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From: josh@v1.UUCP (Josh Knight)
Newsgroups: net.sci
Subject: Re: Re: VB-8B: First Planet Outside Solar System Discovered
Message-ID: <116@v1.UUCP>
Date: Sun, 23-Dec-84 23:00:45 EST
Article-I.D.: v1.116
Posted: Sun Dec 23 23:00:45 1984
Date-Received: Thu, 27-Dec-84 03:09:31 EST
References: , <1279@dciem.UUCP> <170@dmcnh.UUCP>
Organization: IBM Research, Yorktown Heights, N.Y.
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> 	"Igniting" is a continuum.  Jupiter radiates more energy than
> it absorbs due to the fusion occuring in its core from the intense
> pressure.  Larger planets would radiate more and more energy from
> more complete fusing until it could be considered a star (red-
> dwarf status).

Igniting isn't continuous if one means conversion of hydrogen nuclei 
to helium nuclei plus some energy (with or without catalysts like
carbon, oxygen and nitrogen).  If the central temperature and density
get high enough, hydrogen "burning" starts and the star stays basically
in the same condition while some fraction of the hydrogen is converted
into helium...called the "main sequence".  Jupiter hasn't ever "burned"
hydogen (may have consumed it's primordial deuterium, but I'm not sure
about the numbers).  It does indeed radiate more energy than it receives
from the sun, but that is because it is slowly contracting...converting
gravitational potential energy to thermal energy and then radiating it
away.  This is what things that aren't big enough to become stars do.
Below some mass, they don't burn hydrogen at their cores and so don't
have a main sequence phase.  See net.astro for more (better?) info.


			Josh Knight, IBM T.J. Watson Research
    josh at YKTVMX on BITNET, josh.yktvmx.ibm on CSnet, ...!philabs!v1!josh