When you sit down to dinner tonight, take a minute to consider how far your food traveled to get to your plate. Is your steak from Nebraska? Are your carrots from California? Your fruit from New Zealand? Sure, you bought it at the grocery store down the street, but chances are your food traveled hundreds of miles before it landed on your plate. This hour, Ira and guests consider our global grocery shopping. Experts say eating local might make us healthier and be better for the environment.

Plus, new evidence from colliding galaxies suggests that dark matter does exist. Though astronomers have long suspected the presence of a heavy matter that can't be seen via ordinary telescopes, this scientists say this research provides definitive evidence for the mystery matter's existence. Could this settle the debate over the workings of gravity in the universe?

Finally, we'll get the final word on just what counts as a planet. At a meeting of the International Astronomical Union, astronomers voted yesterday to kick Pluto out of the planetary line-up. A new definition of what constitutes a 'planet' leaves the solar system with eight planets -- Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. But the solar system also now contains a new class of objects known as 'dwarf planets,' including Pluto, Ceres, and 2003 UB313. More dwarf planets may be added to the roster soon. We'll talk about the decision and where it leaves the astronomy textbooks.

Call in with your questions and comments at 1-800-989-8255 (2-3 Eastern). Teachers, find more information about using Science Friday as a classroom resource in the Kids' Connection.

Guests:
Sean Carroll
Cosmologist
Senior Research Associate, Physics
California Institute of Technology
Pasadena, California

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Brian Halweil
Author: "Eat Here: Reclaiming Homegrown Pleasures in a Global Supermarket" (2004, W.W. Norton & Company)
Senior Researcher
Worldwatch Institute
Washington, DC

Jennifer L. Wilkins
Kellogg Food and Society Policy Fellow
Senior Extension Associate, Division of Nutritional Sciences
Cornell University
Ithaca, New York

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David Kestenbaum
Science Correspondent
National Public Radio
Washington, DC

Books/Articles Discussed:

"Eat Here: Reclaiming Homegrown Pleasures in a Global Supermarket" by Brian Halweil. W.W. Norton & Company, 2004.

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This segment produced by Annette Heist