An international team of astronomers reports the discovery of a new super-Earth exoplanet orbiting a nearby M dwarf star known as Ross 508. The newly discovered alien world, which has been given the designation Ross 508 b , turns out to be at least four times more massive than our planet. The discovery was detailed in an article published May 24 on arXiv.org.
The “super-Earths” are planets more massive than the Earth but not exceeding the mass of Neptune. Although the term “super-Earth” only refers to the mass of the planet, it is also used by astronomers to describe planets larger than Earth but smaller than the so-called “mini-Neptunes”. (with a radius between two and four Earth radii).
Now, astronomers led by Hiroki Harakawa of the Subaru Telescope have discovered a new super-Earth class planet. Using the InfraRed Doppler (IRD) instrument of the 8.2m Subaru Telescope, they made radial velocity (RV) measurements of Ross 508, a spectral type M4.5 M dwarf, located about 36.5 light years.
“We have shown that the M4.5 dwarf Ross 508 has a significant RV periodicity at 10.75 days with possible aliases at 1.099 and 0.913 days. This periodicity has no equivalent in photometry or indicators of stellar activity , but is well-adjusted by a Keplerian orbit due to a new planet, Ross 508 b,” the researchers explained.
The newly discovered exoplanet Ross 508 b has a minimum mass of four Earth masses and orbits its host every 10.75 days at a distance of about 0.053 AU from it. According to astronomers, this indicates an average insolation in orbit of about 1.4 times Earth’s value, placing this planet near the inner edge of Ross 508’s habitable zone.
The exact orbital eccentricity of Ross 508 b is still unknown and further studies on this could provide important information about the origin of the planet. The researchers speculate that Ross 508 b may have formed beyond the snow line (about 0.16 AU) and undergone a Type I inward migration. They noted that even if the eccentricity of a migrating alien world is initially high, it can be dampened by the force exerted on the planet by density waves.
The parent star Ross 508 has a radius of about 0.21 solar radii and a mass of about 0.18 solar masses, giving a density at a level of 26.5 g/cm3. The star has an effective temperature of 3071 K and its metallicity is estimated at -2.0.
Summarizing the results, the paper’s authors hope that future surveys with the IRD and other high-precision near-infrared spectrographs will allow the discovery of planets around other stars like Ross 508.
“Our discovery demonstrates that near-infrared RV research can play a crucial role in finding a low-mass planet around cold M dwarfs like Ross 508. (…) Exploration of exoplanets will be advanced by further RV investigations late M dwarfs using high-dispersion spectrographs, such as HPF, CARMENES and SPIROU, as well as exoplanet surveys using the transit technique from space (e.g. TESS) and the ground (e.g. SPECULOOS)” , the researchers concluded.
Discovery of two new Saturn-mass exoplanets
A super-Earth orbiting near the inner edge of the habitable zone around the M4.5 dwarf Ross 508, arXiv:2205.11986 [astro-ph.EP] arxiv.org/abs/2205.11986
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