View source for 2007 WD5

{{Short description|Apollo and Mars-crosser asteroid}}
{{Use dmy dates|date=January 2020}}
{{DISPLAYTITLE:{{mp|2007 WD|5}}}}
{{Infobox planet
| minorplanet = yes
| name = {{mp|2007 WD|5}}
| background = #FA8072
| image = 2007wd5.jpg
| caption = Artistic depiction of the [[asteroid]] passing over [[Mars]]
| discovery_ref = <ref name="MPC-2007-WD5" />
| discovered = 20 November 2007
| discoverer = [[Mount Lemmon Survey]]<br />[[Andrea Boattini]]<br />{{small|(unofficial credits)}}
| discovery_site = 
| mpc_name = 
| alt_names = 
| named_after = 
| mp_category = [[Near-Earth object|NEO]]{{·}}[[Apollo asteroid|Apollo]]<ref name="MPC-2007-WD5" /><ref name=jpldata/><br />[[Mars-crosser]]
| orbit_ref = <ref name="jpldata" />
| epoch = 13 January 2016 ([[Julian day|JD]] 2457400.5)
| semimajor = {{Convert|2.4600|AU|Gm|abbr=on}}
| perihelion = {{Convert|0.991120|AU|Gm|abbr=on}}
| aphelion = {{Convert|3.9289|AU|Gm|abbr=on|lk=on}}
| eccentricity = 0.59711
| period = 3.86 [[Julian year (astronomy)|yr]] (1409.3 [[Julian year (astronomy)|d]])
| inclination = 2.4276°
| asc_node = 68.491°
| arg_peri = 309.622°
| mean_anomaly = 49.267[[Degree (angle)|°]]
| avg_speed = {{convert|27900|mi/h|km/s|abbr=on|order=flip}}<ref name="NASA_071221"/>
| dimensions = {{convert|50|m|ft|-1|abbr=on}}<ref name="NEO"/><ref name="h" />
| mass = 
| density = 
| surface_grav = 
| escape_velocity = 
| rotation = 
| spectral_type = 
| abs_magnitude = 24.3
| albedo = 
| single_temperature = 
| mean_motion = {{Deg2DMS|0.25545|sup=ms}} /day
| uncertainty = 5<ref name=jpldata/>{{·}}0<ref name="MPC-2007-WD5" />
| moid = {{Convert|0.0260299|AU|Gm|abbr=on}}
}}

'''{{mp|2007 WD|5}}''' is an [[Apollo asteroid]] some {{convert|50|m|ft|-1|abbr=on}} in diameter<ref name=jpldata /> and a [[Mars-crosser asteroid]] first observed on 20 November 2007, by [[Andrea Boattini]] of the [[Catalina Sky Survey]]. Early observations of {{mp|2007 WD|5}} caused excitement amongst the scientific community when it was estimated as having as high as a 1 in 25 chance of [[impact event|colliding]] with [[Mars]] on 30 January 2008.<ref name="NEO1228"/> However, by 9 January 2008, 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.<ref name="NEO0109"/> {{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 'lost' (see [[lost asteroids]]).<ref name="planetaryorgblog">{{cite web |last=Lakdawalla |first=Emily |title=WD5 most likely missed Mars, but we may never know |date=4 February 2008 |url=https://www.planetary.org/articles/1316 |access-date=24 February 2008| archive-url= https://web.archive.org/web/20080208111123/http://www.planetary.org/blog/article/00001316/| archive-date= 8 February 2008 | url-status= live}}</ref>

