Traci Watson

Special for USA TODAY

An Earth-size planet that could boast water, even an ocean, has been found circling the star nearest our sun, hinting that the conditions for life could exist next door.

Researchers have identified a plethora of planets outside our solar system that both resemble Earth in size and dwell in the “habitable zone,” where liquid water is possible. But no other Earth-like planet outside our solar system is as close to humans and their observatories as this new world, making it the best possible hunting ground for living organisms.

The find, reported in a study published Wednesday in Nature, has scientists reaching for superlatives.

“An absolutely amazing discovery,” says Victoria Meadows of the University of Washington. “This will be the most accessible, closest planet in the habitable zone to our solar system.”

“The excitement is that it’s around the closest star to our sun,” says Rory Barnes, also of the University of Washington, adding that it’s “exciting, too, to realize perhaps the next star over has a planet with life on it.”

Announced after a search by astronomers from around the world, the new planet circles a small star called Proxima Centauri. That star, though invisible to the naked eye, is only 4.2 light-years — about 25 trillion miles — from Earth, making it our nearest stellar neighbor.

The specs of the new planet, called Proxima b, sound much like Earth’s. It is 1.3 times the mass of the Earth or bigger. It is probably rocky, like Earth, and not a Jupiter-like ball of gas. And it’s just the right distance from its star that it would be warm enough for liquid water to pool on the surface, assuming the planet has an atmosphere.

Of course, it may not have an atmosphere, a prerequisite for life. Tipping the odds against life a bit, Proxima b’s star blasts it with far more high-energy radiation than our planet receives from the sun.

All the same, the planet may still be hospitably wet, Meadows says, depending on how and where it formed billions of years ago and how its star behaved during the planet’s infancy.

Picking out the planet has taken some of the most powerful telescopes in the scientific arsenal. The first signals of a world orbiting Proxima Centauri were recorded more than a decade ago, and more such signals have continued to trickle in – but never enough to be convincing. So astronomers recruited multiple telescopes to stare at the star earlier this year.

The intensive observations confirmed that the star quivers slightly, the result of a slight perturbation induced by its small planet. That quiver translates into barely detectable changes in the light streaming from the star.

Other planets outside our solar system have been announced with fanfare, only to quietly fade away when they couldn’t be confirmed. But “the fact that we have been able to see a signal over so many years tells us that there really is a bona fide planet,” says study co-author Richard Nelson of Britain’s Queen Mary University of London. “If you’ve got one in your backyard, it tells you that through the galaxy there are going to be many, many of these types of planets.”

To determine whether organisms thrive on Proxima b, scientists will need to take a picture of the planet itself. Analysis could reveal molecules that would be telltale signs of life.

No existing instrument could snap such pictures. But such technology is under design, and the new discovery will likely galvanize construction of observatories that could take a portrait of this new world. The planet is even close enough that perhaps someday robots could reach it.

A space mission to reach exoplanets won’t be ready until the “coming centuries,” says David Armstrong of Britain’s University of Warwick. “But the first one we’ll send it to will be this.”