[meteorite-list] Asteroid Impacts: Can We Keep Armageddon At Bay?

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Jul 19 12:11:39 2006
Message-ID: <200607191553.IAA26024_at_zagami.jpl.nasa.gov>

http://news.independent.co.uk/world/science_technology/article1185851.ece

Asteroid impacts: can we keep Armageddon at bay?
The Independent (United Kingdom)
July 19, 2006

It's easy to dismiss asteroid impacts as sci-fi scare stories, but
this month's near-miss raises the question: can we stay off the
collision course? Jimmy Lee Shreeve reports


In most circumstances, 432,000km is a long, long way. But not when that
figure is the distance between a large mass of fast-moving rock and
planet Earth. The number in question comes from a "near miss" that
happened earlier this month, when the asteroid named XP14 passed us at
17km per second.

To put it another way, it came within 1.1 times the moon's average
distance from the Earth, close enough to be officially classified as a
potentially hazardous Near Earth Object (NEO), along with some 782 known
others. With an estimated diameter of up to 800 metres, had XP14 hit
Earth it could have wiped out a small country.

Of course, this fly-by came as no surprise. Scientists tracking the
asteroid knew it would not hit us. Astronomers have been tracking large
asteroids for decades - the first near-Earth asteroid, Eros, was
discovered at the end of the 19th century. But an asteroid would not
have to be massive to pose a serious threat. If an asteroid as small as
40m across hit Earth, it would create a crater 1.25km across - just
think if it hit a city. And these comparatively small chunks of rock are
much harder to find - it is only recently that the hunt for them has begun.

In 1998, the US Congress directed Nasa to start an early warning
programme to locate, by 2020, 90 per cent of NEOs measuring 1km or more.
Nearly 800 have been found so far and it is estimated that there are
around 200 or so to be located. But in December last year the goal was
reset to locating the smaller objects, 140m or larger, still by 2020.

This is a two-edged sword for NEO expert Russell "Rusty" Schweickart.
The former Apollo astronaut - and chairman of the California-based B612
Foundation, an independent organisation founded by a group of astronauts
and scientists dedicated to finding ways to protect us against impact
from space rocks - is pleased that the asteroid threat is being taken
seriously. "My guess is that we're going to find thousands of asteroids
that look like they might hit Earth," he warns. "But, due to lack of
funding, Nasa isn't able to develop technology to deflect any oncoming
asteroids."

Nasa currently receives approximately $3.5m per year to research the
subject. Schweickart insists this is nowhere near enough if we are to
properly protect ourselves. "It's a global threat that a lot of people
are working on, but unfortunately not the government agencies," he says.

The irony for Schweickart is that it wouldn't cost a fortune to divert
potentially hazardous asteroids. "It would cost a few hundred million
dollars, which is what we spend on any run-of-the-mill space launch and
there are several of those a year," he says. "This is a matter of
protecting life on Earth, yet there is great reluctance to provide funding."

Current funding has succeeded in building the first of four dedicated
telescopes. Part of the Panoramic Survey Telescope & Rapid Response
System (Pan-Starrs) project, the Hawaii-based PS1 has just begun
capturing its first test images. Once all four telescopes are up and
running they will be capable of locating 99 per cent of NEOs larger than
300m.

Scientists around the world continually run calculations to predict the
likelihood of the Earth and any given asteroid being in the same place
at the same time. The orbits of asteroids are mapped against Earth's
orbit to predict the probability or otherwise of collision. But even
when the full map has been created, there will always be a need for
monitoring, as asteroids on a harmless trajectory could be knocked on to
collision course if they themselves are hit by objects in space.

The NEO that has scientists most worried is a 580m piece of rock called
VD17. Based on current observations, this asteroid has a 1 in 1,600
chance of striking Earth in 2102 and a 1 in 500,000 chance two years
later. Further observations, however, will refine the orbit calculation
for VD17, and hopefully ease concerns.

