People

Thomas StephanSenior Scientist

Research Focus:
Planetary science, cosmochemistry, astrophysics, astrobiology
Email:
tstephan@uchicago.edu
Office:
Hinds 121

Research Interests

Dust plays a major role in the universe. Stars form from clouds of gas and dust. At the end of their lives – after they have developed to red giant stars, AGB stars, or during nova and supernova explosions – dust forms in the outflows of dying stars. This dust eventually becomes part of the interstellar medium where new generations of stars develop. 4.6 Ga ago, our solar system formed from such a cloud of gas and dust. Remnants of preceding stars can be found as so-called presolar grains in primitive meteorites. They still provide information about nucleosynthetic processes in individual stars these dust grains come from. Another source of information about the early solar system are interplanetary dust particles – dust that originate in our solar system from asteroids and comets and that is collected in the stratosphere. Especially cometary material is of special interest since comets are considered the most primitive bodies in the solar system. In 2006, the Stardust spacecraft has returned dust from comet 81P/Wild 2. These samples provide information about processes in the outer solar system, especially the Kuiper belt where Wild 2 originated.

I have used time-of-flight secondary ion mass spectrometry (TOF-SIMS) to study mainly the chemical composition of meteorites and all kinds of available cosmic dust samples: interplanetary dust, presolar dust, and samples from the Stardust mission.

I am also involved in COSIMA (Cometary Secondary Ion Mass Analyser), a TOF-SIMS instrument onboard the European Rosetta spacecraft that recently reached its target, comet 67P/Churyumov-Gerasimenko. COSIMA is analyzing the composition of dust particles from the comet.

In a joint University of Chicago-Argonne National Laboratory project, we have developed the next generation of instruments based on microbeam laser resonance ionization mass spectrometry that will be used to measure isotopic and chemical compositions of various dust samples. First resonance ionization mass spectra have recently been measured with CHILI – the Chicago Instrument for Laser Ionization.