[meteorite-list] Sounding an Alarm, Cautiously (2004 MN4)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue May 31 12:26:14 2005
Message-ID: <200505311625.j4VGPZ903718_at_zagami.jpl.nasa.gov>

http://www.thespacereview.com/article/384/1

Sounding an alarm, cautiously
by Jeff Foust
The Space Review
May 31, 2005

The cosmos, it seems, can have a bad sense of timing. While many people
spent the final days before Christmas 2004 preparing for the holiday,
the small group of astronomers devoted to studies of near Earth objects
(NEOs) focused their attention instead on a newly-discovered asteroid,
2004 MN4. That small asteroid, orbit calculations showed, had a small
but non-zero chance of colliding with the Earth on April 13, 2029 - a
Friday, no less. Such impact probabilities are not uncommon,
particularly for asteroids whose orbits are not yet well-determined, and
usually disappear as new observations refine its orbit. Instead, those
observations increased the chance of a impact: by Christmas Eve the
chance of a 2029 collision was 1-in-60, giving 2004 MN4 a rating of 4 on
the 0-to-10 Torino Scale of asteroid impact hazards, the highest such
score to date. This merited a fair amount of media attention, although
perhaps not as much as what would have happened had the impact hazard
not been uncovered during the holiday season.

Two things then happened. First, archival images of 2004 MN4 dating back
to March 2004, months before its discovery, further refined its orbit
and ruled out any chance of a collision in 2029. Second, any media
attention about the threat of an impact, or the all-clear sounded by the
revised calculations, was lost with the December 26 earthquake and
tsunami that killed over 200,000 people. With the threat of a 2029
collision eliminated, and with very real disasters to worry about, 2004
MN4 faded from view. However, it has not been forgotten by a few, who
are trying to build awareness about the potential of an impact not long
after 2029, and the need to develop strategies - technical and
political - to deal with this or any similar impact hazard.
      
Threading the keyhole

Leading the effort to gain attention about the risks posed by 2004 MN4
is Rusty Schweickart, the 69-year-old former Apollo astronaut.
Schweickart now serves as chairman of the B612 Foundation, an
organization established in 2002 with a simple, if heady, mission
statement: "significantly alter the orbit of an asteroid in a controlled
manner by 2015." Such a deflection would be a critical demonstration of
the technologies needed should astronomers discover a NEO on a collision
course with the Earth.

If 2004 MN4 passes through a "keyhole" in 2029 just 640 meters
across - about twice the diameter of the asteroid itself - the object would
enter a trajectory that would result in a collision with the Earth on
April 13, 2036.

However, in a presentation May 20 at the International Space Development
Conference, and in a paper
<http://www.b612foundation.org/papers/Call_for_Action.pdf> published on
the foundation's web site the same day, Schweickart's attention was
focused not on deflecting asteroids but understanding the impact risks
of 2004 MN4. While the asteroid poses no impact threat to the Earth in
2029, it will pass within about 30,000 kilometers of the planet - closer
than satellites in geosynchronous orbit. That passage will be close
enough to allow the Earth's gravity to significantly alter the
asteroid's orbit. The change in the asteroid's orbit will depend on
exactly how close to the Earth 2004 MN4 approaches, a degree of
precision not yet possible with the currently-known orbit of the object.

Schweickart focused on a particular scenario where the 2029 flyby puts
2004 MN4 on a new orbit with a 7:6 resonance with the Earth's: the
asteroid would complete six orbits of the Sun in the time it takes the
Earth to complete seven. That would bring the asteroid back into the
vicinity of the Earth in 2036. (Other scenarios exist that would bring
the asteroid back near the Earth in 2034, 2035, and 2037, but the 2036
opportunity lies closest to the centroid of the error ellipse for the
asteroid's 2029 flyby.) Schweickart added that if 2004 MN4 passes
through a "keyhole" in the error ellipse just 640 meters across - about
twice the diameter of the asteroid itself - the object would enter a
trajectory that would result in a collision with the Earth on April 13,
2036.

