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Meet: Bill Sjogren

Principal Investigator, Gravity Experiment, Mars Global Surveyor
Jet Propulsion Laboratory, Pasadena, California


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My journals

Who I am

I'm a senior research scientist at the Jet Propulsion Laboratory (JPL) in Pasadena, California. My specialty is the determination of gravity fields of planetary bodies. Presently I'm the principal investigator on the Mars Global Surveyor Mission for the gravity experiment. Over the past many years I have been involved with Ranger, Surveyor, Lunar Orbiter, Apollo, Viking, Pioneer Venus Orbiter, Magellan, and the Galileo missions. It has been a very exciting life, for I've had the good luck to be the very first person to receive and analyze all of these new data, and then discover the new characteristics of a particular planet's or moon's gravity field.

Gravity fields are all different and tell us about the internal structure of the celestial body. The most exciting time for me was the discovery of the inverted gravity signal over the large circular maria on the Moon. It was completely opposite to everyone's thinking at that time. It led to the discovery and naming of these features as the Mascons, which is an abbreviation for "mass concentrations." There are much denser materials within these basins that cause the gravity signal to become very large. This was determined with the Lunar Orbiter data in 1968, but was dramatically visible when the Apollo landing module zipped over them at 10-15 kilometer altitudes.

Mascons have also been found on Mars, but not on Venus or Earth. The data for Mercury have yet to be obtained, but we do have a proposal in to NASA for a Mercury Orbiter. We know from the Viking mission to Mars in 1976 that the largest gravity anomally occurs over Olympus Mons, but we hope to discover many new structures not previously detected, especially in the southern hemisphere. We even hope to detect time-varying gravity at the polar regions due to sublimation of the ice caps.

What I like

I like all kinds of puzzles. As a hobby I fix TVs, which are nice big electronic puzzles. I like to give things away. It makes me happy when I can just give my data, results, repaired TVs, or anything to someone for no compensation. Truly in science we must all share our results freely if we are to understand the big puzzle of our universe.

Personal
I learned to speak English in first grade in a two-room schoolhouse in upstate New York. My parents were Swedish immigrants who came to the United States during the big depression. I have a master's degree in applied math from Northwestern.


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