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 Allan W. Harris 990 >1Km

• p73 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 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 Purdue / Melosh impact calculator

• p115 table estimates by Yeomans

• 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 (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