Astronomers discover two “super-Earths” orbiting a nearby star

An international team of astronomers report the discovery of two new “super-Earth” exoplanets orbiting a nearby late-type M dwarf star. The newly discovered extraterrestrial worlds, designated LP 890-9 b and LP 890-9 c, are slightly larger than Earth. The finding was published in Astronomy & Astrophysics.

“Super-Earths” are planets that are more massive than Earth but do not exceed the mass of Neptune. Although the term “super-Earth” only refers to the planet’s mass, astronomers also use it to describe planets that are larger than Earth but smaller than the so-called “mini-Neptunes” (with a radius between two to four earth radii).

Now, astronomers led by Laetitia Delrez of the University of Liège in Belgium have discovered two new super-Earth class planets. They observed LP 890-9 – a nearby M6V spectral type dwarf star – with NASA’s Transiting Exoplanet Survey Satellite (TESS). This led to the discovery of the inner planet, which was given the designation LP 890-9 b. Follow-up observations of this system with the SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars) Southern Observatory led to the discovery of a second longer-period transiting planet – LP 890-9 c.

“We presented the discovery and first characterization of the LP 890-9 system, which hosts two temperate super-Earths traversing a nearby M6 dwarf,” the researchers wrote in the paper.

LP 890-9 b has a radius of about 1.32 Earth radii and its mass is estimated to be no more than 13.2 Earth masses. The planet orbits its host every 2.73 days at a distance of about 0.018 AU from it. The equilibrium temperature of LP 890-9 b was calculated to be 396 K.

For LP 890-9 c, its radius has been measured to be almost 1.37 Earth radii, while its mass is believed to be less than 25.3 Earth masses. The exoplanet is 0.04 AU from its parent star and has an orbital period of approximately 8.46 days. The planet’s equilibrium temperature is estimated at 272 K.

The host star LP 890-9 has a radius of about 0.15 solar radii and a mass of 0.12 solar masses. The effective temperature of this M dwarf is around 2,871 K and its luminosity is around 0.00143 solar luminosities. The star is about 104 light-years from Earth.

Summarizing the results, the astronomers stressed that their discovery makes LP 890-9 the second coolest planet-hosting star after TRAPPIST-1. They added that LP 890-9 c is the second-most favorable habitable zone terrestrial planet known to date.

“The discovery of the remarkable LP 890-9 system presented in this work provides another rare opportunity to study temperate terrestrial planets around our smallest and coolest neighbors,” the paper’s authors concluded.

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