= Near Earth Objects = == Finding Them Before They Find Us == === Donald K. Yeomans 2016 paperback Princeton 523.44 Yeo Tigard . $12.77 Abebooks === ------ Manager of NASA's Near-Earth Object Program Office at JPL. He was the Radio Science Team Chief for the Near-Earth Asteroid Rendezvous (NEAR) mission and currently he is the US Project Scientist for the Japanese Hayabusa. ----- .xiii 2013 Feb 15 Asteroid 2012 DA L-class, carbon dominated with calcium and aluminum inclusions, .44 albedo, 20x40m .xiii 2013 Feb 15 Chelyabinsk fireball 23 km altitude 18m diameter 10000 tonnes .xiii 1km asteroid every 500K years . p11 Amor: per 1.017 to 1.3 AU, ap < Mars ~ 1.5 AU . Apollo: per < 1.017 AU, semi > 1 AU . Aten: ap > 0.983 AU, semi < 1 AU . Atiras: ap < 0.983 AU, semi < 1 AU .p19 Neptune 30 AU, Kuiper 35AU to 50 AU (<0.1 Me), Oort >1K to 100K AU (1.6 LY) (4 to 80 Me) .p33 Nice model of planetary formation/migration .p44 Yarkowski, prograde rotation outward .p45 YORP, uneven radiation changes rotation .p50 Moon formed 4.5Gya / Late Heavy Bombardment 3.9 Gya / life evidence 3.5 Gya / Oxygen 2.4 Gya / Eukariotes 2.0 Gya .p56 few known NEO until mid 1990s .p63 Eleanor "Glo" Helin 1932-2009 with Gene Shoemaker at Palomar Schmidt 1973 .p65 Gene and Carolyn Shoemaker to USGS Flagstaff, Helin to JPL .p65 1983 Tom Gehrels and Bob !McMillan, Spacewatch at Steward Obsv. near Tucson, 1989 2K*2K CCD .p69 1998 Spaceguard Goal, 90% of 1-2km NEO over next decad, presumed 14% albedo .p71 [[ https://doi.org/10.1016/j.icarus.2015.05.004 | Allan W. Harris 990 >1Km ]] .p73 [[ https://cneos.jpl.nasa.gov/stats/totals.html | NEA discovery graph ]] book as of 2011/08 .p75 LSST expected to find 90% of >140m objects over 70 years .p76 WISE 2009/12 to 2010/10, NEOWISE [[ https://science.jpl.nasa.gov/people/Mainzer/ | Amy Mainzer]] discovered 135 NEOs and 21 comets .p77 hypothetical NEO IR telescope at Venus distance could see more Aten class .p83 (253) Mathilde density 1.3, rubble pile .p84 (25143) Itokawa, 2005 Hyabusa probe, LL chondritic body .p86 rotation rates from several weeks to 30 seconds (30 meter sized) .p86 faster than 2 hours and rubble pile asteroids fly apart .p87 Fig 6.4, graph of rotation period vs diameter, vast majority of larger asteroids are > 2 hrs .p87 Fig 6.5 (66391) 1999 KW4, 1.6km diameter equatorial bulge and 0.6 km moon, 17.4 hours 2.5 km radius .p102 meteorites: '''some''' asteroids are 100 ppm platinum-group metals (Bushveld is 10ppm) .p104 Obama U.S. National Space Vision 2010, human exploration of NEO by 2025 as step towards Mars .p105 LEO to moon surface 6.3 km/s, to NEO is 5.5 km/s (6 month mission) .p105-7 humans in space suits ... Why not minature teleoperated robots, humans stay in spacecraft? .p107 "The inclusion of astronauts on mission to a near-Earth asteroid would greatly improve the quality of the sample collection process ..." .p109 >100 tonnes per day .p110 17 km/s, pancakes and oblates carrying off heat, small fragments land cool or cold .p111 disintegration and airburst, usually does more damage than impact .p113 crater is 10 to 15 times the diameter of the impactor .p113 impact ocean "cratering" produces shorter wavelengths which decay more rapidly than earthquake tsunamis .p114 [[ http://www.purdue.edu/impactearth/ | Purdue / Melosh impact calculator ]] .p115 table estimates by Yeomans || Diam || est. Number || Diam || est. Number || Diam || est. Number || || 1m || 1 billion || 100m || 20,500 to 36,000 || 1km || 980 to 1,000 || || 10m || 10 million || 140m || 13,000 to 20,000 || 550m || 2,400 to 3,300 || || 30m || 1.3 million || 1km || 980 to 1,000 || 10km || 4 || .p115 DOD satellites observe fireball events every few days, Volkswagen sized a few times per year .p116 Satellite largest 1994 Feb 1 over South Pacific, about 10 meters diameter, about 0.1 per year .p119 Tunguska 1908 June 30, est 40m, 4MT, every few hundred years .p122 comets are well below 1% of NEOs, but impacts by largest are same rarity as asteroids .p125-127 2008 TC3 Oct 7 impact Northern Sudan 2:46 GMT, 4 kg "hundreds" of Almahata Sitta meteorites "Station Six" . 20°43.04'N, 32°30.58'E .p133 NEO (29075) 1950 DA, about 1 km diameter, semimajor axis to 100m radar 2001 Mar .p133 Jon Giorgini, remote possibility of impact 2880 Mar 16, model includes planetary mass uncertainties, several other asteroids, Sun evolution, solar wind, sunlight pressure, and galactic gravitation; Yarkowski effect is largest uncertainty. .p134 (101955) 1999 RQ36 orbit error "several meters", possible impacts late 22nd century. .p134 NASA Goddard OSIRIS-REx rendezvous mission in 2020, sample return in 2023 .p135 [[ https://en.wikipedia.org/wiki/99942_Apophis | (99942) Apophis ]] discovered June 19, 2004 by Roy Tucker et al at Kitt Peak .p135 Near miss (6 Earth radii) 2029 April 13, much less predictable after that, with possible impact 2036 April 13 . "keyhole" - a 610 meter movement in 2029 results in 1 Earth radii deflection in 2036 .p137 2011 CA1 1m diameter passed within 5500 km on February 4 .p140 Deflecting - impact unpredictable for uncharacterized asteroid .p144 Gravity tractor - not much effect, perhaps trim the orbit .p145-148 Nuclear - depends on asteroid, an imbedded 300 kT weapon could deflect, standoff weapon results unpredictable . Keith Holsapple U.Wa., Mark Boslough Sandia, Erik Asphaug UCSC, Pete Schultz Brown, Kevin Jousen Boeing. ----- === How big a rock could a small robot lift on a 1 km diameter, 2g/cm3 asteroid? === ... ignoring separation and balance ... . presume 1 cm² cross section, 1 GPa compression strength, 1e5 N "strength" . mass = (π/6)×2000×1e9 kg ≈ 1e12 kg . gravity = 6.67e-11×1e12/(1e3)² ≈ 7e-5 m/s² . lift mass = 1.4e9 kg = (π/6)×2000*D³ ⇒ 85 meters in diameter For balance, there will be many robots, so the mass could be larger. Probably no point to that, this shows that a herd of very small robots can pick apart and re-assemble a gravel pile asteroid quite efficiently. MoreLater