Scientists can now confidently say the asteroid belt's "largest and roundest" object emits water vapor.
A research team observed "plumes" of water vapor coming off of the dwarf planet Ceres; this is the first "definitive" evidence of this phenomenon, a NASA/Jet Propulsion Laboratory news release reported. The water vapor is believed to occur when regions of Ceres' icy surface is slightly heated.
"This is the first time water vapor has been unequivocally detected on Ceres or any other object in the asteroid belt and provides proof that Ceres has an icy surface and an atmosphere," said Michael Küppers of ESA in Spain and lead author of the paper said in the news release.
The findings were made using the Herschel space observatory. NASA's Dawn mission will arrive at Ceres in 2015, where researchers will get to take the closest look in history.
"We've got a spacecraft on the way to Ceres, so we don't have to wait long before getting more context on this intriguing result, right from the source itself," Carol Raymond, the deputy principal investigator for Dawn at NASA's Jet Propulsion Laboratory said. "Dawn will map the geology and chemistry of the surface in high resolution, revealing the processes that drive the outgassing activity."
Over the past century Ceres has been considered to be the largest asteroid in our solar system. In 2006 the International Astronomical Union reclassified the object as a dwarf planet. Ceres is about 590 miles in diameter.
The object is believed to have an ice core that is covered in so much ice that it would amount to more freshwater than is found on Earth if melted. This ice is believed to have accumulated during the formation of the solar system's planets.
Herschel spotted the signature of water vapor four times it looked, but on one occasion did not detect water at all.
"When Ceres swings through the part of its orbit that is closer to the sun, a portion of its icy surface becomes warm enough to cause water vapor to escape in plumes at a rate of about [six] kilograms (13 pounds) per second. When Ceres is in the colder part of its orbit, no water escapes," the researchers believe, as an explanation for the varied results, according to the news release.
The water vapor plumes also moved in and out of Hershel's view as Ceres orbited. The team noticed the water source on Ceres' surface were darker than the rest of the object. Dark material heats up faster than light material, so this could explain why those regions become warm enough to produce water vapor.
Similar objects have been known to produce geysers and plumes, but this phenomenon is rarely seen in the asteroid belt.
"The lines are becoming more and more blurred between comets and asteroids," Seungwon Lee of the Jet Propulsion Laboratory, who helped with the water vapor models, said in the news release. "We knew before about main belt asteroids that show comet-like activity, but this is the first detection of water vapor in an asteroid-like object."
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