Meet: Bill Sjogren
Principal Investigator, Gravity Experiment, Mars Global
Jet Propulsion Laboratory, Pasadena, California
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
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
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.
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.