Hubble Finds Three Surprisingly Dry Exoplanets

Jul 24, 2014

By NASA

Astronomers using NASA’s Hubble Space Telescope have gone looking for water vapor in the atmospheres of three planets orbiting stars similar to the sun — and have come up nearly dry.

The three planets, known as HD 189733b, HD 209458b, and WASP-12b, are between 60 and 900 light-years away from Earth and were thought to be ideal candidates for detecting water vapor in their atmospheres because of their high temperatures where water turns into a measurable vapor.

These so-called “hot Jupiters” are so close to their star they have temperatures between 1,500 and 4,000 degrees Fahrenheit, however, the planets were found to have only one-tenth to one one-thousandth the amount of water predicted by standard planet-formation theories.

“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,” said Nikku Madhusudhan of the Institute of Astronomy at the University of Cambridge, England. “However, the low water abundance we have found so far is quite astonishing.”

Madhusudhan, who led the research, said that this finding presents a major challenge to exoplanet theory. “It basically 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, especially “hot Jupiters,” and investigate how they’re formed.”

He emphasizes that these 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 (rocky planets that are several times the mass of Earth),” Madhusudhan said.

Using near-infrared spectra of the planets observed with Hubble, Madhusudhan and his collaborators estimated the amount of water vapor in each of the planetary atmospheres that explains the data.

The planets were selected because they orbit relatively bright stars that provide enough radiation for an infrared-light spectrum to be taken. Absorption features from the water vapor in the planet’s atmosphere are detected because they are superimposed on the small amount of starlight that glances through the planet’s atmosphere.

2 comments on “Hubble Finds Three Surprisingly Dry Exoplanets

  • These so-called “hot Jupiters” are so close to their star they have temperatures between 1,500 and 4,000 degrees Fahrenheit, however, the planets were found to have only one-tenth to one one-thousandth the amount of water predicted by standard planet-formation theories.

    I’m not sure why this should be surprising in hot planets which have been orbiting near to their stars for quite some time.

    Solar radiation dissociates H2O into H and O2 with the lighter but energetic hydrogen being lost being into space.

    Inner planets like Mercury have, and are having, their atmospheres stripped off by the Solar Wind.
    Even heavier elements boiled off Mercury trail behind it like the tail of a comet.

    http://science.nasa.gov/science-news/science-at-nasa/2009/03nov_hiddenterritory/

    Nov. 3, 2009: The MESSENGER spacecraft’s third flyby of the planet Mercury has given scientists, for the first time, an almost complete view of the planet’s surface and revealed some dramatic changes in Mercury’s comet-like tail.

    Earth is gaining mass from falling space dust, but losing mass from losing hydrogen to space!

    http://scitechdaily.com/earth-loses-50000-tonnes-of-mass-every-year/

    The biggest mass loss comes from escaped hydrogen and helium, which escape with 95,000 tonnes of mass and 1,600 tonnes respectively. These elements are too light to stay permanently in the gravity well, so they tend to escape into space.



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