'Planemos' may spawn planets
2006-06-06 12:09
Washington - 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
mini-planetary systems, astronomers reported on Monday.
Just like some young stars, these so-called planemos have
disks of cosmic dust and gas circling them. These kinds of
disks contain the ingredients for planets; astronomers believe
Earth and the other planets in our solar system were forged
from such a disk.
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.
"These things are not orbiting a star. They're by
themselves," Jayawardhana said.
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 10 trillion km,
the distance light travels in a year.
All four of these objects had dust disks around them, the
astronomers reported.
Scientists also found a disk-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.
An eternal freeze
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 disk 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."