page_title: Near-Earth object
section_title: Highly rated risks
hierarchical_section_title: Near-Earth object / History of human awareness of NEOs / Risk / Highly rated risks
caption_attribution_description: English: Arecibo radar image of 1950 DA on 4 March 2001, from a distance of 0.052 AU (22 lunar distances). Vertical resolution is 15 m and horizontal resolution is 0.125 Hz (7.9 mm s^-1 in radial velocity). Image from S. Ostro (JPL).
context_page_description: A near-Earth object is any small Solar System body whose orbit brings it to proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun is less than 1.3 astronomical units. If a NEO's orbit crosses the Earth's, and the object is larger than 140 meters across, it is considered a potentially hazardous object. Most known PHOs and NEOs are asteroids, but a small fraction are comets.
  There are over 20,000 known near-Earth asteroids, over a hundred short-period near-Earth comets, and a number of solar-orbiting meteoroids large enough to be tracked in space before striking the Earth. It is now widely accepted that collisions in the past have had a significant role in shaping the geological and biological history of the Earth. NEOs have become of increased interest since the 1980s because of greater awareness of this potential danger. Asteroids as small as 20 m can damage the local environment and populations. Larger asteroids penetrate the atmosphere to the surface of the Earth, producing craters if they impact a continent or tsunamis if they impact sea.
context_section_description: NASA maintains an automated system to evaluate the threat from known NEOs over the next 100 years, which generates the continuously updated Sentry Risk Table. All or nearly all of the objects are highly likely to drop off the list eventually as more observations come in, reducing the uncertainties and enabling more accurate orbital predictions.
  In March 2002, (163132) 2002 CU11 became the first asteroid with a positive rating on the Torino Scale, with about a 1 in 9,300 chance of an impact in 2049. Additional observations reduced the estimated risk to zero, and the asteroid was removed from the Sentry Risk Table in April 2002. It is now known that in the next two centuries, 2002 CU₁₁ will pass the Earth at a safe closest distance (perigee) of 0.00425 AU (636,000 km; 395,000 mi) on August 31, 2080.
  Asteroid 1950 DA was lost after its 1950 discovery, since its observations over just 17 days were insufficient to determine its orbit; it was rediscovered on December 31, 2000. It has a diameter of about a kilometer (0.6 miles). It was also observed by radar during its close approach in 2001, allowing much more precise orbit calculations. Although this asteroid will not strike for at least 800 years and thus has no Torino scale rating, it was added to the Sentry list in April 2002 because it was the first object with a Palermo scale value greater than zero. The then-calculated 1 in 300 maximum chance of impact and +0.17 Palermo scale value was roughly 50% greater than the background risk of impact by all similarly large objects until 2880. Uncertainties in the orbit calculations were further reduced using radar observations in 2012, and this decreased the odds of an impact. Taking all radar and optical observations until 2015 into account, the probability of impact is, as of March 2018, assessed at 1 in 8,300. The corresponding Palermo scale value of −1.42 is still the highest for all objects on the Sentry List Table. As of May 2019, only one other object (2009 FD) has a Palermo scale value above −2 for a single impact date.
  On December 24, 2004, 370 m (1,210 ft) asteroid 99942 Apophis (at the time known by its provisional designation 2004 MN₄) was assigned a 4 on the Torino scale, the highest rating ever given, as the information available at the time translated to a 2.7% chance of Earth impact on Friday, April 13, 2029. By December 28, 2004, additional observations had produced a smaller uncertainty zone for the 2029 approach which no longer included the Earth. The 2029 risk of impact consequently dropped to zero, but later potential impact dates were still rated 1 on the Torino scale. Further observations lowered this 2036 risk to a Torino rating of 0 in August 2006. As of March 2018, calculations show Apophis has no chance of impacting Earth before 2060.
  In February 2006, (144898) 2004 VD17 has been assigned a Torino Scale rating of 2 due to a close encounter predicted for May 4, 2102. After more precise calculations, the rating was lowered to 1 in May 2006 and 0 in October 2006, and the asteroid was removed from the Sentry Risk Table entirely in February 2008.
  As of March 2018, 2010 RF12 is listed with the highest chance of impacting Earth, at 1 in 20 on September 5, 2095. At only 7 m (23 ft) across, the asteroid however is much too small to be considered a Potentially Hazardous Asteroid and it poses no serious threat: the possible 2095 impact therefore rates only −3.32 on the Palermo Scale. Observations during the August 2022 close approach are expected to ascertain whether the asteroid will impact Earth in 2095.
caption: Radar image of asteroid 1950 DA
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