  We present results for Chandra observations of comets, 17P/Holmes (17P) and
8P/Tuttle (8P). 17P was observed for 30 ksec right after its major outburst, on
31 Oct 2007 (10:07 UT) and comet 8P/Tuttle was observed in 2008 January for 47
ksec. During the two Chandra observations, 17P was producing at least 100 times
more water than 8P but was 2.2 times further away from the Sun. Also, 17P is
the first comet observed at high latitude (+19.1 degrees) during solar minimum,
while 8P was observed at a lower solar latitude (3.4 degrees). The X-ray
spectrum of 17P is unusually soft with little significant emission at energies
above 500 eV. Depending on our choice of background, we derive a 300 to 1000 eV
flux of 0.5 to 4.5 x 10^-13 ergs/cm2/sec, with over 90% of the emission in the
300 to 400 eV range. This corresponds to an X-ray luminosity between 0.4 to 3.3
x 10^15 ergs/sec. 17P's lack of X-rays in the 400 to 1000 eV range, in a simple
picture, may be attributed to the polar solar wind, which is depleted in highly
charged ions. 8P/Tuttle was much brighter, with an average count rate of 0.20
counts/s in the 300 to 1000 eV range. We derive an average X-ray flux in this
range of 9.4 x 10^-13 ergs/cm2/sec and an X-ray luminosity for the comet of 1.7
x 10^14 ergs/sec. The light curve showed a dramatic decrease in flux of over
60% between observations on January 1st and 4th. When comparing outer regions
of the coma to inner regions, its spectra showed a decrease in ratios of
CVI/CV, OVIII/OVII, as predicted by recent solar wind charge exchange emission
models. There are remarkable differences between the X-ray emission from these
two comets, further demonstrating the qualities of cometary X-ray observations,
and solar wind charge exchange emission in more general as a means of remote
diagnostics of the interaction of astrophysical plasmas.