Locating Near Earth Objects is one thing. But what do we do if an
asteroid is found to be on collision course with us? Would we nuke it
like Bruce Willis did in the 1998 movie Armageddon? "No, that would be a
very bad idea," says Professor Alan Fitzsimmons of the Department of
Physics and Astronomy at Queen's University, Belfast. He cites two
methods that are considered the most viable. One has been dubbed the
"gravity tractor", which was proposed by Nasa astronauts Edward Lu and
Stanley Love. This would hover above the asteroid's surface, and the
craft's thrusters would be angled outward to avoid blasting the
asteroid's surface, while pushing it away. The small gravity attraction
between the space tractor and the asteroid, which would be enough to
hold the two objects together, would be used as a towline to slowly pull
the object on to a non-threatening orbit.

The downside to this proposal, says Fitzsimmons, is that the space
tractor would need a nuclear rocket to get it off the ground - and Nasa
shelved its project to develop nuclear propulsion in favour of
developing a replacement for the space shuttles. "But the simplest
method," says Fitzsimmons, "would be to fly an unmanned spacecraft into
an oncoming asteroid and knock it off collision course. The viability of
this is being studied by the European Space Agency."

Given that the odds of being struck by an asteroid are relatively slim,
is it worth worrying about at all? "The risk is not quite zero, so
there's always a very small chance that a disaster will happen - and it
could occur at any time," says Dr David Asher of Armagh Observatory, one
of the UK's top astronomical research centres.

In 1908, at Tunguska, a remote area of Siberia, an asteroid thought to
have had a diameter of 50m hurtled through the atmosphere at 11km per
second and exploded 6 to 9km above the ground with a force of 20 million
tons of TNT (the equivalent of 1,000 Hiroshima bombs). It is estimated
that 60 million trees were felled over an area of 2,200 square
kilometres. Miraculously, no one was killed. But according to Asher if
such an object exploded above Hyde Park "it would wipe out everything
within the M25".

"Current models suggest something the size of the asteroid that hit
Tunguska impacts possibly every thousand years," says Fitzsimmons. "But
some astronomers believe it could be more frequent - perhaps every 500
years."

The good news is we're getting close to detecting the vast majority of
asteroids of more than 1km across - nearly 800 have been catalogued.
"We've got about 200 or so to find before we know we're safe over the
next hundred years or so," Fitzsimmons says. But could any of those that
haven't yet been detected sneak in and take us unawares? "In theory,
yes, one could take us by surprise. What you have to remember, however,
is the larger asteroids only hit every million or so years. Which means
we'll probably get away with it."

But does monitoring NEOs for a living mean you live in a constant state
of worry? "I certainly don't lay awake at night worrying about it," says
Kevin Yates, project manager of the Near Earth Objects Information
Centre, which was set up as a public information resource in the wake of
a UK government report into the potential threat from asteroid strikes.
"The fact is, asteroids hits happen very rarely. So we will likely have
enough time to develop the technology to do something about it. Although
no one can be sure - especially considering we don't see the smaller
ones until it's too late..."

The hit parade

* HIT: 65 million years ago

Asteroid crashes into Mexico. The "impact winter" leads to extinction of
the dinosaurs.

* HIT: 50 thousand years ago

40m-diameter space rock plunges into Arizona desert, creating a crater
1.25km across.

* HIT: 35 million years ago

A comet or asteroid 4.8km in diameter strikes Earth in Chesapeake Bay,
about 193km south-east of Washington, DC. The impact creates a 80km-wide
crater that changes the courses of many rivers.

* MISS: 1 Sept, 2000

Asteroid 2000 QW7 comes within 3.8 million km of Earth - leading Liberal
Democrat MP Lembit Opik to declare: "It's not a case of if we will be
hit, it is a question of when. Each of us is 750 times more likely to be
killed by an asteroid than to win this weekend's lottery."

* HIT: 6 June, 2002

An object with an estimated diameter of 10mdetonates in mid-air over the
Mediterranean. The energy released was estimated (from infrasound
measurements) to be equivalent to 12 kilotons of TNT.

* MISS: 18 Aug, 2002

Asteroid 2002 NY40, around 800m in diameter, passes within 483,000km of
Earth, close enough to be seen with binoculars.

* MISS: 3 July, 2006

Asteroid 2004 XP14 passes within 432,308km of Earth.
Received on Wed 19 Jul 2006 11:53:15 AM PDT