Department of Earth and Planetary Sciences

Planetary Geoscience

Asteroid Belt

Asteroids, and perhaps comets, are the sources for meteorites.  The Department of Earth & Planetary Sciences hosts an active research program in meteoritics, funded by the NASA Cosmochemistry Program.  Hap McSween and Larry Taylor, and their students and postdocs, are involved in characterizing newly recovered chondrites and achondrites, and in more focused studies of specific meteorite groups. 

Ongoing meteorite projects include:

  • Howardite, eucrite, diogenite (HED) achondrites:  These are basalts, ultramafic cumulate rocks, and regolith breccias thought to derive from the asteroid 4 Vesta.  McSween’s group is studying the mineralogy, petrology, and chemistry of these samples to understand magmatic activity on this large asteroid and to provide critical information useful in interpreting spectral and chemical data to be obtained by the Dawn spacecraft when it maps Vesta from orbit in 2011.
  • Carbonaceous chondrites:  McSween’s group is characterizing the degree of aqueous alteration experienced by various CM chondrites, for comparison with their spectral properties and oxygen isotope compositions.  Taylor’s group is describing newly recovered samples of CV chondrites.
  • Ordinary chondrites:   McSween’s group has a long-term interest in quantifying thermal and shock metamorphism in ordinary chondrites.  This work includes geothermometry to determine peak temperatures, modal analyses to document oxidation reactions, and computer modeling to understand asteroid thermal histories.
  • Other achondrites:  Taylor’s group is involved in the petrologic characterization of unique achondrites that represent magmatic activity on other differentiated asteroids.

Figures:
Chondrite:  Photomicrograph of an ordinary chondrite thin section.
Eucrite:  Photomicrograph of a eucrite thin section.

Asteroid Research

Asteroids are the rocky remnants of the material from which the planets formed.  They therefore hold important clues to how the Solar System formed and evolved.  Researchers in the UT EPS department study various groups of asteroids from a distance using ground- and space-based telescopes, from closer up with NASA’s interplanetary spacecraft missions, and in the laboratory in the form of meteorites (see above).
Ongoing asteroid projects include:

  • Vesta and Ceres:  The asteroid 4 Vesta is one of the largest asteroids, and the only one that shows clear evidence for differentiation and the eruption of lava flows on the surface.  1 Ceres, the first asteroid discovered, is the largest asteroid.  Though it is larger than Vesta, its surface is looks much different, more like very primitive meteorites.  McSween is a member of the science team for the Dawn mission which is on its way to orbit Vesta in 2011 and then Ceres in 2015.
  • Jupiter Trojan asteroids:  These bodies actually orbit the sun far beyond the Main Belt of asteroids.  By virtue of this unique orbital position, they are a key group for distinguishing several models of Solar System evolution and for understanding the distribution of organic material and ices.  Emery’s group has a long-running project to characterize surface properties of these bodies using infrared spectroscopy (both near-infrared reflectance and mid-infrared thermal emission).
  • Outer Main Belt asteroids:   Asteroids in the outer regions of the Main Belt of asteroids appear to be among the most primitive and may be analogs for some carbonaceous chondrite meteorites.  According to recent dynamical models, some may even have originally formed far out in the Solar System, like comets.  Emery’s group is involved in observing these asteroids in the infrared to constrain surface compositions.
  • Asteroid thermal properties:  Most asteroids are thought be covered with a relatively thick regolith layer, like the moon.  But some asteroids show clear signs of bedrock outcrops, while others are thought to be made of metals.  These different surfaces have very different thermal signatures.  Emery’s group has several ongoing projects studying the thermal properties of various asteroid types (V-types, M-types, extinct comets, primitive asteroids).  Along with bulk thermal properties, thermal observations enable determination of size – one of the most basic parameters to know – and thermal spectra can be diagnostic of surface mineralogy.
  • Near-Earth asteroids:  As the name implies, these are asteroids that come close to the Earth.  They therefore pose both exciting opportunity for up-close study, and the hazard of potential collisions.  Emery’s group is involved in thermal and near-infrared observations of near-Earth asteroids to determine size, albedo, surface composition, and thermophysical properties.

Figures:
Asteroid collage
Itokawa