A planet
outside of our solar system, said to be the first ever directly photographed by
telescopes on Earth, has been officially confirmed to be orbiting a sun-like star,
according to follow-up observations.
The alien
planet is eight times the mass of Jupiter and orbits at an unusually great
distance from its host star — more than 300 times farther from the star than
our Earth is from the sun.
Astronomers
first discovered the planet in 2008 using visible light observations from
telescopes on Earth, making it the first direct photo of an extrasolar world.
But at the time there was still the remote chance that it only looked like it
was orbiting the star, from the perspective of Earth, due to a lucky alignment
of object, star and observer.
"Our
new observations rule out this chance alignment possibility, and thus confirms
that the planet and the star are related to each other," said astronomer
David Lafreniere, who led the research team that discovered the planet.
The new
observations that confirm the planet circles its parent star were made using
high-resolution adaptive optics technology at the Gemini Observatory. The
observatory is an international collaboration with two identical 8-meter
telescopes, located at Mauna Kea, Hawaii and Cerro Pachon in northern Chile.
Planet
around young star
The host
star, which has an estimated mass of about 85 percent that of our sun, is
located approximately 500 light-years away in a group of young stars called the
Upper Scorpius Association that formed about 5 million years ago.
The planet
has an estimated temperature of over 2,700 degrees Fahrenheit (about 1,500
degrees Celsius). This makes the planet much hotter than Jupiter, which has an
atmospheric cloud-top temperature of approximately minus 166 degrees Fahrenheit
(minus 110 degrees Celsius).
The
relatively young age of the system — our solar system is 4.6 billion years old
— explains the high temperature of the planet, according to the researchers. [The Strangest Alien Planets]
The
contraction of the planet under its own gravity during its formation quickly
raised its temperature to thousands of degrees. But, once this contraction
phase is over, the planet will slowly cool down by radiating infrared light.
Within billions of years, the planet will eventually reach a temperature that
is much more similar to that of Jupiter.
Tale of a
planet find
Lafreniere and
his research team firstannounced their planet's discovery in September 2008. At the time he
was at the University of Toronto, but is now at the University of Montreal and
Center for Research in Astrophysics of Quebec.
In 2008, the
researchers claimed that the discovery also represented thefirst
picture of a planet that orbits
around a star similar to our sun. Other astronomers have also made
similar claims, including a 2004 discovery of an object that could be a
planet or a type of failed star called a brown dwarf.
"Back
in 2008 what we knew for sure was that there was this young planetary mass
object sitting right next to a young sun-like star on the sky," Lafreniere
said.
The close
proximity of the two cosmic objects seemed to suggest that they were associated
with each other, but there was a possibility — albeit unlikely — that they were
unrelated and had only aligned in the sky by chance. One of the objects might
have been closer or farther by considerable distance. So more observations were
required to confirm the cosmic find.
The results
of the study will be published in an upcoming issue of The Astrophysical
Journal.
The system,
known as 1RXS J160929.1-210524 (or 1RXS 1609 for short), will give scientists a
unique example to study, as its extreme separation from the star seems to
challenge common planetary formation theories.
"The
unlikely locale of this alien world could be telling us that nature has more
than one way of making planets," said the study's co-author Ray
Jayawardhana of the University of Toronto. "Or, it could be hinting at a
violent youth when close encounters between newborn planets hurl some siblings out
to the hinterlands."
The team of
astronomers initially detected the exoplanet using the Gemini Observatory in
April 2008, which made it the first likely planet known to orbit a sun-like
star that was revealed by direct imaging. At the time, the researchers also
obtained a spectrum of the planet and were able to determine many of its
characteristics, which are confirmed in the new study.
"In
retrospect, this makes our initial data the first spectrum of a confirmed
exoplanet ever!," Lafreniere said.
The spectrum
illustrates absorption features due to water vapor, carbon monoxide and
molecular hydrogen in the planet's atmosphere.
Other distant planets photographed
This is not
the only exoplanet to be discovered using direct imaging.
Since initially
observing 1RXS 1609, several other alien worlds have also been found, including
a system of three planets that orbit around the star HR 8799.
This discovery was also made using the Gemini Observatory.
The latest
exoplanet confirmation is unique, however, because the planets around HR 8799
orbit much closer to their host star.
The study of
1RXS 1609 also verified that no additional large planets (between one and eight
times the mass of Jupiter) are present in the system that are closer to the
star.
Future
observations may reveal evidence on the origin of thestrangely far-out planet. In fact, within a few years,
it should be possible to detect a slight difference in the motion of the planet
and its star, due to their mutual orbits.
This
difference, however, will be "very small," said the study's co-author
Marten van Kerkwijk of the University of Toronto, since the fastest possible
orbital period is more than one thousand years.
Clocking
alien planet's speed
But, using
Gemini, it is possible to precisely measure the velocity of the planet relative
to its host star.
This can
help astronomers determine whether the planet is following a roughly circular
orbit — as would be expected if it really formed far from its host star — or
whether it is in a very non-circular or even unbound orbit. The latter could be
the case if it formed closer to the star but was kicked out as a result of an
encounter with another alien planet, researchers said.
The adaptive
optics system on the Gemini telescopes were crucial to making the observations
of 1RXS 1609.
"Without
adaptive optics, we would simply have been unable to see this planet,"
Lafreniere said. "The atmosphere blurs the image of a star so much that it
extends over and is much brighter than the image of a faint planet around it,
rendering the planet undetectable. Adaptive optics removes this blurring and
provides a better view of faint objects very close to stars."
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