Two new ‘super-Earth’ planets have been discovered orbiting a star approximately 100 light years from Earth
The announcement came from an international research team led by the University of Liège, and including astronomers at the University of Birmingham, who say the two ‘super-Earth’ planets are orbiting LP 890-9, a small, cool star located about 100 light-years from Earth.
The star, also called TOI-4306 or SPECULOOS-2, is the second-coolest star found to host planets, after the famous TRAPPIST-1.
This rare discovery is the subject of a forthcoming publication in the journal Astronomy & Astrophysics.
The system’s inner super-Earth planet, called LP 890-9b, is about 30% larger than Earth. It completes an orbit around the star in just 2.7 days.
This first planet was initially identified as a possible planet candidate by NASA’s Transiting Exoplanet Survey Satellite (TESS), a space mission searching for exoplanets orbiting nearby stars.
This candidate was confirmed and characterized by the SPECULOOS telescopes (Search for habitable Planets EClipsing ULtra-cOOl Stars), one of which is operated by the University of Birmingham.
SPECULOOS researchers then used their telescopes to seek additional transiting planets in the system that would have been missed by TESS.
Laetitia Delrez, a postdoctoral researcher at the University of Liège, and the lead author of the article, said: “TESS searches for exoplanets 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.”
Habitable terrestrial planets
This follow-up is particularly important in the case of very cold stars, such as LP 890-9, which emit most of their light in the near-infrared and for which TESS has a rather limited sensitivity.
The telescopes of the SPECULOOS project, installed at ESO’s Paranal Observatory in Chile and on the island of Tenerife, are optimised to observe this type of star with high precision, thanks to cameras that are very sensitive in the near-infrared.
Michaël Gillon, also from the University of Liège, and the principal investigator of the SPECULOOS project, added: “The goal of SPECULOOS 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 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).”
The observations of LP 890-9 gathered by SPECULOOS proved fruitful as they not only confirmed the first planet, but they were critical for the detection of a second, previously unknown planet.
This second super-Earth planet, LP 890-9c (renamed SPECULOOS-2c by the SPECULOOS researchers), is similar in size to the first (about 40% larger than Earth) but has a longer orbital period of about 8.5 days. This orbital period, later confirmed with the MuSCAT3 instrument in Hawaii, places the planet in the so-called ‘habitable zone’ around its star.
Image: Artist’s view showing the red star and its two planets, together with some of the telescopes used for the discovery. The data that led to the discovery is depicted on the solar panels of the TESS satellite.
Credit: University of Birmingham/ Amanda J. Smith