Scientists Have Detected Sunlight's Gentle Nudge on Asteroids

Research by Steven R. Chesley, Steven J. Ostro, Jon D. Giorgini, Lance A.M. Benner, Alan B. Chamberlin, NASA/JPL/CalTech, David Vokrouhlicky, David Capek, Institute of Astronomy,Charles University, Czech Republic, Michael. C. Nolan, Alice A. Hine, Arecibo Observatory, Puerto Rico, Jean-Luc Margot, Department of Earth and Space Sciences, University of California, Los Angeles-- Funding by NASA Planetary Astronomy , PGG

This model of the half-kilometer near-Earth asteroid Golevka, color-coded for gravitational slope, is from Goldstone observations made in 1995. Radar ranging during 1991-2003 has revealed that about one ounce of force shifted Golevka's path by 10 miles.

Tracking an Asteroid

• An international team of researchers led by NASA/JPL's Steven Chesley and Steven Ostro have been conducting radar ranging to the near-Earth asteroid 6489 Golevka since 1991.
• In 2003, the team's precise ranging revealed that Golevka was 15 kilometers further away than had been predicted by considering gravitational forces alone.
• The radar measurement was like a telescope in Los Angeles determining the distance to a basketball in New York with an uncertainty of half an inch, and finding that the basketball was 12 feet further than expected.
• The team concluded that the change in orbit can be explained by the Yarkovsky Effect, which until now had never been measured for a solar system object.

Diagrapm showing the Yarkovsky effect as an acceleration that happens when an asteroid's surface is heated by the sun. Image courtesy Sky & Telescope.

The Yarkovsky Effect

The Yarkovsky Effect is an acceleration that is produced when an asteroid's surface is heated by the sun during the day, and then cools off during the night. The asteroid tends to emit more heat from its afternoon side, just as the evening twilight on Earth is warmer than than morning twilight. This unbalanced thermal radiation produces a net acceleration that Chesley and Ostro et al were able to measure using very precise ranging from ground-based radar observations.

Significance to Solar System Exploration

Using radar measurement of the Yarkovsky acceleration and radar imaging and shape reconstruction, the team has for the first time determined the mass and density of a small solitary asteroid using ground-based observations. This capability will dramatically reduce the cost and risk of spacecraft missions to near-Earth asteroids.

Implications

The Yarkovsky Effect has been invoked to explain such phenomena as the rate of asteroid transport from the main belt to the inner solar system, the ages of meteorite samples, and the characteristics of collisionally produced "asteroid families. The measurement of this phenomenon vindicates the theoretical work and gives scientists a powerful tool for refining what we know about asteroid trajectories and physical properties.

For further information about science highlights and having your research highlighted, please contact Samantha Harvey at NASA's Jet Propulsion Laboratory, Samantha.K.Harvey@jpl.nasa.gov.

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