Two rocky exoplanets discovered around nearby star

Two rocky exoplanets discovered around nearby star

Two rocky exoplanets discovered around nearby star
Two rocky exoplanets discovered around nearby star
Image from TESS target pixel file of HD 260655. Credit: Luque et al, 2022

Using NASA’s Transiting Exoplanet Survey Satellite (TESS), astronomers have detected two rocky alien worlds orbiting a nearby M dwarf star known as HD 260655. The newly discovered exoplanets are more large and at least twice as massive as the Earth. The discovery is reported in an article published April 21 on

TESS is surveying around 200,000 of the brightest stars near the sun in an effort to search for transiting exoplanets. So far, it has identified more than 5,600 candidate exoplanets (TESS Objects of Interest, or TOI), of which 205 have been confirmed so far.

Now, a team of astronomers led by Rafael Luque from the University of Chicago has confirmed two more planets monitored by TESS. They report that transit signals have been identified in the light curve of the bright M-dwarf HD 260655 (or TOI-4599). The planetary nature of these signals has been confirmed by archival measurements and new precise radial velocity (RV) measurements.

“This work presents the discovery and characterization of a multiplanetary system orbiting the neighboring M dwarf HD 260655. TESS transit observations detected two candidate minor planets which were confirmed with independent RV data from the HIRES instruments and CARMENES taken since 1998 and 2016, respectively,” the researchers write in the journal.

The exoplanet closest to the parent star has been given the designation HD 260655 b. It has a radius of about 1.24 Earth radii and is about 2.14 times more massive than our planet, giving a density level of 6.2 g/cm3. HD 260655 b orbits its host every 2.77 days, at a distance of about 0.03 AU from it. Its equilibrium temperature was estimated at 709 K.

The newly discovered second planet, HD 260655 c, is larger and more massive than its neighbor. The results show that it has a radius of 1.53 Earth radii, while its mass is about 3.09 Earth masses. Therefore, the density of this planet was calculated at 4.7 g/cm3. HD 260655 c is separated from the parent star by 0.047 AU, has an orbital period of 5.7 days, and an equilibrium temperature of about 557 K.

The star HD 260655, located about 32.6 light-years away, is of spectral type M0 V and is about 56% smaller and less massive than the Sun. The star has a metallicity level of -0.43 and is estimated to be between two and eight billion years old. HD 260655 is relatively bright (with an apparent luminosity of 6.7 mag) and its effective temperature is 3803 K.

Based on the derived densities of the two new alien worlds, astronomers have concluded that they both have a rocky composition. However, they noted that while HD 260655 b has a density in perfect agreement with that of Earth, the density of HD 260655 c suggests an internal composition devoid of iron and consisting entirely of silicates.

Summarizing the results, the researchers noted that their discovery makes HD 260655 the fourth closest known multi-transit planetary system. They added that due to the relatively high apparent brightness of the host star, the two newly discovered planets would be excellent targets for further atmospheric studies.

Hot Earth-sized exoplanet detected with TESS

More information:
R. Luque et al, The HD 260655 system: Two rocky worlds passing through a bright M dwarf at 10 pc. arXiv:2204.10261v2 [astro-ph.EP]

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