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A newly discovered planet around a distant star may jump to the top of
the list of places where scientists should go looking for alien life.
The alien world known as LHS 1140b is rocky,
like Earth. It is only 40 light-years away from our solar system
(essentially, down-the-street in cosmic terms), and sits in the
so-called habitable zone of its parent star, which means liquid water
could potentially exist on the planet's surface. Several other planets
also meet those criteria, but few of them are as prime for study as LHC
1140b according to the scientists who discovered it, because the type of
star the planet orbits and the planet's orientation to Earth make it
ripe for investigations into whether it’s the kind of place where life
could thrive.
"This is the most exciting exoplanet I've seen in the past decade,"
Jason Dittmann, a postdoctoral fellow at the Harvard-Smithsonian Center
for Astrophysics (CfA) and lead author on the paper describing the
discovery, said in a statement from CfA. "We could hardly hope for a
better target to perform one of the biggest quests in science —
searching for evidence of life beyond Earth." [10 Exoplanets That Might Be Perfect to Support Life
Alien atmosphere
Thousands of exoplanets have been discovered orbiting stars other than the sun in the last 20 years. Many of those planets meet some of the basic requirements for hosting life as we know it — they're rocky like Earth (rather than gaseous, like Saturn or Jupiter) and they sit in the habitable zone of their parent star.LHS 1140b meets those initial requirements. Through multiple observations, Dittmann and colleagues determined that the planet receives about 0.46 times as much light from its parent star as Earth receives from the sun. The planet is about 1.4 times the diameter of Earth and 6.6 times its mass, which makes it a so-called super-Earth and suggests it is also rocky. [How Habitable Zones for Alien Planets and Stars Work (Infographic)]
The next step scientists are taking to find out if exoplanets like LHS 1140b are habitable (or even inhabited) is to examine their atmospheres. An atmosphere could provide life-forms with a necessary ingredient for life (such as oxygen or carbon dioxide on Earth), and could also bear signs that life exists there (most of the methane on Earth, for example, is produced by biological organisms). Scientists are working on understanding what the atmosphere of an exoplanet can reveal about the likelihood that it hosts life, or could.
Dittmann said he and his colleagues think LHS 1140b is a great candidate for follow-up atmospheric studies for multiple reasons.
This alien world was initially discovered using the transit method, in which scientists look at the light from a star and try to measure subtle dips in its brightness that could be caused by a planet passing in front of (transiting) the star. In some cases, telescopes can capture the sliver of sunlight that passes through the planet's atmosphere, and that sunlight reveals information about the chemical composition of the planet's atmosphere. Many other potentially habitable Earth-like planets ― such as Proxima b, the closest exoplanet to our solar system that lies only 4.2 light-years away ― do not transit their parent star as seen from Earth and therefore their atmospheres can't be studied in this way.
The team's precise measurement of LHS 1140b's density will also be important to understanding its atmosphere, Dittmann told Space.com.
"What's great about having a density ahead of an atmospheric study is that this density tells you how tightly the planet holds on to its atmosphere (the atmospheric scale height)," Dittmann told Space.com in an email. Using the transit method, scientists are trying to collect starlight shining through a planet's atmosphere; a thicker atmosphere means more light passes through it, making it easier for scientists to detect the signals from various chemical elements present in that atmosphere. A planet with higher density also has stronger gravity, which further compresses the atmosphere and reduces the size of the signals scientists can detect.
more:::http://www.livescience.com/58746-alien-planet-best-bet-search-for-life.html
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