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arXiv · 2502.16087

TOI-6324b: An Earth-Mass Ultra-Short-Period Planet Transiting a Nearby M Dwarf

Rena A. Lee·Fei Dai·Andrew W. Howard·Samuel Halverson·Jonathan Gomez Barrientos·Michael Greklek-McKeon·Heather A. Knutson·Benjamin J. Fulton·Guðmundur Stefánsson·Jack Lubin·Howard Isaacson·Casey L. Brinkman·Nicholas Saunders·Daniel Hey·Daniel Huber·Lauren M. Weiss·Leslie A. Rogers·Diana Valencia·Mykhaylo Plotnykov·Kimberly Paragas·Renyu Hu·Te Han·Erik A. Petigura·Ryan Rubenzahl·David R. Ciardi·Aaron Householder·Gregory J. Gilbert·J. M. Joel Ong·Jingwen Zhang·Jacob Luhn·Luke Handley·Corey Beard·Steven Giacalone·Rae Holcomb·Judah Van Zandt·Ashley D. Baker·Max Brodheim·Matt Brown·David Charbonneau·Karen A. Collins·Ian J. M. Crossfield·William Deich·Xavier Dumusque·Steven R. Gibson·Emily Gilbert·Grant M. Hill·Bradford Holden·Jon M. Jenkins·Stephen Kaye·Russ R. Laher·Kyle Lanclos·W. Garrett Levine·Joel Payne·Alex S. Polanski·John O'Meara·George R. Ricker·Kodi Rider·Paul Robertson·Arpita Roy·Joshua E. Schlieder·Christian Schwab·Sara Seager·Abby P. Shaum·Martin M. Sirk·Stephanie Striegel·Johanna Teske·John Valliant·Roland Vanderspek·Gautam Vasisht·Josh Walawender·Sharon Xuesong Wang·Joshua N. Winn·Edward Wishnow·Sherry Yeh
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Abstract

We report the confirmation of TOI-6324 b, an Earth-sized (1.059 $\pm$ 0.041 R$_\oplus$) ultra-short-period (USP) planet orbiting a nearby ($\sim$20 pc) M dwarf. Using the newly commissioned Keck Planet Finder (KPF) spectrograph, we have measured the mass of TOI-6324 b 1.17 $\pm$ 0.22 M$_\oplus$. Because of its extremely short orbit of just $\sim$6.7 hours, TOI-6324 b is intensely irradiated by its M dwarf host, and is expected to be stripped of any thick, H/He envelope. We were able to constrain its interior composition and found an iron core mass fraction (CMF = 27$\pm$37%) consistent with that of Earth ($\sim$33%) and other confirmed USPs. TOI-6324 b is the closest to Earth-sized USP confirmed to date. TOI-6324 b is a promising target for JWST phase curve and secondary eclipse observations (Emission Spectroscopy Metric = 25) which may reveal its surface mineralogy, day-night temperature contrast, and possible tidal deformation. From 7 sectors of TESS data, we report a tentative detection of the optical phase curve variation with an amplitude of 42$\pm$28 ppm.

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Rena A. Lee, Fei Dai, Andrew W. Howard, Samuel Halverson, Jonathan Gomez Barrientos, Michael Greklek-McKeon, Heather A. Knutson, Benjamin J. Fulton, Guðmundur Stefánsson, Jack Lubin, Howard Isaacson, Casey L. Brinkman, Nicholas Saunders, Daniel Hey, Daniel Huber, Lauren M. Weiss, Leslie A. Rogers, Diana Valencia, Mykhaylo Plotnykov, Kimberly Paragas, Renyu Hu, Te Han, Erik A. Petigura, Ryan Rubenzahl, David R. Ciardi, Aaron Householder, Gregory J. Gilbert, J. M. Joel Ong, Jingwen Zhang, Jacob Luhn, Luke Handley, Corey Beard, Steven Giacalone, Rae Holcomb, Judah Van Zandt, Ashley D. Baker, Max Brodheim, Matt Brown, David Charbonneau, Karen A. Collins, Ian J. M. Crossfield, William Deich, Xavier Dumusque, Steven R. Gibson, Emily Gilbert, Grant M. Hill, Bradford Holden, Jon M. Jenkins, Stephen Kaye, Russ R. Laher, Kyle Lanclos, W. Garrett Levine, Joel Payne, Alex S. Polanski, John O'Meara, George R. Ricker, Kodi Rider, Paul Robertson, Arpita Roy, Joshua E. Schlieder, Christian Schwab, Sara Seager, Abby P. Shaum, Martin M. Sirk, Stephanie Striegel, Johanna Teske, John Valliant, Roland Vanderspek, Gautam Vasisht, Josh Walawender, Sharon Xuesong Wang, Joshua N. Winn, Edward Wishnow, Sherry Yeh. 2025-02-22. TOI-6324b: An Earth-Mass Ultra-Short-Period Planet Transiting a Nearby M Dwarf. https://arxiv.org/abs/2502.16087

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