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CoRoT-7b
Size comparison of CoRoT-7b (center) with Earth (left) and Neptune (right)
Discovery
Discovered byRouan et al. (CoRoT)
Discovery sitePolar orbit
Discovery dateFebruary 3, 2009
Transit
Orbital characteristics
0.0172 ± 0.00029 AU (2.573 ± 0.043 million km; 1.599 ± 0.027 million mi)[1]
Eccentricity0
0.853585 ± 0.000024 d (20.48604 ± 0.00058 h)[1]
Inclination80.1 ± 0.3[1]
StarCoRoT-7
Physical characteristics
1.528±0.065 R🜨[2]
Mass6.06±0.65M🜨[2]
Temperature1,300–1,800 K (1,030–1,530 °C; 1,880–2,780 °F)[3]

CoRoT-7b (previously named CoRoT-Exo-7b)[3][4] is an exoplanet orbiting the star CoRoT-7 in the constellation of Monoceros, 520 light-years (159 parsecs)[5] from the Earth. It was first detected photometrically by the French-led CoRoT mission and reported in February 2009.[6] Until the announcement of Kepler-10b in January 2011, it was the smallest exoplanet to have its diameter measured, at 1.58 times that of the Earth (which would give it a volume about 3.94 times Earth's) and the first potential extrasolar terrestrial planet to be found. The exoplanet has a very short orbital period, revolving around its host star in about 20 hours.[1]

Combination of the planet's diameter derived from transit data with the planet's mass derived from radial velocity measurements means that the density of CoRoT-7b is about the same as that of Earth; therefore, CoRoT-7b is a terrestrial planet like Earth and not a gas giant like Jupiter. The radial velocity observations of CoRoT-7 also detected a second super-Earth, CoRoT-7c, which has a mass 8.4 times that of Earth and orbits every 3.7 days at a distance of 6.9 million km (0.046 AU; 4.3 million mi).

Discovery

[edit]
Artist conception of CoRoT-7b transiting yellow dwarf CoRoT-7

CoRoT-7b was found by observing its parent star's periodic decrease in apparent magnitude caused by the planet's transit in front of the star as seen from Earth. Measuring this dip in brightness, together with a size estimate for the star, allows calculating the planet's size. (See Transit method.) The space mission CoRoT observed the star CoRoT-7, in the stellar field LRa01, from October 15, 2007, to March 3, 2008. During this period, 153 periodic transit signals of 1.3 h duration with a depth of 3.4 × 10−4 were registered. After 40 days of data acquisition, the Alarm mode pipeline algorithm detected the shallow signal of CoRoT-7b, starting the follow-up observations from the ground to get a confirmation of the planetary nature of the transiting object.

The discovery of CoRoT-7b was announced a year later on February 3, 2009, during the CoRoT Symposium 2009 in Paris.[6] It was published in a special issue of the journal Astronomy and Astrophysics dedicated to results from CoRoT.[7]

Mass

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After the detection of CoRoT-7b in the lightcurve, follow-up observations carried out with a network of ground-based telescopes ruled out nearly completely the possibility of a false positive detection.[8] The HARPS spectrograph was subsequently used to measure the mass of CoRoT-7b with the radial velocity method. The strong activity of the host star, which perturbates radial velocity measurements, made the mass determination troublesome.

The discovery paper, by Queloz et al.,[9] weighed the planet at about 4.8 Earth masses, giving it a density of 5.6 ± 1.3 g cm−3, similar to Earth's. The value was obtained using a pre-whitening procedure and harmonic decomposition. It was also inferred that there was a second non-transiting planet in the system, CoRoT-7c, with a 3.7-day orbital period.

A second paper, by Hatzes et al.,[10] employing Fourier analysis, reported a likely mass of 6.9 Earth masses for CoRoT-7b, and found hints for the presence of a third planet in the system, CoRoT-7d, with mass similar to Neptune's and a 9-day orbital period.

