planets & binary stars

Don't know much astronomy, hope you can help.
Planets in binary star systems are a recurrent theme in sci-fi but it's
been pointed out that binary stars have very strong gravity wells that
won't allow planets to form. Then how come Alpha Centauri is considered
a likely candidate to have not only planets, but Earth-like planets, if
it's very close to Beta Centauri and Proxima Centauri? Does it not count
as a true triple star system?

SEb

Astronomers have written a number of papers about stable orbits in
binary star systems. Apparently, planets can form there.

Saul Levy


On Mon, 18 Oct 2004 17:07:53 +0200, Seb
wrote:

Don't know much astronomy, hope you can help.
Planets in binary star systems are a recurrent theme in sci-fi but it's
been pointed out that binary stars have very strong gravity wells that
won't allow planets to form. Then how come Alpha Centauri is considered
a likely candidate to have not only planets, but Earth-like planets, if
it's very close to Beta Centauri and Proxima Centauri? Does it not count
as a true triple star system?

SEb

In message , Seb
writes
Don't know much astronomy, hope you can help.
Planets in binary star systems are a recurrent theme in sci-fi but it's
been pointed out that binary stars have very strong gravity wells that
won't allow planets to form. Then how come Alpha Centauri is considered
a likely candidate to have not only planets, but Earth-like planets, if
it's very close to Beta Centauri and Proxima Centauri? Does it not
count as a true triple star system?

Minor nitpick, but Beta Centauri is a totally different star!
Proxima Centauri is a red dwarf and a long way from Alpha A & B, so I
doubt it will be a problem.
I think the answer is that people now find that even a G-class star
sufficiently far away doesn't prevent formation of planets. Look at
http://www.solstation.com/orbits/ac-absys.htm and
http://www.astrobiology.com/asc2002/abstract.html?ascid=332, for
instance.
You aren't going to get planets like Neptune and Pluto, but there's
still lots of room.
--
What have they got to hide? Release the ESA Beagle 2 report.
Remove spam and invalid from address to reply.

Seb wrote:

Don't know much astronomy, hope you can help.
Planets in binary star systems are a recurrent theme in sci-fi but it's
been pointed out that binary stars have very strong gravity wells that
won't allow planets to form. Then how come Alpha Centauri is considered
a likely candidate to have not only planets, but Earth-like planets, if
it's very close to Beta Centauri and Proxima Centauri? Does it not count
as a true triple star system?

SEb

Thanks for your responses. Quite interesting that binary stars can have
planets. For a bit of fun:

http://r5d4.dirtyrubbish.com/skippydroid/index.html

I wonder how the sky looks like from a planet surface in Centauri. In
particular how does another star that's very close (but further than the
planet's sun) look like?

Seb

In message , Seb
writes

Thanks for your responses. Quite interesting that binary stars can have
planets. For a bit of fun:

http://r5d4.dirtyrubbish.com/skippydroid/index.html

I wonder how the sky looks like from a planet surface in Centauri. In
particular how does another star that's very close (but further than
the planet's sun) look like?

Seb

There's a lovely description in Isaac Asimov's "The Planet of the Double
Sun", which is reprinted in "Asimov on Astronomy". He simplifies the
situation, but as seen from A, B would be about the same apparent size
as Jupiter, but 150x as bright as the full Moon. A planet orbiting B,
the same size as Uranus and in a 100 million mile orbit would have a
maximum separation of 3 degrees and a magnitude of 1.7 (so an Earth-size
planet in an orbit where it could support life would presumably be
visible with a modest telescope)
For a picture of Proxima Centauri's planet your best bet is to find a
reproduction of David Hardy's "Proxima's Planet". I've got a print on
the wall by my desk!