start of the First Science Sequence (FSS), a pre-programmed series of instrument activations and measurements designed to maximize scientific return within the battery's limited lifespan. The activation prioritized system health checks, confirming the lander's orientation and stability despite its tilted position, before proceeding to core science tasks. Key early activities included panoramic imaging by the Comet Infrared and Visible Analyser (CIVA), which produced a of the surrounding revealing a rugged of exposed outcrops, differential features, and fine-grained layers. Simultaneously, the COSAC gas chromatograph and mass spectrometer collected the first surface spectra, identifying volatile organics such as (CH₄) and (HCN) in the local environment, providing initial insights into the comet's chemical makeup. Science priorities then shifted to in-situ analysis, with the Sample, , and Distribution (SD²) subsystem attempting subsurface sampling; however, the activation failed to penetrate due to the lander's awkward tilt and the hard underlying surface. A test deployment of the Multi-Purpose Sensor for Surface and Sub-Surface (MUPUS) followed, where its hammer mechanism impacted the ground for three hours, registering surface temperatures of 90–130 K and a value of 85 J m⁻² K⁻¹ s⁻¹/², though limited depth penetration highlighted the terrain's consolidated nature. Over the first 24 hours, Philae relayed approximately 80 Mbit of data via the orbiter, including raw images and spectral datasets that corroborated the Abydos site's exposed, cliff-dominated morphology but in a persistently shadowed area restricting solar illumination. The FSS continued for about 60 hours total before battery levels dropped critically low, forcing entry into standby mode and halting further surface operations.

Communication Challenges and Shutdown

Following its unexpected bounces during descent, Philae came to rest in a tilted position against a cliff face in the shadowed region of 67P/Churyumov-Gerasimenko's Abydos site, severely limiting solar illumination to its panels. This orientation allowed only 1-1.5 hours of sunlight per day, far below the 6-7 hours required to recharge the lander's batteries effectively. The failed deployment of the anchoring harpoons during prevented secure fixation and subsequent repositioning maneuvers to optimize solar exposure. As a result, Philae's voltage declined rapidly, dropping to critical levels around 21.5 , prompting the mission team to prioritize data transmission over the intermittent communication link with . Contact became sporadic due to the lander's awkward tilt and the comet's uneven terrain, which intermittently obstructed the line-of-sight to the orbiter. In a final effort, the team uplinked a command to rotate Philae's body slightly, aiming to angle the solar panels toward the faint sunlight, but the power margin was insufficient for sustained operations. By 00:36 UTC on , 2014, after approximately 60 hours on the surface, the battery was fully exhausted, forcing Philae into an unplanned mode where all instruments and most systems shut down to conserve residual energy. Prior to silence, the lander successfully transmitted its remaining housekeeping telemetry and all acquired science data from the initial sequence via . The mission operations team at ESA's ESOC center accepted the shutdown, shifting focus to 's ongoing orbital observations while monitoring for potential future reactivation as the comet approached perihelion.

