“Mega-Earths” are Likely an Artifact of Stellar Activity
- 1McGill University
Abstract
Empirical relations and planet formation simulations suggest an upper mass limit for rocky planets of ∼10 M ⊕ , as cores above this will almost certainly undergo runaway gas accretion. Nevertheless, a small number of planets appear to have densities consistent with rocky Earth-like compositions above this threshold, indicating that unusual formation and evolutionary scenarios are capable of producing extremely massive rocky planets. However, all of these planets orbit active stars with log R HK ′ > −4.75. We find a <1% probability that all literature ultramassive rocky planets would coincidentally orbit such active stars, and find no astrophysical reason to expect mega-Earths to preferentially form around active stars. We therefore conclude that mega-Earths are artifacts of stellar activity, and we question the reliability of Gaussian processes to enable mass measurements for rocky planets around active stars.
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BibTeX
@article{brinkman2026megaearths,
title = {{“Mega-Earths” are Likely an Artifact of Stellar Activity}},
author = {Casey L. Brinkman and Nicolas B. Cowan},
journal = {The Astrophysical Journal Letters},
year = {2026},
month = nov,
doi = {10.3847/2041-8213/aeb5f5},
url = {https://iopscience.iop.org/article/10.3847/2041-8213/aeb5f5},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - “Mega-Earths” are Likely an Artifact of Stellar Activity
AU - Casey L. Brinkman
AU - Nicolas B. Cowan
PY - 2026
DA - 2026/11/06
JO - The Astrophysical Journal Letters
DO - 10.3847/2041-8213/aeb5f5
UR - https://iopscience.iop.org/article/10.3847/2041-8213/aeb5f5
AB - Empirical relations and planet formation simulations suggest an upper mass limit for rocky planets of ∼10 M ⊕ , as cores above this will almost certainly undergo runaway gas accretion. Nevertheless, a small number of planets appear to have densities consistent with rocky Earth-like compositions above this threshold, indicating that unusual formation and evolutionary scenarios are capable of producing extremely massive rocky planets. However, all of these planets orbit active stars with log R HK ′ > −4.75. We find a <1% probability that all literature ultramassive rocky planets would coincidentally orbit such active stars, and find no astrophysical reason to expect mega-Earths to preferentially form around active stars. We therefore conclude that mega-Earths are artifacts of stellar activity, and we question the reliability of Gaussian processes to enable mass measurements for rocky planets around active stars.
SN - 2041-8213
SN - 2041-8205
ER -