Pont et al.[11] evidences larger-than-declared systematic errors in the HARPS measurements, estimating CoRoT-7b to be between one and four Earth masses. The radial velocity confirmation of the planet is in shaky ground too, with a tentative detection of only 1.2 sigma certainty.

Boisse et al.,[12] employing simultaneous fitting of stellar activity and planetary signals in the radial velocity data, calculate for CoRoT-7b a mass of 5.7 Earth masses, though with a very large uncertainty.

The CoRoT team then published a second paper on CoRoT-7b's mass,[13] removing stellar activity through analysis only of radial velocity data for which multiple measurements were taken in a given night. The planet is weighed at 7.42 Earth masses, yielding an average density of 10.4 ± 1.8 g cm−3, far higher than the Earth's and similar to that of the second rocky planet found, Kepler-10b.

A last study by Ferraz-Mello et al.[14] improved the approach used in the discovery paper, finding that it downsized the amplitude of the planets' induced radial velocities. It reports for CoRoT-7b a heavier mass of 8 Earth masses, in agreement with the second paper published by the CoRoT team. Thus, CoRoT-7b may be rocky with a large iron core, with an internal structure more like Mercury than Earth.

Spitzer observations

[edit]

An independent validation of CoRoT-7b as a planet is supplied by follow-up performed with the space based Spitzer telescope. Its observations confirmed the transits of the planet, with the same depth, at different wavelengths than the ones observed by CoRoT.[15] The data then allows to validate CoRoT-7b as a bona-fide planet with a very high degree of confidence, independently from the noisy radial velocity data.

Characteristics

[edit]
Artist's impression of CoRoT-7b.
Credit: ESO/L. Calçada.

CoRoT-7b's mass is somewhat uncertain at 6.06±0.65M🜨,[2] while its radius and orbital period are well known from CoRoT photometry: it orbits very close to its star (1/23rd the distance from the Sun to Mercury[16]) with an orbital period of 20 hours, 29 minutes, and 9.7 seconds and has a radius of 1.58 Earth radii.[17] CoRoT-7b had the shortest orbit of any planet known at the time of its discovery.[18]

Due to the high temperature, it may be covered in lava.[3] The composition and density of the planet, though weakly constrained, make CoRoT-7b a probably rocky planet, like Earth. It could belong to a class of planets that are thought to contain up to 40% water (in the form of ice and/or vapor) in addition to rock.[19] However, the fact that it formed so close to its parent star may mean that it is depleted of volatiles.[20] A strong possibility exists that the planet's rotation is tidally locked to the orbital period, so that temperatures and geologic conditions on the sides of the planet facing towards and away from the star may be dramatically different. Theoretical work suggests that CoRoT-7b could be a chthonian planet (the remains of a Neptune-like planet from which much of the initial mass has been removed due to close proximity to its parent star).[21][22] Other researchers dispute this, and conclude CoRoT-7b was always a rocky planet and not the eroded core of a gas or ice giant,[23] due to the young age of the star system.

Any departure from circularity of its orbit (due to the influence of host star and neighboring planets) could generate intense volcanic activity similar to that of Io, via tidal heating.[24]

A detailed study of the extreme properties of CoRoT-7b has been published,[25] concluding that, despite the mass uncertainty, the planet is Earth-like in composition. The extreme proximity to the star should prevent the formation of a significant atmosphere, with the dayside hemisphere as hot as the tungsten filament of an incandescent bulb, resulting in the formation of a lava ocean. The researchers propose to name this new class of planets, CoRoT-7b being the first of them, "lava-ocean planets".

Model of the interior

[edit]
CoRoT-7b artist view.

Assuming a 5-Earth-masses planet, the planet was modeled to have convection in the mantle with a small core with no more than 15% the mass of the planet, or 0.75 M🜨. The lower mantle above the core-mantle boundary has more sluggish convection than the upper mantle because the greater pressure causes fluids to become more viscous. The temperature of the upper convecting mantle is different from one side of the planet to the other with lateral temperature differences for downwellings up to several hundred kelvins. However, the temperature of the upwelling is unaffected by downwelling and surface temperature variations. On the permanent dayside of the tidally locked planet where the surface temperature is hot from continuously facing its sun, the surface takes part in convection, which is the evidence that all the surface of this hemisphere being covered in oceans of lava. On the permanent nightside, the surface is cool enough for the formation of the crust with pools of lava above the convective mantle with intense volcanism. The dayside of the planet has larger convection cells than the nightside.[26] Researchers also investigated the physical state of the interior of CoRoT-7b,[27] indicating as likely a solid iron core, thus a self-generated magnetic field should be absent on the planet.

