Exoplanetology: Exoplanets & Exomoons

The Compositions of Rocky Planets in Close-in Orbits Tend to be Earth-Like

By Keith Cowing

Status Report

astro-ph.EP

October 2, 2024

Filed under astro-ph.EP, astronomy, Earth-like Planet, exoplanet, Gemini/MAROON-X, HD 93963 A b, imaging, Keck/KPF, Kepler-10 b, Kepler-100 b, Kepler-407 b, rocky exoplanet, super-Mercury, TOI-1444 b

The Compositions of Rocky Planets in Close-in Orbits Tend to be Earth-Like — Planet radius vs. mass for our sample (diamonds) are shown in the context of the rocky planet population (circles). Opaque diamonds represent our mass and radius measurements while translucent diamonds are the previously published values. Lines show mass-radius relations for planets with an Earth-like composition, a purely silicate-rock composition, and a purely iron composition (Zeng et al. 2019). Literature values come from the NASA Exoplanet Archive (Akeson et al. 2013) queried 4/12/2024 for planets with mass and radius measurements with fractional uncertainties <50%, and the circle size is inversely correlated with fractional uncertainty in density. Planets consistent with a rocky composition (mixture of iron and silicate only) are shown in pink. Planets with masses and radii 1σ away from a pure silicate composition (dashed line) are shown in purple, and possibly host envelopes made of high-mean molecular weight (MMW) species. -- astro-ph.EPlanet radius vs. mass for our sample (diamonds) are shown in the context of the rocky planet population (circles). Opaque diamonds represent our mass and radius measurements while translucent diamonds are the previously published values. Lines show mass-radius relations for planets with an Earth-like composition, a purely silicate-rock composition, and a purely iron composition (Zeng et al. 2019). Literature values come from the NASA Exoplanet Archive (Akeson et al. 2013) queried 4/12/2024 for planets with mass and radius measurements with fractional uncertainties <50%, and the circle size is inversely correlated with fractional uncertainty in density. Planets consistent with a rocky composition (mixture of iron and silicate only) are shown in pink. Planets with masses and radii 1σ away from a pure silicate composition (dashed line) are shown in purple, and possibly host envelopes made of high-mean molecular weight (MMW) species. -- astro-ph.EPP

Hundreds of exoplanets between 1-1.8 times the size of the Earth have been discovered on close in orbits. However, these planets show such a diversity in densities that some appear to be made entirely of iron, while others appear to host gaseous envelopes.

To test this diversity in composition, we update the masses of 5 rocky exoplanets (HD 93963 A b, Kepler-10 b, Kepler-100 b, Kepler-407 b, and TOI-1444 b) and present the confirmation of a new planet (TOI-1011) using 187 high precision RVs from Gemini/MAROON-X and Keck/KPF. Our updated planet masses suggest compositions closer to that of the Earth than previous literature values for all planets in our sample.

In particular, we report that two previously identified “super-Mercuries” (Kepler-100 b and HD 93963 A b) have lower masses that suggest less iron-rich compositions. We then compare the ratio of iron to rock-building species to the abundance ratios of those elements in their host stars.

These updated planet compositions do not suggest a steep relationship between planet and host star compositions, contradictory to previous results, and suggest that planets and host stars have similar abundance ratios.

Casey L. Brinkman, Lauren M. Weiss, Daniel Huber, Rena A. Lee, Jared Kolecki, Gwyneth Tenn, Jingwen Zhang, Suchitra Narayanan, Alex S. Polanski, Fei Dai, Jacob L. Bean, Corey Beard, Madison Brady, Max Brodheim, Matt Brown, William Deich, Jerry Edelstein, Benjamin J. Fulton, Steven Giacalone, Steven R. Gibson, Gregory J. Gilbert, Samuel Halverson, Luke Handley, Grant M. Hill, Rae Holcomb, Bradford Holden, Aaron Householder, Andrew W. Howard, Howard Isaacson, Stephen Kaye, Russ R. Laher, Kyle Lanclos, J. M. Joel Ong, Joel Payne, Eric A. Petigura, Daria Pidhorodetska, Claire Poppett, Arpita Roy, Ryan Rubenzahl, Nicholas Saunders, Christian Schwab, Andreas Seifahrt, Abby P. Shaum, Martin M. Sirk, Chris Smith, Roger Smith, Guðmundur Stefánsson, Julian Stürmer, Jim Thorne, Emma V. Turtelboom, Dakotah Tyler, John Valliant, Judah Van Zandt, Josh Walawender, Samuel W. Yee, Sherry Yeh, Jon Zink

Comments: Submitted to AJ 09/30/2024
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2410.00213 [astro-ph.EP] (or arXiv:2410.00213v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2410.00213
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Submission history
From: Casey Brinkman
[v1] Mon, 30 Sep 2024 20:17:05 UTC (11,456 KB)
https://arxiv.org/abs/2410.00213

Astrobiology,

Keith Cowing

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) 🖖🏻

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