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From: bs_wab@ux63.bath.ac.uk (Bains)
Newsgroups: sci.bio,sci.astro,sci.philosophy.tech
Subject: Re: DNA for interstellar messages
Keywords: realities of viruses and VIROIDS
Message-ID: <2863@bath63.ux63.bath.ac.uk>
Date: 26 Jul 88 16:31:20 GMT
References: <2743@bath63.ux63.bath.ac.uk> <2244@ur-tut.UUCP> <3916@ut-emx.UUCP> <6211@bloom-beacon.MIT.EDU>
Organization: University of Bath, England
Lines: 57

In article <6211@bloom-beacon.MIT.EDU> ayermish@athena.mit.edu (Aimee Yermish) writes:
>1.  Why would you *want* to use DNA, which is not a particularly
>obvious code, for communication with another planet?  
That is one question I was hoping the original article might answer, but 
for starters, see 5 below.

>2.  You're assuming that there are cells on the receiving planet that
>can (a) be infected by the virus 
 ... and it can replicate and lyse. No I am not. i) The ORIGINAL PAPER
was talking about viruses, which is why I thought it dodgy. ii) Not all
viruses enter cells by such specific mechanisms as the well-known
bacteriophages: a membrane fusion mechanism could be much more general.
iii) I was not all that interested in viruses themselves anyway, but in
viroids, which appear to be self-replicating RNAs requiring only
RNA precursors to reproduce. The RNA strand is both message and polymerase.
So no host enzymes required. Actually, no host cell lysis required either
as the cell either dies from the metabolic effort of carrying all those
viroids around (which is apparently what happens to plant cells) or does not,
in which case it passes the viroid on vertically.
>
>3. .., space vacuum
>might well do nasty things to the virus.  
... but not to a viroid, which is a single chemical. (Not necessarily to
a virus either, in fact, as the ATCC can provide many of them freeze-dried
with 'keep cold' on the side.)

>4.  Why send a single probe that moves slower than light and gets
>stuck on asteroids and falls into stars and such when you can send a
>electromagnetic radiation-type message?

 ... because  ...

>5.  Speaking of electromagnetic radiation, there's an awful lot of it
>out there in space with no atmosphere to protect you.  UV radiation
>does bad things to DNA. 
 ... and to em signals too. The power required to send a recogniseable
electromagnetic signal half way across the galaxy is fantastic, and
you still run the risk that the receiver will not be listening at the right
time or on the right frequency. Both would be no problems to self-propagating
RNA. 
  The radiation damage to the chemical is a major problem, however. Whether 
it is less of a problem depends critically on how much material you launch, 
how much is needed on landing, interstellar UV and X-ray intensities and
radiation-sensitivity of your molecule. As this was a 'hey, has anyone
heard of this' search for a previously published paper, I have not
worked these points out! But you have hit a serious nail on the head
with this one. 
>
>I'd think of some more, but I have to run.  Sorry to burst bubbles.
>

No problem. The regular sound of bursting bubbles is what distinguishes
science from pseudoscience.

>Aimee Yermish		ayermish@athena.mit.edu

William Bains:  wbains@bionet-20.arpa, bs_wab@uk.ac.bath.ux63