The free-floating planet CFBDSIR J214947.2-040308.9 (annotated)
The free-floating planet CFBDSIR J214947.2-040308.9
Video
Video
Artist's impression of the free-floating planet CFBDSIR J214947.2-040308.9
Orphaned world may help to explain how planets and stars form
Astronomers using ESO’s Very Large Telescope and the Canada-France-Hawaii Telescope have identified a body that is very probably a planet wandering through space without a parent star. This is the most exciting free-floating planet candidate so far and the closest such object to the Solar System at a distance of about 100 light-years. Its comparative proximity, and the absence of a bright star very close to it, has allowed the team to study its atmosphere in great detail. This object also gives astronomers a preview of the exoplanets that future instruments aim to image around stars other than the Sun.
Free-floating planets are planetary-mass objects that roam through
space without any ties to a star. Possible examples of such objects have
been found before [1],
but without knowing their ages, it was not possible for astronomers to
know whether they were really planets or brown dwarfs — “failed” stars
that lack the bulk to trigger the reactions that make stars shine.
But astronomers have now discovered an object, labelled CFBDSIR2149 [2], that seems to be part of a nearby stream of young stars known as the AB Doradus Moving Group.
The researchers found the object in observations from the
Canada-France-Hawaii Telescope and harnessed the power of ESO’s Very
Large Telescope to examine its properties [3].
The AB Doradus Moving Group is the closest such group to the Solar
System. Its stars drift through space together and are thought to have
formed at the same time. If the object is associated with this moving
group — and hence it is a young object — it is possible to deduce much
more about it, including its temperature, mass, and what its atmosphere
is made of [4]. There remains a small probability that the association with the moving group is by chance.
The link between the new object and the moving group is the vital
clue that allows astronomers to find the age of the newly discovered
object [5]. This
is the first isolated planetary mass object ever identified in a moving
group, and the association with this group makes it the most
interesting free-floating planet candidate identified so far.
“Looking for planets around their stars is akin to studying a
firefly sitting one centimetre away from a distant, powerful car
headlight,” says Philippe Delorme (Institut de planétologie et
d’astrophysique de Grenoble, CNRS/Université Joseph Fourier, France),
lead author of the new study. “This nearby free-floating object
offered the opportunity to study the firefly in detail without the
dazzling lights of the car messing everything up.”
Free-floating objects like CFBDSIR2149 are thought to form either as
normal planets that have been booted out of their home systems, or as
lone objects like the smallest stars or brown dwarfs. In either case
these objects are intriguing — either as planets without stars, or as
the tiniest possible objects in a range spanning from the most massive
stars to the smallest brown dwarfs.
“These objects are important, as they can either help us
understand more about how planets may be ejected from planetary systems,
or how very light objects can arise from the star formation process,” says Philippe Delorme. “If
this little object is a planet that has been ejected from its native
system, it conjures up the striking image of orphaned worlds, drifting
in the emptiness of space.”
These worlds could be common — perhaps as numerous as normal stars [6].
If CFBDSIR2149 is not associated with the AB Doradus Moving Group it is
trickier to be sure of its nature and properties, and it may instead be
characterised as a small brown dwarf. Both scenarios represent
important questions about how planets and stars form and behave.
“Further work should confirm CFBDSIR2149 as a free-floating planet,” concludes Philippe Delorme. “This
object could be used as a benchmark for understanding the physics of
any similar exoplanets that are discovered by future special
high-contrast imaging systems, including the SPHERE instrument that will
be installed on the VLT.”
Notes
[1] Numerous candidates for these kinds of planets have been found before (with corresponding press releases and papers, e.g. from Science Magazine, Nature, Royal Astronomical Society).
These objects started to become known in the 1990s, when astronomers
found that the point at which a brown dwarf crosses over into the
planetary mass range is difficult to determine. More recent studies
have suggested that there may be huge numbers of these little bodies in
our galaxy, a population numbering almost twice as many as the main
sequence stars present.
[2] The object was identified as part of an infrared
extension of the Canada-France Brown Dwarfs Survey (CFBDS), a project
hunting for cool brown dwarf stars. It is also referred to as CFBDSIR
J214947.2-040308.9.
[3] The team observed CFBDSIR2149 with both the
WIRCam camera on the Canada France Hawaii Telescope on Hawaii, and the
SOFI camera on the ESO New Technology Telescope in Chile. The images
taken at different times allowed the object’s proper motion across the
sky to be measured and compared to members of the AB Doradus Moving
Group. The detailed study of the object’s atmosphere was made using the
X-shooter spectrograph on ESO’s Very Large Telescope at the Paranal
Observatory.
