L 98-59 : A nearby M dwarf with multiple low-mass planets

Led_Zep wrote:

https://archive.stsci.edu/prepds/tess-data-alerts/
Data Products From TESS Data Alerts ("TESS-DATA-ALERTS")

Apparently we should be watching that page more. Sector 2 planets were added, including a three-planet system around the very nearby (~10 pc) star L 98-59.

I calculated that out of 29 known transit planets within a radius of 30 parsecs, TESS accounts for 7 discoveries or 24%! (L 98-59, Pi Mesa, LHS 3844, GJ 3090, GJ 4332).

Interestingly, the distance to L 98-59 was determined for the first time only with Gaia (only two years ago!).

https://twitter.com/ericmamajek/status/776497265233965057

EricMamajek wrote:

Nearest star in @ESAGaia #GaiaDR1 TGAS that appears to have previously lacked trig parallax is M2 dwarf TYC 9193-2365-1 (d=10.55+-0.11 pc).
12:05 - 15 september 2016 г.

In a couple of years, this little-known system will become the opposite of one of the most famous!

Characterization of the L 98-59 multi-planetary system with HARPS: two confirmed terrestrial planets and a mass upper limit on the third
https://arxiv.org/abs/1905.10669

Quote :

L 98-59 (TIC 307210830, TOI-175) is a nearby M3 dwarf around which TESS revealed three terrestrial-sized transiting planets (0.80, 1.35, 1.57 Earth radii) in a compact configuration with orbital periods shorter than 7.5 days. Here we aim to measure the masses of the known transiting planets in this system using precise radial velocity (RV) measurements taken with the HARPS spectrograph. We consider both trained and untrained Gaussian process regression models of stellar activity to simultaneously model the RV data with the planetary signals. Our RV analysis is then supplemented with dynamical simulations to provide strong constraints on the planets' orbital eccentricities by requiring long-term stability. We measure the planet masses of the two outermost planets to be 2.46±0.31 and 2.26±0.50 Earth masses which confirms their bulk terrestrial compositions. We are able to place an upper limit on the mass of the smallest, innermost planet of <0.98 Earth masses with 95% confidence. Our RV plus dynamical stability analysis places strong constraints on the orbital eccentricities and reveals that each planet's orbit likely has e<0.1 to ensure a dynamically stable system. The L 98-59 compact system of three likely rocky planets offers a unique laboratory for studies of planet formation, dynamical stability, and comparative atmospheric planetology. Continued RV monitoring will help refine the characterization of the innermost planet and potentially reveal additional planets in the system at wider separations.

Sirius_Alpha wrote:

Characterization of the L 98-59 multi-planetary system with HARPS: two confirmed terrestrial planets and a mass upper limit on the third
https://arxiv.org/abs/1905.10669

https://drive.google.com/file/d/14ZfNbPc77kEplcXbUzSxfEhaNOFq7N4I/view

a pdf about the system

Since this system will be getting a lot of interest, I've split it off from the main TESS thread.

New news on the system in the form of an ESO press release. Using ESPRESSO, the mass of the b planet has been determined to be 0.4 Earth-masses -- the lightest exoplanet with an RV-measured mass. They also find one, possibly two more planets in the system. The outermost would be in the star's HZ.

New ESO observations show rocky exoplanet has just half the mass of Venus
https://www.eso.org/public/news/eso2112/?lang

A couple of papers on the transmission spectrum of L 98-59 b, which joins the flat spectrum club.

Damiano et al. "A transmission spectrum of the sub-Earth planet L98-59 b in 1.1-1.7 μm"
https://arxiv.org/abs/2210.10008

Zhou et al. "Hubble WFC3 Spectroscopy of the Rocky Planet L 98-59 b: No Evidence for a Cloud-Free Primordial Atmosphere"
https://arxiv.org/abs/2210.10699