Scientists Find Possible Birth of Tiniest, Known Solar System

http://live.psu.edu/story/14845

Scientists find possible birth of tiniest, known solar system
Pennsylvania State University
November 29, 2005

University Park, Pa. -- Scientists using a combination of ground-based
and orbiting telescopes have discovered a failed star, less than
one-hundredth the mass of the sun, possibly in the process of forming a
solar system. It is the smallest known star-like object to harbor what
appears to be a planet-forming disk of rocky and gaseous debris, which
one day could evolve into tiny planets and create a solar system in
miniature.

A team led by Kevin Luhman, assistant professor of astronomy and
astrophysics at Penn State, will discuss this finding in the Dec. 10
issue of Astrophysical Journal Letters.

The discovered object, called a brown dwarf, is described as a "failed
star" because it is not massive enough to sustain nuclear fusion like
our sun. The object is only eight times more massive than Jupiter. The
fact that a brown dwarf this small could be in the midst of creating a
solar system challenges the very definition of star, planet, moon and
solar system.

"Our goal is to determine the smallest 'sun' with evidence for planet
formation," said Luhman. "Here we have a sun that is so small it is the
size of a planet. The question then becomes, what do we call any little
bodies that might be born from this disk: planets or moons?" If this
protoplanetary disk does form into planets, the whole system would be a
miniaturized version of our solar system -- with the central "sun", the
planets and their orbits all roughly 100 times smaller.

Luhman's team detected the brown dwarf, called Cha 110913-773444, with
NASA's Spitzer Space Telescope, the Hubble Space Telescope and two
telescopes in the Chilean Andes, the Blanco telescope of the Cerro
Tololo Inter-American Observatory and the Gemini South telescope, both
international collaborations funded in part by the National Science
Foundation. Luhman led a similar observation last year that uncovered a
15-Jupiter-mass brown dwarf with a protoplanetary disk.

Brown dwarfs are born like stars, condensing out of thick clouds of gas
and dust. But unlike stars, brown dwarfs do not have enough mass -- and
therefore do not have enough pressure and temperature in their cores --
to sustain nuclear fusion. They remain relatively cool objects visible
in lower-energy wavelengths such as infrared. A protoplanetary disk is
a
flat disk made up of dust and gas that is thought to clump together to
form planets. Our solar system was formed from such a disk about 5
billion years ago. NASA's Spitzer telescope has found dozens of
disk-sporting brown dwarfs so far, several of which show the initial
stages of the planet-building process. The material in these disks is
beginning to stick together into what may be the "seeds" of planets.

With Spitzer, the science team spotted Cha 110913-773444 about 500
light
years away in the constellation Chamaeleon. This brown dwarf is young,
only about 2 million years old. The team studied properties of the
brown
dwarf with infrared instruments on the other observatories. The cool,
dim protoplanetary disk was detectable only with Spitzer's Infrared
Array Camera, which was developed at the Harvard-Smithsonian Center for
Astrophysics.

In the past decade, advances in astronomy have led to the detection of
small brown dwarfs and massive extra-solar planets, which has brought
about a quandary in taxonomy. "There are two camps when it comes to
defining planets versus brown dwarfs," said team member Giovanni Fazio
of the Harvard-Smithsonian Center for Astrophysics. "Some go by size,
and others go by how the object formed. For instance, this new object
would be called a planet based on its size, but a brown dwarf based on
how it formed." If one were to call the object a planet, Fazio said,
then Spitzer may have discovered its first "moon-forming" disk. No
matter what the final label may be, one thing is clear: The universe
produces some strange solar systems very different from our own. Other
members of the discovery team are Lucia Adame and Paola D'Alessio of
the
National Autonomous University of Mexico and Nuria Calvet and Lee
Hartmann of the University of Michigan.

The 4-meter Blanco Telescope at the Cerro Tololo Inter-American
Observatory in Chile is part of the National Optical Astronomy
Observatory, which is operated by the Association of Universities for
Research in Astronomy (AURA) Inc. under a cooperative agreement with
the
National Science Foundation. The nearby 8-meter Gemini South telescope
also is managed by AURA. NASA's Goddard Space Flight Center, Greenbelt,
Md., built Spitzer's Infrared Array Camera. The instrument's principal
investigator is Giovanni Fazio. The Jet Propulsion Laboratory,
Pasadena,
Calif., manages the Spitzer mission for NASA. Science operations are
conducted at the Spitzer Science Center at the California Institute of
Technology in Pasadena.

Contact
Barbara Kennedy

www.science.psu.edu
814-863-4682