Sure, scientists have discovered some important things in the last 125 years -- but there are still some pretty big questions left on the lab bench. In this hour of Science Friday, we'll talk about some of those big questions, and check in with researchers in fields from aging to astronomy who are looking for some of the answers. What are your thoughts on the biggest unanswered questions?

Plus, we'll get an update on NASA's Deep Impact mission. Early in the morning of July 4th, scientists deliberately smashed a 320 kg probe into the surface of Comet Tempel -1 as it hurtled by, blasting out a large crater. The researchers hope that by analyzing what came off the comet in the collision, they will better be able to understand what comets are made of, how a comet's interior is structured, and how comets change over time. We'll talk with one of the project's scientists about what they've learned already from a few days of comet collision analysis. Call in with your questions and comments at 1-800-989-8255 (3-4 Eastern). Teachers, find more information about using Science Friday as a classroom resource in the Kids' Connection.

Guests:

Donald Kennedy
Editor-in-chief
Science
Washington, DC

Steven Austad
Professor
Barshop Institute for Longevity & Aging Studies
Department of Cellular & Structural Biology
University of Texas Heath Science Center
San Antonio, Texas

Meredith Small
Author, "Kids: How Biology and Culture Shape the Way We Raise Our Children" (2001, Doubleday)
Professor, Anthropology
Cornell University
Ithaca, New York

Michael F. A'Hearn
Principal Investigator, Deep Impact Mission
Professor of Astronomy
University of Maryland
College Park, Maryland

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This segment produced by Karin Vergoth