TESS finds an interesting world between the size of Earth and Venus

Using NASA’s Transiting Exoplanet Survey Satellite (TESS) and many other instruments, two international teams of astronomers have discovered an Earth-Venus-sized planet just 40 light-years away. Many factors make it a suitable candidate for further study using NASA’s James Webb Space Telescope.

TESS stares across a large swath of sky for about a month at a time, tracking the brightness changes of tens of thousands of stars at intervals of 20 seconds to 30 minutes. Capturing transits – the brief, periodic dimming of stars caused by the passage of orbiting worlds – is one of the mission’s main goals.

“We have found the closest Earth-sized transiting temperate world to date,” said Masayuki Kuzuhara, a project assistant professor at the Astrobiology Center in Tokyo, who led one research team with Akihiko Fukui, a project assistant. a professor at the University of Tokyo. “Although we don’t yet know if it has an atmosphere, we thought of it as an exo-Venus with a similar size and energy received from its star as our planetary neighbor in the Solar System.”

The host star, called Gliese 12, is a cool red dwarf located nearly 40 light-years away in the constellation Pisces. The star is only about 27% the size of the Sun, with about 60% the surface temperature of the Sun. The newly discovered world, named Gliese 12b, orbits every 12.8 days and is the size of Earth or slightly smaller – comparable to Venus. Assuming the planet has no atmosphere, it has a surface temperature estimated to be around 107 degrees Fahrenheit (42 degrees Celsius).

Astronomers say the small size and mass of red dwarfs make them ideal for searching for Earth-sized planets. A smaller star means more dimming for each transit, and the lower mass means the orbiting planet can produce more wobble in the star, known as “reflective motion.” These effects make it easier to detect smaller planets.

The lower luminosity of red dwarfs also means that 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 transiting planets in the habitable zones around red dwarfs than planets around more energetic stars.

The distance between Gliese 12 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 than Earth does from the Sun, and about 85% of what Venus experiences.

“Gliese 12b represents one of the best targets for studying whether Earth-sized planets orbiting cool stars can retain their atmospheres, a crucial step toward advancing our understanding of planetary habitability throughout our galaxy,” said Shishir Dholakia, a Ph.D. student at the university . Center for Astrophysics at the University of Southern Queensland, Australia. He co-led another research team with Larissa Palethorpe, a PhD student at the University of Edinburgh and University College London.

Both teams suggest that studying Gliese 12b may help unlock some aspects of the evolution of our own solar system.

“The first atmospheres of Earth and Venus are thought to have been removed and then replenished by volcanic outgassing and bombardment from the remnant material in the solar system,” Palethorpe explained. “Earth is habitable, but Venus is not because of its complete loss of water. Because Gliese 12b is between Earth and Venus in temperature, its atmosphere could teach us a lot about the habitability pathways that planets take.”

One important factor in sustaining an atmosphere is the turbulence of its star. Red dwarfs tend to be magnetically active, resulting in frequent, strong X-ray bursts. However, both teams’ analyzes concluded that Gliese 12 showed no signs of extreme behavior.

A sheet led by Kuzuhara and Fukui appears The Astrophysical Journal Letters. The Dholakia and Palethorpe finds were published in Monthly Notices of the Royal Astronomical Society the same day.

During the transit, the host star’s light passes through any atmosphere. Different gas molecules absorb different colors, so the transit provides a set of chemical fingerprints that can be detected by telescopes like Webb.

“We know of only a handful of Earth-like temperate planets that are close enough to us that meet the other criteria needed for this kind of study, called transmission spectroscopy, using current equipment,” said Michael McElwain, an astrophysicist at NASA Goddard. Space Flight Center in Greenbelt, Maryland, and co-authored the article with Kuzuhara and Fukui. “To better understand the diversity of atmospheres and evolutionary outcomes of these planets, we need more examples like Gliese 12b.”

TESS is a NASA Astrophysics Explorer mission managed by NASA Goddard and operated by MIT in Cambridge, Massachusetts. Other partners include Falls Church, Va.-based Northrop Grumman; NASA’s Ames Research Center in Silicon Valley, California; Center for Astrophysics | Harvard & Smithsonian in Cambridge, Massachusetts; MIT’s Lincoln Laboratory; and the Space Telescope Science Institute in Baltimore. The participants of the mission are more than a dozen universities, research institutes and observatories around the world.