[sci.astro] StarDate: October 22 Detecting Alien Spacecraft

dipper@utastro.UUCP (Debbie Byrd) (10/22/86)

Detecting alien spacecraft -- after this.

October 22  Detecting Alien Spacecraft

Maybe there are other civilizations out there in the galaxy.  And maybe
there aren't.  The search for extraterrestrial intelligence -- also
called SETI -- relies mainly on looking for other civilizations by
listening at radio frequencies of the electromagnetic spectrum.  Some
on-going programs utilize radio telescopes.  They hope to detect an
unmistakable pattern that would indicate a non-natural, intelligent
source.

But listening for other life forms is just one possibility.  Another
idea might be to detect the "exhaust" of an alien spacecraft.  We don't
know that other civilizations would want to travel among the stars.
But if they did, then, according to current earthly technology, they
might rely on a propulsion method that produces gamma rays.  For
example, they might use a matter/antimatter propulsion technique --
where matter and antimatter meet -- and mutually annihilate each
other.  If the resulting explosion could be properly channeled, it
could send a spacecraft on a trip among the stars.  A by-product of the
explosion would be gamma rays.

So detect gamma rays, and you've found an alien spacecraft!  Well, not
quite.  There are lots of natural sources for gamma rays.  But an alien
spacecraft would do something no natural source is known to do.  It
would move at a substantial fraction of the speed of light among the
stars of our Milky Way galaxy -- maybe a hundred times faster than
ordinary astronomical objects.  Thus we would see gamma rays from an
interstellar spacecraft with a large proper motion -- a large sideways
motion on the dome of our sky relative to the background stars.

Nobody is using this technique at the moment for the purpose of
detecting alien life.  But it's an exciting possibility -- the
detection of another lifeform by its spacecraft.

Script by Deborah Byrd and Diana Hadley.
(c) Copyright 1985, 1986 McDonald Observatory, University of Texas at Austin

anon@abnji.UUCP (anon) (10/27/86)

"Re: detecting alien spacecraft by their gamma ray exhaust"
But wouldn't that exhaust be focused, like a searchlight, thus being
impossible to detect unless the spacecraft was travelling derectly away from
us on earth?

timothym@tekigm2.UUCP (Timothy D Margeson) (10/30/86)

In article <1277@abnji.UUCP> anon@abnji.UUCP (anon) writes:
>"Re: detecting alien spacecraft by their gamma ray exhaust"
>But wouldn't that exhaust be focused, like a searchlight, thus being
>impossible to detect unless the spacecraft was travelling derectly away from
>us on earth?

So, they're leaving us. Who could blame them.




Bye

-- 
Tim Margeson (206)253-5240
PO Box 3500  d/s C1-937                          @@   'Who said that?'  
Vancouver, WA. 98668
{allegra..inhp4..decvax..ucbvax}!tektronix!tekigm2!timothym 

rwb@scicom.AlphaCDC.COM (Robert Brumley) (11/11/86)

In article <1277@abnji.UUCP>, anon@abnji.UUCP (anon) writes:
> "Re: detecting alien spacecraft by their gamma ray exhaust"
> But wouldn't that exhaust be focused, like a searchlight, thus being
> impossible to detect unless the spacecraft was travelling derectly away from
> us on earth?


A paper by Dr. Robert Forward which was presented at the American Astronautical
Society meeting last month discussed matter/antimatter propulsion.  Due to
their nature, gamma rays are very difficult to use to propel a spacecraft.
However, when a proton encounters an antiproton, gamma rays are not immediately
produced.  I don't have the paper in front of me, so I can not be sure, but
I believe that on the average 3 charged and 2 neutral pions are produced.
The neutral pions almost immediately convert to gamma rays, thus 2/5 of the
energy is lost.  However, the 3 charged pions last long enough to be used in
a variety of ways.  The point is, the gamma radiation is essentially worthless
and need not be directed.  Therefore, though I am no expert, I would think that
it would be possible that the gamma radiation would just radiate in all
directions.

Robert Brumley

UUCP: (isis,hao)!scicom!rwb