Astronomers Discover the First Universe in a Planet in the Habitable Zone of Another Star

The search for life beyond Earth has borne little fruit. That is still true, but scientists have renewed hope. For the first time, astronomers have discovered an atmosphere around an exoplanet in the habitable zone of a host star.

Say hello to LHS 1140b, a rocky Earth-like planet located about 48 light-years away from us. For reference, Voyager 1 is fast approaching its first day in the light after nearly 50 years in flight. LHS 1140b lives in the “Goldilocks” zone of its star, meaning it’s far enough away to be fried like Mercury, but close enough to be warm enough to support liquid water.

According to a new study published in Science, the “special” part of this discovery is not just the habitable zone around the star. It’s that it seems to meet the additional criteria that scientists care about — that is, it’s rocky, not a gas giant, and can still cling to space despite harsh conditions. The atmosphere helps stabilize surface temperatures, which are essential for life to exist.

“It’s very exciting,” said Collin Cherubim, the study’s lead author and a Harvard PhD, in an email. “The main goal of this field was to understand whether any rocky exoplanets could host an atmosphere.”

Cherubim says many rocky planets orbit small M-class stars, which “give off high-energy radiation for much longer than sun-like stars.” Many rocky planets are stripped of their atmosphere early in their life cycle, due to this radiation, the result of stripping the solar wind and other elements, thus eliminating their chance of hosting life.

Until LHS 1140b, Earth was the only rocky planet humans had ever observed that had a cool atmosphere.

It was not easy to find. Cherubs uses a computer model he developed during his career that “simulates how exoplanet atmospheres change over billions of years.” Those models predict the existence of “helium worlds,” or rocky planets with helium atmospheres (or at least helium). Cherubim tested their theory with LHS 1140b and found the proverbial gold.

Is there life in LHS 1140b?

Whether or not LHS 1140b contains life is a difficult question. Cherubs say that science recognizes three main requirements for a planet to support life: an atmosphere, the right temperature to support liquid water, and a planet that is particularly rocky to be hospitable. The LHS 1140b seems to have it all.

The main problem is that the upper atmosphere of LHS 1140b is almost entirely helium, which is also “depleted of hydrogen.” That’s not good for life, since helium generally can’t support life as we know it here on Earth.

The cherubim say that the planet is also locked in its star, like the moon on Earth, meaning that one side of the planet has perpetual day and the other perpetual night. It’s also about 70% larger than Earth, which means that gravity is almost twice as strong there. These findings do not completely rule out life, but if LHS 1140b does harbor life, it will be very different from life on Earth.

Cherubim also admits that researchers do not yet know whether the planet is rocky or completely covered by ocean, the latter of which could be important in the search for life. Computer models built by Cherub predict that the lower atmosphere may contain life-promoting gases, such as carbon dioxide, water and even oxygen.

“Although we need more data to see what’s going on in the rest of the universe, this may be the first known helium world,” Cherubim said. “That these rocky worlds can store helium in the atmosphere is not only good for the prospects of habitation, but also tells us that [computer prediction] models get something right.”

Until then, Mars is the most likely candidate for finding signs of life, as researchers have already identified possible biosignatures in its soil.

Another possible inhabitant is K2-18b, where scientists have reported evidence of dimethyl sulfide, a compound commonly produced by oceanic phytoplankton. Scientists also noticed the Trappist-1 star system, which has seven Earth-sized planets, three of which are in the star’s habitable zone.