My recent Sky & Telescope article on spacecraft imaging for amateurs has just been made free for download in PDF format from the magazine's website (thanks guys!), so I've been getting some good questions on it from readers. One person asked me today: "You mention the public availability of imaging data for planetary photographs from government agencies. Is similar data (both raw and processed) publicly available for physical data, i.e., chemistry, geology, and atmospheric physics of the planets?"
The answer is most assuredly yes. Data from all science instruments on all of NASA's and ESA's space missions, not just cameras, is archived in the Planetary Data System and Planetary Science Archive, and almost all of that data is available online. Some of this data is not hard to understand and access. For instance, I've often dug into Mars Orbiter Laser Altimeter data on Mars' topography. In the PDS you can find two main different versions of this data set, either accessing it as individual topographic profiles or as a gridded image-like map (like I did in this post in my White Rock series). I've never tried to access most other sorts of data, like Mini-TES or Mössbauer spectra from the rovers or Mars Express SPICAM data. But it's all out there, and it's all documented; if you are interested, start poking around!
Image data are available from the Imaging Node of the Planetary Data System, which is operated out of the Jet Propulsion Laboratory and is the node I visit most often. Other sorts of data are curated at different nodes. For instance, there are the Geosciences Node, run by Washington University in St. Louis; the Rings Node, from the SETI Institute; and the Small Bodies Node, run by the University of Maryland. Each node has its own personality. All these other nodes also archive imaging data, because imaging data is so important for providing context for the other sorts of data. Each node has different kinds of search tools. I always go to the Geosciences Node for Mars Exploration Rover data because of its marvelous Analyst's Notebook interfaces; I often use the Rings Node for Voyager and Cassini data because of their handy-dandy ephemeris and planet viewer tools. This is all highly technical stuff, but it's all documented; so grab yourself a cup of coffee, sit down at your computer, and have fun exploring!