NEAR EARTH ASTEROIDS (Neas) a CHRONOLOGY of MILESTONES 1800 - 2200
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INTERNATIONAL ASTRONOMICAL UNION UNION ASTRONOMIQUE INTERNATIONALE NEAR EARTH ASTEROIDS (NEAs) A CHRONOLOGY OF MILESTONES 1800 - 2200 8 July 2013 – version 41.0 on-line: www.iau.org/public/nea/ (completeness not pretended) INTRODUCTION Asteroids, or minor planets, are small and often irregularly shaped celestial bodies. The known majority of them orbit the Sun in the so-called main asteroid belt, between the orbits of the planets Mars and Jupiter. However, due to gravitational perturbations caused by planets as well as non- gravitational perturbations, a continuous migration brings main-belt asteroids closer to Sun, thus crossing the orbits of Mars, Earth, Venus and Mercury. An asteroid is coined a Near Earth Asteroid (NEA) when its trajectory brings it within 1.3 AU [Astronomical Unit; for units, see below in section Glossary and Units] from the Sun and hence within 0.3 AU of the Earth's orbit. The largest known NEA is 1036 Ganymed (1924 TD, H = 9.45 mag, D = 31.7 km, Po = 4.34 yr). A NEA is said to be a Potentially Hazardous Asteroid (PHA) when its orbit comes to within 0.05 AU (= 19.5 LD [Lunar Distance] = 7.5 million km) of the Earth's orbit, the so-called Earth Minimum Orbit Intersection Distance (MOID), and has an absolute magnitude H < 22 mag (i.e., its diameter D > 140 m). The largest known PHA is 4179 Toutatis (1989 AC, H = 15.3 mag, D = 4.6×2.4×1.9 km, Po = 4.03 yr). As of 3 July 2013: - 903 NEAs (NEOWISE in the IR, 1 February 2011: 911) are known with D > 1000 m (H < 17.75 mag), i.e., 93 ± 4 % of an estimated population of 966 ± 45 NEAs (NEOWISE in the IR, 1 February 2011: 981 ± 19) (see: http://targetneo.jhuapl.edu/pdfs/sessions/TargetNEO-Session2-Harris.pdf, http://adsabs.harvard.edu/abs/2011ApJ...743..156M), including 160 PHAs. - 9030 NEAs are known with D < 1000 m, including 1251 PHAs. - the estimated total population of all NEAs with D > 140 m (H < 22.0 mag) is ~ 15,000 (NEOWISE: 13,200 ± 1,900); observed: 5679 (~ 38 %), including 1411 PHAs. - the estimated total population of all NEAs with D > 100 m (H < 22.75 mag) is ~ 20,000; observed: 6326 (~ 32 %). - the estimated total population of all NEAs with D > 40 m (H < 24.75 mag) is ~ 300,000; observed: 8111 (~ 3 %). Estimates: http://targetneo.jhuapl.edu/pdfs/sessions/TargetNEO-Session2-Harris.pdf. Further details: http://ssd.jpl.nasa.gov/sbdb_query.cgi. 1 NEA detection summary (PHAs in purple): D (m) > 1000 1000 - 140 140 - 40 40 - 1 total H (mag) < 17.75 17.75 - 22.0 22.0 - 24.75 > 24.75 N Estimated 966 ± 45 ~ 14,000 ~ 285,000 … N Observed 903 (160) 4,776 (1251) 2,432 1,822 9,933 (1411) O/E 93 % ± 4 ~ 34 % ~ 1 % Several astronomical observatories, at one time or another, have carried out Near Earth Object (NEO) search programs, e.g.: - Asiago DLR Asteroid Survey (ADAS), Italy/Germany - Campo Imperatore Near Earth Object Survey (CINEOS), Italy - Catalina Sky Survey (CSS), USA - China NEO Survey / NEO Survey Telescope (CNEOS/NEOST) - European NEA Search Observatories (EUNEASO) - EUROpean Near Earth Asteroid Research (EURONEAR) - IMPACTON, Brasil - Japanese Spaceguard Association (JSGA), Japan - La Sagra Sky Survey (LSSS), Spain - Las Cumbres Observatory Global Telescope Network (LCOGT), USA - Lincoln Near-Earth Asteroid Research (LINEAR), USA - Lowell Observatory Near-Earth Object Search (LONEOS), USA - Near-Earth Asteroid Tracking (NEAT), USA - Panoramic Survey Telescope And Rapid Response System (Pan-STARRS), USA - Spacewatch, USA - Teide Observatory Tenerife Asteroid Survey (TOTAS), Spain - Wide-field Infrared Survey Explorer (WISE), USA. Those observatories as well as many others have been, and/or are also actively participating in follow- up observations. Currently the vast majority of NEA discoveries are being carried out by the Catalina Sky Survey near Tucson (AZ, USA), the LINEAR survey near Socorro (NM, USA), the Pan-STARRS survey on Maui (HI, USA), and, until recently, the NEO-WISE survey of the Wide-field Infrared Survey Explorer (WISE). A review of NEO surveys is given by: Stephen Larson, 2007, in: A. Milani, G.B. Valsecchi & D. Vokrouhlický (eds.), Proceedings IAU Symposium No. 236, Near Earth Objects, our Celestial Neighbors: Opportunity and Risk, Prague (Czech Republic) 14-18 August 2006 (Cambridge: CUP), p. 323, "Current NEO surveys." The following chronology lists (a) data of known NEAs with past nominal Earth close approach distances d < 1.0 LD; (b) data of known NEAs with future nominal Earth close approach distances d < 10.0 LD and minimum close approach distances d < 1.0 LD; and (c) milestones of NEO/NEA research. Information