Possible atmosphere

[edit]

Due to the high temperatures on the illuminated side of the planet, and the likelihood that all surface volatiles have been depleted, silicate rock vaporization may have produced a tenuous atmosphere (with a pressure approaching 1 Pa or 10−2 mbar at 2,500 K [2,230 °C; 4,040 °F]) consisting predominantly of sodium, O2, O and silicon monoxide, as well as smaller amounts of potassium and other metals.[16][20][28] Magnesium (Mg), aluminium (Al), calcium (Ca), silicon (Si), and iron (Fe) may rain out from such an atmosphere on the planet's daylight side in the form of particles of minerals, such as enstatite, corundum and spinel, wollastonite, silica, and iron (II) oxide, that would condense at altitudes below 10 km (6.2 mi). Titanium (Ti) may be depleted (and possibly iron similarly) by being transported towards the night side before condensing as perovskite and geikielite.[20] Sodium (and to a lesser extent, potassium), being more volatile, would be less subject to condensation into clouds and would dominate the outer layers of the atmosphere.[16][20] Observations carried out with the UVES spectrograph on CoRoT-7b in and out of transit, searching for emission and absorption lines originating in the exosphere of the planet, failed to detect any significant feature.[29] Spectral lines of calcium (Ca I, Ca II) and sodium (Na), expected for a Mercury-like planet, are either absent or below detection limits, and even emission lines expected from volcanic activity, due to tidal forces exerted by the gravity of the nearby star, were not found. The lack of detections is in agreement with the previously cited theoretical work,[25] which points to a cloudless atmosphere made of rocky vapours with a very low pressure. From the data available, scientists can only infer that CoRoT-7b does not resemble any of the rocky planets of the Solar System.

See also

[edit]

References

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[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

CoRoT-7b

View on Grokipedia
from Grokipedia
CoRoT-7b is a orbiting the active K-type dwarf star CoRoT-7, located approximately 500 light-years away in the constellation . Discovered in February 2009 by the European Space Agency's CoRoT space mission using the transit method, it was the first confirmed to have a rocky composition similar to 's, with a radius of about 1.53 times that of and a mass of roughly 6 masses. Its extremely close orbit, with a period of just 0.85 days and a semi-major axis of 0.017 AU, subjects it to intense stellar radiation, resulting in dayside temperatures exceeding 2,000°C and a likely surface of molten rock or lava oceans. The CoRoT mission, a between the French space agency and ESA, detected CoRoT-7b through shallow dips in the star's brightness, indicating transits by a small planetary body. Ground-based follow-up observations, including measurements from ESO's HARPS spectrograph, confirmed its planetary nature and provided initial estimates of its mass, establishing it as a "" with a consistent with a rocky makeup of silicates and iron. Subsequent studies refined these parameters, accounting for the host star's activity, which can mimic planetary signals; the latest analyses yield a mass of 6.06 ± 0.65 masses and a radius of 1.53 ± 0.07 radii, reinforcing its terrestrial classification. CoRoT-7b's proximity to its star—23 times closer than Mercury to the Sun—implies synchronous , with a permanently facing dayside scorching enough to vaporize rock and a cooler nightside around -200°C, potentially allowing for atmospheric redistribution of heat. Theoretical models suggest it may possess a thin atmosphere of rock vapor or silicates, and its equilibrium temperature of about 1,800–2,600 K at the substellar point makes it a prime example of an ultra-short-period planet. The system also hosts at least one additional non-transiting , CoRoT-7c, highlighting CoRoT-7 as a multi-planet system around an active star. As the smallest transiting exoplanet known at the time of discovery, CoRoT-7b marked a milestone in science, providing the first precise measurement of a super-Earth's radius and enabling density calculations that ruled out gaseous compositions. Its study has advanced understanding of planetary formation in the inner regions of protoplanetary disks, where high temperatures favor rocky worlds, and continues to inform models of and surface evolution under extreme irradiation. Ongoing research, including reanalyses of archival data, addresses challenges from stellar activity but confirms CoRoT-7b's status as a key benchmark for rocky exoplanets.

