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LP 890-9
LP 890-9
LP 890-9
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LP 890-9
Observation data
Epoch J2000      Equinox J2000
Constellation Eridanus[1]
Right ascension 04h 16m 31.16176s[2]
Declination −28° 18′ 52.9543″[2]
Apparent magnitude (V) 18.0±0.2[3]
Characteristics
Evolutionary stage Main sequence[3]
Spectral type M6V[4]
Apparent magnitude (V) 18.0±0.2[3]
Apparent magnitude (G) 15.791±0.003[2]
Apparent magnitude (J) 12.258±0.023[3]
Apparent magnitude (H) 11.692±0.025[3]
Apparent magnitude (K) 11.344±0.023[3]
Astrometry
Radial velocity (Rv)28.84±2.84[2] km/s
Proper motion (μ) RA: 218.569 mas/yr[2]
Dec.: −251.145 mas/yr[2]
Parallax (π)30.9326±0.0418 mas[2]
Distance105.4 ± 0.1 ly
(32.33 ± 0.04 pc)
Absolute magnitude (MV)15.45±0.2[note 1]
Details[3]
Mass0.118±0.002 M☉
Radius0.1532+0.0048
−0.0024 R☉
Luminosity (bolometric)0.001438±0.000037 L☉
Surface gravity (log g)5.139+0.013
−0.028 cgs
Temperature2871+32
−45 K
Metallicity [Fe/H]−0.028±0.089 dex
Age7.2+2.2
−3.1 Gyr
Other designations
SPECULOOS-2, LP 890-9, NLTT 12925, TOI-4306, TIC 44898913, 2MASS J04163114-2818526, WISEA J041631.33-281855.5[5]
Database references
SIMBADdata
Exoplanet Archivedata

LP 890-9, also known as SPECULOOS-2 or TOI-4306, is a high proper motion red dwarf star located 105 light-years (32 pc) away from the Solar System in the constellation of Eridanus. The star has 12% the mass and 15% the radius of the Sun, and a temperature of 2,871 K (2,598 °C; 4,708 °F). It is extremely faint and, with an apparent magnitude of 18, is the faintest star with exoplanets discovered by the Transiting Exoplanet Survey Satellite.[6]

Planetary system

[edit]

In 2022, two exoplanets were discovered in orbit around this star. The first planet, LP 890-9 b, was initially identified using TESS. Further observations using SPECULOOS confirmed this planet and discovered a second planet, LP 890-9 c. Both planets are likely terrestrial planets, somewhat larger than Earth. The outer planet LP 890-9 c orbits within the habitable zone, and is a favorable target for atmospheric characterization using JWST.[3][7]

LP 890-9 c orbits near the inner edge of the conservative habitable zone, and models differ as to whether the planet is more likely to resemble Earth or Venus. Spectra from JWST should make it possible to distinguish between these two scenarios.[4] The planet is tidally locked to its host, meaning it has no day-night cycle like Earth.[8] While the planet's location in the habitable zone suggests a strong possibility of an Earth-like atmosphere and climate, the planet's large size may count against its habitability. In addition, the planet is close enough to its star that the powerful radiation may reduce its chances of habitability.[9] Another challenge for the potential habitability of LP 890-9 c is the magma ocean that would have formed during its infancy, which may have lasted for up to 50 million years. This could have removed eight Earth oceans’ worth of water and left 2000 bars of oxygen in its atmosphere, although if its initial hydrogen envelope had 0.1 Earth masses, no water would have been lost. Furthermore, the circulation of the planets orbit would take about 7 billion years, producing hundreds of terawatts of tidal heating.[10]

The habitability of LP 890-9 c depends heavily on the initial volatile content and properties and the planet is unlikely to support life.[10]

The LP 890-9 planetary system[3]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
b <13.2 M🜨 0.01875±0.00010 2.7299025+0.0000034
−0.0000040 		— 89.67+0.22
−0.33° 		1.320+0.053
−0.027 R🜨
c <25.3 M🜨 0.03984±0.00022 8.457463±0.000024 — 89.287+0.026
−0.047° 		1.367+0.055
−0.039 R🜨

