The L 98-59 System: Three Transiting, Terrestrial-Sized Planets Orbiting a Nearby M-dwarf (1903.08017v2)

Abstract: We report the Transiting Exoplanet Survey Satellite (TESS) discovery of three terrestrial-sized planets transiting L 98-59 (TOI-175, TIC 307210830) -- a bright M dwarf at a distance of 10.6 pc. Using the Gaia-measured distance and broad-band photometry we find that the host star is an M3 dwarf. Combined with the TESS transits from three sectors, the corresponding stellar parameters yield planet radii ranging from 0.8REarth to 1.6REarth. All three planets have short orbital periods, ranging from 2.25 to 7.45 days with the outer pair just wide of a 2:1 period resonance. Diagnostic tests produced by the TESS Data Validation Report and the vetting package DAVE rule out common false positive sources. These analyses, along with dedicated follow-up and the multiplicity of the system, lend confidence that the observed signals are caused by planets transiting L 98-59 and are not associated with other sources in the field. The L 98-59 system is interesting for a number of reasons: the host star is bright (V = 11.7 mag, K = 7.1 mag) and the planets are prime targets for further follow-up observations including precision radial-velocity mass measurements and future transit spectroscopy with the James Webb Space Telescope; the near resonant configuration makes the system a laboratory to study planetary system dynamical evolution; and three planets of relatively similar size in the same system present an opportunity to study terrestrial planets where other variables (age, metallicity, etc.) can be held constant. L 98-59 will be observed in 4 more TESS sectors, which will provide a wealth of information on the three currently known planets and have the potential to reveal additional planets in the system.

Analysis of the L 98-59 System: Transiting Terrestrial Planets

The paper dissects the findings from the discovery of three terrestrial-sized planets transiting the nearby M-dwarf, L 98-59, using data from the Transiting Exoplanet Survey Satellite (TESS). This system presents a structured and detailed paper of a planetary system just 10.6 parsecs away, establishing it as a prospective target for future detailed exoplanet exploration, particularly atmospheric studies.

Key Findings

The identified planets, L 98-59 b, c, and d, orbit an M3 dwarf star, which is characterized as relatively bright, with a V magnitude of 11.7. The paper leverages Gaia-derived stellar parameters in tandem with TESS data, identifying that the planet radii range from 0.8 to 1.6 Earth radii, with short orbital periods between 2.25 and 7.45 days. Notably, the outer two planets are near a 2:1 period resonance, allowing this system to serve as a model for studying planetary system dynamics.

Verification and Analysis

The researchers employed the TESS Data Validation Report and the DAVE vetting package to rule out standard false-positive scenarios, such as signal contamination from other astrophysical sources. This vigorous vetting supports the authenticity of the transit signals as planetary in nature. The authors have integrated ground-based follow-up to augment TESS findings and ascertain the planetary status of these bodies.

Implications

The L 98-59 system, by virtue of its short-period and the near-resonant nature of the outer planets, presents multiple opportunities:

• Dynamical Studies: Its near-resonant configuration provides a unique opportunity to extrapolate the dynamical interplays within multi-planet systems, potentially enhancing our understanding of planetary migration and resonances.
• Atmospheric Characterization: Due to its proximity and the brightness of the host star, the system is a viable candidate for atmospheric characterization, notably with technologies like the James Webb Space Telescope (JWST). The ability to hold constant various parameters such as metallicity and stellar age across different planets enhances comparative planetary atmospheric studies.
• Habitability Considerations: Despite the high levels of stellar irradiation receiving by these planets, making them unlikely candidates for life as traditionally conceived, they nevertheless contribute to the paper of potential Venus analogs, offering insights into atmospheric retention and evolution under high radiation conditions.

Theoretical and Future Development

This paper opens several pathways for theoretical and observational advancements:

1. Evolutionary Dynamics: It invites further exploration into understanding the evolutionary pathways of compact planetary systems.
2. Follow-up Campaigns: Using radial velocity follow-ups to measure planetary masses more precisely could solidify the mass-radius context of these planets, making them critical for calibrating relations relevant to terrestrial planets.
3. Transit Timing Variations: Further transit observations may observe timing variations, sharpening our understanding of the planet's interactions and orbit evolution.

Considering these aspects, the L 98-59 system stands poised to become a benchmark for studies of terrestrial planets orbiting M-dwarfs, with implications for both exoplanet atmospheric science and the modeling of planetary system dynamics.