[meteorite-list] First Strike or Asteroid Impact? The Urgent Need to Know the Difference

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:01:31 2004
Message-ID: <200206061542.IAA22826_at_zagami.jpl.nasa.gov>

http://space.com/scienceastronomy/astronomy/nss_asteroid_020606.html

First Strike or Asteroid Impact? The Urgent Need to Know the Difference
By Leonard David
space.com
06 June 2002
              
DENVER, COLORADO -- Military strategists and space scientists that
wonder and worry about a run-in between Earth and a comet or asteroid
have additional worries in these trying times. With world tensions
being the way they are, even a small incoming space rock, detonating
over any number of political hot-spots, could trigger a country's
nuclear response convinced it was attacked by an enemy.

Getting to know better the celestial neighborhood, chock full of
passer-by asteroids and comets is more than a good idea. Not only can
these objects become troublesome visitors, they are also resource-rich
and scientifically bountiful worlds.

Slowly, an action plan is taking shape.

Noted asteroid and comet experts met here May 23-27, taking part in the
National Space Society's International Space Development Conference
2002.

Sweat the small stuff

Being struck by a giant asteroid or comet isn't the main concern for
Air Force Brigadier General Simon Worden, deputy director of operations
for the United States Space Command at Peterson Air Force Base,
Colorado. He sweats the small stuff.

Worden painted a picture of the next steps needed in planetary defense.
His views are not from U.S. Department of Defense policy but are his
own personal perspectives, drawing upon a professional background of
astronomy.

For example, Worden said, several tens of thousands of years ago an
asteroid just 165-feet (50 meters) in diameter punched a giant hole in
the ground near Winslow, Arizona. Then there was the Tunguska event. In
June 1908, a massive fireball breached the sky, then exploded high
above the Tunguska River valley in Siberia. Thought to be in the range
of 165-feet (50 meters) to 330 feet (100 meters) in size, that object
created a devastating blast equal to a 5 to 10 megaton nuclear
explosion. A similar event is thought to have taken place in the late
1940s in Kazakhstan.

"There's probably several hundred thousand of these 100-meter or so
objects - the kind of ones that we worry about," Worden said. However,
these are not the big cosmic bruisers linked with killing off dinosaurs
or creating global catastrophes.

On the other hand, if you happen to be within a few tens of miles from
the explosion produced by one of these smaller near-Earth objects, "you
might think it's a pretty serious catastrophe," Worden said.

"The serious planetary defense efforts that we might mount in the next
few decades will be directed at much smaller things," Worden said. Some
80 percent of the smaller objects cross the Earth's orbit, "some of
which are potentially threatening, or could be in the centuries ahead,"
he said.

Nuclear trigger

One set of high-tech military satellites is on special round-the-clock
vigil. They perform global lookout duty for missile launches. However,
they also spot meteor fireballs blazing through Earth's atmosphere.
Roughly 30 fireballs detonate each year in the upper atmosphere,
creating equivalent to a one-kiloton bomb burst, or larger, Worden
said.

"These things hit every year and look like nuclear weapons. And a
couple times a century they actually hit and cause a lot of damage,"
Worden said.

"We now have 8 or 10 countries around the world with nuclear
weapons - and not all of them have very good early warning systems. If
one of these things hits, say anywhere in India or Pakistan today, we
would have a very bad situation. It would be awfully hard to explain to
them that it wasn't the other guy," Worden pointed out.

Similarly, a fireball-caused blast over Tel Aviv or Islamabad "could be
easily confused as a nuclear detonation and it may trigger a war,"
Worden said.

Meanwhile, now moving through the U.S. Defense Department circles,
Worden added, is a study delving into issues of possibly setting up an
asteroid warning system. That system could find a home within the
Cheyenne Mountain Complex outside Colorado Springs, Colorado. The
complex is the nerve center for the North American Aerospace Defense
Command (NORAD) and United States Space Command missions.

Next steps

Where do we go from here?

An important step, Worden said, is cataloging all of the objects that
are potentially threatening, down to those small objects that could hit
and destroy a city. To do this type of charting, military strategists
now champion a space-based network of sensors that keep an eye on
Earth-circling satellites. These same space sentinels could serve
double-time and detect small asteroids, he said.

Secondly, more money should be applied to building microsatellites.
Some of these tiny craft might be placed in a kind of sleep mode - put
in parking orbits and ready to spring into action in the event of a
intimidating intruder of the asteroid kind.

For one, these microsatellites can offer "up-close and personal" looks
at menacing objects. Is an asteroid, for example, solid rock or rubble
pile? The answer would make a big difference in dealing with an object
having Earth's name on it. These microsatellites could ram an object
too, adding extra energy to the body and putting it on an
out-of-harms-way trajectory.

"Before we start detonating nuclear weapons in space to move something,
we ought to think long and hard how we really want to do this," Worden
said. "A lot of folks believe the next step for NASA is not go back to
the Moon or on to Mars, but go to the asteroids. That's something we
ought to be thinking about," he added.

