Baby 'planemos' can be born as twins: U.Toronto astronomy breakthrough(Forwarded)

Department of Public Affairs
University of Toronto
Toronto, Canada

Contact:
Ray Jayawardhana, Department of Astronomy and Astrophysics
Phone: 416-946-7291

Valentin D. Ivanov, European Southern Observatory, Chile
Phone: +56 2 463 3000

Sonnet L'Abbé, News Services Officer
Phone: (416) 978-6974

August 3, 2006

Baby 'planemos' can be born as twins: U of T astronomy breakthrough

Discovery of planetary masses in orbit of one another thrills astronomy
community

By Sonnet L'Abbé

A team led by a U of T astronomy professor is challenging an existing
theoretical model and thrilling the astronomy community with its discovery
of a seven-Jupiter-mass companion next to a planemo, or planetary mass
object, only twice as heavy. Both objects have masses similar to those of
extra-solar giant planets, usually found in orbit around a star.
Unexpectedly, these bodies appear to circle each other.

"This is a truly remarkable pair of twins -- each weighing some hundred
times less than our sun," says Ray Jayawardhana, an associate professor of
astronomy and astrophysics at the University of Toronto. "Their mere
existence is a surprise, and their origin and fate a bit of a mystery."

Jayawardhana and Valentin D. Ivanov of the European Southern Observatory
(Chile) report the discovery in the August 3 issue of Science Express, the
rapid online publication service of the journal Science.

The researchers discovered the companion candidate in an optical image
taken with the European Southern Observatory's 3.5-meter New Technology
Telescope on La Silla, Chile, and investigated it further with optical
spectra and infrared images obtained with ESO's 8.2-meter Very Large
Telescope on Paranal, Chile. These followup observations confirmed that
both objects are young, at the same distance, and much too cool to be
stars. By comparing the companion to widely used theoretical models,
Jayawardhana and Ivanov estimate that it weighs about seven times as much
as Jupiter, while the primary planemo is an estimated 14 times Jupiter's
mass. The newborn pair, barely a million years old, are separated by about
six times the distance between the sun and Pluto, and are located in the
Ophiuchus star-forming region approximately 400 light years away.

"Roughly half of all sun-like stars, and about a sixth of brown dwarfs,
come in pairs," says Jayawardhana. Brown dwarfs are 'failed stars' that
weigh less than 75 Jupiter masses and are unable to sustain nuclear
fusion. "Oph 162225-240515, or Oph1622 for short, is the first planemo to
be resolved into a double."

The existence of this wide pair poses a challenge to a popular theory
which suggests that brown dwarfs and planemos are embryos ejected from
multiple proto-star systems. Since the two objects in Oph1622 are so far
apart, and only weakly bound to each other by gravity, they would not have
survived such a chaotic birth.

Planets are thought to form out of disks of gas and dust that surround
stars, brown dwarfs and even some planemos. The researchers think that
these planemo twins formed together out of a contracting gas cloud that
fragmented, like a miniature stellar binary.

"We are resisting the temptation to call it a 'double planet' because this
pair probably didn't form the way that planets in our solar system did,"
says Ivanov. "Now we're curious to find out whether such pairs are common
or rare. The answer could shed light on how free-floating planetary-mass
objects form."

Andrew Yee wrote:

The researchers discovered the companion candidate in an optical image
taken with the European Southern Observatory's 3.5-meter New Technology
Telescope on La Silla, Chile, and investigated it further with optical
spectra and infrared images obtained with ESO's 8.2-meter Very Large
Telescope on Paranal, Chile. These followup observations confirmed that
both objects are young, at the same distance, and much too cool to be
stars. By comparing the companion to widely used theoretical models,
Jayawardhana and Ivanov estimate that it weighs about seven times as much
as Jupiter, while the primary planemo is an estimated 14 times Jupiter's
mass. The newborn pair, barely a million years old, are separated by about
six times the distance between the sun and Pluto, and are located in the
Ophiuchus star-forming region approximately 400 light years away.

"Roughly half of all sun-like stars, and about a sixth of brown dwarfs,
come in pairs," says Jayawardhana. Brown dwarfs are 'failed stars' that
weigh less than 75 Jupiter masses and are unable to sustain nuclear
fusion. "Oph 162225-240515, or Oph1622 for short, is the first planemo to
be resolved into a double."

Hello, there, and thank you very much for an exciting story that could
illustrate one dilemma of defining a planet: objects close to the border
between a planemo and a very small brown dwarf.

If we define the lower limit for a brown dwarf at the point where there is
sufficient mass for the fusion of deuterium, then this limit has been
estimated at about 13 Jupiter masses -- just about the size of the larger
or primary planemo in this system.

Thus maybe we could actually have a 7-Jupiter mass planet orbiting a very
small fusor or brown dwarf -- with the smaller body qualifying as a "planet"
under a definition with the circumstantial requirement of a planemo
orbiting a fusor. If the larger or "primary" body were a bit smaller, then
under this type of approach we'd have a "binary planemo" system without a
fusor -- and thus neither body would qualify as a "planet."

Anyway, as pointed out, the possible implications for theories of cosmogony
which serve as an element in some proposed definitions are significant; a
series of cases like this might help both in shaping definitions and in
testing how they might play out operationally with available real-world
data.

Thank you again for a story maybe yet more timely than when it was posted
pre-August 24.

Most appreciatively,

Margo