NASA is a couple of years away from launching the James Webb space telescope, and reports say it will be twice the size and 100 times more powerful than the Hubble telescope we use now. That means that distant, unreachable planets will be easier to assess from the comfort of our own home – or NASA’s offices, at any rate.

See related Space shotgun isn’t a return to armed astronauts Alcohol in space: From communion wine to zero-gravity whisky After New Horizons, when will we next revisit the outer solar system? Rather than pointing it indiscriminately at planets in the hopes of finding a new Earth, scientists at the University of Washington have published a new habitability index for ranking the planets, making them form an orderly queue for telescopic analysis. Given that the Kepler telescope has now discovered over 1,000 exoplanets, with an additional 3,200 further candidates, you can see the need for a little order.

“Basically, we’ve devised a way to take all the observational data that are available and develop a prioritisation scheme, so that as we move into a time when there are hundreds of targets available, we might be able to say ‘okay, that’s the one we want to start with,’” said Rory Barnes, astronomy professor at the University of Washington.

In the past, astronomers looking to compile a list of Earth-like planets have concentrated on exoplanets’ mass relative to Earth, as well as where their orbit sits in the “Goldilocks zone” – where it’s warm enough for liquid water to exist, but not evaporate. “That was a great first step, but it doesn’t make any distinctions within the habitable zone,” explained Barnes. “Now it’s as if Goldilocks has hundreds of bowls of porridge to choose from.”

Published in Astrophysical Journal, the paper, “Comparative Habitability of Transiting Exoplanets”, analyses planets according to a number of additional factors including “transit data, stellar properties and previously reported limits on planetary emitted flux”.

Taking all of this into account, the paper actually has a surprising take-home: Earth doesn’t get the highest score for habitability. That honour goes to a still unconfirmed planet known as KOI-3456.02, some 1,460 light years away. KOI-3456.02 scored 0.955, followed by Kepler-442b (1,100 light years away) on 0.836. Earth gets a rating of 0.829, with Mars achieving a lowly 0.422 score.

Still, we make do with what we’ve got. A more habitable planet would be lovely, but at 1,460 light years away, it’d take New Horizons more than 25 million years to get to KOI-3456.02. Call me impatient, but that feels like too long for a slightly more comfortable life. Mars, for all its weaknesses, is significantly more attainable.

Don’t worry, there’s always Kepler-452b. Although, even if Kepler-452b is fit for humans, if you’re reading this, you’ll die on Earth.

Images: Hubble Heritage and NASA Goddard Space Flight Centre used under Creative Commons