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Building a Better Guide to the Galaxy
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NARRATOR: Welcome to the NASA's PlanetQuest Podcast, Episode 4 (For episodes 1-3 visit the PlanetQuest Podcast page). I'm Dr. Jo Pitesky

CHARACTER VOICE: "If you've done six impossible things this morning, why not round it off with breakfast at Milliways, the restaurant at the end of the universe."

NARRATOR: With apologies to Douglas Adams and his "Hitchhikers Guide to the Galaxy" series, as far as we know, there isn't really a restaurant at the end of the universe. However, scientists have recently discovered a very nice bar at the center of the galaxy. It's one of many features of our home galaxy that the University of Virginia's Steve Majewski would like to understand better.

Majewski and his team plan to use NASA's SIM PlanetQuest mission to learn more about the nature of our Milky Way galaxy than ever before possible.

MAJEWSKI: It's interesting that even though the Milky Way is the closest galaxy, in that we're inside of it, in some ways we know the least about it because we are actually inside the Milky Way. We can't go outside and look in.

We know our nearby neighborhood very well, but we don't know what's going on in the next city.

NARRATOR: With SIM PlanetQuest, scheduled to launch within the next decade, Majewski and his team plan to measure the Milky Way's size and shape, the amount and distribution of its mass, and the motions of its stars. En route, they'll describe some fascinating tourist attractions, including that bar at the center of the galaxy.

It's not the sort of place where interstellar travelers go for Happy Hour to drink some pan-galactic concoction. Instead, it's a wave pattern that pulls and pushes large groups of stars into the shape of a candy bar. The wave pattern spins like a propeller about the galactic center, continually adding new stars into its pattern and leaving old ones behind.

SIM PlanetQuest will also shed light on the invisible substance that most of galaxy is made of: Dark matter. You can't see it directly, but from its gravitational effects scientists estimate that dark matter makes up as much as 93 percent of the universe.

MAJEWSKI: SIM is the first instrument that will allow us to measure very accurately the distances of objects at the outer parts of the galaxy. These are the kinds of information we need to assess, for example, how much the galaxy weighs, how much is it rotating, what is inside the galaxy, where is the dark matter located? What is the dark matter?

NARRATOR: SIM PlanetQuest will also answer a number of basic questions, like how big is the Milky Way? And precisely where, in this vast island of stars, are we located?

MAJEWSKI: Knowledge of the size of our galaxy has been a problem for a century. We still don't know how big the galaxy is; we don't know how far we are from the galactic center to 10-20 percent. We don't know the basic things about our place in the galaxy, our sun's place in the galaxy.

NARRATOR: To answer these questions, scientists need a better roadmap of the Milky Way Galaxy. Using the ability of SIM PlanetQuest to measure the distance between stars with unprecedented accuracy, Majewski and his team hope to create the first real-life guide to the galaxy.

For NASA's PlanetQuest, I'm Dr. Jo Pitesky.

ANNOUNCER: To learn more about NASA's search for new worlds, visit PlanetQuest online, at http://planetquest.jpl.nasa.gov.