Reactivation Efforts

Following the initial hibernation in November 2014 due to insufficient , mission scientists anticipated a potential reactivation as 67P/Churyumov–Gerasimenko approached perihelion, where increased solar illumination could recharge Philae's batteries. On June 13, 2015, after 211 days of silence, Philae autonomously awoke and established a brief radio link with the orbiter, transmitting for 85 seconds and sending over 300 data packets of housekeeping , including status on its power subsystem and internal of about -5°C. The next day, , 2015, contact resumed, allowing Philae to downlink 32 minutes of stored before the link was lost, providing insights into the lander's condition during , such as battery voltage recovery to around 0 V and partial illumination. Sporadic communications continued through early July, with additional short bursts totaling over 8,000 packets, but no commands could be uploaded due to the unstable links. These brief successes were attributed to the comet's proximity to the Sun—reaching 186 million km on , 2015—which intensified solar flux, likely melting surface ice or shifting dust to expose portions of Philae's , generating up to 25 milliwatts of power initially. However, the lander's entrapment in a shadowed crevice at Abydos limited full panel exposure, preventing sustained charging, while rising surface temperatures posed overheating risks to the electronics if power demands exceeded capacity. Rosetta's operations were adjusted to facilitate communication, including orbit optimizations to reduce distance to 180 km and pointing toward Philae's presumed , enabling relay of signals to via ground stations. From mid-2015 through 2016, the orbiter conducted more than 300 contact attempts during dedicated listening periods, but no further signals were received after July 9, 2015, when the final 11-minute transmission occurred. On 2 September 2016, Rosetta's narrow-angle camera captured images of Philae wedged head-down in a narrow crevice at Abydos from a distance of about 2.7 km, confirming its exact and orientation, which explained the communication difficulties due to the shadowed position. Efforts persisted until Rosetta's mission conclusion on September 30, 2016, with the Electrical Support System for lander communications powered down on July 27, 2016, to conserve orbiter resources. Despite these revival attempts, no sustained scientific operations were achieved, as the intermittent power proved inadequate for instrument activation or attitude maneuvers. Philae is now presumed in permanent , likely due to irreversible degradation of its primary lithium battery after multiple deep discharge cycles and the comet's post-perihelion trajectory, which diminished solar illumination and dropped temperatures below operational thresholds.

Scientific Discoveries

Instrument Measurements

During its brief active periods on the surface of Comet 67P/Churyumov-Gerasimenko, the Philae lander's instruments captured key datasets that provided initial glimpses into the cometary environment. The CIVA (Comet Infrared and Visible Analyser) system produced panoramic mosaics from seven micro-cameras, revealing a shadowed, rugged terrain at the Abydos landing site characterized by fissures, boulders, and low illumination levels that limited intake. These images, acquired shortly after touchdown on November 12, 2014, documented the lander's orientation in a cavity with uneven, dust-covered features extending across a spanning approximately 360 degrees. The COSAC (Cometary Sampling and Composition) instrument conducted gas chromatography-mass spectrometry analyses during descent and surface operations, detecting 16 organic compounds on the comet's surface, including alcohols, amines, and previously unidentified species such as , trimethyl amine, and . These measurements, performed over limited sniffing and sampling attempts, identified complex molecules through mass spectra peaks, though full identification was constrained by incomplete sample delivery. Notably, COSAC did not confirm in its surface readings, with detections limited to volatile and semi-volatile organics released near the lander. Other instruments yielded complementary raw data on physical conditions. The MUPUS (Multi-Purpose Sensors for Surface and Sub-Surface Science) penetrator recorded temperature profiles ranging from lows of about -180°C to highs of -140°C, synchronized with the comet's 12.4-hour rotation, using thermal sensors on its anchor and a mapper on the lander's balcony. These profiles showed rapid diurnal variations indicative of a thin dust layer over a compacted subsurface, with the hammer mechanism achieving only shallow penetration of a few millimeters into a hard, ice-like crust. The ROLIS (ROsetta Lander Imaging System) camera captured close-up images during descent and at touchdown, resolving surface features at the final site with pixel scales down to 6 cm, depicting a mottled, pebble-strewn landscape under LED illumination. Meanwhile, the SESAME (Surface Electrical, Sounding, and Acoustic Monitoring Experiments) suite, including the Dust Impact Monitor (DIM), registered low levels of dust flux and particle impacts, with no significant wind activity detected by its acoustic and electrical sensors during the short operational window. The ROMAP (ROsetta Lander Magnetometer and Plasma Monitor) instrument detected no intrinsic magnetic field in the comet's nucleus during descent and surface operations. Philae transmitted a significant volume of scientific data from the surface via the Rosetta orbiter, encompassing images, spectra, and telemetry from the first science sequence, supplemented by brief snippets during later reactivations in 2015. However, operations were hampered by low battery power after 60 hours, resulting in incomplete instrument runs; for instance, the SD2 (Sampling, Drilling, and Distribution) system failed to successfully drill subsurface samples due to insufficient anchoring and surface hardness, delivering no material to onboard analyzers.

