An international collaboration of researchers has identified a rocky exoplanet half the size of Venus, making it the lowest-mass planet measured so far. They published their findings in Astronomy and Astrophysics.
Advancements in radial velocity instruments have allowed scientists to detect planets with increasingly lower masses. These instruments work by calculating the wobble of a star caused by small gravitational tugs of orbiting planets.
In this research, scientists studied the L-98 59 planetary system, located just 35 light-years away from Earth. Studies from 2019 on the solar system had spotted just three planets using NASA's Transiting Exoplanet Survey Satellite (TESS). This satellite works by detecting dips in light coming from stars caused by planets passing in front.
However, using radial velocity measurements made with Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO), as well as those from its predecessor, the High Accuracy Radial velocity Planet Searcher (HARPS), researchers were able to identify a fourth and potentially a fifth orbiting planet.
Radial velocity measurements also determined that the mass of the solar system's innermost planet is half that of Venus. This makes it the lightest exoplanet ever observed with the technique.
While the two exoplanets closest to the star are likely dry and may contain small amounts of water, the third planet's mass could be 30% water.
Although yet to be confirmed, data on the potential fifth planet suggest that it may sit in the middle of the habitable zone of L 98-59. This means it could have an atmosphere capable of protecting and supporting life.
Currently, telescopes are not large enough to assess these planets for biosignatures that could confirm the presence of an atmosphere. The research nevertheless makes L 98-59 an attractive target for future research.
"This system announces what is to come," said Oliver Demangeon. "We, as a society, have been chasing terrestrial planets since the birth of astronomy and now we are finally getting closer and closer to the detection of a terrestrial planet in the habitable zone of its star, of which we could study the atmosphere."