History

Discovery

CoRoT-7b was detected via the transit method using the CoRoT space telescope during its first long-duration observational run (LRa01) toward the constellation Monoceros, which spanned approximately 150 days from October 2007 to March 2008. The analysis of the high-precision photometric light curve identified periodic dimmings in the host star's brightness every 20.4 hours, corresponding to an orbital period of 0.85359 ± 0.000024 days, with a transit depth of ΔF/F ≈ 3.35 × 10⁻⁴. A total of 153 transits were recorded, enabling a precise determination of the planet's radius as 1.68 ± 0.09 Earth radii, marking it as the smallest transiting exoplanet known at the time. The discovery was publicly announced on February 3, 2009, during a at the CoRoT Symposium in , and it was presented as the smallest transiting known at the time, with an estimated surface temperature exceeding 1000°C due to its close orbit. This announcement highlighted CoRoT-7b's significance as the first for which a radius had been measured, opening new avenues for studying small, terrestrial-like worlds. The full details were published later that year in Astronomy & Astrophysics. Initial confirmation of CoRoT-7b's planetary nature was achieved through ground-based follow-up using the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph mounted on the 3.6-meter ESO telescope at in . Observations began in October 2008 and continued through early 2009, yielding over 100 high-precision measurements that detected a signal at the with a semi-amplitude of 3.3 m/s. These early data provided a minimum mass estimate of 4.8 ± 0.8 masses, leading to an average of 5.6 ± 1.3 g/cm³, which offered the first evidence of a composition for a , akin to 's of 5.52 g/cm³ and consistent with a terrestrial makeup rather than a gaseous one. This characterization solidified CoRoT-7b's status as the inaugural confirmed beyond the Solar System.

Follow-up Observations

Following the initial detection of CoRoT-7b through transits observed by the CoRoT space , post-discovery efforts centered on ground-based (RV) campaigns to confirm the planet's existence and measure its mass despite interference from the host star's activity. The first follow-up spectroscopic observations began in spring 2008 using the SOPHIE spectrograph on the 1.93 m at Observatoire de Haute-Provence, providing initial RV data to search for the planetary signal. This was quickly followed by an intensive four-month campaign with the HARPS spectrograph on the 3.6 m ESO at La Silla, yielding over 100 high-precision measurements from late 2008 through early 2009, and extended with additional observations into 2010 to refine the signal amid stellar noise. These campaigns faced significant challenges from the active nature of the K-type host star, whose 23-day rotation period and cool starspots generated RV of around 10 m/s, often mimicking or masking the weak planetary signal expected from a . During the HARPS observations, an additional RV signal was identified, attributed to a second , CoRoT-7c, with an of approximately 3.7 days, which further complicated efforts to isolate the inner signal of CoRoT-7b and raised questions about potential additional companions. The stellar activity-induced variations led to ongoing debates in 2009–2011 regarding the reliability of early mass estimates, with some analyses suggesting overestimation due to unmodeled spot effects that could alias as planetary signals. Initial properties were reported in Léger et al. (2009), while subsequent reanalyses, such as Pont et al. (2010), examined the RV data and suggested that the signal might be influenced by stellar activity, leading to debates on the reliability of early mass estimates. Later reanalyses of the RV data, accounting for multiple planets and advanced activity modeling, confirmed CoRoT-7b's at 6.06 ± 0.65 Earth masses as of 2022, resolving much of the early debate.

