We all need a sense of purpose in our lives, a sense of direction -- a north star. That's why it's with a heavy heart that we report that scientists have found a lonely, directionless planet that has no star.
Astronomers
using the Pan-STARRS 1 wide-field survey telescope on Haleakala, Maui,
have discovered a very young free-floating planet named PSO J318.5-22.
Located
approximately 80 light-years away in the constellation Capricornus, PSO
J318.5-22 has a mass only six times that of Jupiter. It belongs to a
collection of young stars called the Beta Pictoris moving group that
formed about 12 million years ago.
In
fact, the eponymous star of the group, Beta Pictoris, has a young
gas-giant planet in orbit around it. PSO J318.5-22 is even lower in mass
than the Beta Pictoris planet and probably formed in a different
fashion.
The
exoplanet is one of the lowest-mass free-floating objects known,
perhaps the very lowest. But its most unique aspect is its similar mass,
color, and energy output to directly imaged planets.
PSO
J318.5-22 is extremely cold and faint, about 100 billion times fainter
in optical light than Venus. Most of its energy is emitted at infrared
wavelengths.
"Planets
found by direct imaging are incredibly hard to study, since they are
right next to their much brighter host stars. PSO J318.5-22 is not
orbiting a star so it will be much easier for us to study. It is going
to provide a wonderful view into the inner workings of gas-giant planets
like Jupiter shortly after their birth," said Dr Niall Deacon of the
Max Planck Institute for Astronomy in Germany, co-author of the paper
accepted for publication in the Astrophysical Journal Letters.
PSO
J318.5-22 was discovered during a search for the failed stars known as
brown dwarfs. Due to their relatively cool temperatures, brown dwarfs
are very faint and have very red colors.
To
circumvent these difficulties, the astronomers have been mining the
data from the Pan-STARRS 1 (PS1) telescope. PS1 is scanning the sky
every night with a camera sensitive enough to detect the faint heat
signatures of brown dwarfs.
"We
often describe looking for rare celestial objects as akin to searching
for a needle in a haystack. So we decided to search the biggest haystack
that exists in astronomy, the dataset from PS1," said co-author Dr
Eugene Magnier of the Institute for Astronomy at the University of
Hawaii at Manoa.
The
scientists followed up the PS1 discovery with multiple telescopes on
the summit of Mauna Kea on the island of Hawaii. Infrared spectra taken
with the NASA Infrared Telescope Facility and the Gemini North Telescope
showed that PSO J318.5-22 was not a brown dwarf, based on signatures in
its infrared light that are best explained by it being young and
low-mass.
'We
have never before seen an object free-floating in space that that looks
like this. It has all the characteristics of young planets found around
other stars, but it is drifting out there all alone. I had often
wondered if such solitary objects exist, and now we know they do," said
lead author Dr Michael Liu, also from the Institute for Astronomy at the
University of Hawaii at Manoa.
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