[meteorite-list] Science's Doomsday Team vs. the Asteroids (2004 MN4)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Apr 11 14:12:28 2005
Message-ID: <200504111811.j3BIBxj17681_at_zagami.jpl.nasa.gov>

http://www.washingtonpost.com/wp-dyn/articles/A38306-2005Apr8.html

Science's Doomsday Team vs. the Asteroids
By Guy Gugliotta
Washington Post
April 9, 2005; Page A01

Astronomer David Tholen spotted it last year in the early evening of
June 19, using the University of Arizona's Bok telescope. It was a new
"near-Earth object," a fugitive asteroid wandering through space to pass
close to Earth.

Tholen's team took three pictures that night and three the next night,
but storm clouds and the moon blocked further observations. They
reported their fixes to the Minor Planet Center in Cambridge, Mass., and
moved on.

Six months later, Tholen's object was spotted again in Australia as
asteroid "2004 MN4." In the space of five days straddling Christmas,
startled astronomers refined their calculations as the probability of
the 1,000-foot-wide stone missile hitting Earth rose from one chance in
170 to one in 38.

They had never measured anything as potentially dangerous to Earth.
Impact would come on Friday the 13th in April 2029.

The holidays and the tsunami in South Asia pushed 2004 MN4 out of the
news, and in the meantime additional observations showed that the
asteroid would miss, but only by 15,000 to 25,000 miles -- about
one-tenth the distance to the moon. Asteroid 2004 MN4 was no false
alarm. Instead, it has provided the world with the best evidence yet
that a catastrophic encounter with a rogue visitor from space is not
only possible but probably inevitable.

It also demonstrated the tenacity of the small band of professionals and
amateurs who track potential impact asteroids, and highlighted the
shortcomings of an international system that pays scant attention to
their work.

"I used to say the total number of people interested in this was no more
than one shift at a McDonald's restaurant," said David Morrison, an
astronomer at NASA's Ames Research Center and a student of near-Earth
objects for nearly three decades. "Now it's maybe two shifts." Awareness
of the apocalyptic potential of near-Earth objects has been slow to
develop. It took years for Nobel laureate Luis Alvarez and his son
Walter to win acceptance for their 1980 research showing that a
near-Earth object impact quite likely caused the extinction of the
dinosaurs 65 million years ago.

"The human brain wouldn't grasp reality until it had somewhat more
direct evidence," said Colorado-based planetary scientist Clark R.
Chapman of the Southwest Research Institute, another longtime expert on
near-Earth objects. "Alvarez provided that."

The vast majority of near-Earth objects are asteroids -- huge rocks or
chunks of iron that travel around the sun in eccentric orbits that cross
Earth's path periodically. The rest are comets -- ancient piles of dust,
stones and ice that come in from the edges of the solar system.

"The good news is that comets represent 1 percent of the danger," said
Donald K. Yeomans, who manages NASA's Near-Earth Object Program at the
Jet Propulsion Laboratory. "The bad news is that should we find one,
there's not a lot we can do about it. . . . We detect them only nine
months from impact."

Asteroids, by contrast, generally offer decades or even centuries of
warning -- unless they are too small to detect, in which case there is
no warning at all. But today's technology enables astronomers to get a
fix on any asteroid capable of causing a global "extinction event" --
six miles in diameter or bigger.

Asteroid 2004 MN4 is a "regional" hazard -- big enough to flatten Texas
or a couple of European countries with an impact equivalent to 10,000
megatons of dynamite -- more than all the nuclear weapons in the world.
Even though it will be a near miss in 2029, that will not be the last word.

"You don't know what the gravitational effect of the Earth will be,"
said Brian G. Marsden, who oversees the hunt for near-Earth objects as
director of the Minor Planet Center at the Harvard-Smithsonian Center
for Astrophysics.

"In 2029, the [close encounter with] Earth will increase the size of the
orbit, and the object could get into a resonance with the Earth," he
added. "You could get orbit matchups every five years or nine years, or
something in between." In fact, 2004 MN4 could come close again in 2034,
2035, 2036, 2037, 2038 or later.

So, what can be done? The first thought, dramatically depicted in the
1998 movies "Deep Impact" and "Armageddon," is to nuke the intruder into
small pieces so it will burn up in Earth's atmosphere.

Many scientists say, however, that this is unacceptably sloppy --
instead of obliterating the target, the bomb could break the asteroid
into large radioactive chunks capable of transforming huge stretches of
Earth into wasteland.

Or the explosion could deflect but not destroy the asteroid, putting it
on a future collision course. A nuclear strategy would also forever
require a stockpile of doomsday weapons.

