2007 WD5

Minor Planet
name=mp|2007 WD|5
discoverer= Andrea Boattini
discovery_date=November 202007
designations="none"
category=Apollo asteroid,
Mars-crosser asteroid
epoch=April 10, 2007
semimajor= 2.541 AU
perihelion= 1.01016 AU
aphelion= 4.072 AU
eccentricity= 0.60245
period= 1479 days
inclination= 2.371°
asc_node= 67.54°
arg_peri= 312.647°
mean_anomaly= 313.4°
speed= 27,900 miles per hour
dimensions= convert|50|m|ft|-1|lk=on|abbr=on ^{[http://neo.jpl.nasa.gov/glossary/h.html H]}
mass= ?e|9 kg
density= ? g/cm³
gravity= ? m/s²
escape_velocity= ? km/s
rotation= ? d
spectral_class= ?
abs_mag= 24.308
albedo= ?
temperature= ? K

mp|2007 WD|5 is a convert|50|m|ft|-1|lk=on|abbr=on diameter Apollo class [cite web |title =JPL Small-Body Database Browser: 2007WD5 |url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2007wd5| accessdate=2008-01-12] Near-Earth object and a Mars-crosser asteroid discovered on November 202007 by Andrea Boattini of the Catalina Sky Survey. Early observations of 2007 WD₅ caused excitement amongst the scientific community when it was estimated as having as high as a 1 in 25 chance of colliding with Mars on January 30, 2008. However, by January 92008 additional observations allowed NASA's Near Earth Object Program (NEOP) to reduce the uncertainty region resulting in only a 1-in-10,000 chance of impact. mp|2007 WD|5 most likely passed Mars at a distance of 6.5 Mars radii. Due to this relatively small distance and the uncertainty level of the prior observations, the gravitational effects of Mars on its trajectory are unknown and, according to Steven Chesley of NASA's Jet Propulsion Laboratory Near Earth Object program, mp|2007 WD|5 is currently considered as 'lost'. citeweb |last=Lakdawalla |first=Emily |title=WD5 most likely missed Mars, but we may never know |date=February 4, 2008 |url=http://www.planetary.org/blog/article/00001316/ |accessdate=2008-02-24]

Discovery

The asteroid was discovered on November 202007 by Andrea Boattinicite web
date=December 212007
title=Catalina Sky Survey Discovers Space Rock That Could Hit Mars|publisher=The University of Arizona
author=Lori Stiles, University Communications
url=http://uanews.org/node/17415
accessdate=2007-12-23] of the NASA-funded Catalina Sky Survey on Mount Lemmon, near Tucson, Arizona, USA, using a 1.5m telescope.cite web
date=December 212007
title=Recently Discovered Asteroid Could Hit Mars in January|publisher=NASA/JPL Near-Earth Object Program Office
author=Steve Chesley and Paul Chodas
url=http://neo.jpl.nasa.gov/news/news151.html
accessdate=2007-12-21] It was discovered in the constellation Taurus at an apparent magnitude of +20. This is about 400,000 times fainter than most people can see with the naked eye on a dark night far from city lights. It was discovered nineteen days after passing near the Earth. By the time it arrived at Mars it had an apparent magnitude of roughly +26 and appeared over 100x fainter than at the time of discovery. [Horizons Brightness Difference between 11-20-07 and 01-30-08: (5th root of 100) ^ (@marsJan30th APmag 25.9 - DiscoveryNov20th APmag 20.2) = 190x]

January 2008 Mars encounter - chance of impact

Timeline of observations and events

*November 12007: Nineteen days before its discovery, this small asteroid passed within 7.5 million km (5 million miles or 0.0476 AU) of the Earth.

*November 202007: The asteroid was first discovered by Andrea Boattini of the Catalina Sky Survey.

*December 212007: mp|2007 WD|5 was approximately half way between Earth and Mars traveling at convert|27900|mph|lk=on|abbr=on. It was estimated by NASA's Near Earth Object Program (NEOP) to have a 1-in-75 chance of colliding with Mars on January 302008 at approximately 10:55 UT. It was thought it would pass about 50,000 km (0.00034AU) from Mars.

*December 28 2007: NASA scientists at the Near-Earth Object program office at JPL announced they had found mp|2007 WD|5 in 3 precovery images from November 8 2007. The refined orbit placed the odds of a Mars impact at 1-in-25. The uncertainty region was reduced from 1 million km to roughly 400,000 km.cite web
date=December 282007
title=Mars Impact Probability Increases to 4 Percent
publisher=NASA/JPL Near-Earth Object Program Office
author=Don Yeomans, Paul Chodas and Steve Chesley
url=http://neo.jpl.nasa.gov/news/news153.html
accessdate=2007-12-28] The best fit trajectory had the asteroid passing within 21,000 km of Mars and only 16,000 km from the moon Deimos.cite web |url=http://home.comcast.net/~kpheider/2007WD5.txt |title=Horizons Archive Mars/Earth 2003/2008 |accessdate=2007-12-23 (Soln.date: 2007-Dec-23)] The pre-discovery observations were located by Andy Puckett in the archive of the Sloan Digital Sky Survey II at the Apache Point Observatory.