Such a collision - admittedly unlikely - would be devastating. The impact
location would be somewhere along a path thousands of kilometers long
but only 51 kilometers across, extending from the Kurile Islands in the
Russian Far East across the North Pacific to the Mexican coast near the
southern tip of Baja California. The path then extends across central
Mexico and into the southern Gulf of Mexico and Caribbean Sea before
terminating in the central Atlantic.

The center of that path lies in the Pacific about 1,100 kilometers from
the coast of southern California. An impact there would create a tsunami
that would strike the California coast with a height in excess of 10
meters, comparable to hard-hit Banda Aceh, Indonesia, in last December's
tsunami, according to a computer model of the impact calculated by
Steven Ward of the University of California Santa Cruz. The rest of the
West Coast of the US, as well as Baja California, would also be
subjected to a powerful tsunami. A model of the economic effects of
impact-induced tsunami estimated that the costs of such an event could
exceed $400 billion, based on globally-averaged infrastructure costs.
Schweickart notes that the actual cost could be significantly higher
given the built-up, valuable nature of the California coast. However,
unlike the December 2004 tsunami, loss of life would presumably be
minimal since people would have up to years of advance notice to
evacuate vulnerable sites.

Why worry now?

While Schweickart makes a compelling case for the potential hazard of a
2036 collision by 2004 MN4, why think about an event that is more than
30 years in the future, and one that, at the present, he estimates has
only a 1-in-10,000 chance of happening? Schweickart believes that,
despite the long lead time, now is the time to at least start
considering what should be done. He noted that if we wait until after
the 2029 flyby - when the asteroid's trajectory and potential impact risk
will be far more certain - any mission to deflect the asteroid will
require a large amount of energy to deflect its orbit: a change in
velocity (delta-v) of about 0.1 meters per second. However, if such a
deflection is attempted prior to the 2029 flyby, far less energy will be
needed - a delta-v of as little as one-millionth of a meter per
second - since such a mission would only have to shift the asteroid's path
out of the 640-meter-wide keyhole.

Working backwards, Schweickart estimates that if an asteroid deflection
mission is completed by 2028, it would need to arrive at the asteroid
and start work by 2026. This, in turn, requires a launch by 2022 or
2023, depending on the spacecraft's trajectory to 2004 MN4. Meeting that
launch window, he concludes, requires making a decision to begin design
and development of that mission by around 2014. This gives astronomers
less than a decade to refine the asteroid's orbit to the point where the
odds of an impact are known well enough to support any decision to
proceed with the mission.

This, though, raises another problem. While the asteroid will be in view
of Earth-based telescopes next year, its orbit will take it out of view,
obscured by the Sun, from mid-2006 through late 2012. After 2013 it will
similarly be out of view until around 2020. This gives astronomers
limited time to refine the asteroid's orbit and thus the odds of a 2036
impact. By next year the odds of an impact, assuming 2004 MN4 is
actually on a collision trajectory, would only be refined to about
1-in-3000, and by 2013 to 1-in-140. Radar observations in 2013 could
further reduce the error by a factor of four, but by the time a decision
would have to be made to develop a costly, risky deflection mission, the
probably of an impact would still lie at only a few percent.

One way to better refine the asteroid's orbit would be to launch a
spacecraft to 2004 MN4 in the next few years and place a radio
transponder on it, allowing it to be tracked even when it is out of view
of Earth-based optical telescopes. Such a mission, which Schweickart
estimates would cost on the order of $300 million (the typical cost of a
NASA Discovery-class planetary science mission), could also carry other
instruments to perform scientific studies of the asteroid. This
additional tracking data from the transponder would refine the
probability of an impact to about 10% at the 2014 decision point. "I
would suggest that a 1-in-10 chance that you're going to have a
$400-billion-plus consequence if this thing hits the Earth is probably
adequate enough justification to decide to go ahead and launch," he
said. "But without the transponder, we're not going to have adequate
enough information."

Schweickart's call for "considered action"

At the conference, and in his paper, Schweickart did not call directly
for planning an asteroid deflection mission, or even demand a robotic
mission to 2004 MN4 to place a transponder there. He said he was well
aware that the current 1-in-10,000 odds of an impact mean that there's a
9,999-in-10,000 chance that this asteroid poses no risk at all in 2036.
The problem, he concluded, is that we don't know for certain what risk
the asteroid poses, and are ill-equipped to deal with an impact hazard
if this or another NEO poses a threat. The 1-in-10,000 current impact
odds are about the same, he noted, that the average American faces in
getting into an auto accident on any given day, risks mitigated with
insurance. "Right now we're driving around the solar system uninsured,"
he said.