== Discovery ==

The asteroid was discovered on 20 November 2007 by Andrea Boattini<ref name="Boattini">{{cite web
  |date=21 December 2007
  |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
  |archive-url=https://web.archive.org/web/20080510115105/http://uanews.org/node/17415
  |url-status=usurped
  |archive-date=10 May 2008
  |access-date=23 December 2007}}</ref> of the [[NASA]]-funded [[Catalina Sky Survey]] on [[Mount Lemmon]], near [[Tucson]], [[Arizona]], United States, using a 1.5-meter telescope.<ref name="NEO">{{cite web
  |date=21 December 2007
  |title=Recently Discovered Asteroid Could Hit Mars in January|publisher=NASA/JPL Near-Earth Object Program Office
  |author=Steve Chesley
  |author2=Paul Chodas
  |name-list-style=amp
  |url=https://cneos.jpl.nasa.gov/news/news151.html
  |access-date=21 December 2007| archive-url= https://web.archive.org/web/20071224120701/http://neo.jpl.nasa.gov/news/news151.html| archive-date= 24 December 2007 | url-status= live}}</ref> It was discovered in the [[constellation]] [[Taurus (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 [[Light pollution|city lights]].<ref name="Boattini"/> It was discovered nineteen days after passing near Earth. By the time it arrived at Mars it had an apparent magnitude of roughly +26 and therefore appeared over 100 times fainter than at the time of discovery.<ref>Horizons Brightness Difference between 11-20-07 and 01-30-08: (5th root of 100) ^ (@marsJan30th [[Apparent magnitude|APmag]] 25.9 - DiscoveryNov20th APmag 20.2) = 190x</ref>

== Orbit ==
[[File:Орбита астероида 2007 WD5.png|thumb|Orbit of 2096 WD5]]
2007 WD5 orbits the Sun at a distance of 2.46 astronomical units. The orbit's eccentricity is 0.59 and its inclination is 2.4°.

== Mars encounter: chance of impact ==

=== Timeline of observations and events ===
* 1 November 2007: Nineteen days before its discovery, this small asteroid passed within 7.5 million km (5 million miles or 0.0476 [[astronomical unit|AU]]) of the Earth.<ref name="NEO"/>
*20 November 2007: The asteroid was first discovered by Andrea Boattini of the [[Catalina Sky Survey]].<ref name="Boattini"/>
* 21 December 2007: {{mp|2007 WD|5}} was approximately halfway between Earth and Mars traveling at {{convert|27900|mph|abbr=on}}. It was estimated by NASA's Near Earth Object Program (NEOP) to have a 1-in-75 chance of [[impact event|colliding]] with [[Mars]] on 30 January 2008 at approximately 10:55 UT.<ref name="NEO"/> It was thought it would pass about 50,000&nbsp;km (0.00034AU) from Mars.
* 28 December 2007: [[NASA]] scientists at the Near-Earth Object program office at [[Jet Propulsion Laboratory|JPL]] announced they had found {{mp|2007 WD|5}} in 3 [[precovery]] images from 8 November 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&nbsp;km.<ref name="NEO1228">{{cite web
  |date=28 December 2007
  |title=Mars Impact Probability Increases to 4 Percent
  |publisher=NASA/JPL Near-Earth Object Program Office
  |author=Don Yeomans
  |author2=Paul Chodas
  |author3=Steve Chesley
  |name-list-style=amp
  |url=http://cneos.jpl.nasa.gov/news/news153.html
  |access-date=28 December 2007| archive-url= https://web.archive.org/web/20071229233152/http://neo.jpl.nasa.gov/news/news153.html| archive-date= 29 December 2007 | url-status= live}}</ref> The best fit trajectory had the asteroid passing within 21,000&nbsp;km of Mars and only 16,000&nbsp;km from the moon [[Deimos (moon)|Deimos]].<ref name="Horizons1223">{{cite web |url=http://home.surewest.net/kheider/astro/2007WD5.txt |title=Horizons Archive Mars/Earth 2003/2008 |access-date=23 December 2007 |url-status=dead |archive-url=https://web.archive.org/web/20120309120516/http://home.surewest.net/kheider/astro/2007WD5.txt |archive-date=9 March 2012 }} (Soln.date: 2007-Dec-23)</ref> The pre-discovery observations were located by Andy Puckett in the archive of the [[Sloan Digital Sky Survey]] II at the [[Apache Point Observatory]].
* 2 January 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&nbsp;km and still intersected Mars, but the most likely path moved a little farther away from the planet.<ref name="NEO0102">{{cite web
  |date=2 January 2008
  |title= New Observations Slightly Decrease Mars Impact Probability
  |publisher=NASA/JPL Near-Earth Object Program Office
  |author=Don Yeomans
  |author2=Paul Chodas
  |author3=Steve Chesley
  |name-list-style=amp
  |url=http://cneos.jpl.nasa.gov/news/news154.html
  |access-date=2 January 2008| archive-url= https://web.archive.org/web/20080105134058/http://neo.jpl.nasa.gov/news/news154.html| archive-date= 5 January 2008 | url-status= live}}</ref>
* 8 January 2008: NASA scientists revised the probability of an impact with Mars to 1-in-40 after refinements to the analysis of 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.<ref name="NEO0108">{{cite web
  |date=8 January 2008
  |title= Mars Impact Seems Less Likely
  |publisher=NASA/JPL Near-Earth Object Program Office
  |author=Steve Chesley
  |author2=Paul Chodas
  |author3=Don Yeomans
  |name-list-style=amp
  |url=http://cneos.jpl.nasa.gov/news/news155.html
  |access-date=8 January 2008| archive-url= https://web.archive.org/web/20080112075051/http://neo.jpl.nasa.gov/news/news155.html| archive-date= 12 January 2008 | url-status= live}}</ref>
* 9 January 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%).<ref name="NEO0109">{{cite web
 |date=9 January 2008 
 |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 
 |author2=Paul Chodas 
 |author3=Don Yeomans 
 |name-list-style=amp 
 |url=http://cneos.jpl.nasa.gov/news/news156.html 
 |access-date=9 January 2008 
 |archive-url=https://web.archive.org/web/20080111142119/http://neo.jpl.nasa.gov/news/news156.html 
 |archive-date=11 January 2008 
 |url-status=live 
}}</ref> The best estimate was that around 12:00 [[UTC]] the asteroid passed about 26,000&nbsp;km (0.00017AU)<ref name="Mars2003"/> 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.<ref name="NEO0109"/> 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%.

