2007 WD5
Encyclopedia
is a 50 m diameter Apollo
class near-Earth object
and a Mars-crosser asteroid
discovered on November 20, 2007, 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 9, 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
's Jet Propulsion Laboratory
Near-Earth Object program, is currently considered 'lost' (see lost asteroids
).
-funded Catalina Sky Survey
on Mount Lemmon
, near Tucson, Arizona
, USA, using a 1.5m telescope. 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 therefore appeared over 100x fainter than at the time of discovery.
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%.
. 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 0.8 km (0.497098189319845 mi) in diameter. 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
.
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. Since Mars has only 1/10 the mass to attract objects, these types of impacts occur roughly every one thousand years on Mars.
, 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
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.
Apollo asteroid
The Apollo asteroids are a group of near-Earth asteroids named after 1862 Apollo, the first asteroid of this group to be discovered by Karl Wilhelm Reinmuth...
class near-Earth object
Near-Earth object
A near-Earth object is a Solar System object whose orbit brings it into close proximity with the Earth. All NEOs have a perihelion distance less than 1.3 AU. They include a few thousand near-Earth asteroids , near-Earth comets, a number of solar-orbiting spacecraft, and meteoroids large enough to...
and a Mars-crosser asteroid
Mars-crosser asteroid
A Mars-crosser is an asteroid whose orbit crosses that of Mars. The known numbered Mars-crossers are listed here. They include the two numbered Mars trojans 5261 Eureka and ....
discovered on November 20, 2007, by Andrea Boattini
Andrea Boattini
Andrea Boattini is an Italian astronomer, a prolific discoverer of asteroids and comets.After developing a growing interest in minor planets, he graduated in 1996 from the University of Bologna with a thesis on near-Earth objects...
of the Catalina Sky Survey
Catalina Sky Survey
Catalina Sky Survey is a project to discover comets and asteroids, and to search for Near-Earth objects. More specifically, to search for potentially hazardous asteroids , that may pose a threat of impact.-Mission:...
. 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
Impact event
An impact event is the collision of a large meteorite, asteroid, comet, or other celestial object with the Earth or another planet. Throughout recorded history, hundreds of minor impact events have been reported, with some occurrences causing deaths, injuries, property damage or other significant...
with Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
on January 30, 2008. However, by January 9, 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
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
's Jet Propulsion Laboratory
Jet Propulsion Laboratory
Jet Propulsion Laboratory is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. The facility is headquartered in the city of Pasadena on the border of La Cañada Flintridge and Pasadena...
Near-Earth Object program, is currently considered 'lost' (see lost asteroids
Lost asteroids
Lost asteroids or lost planets are asteroids that observers lose track of after discovering. Many early lost asteroids were rediscovered in the 1980s and 1990s, but a number of asteroids and other types of small Solar System bodies continue to be lost...
).
Discovery
The asteroid was discovered on November 20, 2007 by Andrea Boattini of the NASANASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
-funded Catalina Sky Survey
Catalina Sky Survey
Catalina Sky Survey is a project to discover comets and asteroids, and to search for Near-Earth objects. More specifically, to search for potentially hazardous asteroids , that may pose a threat of impact.-Mission:...
on Mount Lemmon
Mount Lemmon
Mount Lemmon is in the Santa Catalina Mountains located in the Coronado National Forest north of Tucson, Arizona, United States. It is above sea-level, and receives approximately 180 inches of snow annually. Mount Lemmon was named in honor of botanist Sarah Lemmon, who trekked to the top of...
, near Tucson, Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...
, USA, using a 1.5m telescope. It was discovered in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Taurus
Taurus (constellation)
Taurus is one of the constellations of the zodiac. Its name is a Latin word meaning 'bull', and its astrological symbol is a stylized bull's head:...
at an apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
of +20. This is about 400,000 times fainter than most people can see with the naked eye
Naked eye
The naked eye is a figure of speech referring to human visual perception unaided by a magnifying or light-collecting optical device, such as a telescope or microscope. Vision corrected to normal acuity using corrective lenses is considered "naked"...
on a dark night far from city lights
Light pollution
Light pollution, also known as photopollution or luminous pollution, is excessive or obtrusive artificial light.The International Dark-Sky Association defines light pollution as:...
. 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 therefore appeared over 100x fainter than at the time of discovery.
Timeline of observations and events
- November 1, 2007: Nineteen days before its discovery, this small asteroid passed within 7.5 million km (5 million miles or 0.0476 AUAstronomical unitAn astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
) of the Earth.
- November 20, 2007: The asteroid was first discovered by Andrea Boattini of the Catalina Sky SurveyCatalina Sky SurveyCatalina Sky Survey is a project to discover comets and asteroids, and to search for Near-Earth objects. More specifically, to search for potentially hazardous asteroids , that may pose a threat of impact.-Mission:...
.
