She was in charge of sending Galileo to crash into the atmosphere of Jupiter to ensure that it would not contaminate the oceans under the icy surface of the moon Europa with Terran microorganisms. If there’s life there, we want to make sure that it stays Europan life.
She is currently, amongst other projects, a staff scientist on the Cassini Equinox Mission to Saturn.
From one bio aimed at schoolkids, which reveals that Dr Alexander is also a very keen equestrian:
I am a scientist who specializes in the physics of comet interiors and comet evolution. This means I know a lot about different kinds of ice in the solar system. I spend a lot of time thinking about how comets and the solar system evolved. I also study magnetospheres. Part of my current job at the Jet Propulsion Laboratory in Pasadena, California, involves working for two instruments studying Jupiter’s magnetosphere on the Galileo spacecraft. Other kinds of science I especially like are climate studies, especially paleoclimate, atmospheric science, and everything related to other planets.
I got to be a scientist by accident. I wanted to be a journalist but my parents wanted me to be an engineer, and they were paying for school, so I had to do what they said. I found it was a lot more fun to think about the flow of water in a river than water in the city sewer, so I switched to earth-science (geophysics). I always hated math, but I am sure glad I took all the classes I did, because math is a very important tool to use when studying the Earth and planets!