[[File:Asteroid 2007 WD5.gif|thumb|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. ''Orbital data as known on 21 December 2007'']]

=== Estimates of resulting impact ===
[[File:Mars asteroid.jpg|right|thumb|Track of asteroid {{mp|2007 WD|5}} over Mars (NASA/JPL)]]

If the asteroid had collided with Mars, it would have hit with a velocity of about 13.5&nbsp;km/s (8.4 miles per second), and would have produced an explosion equivalent to about 3 [[TNT equivalent|megatons of TNT]].<ref name="NEO"/> 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|abbr=on}} in diameter.<ref name="latimes">{{cite news
 |last=Johnson Jr. 
 |first=John 
 |title=Asteroid on track for possible Mars hit 
 |work=[[Los Angeles Times]] 
 |date=21 December 2007 
 |url=http://www.latimes.com/news/science/la-sci-mars21dec21,0,6729483.story?coll=la-home-center 
 |access-date=21 December 2007 
 |archive-url=https://web.archive.org/web/20071222035734/http://www.latimes.com/news/science/la-sci-mars21dec21%2C0%2C6729483.story?coll=la-home-center 
 |archive-date=22 December 2007 
 |url-status=live 
}}</ref> A crater this size would be equal to the size of the [[Meteor Crater]] in [[Arizona]], United States. NASA officials say if it had hit Mars, it would have done so north of the location of the ''[[Opportunity rover|Opportunity]]'' rover.<ref name="Boattini"/>

{{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.<ref name="Tunguska">{{cite web
 |title       = Tunguska Revision, and a Possible NEA Impact on Mars
 |publisher   = Asteroid and Comet Impact Hazards ([[NASA]])
 |date        = 21 December 2007
 |author      = David Morrison
 |url         = http://impact.arc.nasa.gov/news_detail.cfm?ID=179
 |access-date  = 3 January 2008
 |archive-url  = https://web.archive.org/web/20080102075735/http://impact.arc.nasa.gov/news_detail.cfm?ID=179
 |archive-date = 2 January 2008
 |url-status     = dead
}}</ref> Since Mars has only 1/10 the mass to attract objects, these types of impacts occur roughly every one thousand years on Mars.<ref name="NASA_071221">{{cite web
  | title=Astronomers Monitor Asteroid to Pass Near Mars
  | publisher=[[NASA]]/[[Jet Propulsion Laboratory|JPL]]
  | date=21 December 2007
  | url=http://www.jpl.nasa.gov/news/news.cfm?release=2007-152
  | access-date=22 December 2007
| archive-url= https://web.archive.org/web/20071224005122/http://www.jpl.nasa.gov/news/news.cfm?release=2007-152| archive-date= 24 December 2007 | url-status= live}}</ref>

