Astronomers have found a rocky planet half the size of Venus in the L98-59 star system of the Flying Fish constellation. This is the smallest exoplanet discovered using the method of measuring radial velocities, writes the press service of the European Southern Observatory (ESO).
“We have made a big step in determining the masses of the smallest planets outside the solar system. This has become possible thanks to the improvement of instruments and methods of observation. If the Espresso spectrograph did not have such high accuracy and stability, we would not be able to measure the mass of the planet L 98-59b ", - said Maria Osorio, researcher at the Astrobiological Center (Spain).
Over the past 15 years, astronomers have discovered more than 4,000 exoplanets. Most of them were discovered using the so-called radial velocity method. So scientists call the approach that allows you to find planets by characteristic shifts in the spectrum of the star, which arise as a result of the gravitational interaction of the star and its satellites.
The amplitude of these oscillations depends on the mass of exoplanets and the distance between them and the star. For this reason, this technique is still quite difficult to apply to search for planets located at a large distance from stars or having a small mass in relation to the star. Therefore, it is mainly used to search for planets in the immediate vicinity of red dwarfs, which have a low luminosity and a relatively calm nature.
Osorio and her colleagues set a new radial velocity record for the detection of extremely small planets while observing the star system L98-59, located in the constellation Flying Pisces, 34 light-years from Earth. At its center is a small red dwarf, about four times the mass of the Sun.
Two years ago, astronomers working with the orbiting TESS observatory found evidence of at least three planets orbiting the star. The mass, size and properties of two of them, super-earths L98-59c and L98-59d, were measured, while the existence of exoplanet L98-59b, located as close as possible to the red dwarf, remained unconfirmed until recently.
Guided by similar considerations, Osorio and her colleagues began observing L98-59 with the Espresso spectrograph mounted on the VLT telescope at the high-altitude Paranal Observatory in Chile. Their observations not only confirmed the existence of the planet L98-59b and allowed scientists to determine its size and mass, but also pointed to the existence of two other planets.
As Osorio notes, the mass and size of the first planet in the star system L98-59 turned out to be noticeably smaller than their colleagues who worked with TESS assumed. In this respect, this exoplanet is twice as small as Venus, which makes L98-59b about 2.1 times larger in diameter than Mercury and 7 times larger in mass.
Astronomers doubt that this planet can be habitable - it makes one revolution around the star in just three incomplete days, and the average temperature on its surface exceeds 350 ° C. On the other hand, the two other super-earths they discovered, named L98-59d and L98-59e, are at such a distance from the red dwarf that life can exist on their surface.
A similar feature of these exoplanets, if their existence is confirmed in the future, makes them extremely interesting to study with the orbiting James Webb telescope, which will be launched into space this fall. The small distance between the Sun and the L98-59 star system, as well as a convenient observation angle, will allow scientists to take the first direct photographs of these planets and study the composition of their atmosphere, Osorio and her colleagues summed up.