Exoplanets & Exomoons

HST/WFC3 Light Curve Confirms the Closest Exoplanet to Transit an M Dwarf is Terrestrial

By Keith Cowing
Status Report
July 7, 2023
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HST/WFC3 Light Curve Confirms the Closest Exoplanet to Transit an M Dwarf is Terrestrial
The phased light curve of LTT 1445A, highlighting the transit of planet c. The detrended TESS observations are show in black and our new HST observations in orange. In blue, we show our MAP orbital solution. — astro-ph.EP

Previous studies of the exoplanet LTT 1445Ac concluded that the light curve from the Transiting Exoplanet Survey Satellite (TESS) was consistent with both grazing and non-grazing geometries. As a result, the radius and hence density of the planet remained unknown.

To resolve this ambiguity, we observed the LTT 1445 system for six spacecraft orbits of the Hubble Space Telescope (HST) using WFC3/UVIS imaging in spatial scan mode, including one partial transit of LTT 1445Ac. This imaging produces resolved light curves of each of the three stars in the LTT 1445 system.

We confirm that the planet transits LTT 1445A and that LTT 1445C is the source of the rotational modulation seen in the TESS light curve, and we refine the estimate of the dilution factor for the TESS data. We perform a joint fit to the TESS and HST observations, finding that the transit of LTT 1445Ac is not grazing with 97% confidence.

We measure a planetary radius of 1.10+0.10βˆ’0.07 RβŠ•. Combined with previous radial velocity observations, our analysis yields a planetary mass of 1.36Β±0.19 MβŠ• and a planetary density of 5.6+1.7βˆ’1.5 g cmβˆ’3. LTT 1445Ac is an Earth analog with respect to its mass and radius, albeit with a higher instellation, and is therefore an exciting target for future atmospheric studies.

Emily K Pass, Jennifer G Winters, David Charbonneau, Aurelia Balkanski, Nikole Lewis, Maura Lally, Jacob L Bean, Ryan Cloutier, Jason D Eastman

Comments: Submitted to AJ. 9 pages, 7 figures, 3 tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2307.02970 [astro-ph.EP] (or arXiv:2307.02970v1 [astro-ph.EP] for this version)
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Submission history
From: Emily Pass
[v1] Thu, 6 Jul 2023 13:16:51 UTC (693 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) πŸ––πŸ»