Asteroids are interesting from a scientific and space industrialization
basis, as well as being a threat, Worden said.

"For fear - for greed - for curiosity. Asteroids are about the only thing
in space that combine all three of those," Worden concluded.

Unlike the dinosaurs

Advancements are being made to take the edge off impact hazard worry,
said Clark Chapman, planetary scientist at the Southwest Research
Institute in Boulder, Colorado.

"For one, to mitigate impact hazard is simply to hunt for them. In
hunting for them, first we learn that many of the objects aren't going
to hit the Earth. In fact, none of them that we've found so far, that
are large, are going to hit the Earth," Chapman said.

Chapman said that while the impact hazard from large objects is real,
it is very unlikely to happen in our lifetimes. He remarked that he
wasn't sure the logic is in favor of ramping up efforts to search for
every object that might cause a smaller, Tunguska-like blast.

Underscoring the demolition stemming from a mega-Earth impactor,
Chapman said that, indeed, the "potential consequences are horrific,
exceeding any other natural hazard and roughly that of an all-out
nuclear war." Nations do have the wherewithal to avert a threatening
impact, he said.

"Unlike the dinosaurs, the big picture is that we do have the
capability and intelligence to protect ourselves from this threat. The
questions are - will we take a gamble and submit to fate? Or do we
undertake a measured, rationale response? The first element is to
educate ourselves and our leaders about this issue, and rationally
decide what fraction of our budget should be devoted to protecting our
planet," Chapman said.

Lingering hazard

Chapman emphasized that once all the asteroids have been located,
comets remain a "lingering hazard." They can creep into our solar
system on short notice.

Comet Hale-Bopp -- slipping by Earth in 1997 -- was likely 100 times
more massive than the object that wiped out the dinosaurs, Chapman
explained.

"It was a big one, and it was only discovered something like a year
before it came in," Chapman said.

There is a current dilemma, the planetary scientist added.

In the event a hostile object is on a collision course with our home
planet, who does the astronomer call? Furthermore, the existing
infrastructure within which to communicate, then do something about the
troubling impactor, is very disorganized, Chapman emphasized.

"Astronomers are just learning how to communicate. But the relevant
agencies are not prepared to listen and act," Chapman said.

Round-trip rockfest

A top priority on the "to do" list of future space projects is a
"hands-on" near-Earth asteroid (NEA) mission. That's the belief of
planetary scientist, Daniel Durda of the Southwest Research Institute
in Boulder, Colorado. Asteroids are "tempting targets" for human
explorers, he said.

Durda points out that there are about 10,000 near-Earth asteroids
larger than 33 feet (10 meters) across - and they are easier to reach
from an orbital energy standpoint than the surface of the Moon. "That
suggests that there should be many launch opportunities over the course
of any given year," he said.

One prime piece of unreal estate for human exploration, Durda said, is
asteroid 1991 VG. It passed about 1.2 lunar distances of Earth in
December of 1991. The orbit of this tiny world is very Earth-like.

Outbound and return trek times involving asteroid 1991 VG would each be
in the neighborhood of 15 days. Once at the body, a crew could study
the space rock for 30 days. The entire mission would take about two
months, "well within our experience base when you consider the stay
times that we become accustomed to for International Space Station
(ISS) expeditions," Durda said.

"It turns out that during the entire mission, the crew would never
venture farther from Earth than about 4.5 lunar distances. The Earth
would never appear smaller in the sky than the full Moon appears to us
from here on Earth! That's not such a daunting trip at all," Durda
remarked.

Cling ons

Once a crew is on-location at an asteroid, it's not a cakewalk.

Because of the very low surface gravity of a small asteroid -- even one
under a mile (1-kilometer) in diameter sports a gravity only 1/28000th
that of Earth -- operations in the vicinity of a NEA would be more like
docking with and spacewalking around the ISS.

In that sense, Durda said, the experience base we are gaining with
space station hookups and crew members moving about outside the complex
are invaluable. Also, the rapidly changing orbital day-night lighting
conditions are similar to what an astronaut would experience on a
small, rapidly rotating asteroid.

"However, we still need to learn a great deal about interacting with
the surface of a small asteroid in essentially non-existent gravity,"
Durda said. For instance, he added, how will electrostatically charged
dust from an asteroid's surface cling to space suits and equipment? How
might we need to alter or redesign maneuvering backpacks for extended
transportation and navigation around the rocky world?

There are many benefits from visiting a giant hunk of space flotsam.

"The NEAs provide the ideal means to expand our experience base and our
presence beyond low-Earth orbit and beyond the Earth-Moon system,"
Durda said. Asteroid journeys would provide a bonanza of data useful to
asteroid and meteorite science.

"Development of an asteroid visit capability will also give us
invaluable data and skills to develop credible deflection and or
destruction technologies for dealing with the asteroid impact hazard,"
Durda concluded.
Received on Thu 06 Jun 2002 11:42:18 AM PDT