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

From: Larry Lebofsky <lebofsky_at_meteoritecentral.com>
Date: Wed Jun 7 00:07:14 2006
Message-ID: <1149615488.4485bd80f29c1_at_hindmost.LPL.Arizona.EDU>

Hi Sterling:

1. According to the IAU, there are no free floating planets. Their official
name is "sub-brown dwarf." This is probably to avoid people trying to name them
or run into problems when you really do not know their mass acurately and so
they may just be on the smallish end of brown dwarves.

2. What is the difference between an object orbiting another and the two
revolving around each other? Thanks to Newton, any two objects revolve around
their center of mass. So, for example, the center of mass of the Jupiter/Sun
system is 46,000 km OUTSIDE the surface of the Sun. So does Jupiter orbit the
Sun or do they revolve around one another?

Larry


Quoting "Sterling K. Webb" <sterling_k_webb_at_sbcglobal.net>:

> 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.
>
>
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Received on Tue 06 Jun 2006 01:38:08 PM PDT


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