Host System

The Star CoRoT-7

CoRoT-7 is classified as a G9V situated in the constellation , approximately 520 light-years from . Its apparent visual magnitude of 11.7 renders it relatively faint, posing challenges for detailed ground-based observations despite enabling the initial transit detection of CoRoT-7b by the space-based CoRoT mission. The star exhibits an of 5275 ± 75 K, a radius of 0.83 ± 0.04 R⊙, and a of 0.915 ± 0.017 M⊙. It has a of [M/H] = 0.06 ± 0.14, indicating a composition similar to the Sun in heavy elements. CoRoT-7 displays high stellar activity, characterized by a spotted surface and a rapid rotation period of approximately 23 days, which introduces variability that can affect the precision of detection methods. Based on gyrochronology, its age is estimated at 1.8 +0.5/-0.6 billion years. The system is a wide binary, with an M4V companion (CoRoT-7 B) at a separation of approximately 12,000 AU.

Orbital Parameters

CoRoT-7b completes one around its host star every 0.8536 days, or approximately 20.43 hours, making it one of the shortest-period transiting exoplanets known. This close-in has a semi-major axis of 0.017 AU, subjecting the to intense stellar that drives its extreme thermal environment. The is nearly circular, with an eccentricity consistent with zero (upper limit <0.01), a configuration likely enforced by tidal interactions with the star over its lifetime. The transiting geometry implies an orbital inclination near 90°, measured at 80.1° ± 0.3°, enabling the detection of periodic dips in the star's . Transits occur over a duration of approximately 1.1 hours, providing key constraints on the system's . The resulting equilibrium reaches about 1760 K, calculated under assumptions of zero and efficient redistribution of heat across the planet's surface. The CoRoT-7 system includes an outer companion, CoRoT-7c, with an of 3.70 days; dynamical models suggest that mean-motion resonances between CoRoT-7b and such outer planets could have stabilized the inner orbit during inward migration driven by disk interactions or tides.

Physical Properties

Mass and Radius

The radius of CoRoT-7b has been determined primarily through transit photometry observations conducted by the CoRoT space telescope, supplemented by ground-based follow-up data. The latest analysis yields a planetary radius of 1.53±0.071.53 \pm 0.07 radii (R⊕R_\oplus). The of CoRoT-7b is derived from measurements, which detect the star's motion due to the planet's gravitational pull. Early estimates reported a of approximately 5 masses (M⊕M_\oplus), inferred from a semi-amplitude K≈3.3K \approx 3.3 m/s and assumptions about the host star's . This minimum calculation relies on the standard equation, simplified for the planet's near-edge-on (i≈90∘i \approx 90^\circ) and negligible eccentricity (e≈0e \approx 0): Mpsin⁡i≈(P2πG)1/3KM⋆2/3,M_p \sin i \approx \left( \frac{P}{2\pi G} \right)^{1/3} K M_\star^{2/3}, where PP is the orbital period, GG is the gravitational constant, KK is the semi-amplitude, and M⋆M_\star is the stellar mass. Subsequent analyses have revised the mass due to challenges in disentangling planetary signals from the host star's activity-induced radial velocity jitter. Earlier estimates included 4.07±0.764.07 \pm 0.76 M⊕M_\oplus from 2017. The current adopted value from a 2022 reanalysis of the full HARPS dataset, using Gaussian process regression and line-profile analysis (SCALPELS) to model stellar activity from spots and faculae, is 6.06±0.656.06 \pm 0.65 M⊕M_\oplus. These uncertainties stem largely from imprecise knowledge of the host star's mass (∼0.91M⊙\sim 0.91 M_\odot) and the variable amplitude of stellar activity, which can mimic or mask the planet's signal.

