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 gray) were grouped into 30-minute intervals to produce the black dots, 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 has been impacted by thermal effects and therefore 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 M-type dwarf star. The new alien worlds, designated LP 890-9 b and LP 890-9 c, are slightly larger than Earth. The discovery was published in Astronomy & Astrophysics.

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 Laetitia Delrez of the University of Liège in Belgium have discovered two new super-Earth class planets. They observed LP 890-9, a nearby M dwarf star of spectral type M6V, using NASA’s Transiting Exoplanet Survey 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 (Search for habitable Planets EClipsing ULtra-cOOl Stars) resulted in the detection of a second longer-period transiting planet – LP 890-9 c.

“We 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 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 has been calculated at 396 K.

Regarding LP 890-9 c, its radius has been measured at nearly 1.37 Earth radii, while its mass is assumed to be less than 25.3 Earth masses. The exoplanet is separated from its parent star by 0.04 AU and has an orbital period of about 8.46 days. The equilibrium temperature of the planet is estimated at 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 about 2871 K and its luminosity is at a level of 0.00143 solar luminosity. The star is located about 104 light years from Earth.

Summarizing the results, the astronomers pointed out 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 to date.

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

Two planets orbiting a star discovered with TESS

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

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