See also

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Notes

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

LP 890-9

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LP 890-9, also known as TOI-4306 or -2, is an M6V star of approximately 0.118 solar masses and 0.156 solar radii, with an of 2850 K, situated 32 parsecs (about 105 light-years) from the Solar System. It hosts two transiting exoplanets, designated LP 890-9 b and LP 890-9 c, which were discovered in 2022 through observations by NASA's (TESS) for the inner planet and the survey for the outer one. The system is notable for its potential to study temperate terrestrial worlds around cool stars, with LP 890-9 c orbiting within the . The inner planet, LP 890-9 b, has a radius of about 1.32 radii and completes an orbit every 2.73 days, receiving roughly 4.09 times the stellar flux incident on , which places it outside the and suggests a hot, likely Venus-like environment. In contrast, LP 890-9 c is slightly larger, with a radius of 1.37 radii, and orbits its star in 8.46 days while receiving 0.906 times 's insolation, positioning it as a prime candidate for atmospheric characterization to assess liquid , though its depends on factors like atmospheric composition and internal heating. measurements provide upper limits on the minimum masses of approximately 13 masses for LP 890-9 b and 25 masses for LP 890-9 c, consistent with both being dense, rocky super-Earths. LP 890-9's low activity level and proximity make it an attractive target for future observations with telescopes like the , enabling detailed studies of planetary atmospheres and the system's dynamical evolution. Recent modeling suggests the planets formed beyond the current orbits and migrated inward, with LP 890-9 c retaining enough water to potentially support subsurface despite . The star's faint in visible light underscores the importance of surveys like in detecting such systems around ultracool dwarfs.

Stellar properties

Physical characteristics

LP 890-9 is a main-sequence star of spectral type M6 V. As a late-type M dwarf, it exhibits typical characteristics of cool, low-mass stars, including a dim red appearance due to its low surface temperature and small size. The star has a of 0.118 ± 0.002 M⊙ and a radius of 0.1556 ± 0.0086 R⊙, making it significantly smaller and less massive than the Sun. Its is 2850 ± 75 K, which contributes to its low luminosity of approximately 1.44 × 10^{-3} L⊙, calculated from fitting and evolutionary models. , derived from the mass and radius, is log g = 5.126^{+0.050}_{-0.047} (cgs units), consistent with expectations for a compact M dwarf. Located at a distance of 32.43 +0.07/-0.07 pc (equivalent to 105.8 +0.2/-0.2 light-years) in the constellation Eridanus, LP 890-9 is a relatively nearby stellar object. Its apparent visual magnitude is 18.0 ± 0.2, rendering it extremely faint and the faintest known host star for confirmed exoplanets detected by the (TESS). The star displays high , with components of 218.53 ± 0.10 mas yr^{-1} in and -251.13 ± 0.12 mas yr^{-1} in , indicating rapid transverse velocity across the sky.

Age and activity

LP 890-9 is estimated to be 7.2 Gyr old, with uncertainties of +2.2 Gyr and -3.1 Gyr, based on comparisons of its Galactic and to a sample of nearby stars from the DR3 survey. This method adapts kinematic age indicators originally developed for younger stars, reflecting the star's mature evolutionary stage as a late-type M dwarf. The star exhibits a rotation period of approximately 50–55 days, typical for mid-to-late M dwarfs of similar age, as derived from Lomb-Scargle periodograms of ground-based photometry. Magnetic activity is low, characterized by weak Hα emission with an of -1.5 ± 0.3 and a normalized of log₁₀(L_{Hα}/L_{bol}) = -4.58 ± 0.10, alongside an XUV of (5 ± 2) × 10^{-5} L_{bol}. No definitive were detected in available light curves, but as with many late M dwarfs, sporadic flare activity remains possible and could erode planetary atmospheres through high-energy over the system's lifetime. During its pre-main sequence phase, LP 890-9 took approximately 1 Gyr to reach the , a prolonged contraction period for such low-mass stars that influences early planetary dynamics. This extended phase likely exposed forming to intense stellar and , potentially affecting volatile retention and the delivery of or other ices to inner orbits. LP 890-9 has a low metallicity of [Fe/H] = -0.03 ± 0.09, consistent with typical field M dwarfs. This subsolar composition may reduce the efficiency of planet formation by limiting the availability of solid building blocks for rocky cores, particularly in the inner disk where super-Earths like those in this system likely accreted.

