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An asteroid is a minor planet—an object that is neither a true planet nor a comet—that orbits within the inner Solar System. They are rocky, metallic or icy bodies with no atmosphere. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter.
A near-Earth object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun (perihelion) is less than 1.3 astronomical units (AU). If a NEO's orbit crosses the Earth's orbit, and the object is larger than 140 meters (460 ft) across, it is considered a potentially hazardous object (PHO). Most known PHOs and NEOs are asteroids, but a small fraction are comets.
(35396) 1997 XF11, provisional designation 1997 XF11, is a kilometer-sized asteroid, classified as a near-Earth object, Mars-crosser and potentially hazardous asteroid of the Apollo group.
69230 Hermes is a sub-kilometer sized asteroid and binary system on an eccentric orbit, classified as a potentially hazardous asteroid and near-Earth object of the Apollo group, that passed Earth at approximately twice the distance of the Moon on 30 October 1937. The asteroid was named after Hermes from Greek mythology. It is noted for having been the last remaining named lost asteroid, rediscovered in 2003. The S-type asteroid has a rotation period of 13.9 hours. Its synchronous companion was discovered in 2003. The primary and secondary are similar in size; they measure approximately 810 meters (2,700 ft) and 540 meters (1,800 ft) in diameter, respectively.
Catalina Sky Survey is an astronomical survey to discover comets and asteroids. It is conducted at the Steward Observatory's Catalina Station, located near Tucson, Arizona, in the United States.
Roy A. Tucker (1951 – 2021) was an American astronomer best known for the co-discovery of near-Earth asteroid 99942 Apophis (formerly known as 2004 MN4) along with David J. Tholen and Fabrizio Bernardi of the University of Hawaii. He was a prolific discoverer of minor planets, credited by the Minor Planet Center with the discovery of 702 numbered minor planets between 1996 and 2010. He also discovered two comets: 328P/LONEOS–Tucker and C/2004 Q1, a Jupiter-family and near-parabolic comet, respectively.
99942 Apophis is a near-Earth asteroid and a potentially hazardous object with a diameter of 370 metres that caused a brief period of concern in December 2004 when initial observations indicated a probability up to 2.7% that it would hit Earth on April 13, 2029. Additional observations provided improved predictions that eliminated the possibility of an impact on Earth in 2029. Until 2006, a small possibility nevertheless remained that, during its 2029 close encounter with Earth, Apophis would pass through a gravitational keyhole of no more than about 800 kilometres (500 mi) in diameter, which would have set up a future impact exactly seven years later on April 13, 2036. This possibility kept it at Level 1 on the Torino impact hazard scale until August 2006, when the probability that Apophis would pass through the keyhole was determined to be very small and Apophis's rating on the Torino scale was lowered to zero. By 2008, the keyhole had been determined to be less than 1 km wide. During the short time when it had been of greatest concern, Apophis set the record for highest rating ever on the Torino scale, reaching level 4 on December 27, 2004.
2007 WD5 is an Apollo asteroid some 50 m (160 ft) in diameter and a Mars-crosser asteroid first observed on 20 November 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 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. 2007 WD5 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, 2007 WD5 is currently considered 'lost' (see lost asteroids).
2008 TC3 (Catalina Sky Survey temporary designation 8TA9D69) was an 80-tonne (80-long-ton; 90-short-ton), 4.1-meter (13 ft) diameter asteroid that entered Earth's atmosphere on October 7, 2008. It exploded at an estimated 37 kilometers (23 mi) above the Nubian Desert in Sudan. Some 600 meteorites, weighing a total of 10.5 kilograms (23.1 lb), were recovered; many of these belonged to a rare type known as ureilites, which contain, among other minerals, nanodiamonds.
A potentially hazardous object (PHO) is a near-Earth object – either an asteroid or a comet – with an orbit that can make close approaches to the Earth and which is large enough to cause significant regional damage in the event of impact. They are conventionally defined as having a minimum orbit intersection distance with Earth of less than 0.05 astronomical units and an absolute magnitude of 22 or brighter, the latter of which roughly corresponds to a size larger than 140 meters. More than 99% of the known potentially hazardous objects are no impact threat over the next 100 years. As of September 2022, just 17 of the known potentially hazardous objects listed on the Sentry Risk Table could not be excluded as potential threats over the next hundred years. Over hundreds if not thousands of years though, the orbits of some "potentially hazardous" asteroids can evolve to live up to their namesake.
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 observation arc for the object is too short, or too few observations were made before the object became unobservable.
The 2009 Jupiter impact event, occasionally referred to as the Wesley impact, was a July 2009 impact event on Jupiter that caused a black spot in the planet's atmosphere. The impact area covered 190 million square kilometers, similar in area to the planet's Little Red Spot and approximately the size of the Pacific Ocean. The impactor is estimated to have been about 200 to 500 meters in diameter.
2010 KQ is a small asteroid-like object that has been discovered in an orbit about the Sun that is so similar to the Earth's orbit that scientists strongly suspect it to be a rocket stage that escaped years ago from the Earth–Moon system. The object was discovered on May 16, 2010 by Richard Kowalski at the Catalina Sky Survey, and has subsequently been observed by many observers, including Bill Ryan and Peter Birtwhistle (England). It was given the asteroid designation 2010 KQ by the Minor Planet Center in Cambridge, Massachusetts, who identified its orbit as being very similar to that of the Earth.
