Dec. 14--As astronomers discover more and more gas giants around other stars, they've increasingly wondered: Where's the water? These distant worlds, known as hot Jupiters, have appeared to be strangely dry -- a mystery that seemed to contradict our ideas of planet formation.
But now, scientists using the Hubble and Spitzer space telescopes think they may have solved the mystery: The water has been blocked by thick clouds in these gassy planets' atmospheres.
The findings, published by the journal Nature, could shed new light on how planets form and evolve, and could help scientists better understand these distant worlds' atmospheres.
While gas giants might be relatively easy to spot due to their size, their interiors remain largely shrouded in layers of mystery. We don't even know all that much about our own Jupiter, said study coauthor Jonathan Fortney, a planetary astrophysicist at UC Santa Cruz. The last time NASA sent a probe plunging into the planet's thick atmosphere was the Galileo 20 years ago, he pointed out.
Researchers have long assumed that gas giant planets would have plenty of water within them -- after all, oxygen, after hydrogen and helium, is the most abundant element in the universe. And at planetary temperatures, much of that oxygen is locked in water molecules -- so gas giants, forming out of the disc of debris around a newborn star, should have incorporated plenty of the stuff into their bodies.
But for a planet like Jupiter, that's hard to tell, because the water is actually hidden deep within the planet's many-layered atmosphere. (While the Galileo probe descended deep through the atmosphere, sending back some water data, it succumbed to the high temperatures and pressures before it could get a full reading, Fortney said.)
But hot Jupiters were thought to skirt this problem -- their atmospheres, heated by the sun, are very well mixed, so the water vapor would be distributed throughout the atmosphere, not hidden below. And so, ironically, it should be easier to detect water in these distant gas giants than in our own.