Discovery

Initial detection

The planetary system around LP 890-9 was initially detected in 2022 as part of NASA's (TESS) mission, which conducts wide-field photometric surveys to identify transiting exoplanets around nearby stars. The star, alternatively designated as TOI-4306 (TESS Object of Interest) or (from the survey), was monitored by TESS in sectors 4, 5, 31, and 32, spanning observations from October 2018 to December 2020. In these datasets, transit photometry revealed periodic dips in the star's brightness, flagging a single transiting candidate, TOI-4306.01, which was publicly announced by the TESS Science Office on July 21, 2021. This method relies on detecting the slight dimming of stellar light as a crosses the , providing the first evidence of an orbiting companion. A second transiting candidate was identified shortly thereafter through ground-based support observations with the Southern Observatory telescopes, which began intensive monitoring of the target on August 9, 2021. These early photometric follow-ups confirmed the initial TESS transit events and detected additional periodic signals not visible in the space-based data, establishing two super-Earth-sized candidates in the system. Subsequent validation efforts, including measurements, refined these initial findings but were part of later characterization phases.

Confirmation and characterization

Following the initial detection of a transiting planetary candidate around LP 890-9 by the (TESS), confirmation and characterization efforts relied on intensive ground-based photometric monitoring with the (Search for Planets EClipsing ULtra-cOOl Stars) network of 1-meter telescopes. These observations, conducted primarily at SPECULOOS-South in from August 2021 to January 2022, spanned 614 hours over 119 nights using an I+z' broadband filter, successfully confirming the transit of the inner candidate LP 890-9 b (depth ≈0.82%) and revealing the outer planet LP 890-9 c (depth ≈0.64%, period 8.46 days). Multi-color photometry from the MuSCAT3 instrument on the 1.88 m telescope at further validated the transits, ruling out blended eclipsing binaries through color-dependent depth analysis. Statistical validation using the tool yielded false positive probabilities below 10^{-6} for both planets, solidifying their planetary nature without radial velocity (RV) confirmation at the time. High-precision RV follow-up was performed using the Doppler (IRD) spectrograph on the , acquiring 14 spectra between September 2021 and January 2022 with a resolution of R=70,000 in the near-infrared Y, J, and H bands. The data constrained the RV semi-amplitudes to K < 25.1 m/s for LP 890-9 b and K < 33.0 m/s for LP 890-9 c at 2σ confidence, translating to upper mass limits of 13.2 M_⊕ and 25.3 M_⊕, respectively, under the assumption of circular, edge-on orbits. These limits, while not detecting the planets directly due to the faintness of the M6V host star (J=12.5 mag), provide critical bounds for mass-radius modeling. Predicted masses from empirical mass-radius relations for small planets yield ~2.3 M_⊕ for b and ~3.0 M_⊕ for c, implying bulk densities of ~6-8 g/cm³—indicative of rocky compositions dominated by iron-rich cores and silicate mantles, with minimal volatile envelopes. High-resolution imaging with Zorro on Gemini South excluded stellar companions within 1" that could mimic the signals. Transit timing variation (TTV) analysis of the combined TESS and SPECULOOS light curves, covering ~150 days of baseline, revealed no significant timing deviations beyond photometric uncertainties (~1 minute per transit). This absence of TTVs, despite the planets' proximity to a 3:1 mean-motion resonance (period ratio 3.098), constrains possible gravitational interactions and rules out close resonant configurations that would produce detectable signals >1-2 minutes. Dynamical simulations using the N-body integrator confirmed long-term orbital stability without mean-motion resonance trapping. The transit depths from these datasets informed derivations of 1.320^{+0.053}{-0.027} R⊕ for b and 1.367^{+0.050}{-0.027} R⊕ for c, establishing the planets as super-Earths with equilibrium temperatures of ~368 K (b) and ~264 K (c). Theoretical transmission spectroscopy models for LP 890-9 c, tailored for (JWST) observations, predict flat spectra under CO_2-dominated Venus-like atmospheres or H_2O features in hydrated scenarios, providing preliminary constraints on atmospheric retention and detectability with NIRSpec/ (signal-to-noise ~10 per transit at 3σ for key bands). These efforts highlight the system's suitability for future RV campaigns with next-generation instruments to refine masses below current limits. As of November 2025, JWST observations of the LP 890-9 planets have been proposed but not yet executed.

