Two Rocky Earth-Sized Planets Discovered Just 33 Light-Years Away
MIT astronomers presented the discovery of two solid planets located only 33 light years from Earth. These planets, discovered thanks to NASA's TESS satellite, are comparable in size to Earth and orbit around a red dwarf star.
A system with a red dwarf and two rocky planets
This system containing two rocky planets has in its center an M-type red dwarf star named HD260655. A red dwarf, also known as a red main sequence star, is a star of spectral type M. It is a small, cool star. Its mass is generally between 0.075 and 0.4 solar masses. And it has a surface temperature not exceeding 4000 Kelvins. Red dwarfs are common stars in the Universe. In the Milky Way alone, they represent 80 to 85% of all known celestial bodies.
HD260655 are home to two rocky Earth-sized planets. However, due to their very narrow orbits, these planets are definitely not habitable. The temperatures prevailing on these exoplanets must be much too high to maintain liquid water on the surface.
Because their star is very bright, astronomers and astrophysicists have benefited from ideal conditions to study their atmosphere. They asked themselves the following questions. Do these planets benefit from an atmosphere rich in volatile matter? Is it possible to discover signs of the presence of water there? And carbonaceous matter?
The discovery of this star and these two rocky planets was possible thanks to NASA's Transiting Exoplanet Survey Satellite (TESS). It is a small 350 kg space telescope that was put into high Earth orbit in April 2018. This satellite was developed to observe the closest and brightest stars. It is also used to detect periodic decreases in luminosity, characteristic of the passage of a planet in front of a star.
Two periodic dips in the light of the red dwarf
The TESS satellite is a small telescope dedicated to the study of exoplanets.
The presence of the two rocky planets was first reported in October 2021 when an astronomer on the TESS team for MIT was working on the analysis of data transmitted by the satellite. She noticed at one point the periodic appearance of two dips in the light of the red dwarf star. After evaluation, these signals quickly became interesting and were classified as potential planets.
These signals from the TESS satellite were also detected and studied quite independently by SPOC (Science Processing Operations Center), the official TESS data analysis pipeline at NASA.
Generally, the process of classifying and confirming the presence of new planets takes a long time. For the HD260655 system, this delay was greatly reduced due to a fairly large amount of collected data and archived data.
For example, the red dwarf HD260655 has been known and even monitored since 1998 by the High Resolution Scale Spectrometer (HIRES), an astronomical observation instrument at the Keck Observatory on the island of Hawaii. Other information on HD260655 has been provided by observations made by CARMENES, an instrument located in Spain and composed of two high-resolution scale spectrographs operating in the visible for one and in the infrared for the other.
The pooling of all this data, thanks to the collaboration of all the teams, has made it possible to shorten the process of confirming the presence of these two rocky planets orbiting around HD260655.
Une mesure de l’oscillation gravitationnelle
Pour confirmer qu’il s’agit bien de deux planètes rocheuses qui orbitent autour de HD260655, les astronomes ont analysé les données en provenance de HIRES et de CARMENES. Ils ont pu obtenir des informations sur l’oscillation gravitationnelle ou vitesse radiale.
« Chaque planète en orbite autour d’une étoile va avoir une petite attraction gravitationnelle sur son étoile », explique Madame Kunimoto, l’une des scientifiques TESS du MIT. « Ce que nous recherchons, c’est un tout léger mouvement de cette étoile. Ceci pourrait indiquer la présence d’un objet de taille planétaire ». Les données d’archives des instruments et les données de TESS ont bien confirmé que les signaux détectés proviennent des deux planètes.
Les astronomes ont déterminé les caractéristiques de ces deux planètes. La planète la plus interne du système nommé HD260655b tourne autour de la naine rouge en 2,8 jours. Elle est 1,2 fois plus grande que la Terre. L’autre planète, la plus externe est nommée HD260655c. Elle tourne en 5,7 jours autour de l’étoile et est 1,5 fois plus grande que la Terre.
Les scientifiques ont estimé que HD260655b est une planète tellurique deux fois plus massive que la Terre. Alors que HD260655c possède 3 fois la masse de la Terre. En ce qui concerne la densité, la planète interne est un peu plus dense que la Terre. De son côté, la planète extérieure est un peu moins dense.
À partir de l’analyse de leur orbite, ils ont pu déterminé la température de surface de la planète intérieure. Elle était de 710 kelvins. Et celle de la planète extérieurs était de 560 Kelvins.
Les chercheurs espèrent détecter d’autres planètes rocheuses au sein du système HD260655 avec l’espoir d’en trouver une qui pourrait se situer dans la zone habitable.
Source :
Jennifer Chu, « Astronomers discover a multiplanet system nearby », MIT News Office, 15 juin 2022, https://news.mit.edu/2022/multiplanet-system-nearby-0615
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