Dusky Disk Around Nearby Star May Hide Earth-Like Planet

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8 February 2008

DUSTY DISK AROUND NEARBY STAR MAY HIDE EARTH-LIKE PLANET

HILO, HAWAII -- A recent survey by a team of Japanese astronomers may
have
found an Earth-like planet hidden in the dust around a nearby star.
Using
the Coronagraphic Imager with Adaptive Optics (CIAO) at the Subaru
Telescope, researchers recently resolved a circumstellar disk around
the
young lightweight star FN Tau. The diminutive star is located in a
star-forming region toward the Constellation Taurus at a distance 460
light
years from Earth. This star is a youthful 100 thousand years old and
weighs
only one tenth of the Sun.

To ease understanding, a circumstellar disk is a mixture of gas and
dust
around a newly forming star. The disk accompanies almost most, if not
all,
sun-like star formation processes, and planets commonly form in this
disk.
The disk can also be referred to as a protoplanetary disk because the
solid
particles inside the disk collide and stick together and grow into
planetesimals, which then crash into each other eventually
accumulating
enough mass to be stabilized as planets. In response to this
scenario, the
study of young stars and their surrounding structures provide details
into
the formation of planetary systems, and the search for planets outside
our
solar system motivates much of modern astronomy. Although hundreds
have
been found through indirect methods, being the first to directly image
a
planet around a nearby star is one of the primary goals of Subaru.
The
findings at FN Tau show that Subaru is on the right path toward
planet
discovery.

The FN Tau researchers pointed the Subaru Telescope toward the tiny
star
trying to detect lightweight disks. Their study found a thick,
compact, and
roughly circular protoplanetary disk with a radius 260 times the Earth-
Sun
distance. The disk is rather featureless, and does not have any
anomalies or
asymmetries, such as rings, spirals, or arms. The mass of the disk
was
estimated to be 6% of the central FN Tau star, and, by far, the least
massive one directly detected. In result, the discovery is the
combination
of the most lightweight protoplanetary disk around the least massive
star.

One of the questions to come out during the study was what kind of
planets
can be formed from the disk around FN Tau? To date, astronomers
worldwide
have found 270 extrasolar planets using the indirect detection method,
and
all are primarily Jupiter-like giant planets; the least massive
exoplanet is
still 5 times heavier than Earth. Because it surrounds a smaller
star, the
disk about FN Tau is believed to more likely contain Earth-like
planets.
The best-fit model used during this study shows that the lightweight
disk
around FN Tau could only produce Earth-like planets. The planetary
system
formation theory also predicted that the disk is able to form planets
lighter than the Earth within 30 astronomical units (AU), the distance
where
we find planets in our Solar System. For the future, astronomers are
hopeful of using Subaruâs newest technologies for resolving the
detailed
structure of the disk to analyze the size and composition of the
dust,
culminating in the first image of a terrestrial planet near FN Tau.

This discovery is reported in the Astrophysical Journal Letters in
its
January 20, 2008 issue, Volume 673, page L67. Dr. Tomoyuki Kudo,
principal
investigator, presents the findings of this project to the public in a
press
conference at the NAOJ headquarters in Mitaka, Japan on Friday,
February 8,
2008 at 2 p.m. (JST). Further details about this study, other
research
findings, and the state-of-the art technologies at the Subaru
Telescope are
found on our website at www.subarutelescope.org.

Contact (Supervisor):
Dr. Motohide Tamura
National Astronomical Observatory of Japan
Phone: +81-422-34-3513
Email: hide@xxxxxxxxxxxxxxx

Contact (Principal Investigator):
Dr. Tomoyuki Kudo
National Astronomical Observatory of Japan
Phone: +81-422-34-3528
Email: tomoyuki.kudo@xxxxxxxxx

Contact (Subaru Telescope):
Mr. Pablo McLoud
Public Information Office
Subaru Telescope, NAOJ
Phone : 808-934-5022
Email: pablo@xxxxxxxxxxxxxxx

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