Density and Composition

The of CoRoT-7b is 9.4±0.29.4 \pm 0.2 g/cm³, derived from the latest measurements of its and . This high value supports a predominantly rocky composition, primarily consisting of silicates in and metals such as iron in , consistent with terrestrial-like planets but adapted to extreme irradiation. The planet's structure excludes significant volatile components, aligning it with super-Earths formed from refractory materials. Compared to , which has a mean of 5.51 g/cm³, CoRoT-7b's suggests a substantially elevated iron content in its core—potentially exceeding 70% by mass—or significant structural compression effects from intense stellar heating and tidal forces. Such enhancements could arise from differentiation processes under high temperatures, where metallic phases dominate the interior. This composition places CoRoT-7b among the densest known exoplanets, emphasizing its role as a for volatile-poor, metal-silicate worlds. The high density precludes a substantial hydrogen-helium , as even a minimal gaseous layer would inflate the radius beyond observed limits; models indicate an upper bound on the H/He mass fraction of less than 1%, likely much lower at around 0.01%. Any primordial envelope would have been stripped away rapidly due to the planet's proximity to its host star, leaving a bare rocky surface exposed to extreme conditions. This absence reinforces the planet's classification as a naked without a protective gas layer. Evolutionary models propose that CoRoT-7b formed beyond the of its , where it accreted primarily refractory silicates and metals, before undergoing inward migration to its current orbit at approximately 0.017 AU. This migration process depleted volatiles through dynamical interactions and photoevaporation, resulting in the observed iron- and silicate-rich, volatile-poor state. Such scenarios explain the planet's current composition as a remnant of core accretion followed by disk-driven transport.

Observational Studies

Transit Photometry

The transit photometry of CoRoT-7b was primarily derived from the light curve obtained by the during its long run in the direction of from October 2007 to March 2008. The analysis identified 153 periodic transit events with a duration of approximately 1.3 hours and a depth of 3.35×10−4±1.2×10−53.35 \times 10^{-4} \pm 1.2 \times 10^{-5}, corresponding to a flux decrease of about 0.0335%. This shallow depth yielded a planet-to-star radius ratio of Rp/R⋆=0.0172±0.0008R_p / R_\star = 0.0172 \pm 0.0008, determined through fitting a trapezoidal model to the phase-folded after preprocessing to remove stellar variability and instrumental effects. The was refined to 0.853585±0.0000240.853585 \pm 0.000024 days using bootstrap resampling for estimation. Subsequent analyses, including from TESS observations in Sectors 6 and 33 (2019–2020), confirmed the transit signal with a depth of 0.0350 ± 0.0011% and refined Rp/R⋆=0.01784±0.00047R_p / R_\star = 0.01784 \pm 0.00047, with the period further precise to 0.8535 ± 0.000000587 days. These updates, combined with improved stellar radius R⋆=0.83±0.04 R⊙R_\star = 0.83 \pm 0.04\, R_\odot, yield Rp=1.528±0.065 R\EarthR_p = 1.528 \pm 0.065\, R_\Earth. Ground-based follow-up observations confirmed the planetary nature of the transits and ruled out binary blends or background eclipsing systems. Photometric monitoring with the 1.2-m Euler Swiss Telescope at , conducted from December 2008 to February 2009, detected multiple transits consistent with the CoRoT , demonstrating stable periodicity without evidence of dilution from nearby sources. Additional with the IAC-80 and the Canada-France-Hawaii Telescope excluded false positives at separations greater than 4 arcseconds, while high-resolution with FASTCAM and NACO limited contaminants within 0.4 arcseconds to less than 8 in 10,000 probability. These observations collectively validated the transit signal as originating from a transiting companion to CoRoT-7. Precise modeling of the incorporated corrections using quadratic laws tailored to the CoRoT passbands, based on stellar atmosphere models for the K-type host star. The ingress and egress timings, spanning about 12 minutes each, constrained the transit geometry, yielding an impact parameter b=0.70±0.06b = 0.70 \pm 0.06 and i=80∘±2∘i = 80^\circ \pm 2^\circ. Refined values are b=0.713±0.017b = 0.713 \pm 0.017 and i=80.98∘±0.51∘i = 80.98^\circ \pm 0.51^\circ. These parameters indicate a nearly equatorial transit view, which, combined with data, supports mass determinations by assuming near-edge-on geometry.

