[meteorite-list] An Asteroid Headed Our Way (2004 MN4 - 99942 Apophis)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Jul 25 19:06:12 2005
Message-ID: <200507252305.j6PN5IW27001_at_zagami.jpl.nasa.gov>

http://www.csmonitor.com/2005/0726/p01s04-stss.html

An asteroid, headed our way
By Peter N. Spotts
The Christian Science Monitor
July 26, 2005

Humans live in a vast solar system where 2,000 feet seems a razor-thin
distance.

Yet it's just wide enough to trigger concerns that an asteroid due to
buzz Earth on April 13, 2029 may shift its orbit enough to return and
strike the planet seven years later.

The concern: Within the object's range of possible fly-by distances lie
a handful of gravitational "sweet spots," areas some 2,000 feet across
that are also known as keyholes.

The physics may sound complex, but the potential ramifications are plain
enough. If the asteroid passes through the most probable keyhole, its
new orbit would send it slamming into Earth in 2036. It's unclear to
some experts whether ground-based observatories alone will be able to
provide enough accurate information in time to mount a mission to divert
the asteroid, if that becomes necessary.

So NASA researchers have begun considering whether the US needs to tag
the asteroid, known as 99942 Apophis, with a radio beacon before 2013.

Timing is everything, astronomers say. If officials attempt to divert
the asteroid before 2029, they need to nudge the space rock's position
by roughly half a mile - something well within the range of existing
technology. After 2029, they would need to shove the asteroid by a
distance as least as large as Earth's diameter. That feat would tax
humanity's current capabilities.

NASA's review of the issue was triggered by a letter from the B612
Foundation. The foundation's handful of specialists hope to demonstrate
controlled asteroid-diversion techniques by 2015.

Last Wednesday, representatives from the foundation met with colleagues
at NASA's Jet Propulsion Laboratory (JPL) to review the issue. The
foundation's letter marks the first time specialists in the
asteroid-hazard field have called for a scouting mission to assess such
a threat.

"We understand the risk from this object, and while it's small, it's not
zero," says David Morrison, the senior scientist at NASA's Astrobiology
Institute at the Ames Research Center at Moffett Field, Calif.

The call for a reconnaissance mission also illustrates how far the field
of asteroid-hazard assessment has come.

"Ten years ago, we would have been blissfully ignorant," says Donald
Yeomans, who heads NASA's near-Earth object project at JPL. Today, at
least five programs worldwide are hunting down near-Earth objects. NASA
is well on its way toward achieving its goal of cataloging 90 percent of
the near-Earth objects larger than 0.6 miles across by 2008. And it is
devising ways to ensure that information about potential hazards reaches
top decisionmakers throughout the government.

Based on available data, astronomers give Apophis - a 1,000-foot wide
chunk of space debris - a 1-in-15,000 chance of a 2036 strike. Yet if
the asteroid hits, they add, damage to infrastructure alone could exceed
$400 billion. When the possibility of the asteroid passing through two
other keyholes is taken into account, the combined chance of the
asteroid hitting the planet shifts to 1 in 10,000, notes Clark Chapman,
a senior scientist with the Southwest Research Institute in Boulder, Colo.

"A frequent flier probably would not want to board an airliner if
there's a 1-in-10,000 chance it's going to crash," he says.

The asteroid in question was discovered last June. Initially, it looked
as though it might strike Earth in 2029. But additional observations
eliminated that possibility. Instead the asteroid will come within
22,600 miles of Earth - just inside the altitude where major
communications satellites orbit. The asteroid will be visible to the
naked eye in the night skies over Europe and western Africa, where it
will appear a bit dimmer than the North Star.

But this estimated distance carries an uncertainty that spans several
thousand miles either side of its expected path - a region of space that
includes three gravitational keyholes.

JPL's analysis will look at several factors. One involves estimating
whether additional ground observations will be sufficient to resolve the
question of whether the asteroid will pass through one of the keyholes.
The asteroid belongs to a class known as Atens, which orbit the sun in
less than a year and pass through Earth's orbit. Because Atens spend so
much of their time in the direction of the Sun, observations from Earth
are difficult. After next year, the next opportunity to gather data on
the asteroid from the ground will come in 2012-2013.

In addition, questions remain over how long a tagging mission - and if
necessary a deflection mission - would take to plan and execute. If
missions can be mounted in six years or less, NASA could postpone a
decision to tag the asteroid until 2014. This would give astronomers
time to incorporate their latest observations as they refine
calculations of Apophis's orbit. But if a tagging mission took seven to
eight years and a diversion mission took another 12 years, the case
grows for launching the tagging mission sooner rather than later.

Dr. Yeomans, the head of the near-Earth-object program at JPL, says the
next step is to examine whether additional ground-based observations are
likely to solve the collision riddle in a timely fashion.

"I can't stress this enough: The overwhelming most-likely scenario is
that radar and optical data this year and next or in 2012 and 2013 will
completely remove the impact probabilities," he says.

"If this is the case, why are we worried now? If it's a 1-in-15,000 shot
and we come up a loser," there's still time to mount a tagging and a
deflection mission, he says.
Received on Mon 25 Jul 2005 07:05:18 PM PDT