Astronomers looking for exoplanets that might be habitable have focused on worlds that are earth-like.

They’ve looked at planets that are roughly the same size as ours, with more or less the same amount of heat and light from their parent sun, and are likely to have a similar atmosphere.

But as the catalogue of exoplanets spotted by the Kepler space telescope increases, astrobiologists say they’re beginning to identify a new class of planet that is not only habitable but super habitable.

Conditions on their surface could be more hospitable to life than those we currently find on Earth.

A research team led by Dirk Schulze-Makuch from Washington State University has identified a number of potentially "super habitable" worlds. The team has also explained the reasoning behind the "super habitable world" theory.

An artist's impression of the newly discovered "impossible planet" tightly orbiting a white dwarf star
Earth is around 4.5 billion years old, but the researchers suggest the ideal age for an inhabited planet is between 5 billion to 8 billion years old.

"We have to be careful to not get stuck looking for a second Earth because there could be planets that might be more suitable for life than ours," explained Dr Schulze-Makuch.

These superhabitable worlds are all bigger and older than Earth. They are likely to be warmer, with more surface water, and they orbit stars with a longer stable lifespan than our own Sun.

Dirk Schulze-Makuch
While none of the 24 most promising superhabitable planets fulfilled all of Dirk Schulze-Makuch's criteria, one had at least 4 of the most important qualities but one has four of the critical characteristics

All these "upgrades" would mean life could evolve on this planets earlier and have more chance evolving to maturity undisturbed by solar flares or other cosmic nasties that would bring extraterrestrial ecosystems to a sudden halt.

A big heavy planet would tend to have a dense atmosphere that would help to protect a growing biosphere from deadly radiation, and even be more likely to burn up meteors and asteroids that came calling.

It would also be more likely to have an electromagnetic field like the one that protects its from deadly solar radiation.

Planets
There are over 4,500 known exoplanets, and many more waiting to be discovered

Larger, heavier worlds would also be more likely to give rise to large continents and active plate tectonics – giving rise to the earthquakes and volcanoes that bring essential chemicals and minerals from the planet’s interior.

While a warmer world might seem like a negative feature, given the problems we’re currently experiencing with climate change, a world that was naturally warmer form the outset would promote the evolution of life that – unlike us – would be able to cope with higher temperatures.

"Global warming for current Earth would be a really bad thing, because we already have an established biosphere and atmospheric circulation pattern, and changes would result in extreme weather putting a lot of stress on the biosphere, resulting in extinction events," the researchers told Gizmodo.

"In addition, it would raise sea water levels and decrease the land areas and coastal areas taking away valuable habitats and putting even more stress on many parts of the biosphere."

So-called 'Super Earths" could be more hospitable to life that smaller planets like ours

But for an ecosystem that had evolved to cope with those conditions, "a higher temperature together with a higher moisture content than Earth could be quite beneficial," they added.

Having set their criteria, Schulze-Makuch’s researchers sifted the nearly 5,000 known exoplanets to see how many of them fitted their "superhabitable" criteria.

24 came close, offering conditions that might prove particularly hospitable to life. Just one really stood out.

Somewhere out there, there's another world suitable for humans

"Kepler Object of Interest" number 5715.01 is 1.16 times larger than Earth with a mean temperature estimated at 81ºF.

It’s thought to be some 4.3 billion years old - so plenty of time for complex life to develop. Going to find out might be a problem though. It’s 2,700 light years away. Even if we could build the starship Enterprise it’d take around 11 years to get there at warp seven.