| MadSci Network: Astronomy |
The short answer to your question is that, yes, there are maps of magnetic and gravitational fields of many of the solar system bodies. Unfortunately, the long answer can be extremely long! Therefore, what I’ll try to do is tell you a bit about how spacecraft measure gravity and magnetic data. Then I’ll give you some good web page links that discuss the many NASA missions to the other planets in our solar system. This way, you can look for a given planet and mission, find out whether that particular mission retrieved gravity and magnetic data, and then hopefully find some maps of the results. Often, gravity and magnetic maps are published in scientific journals, so I will also give you some references to published maps of gravity and magnetic data of the more thoroughly studied planets. One of the best locations to go and look for raw (straight-from-the-spacecraft) geophysical data that NASA has collected is to check out NASA’s Planetary Data System (PDS) Geoscience Node. The PDS Geoscience Node is located at the Earth and Planetary Remote Sensing Laboratory at Washington University in St. Louis, MO, so you can contact them with your questions as well (contact information is on their website).
NASA’s Solar System Exploration Missions site has a (nearly) complete list of NASA missions that have traveled to the planets in our solar system, listed by planet. (It’s a very good, general reference site for mission and planetary information.) After you’ve chosen a mission around a particular planet about which to learn more, go to that mission’s homepage, and look at the list of instruments onboard. For magnetic data, you are just looking for a magnetometer. For gravity data, you are looking for a radio science team.
The best missions for gathering magnetic and gravity data globally are missions that orbited the planet, like Mars Global Surveyor at Mars. If a spacecraft simply flies by a planet, like Mariner 10 past Mercury, the magnetometer will only be able to identify the presence of a magnetic field, but not the details of that field. The same is true for gravity data. Radio Science is actually not an instrument on board the spacecraft, but rather the spacecraft itself. Small wobbles in the spacecraft’s position as it orbits the planet are observed on Earth as slight differences in the time it takes to get the signal from the spacecraft (hence the term "radio science," since the scientists are studying the radio signals they are receiving from the spacecraft). These small time differences or wobbles are caused when the gravity field of the planet directly beneath the spacecraft changes slightly.
Here are some specific scientific paper references for different planets. It is by no means complete but should give you a start. I’ve included only those articles that have maps of the gravity or magnetic fields. Many of these articles are from special journal volumes dedicated to the mission discussed, so be sure to look through the other nearby papers for more information. I hope this is helpful and gets you off to a good start!
Try the links in the MadSci Library for more information on Astronomy.