Schweickart also stressed that his analysis of the 2036 impact threat
requires additional, independent analysis to verify his conclusions.
Thus, the first recommendation he made at the conference was to ask
Congress to have the National Research Council (NRC), or another entity,
review the impact risk analysis he presented and make a recommendation
on a course of action.

The second recommendation was more general. Right now, Schweickart
noted, there is no office of the US government - not NASA, the Defense
Department, nor another organization - specifically charged with the
responsibility of asteroid impact mitigation and its assorted policy
issues. Specifically, if the US was to deflect an incoming asteroid, any
impact could no longer be considered an act of God. "What if you move it
away from the California coast but put it over Guatemala by accident?"
he asked. Thus, he believes that Congress should have the NRC study the
issue and recommend where in the government such responsibility should lie.

Schweickart made his presentation during a panel session of the
conference devoted to NEO impact threats. Other panelists, while not
fully endorsing Schweickart's recommendations, did agree that NEOs in
general can pose a risk and are worthy of further study. Lindley
Johnson, manager of NASA's NEO observation program, said that continuing
search programs will likely produce an object with an ever greater risk
of impact than 2004 MN4, which Johnson nicknamed "Minnesota 4" because
that state's postal abbreviation is MN. "By the time we get to 2014,
there will probably be some other object with an even higher probability
that what we found" with 2004 MN4, he said. "We won't even be thinking
about Minnesota 4, since there will be something else with an even
higher probability of impact if we continue the search effort and are
able to extend it down to objects with diameters in the 100-meter range."

Another issue not directly addressed by Schweickart's proposal is the
need for regular tracking of already-discovered NEOs. "You have to keep
tracking them because of modeling inadequacies, an understanding of all
the forces than impact an orbit," Johnson said. An example is the
Yarkovsky effect, a force linked to the solar heating of asteroids and
the emission of thermal radiation from them, which Johnson estimated
could alter 2004 MN4's orbit by as much as 20 to 50 meters between now
and 2013.

Johnson agrees with Schweickart that a spacecraft mission to place a
transponder on 2004 MN4 may be worthwhile. "Not only do we need to put a
transponder on it," he said, "we need to put a full science station on
it so we are able to fully characterize it and all the others that are
going to come close to us over the next 10, 20, 30 years."

Also backing the idea of a spacecraft mission to 2004 MN4 is Brian
Marsden, director of the Minor Planets Center at the Harvard-Smithsonian
Center for Astrophysics, the nexus for coordinating NEO observations and
calculating orbits. "It's really a very good idea to think about a
transponder," he said. "We may find that in 2013 the whole thing
disappears, but we do get science out of it."

Marsden also believes that more funding is warranted for NEO studies in
general. In one case, his center was not able to pay a salary for one of
his few employees earlier this year because of a funding glitch. "Really
not enough money is being put into this effort at the present time," he
said.

Whether such funding is forthcoming remains to be seen. Earlier this
month the House Science Committee approved HR 1022, a bill
introduced by Rep. Dana Rohrabacher (R-CA) that would authorize $20
million for NASA in 2006 and 2007 to expand NEO searches to objects as
small as 100 meters across. Schweickart said that he has already been
talking to members of Congress about his two recommendations, but didn't
offer any more details.

Schweickart made it clear he was not trying to raise alarm about 2004
MN4, but instead trying to kickstart the government to think about the
risks of such impacts and the need to plan accordingly. "There's not a
reason in the world for anyone to lose any sleep about this, unless
you're the one assigned responsibility for this," he said. "Then you
should be staying awake a bit."

Such caution was shared by panel moderator Pete Worden, the retired Air
Force general and current University of Arizona astronomy professor who
has sought for years to get the government more interested in NEO impact
risks. "This is a very real issue," he said, "but it also has a rather
large giggle factor."
Received on Tue 31 May 2005 12:25:34 PM PDT


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