Astronomers discover two 'super-Earths' orbiting nearby star

Astronomers discover two “super-Earths” orbiting nearby star
TESS photometry of LP 890-9. For each of the four sectors, the 2-minute data points (in grey) have been binned into 30-minute intervals to produce the black points, with error bars corresponding to the root-mean-square of the uncertainties of the points in the bins. The transits of LP 890-9 b and c are indicated by red and blue dotted lines, respectively. The region marked in orange in sector 4 was impacted by thermal effects and thus excluded from the analysis. Credit: Delrez et al., 2022.

An international team of astronomers reports the discovery of two new "super-Earth" exoplanets orbiting a nearby late-type M dwarf star. The newfound alien worlds, designated LP 890-9 b and LP 890-9 c, are slightly larger than the Earth. The finding has been published in Astronomy & Astrophysics.

"Super-Earths" are planets more massive than Earth but not exceeding the mass of Neptune. Although the term "super-Earth" refers only to the mass of the planet, it is also used by to describe planets bigger 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 planets of the super-Earth class. They observed LP 890-9—a nearby M dwarf star of M6V spectral type, using NASA's Transiting Exoplanet Survey Satellite (TESS). This led to the discovery of the inner planet, which received designation LP 890-9 b. Follow-up observations of this system with the SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars) Southern Observatory, resulted in the detection 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 transiting 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 not greater than 13.2 Earth masses. The planet orbits its host every 2.73 days at a distance of approximately 0.018 AU from it. The equilibrium temperature of LP 890-9 b was calculated to be 396 K.

When it comes to LP 890-9 c, its radius was measured to be nearly 1.37 Earth radii, while its mass is assumed to be less than 25.3 Earth masses. The exoplanet is separated from its by 0.04 AU and has an of approximately 8.46 days. The planet's equilibrium temperature is estimated to be at a level of 272 K.

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

Summing up the results, the astronomers underlined 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 favorable habitable-zone terrestrial planet known so far.

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

More information: L. Delrez et al, Two temperate super-Earths transiting a nearby late-type M dwarf, Astronomy & Astrophysics (2022). DOI: 10.1051/0004-6361/202244041

Journal information: Astronomy & Astrophysics

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