An international team with the Very Large Telescope in Chile has achieved an impressive achievement: the discovery of an exoplanet of around 40% of the earth’s mass in a star 35 light-years away. It was the first time such a humble world was examined using the radial velocity technique, which measures distortions in the star’s light signature as planets revolve around it, causing it to wobble due to gravitational interaction.
The feat was only possible thanks to the Espresso, a spectrograph installed on the VLT in 2018 that is much more precise than its predecessors. The results of the group, led by Olivier Demangeon of the University of Porto in Portugal, were accepted for publication in the journal Astronomy & Astrophysics and indicate the presence of at least four planets, possibly five, around the star L 98-59. Three of them were already known and were discovered by the Tess satellite in 2019.
NASA’s exoplanet hunting probe detects them using the transit method and measures the darkening of the star as it passes by. This allows us to estimate the diameter of these worlds, but not the mass. The radial velocity technique, in turn, provides the mass, but not the diameter. Hence the motivation for the new course.
Comparison between the equilibrium temperature in Kelvin of Mercury, Venus and Earth and that of the planets of the system L 98-59. The fourth planet, d, is dotted because the diameter is unknown, and the fifth has yet to be confirmed. (Image credit: ESO)
The planets b, c and d have very short periods and complete a circle around their star every 2.2, 3.7 and 7.45 earth days. They are certainly uninhabitable that close, even if you consider that L 98-59 is a red dwarf star, smaller and cooler than the sun, yet they arouse interest. And the combination of mass and diameter data makes it possible to estimate its density and thus to project the possible composition.
The two inner ones, the smallest of which is the first, are stony and dry. The third of them, d, appears to be a planet that has 30% of its mass made up of water, which would make it an ocean world. Even so, the temperature likely makes it uninhabitable.
In addition, the radial velocity data showed the presence of a fourth planet, which Tess had not identified, with a mass at least three times the mass of Earth and a period of 12.8 days. There are also indications of a fifth planet, not yet confirmed, with a period of 23 days. If it exists, it must be right in the center of the system’s so-called habitable zone, where the distance to the star would allow a stable presence of liquid water on the surface.
In addition to breaking sensitivity records in the detection of planets based on radial velocity, the knowledge is important for future research on these objects. The L 98-59 system is close enough to enable the James Webb Space Telescope, due to be launched later this year, to study the atmospheric composition of its planets.
This column is published in Folha Corrida on Mondays.
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