An international group of astronomers has reported the discovery of Neptune, a new mini-exoplanet orbiting a nearby star. The newly discovered alien world, designated TOI-2018 b, is about twice as large and nine times larger than Earth. The discovery was detailed in an article posted on the prepress server on June 13. arXiv.

NASA’s Transiting Exoplanet Survey Satellite (TESS) surveys about 200,000 of the brightest stars near the Sun in search of transiting exoplanets ranging from small rocky worlds to gas giants. To date, approximately 6,700 candidate exoplanets (TESS Objects of Interest or TOIs) have been identified, of which 350 have been confirmed to date.

Now, a team of astronomers led by Fei Dai from Caltech (California Institute of Technology) recently confirmed another TOI tracked by TESS as part of a systematic search for planets transiting between low-metal dwarf stars. They reported that the transit signal was identified in the light curve of TOI-2018 (also known as BD+29 2654), a metal-poor K-dwarf star located about 91.4 light-years away. The planetary nature of this signal has been confirmed by further observations.

According to the article, TOI-2018 b has a radius of about 2.27 Earth radii and a mass of about 9.2 Earth masses, suggesting an Earth core with a hydrogen-helium shell or a mixture of ice and rock. The planet orbits its host star every 7.44 days and its equilibrium temperature is estimated to be 652 K.

Given TOI-2018 b’s relatively large mass, this extrasolar world is close to the threshold for spiraling out of control and thus giant planet formation (about 10 Earth masses or less for low metal environments), the researchers said. Therefore, the authors of the paper suggest that TOI-2018 b may be an unaccumulated planetary core that got out of control.

“Given the large mass of the core, it may seem surprising that TOI-2018 b failed to go through an uncontrolled accumulation. Perhaps TOI-2018 b just didn’t have enough time to initiate the runaway. [протопланетного] the disk disintegrated,” explained the astronomers.

Day’s team also discovered another object around TOI-2018 that could be an exoplanet. It is approximately 50% larger than Earth and its mass is estimated to be no more than 3.6 Earth masses. More observations are needed to confirm the planetary status of this object.

As for the characteristics of the main star, it is about 40% smaller and less massive than the Sun. The effective temperature of the star, which is estimated to be 2.4 billion years old, was 4174 K and its metallicity was -0.58.