Two
independent groups of astronomers have detected the atmospheres of planets
around other stars from ground-based telescopes.
Previous
observations of the atmospheres of extrasolar planets had been made almost
entirely by space-based instruments, such as the Hubble and Spitzer space
telescopes, although another team last year detected the signature of sodium
in an exoplanet atmosphere.
To date,
astronomers have detected several key gases in planets' atmospheres, including:
- Carbon
dioxide – a potential sign of life, though the planet where the gas
was observed was too hot to be habitable.
- Water
vapor – a key molecule required to support life as we know it.
- Silicates
(combinations of silicon and oxygen) – components of most rocks on Earth,
likely in the form of clouds of dust grains on massive exoplanets.
- Sodium
– detected in 2001, it marked the first space-based observation of an
exoplanet atmosphere.
Ground-based
detection is becoming a priority as Hubble ages and Spitzer is set to run out
of cryogens, which keep its instruments cool enough to detect infrared
radiation (heat), limiting its abilities.
"Others
have tried to detect planetary atmospheres from Earth, but to no avail,"
said the co-author of one of the new studies, Mercedes López-Morales of the
Carnegie Institution in Washington, D.C. "We hit it right two nights last
summer."
López-Morales
and her team observed the planet OGLE-TR056b, a so-called "hot
Jupiter."
Hot
Jupiters
Hot
Jupiters are massive gaseous planets that orbit very close to their stars,
whipping around them in two to three days. Their proximity to their parent
stars indicates the planets are hot enough to emit radiation in the optical and
near-infrared wavelengths and that their radiation is detectable from Earth.
But
OGLE-TR056b is faint, sitting about 5,000 light-years away and in a crowded
part of the night sky, located in the direction of the center of our galaxy
from the Earth's perspective. So López-Morales and her colleagues used the
European Southern Observatory's Very
Large Telescope (on July 2) and Carnegie's Magellan-Baade telescope (on
Aug. 3). Both telescopes are located in Chile.
Only about
one out of every 3,000 photons from the star comes from the planet itself. The
rest is from the overwhelming light of the star. So astronomers wait until the
planet is eclipsed as it orbits behind the star (from the Earth's perspective),
which allows for separation of the emissions of the planet from those of the
star.
"The
planet is glowing red-hot like a kitchen stove burner, but we had to know
precisely when the eclipse was going to happen and measure the stellar flux
very accurately so it could be removed to reveal the planet's thermal
emissions," said lead author of the study David Sing of Institut
d'Astrophysique de Paris.
Real hot
The team
took more than 600 images of OGLE-TR056b with both telescopes. The planet is
hotter than any detected by Spitzer so far — its atmosphere is more than 4,400
degrees Fahrenheit (2,400 degrees Celsius).
The
observations also indicated that the planet has little to no cloud cover and a
static atmosphere with little circulation, López-Morales told SPACE.com
in an email.
Their work
will be detailed in an upcoming issue of the journal Astronomy &
Astrophysics.
In the same
issue of the journal, a Dutch team will explain their detection of the thermal
emission in the near-infrared of another exoplanet dubbed TrES-3b. Its
atmosphere registered at about 3,000 F (1,700 C).
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