Radial Velocity Analysis

The radial velocity (RV) analysis of CoRoT-7b has been pivotal in determining its mass, but it has faced significant challenges due to the host star's high activity level, which introduces correlated noise and mimics planetary signals in the RV curve. Initial follow-up observations using the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph on the ESO 3.6 m telescope detected a low-amplitude RV signal consistent with a super-Earth companion, but stellar spots and plages complicated the isolation of the planetary component. Early processing of HARPS data employed the CLEAN , a Fourier-based pre-whitening technique, to extract periodic signals from the RV by iteratively subtracting dominant frequencies. This approach identified a semi-amplitude KK for CoRoT-7b by fitting a Keplerian model, incorporating the and eccentricity derived from transit photometry, while simultaneously accounting for a second signal from the non-transiting CoRoT-7c. Activity indicators, such as the bisector inverse slope (BIS) of the cross-correlation function (CCF), the (FWHM) of the CCF, and the Ca II H&K emission index, were analyzed to assess correlations with RV variations, revealing that some signals aligned with rather than planetary orbits. A 2011 reassessment of the HARPS dataset questioned the planetary nature of the CoRoT-7b signal, attributing it primarily to stellar activity based on low (1.2σ) and modeling with line bisectors and width indicators, which suggested no robust detection of a massive companion. Subsequent studies from 2012 to 2022 refuted this by incorporating additional HARPS observations and advanced modeling; for instance, simultaneous photometric data from CoRoT helped constrain activity patterns. Key advancements involved (GP) regression to model and subtract stellar activity signals from the RV curve, treating activity as quasi-periodic noise with a kernel that captures , decay timescale, and the star's ~23-day rotation period. In multi-planet fits, the GP framework isolated the planetary semi-amplitude KK for CoRoT-7b (~3.3 m/s) alongside CoRoT-7c, using and birth-death to select the optimal number of Keplerian signals while marginalizing over activity parameters. A 2022 analysis of extended HARPS data confirmed the signal, yielding a of 6.06 ± 0.65 masses for CoRoT-7b.

Infrared Observations

In 2011, the on the conducted observations of four transits of CoRoT-7b at 4.5 μm and 8.0 μm to validate the planetary signal in the near-infrared and mitigate uncertainties from stellar activity. These observations measured a transit depth of 0.426 ± 0.115 mmag at 4.5 μm, consistent with the visible-light depth of 0.350 ± 0.011 mmag from CoRoT (corresponding to flux depths of ~0.039% and ~0.032%, respectively), demonstrating an achromatic signal that rules out significant contamination from cooler stellar spots. At 8.0 μm, the measured depth was 0.11 ± 0.30 mmag, which is statistically insignificant due to higher instrumental noise but remains compatible with the expected planetary transit. No significant phase variations were detected in the Spitzer light curves beyond the transit events themselves, consistent with the limited thermal emission expected from this small, hot planet. This lack of detectable out-of-transit modulation suggests inefficient heat redistribution across the planet's surface, pointing to a thin or absent atmosphere. The infrared transits enabled refinements to CoRoT-7b's radius by reducing wavelength-dependent distortions from stellar spots, yielding a value of 1.585 ± 0.064 R⊕ at the time; combined later analyses give 1.528 ± 0.065 R⊕. The planet's dayside brightness temperature, derived from equilibrium models assuming low albedo, reaches approximately 2600 K, aligning with expectations for a bare-rock world lacking substantial atmospheric insulation.

