Exoplanet little warmer than Earth found

Newswand: Astronomers have made the rare and tantalising discovery of an Earth-like exoplanet 40 light-years away that may be just a little warmer than our own world.

Credit: NASA/JPL-Caltech/R. Hurt (Caltech-IPAC)

The potentially-habitable planet, named Gliese 12 b, orbits its host star every 12.8 days, is comparable in size to Venus – so slightly smaller than Earth – and has an estimated surface temperature of 42°C (107°F), which is lower than most of the 5,000-odd exoplanets confirmed so far.

That is assuming it has no atmosphere, however, which is the crucial next step to establishing if it is habitable.

Gliese 12 b is by no means the first Earth-like exoplanet to have been discovered, but as NASA has said, there are only a handful of worlds like it that warrant a closer look.

It has been billed as “the nearest, transiting, temperate, Earth-size world located to date” and a potential target for further investigation by the US space agency’s £7.5billion James Webb Space Telescope.

Gliese 12 b could also be significant because it may help reveal whether the majority of stars in our Milky Way galaxy – i.e. cool stars – are capable of hosting temperate planets that have atmospheres and are therefore habitable.

It orbits a cool red dwarf star called Gliese 12, which is almost 40 light-years away from Earth in the constellation Pisces.

The exoplanet’s host star is about 27 per cent of the size of our Sun and has a surface temperature that is around 60 per cent of our own star.

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

This difference in solar radiation is important because it means the planet’s surface temperature is highly dependent on its atmospheric conditions. As a comparison to Gliese 12 b’s estimated surface temperature of 42°C (107°F), Earth has an average surface temperature of 15°C (59°F).

The researchers, along with another team in Tokyo, used observations by NASA’s TESS (Transiting Exoplanet Survey Satellite) to help make their discovery.

At 40 light-years from Earth, Gliese 12 b is about the same distance as the TRAPPIST-1 system. This is made up of seven planets, all roughly in Earth’s size range and likely rocky, orbiting a red dwarf star.

Three of these are in the habitable zone but at least two – and probably all of them – have no atmosphere and are likely barren, dismissing hopes when they were first discovered eight years ago that they could be water worlds hosting life.

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Webb gives clues to ballooning of an exoplanet

Newswand: Astronomers have proposed that the tidal heating was the cause of the ballooning of the warm gas-giant exoplanet WASP-107 b with the help of findings from the James Webb Space Telescope.

Photo credit: NASA, ESA, CSA, Ralf Crawford (STScI)

Data collected using NASA’s James Webb Space Telescope, combined with prior observations from NASA’s Hubble Space Telescope, show surprisingly little methane (CH4) in the planet’s atmosphere, indicating that the interior of WASP-107 b must be significantly hotter and the core much more massive than previously estimated.

The unexpectedly high temperature is thought to be a result of tidal heating caused by the planet’s slightly non-circular orbit, and can explain how WASP-107 b can be so inflated without resorting to extreme theories of how it formed.

The results, which were made possible by Webb’s extraordinary sensitivity and accompanying ability to measure light passing through exoplanet atmospheres, may explain the puffiness of dozens of low-density exoplanets, helping solve a long-standing mystery in exoplanet science.

The problem with WASP-107 b

At more than three-quarters the volume of Jupiter but less than one-tenth the mass, the “warm Neptune” exoplanet WASP-107 b is one of the least dense planets known. While puffy planets are not uncommon, most are hotter and more massive, and therefore easier to explain.

“Based on its radius, mass, age, and assumed internal temperature, we thought WASP-107 b had a very small, rocky core surrounded by a huge mass of hydrogen and helium,” explained Luis Welbanks from Arizona State University (ASU), lead author on a paper published in Nature. “But it was hard to understand how such a small core could sweep up so much gas, and then stop short of growing fully into a Jupiter-mass planet.”

If WASP-107 b instead has more of its mass in the core, the atmosphere should have contracted as the planet cooled over time since it formed. Without a source of heat to re-expand the gas, the planet should be much smaller. Although WASP-107 b has an orbital distance of just 5 million miles (one-seventh the distance between Mercury and the Sun), it doesn’t receive enough energy from its star to be so inflated.

A likely source of WASP-107 b’s extra internal energy is tidal heating caused by its slightly elliptical orbit. With the distance between the star and planet changing continuously over the 5.7-day orbit, the gravitational pull is also changing, stretching the planet and heating it up.

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