- December 21, 2007: was approximately half way between Earth and Mars traveling at 27900 mph (12,472.4 m/s). It was estimated by NASA's Near Earth Object Program (NEOP) to have a 1-in-25 chance of collidingImpact eventAn impact event is the collision of a large meteorite, asteroid, comet, or other celestial object with the Earth or another planet. Throughout recorded history, hundreds of minor impact events have been reported, with some occurrences causing deaths, injuries, property damage or other significant...
with MarsMarsMars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
on January 30, 2008 at approximately 10:55 UT. It was thought it would pass about 50,000 km (0.00034AU) from Mars.
- December 28, 2007: NASANASAThe National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
scientists at the Near-Earth Object program office at JPLJet Propulsion LaboratoryJet Propulsion Laboratory is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. The facility is headquartered in the city of Pasadena on the border of La Cañada Flintridge and Pasadena...
announced they had found in 3 precoveryPrecoveryPrecovery is a term used in astronomy that describes the process of finding the image of an object in old archived images or photographic plates, for the purpose of calculating a more accurate orbit...
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. The best fit trajectory had the asteroid passing within 21,000 km of Mars and only 16,000 km from the moon DeimosDeimos (moon)Deimos is the smaller and outer of Mars's two moons . It is named after Deimos, a figure representing dread in Greek Mythology. Its systematic designation is '.-Discovery:Deimos was discovered by Asaph Hall, Sr...
. The pre-discovery observations were located by Andy Puckett in the archive of the Sloan Digital Sky SurveySloan Digital Sky SurveyThe Sloan Digital Sky Survey or SDSS is a major multi-filter imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, United States. The project was named after the Alfred P...
II at the Apache Point ObservatoryApache Point ObservatoryThe Apache Point Observatory is located in the Sacramento Mountains in Sunspot, New Mexico 18 miles south of Cloudcroft. The observatory consists of the Astrophysical Research Consortium's 3.5-meter telescope, the Sloan Digital Sky Survey 2.5-m telescope with a 20" photometric telescope,...
.
- 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 ObservatoryMagdalena Ridge ObservatoryMagdalena Ridge Observatory is an astronomical observatory under construction in Socorro County, New Mexico about 20 miles west of the town of Socorro off the exit for Water Canyon US 60. MRO is an entity of New Mexico Tech's Office of Research and Economic Development...
. 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.
- January 8, 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 ObservatoryCalar Alto ObservatoryThe Calar Alto Observatory is an astronomical observatory owned and operated jointly by the Max-Planck-Institut für Astronomie in Heidelberg, Germany, and the Instituto...
in Spain. The uncertainty region was reduced by a factor of 3.
- 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%). 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
99942 Apophis
99942 Apophis is a near-Earth asteroid that caused a brief period of concern in December 2004 because initial observations indicated a small probability that it would strike the Earth in 2029. Additional observations provided improved predictions that eliminated the possibility of an impact on...
where the predicted probability of impact with Earth in 2029 at one point reached as high as 2.7%.
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 TNTTNT equivalent
TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT...
. Due to the thin atmosphere of Mars
Atmosphere of Mars
The atmosphere of Mars is relatively thin and is composed mostly of carbon dioxide . There has been interest in studying its composition since the detection of trace amounts of methane, which may indicate the presence of life on Mars, but may also be produced by a geochemical process, volcanic or...
, it was predicted that the asteroid would have reached the surface intact and blasted out a crater approximately 0.8 km (0.497098189319845 mi) in diameter. A crater this size would be equal to the size of the Meteor Crater
Meteor Crater
Meteor Crater is a meteorite impact crater located approximately east of Flagstaff, near Winslow in the northern Arizona desert of the United States. Because the US Department of the Interior Division of Names commonly recognizes names of natural features derived from the nearest post office, the...
in Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...
, USA. NASA officials say if it had hit Mars, it would have done so north of the location of the Opportunity rover
Opportunity rover
Opportunity, MER-B , is a robotic rover on the planet Mars, active since 2004. It is the remaining rover in NASA's ongoing Mars Exploration Rover Mission...
.
is roughly the size of the cometary object that caused the Tunguska event
Tunguska event
The Tunguska event, or Tunguska blast or Tunguska explosion, was an enormously powerful explosion that occurred near the Podkamennaya Tunguska River in what is now Krasnoyarsk Krai, Russia, at about 7:14 a.m...
in 1908, in remote central Siberia
Siberia
Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...
, Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
. 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 0.012AU of Mars. The exact fate of 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 JupiterJupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
, 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
Ecliptic
The ecliptic is the plane of the earth's orbit around the sun. In more accurate terms, it is the intersection of the celestial sphere with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun...
of only 2.3 degrees and high eccentricity
Orbital eccentricity
The orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...
of 0.6 could cause it to swing close to Mars or Earth for years or decades into the future.
External links
- Orbital simulation from JPL (Java) / Horizons Ephemeris
- Near Earth Object Program (at NASA.gov)
- A Meteoroid Hits the Moon (25 cm wide) on May 2, 2006
- Gravity Simulator Diagram of Mars Passage (based on Dec 23rd orbital elements)
- Computing Crater Size from Projectile Diameter (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)
