A group of international scientists, including astronomers from the University of Birmingham, have just announced the finding of two “super-Earth” planets orbiting LP 890-9, a small, cold star situated approximately 100 light-years from Earth.

This star, which is also known as TOI-4306 or SPECULOOS-2, is the second-coolest star yet discovered to host planets, after the well-known TRAPPIST-1. The results of this unusual observation will soon be published in the prestigious journal Astronomy & Astrophysics.

The inner planet of the system is called LP 890-9b. It is about 30% bigger than Earth and takes only 2.7 days to circle the star. The NASA Transiting Exoplanet Survey Satellite (TESS), a satellite project looking for exoplanets circling nearby stars, originally recognized this first planet as a potential planet candidate. Search for habitable Planets EClipsing ULtra-cOOl Stars (SPECULOOS) telescopes, one of which is operated by the University of Birmingham, confirmed and characterized this candidate. After that, the researchers working on SPECULOOS made use of their telescopes to look for more transiting planets in the system that TESS would have missed.

“TESS searches for exoplanets,” explains Laetitia Delrez, a postdoctoral researcher at the University of Liège, and the lead author of the article, “using the transit method, by monitoring the brightness of thousands of stars simultaneously, looking for slight dimmings that might be caused by planets passing in front of their stars.

“However, a follow-up with ground-based telescopes is often necessary to confirm the planetary nature of the detected candidates and to refine the measurements of their sizes and orbital properties.”

This follow-up is especially important for stars like LP 890-9 that are very cold and give off most of their light in the near-infrared, which TESS can’t see very well.

Thanks to cameras that are extremely sensitive in the near-infrared, the SPECULOOS project’s telescopes, which are located at the ESO’s Paranal Observatory in Chile and on the island of Tenerife, are optimized to observe this sort of star with high precision.

“The goal of SPECULOOS,” according to Michaël Gillon, the principal investigator of the SPECULOOS project, “is to search for potentially habitable terrestrial planets transiting some of the smallest and coolest stars in the solar neighbourhood, such as the TRAPPIST-1 planetary system, which we discovered in 2016.”

“This strategy,” as explained by the investigator, “is motivated by the fact that such planets are particularly well suited to detailed studies of their atmospheres and to the search for possible chemical traces of life with large observatories, such as the James Webb Space Telescope (JWST).”

SPECULOOS’s observations of LP 890-9 were useful because they not only confirmed the first planet, but also helped find a second planet that had never been seen before. Although it is slightly larger than the first planet (approximately 40% larger than Earth), the second planet, LP 890-9c (renamed SPECULOOS-2c by the SPECULOOS researchers), has a longer orbital period of around 8.5 days. This orbital period placed the planet in what is known as the “habitable zone” surrounding its star, which was later confirmed by the MuSCAT3 instrument in Hawaii.

“The habitable zone is a concept under which a planet with similar geological and atmospheric conditions as Earth, would have a surface temperature allowing water to remain liquid for billions of years,” adds Amaury Triaud, a professor of Exoplanetology at University Birmingham and the leader of the SPECULOOS working group that scheduled the observations leading to the discovery of the second planet. 

“This gives us a license to observe more and find out whether the planet has an atmosphere, and if so, to study its content and assess its habitability.”

The next step will be to investigate this planet’s atmosphere, perhaps using the JWST, for which LP 890-9c appears to be the second-most promising target among the known potentially habitable terrestrial planets, trailing only the TRAPPIST-1 planets in this regard (for which Professor Triaud was also co-discoverer).

“It is important to detect as many temperate terrestrial worlds as possible,” adds Professor Triaud, “to study the diversity of exoplanet climates, and eventually to be in a position to measure how frequently biology has emerged in the Cosmos.”

Image Credit: Getty

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