Analysing Stardust

22 January 2006

Interview with

Prof. Donald Brownlee, Principle Investigator on the Stardust Mission, University of Washington


Chris - Tell us about the Stardust Mission. What's it all about?

Don - Stardust is a comet sample return mission. We went to a comet, grabbed a piece of it and brought it home.

Chris - And how does it actually work? What was the nature of the mission and what did you actually do?

Don - We flew for seven years in space and travelled almost three billion miles. Two years ago, we travelled close to a comet called Wild 2, which formed at the very edge of the solar system about where Pluto is. During the fly-by we took fabulous pictures of it and we exposed a collector composed of this amazing material called aerogel. We collected thousands of millions of particles that impacted into this collecter, folded it up and brought it home last week.

Chris - Why did you choose Wild 2? What was special about that comet?

Don - There are a lot of comets in the solar system but very few of them are inplaces we can get to. Most of them are very far away, and most of them are either very close to the sun or out beyond Neptune. This one was conveniently located and we could fly by it at a pretty low velocity for interplanetary speeds and get a sample. But this comet is also interesting because it's only been in its present orbit since 1974. It now travels between the orbit of Jupiter and Mars. Before 1974, it was in a much larger orbit.

Chris - Why has it moved?

Don - It moved because of planetary billiards! If comets get anywhere close to planets and they have gravitational encounters with them, their orbits change. They change all the time, and have very unstable orbits compared to the orbits of planets like the Earth, Mars and Venus.

Kat - So you've been flying this little capsule miles out in space. How do you actually control a space craft like that from such a distance?

Don - Well the space craft is controlled by a combination of the Jet Propulsion Lab in Pasadena, California and Lockheed Martin in Denver, Colorado. We track it using something called a deep space network, which is a series of antennae around the world. We send radio signals to it and we get radio signals back, and we track so that we know where it is. When we want to change its direction, we fire some of the sixteen little engines for a period of time and send it in a different direction.

Chris - Now why is a comet so interesting to you? What can it tell you about things that you couldn't learn from Earth?

Don - The most fundamental reason why we would want to go to a comet is to learn about the origin of the solar system. The sun and the planets formed four and a half billion years ago and they formed from a disk of gas and dust, which is called a solar nebula. The solar nebula was originally filled with things like comets and also asteroids. Yet almost all of those comets are now gone. They were either eaten by other planets, or they went into the sun, or they were thrown out into the galaxy.

Chris - And so this is almost like a time capsule really. You can look back at the four and a half billion years that have gone by since our planets were forming.

Don - Exactly. And at the very edge of the solar system, some of those bodies have survived from the very early beginnings. I look on it as a cosmic library. The records of our formation have been stored out there for the entirety of this phase of the solar system. We grabbed a piece of it and have it in our lab right now.

Kat - So really briefly, what kind of techniques will you be using to study these particles? Presumably they're absolutely tiny.

Don - The particles are very tiny but they are much larger than, say, DNA, and we know how much information is stored in one DNA molecule. These are not particles of DNA. They are particles of minerals, glass, sulphides, and all sorts of organic materials. There are people all over the world using a variety of instruments to studying the mineralogy, the isotope composition, and everything we can measure on the atomic scale. One of the ironies of this is that to study the very smallest samples, you use some of the largest instruments. In fact the largest instrument used is the Stanford Linear Accelerator, which is several kilometres long. This puts x-rays into small samples and works out their composition.


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