Two exoplanets in the top-10 for follow-up characterization of their atmospheres

An international team led by a researcher from the Institute of Astrophysics of Andalusia (IAA-CSIC) has found two telluric planets orbiting, while partially eclipsing, the nearby dwarf star HD 260655.

The discovery was made combining space- and multiple ground-based facilities, in particular the CARMENES spectrograph at the Calar Alto 3.5 m telescope. These two newly found hot super-Earths are among the top 10 candidates for follow-up studies of their atmospheres. 

Credits: NASA / JPL-Caltech


In the last 30 years, over 5000 planets have been discovered outside our Solar System. Still, only a small fraction of these exoplanets were found to be telluric, that is, rocky, like Mercury, Venus, the Earth, and Mars.

Combining data from the CARMENES spectrograph at Calar Alto and from the NASA TESS satellite, among others, a team of astronomers led by Rafael Luque (Institute of Astrophysics of Andalusia, IAA/CSIC, and University of Chicago), has found two of those rocky worlds around the nearby red dwarf star HD 260655, lying in the Gemini constellation.

TESS observed tiny dimmings in the light of this star every few days, revealing that two planets, HD 260655 b and HD 260655 c, cross the face of their star from Earth’s point of view. Quantifying accurately these mini eclipses allowed to determine the exoplanet sizes. On the other hand, the CARMENES spectra taken since 2016 with the Calar Alto 3.5 m telescope provided the masses of the planets. Knowing the mass and size of both planets, Luque et al. inferred their density, which was found similar to telluric planets, around 5 grams per cubic centimeter.

interior creditosBoth HD 260655 b and HD 260655 c planets are actually “super-Earths” – terrestrial planets like ours, only bigger. Planet b is about 1.2 times as big around as Earth, planet c 1.5 times. In this case, however, neither world is likely to harbor liquid water on its surface. The temperature on planet b, nearest to the star, is estimated at 435ºC, and on planet c, at 284ºC.

Still, the scientific team that discovered the planets says they are well worth further investigation. At only 33 light-years, they are relatively close to us, and their star, HD 260655, though smaller than ours, is among the brightest of its class in the sky. These and other factors raise the likelihood that the Hubble and James Webb space telescopes could capture data from the star’s light shining through these planets’ atmospheres. Such light can be spread into a spectrum, revealing the fingerprints of molecules within the atmosphere itself.

"This is a new proof of the CARMENES potential to reveal exoplanets that are the best targets for follow-up studies with the new generation of space and giant telescopes" state Jesús Aceituno, director of the Calar Alto observatory.

The discovery of HD 260655 b indeed comes at an ideal moment: The giant James Webb Space Telescope, soon to deliver its first science images, can examine the atmospheres of exoplanets when they transit their star. Learning more about the atmospheres of rocky exoplanets helps us scientists understand the formation and development of worlds like our own.

Rafael Luque (IAA-CSIC and University of Chicago) confirms that “both planets are in the top-10 for observations of their atmospheres with the James Webb space telescope, launched last Christmas and about to finish its calibration phase. These data will allow us to determine if those planets have a thin atmosphere, and if this is the case, to determine their chemical composition.”

Today, June 15th, 2022, Rafael Luque and his team present their findings on HD 260655 b & c at the 240th American Astronomical Society meeting in Pasadena, California.

Calar Alto Observatory is one of the infrastructures that belong to the national map of Unique Scientific and Technical Infrastructures (Spanish acronym: ICTS), approved on November 6th, 2018, by the Science, Technology and Innovation Policy Council


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