Alien worlds containing liquid water may be more rare than astronomers once believed, according to a new study of so-called "hot-Jupiters," orbiting other suns.
The Hubble Space Telescope was used by astronomers to examine three exoplanets, searching for signs of water vapor in their atmospheres. Examinations in near-infrared light showed each of the worlds was found to be surprisingly dry.
The alien worlds HD 209458b, HD 189733b, and WASP-12b are classified as hot Jupiters, due to their great mass and proximity to their companion stars. Temperatures on the giant worlds range from 1,500 and 4,000 degrees Fahrenheit.
These hot conditions were believed to make them ideal candidates for detection of water. The high thermal energies would cause much of the water on the planet to rise as vapor into the atmosphere. As that planet orbited between its sun and the Earth, light passing through the alien air would announce the presence of water vapor. Concentrations of water in the alien atmospheres were predicted to be 10 and 1,000 times higher than what researchers measured.
"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. However, the low water abundance we have found so far is quite astonishing," Nikku Madhusudhan from the University of Cambridge in England, said.
The trio of hot Jupiters lie between 60 and 900 light years away from our own family of planets. They were chosen for study because their companion stars are bright, as seen from Earth. Certain wavelengths of this light, pouring through the atmosphere of the alien world, are absorbed by water vapor. Astronomers, taking spectrographs of the light, determine concentrations of atmospheric water by measuring these absorption lines.
If other planets are found to be as dry as these worlds, it could have a profound influence on the search for alien life outside the solar system. Super-earths, planets much like our own world but larger, are believed to be prime spots to find alien life. Water is also thought to be a prerequisite for life on other worlds. The essential liquid be be a vital medium for the development of living beings.
"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," Drake Deming from the University of Maryland, who led an earlier study of water on worlds outside our solar system, told the press.
Study of the surprisingly dry hot Jupiters and what they could tell astronomers about the chance of finding water on alien worlds was published in The Astrophysical Journal Letters.