April
2025
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2025ApJ...983L..36L
Authors
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Lee, Rena A.
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Dai, Fei
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Howard, Andrew W.
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Halverson, Samuel
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Gomez Barrientos, Jonathan
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Greklek-McKeon, Michael
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Knutson, Heather A.
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Fulton, Benjamin J.
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Stefánsson, Guđmundur
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Lubin, Jack
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Isaacson, Howard
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Brinkman, Casey L.
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Saunders, Nicholas
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Hey, Daniel
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Huber, Daniel
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Weiss, Lauren M.
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Rogers, Leslie A.
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Valencia, Diana
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Plotnykov, Mykhaylo
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Paragas, Kimberly
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Hu, Renyu
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Han, Te
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Petigura, Erik A.
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Rubenzahl, Ryan
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Ciardi, David R.
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Householder, Aaron
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Gilbert, Gregory J.
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Ong, J. M. Joel
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Zhang, Jingwen
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Luhn, Jacob
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Handley, Luke
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Beard, Corey
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Giacalone, Steven
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Holcomb, Rae
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Van Zandt, Judah
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Baker, Ashley D.
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Brodheim, Max
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Brown, Matt
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Charbonneau, David
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Collins, Karen A.
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Crossfield, Ian J. M.
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Deich, William
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Dumusque, Xavier
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Gibson, Steven R.
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Gilbert, Emily
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Hill, Grant M.
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Holden, Bradford
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Jenkins, Jon M.
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Kaye, Stephen
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Laher, Russ R.
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Lanclos, Kyle
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Levine, W. Garett
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Payne, Joel
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Polanski, Alex S.
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O'Meara, John
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Ricker, George R.
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Rider, Kodi
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Robertson, Paul
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Roy, Arpita
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Schlieder, Joshua E.
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Schwab, Christian
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Seager, Sara
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Shaum, Abby P.
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Sirk, Martin M.
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Striegel, Stephanie
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Teske, Johanna
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Valliant, John
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Vanderspek, Roland
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Vasisht, Gautam
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Walawender, Josh
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Wang, Sharon Xuesong
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Winn, Joshua N.
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Wishnow, Edward
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Yeh, Sherry
Abstract
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We report the confirmation of TOI-6324 b, an Earth-sized (1.059 ± 0.041 R⊕) ultra-short-period (USP) planet orbiting a nearby (∼20 pc) M dwarf. Using the newly commissioned Keck Planet Finder spectrograph, we have measured the mass of TOI-6324 b 1.17 ± 0.22 M⊕. Because of its extremely short orbit of just ∼6.7 hr, 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% ± 37%) consistent with that of Earth (∼33%) and other confirmed USPs. TOI-6324 b is the closest to an 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 seven sectors of TESS data, we report a tentative detection of the optical phase-curve variation with an amplitude of 42 ± 28 ppm.
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