Are there Habitable Worlds near us?

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Although Gliese 12b could tell us how planets close to their suns can lose their atmospheres, this artist’s rendering of the planet depicts it with a thin atmosphere.

In May 2024, two research teams confirmed the presence of a nearby exoplanet named Gliese 12b using the equipment aboard TESS. 

TESS (Transiting Exoplanet Survey Satellite) is a satellite made for finding exoplanets orbiting bright dwarf stars. Although it's primary mission ended in July 4th 2020 it has continued working helping us to understand our universe to a higher degree`It was made for finding exoplanets orbiting bright dwarf stars by monitoring the periodic dips in brightness observed in these dwarf stars that is usually indicative of planetary transits. During its primary mission period, it imaged about 75% of the observable sky and put it into a huge mosaic which found 66 new confirmed exoplanets and 2,100 candidates that require further research to be confirmed.

What makes this exoplanet Gliese 12b particularly special is its  only 40 lightyears away from us and is in the habitable zone (assuming an atmosphere). It has been observed to be about the size of Venus and orbits close to its  dwarf star, (which is the smallest kind of star on the main sequence and also the coolest), only 7% of the distance between the Earth and the sun, but due to the lower temperatures it only receives 1.6 times the energy that we get from the sun meaning its surface temperature will be about 42 degrees Celsius. At this temperature it could harbour liquid water.

“We’ve found the nearest, transiting, temperate, Earth-size world located to date,” said Masayuki Kuzuhara, a project assistant professor at the Astrobiology centre in Tokyo, who co-led one research team with Akihiko Fukui, a project assistant professor at the University of Tokyo. “Although we don’t yet know whether it possesses an atmosphere, we’ve been thinking of it as an exo-Venus, with similar size and energy received from its star as our planetary neighbour in the solar system.”

Due to how close the relatively temperate, transiting exoplanet is, it will be a promising target for the JWST, which should be able to determine whether it has an atmosphere. “We know of only a handful of temperate planets similar to Earth that are both close enough to us and meet other criteria needed for this kind of study, called transmission spectroscopy [During a transit, the light from the host star passes through the planet's atmosphere. Various gas molecules absorb different wavelengths of light, creating unique chemical signatures that telescopes such as the JWST can detect] using current facilities,” said Michael McElwain, a research astrophysicist at NASA’s Goddard Space Flight Centre in Greenbelt, Maryland, and a co-author of the Kuzuhara and Fukui paper. “To better understand the diversity of atmospheres and evolutionary outcomes for these planets, we need more examples like Gliese 12 b.”

The diminutive sizes and masses of red dwarf stars make them ideal for finding Earth-sized planets as they will present themself with greater dimming for every transit across their star, which with its lower mass, also allows for a greater reflex motion -which is the movement of a star in response to the gravity of the orbiting planet (If you want to learn more, especially about the Kepler’s laws, https://ethz.ch/content/dam/ethz/special-interest/phys/particle-physics/quanz-group-dam/documents-old-s-and-p/Courses/ExtrasolarPlanetsFS2016/exop2016_chapter2_part1.pdf is a great resource) and this appears as a greater “wobble” during the transit of the planetary body. Although red dwarf stars are known for their powerful solar flares, due to their particularly magnetically active nature (You can read https://www.theweeklyspaceman.com/post/the-sun-s-magnetic-field-is-flipping-here-is-why about the correlation between the magnetic fields and solar activity), that could potentially rip the atmosphere of a planet so close to it, Gliese 12b's star, GJ 12, has not been observed to demonstrate any extreme behavior. The star is only about 27% of the size of our own with a surface temperature about 60% of our sun’s.

“Gliese 12b represents one of the best targets to study whether Earth-size planets orbiting cool stars can retain their atmospheres, a crucial step to advance our understanding of habitability on planets across our galaxy,” said Shishir Dholakia, a doctoral student at the Centre for Astrophysics at the University of Southern Queensland in Australia. He co-led a different research team with Larissa Palethorpe, a doctoral student at the University College London and at the University of Edinburgh.

But why is this discovery so interesting? Well, its because studying the exoplanet could give insight about our own solar system’s evolution. “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,” Palethorpe explained. “The Earth is habitable, but Venus is not due to 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 planets take as they develop.” It could also help us on our search for life, allowing us to see correlations between the distances between stars and their planets as well as the type of stars that these exoplanets orbit and their conditions.