This is planetary radio. Hello again space fans I'm Matt Kaplan. It's bound to be an anxious week for some terrific scientists and engineers.

We are just days away from hearing NASA's choice for the 2007 Mars Scout Mission, Only one of four outstanding teams will get the green light

for the red planet. We'll meet two team leaders today and two next week.

Of course, we'll also hear from Bruce Betts,

who's here with a new trivia contest.

And Emily stops by to explain why comets

come from every which way. I'll be back in a minute with the first of our Mars Scout Principal Investigators. Hi, I'm Emily Lochuwala with questions and answers. A listener asked, why is the

Ort Cloud believed to be spherical in shape?

Why wouldn't it be spread out into a disk in line with the plane of the solar system?

The oort cloud is a sphere of cometary material located at the far reaches of the solar system

50,000 times farther from the Sun than the Earth. Like the rest of the bodies in the

solar system, planets, planetes, and asteroids, the oort cloud probably began with a disk-like shape.

This disk-like shape was caused by the rotation of the primordial nubula from which the sun formed.

The spin resulted in faster motion of particles in the plane of the solar system,

so collisions between particles were more likely to cause them to scatter outward in this plane.

As a result, most of the bodies in the solar system, including all of the large

planets and most asteroids, revolve around the sun within a flat plane called the ecliptic.

However, we know that a group of objects known as the long period

comets fall into our solar systems planetary region from every possible

direction including above and below the ecliptic plane. How do the long period comets manage to come at us from all directions?

Stay tuned to planetary radio to find out. You've spent years planning and preparing. You've given it your absolute best. Your team is as anxious as you are as you are as you wait for the big announcement and you know

there are three competing teams that have worked just as hard who are just as anxious and

...