Habitable' Super-Earth Might Exist After All

Artist’s impression of Gliese 581d, a controversial exoplanet that may exist only 20 light-years from Earth.

Excerpt from news.discovery.com


Despite having discovered nearly 2,000 alien worlds beyond our solar

system, the profound search for exoplanets — a quest focused on finding a

true Earth analog — is still in its infancy. It is therefore not

surprising that some exoplanet discoveries aren’t discoveries at all;

they are in fact just noise in astronomical data sets.

But when disproving the existence of extrasolar planets that

have some characteristics similar to Earth, we need to take more care

during the analyses of these data, argue astronomers from Queen Mary,

University of London and the University of Hertfordshire.




In a paper published by the journal Science last week, the researchers focus on the first exoplanet discovered to orbit a nearby star within its habitable zone.

Revealed in 2009, Gliese 581d hit the headlines as a “super-Earth”

that had the potential to support liquid water on its possibly rocky

surface. With a mass of around 7 times that of Earth, Gliese 581d would

be twice as big with a surface gravity around twice that of Earth.

Though extreme, it’s not such a stretch of the imagination that such a

world, if it is proven to possess an atmosphere and liquid ocean, that

life could take hold.

And the hunt for life-giving alien worlds is, of course, the central motivation for exoplanetary studies.




But the exoplanet signal has been called into doubt.

Gliese 581d’s star, Gliese 581, is a small red dwarf around 20

light-years away. Red dwarfs are known to be tempestuous little stars,

often generating violent flaring outbursts and peppered in dark features

called starspots. To detect the exoplanet, astronomers measured the

very slight frequency shift (Doppler shift) of light from the star — as

the world orbits, it exerts a tiny gravitational “tug”, causing the star

to wobble. When this periodic wobble is detected, through an

astronomical technique known as the “radial velocity method,” a planet

may be revealed.

Last year, however, in a publication headed by astronomers at

The Pennsylvania State University, astronomers pointed to the star’s

activity as an interfering factor that may have imitated the signal from

an orbiting planet when in fact, it was just noisy data.




But this conclusion was premature, argues Guillem

Anglada-Escudé, of Queen Mary, saying that “one needs to be more careful

with these kind of claims.”

“The existence, or not, of GJ 581d is significant because it

was the first Earth-like planet discovered in the ‘Goldilocks’-zone

around another star and it is a benchmark case for the Doppler

technique,” said Anglada-Escudé in a university press release.

“There are always discussions among scientists about the ways we

interpret data but I’m confident that GJ 581d has been in orbit around

Gliese 581 all along. In any case, the strength of their statement was

way too strong. If the way to treat the data had been right, then some

planet search projects at several ground-based observatories would need

to be significantly revised as they are all aiming to detect even

smaller planets.”

The upshot is that this new paper challenges the statistical

technique used in 2014 to account for the signal being stellar noise —

focusing around the presence of starspots in Gliese 581′s photosphere.




Gliese 581d isn’t the only possible exoplanet that exists around that star — controversy has also been created

by another, potentially habitable exoplanet called Gliese 581g. Also

originally detected through the wobble of the star, this 3-4 Earth mass

world was found to also be in orbit within the habitable zone. But its

existence has been the focus of several studies supporting and

discounting its presence. Gliese 581 is also home to 3 other confirmed

exoplanets, Gliese 581e, b and c.

Currently, observational data suggests Gliese 581g was just

noise, but as the continuing debate about Gliese 581d is proving, this

is one controversy that will likely keep on rumbling in the scientific

journals for some time.

Source Article from http://feedproxy.google.com/~r/AscensionEarth2012/~3/2JXUUWQVpWY/habitable-super-earth-might-exist-after.html

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Habitable' Super-Earth Might Exist After All