By Steve Gorman
Aug 19 (Reuters) - Direct observations from a NASA spacetelescope have for the first time revealed the atmospheric voidof a rocky, Earth-sized world beyond our own solar systemorbiting the most common type of star in the galaxy, accordingto a study released on Monday.
The research, published in the scientific journal Nature,also shows the distant planet's surface is likely to resemblethe barren exterior of the Earth's moon or Mercury, possiblycovered in dark volcanic rock.
The planet lies about 48.6 light years from Earth and is oneof more than 4,000 so-called exoplanets identified over the pasttwo decades circling distant stars in our home galaxy, the MilkyWay.
Known to astronomers as LHS 3844b, this exoplanet about 1.3times the size of Earth is locked in a tight orbit - onerevolution every 11 hours - around a small, relatively cool starcalled a red dwarf, the most prevalent and long-lived type ofstar in the galaxy.
The planet's lack of atmosphere is probably due to intenseradiation from its parent red dwarf, which, though dim bystellar standards, also emits high levels of ultraviolet light,the study says.
The study will likely add to a debate among astronomersabout whether the search for life-sustaining conditions beyondour solar system should focus on exoplanets around red dwarfs -accounting for 75% of all stars in the Milky Way - or lesscommon, larger, hotter stars more like our own sun.
The principal finding is that it probably possesses littleif any atmosphere - a conclusion reached by measuring thetemperature difference between the side of the planetperpetually facing its star, and the cooler, dark side facingaway from it.
A negligible amount of heat carried between the two sidesindicates a lack of winds that would otherwise be present totransfer warmth around the planet.
"The temperature contrast on this planet is about as big asit can possibly be," said researcher Laura Kreidberg of theHarvard-Smithsonian Center for Astrophysics in Cambridge,Massachusetts. She is lead author of the study.Similar analysis previously was used to determine thatanother exoplanet, 55 Cancri e, about twice as big as Earth andbelieved to be half-covered in molten lava, likely possesses anatmosphere thicker than Earth's. This exoplanet, unlike LHS3844b, orbits a sun-like star.
The planet in the latest study was detected last year byNASA's newly launched Transiting Exoplanet Survey Satellite, anorbiting telescope that pinpoints distant worlds by spottingperiodic, dips in the light observed from their parent starswhen an object passes in front of them.
But it was follow-up observations from another orbitinginstrument, the Spitzer Space Telescope, which can detectinfrared light directly from an exoplanet, that provided newinsights about its features.
(Reporting by Steve Gorman in Los Angeles; Editing by BillTarrant and Lisa Shumaker)