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Professor Bryan Penprase Participates in Largest Study Ever of Near-Earth Asteroids

Prof. Penprase and Catherine Wilka '12 at the Cerro Tolo Inter-American Observatory in northern Chile

Prof. Penprase and Catherine Wilka '12 at the Cerro Tolo Inter-American Observatory in northern Chile, where Wilka spent a week gathering data for the ExploreNEOs project.

Asteroid photo from NASA

Asteroid photo from NASA

Bryan Penprase, professor of physics and astronomy, is a member of an international team conducting the largest study ever of near-Earth objects (NEOs). The goal of the ExploreNEOs team is to analyze 600 more NEOs over the next year.

According to Penprase, “Given the capacity of those near Earth objects to destroy life on Earth, they are amazingly very poorly understood.”

The ExploreNEOs team published its preliminary analysis of 101 near-Earth asteroids in the September issue of Astrophysical Journal. Their data revealed a surprisingly mixed bunch of asteroids.

While thousands of NEOs have been catalogued in the past, most of those have been found with optical telescopes, which can’t differentiate between a large, dark object and a small, light asteroid since both would reflect the same amount of visible light.

The ExploreNEOs team is using infrared data from the NASA Spitzer Space Telescope to determine an object’s temperature and then are combining that data with new measurents of the object’s optical brightness to determine its actual size and albedo, a measure of how strongly it reflects sunlight. What they found is a very wide range in albedos indicating that the asteroids have a wide range of compositions and probably different origins.

The team also discovered that some of the smaller objects have surprisingly high albedos. According to the team’s news release, “Since asteroid surfaces become darker with time due to exposure to solar radiation, the presence of lighter, brighter surfaces for some asteroids may indicate that they are relatively young. This is evidence for the continuing evolution of the near-Earth object population.”

Comets and asteroids are considered to be largely unchanged remnant debris from the solar system’s formation, which occurred approximately 4.6 billion years ago. Revealing the chemical compositions of NEOS will bring science closer to understanding the chemical mixture of the solar system’s origins.

The ExploreNEOs team is led by David Trilling of Northern Arizona University (NAU), Flagstaff. Penprase has been working on the project for two years and has been leading the ground-based optical observations of the asteroids, using the Pomona College telescopes, a robotic telescope in New Mexico, and observatories in Chile.

“What’s really been great is that this is an ideal project for students to work on because they can help with the observations and data analysis. It is also well suited to small telescopes like Brackett and Pomona’s 1-meter telescope at Table Mountain,” says Penprase.

So far, Catherine Wilka ’12 and Alex Hagen, HMC ’10, have worked with Penprase on the project. Hagen did his senior thesis on the ExploreNEO project and is now working NAU, for Trilling, and “is in charge of the optical data reduction as well as writing some really advanced software for the image processing necessary to analyze the data,” reports Penprase.

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TERMS: A near-Earth object is defined as an object whose orbit brings it within 1.3 astronomical units (AU), which is 1.3 times the distance from Earth to the Sun.