An international team of astronomers reports the discovery of two new “super-Earths” exoplanets orbiting a nearby dwarf star of type M. The newly discovered alien worlds, designated LP 890-9 b and LP 890-9 c, are slightly larger than Earth. The results have been published in Astronomy and astrophysics.
“Super planets” are planets larger than Earth but only the mass of Neptune. Although the term “super-Earth” refers only to the mass of the planet, it is also used by astronomers to describe planets larger than Earth but smaller than the so-called “minor Neptune” (with a radius of two to four half Earth’s Diameter).
Now, astronomers led by Laetitia Delris of the University of Liège in Belgium have discovered two new super-Earths. They observed LP 890-9 – a nearby dwarf star in type M6V spectroscopically, using NASA’s Transiting Exoplanet Reconnaissance Satellite (TESS). This led to the discovery of the inner planet, which received the designation LP 890-9 b. Follow-up observations of this system with the Southern Observatory SPECULOOS (EClipsing ULtra-cOOl Stars) led to the discovery of a second, longer-period transiting planet – LP 890-9 c.
“We have presented the discovery and initial characterization of the LP 890-9 system, which hosts two temperate super-Earths passing through a nearby M6 dwarf,” the researchers wrote in the paper.
LP 890-9 b has a radius of about 1.32 Earth’s radius 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 astronomical units from it. The equilibrium temperature for LP 890-9 b was calculated to be 396 K.
When it comes to LP 890-9c, its radius has been measured to be about 1.37 Earth radii, while its mass is assumed to be less than 25.3 Earth masses. An exoplanet is separated from its parent star by 0.04 AU and has an orbital period of about 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 about 2871 K and its luminosity is at 0.00143 solar luminosity. The star is located about 104 light years from Earth.
Summing up the results, the astronomers confirmed that their discovery makes LP 890-9 the second-coolest star found to host planets after TRAPPIST-1. They added that LP 890-9 c is the second most habitable terrestrial planet known to date.
The authors of the paper conclude that “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 most magnificent neighbours.”
Two planets orbiting a nearby star discovered by TESS
L. Delrez et al, two temperate super-Earths crossing a nearby M-type dwarf, Astronomy and astrophysics (2022). DOI: 10.1051 / 0004-6361 / 202244041
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