Parsing numbers in Scientific Notation

Hey all, I'm an XML newbie so go easy on me :o)
I am writing a DTD and XSLT file for a table of astronomical data, and 
would like values to be given in SI units. For many things this means 
astronomically large numbers like 5.0 x 10^30. I would like not to have 
to specify that using standard decimal notation (as used by 
format-number() and xsl:decimal-number) as it would be prone to errors 
and look awful! Is there a built-in way to parse a string such as "5.0 
x 10^30" and then perform mathematical operations on it, like divide it 
by the mass of the sun (1.99 x 10^30), so it outputs a simpler number 
like "2.5" ?
If there is no such built in method, how would I go about writing some 
XSL/XPath voodoo to make it happen?

The lists.xml.org server doesn't seem to be responding to http requests 
at the moment so I was unable to check the archives. Apologies for 
this.

- Nick.