From: dbriggs@zia.aoc.nrao.edu (Daniel Briggs)
Subject: Re: A 100 Billion?  (and Nemesis again)
Organization: National Radio Astronomy Observatory, Socorro NM
Date: Wed, 14 Oct 92 04:52:50 GMT

In article <STEINLY.92Oct13114043@topaz.ucsc.edu>
  steinly@topaz.ucsc.edu (Steinn Sigurdsson) writes:
>In article <1959@shaman.wv.tek.com>
  harmons@mithril.wv.tek.com (Harmon Sommer) writes:
>  A local newspaper article on SETI mentioned that there are 100 Billion stars
>  in our solar system. How is this quantity arrived at? 
>
>Through profound ignorance.
>There is one star in our solar system.

Well, *probably*.  ;)  If the Nemesis crowd ever gets positive results,
we're going to have to rethink things a bit here.  (These are astronomers
who are postulating a solar companion that periodically disturbs the Oort
cloud, resulting in a barrage of comets.)  It's not a mainstream theory,
but it's not completely out of the question, either.  The basic idea is
that we could have a red dwarf right next door, and we might never know it
because it has never had a parallax measurement done on it, and it wouldn't
be all that bright.  There are a *lot* of red dwarfs out there!  Or it
could be a brown dwarf and not luminous, which would be a real trick to
find.  There are problems with the orbital dynamics which look pretty
damning, but it's hard to say.  They are postulating semimajor axes of a
light year or so, with a very high eccentricity.  With such an orbit, it's
difficult to see why it wouldn't be disrupted by passing stars.  (They need
it to be stable for at least a few hundred million years to account for the
cratering/extinction data.  And even this data is quite controversial.
While the data presented is undoubtedly periodic, there are concerns that
the periodicity might be introduced by sampling bias.)  The basic search
strategy is to teach an automated telescope to do the parallax
measurements, and go through the whole sky down to some reasonable limiting
magnitude.  It'll take several years at least, so don't hold your breath.
It's a bit tricky, since with reasonable fields of view, they have to be
able to see displacements on the order of 1/100 pixels.  By ordinary
parallax standards, the measurements will be crude, but then they are
looking for an extremely close object.  I'm pretty sure that the northern
hemisphere telescope is basically done, and in early production mode.
(Anyone with more recent information out there?)  If they don't find
anything in the northern sky, they want to go down south, though I don't
know if there is any money for it.  Personally, I think it would be kind of
neat if they find it, if only to watch all the other astronomers say, "uh
-- you know that we've always told you that Sol is an isolated star?  Well,
we were wrong.  Sol is a double system!"  It's probably too cute to be
real, but if it *were* it would sure tie a lot of interesting things
together.  And note also that if they do find anything, it will be
absolutely incontrovertible.  You have to admire a scientist who is willing
to bet a fair chunk of his career on a search that could be fantastically
important, but in all probability will come up null.

-- 
| Daniel Briggs  (dbriggs@nrao.edu)                      |        USPA B-14993
| New Mexico Tech / National Radio Astronomy Observatory |            DoD #387
| P.O. Box O / Socorro, NM 87801   (505) 835-7391        |
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