[4] The association with the AB Doradus Moving Group
would pin down the mass of the planet to approximately 4–7 times the
mass of Jupiter, with an effective temperature of approximately 430
degrees Celsius. The planet’s age would be the same as the moving group
itself — 50 to 120 million years.
[5] The team’s statistical analysis of the object’s
proper motion — its angular change in position across the sky each year —
shows an 87% probability that the object is associated with the AB
Doradus Moving Group, and more than 95% probability that it is young
enough to be of planetary mass, making it much more likely to be a rogue
planet rather than a small “failed” star. More distant free-floating
planet candidates have been found before in very young star clusters,
but could not be studied in detail.
[6] These free-floating objects can also reveal their
presence when they pass in front of a star. The light travelling
towards us from the background star is bent and distorted by the gravity
of the object, causing the star to suddenly and briefly brighten — a
process known as gravitational microlensing. Microlensing surveys of the
Milky Way, such as OGLE, may have detected free-floating planets in
this way (for example, a Microlensing Experiment published in Nature in 2011).
More information
This research is presented in a paper,
“CFBDSIR2149-0403: a 4-7 Jupiter-mass free-floating planet in the young
moving group AB Doradus?” to appear in Astronomy & Astrophysics on 14 November 2012.
The team is composed of P. Delorme (Institut de planétologie et
d’astrophysique de Grenoble, CNRS/Université Joseph Fourier, France
[IPAG]), J. Gagné (Université de Montréal, Canada), L. Malo (Université
de Montréal, Canada), C. Reylé (Institut UTINAM, CNRS/OSU THETA
Franche-Comté-Bourgogne/Université de Franche Comté, France), E. Artigau
(Université de Montréal, Canada), L. Albert (Université de Montréal,
Canada), T. Forveille (Institut de planétologie et d’astrophysique de
Grenoble, CNRS/Université Joseph Fourier, France [IPAG]), X. Delfosse
(Institut de planétologie et d’astrophysique de Grenoble,
CNRS/Université Joseph Fourier, France [IPAG]), F. Allard (Université
Claude Bernard Lyon 1, France), D. Homeier (Université Claude Bernard
Lyon 1, France).
The year 2012 marks the 50th anniversary of the founding of the
European Southern Observatory (ESO). ESO is the foremost
intergovernmental astronomy organisation in Europe and the world’s most
productive ground-based astronomical observatory by far. It is supported
by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark,
France, Finland, Germany, Italy, the Netherlands, Portugal, Spain,
Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious
programme focused on the design, construction and operation of powerful
ground-based observing facilities enabling astronomers to make
important scientific discoveries. ESO also plays a leading role in
promoting and organising cooperation in astronomical research. ESO
operates three unique world-class observing sites in Chile: La Silla,
Paranal and Chajnantor. At Paranal, ESO operates the Very Large
Telescope, the world’s most advanced visible-light astronomical
observatory and two survey telescopes. VISTA works in the infrared and
is the world’s largest survey telescope and the VLT Survey Telescope is
the largest telescope designed to exclusively survey the skies in
visible light. ESO is the European partner of a revolutionary
astronomical telescope ALMA, the largest astronomical project in
existence. ESO is currently planning the 39-metre European Extremely
Large optical/near-infrared Telescope, the E-ELT, which will become “the
world’s biggest eye on the sky”.
The Canada-France-Hawaii Telescope (CFHT) is operated by the National
Research Council of Canada, the Institut National des Sciences de
l'Univers of the Centre National de la Recherche Scientifique of France,
and the University of Hawaii.
Links
Contacts
Philippe DelormeIPAG-OSUG (Observatoire des Sciences de l'Univers de Grenoble)
Grenoble, France
Tel: +33 4 76 51 49 42
Email: philippe.delorme@obs.ujf-grenoble.fr
Jonathan Gagné
Université de Montréal
Montréal, Canada
Tel: +1 514 343 6111 #3219
Email: jonathan.gagne@astro.umontreal.ca
Xavier Delfosse
IPAG-OSUG (Observatoire des Sciences de l'Univers de Grenoble)
Grenoble, France
Tel: +33 4 76 63 55 10
Email: xavier.delfosse@obs.ujf-grenoble.fr
Olivier Hernandez
Université de Montréal
Montréal, Canada
Tel: +1 514 343 6111 #4681
Email: olivier@astro.umontreal.ca
Céline Reylé
Observatoire de Besançon
Besançon , France
Tel: +33 3 81 66 69 01
Email: celine.reyle@obs-besancon.fr
Richard Hook
ESO, La Silla, Paranal, E-ELT & Survey Telescopes Press Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
Christian Veillet
Canada-France-Hawaii Telescope
Kamuela, Hawaii, USA
Tel: +1 808 938 3905
Email: veillet@cfht.hawaii.edu