== Future encounters ==

In July 2003, the asteroid passed within 0.012 AU of Mars.<ref name="Mars2003">{{cite web |url=http://home.surewest.net/kheider/astro/2007WD5-0109.txt |title=Horizons Output Mars/Earth 2003/2008 |access-date=9 January 2008 |url-status=dead |archive-url=https://web.archive.org/web/20150403220304/http://home.surewest.net/kheider/astro/2007WD5-0109.txt |archive-date=3 April 2015 }} (Soln.date: 2008-Jan-09)</ref> The exact fate of {{mp|2007 WD|5}} following the January 2008 Mars encounter is unknown although it likely passed Mars 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 minor planet|lost]]'.<ref name="planetaryorgblog"/> Assuming {{mp|2007 WD|5}} passed Mars safely, its low inclination to the [[ecliptic]] of only 2.3 degrees and high [[Orbital eccentricity|eccentricity]] of 0.6 could cause it to swing close to Mars or Earth for years or decades into the future.{{citation needed|date=October 2019}}

== See also ==
* [[C/2013 A1]] - Comet that passed extremely close to Mars on 19 October 2014
* [[Comet Shoemaker–Levy 9]] - Jupiter impact 1994
* [[Impact events on Mars]]

== References ==
{{Reflist
|refs=

<ref name="jpldata">{{cite web
  |type       = 2008-01-09 last obs.
  |title      = JPL Small-Body Database Browser: 2007 WD5
  |url        = http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2007wd5
  |publisher  = Jet Propulsion Laboratory
  |access-date = 2 February 2017}}</ref>

<ref name="MPC-2007-WD5">{{cite web
  |title      = 2007 WD5
  |work       = Minor Planet Center
  |url        = http://www.minorplanetcenter.net/db_search/show_object?object_id=2007+WD5
  |access-date = 2 February 2017}}</ref>

<ref name="h">{{cite web
  |title      = Absolute Magnitude (H)
  |publisher  = NASA/JPL
  |url        = http://cneos.jpl.nasa.gov/glossary/h.html
  |archive-url = https://web.archive.org/web/20010302182040/http://neo.jpl.nasa.gov/glossary/h.html
  |url-status = live
  |archive-date = 2 March 2001
  |access-date= 2 February 2017}}</ref>

}} <!-- end of reflist -->

== External links ==
* [https://cneos.jpl.nasa.gov/ CNEOS – Center for Near Earth Object Studies], ''JPL–NASA''
* [https://web.archive.org/web/20060616011442/http://science.nasa.gov/headlines/y2006/13jun_lunarsporadic.htm A Meteoroid Hits the Moon] (25&nbsp;cm wide) on 2 May 2006
* [http://orbitsimulator.com/gravity/images/MarsDec21.GIF Gravity Simulator Diagram of Mars Passage] (based on 23 December orbital elements)
* [https://web.archive.org/web/20141117083517/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!)
* [https://web.archive.org/web/20080101094420/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)
* {{NeoDys|2007+WD5}}
* {{ESA-SSA|2007WD5}}
* {{JPL small body}}

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{{DEFAULTSORT:2007 WD5}}
[[Category:Apollo asteroids|#]]
[[Category:Minor planet object articles (unnumbered)]]
[[Category:Discoveries by Andrea Boattini]]
[[Category:Mars impact events]]
[[Category:Lost minor planets]]
[[Category:Astronomical objects discovered in 2007|20071120]]
[[Category:Predicted impact events]]