"The cure's worse than the disease," said former Apollo astronaut
Russell L. "Rusty" Schweickart. He is a board member of the B612
Foundation, a group of experts promoting a space mission by 2015 to send
a "tugboat" spacecraft to a near-Earth object, dock with it and gently
alter its speed enough to change its orbit -- to show that it can be
done. (B612 is the name of the asteroid home of "The Little Prince," in
the Antoine de Saint-Exupery story.) "You want to delay or speed up the
asteroid a little," said Berlin-based Alan Harris, chairman of the
European Space Agency's Near-Earth Object Mission Advisory Panel. "What
kind of surface do you have: Is it rocky? Dusty? Rubbly? How much force
can I apply? I don't want to break it up -- unless I really break it up."

B612 has a design but little money, while ESA has spent only a nominal
amount to study the feasibility of a reconnaissance mission to an
asteroid. NASA, at $4 million a year, is currently the big spender for
near-Earth object research.

With this, NASA maintains a database at JPL to plot and record orbits
for all known near-Earth objects, and contributes money to the Minor
Planet Center and to sky surveys underway at telescopes in Arizona,
California, Hawaii, New Mexico and Australia.

The money was authorized after a push from Congress led by Rep. Dana
Rohrabacher (R-Calif.), a conservative, and former House Science
Committee chairman George E. Brown Jr. (D-Calif.), known as one of
Congress's most liberal members before his death in 1999. "I have a
vision of something terrible happening, and I feel compelled to see that
it doesn't happen," Rohrabacher said.

NASA's task -- which Congress imposed in 1998 -- is to find 90 percent
of the estimated 1,100 near-Earth objects that are one kilometer (0.6
miles) or greater in diameter by 2008. As of mid-March, JPL's database
included 762 of these.

On March 1, Rohrabacher introduced the George E. Brown Jr. Near-Earth
Object Survey Act, mandating $40 million for a two-year start-up to
survey every object 100 meters (328 feet) across or larger, of which
there may be 300,000. To date, Marsden has registered 3,265 near-Earth
objects of all sizes.

Tholen, of the University of Hawaii, is a frequent contributor in the
search for threatening objects. He specializes in "Atens," a subspecies
that orbit mostly between the Earth and the sun and are difficult to see
in the glare of the sun. To spot Atens, astronomers must work at dawn or
dusk.

Tholen's team, on a field trip to the University of Arizona's Steward
Observatory, had booked an hour on the evenings of June 19, 20, 23 and
24, 2004. They found a new Aten on the first evening and saw it again on
the second evening. It was about 106 million miles away.

The team recorded the sightings and sent them electronically to Marsden,
who published the object's position, which he named 2004 MN4 in
accordance with a complicated coding system based on the date of discovery.

Tholen waited for another opportunity, but rain clouds cloaked the sky.
When the storm passed, the moon was squatting right where the team
wanted to look. For the next six months, nobody looked for it.

Then, on Dec. 18, astronomer Gordon Garradd, working at the Siding
Springs telescope in Coonabarabran, Australia, 240 miles northwest of
Sydney, spotted what he thought was a new near-Earth object, "brightly
lit and traveling fast," he recalled. He took four images in his first
set, then followed up with two more sets.

Marsden's team put Garradd's data on the center's Web page, a signal for
astronomers to get more fixes. On Dec. 20, JPL produced its solution.
Chance of impact was one in 2,500 -- nothing to get excited about.
"Usually the probability goes down with more observations," Marsden said.

Not this time. On Dec. 23, the risk rose to one in 270, and rose
steadily over Christmas and beyond. "We'd never had anything this big
come this close, and we'd never predicted anything like it," Marsden
said. "It was quite fantastic." The asteroid was 9 million miles away --
about as close as it would get this trip.

In Tucson, astronomers at the Spacewatch Project, at the University of
Arizona's Lunar and Planetary Laboratory, started searching their
archive. Spacewatch has been surveying the solar system for 20 years,
and precovery is a specialty.

"We store [our images] on DVDs," Spacewatch leader Robert S. McMillan
said. "If there's something that wasn't automatically sorted by our
software, we can usually find it -- if we were looking in the right
place at the right time."

They were. On Dec. 27, Spacewatch astronomers Jeffrey Larsen and Anne
Descour found 2004 MN4 in a series of images taken March 15, more than
three months before Tholen's sighting. They passed the word to JPL,
which issued a news bulletin: "An Earth impact on 13 April 2029 can now
be ruled out."

Since then, astronomers have continued to observe 2004 MN4 whenever
possible, but most of the time it is obscured.

"It would be awfully nice to have information so we don't get
surprised," said Schweickart, who advocates flying a small interceptor
mission to plant a transponder on 2004 MN4 that would constantly radio
its location, tagging it like a grizzly bear. "Our favorite little
asteroid might provide enough reality here to provoke people. Maybe we
should get serious."
Received on Mon 11 Apr 2005 02:11:59 PM PDT