The prevailing idea about Gliese 581c is that it has a diameter about 1.5 times bigger than Earth. This means 581c would have an atmosphere, but what's in that atmosphere remains a mystery. The European research team that discovered the planet believes the average surface temperature on 581c is between a comfortable 32 and 104 degrees Fahrenheit.
However, most skeptical astronomers are cautioning that it's just too early to tell whether there is water on 581c.
"You need more work to say it's got water or it doesn't have water," said ex-NASA astronomer Steve Maran, press officer for the American Astronomical Society. "(Even if we had the spacecraft technology available today) you wouldn't send a crew there assuming that when you get there, they'll have enough water to get back."
Lou Varricchio is a former NASA senior science writer. He lives in Middlebury, Vt.