Birth Of Lonely Giant Planets Observed

Instituto de Astrofisica de Canarias

La Laguna, Tenerife, Spain

Contact:

José Manuel Abad Liñán, +34922605182, jmabad@ll.iac.es

Researchers from the Instituto de Astrofisica de Canarias (IAC), the
California Institute of Technology and the Max Planck Institut für
Astronomie, co-ordinated by Professor Rafael Rebolo (IAC/CSIC), have
discovered in the Orion region three giant planets and another fifteen
bodies, whose planet status could be confirmed once analyses are
completed. The planets detected are reported to have masses between 5
and 15 times the mass of Jupiter, the largest planet in the Solar System.
The results to be published by the specialised journal Science, include
unprecedented images and spectra of bodies whose planetary masses are
not associated to a given star. The superjupiters examined roam freely
in Orion’s Sigma cluster, a very active star formation region located
at approximately 1000 light years from Earth. The age of these
extraordinarily young planets is expected to be less than five million
years.

Images of these solitary planets have been obtained, in the visible range,
with the 2.5-m Isaac Newton Telescope, at the IAC’s Spanish Observatorio
del Roque de Los Muchachos (La Palma), and in the infrared, with the 3.5-m
telescope at Calar Alto Observatory (Almeria, Spain). The combination of
these data has allowed identification of a large concentration of very dim,
exceedingly red objects, in a small region surrounding Orion’s stellar
system known as Sigma. These features are characteristic of giant
planets currently undergoing a formation process. Subsequently, the
spectra obtained with the world’s largest telescope — the 10-m Keck
telescope on Mauna Kea Observatory (Hawaii)- confirmed these findings.

Although the existence of Jupiter-like bodies orbiting stars has been
known since 1995, images of these giants have not been obtained to date,
essentially because they are as much as one thousand million times
fainter than the stars they are orbiting. The contraction process affecting
these newly detected planets is in full swing — which means that their
size is diminishing due to gravity — and they irradiate about ten thousand
times more energy than is to be expected once they reach the size of
Jupiter, i.e. when they become more stable.

To capitalise fully on this circumstance, researches began exploring in
1998, surveying the Orion region — renowned for hosting huge numbers of
young stars — in the search for giant planets. The results to be released
today by Science show, for the very first time, images and spectra of
bodies showing planetary masses which oddly enough are not linked to
any of the surrounding stars.

These so-called superjupiters float freely within a star cluster, but at
distances sufficiently large to allow them to avoid the gravitational
attraction of other stars. Of the eighteen candidates detected so far,
three have been scrutinised using spectroscopic techniques and have
been confirmed as gaseous objects with surface temperatures in the
range 1,500 degrees Celsius, as expected for planets slightly less
massive than Jupiter undergoing very early evolutionary phases.

In the words of Prof Rafael Rebolo, “this discovery is a challenge for
current theories. In fact, a definitive explanation is still lacking. These
bodies appear to be far too numerous and young to have formed in
protoplanetary disks and later ejected as a result of the collisions
between stars present in the disks. A more plausible hypothesis is that
they emerged directly from the fragmentation and collapse of clouds
of dust, a process that may well occur in a few million years time”.
However, the fragmentation scenario poses difficulties from the
theoretical point of view when attempting to explain the formation
of bodies with masses so close to Jupiter’s, and hence a definitive
explanation for their existence is still pending.

The objects detected in Orion will cool down progressively,” according
to Víctor Sánchez Béjar, a PhD student and team member at the IAC,
“and in a few hundred million years will reach surface temperatures in
the range 0 to 100 degrees centigrade. They will never develop rocky
regions and temperatures will continue to drop until they fall in the
range of Jupiter’s”.

It is still premature to affirm how many of these giant planets may be
present in the Galaxy. However, if the statistics inferred for Orion were
representative of the entire Milky Way, hundreds of millions of isolated
superjupiters would be found populating interstellar space. According
to the researchers involved in the study, there are indications that they
could be as numerous as solar-type stars. In the Sun’s neighbourhood
(i.e. in a radius of 20 light years) there could be 30 or 40 such objects.
Their discovery is clearly a challenge for current technologies.

AUTHORS AND INSTITUTIONS (IN ORDER OF AUTHORSHIP):

* María Rosa Zapatero Osorio (IAC- California Institute of Technology)

* Víctor Sánchez Béjar (IAC)

* Eduardo Martín (California Institute of Technology – Institute of
Astronomy, University of Hawaii)

* Rafael Rebolo (IAC-Spanish Council of Scientific Research)

* David Barrado y Navascués (Max Planck Institut für Astronomie –
Universidad Autónoma de Madrid)

* Coryn Bailer-Jones (Max Planck Institut für Astronomie)

* Reinhard Mundt (Max Planck Institut für Astronomie)

Notes for Editors:

3D animated movies and interview with one of the researchers [and
images] available in avi and mov (Quick Time) format at
ftp://ftp.ll.Iac.es/outlong/lcc/.

For further information contact the IAC Press Office at
+34 922 605 371 / 182 / 293