Finding a planet out in deep space that we could potentially live on has been a science fiction trope for decades, but little more than that.
Yet with scientists discovering a growing number of exoplanets all around the universe, many new candidates to be the perfect Earth 2.0 have emerged.
For example, in February 2022 Newsweek reported that astronomers have spotted two mini-Neptune exoplanets, which, as they lose their puffy atmospheres, are possibly transforming into so-called “super-Earths“.
But have we actually found any exoplanets that we could live on, and, if so, how can we tell from so far away?
A Reddit post claiming that “Earth’s distant twin”, Kepler-442b, is actually more habitable than Earth hit the site’s front page this week with more than 42,000 upvotes.
“Kepler-442b, a rocky exoplanet 1206 light years from Earth and orbiting [in] its star’s habitable zone, has a rating of 0.836. The Earth is at 0.829,” the post reads.
The image of the planet is labeled as “Kepler-422B,” which appears to be a typo.
The post references an index of planetary habitability first published in The Astrophysical Journal in 2015, which uses various data about the exoplanet and its orbit to score how habitable it may be.
Kepler-442b is a rocky planet found orbiting around the star Kepler-442, which is about 40 percent the mass of our Sun and is labeled a “super-Earth” by NASA.
While Kepler-442b may have been given a higher rating on this index than the Earth, that doesn’t mean that it’s more habitable than our home planet, and therefore may not necessarily be capable of hosting life.
“The rating is based on planets that are transiting from our observing perspective (i.e, those systems where planets are crossing in front of their star, and blocking its light). And it is based on whether a planet is rocky, or receiving enough star light, or how ‘un-circular’ (eccentric) a planet is,” Ravi Kopparapu, an extrasolar planet habitability expert at NASA‘s Goddard Space Flight Center, told Newsweek.
“For Kepler 442b, based on how much star light the planet is receiving and other factors that I mentioned above, it turns out this planet has an index higher than a potential Earth-size planet around a Sun-like star. Or perhaps a more accurate way to say it is, better conditions for habitability rather than saying ‘more habitable,’ which is a vague statement.
He added: “It says nothing about if the planet could be ‘inhabited.’ Just because a planet is habitable doesn’t mean it should be inhabited.”
While exoplanets were previously assessed only based on where they were positioned in relation to their star, and if that was in the “Goldilocks” or habitable zone (where water could exist in liquid form), this updated index considers a wider range of factors that determine if life would survive.
“The new habitability score … adds information about the stability of the climate, given what is known about the planetary orbit and the type of star it’s orbiting,” Andrew Cole, a professor in astrophysics at the University of Tasmania, told Newsweek.
“Climate stability is very important to the long term suitability of a planet for complex multicellular life. (Bacteria are much tougher, and could probably survive under much more hostile conditions).
“There are two important points though: One is that we don’t actually know the conditions on the planets, without analysis of the atmospheric and surface composition; we can just make our best guess from the available information.
“The current state of the climate on Earth shows us that things can vary quite dramatically in a way that wouldn’t really be detectable from outside the solar system to an alien observer.
“The second important point is that there is no current or known future technology that could allow us to run away to any secondary homeworld for humanity—the distances involved are just too large.”
From such a great distance, it is very difficult to gather much information about the conditions on an exoplanet, so habitability estimates have to be drawn from the bare-bones data available. Other factors not measured in the index may make a planet much more habitable, such as a strong magnetic field or a lunar satellite.
“The hallmarks of a supremely habitable planet would be a super-Earth with more water content than Earth, a nearly circular orbit, and a thicker and so better insulating atmosphere than ours,” Chris Impey, a professor of astronomy at the University of Arizona, Tucson, told Newsweek.
“We have found near ‘clones’ of the Earth, but as this research shows, we could do better than Earth for ‘Planet B.’ But the catch is that it is likely to be 100 light-years or more away, and the energy costs of going there, even with small spacecraft, are prohibitive. Far cheaper to take care of Planet A.”