SPECULOOS discovers a potentially habitable super-Earth
IMAGE: COMPARISON BETWEEN THE LP 890-9 SYSTEM AND THE INNER SOLAR SYSTEM. THE LP 890-9 SYSTEM IS MUCH MORE COMPACT: ITS TWO PLANETS COULD EASILY FIT INSIDE THE ORBIT OF MERCURY, THE INNERMOST PLANET OF OUR SOLAR SYSTEM. view more
CREDIT: @ADELINE DEWARD
An international team of scientists, led by Laetitia Delrez, astrophysicist at the University of Liège (Belgium), has just announced the discovery of two 'super-Earth' type planets orbiting LP 890-9. Also known as TOI-4306 or SPECULOOS-2, this small, cool star located about 100 light-years from our Earth is the second coolest star around which planets have been detected, after the famous TRAPPIST-1. This important discovery is published in the journal Astronomy & Astrophysics.
A first planet, LP 890-9b (or TOI-4306b), the innermost in the system, was initially identified by NASA's Transiting Exoplanet Survey Satellite (TESS), a space mission dedicated to the search for exoplanets orbiting nearby stars. This planet, which is about 30% larger than the Earth, completes an orbit around the star in just 2.7 days. The ULiège researchers used their ground-based SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars) telescopes to confirm and characterise this planet, and also to probe the system in depth for other planets that might have been 'missed' by TESS.
"TESS searches for exoplanets using the transit method, by monitoring the brightness of thousands of stars simultaneously, looking for slight dimmings that could be caused by planets passing in front of their stars," explains Laetitia Delrez, FNRS Postdoctoral Researcher in the Astrobiology and STAR (Faculty of Sciences) research units at ULiège, and lead author of the article. "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 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.
In contrast, the telescopes of the SPECULOOS consortium, led by ULiège and installed at the European Southern Observatory (ESO) in Paranal, Chile (SPECULOOS South) and at the Teide Observatory in Tenerife (SPECULOOS North), are optimised to observe this type of star with high precision, thanks to cameras that are very sensitive in the near infrared. "The goal of SPECULOOS is to search for potentially habitable terrestrial planets transiting the smallest and coolest stars in the solar neighbourhood, such as the TRAPPIST-1 planetary system, which we discovered in 2016 thanks to a pilot project with our TRAPPIST-South telescope," recalls Michaël Gillon, FNRS Senior Research Associate, co-director of the Astrobiology research unit at ULiège and principal investigator of the SPECULOOS project. "This strategy is motivated by the fact that such planets are particularly well suited to detailed studies of their atmospheres and the search for possible chemical traces of life with large observatories, such as the JWST.”
The observations of LP 890-9 obtained by SPECULOOS have proved fruitful, as they have not only helped to confirm the first planet, but have also made it possible to detect a second, previously unknown one. This second planet, LP 890-9c (renamed SPECULOOS-2c by the ULiège researchers), is similar in size to the first one (about 40% larger than the 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. "Although this planet orbits very close to its star, at a distance about 10 times shorter than that of Mercury around our Sun, the amount of stellar irradiation it receives is still low, and could allow the presence of liquid water on the planet's surface, provided it has a sufficient atmosphere," explains Francisco J. Pozuelos, researcher at the Institute of Astrophysics of Andalusia, a former postdoctoral researcher in the Astrobiology and STAR research units at ULiège and one of the main co-authors of the paper. "This is because the star LP 890-9 is about 6.5 times smaller than the Sun and has a surface temperature half that of our star. This explains why LP 890-9c, despite being much closer to its star than the Earth is to the Sun, could still have conditions that are suitable for life.
The research team will then study the atmosphere of this planet, for example with the JWST, for which LP 890-9c appears to be the second most favourable target among the potentially habitable terrestrial planets currently known, surpassed only by the TRAPPIST-1 planets. “This comparison does not, however, consider the fact that LP 890-9c is located close to the inner boundary of the habitable zone and could therefore have an atmosphere that is particularly rich in water vapour, which would then boost its atmospheric signals," explains Laetitia Delrez. "Moreover, models often differ as to the exact position of this inner boundary of the habitable zone depending on the characteristics of the star. The discovery of LP 890-9c therefore offers a unique opportunity to better understand and constrain the habitability conditions around the smallest and coolest stars in our solar neighbourhood", concludes the researcher.
About SPECULOOS
SPECULOOS is a project led by the University of Liège (principal investigator: Michaël Gillon) in partnership with the University of Cambridge, the University of Birmingham, the Massachusetts Institute of Technology (MIT), the University of Bern, the Canary Islands Institute of Astrophysics and the European Southern Observatory (ESO). SPECULOOS is based on a network of robotic telescopes distributed over two main observatories, SPECULOOS-South at ESO's Paranal Observatory in Chile (4 telescopes) and SPECULOOS-North in Tenerife (currently 1 telescope), complemented by the SAINT-EX (1 telescope in Mexico) and TRAPPIST (2 telescopes, 1 in Chile, 1 in Morocco) telescopes.
JOURNAL
Astronomy and Astrophysics
ARTICLE TITLE
Two temperate super-Earths transiting a nearby late-type M dwarf
ARTICLE PUBLICATION DATE
7-Sep-2022
Birmingham telescope discovers
two new temperate rocky worlds
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. view more
CREDIT: CREDIT: UNIVERSITY OF BIRMINGHAM / AMANDA J. SMITH
An international research team including astronomers at the University of Birmingham, has just announced the discovery of two "super-Earth" planets 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 planet, called LP 890-9b, is about 30% larger than Earth and 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.
"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," explains Laetitia Delrez, a postdoctoral researcher at the University of Liège, and the lead author of the article.
"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 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.
"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", recalls Michaël Gillon, from the University of Liège, and the principal investigator of the SPECULOOS project. "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 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.
“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” explains 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 study the atmosphere of this planet, for example with the JWST, for which LP 890-9c appears to be the second-most favourable target among the potentially habitable terrestrial planets known so far, surpassed only by the TRAPPIST-1 planets (for which Professor Triaud was also co-discoverer).
“It is important to detect as many temperate terrestrial worlds as possible to study the diversity of exoplanet climates, and eventually to be in a position to measure how frequently biology has emerged in the Cosmos,” added Professor Triaud.
JOURNAL
Astronomy and Astrophysics
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Two temperate super-Earths transiting a nearby late-type M dwarf
ARTICLE PUBLICATION DATE
7-Sep-2022
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