Andy Cheng
Project Scientist, NEAR
Johns Hopkins University / APL, NASA

Asteroids are primitive objects, many of them left behind from the formation of the solar system.

The planets condensed out of a ball of gas and dust... some of them never survived the process.

They grew up to almost the size of planets, and they were crashed into at high speed by another forming object and broken into pieces again.

Others formed into bigger objects, and grew large enough for some planetary processes to begin, with internal heating separating their materials into distinct and differentiated layers.

Some of these then smashed into others and broke apart once more into smaller chunks.

Down here on Earth, asteroids are just points of light.

Even with powerful radars, all you get are tumbling shapes, looking more like large potatoes than a minor planet.

The first close-up images of asteroids were captured in 1991 and 1993 when the Galileo spacecraft flew past Gaspra and Ida on its way to Jupiter.

Galileo even found that Ida had its own tiny moon, Dactyl, in orbit round it...

The NEAR spacecraft is currently taking a close up view of Eros, one of the largest near-Earth asteroids. NEAR stands for the Near Earth Asteroid Rendezvous Mission.

We knew the "NEAR" spacecraft was soon going to give us revolutionary insights when it passed within 1200 kilometers of asteroid 253 Mathilde...

Then it was on to its primary target... Eros.

Andy Cheng
Project Scientist, NEAR
Johns Hopkins University / APL, NASA

Eros was picked because it is one of the largest of the Near Earth asteroids. It was the first asteroid that was discovered to cross inside the orbit of Mars. Before that people thought all the asteroids sat calmly between the orbits of Mars and Jupiter.

Every day during the primary mission, the "NEAR" team posts a picture of the day on the Internet.

You can see objects as small as 3 meters across.

Andy Cheng
Project Scientist, NEAR
Johns Hopkins University / APL, NASA

It just happens the image for August 1st 2000 is a particularly fascinating image, because it shows us peering over the end of the asteroid. And... in fact, the whole asteroid is 32 kilometers from end to end.

The asteroid is like a peanut, and so you're looking at the concave side. You're looking over one end of it, that's down here, right towards the middle, right at the bottom.

It happens that in the middle of the asteroid there is a big crater, the biggest crater on the asteroid. And fascinating things about this image... you can see the boulders that are just perched on the surface.

We wanted to study the asteroids because some of them are among the oldest objects in the solar system. They are remnants of the processes that assembled the planets. So in some sense what we are studying is clues to at least... what happened to Eros at the same time, basically, that the terrestrial planets were forming.

So it is, in that sense, a window back into the period when the solar system was being born.

Eros is a near-Earth asteroid.

That means at some point it just might impact Earth.

Andy Cheng
Project Scientist, NEAR
Johns Hopkins University / APL, NASA

If we do discover an object, an asteroid that is heading for the Earth what you would want to do is deflect it, push it a little bit, so it does not hit the Earth.

It turns out that knowing the composition and history of such near-Earth asteroids may be key to the kind of protective measures humans may be able to adopt in the future.

Andy Cheng
Project Scientist, NEAR
Johns Hopkins University / APL, NASA

If we set off a bomb and we push it somewhere in the middle, let's say, and it breaks up into five large pieces, all of which still hit the Earth, that outcome would actually create more damage, probably, than just leaving the asteroid alone.

So what we have to understand is whether we are looking at a very loose jumble of rocks, that are not very well stuck together, as opposed to a single relatively consolidated object which we could push fairly hard and it would relatively easy to deflect.

Asteroids and comets may be some of the smallest objects in our solar system, but as we understand them more we may discover how our home planet began.

And if we recognize that collisions and impacts are as much a part of life in our solar system as regular orbits and routine seasons, we may take precautions to ensure our species avoids the fate of the dinosaurs.

It may be that what we discover about the composition of comets and space rocks is just what we need to know to divert them away from earth.

It's hard to think of scientific knowledge that's any more valuable than that...

NEAR Shoemaker (Near-Earth Asteroid Rendezvous)
Deep Space 1
Recent Articles:

Astronomers Image Double Asteroid And A New Asteroid Moon

NEAR Shoemaker Closes in For Unprecedented View of an Asteriod

NEAR Mission Discoveries Highlighted in Latest Issue of Science

Eros Asteroid May Have Been Present At The Birth Of The Solar System

Additional Links:
 • JPL's Solar System Exploration
 • The Nine Planets
 • Views of the Solar System
 • Windows to the Universe