NASA’s TESS Finds a World Sized Between Earth and Venus

The planet was located just 40 light years away in the constellation Pisces using observations by NASA’s TESS (Transiting Exoplanet Survey Satellite), and other monitoring facilities. Named Gliese 12 b, the planet orbits a red dwarf star, Gliese 12. Its distance from the star, and the amount of energy it receives from it makes it an exciting target for further investigation by NASA’s James Webb Space Telescope.

Dr Annelies Mortier, of the University of Birmingham’s School of Physics and Astronomy, is a co-author on one of the papers describing the findings, published today in Monthly Notices of the Royal Astronomical Society. She said: “This temperate and close-by planet offers the exciting opportunity to investigate the nature of Earth-like planets orbiting a much cooler host star than the Sun.”

Researchers at the University of Birmingham are part of different international consortia that contributed data to this project, which has resulted in two separate papers published in MNRAS and Astrophysical Journal Letters. In particular, Birmingham experts used the CHEOPS satellite, and the ground-based facilities SPECULOOS and HARPS-N, to confirm the planetary nature of Gliese 12 b. They are also leading the follow-up observations that will allow to eventually measure the mass of this exciting new world beyond the Solar System.

TESS stares at a large swath of the sky for about a month at a time, tracking the brightness changes of tens of thousands of stars at intervals ranging from 2 seconds to 30 minutes. Capturing transits — brief, regular dimmings of stars caused by the passage of orbiting worlds — is the mission’s primary goal.

Astronomers using data from TESS have been particularly interested in red dwarf stars, since their diminutive sizes and masses make them ideal for finding Earth-size planets. A smaller star means greater dimming for each transit, and a lower mass means an orbiting planet can produce a greater wobble, known as “reflex motion,” of the star. These effects make smaller planets easier to detect.

The lower luminosities of red dwarf stars also mean their habitable zones — the range of orbital distances where liquid water could exist on a planet’s surface — lie closer to them. This makes it easier to detect planets within habitable zones around red dwarfs than those around stars emitting more energy.

In the case of Gliese 12 b, the distance separating the star and the new planet is just 7% of the distance between Earth and the Sun. The planet receives 1.6 times more energy from its star as Earth does from the Sun and about 85% of what Venus experiences.

Larissa Palethorpe, a doctoral student at the University of Edinburgh and University College London was co-lead author of the MNRAS paper. She said: “It is thought that Earth’s and Venus’s first atmospheres were stripped away and then replenished by volcanic outgassing and bombardments from residual material in the solar system.

“The Earth is habitable, but Venus is not due to its complete loss of water. Because Gliese 12 b is between Earth and Venus in temperature, its atmosphere could teach us a lot about the habitability pathways planets take as they develop.”

The sensitive instruments on the James Webb Space Telescope will be able to provide further important insights into the important question of whether Gliese 12 b has an atmosphere. The instruments use spectroscopy to determine the composition of exoplanet atmospheres, including determining how similar they may be to that of Earth.