"Killer Asteroids . . . and what we can do about them"
by Louise Good
At the January Frontiers of Astronomy Community Lecture in Manoa
(left to right), Ed Lu explains why we must be able to deflect asteroids,
David Tholen defines the properties of asteroids, Robert Jedicke
shows computer simulations, and Nick Kaiser explains how the Pan-STARRS
project "will find killer asteroids before they find us." Photos
by Karen Teramura.
"The chance of any one of us dying in an asteroid impact
is roughly similar to the chances of you dying in a plane crash,
but there is one big difference. Everyone of us is riding in the
same airplane at the same time." So said Ed Lu, the former
IfA solar physicist who is now a NASA astronaut in explaining why
we must be prepared to deflect a large asteroid headed toward Earth.
He participated in a Frontiers of Astronomy Community Lecture, "Killer
Asteroids . . . and what we can do about them" on January
19 at UH Hilo and on January 22 at UH Manoa. Three IfA astronomers,
David Tholen, Robert Jedicke, and Nicholas Kaiser, also spoke.
Lu compared an asteroid headed for a collision with Earth with
two vehicles entering an intersection at the same time. If one speeds
up or slows down even slightly so that they are not in the intersection
at the same time, they will miss each other. Lu proposed building
a gravity tractor--a spaceship that would hover over the asteroid
headed for Earth. Such a spaceship would have enough gravity to
change the speed of the asteroid by 0.001 mph, and if this were
done over a long enough period of time, it could delay or speed
up the asteroid just enough to miss Earth.
Lu explained why it would not be wise to blow up an asteroid: It
would mean that the pieces would probably still hit Earth, doing
considerable damage. He cited the case of Comet Shoemaker-Levy
9, which broke up into several pieces, all of which hit Jupiter.
Lu further explained that trying to land on an asteroid or attach
something to it might not work because many asteroids are essentially
rubble piles held together by gravity. They are not very solid.
Lu advocates a mission to test the gravity tractor before we know
an asteroid is headed our way. He pointed out that, though rare,
major disasters do occur, and that being prepared is better than
cleaning up the mess afterward. Much of the destruction wrought
by Hurricane Katrina could have been prevented if the levees had
been strengthened, and many of the lives lost in the December 2004
tsunami in Asia could have been saved if a tsunami warning system
had been in place. He declared, "If we are wiped out by an
asteroid, it will be our own fault," because unlike people
living in earlier eras, "we do have a space program."
Astronomer Antoinette Cowie (center) examines a meteorite (piece
of an asteroid that made it to Earth) after Ed Lu (lower right)
spoke about gravity tractors at IfA in January. Photo by Karen Teramura.
Speaking first, Tholen told the audience all about asteroids--where
they are and what they are made of. Tholen is a co-discoverer of
the asteroid Apophis, which will miss Earth by only about 24,000
miles in 2029. This close encounter could change the asteroid's
orbit, so that on its next close encounter with Earth in 2036, it
will hit us. Tholen continues to observe Apophis with the UH telescope
on Mauna Kea, "one of the few observatories in the world where
we can still track it because it is so close to the Sun right now." He
said we should know by 2013 whether we will be on a collision course
Jedicke described how laboratory and computer simulations are used
to determine what kind of threat asteroids pose to our planet. It
is those larger than the size of a football field (about 100 yards
in diameter) that we must worry about, since smaller ones burn up
in the atmosphere, he said. (Apophis is about 425 yards in diameter.)
Kaiser likened our current condition to driving down the highway
with our eyes closed because we don't know if there are any
asteroids headed our way. Fortunately, the Pan-STARRS project, which
he heads, will detect at least 90 percent of near-Earth asteroids
that are large enough to pose a threat. He noted that people in
Hawaii are playing key roles in developing the technology for this
project. "The technology is happening fast, the technology
is happening here," Kaiser stated.