238P/Read is a main-belt comet discovered on 24 October 2005 by astronomer Michael T. Read using the Spacewatch 36-inch telescope on Kitt Peak National Observatory. It has an orbit within the asteroid belt and has displayed the coma of a traditional comet. It fits the definition of an Encke-type comet with.
367943 Duende (provisional designation 2012 DA14) is a micro-asteroid and a near-Earth object of the Aten and Atira group, approximately 30 meters (98 ft) in diameter. It was discovered by astronomers of the Astronomical Observatory of Mallorca at its robotic La Sagra Observatory in 2012, and named for the duende, a goblin-like creature from Iberian and Filipino mythology and folklore. Duende is likely an uncommon L-type asteroid and significantly elongated. For an asteroid of its size, it has a relatively long rotation period of 9.485 hours.
2014 AA was a small Apollo near-Earth asteroid roughly 2–4 meters in diameter that struck Earth on 2 January 2014. It was discovered on 1 January 2014 by Richard Kowalski at the Mount Lemmon Survey at an apparent magnitude of 19 using a 1.52-meter (60 in) reflecting telescope at Mount Lemmon Observatory. 2014 AA was only observed over a short observation arc of about 70 minutes, and entered Earth's atmosphere about 21 hours after discovery. Nonetheless, it remains one of only a few asteroids observed before impact.
(177049) 2003 EE16, provisionally known as 2003 EE16, is an Apollo near-Earth asteroid and potentially hazardous object. It was discovered on 8 March 2003 by LPL/Spacewatch II at an apparent magnitude of 20 using a 1.8-meter (71 in) reflecting telescope. It has an estimated diameter of 320 meters (1,050 ft). The asteroid was listed on Sentry Risk Table with a Torino Scale rating of 1 on 2 April 2003.
2018 LA, also known as ZLAF9B2, was a small Apollo near-Earth asteroid 2.6–3.8 m (9–12 ft) in mean diameter that impacted the atmosphere with small fragments reaching the Earth at roughly 16:44 UTC on 2 June 2018 near the border of Botswana and South Africa. It had been discovered only 8 hours earlier by the Mount Lemmon Survey, Arizona and based on 1+1⁄2 hours of observations, was calculated to have a roughly 85% chance of impact likely somewhere between Australia and Madagascar.
2019 MO, temporarily designated A10eoM1, was a small, harmless 3-meter near-Earth asteroid discovered by ATLAS–MLO that impacted Earth's atmosphere on 22 June 2019 at 21:25 UT. The impact of the bolide generated a 5-kiloton-equivalent explosion off the south coast of Puerto Rico which was detected by infrasound detectors. The strewn field would be spread over the Caribbean Sea.
References
- ↑ Richard Kowalski (21 July 2008). "10 Years of the Minor Planet Mailing List". Minor Planet Mailing List. Archived from the original on January 5, 2013. Retrieved 2009-12-22.
- ↑ D. Nesvorný; D. Vokrouhlický (2006). "New Candidates for Recent Asteroid Breakups". Astronomical Journal . 132 (5): 1950–1958. Bibcode:2006AJ....132.1950N. CiteSeerX 10.1.1.693.3963 . doi:10.1086/507989. S2CID 54038063.
- ↑ Comba, P. G. (1999). Paul G. Comba (ed.). "Proceedings of the 1999 Minor Planet Amateur/Professional Workshop". 1999 Minor Planet Amateur/Professional Workshop. Proceedings. Bibcode:1999mpap.work.....C.
- ↑ Steve Chesley; Paul Chodas; Don Yeomans (4 November 2008). "Asteroid 2008 TC3 Strikes Earth: Predictions and Observations Agree". NASA/JPL. Archived from the original on 17 January 2009. Retrieved 2009-12-22.
- ↑ Richard Kowalski (21 September 2009). "2008 TC3 to Almahatta Sitta and back to Tucson". Minor Planet Mailing List. Archived from the original on July 18, 2012. Retrieved 2009-12-22.
- ↑ NASA (3 January 2014). "The First Discovered Asteroid of 2014 Collides With The Earth - An Update". Archived from the original on 7 January 2014.
- ↑ Kelly Beatty - Sky & Telescope (3 January 2014). "Small Asteroid 2014 AA Hits Earth".
- ↑ Farnocchia, Davide; Chesley, Steven R.; Brown, Peter G.; Chodas, Paul W. (1 August 2016). "The trajectory and atmospheric impact of asteroid 2014 AA". Icarus . 274: 327–333. Bibcode:2016Icar..274..327F. doi:10.1016/j.icarus.2016.02.056.
- ↑ de la Fuente Marcos, C.; de la Fuente Marcos, R.; Mialle, P. (13 October 2016). "Homing in for New Year: impact parameters and pre-impact orbital evolution of meteoroid 2014 AA". Astrophysics and Space Science . 361 (11): 358 (33 pp.). arXiv: 1610.01055 . Bibcode:2016Ap&SS.361..358D. doi:10.1007/s10509-016-2945-3. S2CID 119251345.
- ↑ "7392 Kowalski (1984 EX)". JPL Small-Body Database Browser. NASA/JPL . Retrieved 2009-12-22.