[meteorite-list] It's a star, it's a planet, it's a 'planemo'

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Tue Jun 6 12:07:39 2006
Message-ID: <004401c68931$7ce05fc0$f45ae146_at_ATARIENGINE>

Hi,


It's a star, it's a planet, it's a 'planemo'
http://news.com.com/Its+a+star,+its+a+planet,+its+a+planemo/2100-11397_3-6080197.html

Too lightweight to be stars but bigger than most planets, a handful of hot,
young, free-floating objects have the raw materials to make their own
miniplanetary systems, astronomers reported on Monday.

Just like some young stars, these so-called planemos have discs of cosmic
dust and gas circling them. These kinds of discs contain the ingredients for
planets; astronomers believe Earth and the other planets in our solar system
were forged from such a disc.

But planemos--short for planetary mass objects--are unlike normal planets
because they do not orbit stars, said Ray Jayawardhana of the University of
Toronto. He and other researchers presented their findings at a meeting of
the American Astronomical Society in Calgary, Alberta.
"These things are not orbiting a star. They're by themselves," Jayawardhana
said in a telephone interview.

The researchers detected four newborn planemos, just a few million years
old, in a star-forming region about 450 light-years from Earth, a relative
stone's throw in cosmic terms. A light-year is about 6 trillion miles, the
distance light travels in a year.

All four of these objects had dust discs around them, the astronomers
reported.
Scientists also found a disc-skirted planemo interacting with a brown
dwarf--a failed star--even closer to Earth, just 170 light-years away.

Such a planet-sized object might have been expected to be pulled into orbit
around the brown dwarf, but instead the two revolve around each other, and
both have the makings for more satellites.

These objects, with several times the mass of the giant planet Jupiter but
100 times less massive than our sun, are cosmic infants only a few million
years old.

Even Jupiter had a disc when it was young, and its dozens of moons were
formed from the dust and gas it contained. However, Earth's rocky moon
probably was born when our world collided with another heavenly body early
on, and Mars' moons were asteroids captured by the planet's gravity.

But planemos are a relatively new player on the cosmic scene, filling the
gap between the least massive stars and the most massive planets,
Jayawardhana said.

"These are the lowest-mass brown dwarfs or really big giant planets,
especially when they're young," he said.

When young, planemos are still warmed by the heat of formation and are more
like stars, he said. But as they age, these planet-esque objects shrink and
cool.

Other researchers do not use the term "planet" to describe any satellites
that might be formed around a planemo, referring to these as moons or
moonlets.

If such bodies do form, they would be inhospitable to Earth-type life. If a
satellite formed very close to a young planemo, it might be temporarily warm
enough for liquid water to exist, and water is a requirement for earthly
life.

But Jayawardhana acknowledged that in the long run, life would have dim
prospects: "Any kind of planet that forms around them is committed to an
eternal freeze."

Story Copyright ? 2006 Reuters Limited. All rights reserved.
Received on Tue 06 Jun 2006 02:21:46 AM PDT