Astronomers have discovered a planet within the habitable zone of one the closest stars to Earth, indicating it could have liquid water on its surface.
The planet is believed to be one of five planets orbiting Tau Ceti, a star which is more similar to our sun in size and makeup than any other nearby star. Tau Ceti is less than 12 light years away and can be seen with the naked eye. It's a slightly yellowish star between the moon and Jupiter in the sky, within the constellation Cetus (the Whale), according to SPACE.com.
There has only one been one exoplanet discovered closer to Earth: Alpha Centauri Bb, and that planet's surface is likely molten lava with a surface temperature estimated at 2,240 degrees Fahrenheit. It was discovered in the closest star system to Earth, Alpha Centauri.
The potentially livable planet orbiting Tau Ceti, which was discovered in a study by an international team of astronomers, is likely to be closer to the temperature of Earth, but may not be rocky like Earth.
"It is impossible to tell the composition, but I do not consider this particular planet to be very likely to have a rocky surface," the study's lead author Mikko Tuomi, of the University of Hertfordshire in England, told SPACE.com. "It might be a 'water world,' but at the moment it's anybody's guess."
The planet orbits its sun every 168 days and is about 4.3 times bigger than Earth, making it the smallest planet ever discovered in a habitable zone of a star. The planets within these zones are often referred to as "Goldilocks planets" in that their likely surface temperatures are neither too hot, nor too cold, but just right for liquid water.
"This discovery is in keeping with our emerging view that virtually every star has planets, and that the galaxy must have many such potentially habitable Earth-sized planets," said study coauthor Steve Vogt, of the University of California—Santa Cruz, in a statement. "They are everywhere, even right next door."
While hundreds of planets outside our solar system have been discovered, the close proximity of Tau Ceti could make it ripe for future study.
"Tau Ceti is one of our nearest cosmic neighbors and so bright that we may be able to study the atmospheres of these planets in the not-too-distant future," said James Jenkins of Universidad de Chile, a visiting fellow at the University of Hertfordshire and coauthor of the study.
The Goldilocks planet and its four neighbors orbiting Tau Ceti were discovered using high-tech instruments on telescopes in Chile, Australia, and Hawaii. The astronomers analyzed 6,000 observations of Tau Ceti and detected tiny wobbles they believe were caused by orbiting planets. They used new techniques to distinguish the relatively small planets from the "noise" that typically obscures the detection of small objects. One scientist described searching for planets around bright stars as "akin to studying a firefly sitting one centimetre away from a distant, powerful car headlight."
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Seth Cline is a reporter for U.S. News & World Report. You can follow him on Twitter or reach him at firstname.lastname@example.org.