The Compositions of Rocky Planets in Close-in Orbits Tend to Be Earth-like

August 2025 • 2025AJ....170..109B

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

Abstract • Hundreds of exoplanets between 1 and 1.8 times the size of 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 five 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 radial velocities from Gemini/MAROON-X and Keck/KPF. Our updated planet masses suggest compositions closer to that of 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 with 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.

Links

• PDF https://iopscience.iop.org/article/10.3847/1538-3881/ade677/pdf
• PREPRINT http://arxiv.org/abs/2410.00213
• ELECTR https://doi.org/10.3847/1538-3881/ade677