Issue |
A&A
Volume 688, August 2024
|
|
---|---|---|
Article Number | L34 | |
Number of page(s) | 9 | |
Section | Letters to the Editor | |
DOI | https://doi.org/10.1051/0004-6361/202451332 | |
Published online | 23 August 2024 |
Letter to the Editor
Climate change in hell: Long-term variation in transits of the evaporating planet K2-22b
1
Institute for Astrophysics, University of Vienna, 1180 Vienna, Austria
2
Department of Earth Sciences, University of Hawai’i at Mänoa, Honolulu, Hawai’i 96822, USA
3
Departamento Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
4
Instituto de Astrofísica de Canarias (IAC), 38200 La Laguna, Tenerife, Spain
5
Department of Physical Sciences, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan
6
Komaba Institute for Science, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
7
Department of Multi-Disciplinary Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
8
Okayama Observatory, Kyoto University, 3037-5 Honjo, Kamogatacho, Asakuchi, Okayama 719-0232, Japan
9
Astrobiology Center, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
10
National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
Received:
1
July
2024
Accepted:
23
July
2024
Context. Rocky planets on ultra-short period orbits can have surface magma oceans and rock-vapour atmospheres in which dust can condense. Observations of that dust can inform us about the composition and surface conditions on these objects.
Aims. We constrained the properties and long-term (decade) behaviour of the transiting dust cloud from the evaporating planet K2-22b.
Methods.We observed K2-22b around 40 predicted transits with MuSCAT ground-based multi-optical channel imagers, and complemented these data with long-term monitoring by the ground-based ATLAS (2018-2024) and space-based TESS (2021–2023) surveys.
Results. We detected signals during 7 transits, none of which showed significant wavelength dependence. The expected number of MuSCAT-detected transits is ≥22, indicating a decline in mean transit depth since the K2 discovery observations in 2014.
Conclusions. The lack of a significant wavelength dependence indicates that dust grains are large or the cloud is optically thick. Long-term trends of depth could be due to a magnetic cycle on the host star or to overturn of the planet’s dayside surface magma ocean. The possibility that K2-22b is disappearing altogether is ruled out by the stability of the transit ephemeris against non-gravitational forces, which constrains the mass to be at least comparable to Ceres.
Key words: planets and satellites: atmospheres / planets and satellites: physical evolution / planets and satellites: terrestrial planets
© The Authors 2024
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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