Insights into Comet Composition

Philae's local measurements, combined with orbiter data, contributed to understanding 67P/Churyumov-Gerasimenko's highly porous structure, with a of approximately 0.533 g/cm³ (533 kg/m³). This low indicates significant void space throughout the nucleus. Data from the MUPUS penetrator detected a hardened layer overlying softer material, suggesting a porous matrix of ice grains and aggregates, with local in the upper meter estimated at 40-75% depending on composition. The surface at Philae's landing site, Abydos, consists of a thin mantle, 10-20 cm thick, covering water ice mixed with refractory , where the ice content is relatively low, comprising about 20-30% by mass based on thermal and mechanical properties. Analysis of organic compounds by the COSAC mass spectrometer identified a diverse suite of complex hydrocarbons, including aliphatic and aromatic species, as well as oxygen- and nitrogen-bearing molecules like alcohols and amines, but no definitive were detected in the surface samples. These findings indicate a carbon-rich, organic component integrated into the dust-ice matrix, with no of extensive prebiotic polymers, pointing to primitive material preserved from the comet's formation. The Ptolemy instrument complemented this by detecting carbon monoxide and hydrogen-bearing organics, further highlighting the prevalence of volatile and semi-volatile . Surface activity insights from Philae's instruments showed sublimation primarily driven by beneath the dust mantle, with rates varying due to the comet's and seasonal heating, leading to localized outbursts correlated with perihelion approach and rotational phases. The dust mantle thickness, inferred from penetration resistance and thermal gradients, limits direct sublimation, resulting in gas flow through pores and fractures, which sustains outbursts observed during the brief surface operations. Comparisons to reveal similarities in low overall content but greater heterogeneity in 67P's structure, suggesting accretion from diverse building blocks in the early Solar System.

Implications for Solar System Origins

The Philae lander's measurements of the surface and subsurface properties of 67P/Churyumov-Gerasimenko provided key evidence for the comet's primordial nature, linking it to the early solar system's formation processes. Philae's instruments, including the MUPUS probe and the COSAC mass spectrometer, revealed a highly porous, low-density nucleus with bulk densities around 532–535 kg/m³ and porosities of 57–87%, indicative of gentle accretion through low-velocity mergers of cometesimals in a dynamically disk at 15–30 AU from the Sun. This structure, lacking signs of aqueous alteration or significant heating, suggests that 67P formed via hierarchical agglomeration over millions of years without disruptive collisions, preserving materials from the solar nebula. The detection of supervolatiles like CO and CO₂ at low ratios by Philae's instrument further supports this scenario of minimal thermal processing during accretion in the outer solar system. Philae's COSAC instrument identified 16 organic compounds on the comet's surface, including nitrogen-bearing species such as and acetone, which serve as precursors to prebiotic molecules. These findings bolster the hypothesis that comets acted as vectors for delivering simple organics to the , potentially contributing to the origins of life, although the detected compounds exhibit low complexity and no direct were identified by Philae. The presence of such organics in the dust, combined with the comet's primitive composition, implies that interstellar chemistry in dust grains could have seeded life's building blocks, with cometary impacts providing a mechanism for their transfer to habitable zones. The lander's data on 67P's bi-lobed morphology and weak mechanical strength (tensile/ of 3–30 Pa) challenge models of a purely in-situ origin, instead favoring dynamic migration scenarios like the Nice model, where early instabilities scattered objects from beyond 30 AU inward. Philae's observations of extensive layering and the absence of compaction from high-velocity impacts indicate that the comet's structure resulted from low-energy mergers post-scattering, with migration efficiencies around 0.19% transporting such primitives into the inner solar system. This supports revised formation timelines, with accretion completing within 1–4 million years after calcium-aluminum-rich inclusions, followed by ~0.4 billion years of evolution in a gas-free disk before dynamical ejection. Philae's dataset, archived in the ESA Planetary Science Archive, continues to inform ongoing studies of cometary evolution and has directly influenced the design of future missions, such as ESA's , by highlighting the need for multi-spacecraft observations to map nucleus activity and plasma interactions in pristine, dynamically new comets. The lander's insights into surface diversity and low-gravity operations have shaped Interceptor's three-probe configuration for comprehensive 3D profiling, building on Philae's baseline of primitive material properties to target less-evolved objects.

