Hi, Larry, List
I never argue with old Isaac.
Well, the IAU has its agenda. Being entirely French,
their agenda is to equivocate as long as possible and then
just a bit longer to be absolutely sure to avoid any
embarrassment...
The problem is that the definition of "planet" is both
endogenous and exogenous, by innate characteristics
(size, composition, temperature, etc.) and circumstantial,
orbitally subservient to what other object. I suppose that
any object that is not in orbit around another object that
is not a star is not a planet.
So, according to the IAU, an 8-Jupiter-mass body
in orbit around a 15-Jupiter-mass body is a planet, since
the 15-Jupiter-mass body can fuse deuterium and the
8-Jupiter-mass body cannot. But if the 8-Jupiter-mass
body is on its own, it's a star.
Have I got that right?
What if it's a 7.99-Jupiter-mass body in orbit around an
8.00-Jupiter-mass body? Is one a planet and one a star,
both cold, dark, and dead? Or is it a sub-brown-dwarf
binary system?
What if it's a 1-Jupiter-mass body on its own? Is it
still a star, a sub-sub-sub-brown-dwarf, a cold, dark,
dead star? It's not a planet...
Hey, maybe it's an asteroid! Since deuterium burning
is only possible at 12 or 13 Jupiter-masses, I guess an
11.99-Jupiter-mass body is like, the Universe's biggest
asteroid!
See, we went and wasted "asteroid" on minor planets,
when it literally means "tiny star," ASTER being Greek
for "star." It would have been the perfect terminology!
This definition game is tiring, like playing handball.
My wrists hurt. The IAU can have it.
Sterling K. Webb
-------------------------------------------------------
----- Original Message -----
From: "Larry Lebofsky" <[EMAIL PROTECTED]>
To: "Sterling K. Webb" <[EMAIL PROTECTED]>
Cc: "Meteorite List" <meteorite-list@meteoritecentral.com>
Sent: Tuesday, June 06, 2006 12:38 PM
Subject: Re: [meteorite-list] It's a star, it's a planet, it's a 'planemo'
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" <[EMAIL PROTECTED]>:
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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