If you were having breakfast on Mars, would you like some Martian blueberries on your cereal?

Although there are things on Mars called "blueberries," you would probably not want to try to eat them. In fact, Martian blueberries are neither berries nor blue.

As the Opportunity rover began its exploration of the part of Mars called Meridiani Planum, it encountered a rock formation that had layers. Embedded in these layers were small, gray spheres of rock. To the scientists studying the images, it looked like blueberries in a muffin, hence the nickname for these geologic features. Later, Opportunity found collections of these BB-sized rocks scattered on the ground, probably having fallen out of the rock formation as it eroded.

The significance of these rocks, however, is not in their clever name but in their composition. What the instruments on Opportunity found was that these "blueberries" contained hematite, an iron compound. Hematite structures like this usually form in the presence of water. These blueberries therefore add one more piece of evidence to the growing list of findings that Mars was once wet.

The Opportunity and Spirit rovers continue their mission on Mars, long past their original expected lifetime. The latest information about what these robotic explorers are seeing can be found at: http://athena.cornell.edu/

and http://marsrovers.jpl.nasa.gov/home/index.html

Some details about the discoveries of Martian blueberries can be found at:http://www.jpl.nasa.gov/releases/2004/88.cfm

and http://www.csmonitor.com/2004/0319/p25s01-stss.html

This week's question comes from Dr. Dave Thompson. Dr. Thompson is an astrophysicist who studies gamma rays in the Laboratory for High Energy Astrophysics. He helped build, test, and analyze data from EGRET on the Compton Gamma Ray Observatory, and he is now helping build part of the Gamma Ray Large Area Space Telescope (GLAST), scheduled for launch in 2006. His particular scientific interest is gamma-ray pulsars.