Three exoplanets nearly dry

In a significant discovery using NASA's Hubble Space Telescope, astronomers, including an Indian-origin researcher, who went looking for water vapour in three exoplanets orbiting stars similar to our sun have come up nearly dry.

The three "hot Jupiters" are between 60 and 900 light-years away from Earth and were thought to be ideal candidates for detecting water vapour in their atmospheres because of their high temperatures where water turns into a measurable vapour.

"It opens a whole can of worms in planet formation. We expected all these planets to have lots of water in them. We have to revisit planet formation and migration models of giant planets and probe how they are formed," said Nikku Madhusudhan from the Institute of Astronomy at the University of Cambridge.

Known as HD 189733b, HD 209458b, and WASP-12b, these so-called "hot Jupiters" were found to have only 1/10th to one 1/1,000 the amount of water predicted by standard planet-formation theories.

The 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.

"We can say with much greater certainty than ever before that we have found water in an exoplanet," Madhusudhan added.

The results may have major implications in the search for water in potentially habitable Earth-sized exoplanets.

Instruments on future space telescopes may need to be designed with a higher sensitivity if target planets are drier than predicted.

"We should be prepared for much lower water abundances than predicted when looking at super-Earths," Madhusudhan said.

These three planets were selected because they orbit relatively bright stars that provide enough radiation for an infrared-light spectrum to be taken.

"There are so many things we still do not know about exoplanets so this opens up a new chapter in understanding how planets and solar systems form," said Drake Deming from University of Maryland.

The findings appeared in The Astrophysical Journal Letters.