is an Apollo asteroid some in diameter and a Mars-crosser asteroid first observed on 20 November 2007, by

Andrea Boattini Andrea Boattini (born 16 September 1969) is an Italian astronomer and a prolific discoverer of minor planets and comets. Career After developing a growing interest in minor planets, he graduated in 1996 from the University of Bologna with ...

of the Catalina Sky Survey. Early observations of caused excitement amongst the scientific community when it was estimated as having as high as a 1 in 25 chance of

colliding In physics, a collision is any event in which two or more bodies exert forces on each other in a relatively short time. Although the most common use of the word ''collision'' refers to incidents in which two or more objects collide with great fo ...

with

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin atmos ...

on 30 January 2008. 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. 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 The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedi ...

Jet Propulsion Laboratory The Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center in the City of La Cañada Flintridge, California, United States. Founded in the 1930s by Caltech researchers, JPL is owned by NASA ...

Near-Earth Object program, is currently considered 'lost' (see

lost asteroids A minor planet is "lost" when today's observers cannot find it, because its location is too uncertain to target observations. This happens if the orbital elements of a minor planet are not known accurately enough, typically because the observat ...

Discovery

The asteroid was discovered on 20 November 2007 by Andrea Boattini of the

-funded Catalina Sky Survey on

Mount Lemmon Mount Lemmon, with a summit elevation of , is the highest point in the Santa Catalina Mountains. It is located in the Coronado National Forest north of Tucson, Arizona, United States. Mount Lemmon was named for botanist Sara Plummer Lemmon, ...

, near

Tucson , "(at the) base of the black ill , nicknames = "The Old Pueblo", "Optics Valley", "America's biggest small town" , image_map = , mapsize = 260px , map_caption = Interactive map ...

Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a U.S. state, state in the Southwestern United States. It is the list of U.S. states and territories by area, 6th largest and the list of U.S. states and territories by population, 14 ...

, United States, using a 1.5-meter telescope. It was discovered in the constellation Taurus at an

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

of +20. This is about 400,000 times fainter than most people can see with the

naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection. Vision corrected to normal ...

on a dark night far from city lights. 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.Horizons Brightness Difference between 11-20-07 and 01-30-08: (5th root of 100) ^ (@marsJan30th APmag 25.9 - DiscoveryNov20th APmag 20.2) = 190x

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 AU) of the Earth. *20 November 2007: The asteroid was first discovered by Andrea Boattini of the Catalina Sky Survey. * 21 December 2007: was approximately halfway between Earth and Mars traveling at . It was estimated by NASA's Near Earth Object Program (NEOP) to have a 1-in-75 chance of

with

on 30 January 2008 at approximately 10:55 UT. It was thought it would pass about 50,000 km (0.00034AU) from Mars. * 28 December 2007:

scientists at the Near-Earth Object program office at JPL announced they had found in 3

precovery In astronomy, precovery (short for pre-discovery recovery) is the process of finding the image of an object in images or photographic plates predating its discovery, typically for the purpose of calculating a more accurate orbit. This happens mo ...

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 km. The best fit trajectory had the asteroid passing within 21,000 km of Mars and only 16,000 km from the moon Deimos. (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. * 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 km and still intersected Mars, but the most likely path moved a little farther away from the planet. * 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 The Calar Alto Observatory (Centro Astronómico Hispano en Andalucía or "Spanish Astronomical Centre in Andalusia") is an astronomical observatory located in Almería province in Spain on Calar Alto, a mountain in the Sierra de Los Filabres ra ...

in Spain. The uncertainty region was reduced by a factor of 3. * 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%). 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%. Asteroid 2007 WD5

Estimates of resulting impact

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 The atmosphere of Mars is the layer of gases surrounding Mars. It is primarily composed of carbon dioxide (95%), molecular nitrogen (2.8%), and argon (2%). It also contains trace levels of water vapor, oxygen, carbon monoxide, hydrogen, and no ...

, it was predicted that the asteroid would have reached the surface intact and blasted out a crater approximately in diameter. A crater this size would be equal to the size of the

Meteor Crater Meteor Crater, or Barringer Crater, is a meteorite impact crater about east of Flagstaff and west of Winslow in the desert of northern Arizona, United States. The site had several earlier names, and fragments of the meteorite are official ...

, United States. NASA officials say if it had hit Mars, it would have done so north of the location of the

Opportunity rover ''Opportunity'', also known as MER-B (Mars Exploration Rover – B) or MER-1, is a robotic rover that was active on Mars from 2004 until 2018. ''Opportunity'' was operational on Mars for sols (). Launched on July 7, 2003, as part of NASA' ...

. is roughly the size of the cometary object that caused the

Tunguska event The Tunguska event (occasionally also called the Tunguska incident) was an approximately 12- megaton explosion that occurred near the Podkamennaya Tunguska River in Yeniseysk Governorate (now Krasnoyarsk Krai), Russia, on the morning of June ...

in 1908, in remote central

Siberia Siberia ( ; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part o ...

, Russia. Due to the Earth's greater gravity, an impact with the power of Tunguska is expected to occur once every few hundred years. Since Mars has only 1/10 the mass to attract objects, these types of impacts occur roughly every one thousand years on Mars.

Future encounters

In July 2003, the asteroid passed within 0.012 AU of Mars. (Soln.date: 2008-Jan-09) The exact fate of following the January 2008 Mars encounter is unknown although it likely passed Mars at a distance of 6.5 Mars radii. Mars, unlike

Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousandt ...

, 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 passed Mars safely, its low inclination to the

ecliptic The ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic agai ...

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.

References

External links

CNEOS – Center for Near Earth Object Studies
''JPL–NASA''

(25 cm wide) on 2 May 2006
Gravity Simulator Diagram of Mars Passage
(based on 23 December orbital elements)

(H. Jay Melosh and Ross A. Beyer)
Solar System Collisions
(Send an asteroid or comet hurtling toward your favorite planet!)
Science Friday Podcast with Don Yeomans
(2007-12-28)
Possible Asteroid Strike on Mars: Scientific Paydirt
(2008-01-03) * * * {{DEFAULTSORT:2007 WD5 # Minor planet object articles (unnumbered) Discoveries by Andrea Boattini Mars impact events Lost minor planets 20071120