CHEOPS Papers in Brief

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Rapidly rotating stars and their transiting planets: KELT-17b, KELT-19Ab, and KELT-21b in the CHEOPS and TESS erA

Garai et al. 2022

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A Mini-Neptune from TESS and CHEOPS Around the 120 Myr Old AB Dor member HIP 94235

Zhou et al. (2022)

Planets evolve rapidly in the first few hundred million years after they are formed. Their atmospheres can be modified quickly by the intense high energy irradiation from the young stars they orbit. They can also gravitationally interact with adjacent planets, changing the orbits they reside in. Finding young planets around other stars allows us to timestamp this evolution process as it is happening in other planetary systems.

HIP 94235 b is a 120 million year old Neptune-sized planet discovered with the help of CHEOPS and TESS. It transits a young Sun-like star in the AB Doradus moving group, an association of young stars born at around the same time, and moving along the same trajectory in space. At its current age, HIP 94235 b is experiencing intense X-ray irradiation from the young star it orbits. It should be losing its outer atmosphere at a rate of 5 Earth masses per billion years – a rapid evolution that should be observable with space and ground-based observations in the near future. HIP 94235 b is one of the closest newly born planets we have found. CHEOPS observations allowed us to confirm the transits of the planet, and refine the timing predictions so that future observations of its transits can be possible. Our observations of HIP 94235 b demonstrate the synergy between TESS and CHEOPS. Without CHEOPS, the planet would have been lost within a year of its initial discovery from the TESS observations.