Planetary system

System architecture

The LP 890-9 planetary system consists of two confirmed transiting super-Earths, designated LP 890-9 b and LP 890-9 c, orbiting a nearby late-type M dwarf star at a distance of approximately 105 light-years. Both planets were detected through transit photometry, indicating that their orbital planes are closely aligned with our line of sight to the host star. The inner planet, LP 890-9 b, has an orbital period of 2.73 days and a semi-major axis of 0.01875 AU, while the outer planet, LP 890-9 c, orbits with a period of 8.46 days and a semi-major axis of 0.03984 AU. These short-period orbits place both planets well within 0.04 AU of the star, characteristic of compact multi-planet systems around cool dwarfs. The orbital eccentricities are near zero for both planets, a consequence of tidal circularization driven by the host star's gravitational influence, which is expected to dampen any initial eccentricity within approximately 0.5 Gyr assuming constant tidal dissipation. The system's orbital inclinations are 89.67° for LP 890-9 b and 89.29° for LP 890-9 c, confirming co-planar orbits aligned nearly edge-on to , which facilitates their mutual transits. Analysis indicates that the planets are not in a 3:1 resonance, as their period ratio of approximately 3.1 deviates from exact commensurability. Despite this, N-body simulations demonstrate long-term dynamical stability over gigayear timescales, with no significant perturbations leading to in the compact configuration. LP 890-9 c resides near the inner edge of the conservative , receiving an incident stellar flux of 0.906 ± 0.026 times that of (S⊕), as determined from the host star's of 0.00144 L⊙. This positioning highlights the system's potential for temperate conditions on the outer , though the inner receives over four times 's flux, rendering it too hot for .

LP 890-9 b

LP 890-9 b is a with a radius of 1.320 ± 0.053 R⊕, classifying it as a rocky world larger than but smaller than Neptune-sized planets. Its equilibrium temperature is approximately 396 K, assuming zero and efficient heat redistribution, rendering it a hot environment far interior to the system's . This places LP 890-9 b among the innermost planets orbiting its M6-type host star, receiving intense stellar irradiation due to its close-in orbit of 2.73 days at a semi-major axis of 0.01875 AU. The planet's mass is estimated at 2.3^{+1.7}_{-0.7} M⊕ based on mass-radius relations for compositions, with observations providing an upper limit of <13.2 M⊕ at 2σ confidence. This implies a of approximately 7 g/cm³ if assuming an iron-rich core and minimal volatile envelope, consistent with a differentiated structure featuring a substantial metallic core and thin mantle. The high inferred suggests limited retention of lighter elements, aligning with models of super-Earths that have undergone significant core formation and . Due to its proximity to the star, LP 890-9 b is likely tidally locked, with one hemisphere perpetually facing the host star and experiencing extreme daytime temperatures. The intense irradiation promotes potential , particularly during the star's pre-main-sequence phase when elevated and fluxes could strip volatiles; simulations indicate the planet may have lost up to 9.9 oceans of water in the first 370 Myr without a primordial envelope. Tidal effects have likely circularized the orbit within ~100 Myr, minimizing ongoing heating from eccentricity. LP 890-9 b was identified through a deeper transit signal of ~0.6% depth in TESS photometry, deeper than that of its outer companion, facilitating its detection despite the faint host star. Initial transmission spectroscopy from ground-based observations shows no significant atmospheric features, consistent with a thin or absent atmosphere, though JWST follow-up is anticipated to probe for residual gases or potential oxygen accumulation from escape processes. The planet likely formed within the , accreting rocky material close to the star before losing volatiles during the host's luminous pre-main-sequence evolution. This formation scenario explains its current iron-enriched composition and lack of substantial gaseous , typical for inner s around cool dwarfs.

LP 890-9 c

LP 890-9 c is a orbiting the star LP 890-9, positioned as the outer planet in the system's compact architecture. It has a radius of 1.367 ± 0.055 radii, measured via transit photometry from the TESS and telescopes. The planet's mass remains unconstrained by direct measurements, with an upper limit of less than 25.3 masses at 2σ confidence, though probabilistic estimates based on mass-radius relations suggest a value around 2.5 ± 1.8 masses, implying a of approximately 5.4 g/cm³ consistent with an Earth-like rocky composition or a world with a modest volatile . The completes one every 8.457 ± 0.013 days at a semi-major axis of 0.03984 ± 0.00022 AU, placing it significantly closer to its host star than Mercury is to the Sun. Given this proximity and the star's , is expected on timescales of about 1.5 million years, resulting in permanent day and night sides. The equilibrium temperature, assuming zero and full heat redistribution, is approximately 272 ± 2 , positioning the within the stellar but near its inner boundary. If volatiles such as water have been retained during formation and early evolution, surface conditions could support liquid water oceans, particularly under a thin atmosphere that moderates extremes. Transmission spectroscopy observations with the are anticipated to probe for such an atmosphere, potentially revealing signatures of a tenuous rich in or other volatiles. In scale, LP 890-9 c exceeds in size and mass but maintains a profile more akin to a scaled-up terrestrial world than the lower-density ice giants like , suggesting a predominantly rocky interior possibly overlaid with a hydrated layer.