*January 2 2008: NASA scientists revised the probability of an impact with Mars to 1-in-28 after more observations were reported by Bill Ryan with the 2.4 meter telescope at New Mexico Tech's Magdalena Ridge Observatory. The uncertainty region was reduced to roughly 200,000 km and still intersected Mars, but the most likely path moved a little farther away from the planet.cite web
date=January 22008
title= New Observations Slightly Decrease Mars Impact Probability
publisher=NASA/JPL Near-Earth Object Program Office
author=Don Yeomans, Paul Chodas and Steve Chesley
url=http://neo.jpl.nasa.gov/news/news154.html
accessdate=2008-01-02]

*January 8 2008: NASA scientists revised the probability of an impact with Mars to 1-in-40 after refinements to the Sloan precovery observations and observations with the 3.5 meter telescope at the Calar Alto Observatory in Spain. The uncertainty region was reduced by a factor of 3.cite web
date=January 82008
title= Mars Impact Seems Less Likely
publisher=NASA/JPL Near-Earth Object Program Office
author=Steve Chesley, Paul Chodas and Don Yeomans
url=http://neo.jpl.nasa.gov/news/news155.html
accessdate=2008-01-08]

*January 9 2008: Following several new observations NASA reduced the uncertainty region and effectively ruled out a Mars collision. The chance of collision became only 1-in-10,000 (0.01%).cite web
date=January 92008
title= 2007 WD5 Mars Collision Effectively Ruled Out - Impact Odds now 1 in 10,000
publisher=NASA/JPL Near-Earth Object Program Office
author=Steve Chesley, Paul Chodas and Don Yeomans
url=http://neo.jpl.nasa.gov/news/news156.html
accessdate=2008-01-09] The best estimate was that around 12:00 UTC the asteroid passed about 26,000 km (0.00017AU) from the planet's center (about 7 Mars radii from the surface). Analyses show there is no possibility of an impact with either Mars or Earth in the next century.

This trend of increasing probability of impact followed by a dramatic decrease is typical as uncertainties are gradually reduced. In December 2004, a similar trend was observed with 99942 Apophis where the predicted probability of impact with Earth in 2029 at one point reached as high as 2.7%.

Estimates of resulting impact

[

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right|thumb|200px|_NASA_Animation_showing_the_motion_of_the_uncertainty_region_of_2007_WD5_as_it_approaches_Mars._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._December 212007"]

If the asteroid had collided with Mars, it would have hit with a velocity of about 13.5 km/s (8.4 miles per second), and would have produced an explosion equivalent to about 3 megatons of TNT. Due to the thin atmosphere of Mars, it was predicted that the asteroid would have reached the surface intact and blasted out a crater approximately convert|0.8|km|mi|1|lk=on|abbr=on in diameter.cite news
last = Johnson Jr.
first = John
title = Asteroid on track for possible Mars hit
work = Science
publisher = Los Angeles Times
date = 2007-12-21
url = http://www.latimes.com/news/science/la-sci-mars21dec21,0,6729483.story?coll=la-home-center
accessdate = 2007-12-21] A crater this size would be equal to the size of the Meteor Crater in Arizona, USA. NASA officials say if it had hit Mars, it would have done so north of the location of the Opportunity rover.

mp|2007 WD|5 is roughly the size of the cometary object that caused the Tunguska event in 1908, in remote central Siberia, Russia. Due to the Earth's greater gravity an impact with the power of Tunguska is expected to occur once every few hundred years.cite web
title=Tunguska Revision, and a Possible NEA Impact on Mars
publisher=Asteroid and Comet Impact Hazards (NASA)
date=2007-12-21
author=David Morrison
url=http://impact.arc.nasa.gov/news_detail.cfm?ID=179
accessdate =2008-01-03 ] Since Mars has only 1/10th the mass to attract objects, these types of impacts occur roughly every one thousand years on Mars.cite web
title=Astronomers Monitor Asteroid to Pass Near Mars
publisher=NASA/JPL
date=2007-12-21
url=http://www.jpl.nasa.gov/news/news.cfm?release=2007-152
accessdate=2007-12-22 ]

Future encounters

In July 2003, the asteroid passed within 0.012AU of Mars.cite web |url=http://home.comcast.net/~kpheider/2007WD5-0109.txt |title=Horizons Output Mars/Earth 2003/2008 |accessdate=2008-01-09 (Soln.date: 2008-Jan-09)] The exact fate of mp|2007 WD|5 following the January 2008 Mars encounter is unknown although it is most likely that it safely passed the planet at a distance of 6.5 Mars radii. Mars, unlike Jupiter, is not big enough to eject the asteroid from the solar system, however, the gravitation effect from the encounter on the asteroid's trajectory is uncertain and the asteroid is currently considered 'lost'. Assuming mp|2007 WD|5 passed Mars safely, its low inclination to the Ecliptic of only 2.3 degrees and high eccentricity of 0.6 could cause it to swing close to Mars or Earth for years or decades into the future.

ee also

*Comet Shoemaker-Levy 9 (Jupiter Impact 1994)

References

External links

* [http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2007WD5;orb=1 Orbital simulation] from JPL (Java) / [http://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=sb&sstr=2007WD5 Horizons Ephemeris]
* [http://neo.jpl.nasa.gov/ Near Earth Object Program] (at "NASA.gov")
* [http://science.nasa.gov/headlines/y2006/13jun_lunarsporadic.htm A Meteoroid Hits the Moon] (25cm wide) on May 2, 2006
* [http://orbitsimulator.com/gravity/images/MarsDec21.gifGravity Simulator Diagram of Mars Passage] (based on Dec 23rd orbital elements)
* [http://www.lpl.arizona.edu/tekton/crater_c.html Computing Crater Size from Projectile Diameter] (H. Jay Melosh and Ross A. Beyer)
* [http://janus.astro.umd.edu/astro/impact/ Solar System Collisions] (Send an asteroid or comet hurtling toward your favorite planet!)
* [http://www.sciencefriday.com/program/archives/200712281 Science Friday Podcast with Don Yeomans] (2007-12-28)
* [http://www.livescience.com/blogs/2008/01/03/possible-asteroid-strike-on-mars-scientific-paydirt/ Possible Asteroid Strike on Mars: Scientific Paydirt] (2008-01-03)