Astronomers were hoping to find plenty of water in the atmospheres of three exoplanets, but came up almost dry.
The planets, HD 189733b, HD 209458b, and WASP-12b, were thought to be winning candidates for holding water, the Space Telescope Science Institute (STScI) reported. The "hot Jupiters" proved to have only between one-tenth to one one-thousandth the amount of atmospheric water predicted. The observations were made by NASA's Hubble telescope and the findings were published July 24 in The Astrophysical Journal Letters.
"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," Nikku Madhusudhan of the Institute of Astronomy at the University of Cambridge, England said. "However, the low water abundance we have found so far is quite astonishing."
The findings mean researchers need to take a second look at exoplanet formation. They also suggest researchers could have to design equipment with higher sensitivity if water is that scarce on these types of planets.
"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)," Madhusudhan said.
Currently accepted planet formation theories suggest these planets form around a young star in a protoplanetary disk made of " hydrogen, helium, and particles of ices and dust." These particles eventually stick to each other and form a solid planetary core. Once the planet forms its atmosphere is believed to be full of water vapor. The low level of water vapor found on these planets challenges that theory.
"There are so many things we still don't know about exoplanets, so this opens up a new chapter in understanding how planets and solar systems form," Drake Deming of the University of Maryland, College Park, who led one of the precursor studies said. "The problem is that we are assuming the water to be as abundant as in our own solar system. What our study has shown is that water features could be a lot weaker than our expectations."