Theoretical Models

Interior Structure

CoRoT-7b is modeled as a differentiated with a layered interior consisting of a large central iron core comprising approximately 60-70% of the planet's total mass (similar to Mercury), an overlying silicate mantle, and a possible thin crust, with no icy layers present due to the planet's extreme surface temperatures exceeding 2000 K. The core is likely solid under the high central pressures reaching several terapascals, while the mantle is composed primarily of high-pressure such as (Mg,Fe)SiO₃ transitioning to post-perovskite phases at depths where pressures surpass approximately 120 GPa. These models align with the planet's constraints of around 9.4 g/cm³ (John et al. 2022), indicating a predominantly rocky composition without significant volatile envelopes. The internal structure is governed by , expressed as dPdr=−ρg,\frac{dP}{dr} = -\rho g, where PP is , ρ\rho is , g=Gm(r)r2g = \frac{G m(r)}{r^2} is local gravity (with GG the , m(r)m(r) the interior to radius rr, and rr the radial distance from the center), solved alongside the continuity equation dmdr=4πr2ρ\frac{dm}{dr} = 4\pi r^2 \rho. Equations of state for each layer, such as the Birch-Murnaghan or Vinet forms adapted for high-pressure phases like post-perovskite, are integrated numerically to compute profiles that satisfy the observed of 6.06 ± 0.65 masses and radius of 1.53 ± 0.07 radii (John et al. 2022). In the mantle, post-perovskite's distinct elastic properties influence propagation, though direct observations remain infeasible. Thermal evolution models indicate that CoRoT-7b's mantle experiences vigorous in the upper layers but stalled or sluggish flow in the lowermost mantle due to pressure-induced viscosity increases and the planet's , which synchronizes rotation with its 0.85-day orbit around the host star. This locking creates stark dayside-nightside temperature contrasts, fostering a stagnant regime on the cooler nightside while enabling mobile on the irradiated dayside, with lateral temperature variations of several hundred . The intense stellar sustains a potential global or dayside magma ocean, with depths up to tens of kilometers and compositions rich in silicates like Al₂O₃ and CaO, inhibiting full mantle overturn and preserving a hot interior with central temperatures exceeding 6000 K. Numerical simulations of the density profile, incorporating these layered structures and thermal profiles, reproduce the observed planetary dimensions, with the core-mantle boundary typically located at a depth corresponding to a large core radius of about 0.8-0.9 planetary radii. These models demonstrate that an iron core mass fraction in the 60-70% range best matches the geophysical constraints, ruling out carbon-rich or volatile-dominated interiors.

Atmosphere and Surface

CoRoT-7b's atmosphere is theorized to consist primarily of rock vapors evaporated from its silicate-rich surface due to intense stellar irradiation, forming a tenuous envelope dominated by sodium (Na), oxygen (O₂ and O), and , with lesser amounts of metals like . These components arise from the of rock at temperatures exceeding 2000 K, where SiO emerges as the primary silicon-bearing gas and Na dominates the upper layers with column densities ranging from 10¹⁵ to 10²⁰ cm⁻². The atmosphere's low pressure, varying from about 1.5 Pa at the substellar point to less than 10⁻¹⁰ Pa on the nightside, precludes the formation of clouds or a thick envelope. Hydrodynamic escape, driven by extreme ultraviolet (XUV) irradiation from the host star, significantly influences atmospheric retention on CoRoT-7b. Models indicate a mass-loss rate of approximately 0.3 masses per gigayear through blow-off of this mineral atmosphere, primarily depleting volatile elements like Na while leaving the bulk rocky composition largely intact. This process is efficient due to the planet's close (0.017 AU), where XUV heating ionizes atmospheric constituents such as Na, Mg, O, and Si, enabling hydrodynamic outflow. The planet's surface exhibits stark hemispheric contrasts owing to its probable , with the dayside featuring a global of molten lava at temperatures around 2474 , composed mainly of Al₂O₃ and CaO, while the nightside cools to 50–75 , allowing rock solidification and crust formation. This thermal dichotomy results from minimal heat redistribution in the thin atmosphere, confining vaporization to the illuminated hemisphere. Transmission spectroscopy offers a pathway to detect these atmospheric and surface signatures, with models predicting prominent (Si–O) absorption features around 10 μm in the planet's , arising from the vapor and surface materials. Such observations could distinguish CoRoT-7b's -dominated composition from other types. Regarding , the extreme dayside temperatures preclude the presence of liquid water, rendering the planet uninhabitable by conventional standards, though tidal forces may induce intense akin to a "super-Io," potentially exceeding 10⁶ W m⁻² in if surpasses 10⁻⁴.

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