Habitability and future research

Potential habitability of LP 890-9 c

LP 890-9 c, a orbiting near the inner edge of the around its M6V host star, formed 5–20 million years after the star's formation, with in situ accretion unlikely to position it in the observed 3:1 mean-motion with planet b. During the early evolution of the system, the planet experienced a ocean phase lasting up to 50 million years, which led to significant and the potential accumulation of abiotic oxygen in the atmosphere at pressures reaching 2000 bars, depending on the planet's mass and the timing of dissipation. This phase is estimated to have removed the equivalent of 8 oceans of through , shaping the planet's initial volatile inventory and atmospheric composition. Tidal interactions play a crucial role in the planet's long-term , with orbital circularization occurring over timescales ranging from 0.5 billion years under constant to more than 7 billion years if varies with mantle . from these interactions could generate up to hundreds of terawatts of energy, potentially sustaining geological activity such as , while the planet is expected to become tidally locked within tens of thousands of years due to spin-orbit . The retention of volatiles is influenced by the presence of a thin envelope, as small as 0.1 masses, which could shield from loss during the host star's pre-main-sequence phase through escape processes. Overall thus depends heavily on the initial volatile content and internal heat sources, including both and radiogenic contributions. Recent models from 2024–2025 indicate that no current data preclude the existence of an active on LP 890-9 c, though challenges persist from the star's frequent flares and the consequences of , which could lead to diverse climate outcomes akin to the Venus-Earth dichotomy. These simulations highlight the planet's position near the inner boundary, where it spends 100–600 million years inside the zone during the system's early evolution, emphasizing the need for further constraints on atmospheric and internal properties to assess potential.

Planned observations

The (JWST) has been prioritized for observations of the LP 890-9 system, particularly targeting planet c for atmospheric characterization via transmission spectroscopy. Approved programs, such as GO 7073 ("Charting the Cosmic Shoreline"), utilize the Near-Infrared Spectrograph (NIRSpec) in prism mode to probe the planet's atmosphere across 0.6–5.3 μm, aiming to detect key molecules including (H₂O), (CO₂), and potential biosignatures like (N₂O). These observations, including multi-epoch transits scheduled for 2025, are expected to achieve signal-to-noise ratios sufficient for distinguishing atmospheric compositions, with predictions indicating H₂O detection possible in 3–11 transits for a water-rich scenario and CO₂ in about 8 transits for a cloud-free Venus-like atmosphere. The (MIRI) Low Resolution Spectrometer (LRS) in the 5–12 μm range is also considered for complementary thermal emission studies, though it faces larger error bars due to the system's faintness. Ground-based facilities offer prospects for refining planetary masses and searching for companions, though challenges arise from the host star's faintness (J ≈ 14.5 mag). The (ELT) with its spectrograph and the (GMT) are planned for high-precision (RV) measurements to determine the masses of s b and c, potentially achieving 7–9σ detections with around 60 spectra per instrument, given the expected RV semi-amplitude of ~3.3 m/s for planet c. High-contrast imaging efforts, such as those with on 8–10 m telescopes, are limited by the system's low contrast and proximity to the star, making direct detection of additional planets or circumstellar material difficult without next-generation facilities. Atmospheric modeling efforts tied to these observations seek to differentiate between a Venus-like runaway greenhouse state (dominated by thick CO₂ clouds) and an Earth-like habitable environment on planet c, using JWST spectra to constrain pressure-temperature profiles and cloud properties. For instance, unocculted starspots could mimic molecular absorptions, necessitating multi-epoch data to isolate planetary signals from stellar variability. Long-term photometric monitoring continues with the network and extended (TESS) surveys to detect additional transiting planets or variability in the known worlds, building on prior coverage that reached 86% phase completeness out to 25 days. These efforts aim to reveal outer system architecture or orbital perturbations. Key challenges include stellar activity interference in RV datasets, which can mask planetary signals and requires extensive multi-epoch observations post-2025 to model and subtract chromospheric noise effectively. The faint host star further demands long integration times, emphasizing the need for coordinated space- and ground-based campaigns.
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