TESS discovers an intriguing world between Earth and Venus in size

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

TESS observes a large portion of the sky for about a month at a time, tracking changes in the brightness of tens of thousands of stars at intervals ranging from 20 seconds to 30 minutes. Capturing transits – brief, regular dimming of stars caused by passing worlds in orbit – is one of the mission’s main goals.

“We have found the closest transit, temperate, Earth-sized world to date,” said Masayuki Kuzuhara, project assistant professor at the Tokyo Astrobiology Center, who co-led a research team with Akihiko Fukui, project assistant. professor at the University of Tokyo. “Although we do not yet know whether it has an atmosphere, we consider it to be 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 temperature of the sun’s surface. The newly discovered world, named Gliese 12 b, orbits every 12.8 days and is the size of Earth or slightly smaller, comparable to Venus. Assuming it has no atmosphere, the planet’s surface temperature is estimated to be around 107 degrees Fahrenheit (42 degrees Celsius).

Astronomers say the small size and mass of red dwarf stars make them ideal for finding Earth-sized planets. A smaller star means greater attenuation with 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 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 habitable zones around red dwarfs than those around more energy-emitting stars.

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 represents one of the best targets for studying whether Earth-sized planets orbiting cool stars can retain their atmospheres, a crucial step in advancing our understanding of the habitability of planets in our galaxy,” said Shishir Dholakia, a doctoral student at the Institute. Center for Astrophysics at the University of Southern Queensland in Australia. He co-led another research team with Larissa Palethorpe, a doctoral student at the University of Edinburgh and University College London.

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

“The early atmospheres of Earth and Venus are thought to have been destroyed and then replenished by volcanic outgassing and bombardment from residual material in the solar system,” Palethorpe explained. “Earth is habitable, but Venus is not due to its complete loss of water. As Gliese 12 b lies between Earth and Venus in temperature, its atmosphere could teach us a lot about pathways to habitability taken by the planets as they develop.”

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

An article edited by Kuzuhara and Fukui appears in Letters from the astrophysical journal. The findings from Dholakia and Palethorpe were published in Monthly Notices of the Royal Astronomical Society the same day.

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

TESS is a NASA Astrophysics Explorer mission managed by NASA Goddard and operated by MIT in Cambridge, Massachusetts. Other partners include Northrop Grumman, based in Falls Church, Virginia; NASA Ames Research Center in California’s Silicon Valley; the Astrophysics Center | Harvard and Smithsonian in Cambridge, Massachusetts; MIT 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 this mission.