Legacy and Impact

International Contributions

The Philae lander represented a major international collaboration, primarily under the leadership of the (ESA), which coordinated the overall mission of which Philae was a key component. The lander itself was developed and provided by a consortium led by the (DLR), with major contributions from the Max Planck Institute for Solar System Research (MPS) in , the French space agency (CNES), and the Italian Space Agency (ASI). The ' National Aeronautics and Space Administration (NASA) contributed to the overall mission through technical support and instruments on the orbiter. This multinational effort drew on expertise from institutions across and the US, ensuring the lander's design met the demands of comet surface operations. Funding for Philae's development came primarily from ESA member states via the , with significant shares allocated to the lead agencies: DLR managed overall lander integration and operations, contributing key subsystems like the landing gear and control systems; MPS led the development of the COSAC instrument for analyzing cometary volatiles; ASI provided the SD2 drilling and sampling mechanism for subsurface access; and MPS headed the ROMAP suite for measuring magnetic fields and plasma interactions. Ground operations, including real-time command and telemetry during descent, were centralized at ESA's (ESOC) in , , with support from the Lander Control Centre at DLR in . These contributions reflected a distributed model where ESA provided overarching and launch integration, while national agencies handled specialized hardware. The project involved and engineers from more than 20 , spanning ESA's member states and extending to international partners for instrument calibration and testing. Post-mission, collaborative teams from institutions in , , , the , , , , and the continued to process Philae's archived measurements, fostering ongoing interdisciplinary . One notable challenge was coordinating the high-stakes landing sequence across global teams operating in different time zones, which necessitated 24/7 shifts and synchronized simulations to align efforts during the November 2014 touchdown window. This international framework not only distributed technical risks but also amplified the mission's scientific reach through shared resources and expertise.

Media Coverage and Public Engagement

The Philae lander's touchdown on 67P/Churyumov–Gerasimenko on November 12, 2014, garnered extensive global media attention, with live broadcasts from the European Space Agency's (ESA) operations center in , , drawing widespread coverage from major outlets including , , and , which featured the event on front pages and in prime-time segments. The event's social media buzz peaked with the hashtag, which amassed over 804,000 tweets from 339,000 contributors, achieving 4.3 billion timeline deliveries and 910 million reach worldwide during the week of the landing. ESA's channel alone recorded 4.3 billion page impressions tied to the mission's climax, underscoring the unprecedented public fascination with this first-ever comet landing. ESA's outreach initiatives amplified the mission's accessibility, including the Rosetta Blog, which provided real-time updates, mission diaries, and interactive content to engage a broad audience during key phases like the lander's descent. School programs featured prominently, such as the 2004 naming competition for the lander, where 15-year-old Italian Serena Olga Vismara won with "Philae," inspired by the ancient obelisk that aided in deciphering , selected from entries across contributor nations' school contests. Additional campaigns like #WakeUpRosetta in January 2014 collected over 200 global video submissions with 75,000 votes to "awaken" the from hibernation, while #RosettaAreWeThereYet in August 2014 garnered 23,000 photo votes, fostering educational ties with students and teachers through downloadable resources and competitions. The mission inspired cultural depictions, including the 2014 documentary Landing on a Comet: Rosetta Mission, which chronicled the spacecraft's journey and Philae's challenges with behind-the-scenes access to ESA teams. Social media memes and humorous tweets, such as those joking about Philae's bumpy , proliferated on platforms like , humanizing the robotic explorer and amplifying its viral appeal. Books like : The Remarkable Story of Europe's Explorer by Peter Bond detailed the mission's narrative, including Philae's role, contributing to literature. Philae's saga significantly boosted in space science, with ESA campaigns inspiring STEM engagement among youth through featuring anthropomorphized and Philae characters on . The mission's outreach efforts earned the Sir Arthur Clarke Space Achievement Award for education and public engagement, recognizing its role in captivating a global audience and promoting scientific curiosity.

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