[meteorite-list] 2007 WD5 Mars Collision Effectively Ruled Out - Impact Odds now 1 in 10, 000

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 9 Jan 2008 16:43:32 -0800 (PST)
Message-ID: <200801100043.QAA14199_at_zagami.jpl.nasa.gov>

http://neo.jpl.nasa.gov/news/news156.html

2007 WD5 Mars Collision Effectively Ruled Out - Impact Odds now 1 in 10,000
Steve Chesley, Paul Chodas and Don Yeomans
NASA/JPL Near-Earth Object Program Office
January 9, 2008

Since our last update, we have received numerous tracking measurements
of asteroid 2007 WD5 from four different observatories. These new data
have led to a significant reduction in the position uncertainties during
the asteroid's close approach to Mars on Jan. 30, 2008. As a result, the
impact probability has dropped dramatically, to approximately 0.01% or 1
in 10,000 odds, effectively ruling out the possible collision with Mars.

Our best estimate now is that 2007 WD5 will pass about 26,000 km from
the planet's center (about 7 Mars radii from the surface) at around
12:00 UTC (4:00 am PST) on Jan. 30th. With 99.7% confidence, the pass
should be no closer than 4000 km from the surface.

[Graphic]
Updated Uncertainty Region for 2007 WD5 at encounter with Mars, shown as
white dots. The thin white line is the orbit of Mars. The blue line
traces the motion of the center of the uncertainty region, which is the
most likely position of the asteroid. Image of 2007 WD5 from the
University of Hawaii 2.2-meter telescope on Mauna Kea, Hawaii.

[Image]
Image of 2007 WD5 from the University of Hawaii 2.2-meter telescope on
Mauna Kea, Hawaii. The circled dot is the asteroid. Other dots are
artifacts from cosmic rays. The stars are trailed because the telescope
is tracking the asteroid as it moves among the stars. (Credit: Tholen,
Bernardi, Micheli with support from the National Science Foundation).

The sequence of updates over the last few weeks has been typical of past
potential impact scenarios, with the odds of impact initially surging
and later plummeting towards zero. Early on, the uncertainty region is
very large and the probability of impact is rather low. As the
uncertainty narrows, but still includes the planet, the probability
initially increases. But eventually, as in this case, the uncertainty
region shrinks to the point that it no longer overlaps the planet, and
the probability of impact begins a precipitous decline. This rise and
fall of the computed hazard was most notably seen in Dec. 2004 when
asteroid 99942 Apophis briefly reached a 2.7% chance of impact with
Earth in April 2029. In every case, the height and the timing of the
peak probability - and the subsequent decline - cannot be known until
the uncertainty region has shrunk to the point where it no longer
intersects the planet.

NASA's Spaceguard Survey continues searching for Near-Earth Asteroids
such as 2007 WD5, endeavoring to discover 90% of those larger than 1 km
in size, a goal that should be met within the next few years. Each
discovered asteroid is continually monitored for the possibility of
impact. For 2007 WD5, these analyses show there is no possibility of
impact with either Mars or Earth in the next century.

This unfolding story and the present results have been made possible by
the tracking efforts of many astronomers at several observatories around
the world:

    * 2007 WD5 was discovered using the Mt. Lemmon 1.5-meter telescope
      by Andrea Boattini of the University of Arizona's Catalina Sky
      Survey, which is led by Steve Larson.

    * Follow-up from archival images taken by the 1.8-meter telescope on
      Kitt Peak in Arizona were provided by Terrence H. Brezzi of the
      University of Arizona's Spacewatch Project, which is led by Robert
      McMillan.

    * Andy Puckett of the Univ. of Alaska obtained pre-discovery
      measurements from archival images of the Sloan Digital Sky
      Survey?s 2.5-meter telescope on Apache Point, NM.

    * Bill Ryan of New Mexico Tech's Magdalena Ridge Observatory
      observed 2007 WD5 on several crucial nights, with critical support
      from university and observatory staff.

    * Observations from the 6.5-meter Multi-Mirror Telescope (MMT)
      Observatory in Arizona were provided by a team consisting of
      Holger Israel (Univ. Bonn), Matt Holman (Harvard/CfA), Steve
      Larson (Univ. Ariz.), Faith Vilas (MMTO), Cesar Fuentes
      (Harvard/CfA), David Trilling (Univ. Ariz.) and Maureen Conroy
      (Harvard/CfA).

    * The 3.5-meter telescope at the Calar Alto Observatory in Spain
      provided follow-up through a team consisting of Adriano Campo
      Bagatin (Univ. Alicante), Gilles Bergond (Calar Alto Obs.), Rene
      Duffard (Inst. de Astrofisica de Andalucia), Jose Luis Ortiz
      (Inst. de Astrofisica de Andalucia), Reiner Stoss (Obs.
      Astronomico de Mallorca and Astronomisches Rechen-Institut) and
      Javier Licandro (Inst. de Astrofisica de Canarias).

    * Fabrizio Bernardi, Marco Micheli and Dave Tholen of the Univ. of
      Hawaii Institute for Astronomy observed the asteroid at its
      faintest using the 2.2-meter UH telescope on Mauna Kea in Hawaii.
Received on Wed 09 Jan 2008 07:43:32 PM PST