UND astronomer makes asteroid discovery

While searching the skies last May for a suitable destination to land a space probe, UND astronomer Vishnu Reddy encountered something unusual: an asteroid that appears to have come from the inside of another much larger asteroid, testifying to the violence that heavenly bodies can inflict on one another.

It's all the more unusual that the larger asteroid appears to be 4 Vesta, long considered by scientists to be a kind of primitive planet from the Solar System's youth. Because of this connection, studying the smaller asteroid, named 1999 TA10, could shed more light on those early days.

Reddy and his collaborators used a NASA infrared telescope atop Mauna Kea, a dormant Hawaiian volcano, to determine that 1999 TA10 is made of the same kind of mineral that's likely to be found inside Vesta.

This geology-at-a-distance is a specialty of UND Aerospace's Space Studies Department, found at few other universities around the world. It's a useful astronomy tool because there isn't enough money in the world to send a probe to every one of the millions of asteroids in the sky to determine what they're made of.

In December, the journal Icarus published in its online edition the discovery made by Reddy, an assistant professor with UND's Space Studies Department; Andreas Nathues with Germany's Max Planck Institute; and UND astronomer Mike Gaffey.

The survivor

Vesta is a massive 360-mile long rock, a little longer than North Dakota is wide, and the third largest body in the asteroid belt that circles the sun between the orbits of Mars and Jupiter. Where its south pole had been once upon an epoch, there's now a gaping hole 15 miles deep and 280 miles wide.

Scientists believe that Vesta, unlike most asteroids today, is divided into layers like a planet because it formed like a planet, a molten ball of matter that cooled over time, with the heavier elements sinking to form the core and lighter elements rising to form the mantle and the crust.

Billions of years ago, there may have been many more planet-like asteroids like it, but collision with one another and with true planets left only a few. Smaller asteroids would then be the remnant of those long destroyed protoplanets. That's the theory anyway because nobody's sent a probe to any of the remaining protoplanets; NASA's Dawn probe will be the first this summer to do so with a stop at Vesta and, later, 1 Ceres.

How he knows

What makes Vesta unique is that it's not only a protoplanet, but one that may have chunks of itself floating around our star system; astronomers think that big crater had something to do with it. They've linked a whole family of asteroids to Vesta, called Vestoids.

One of these is 1999 TA10, a rock about two-thirds of a mile long circling the sun between the orbits of Earth and Mars. And 1999 TA10 itself is unique because it appears to be a piece of pure mantle, according to Reddy. Other Vestoids are either purely crust or mantle and crust, meaning they probably weren't as deep inside Vesta as 1999 TA10 had been.

How did Reddy and company figured this?

Their method was to look at how infrared light is reflected and absorbed by 1999 TA10 and comparing it to the way infrared light is reflected and absorbed by different kinds of minerals. In this way, they determined that the asteroid is primarily made of pyroxene, a mineral that forms only in the mantle of a protoplanet or planet.

If 1999 TA10 had to be a piece of something bigger, they further inferred that it likely came from Vesta, which is made of the right kind of stuff, is in the right orbital position and, of course, is in possession of that large crater.

Unanswered

But discovering these things raise more questions about our star system's ancient past, as Reddy's paper acknowledges.

For example, why aren't there more pieces of pure mantle? Answer: Maybe there are and astronomers haven't seen them yet. There are millions of asteroids and not all have been studied as 1999 TA10 has been.

In another example, the paper's authors noted that studies have shown that there were at least two violent impacts involving Vesta and its remnants, an extremely violent one 3.4 billion to 4.1 billion years ago, and a less violent one 22 million to 36 million years ago. You would think it was the first impact that carved out a piece of Vesta's mantle, yet many asteroids that have pieces of mantle, like 1999 TA10, date back only to the second impact. How's that possible?

1999 TA10 itself has not been dated and the paper conjectured that the first impact could've made a crater and second impact in that crater could carved out 1999 TA10 and others like it. On the other hand, the second impact could've struck 1999 TA10 and the asteroids that date back to that second impact came from 1999 TA10.

Those questions will have to await other astronomers.

Reach Tran at (701) 780-1248; (800) 477-6572, ext. 248; or send e-mail to ttran@gfherald.com .