Theories on how planets form may have to be revisited after searches of several "hot Jupiter" planets failed to find expected water, scientists say.
The results go against currently held models of predicted water presence on distant worlds, models that suggest three distant planets examined by the Hubble Space Telescope should have had considerable water vapor present in their atmospheres.
Writing in Astrophysical Journal Letters, the researchers admit the failure to find the water they were expecting to see there will require another look at present theories about how such "hot Jupiters" form.
"It basically opens a whole can of worms in planet formation," lead researcher Nikku Madhusudhan at Cambridge University's Institute of Astronomy says. "We expected all these planets to have lots of water in them."
Although the planets were much drier than anticipated, the research proved they weren't entirely without moisture, says Madhusudhan.
"Our water measurement in one of the planets, HD 209458b, is the highest-precision measurement of any chemical compound in a planet outside our solar system, and we can now say with much greater certainty than ever before that we've found water in an exoplanet."
Water on "hot Jupiters" would only exist as vapor in the atmosphere, as the giant gas worlds orbit in close proximity to their host stars and can be as hot as 1,500 to 4,000 degrees Fahrenheit.
The findings may have a bearing on the search for water on exoplanets that more closely resemble Earth, and researchers conducting such searches may have to scale back their expectations accordingly, Madhusudhan says.
"We should be prepared for much lower water abundances than predicted when looking at super-Earths (rocky planets that are several times the mass of Earth,)" he says.
Future space telescopes may need to be equipped with instruments of higher sensitivity if target planets are drier than predicted, he says.
Space telescopes are the best tools for the task because detecting water on distant exoplanets from Earth is difficult since our atmosphere contains a lot of water, which contaminates the observations, the researchers say.
"We really need the Hubble Space Telescope to make such observations," says study co-author Nicolas Crouzet at the University of Toronto.
The water vapor levels Hubble detected in the three exoplanets studied were somewhere between a tenth to a thousandth of levels that current models of planet formation had predicted, Crouzet says.
"The very low water vapor levels we measure challenge our understanding of the chemistry involved in planet formation," he says.