on categories (a) and (b) is quoted from the NASA JPL NEO Program Close Approach Tables for the period 1900 – 2200 A.D. as of 3 July 2013, available at http://neo.jpl.nasa.gov/ca/. By listing in chronological order this broad selection of milestones on NEA research, an impression is offered of what has been done and what is being done in those fields. * * * 2 GLOSSARY AND UNITS GLOSSARY Amor asteroid The Amor asteroids are a group of near-Earth asteroids (NEAs) named after the asteroid 1221 Amor. They have orbital semi-major axes a > 1 AU and perihelium distance 1.0167 < q < 1.3 AU. They approach the orbit of the Earth from beyond, but do not cross it. Most Amors do cross the orbit of Mars. It is estimated that 32% of the total number of NEAs are Amors. Apollo asteroid The Apollo asteroids are a group of near-Earth asteroids named after asteroid 1862 Apollo. They are Earth-crosser asteroids that have orbital semi-major axes greater than that of the Earth (a > 1 AU) and a perihelion distance q < 1.0167 AU. It is estimated that 62% of the total number of NEAs are Apollos. Aten asteroid The Aten asteroids are a group of near-Earth asteroids, named after asteroid 2062 Aten. They have orbital semi-major axes a of less than 1 AU and aphelion distances Q > 0.9833. It is estimated that 6% of the total number of NEAs are Atens. Interior to Earth Orbit (IEO) IEO asteroids have a < 1 AU and Q < 0.983 AU and so never cross Earth's orbit. Main-belt asteroid The asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets. The asteroid belt region is also termed the main belt to distinguish it from other concentrations of minor planets within the Solar System. MOID Minimum Orbit Intersection Distance (see Introduction) NEA Near Earth Asteroid (see Introduction) NEO Near Earth Object (asteroid, comet) PHA Potentially Hazardous Asteroid (see Introduction) UNITS 3 1 Earth Radius (REarth) 6.37103 × 10 km = mean radius of the Earth 5 1 Lunar Distance (LD) 3.84401 × 10 km = 0.00257 AU = 60.34 REarth, the mean distance from the Earth to the Moon 1 Astronomical Unit (AU) 1.495979 × 108 km = 389.17 LD, the mean distance from the Earth to the Sun 3 H magnitude V-band magnitude an asteroid would have at 1 AU distance from the Earth, viewed at opposition * * * 4 CHRONOLOGY 1801, Jan 1 First and largest asteroid discovered, 1 Ceres (H = 3.34 mag, D = 952 km, main-belt asteroid), by Giuseppe Piazzi (1746 – 1826, Italy) at the Osservatorio Astronomico di Palermo. Asteroid Cerere Ferdinandea was named in honour of King Ferdinand IV of Sicily, and later became known simply as Ceres. Carl Gauss developed the math to determine an accurate orbit for Ceres and published his results in November 1801. Given the definition of planets and dwarfplanets accepted by the IAU XXVI General Assembly in 2006, Ceres is considered a dwarf planet rather than an asteroid. See: http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=1+Ceres&orb=1. Ref: - G. Piazzi, 1802, Della scoperta del nuovo planeta Cerere Ferdinandea (Palermo: Nella Stamperia Reale). See also: http://en.wikipedia.org/wiki/Ceres_(dwarf_planet), http://www.space.com/12969-giant-asteroid-ceres-telescopes- skywatching.html. 1803, 26 Apr L'Aigle Meteorite. In the early afternoon of 26 April 1803 a meteorite shower of more than 3000 fragments fell upon the town of L'Aigle (Normandy, France). See: http://en.wikipedia.org/wiki/L'Aigle_(meteorite). 1807, Dec 14 Weston Meteorite. At 6:30 on the morning of 14 December 1807, a blazing fireball about two-thirds the size of the Moon was seen traveling southwards by early risers in Vermont and Massachusetts (USA). Three loud explosions were heard over the town of Weston in Fairfield County, Connecticut. Stone fragments fell in at least 6 places. See: http://peabody.yale.edu/collections/meteorites-and- planetary-science/weston-meteorite, http://en.wikipedia.org/wiki/Weston_meteorite . 1840, Jun 12 Uden Meteorite (Netherlands). A 600 g meteorite was found. See: http://www.dwc.knaw.nl/DL/publications/PU00015500.pdf, http://www.sterrenkunde.nl/index/encyclopedie/meteoren.html. 1843, June 2 Blauwkapel Meteorite (Netherlands). Two pieces were found, of 2.7 and 7 kg. See: http://www.dwc.knaw.nl/DL/publications/PU00015500.pdf, http://www.sterrenkunde.nl/index/encyclopedie/meteoren.html. 1859, Nov 15 New York City Fireball and Airburst (USA). See: http://www.meteoritehistory.info/AJS/S2VIEWS/V30P186.HTM, http://en.wikipedia.org/wiki/List_of_meteor_air_bursts. 1860, Jul 20 The Meteor Procession of 20 July 1860, visible from the Great Lakes to New York State (USA), continuing out over the Atlantic Ocean. 5 Ref: - Walt Whitman, 1859-1860, in Leaves of Grass, "Year of Meteors."; - A.G.