TESS finds intriguing world size between Earth and Venus

Using observations from NASA’s TESS (Transiting Exoplanet Survey Satellite) and many other facilities, two international teams of astronomers have discovered a planet about the size of Earth and Venus, just 40 light-years away. Several factors make it a candidate well suited for further study using NASA’s James Webb Space Telescope.

TESS stares at a large portion of the sky for about a month, tracking the brightness changes of tens of thousands of stars at 20-second to 30-minute intervals. Capturing transits – short, regular eclipses of stars caused by the passage of orbiting worlds – is one of the mission’s main goals.

“We have found the closest, continuous, Earth-sized temperate world to date,” said Masayuki Kuzuhara, a project assistant professor at the Astrobiology Center in Tokyo, who led a research team with Akihiko Fukui, a project assistant . professor at the University of Tokyo. “Although we don’t yet know if it has an atmosphere, we have seen 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% of the Sun’s surface temperature. The newly discovered world, called Gliese 12 b, rotates every 12.8 days and is the size of Earth, or slightly smaller, comparable to Venus. Assuming no atmosphere, the planet has a surface temperature estimated at about 107 degrees Fahrenheit (42 degrees Celsius).

Astronomers say the small sizes and masses of red dwarf stars make them ideal for finding Earth-sized planets. A smaller star means greater dimming on each pass, and a lower mass means an orbiting planet can cause a greater wobble of the star, known as “reflex motion.” These effects make smaller planets easier to detect.

The lower brightness of red dwarf stars also means that their habitable zones – the range of orbital distances where liquid water could exist on a planet’s surface – are closer to them. This makes it easier to detect planets in habitable zones around red dwarfs than planets around stars that radiate more energy.

The distance between Gliese 12 and the new planet is only 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 12 b is one of the best targets to study whether Earth-sized planets orbiting cool stars can maintain their atmospheres, a crucial step in advancing our understanding of the habitability of planets in our Milky Way,” says Shishir Dholakia, a PhD candidate at the Center for Astrophysics at the University of Southern Queensland in Australia. He led another research team with Larissa Palethorpe, a PhD candidate at the University of Edinburgh and University College London.

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

“It is thought that the initial atmospheres of Earth and Venus were stripped away and then replenished by volcanic outgassing and bombardment of residual material in the solar system,” Palethorpe explains. “Earth is habitable, but Venus is not due to the complete loss of water. Because Gliese 12 b is between Earth and Venus in temperature, its atmosphere could tell us a lot about the habitability pathways that planets take as they develop.”

An important factor in maintaining an atmosphere is the storminess of the star. Red dwarfs tend to be magnetically active, resulting in frequent, powerful X-ray flares. However, analyzes from both teams show that Gliese 12 shows no signs of extreme behavior.

An article led by Kuzuhara and Fukui appears The astrophysical diary letters. Dholakia and Palethorpe’s findings were published in Monthly notices of the Royal Astronomical Society on the same day.

During a transit, light from the host star passes through each atmosphere. Different gas molecules absorb different colors, so the transit produces a series of chemical fingerprints that can be detected by telescopes such as Webb.

“We know of only a handful of temperate planets that are similar to Earth and both of which are close enough to us and meet other criteria needed for this type of research, called transmission spectroscopy, using current facilities,” says Michael McElwain, a research astrophysicist at NASA’s Goddard. Space Flight Center in Greenbelt, Maryland, and co-author of the paper Kuzuhara and Fukui. “To better understand the diversity of atmospheres and evolutionary outcomes for these planets, we need more examples like Gliese 12 b.”

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