Using data from the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO) on ESO’s Very Large Telescope (VLT), astronomers have detected a candidate short-period sub-Earth planet circling Proxima Centauri, a red dwarf located only 4.23 light-years away in the constellation of Centaurus.
An artist’s impression of Proxima d. Image credit: ESO / L. Calçada.
Proxima Centauri is an M5.5-type star located 4.244 light-years away in the southern constellation of Centaurus.
The star is the smallest member of the Alpha Centauri system, and lies near to the much brighter pair, Alpha Centauri AB.
It has a measured radius of 14% the radius of the Sun, a mass of about 12% solar, and an effective temperature of only 2,777 degrees Celsius (5,031 degrees Fahrenheit).
Proxima Centauri is 1,000 times less luminous than the Sun, which even at its close distance makes it invisible to the naked eye.
It has a very slow rotation of 83 days and a long-term activity cycle with a period of approximately 7 years. Its habitable zone ranges from distances of 0.05 to 0.1 AU.
Proxima Centauri is already known to host Proxima b, an Earth-mass exoplanet with an orbital period of 11.2 days within the habitable zone, as well as Proxima c, a long-period planet candidate with an orbital period of close to 5 years.
The new planet candidate orbits closer to the parent star (at 0.029 AU, less than a tenth of Mercury’s distance from the Sun) than to the inner edge of the habitable zone.
Named Proxima d, it has a mass of 0.26 Earth masses and an orbital period of 5.12 days.
“The discovery shows that our closest stellar neighbor seems to be packed with interesting new worlds, within reach of further study and future exploration,” said Dr. João Faria, an astronomer with the Instituto de Astrofísica e Ciências do Espaço and the Departamento de Física e Astronomia at the Universidade do Porto.
The 5.12-day signal of Proxima d was detected in the data from the ESPRESSO instrument on ESO’s Very Large Telescope.
“I was excited by the challenge of detecting such a small signal and, by doing so, discovering an exoplanet so close to Earth,” Dr. Faria said.
Proxima d is the lightest exoplanet ever measured using the radial velocity (RV) technique, surpassing the recently-discovered planet L 98-59b.
The RV technique works by picking up tiny wobbles in the motion of a star created by an orbiting planet’s gravitational pull.
The effect of Proxima d’s gravity is so small that it only causes the host star to move back and forth at around 1.44 km (0.9 miles) per hour.
“This achievement is extremely important,” said ESPRESSO project scientist Dr. Pedro Figueira, an astronomer with ESO.
“It shows that the radial velocity technique has the potential to unveil a population of light planets, like our own, that are expected to be the most abundant in our galaxy and that can potentially host life as we know it.”
“This result clearly shows what ESPRESSO is capable of and makes me wonder about what it will be able to find in the future,” Dr. Faria said.
The discovery is reported in a paper in the journal Astronomy & Astrophysics.
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J.P. Faria et al. 2022. A candidate short-period sub-Earth orbiting Proxima Centauri. A&A 658, A115; doi: 10.1051/0004-6361/202142337
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