Meteors, NEOs, & PHOs AS3141 Benda Kecil dalam Tata Surya Prodi Astronomi 2007/2008 Budi Dermawan.
Post on 17-Dec-2015
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Meteoroids Swarm & Size
• When a comet approaches perihelion, sublimation of the nucleus liberates particles trapped in ice of which it is formed
a swarm• When the Earth encounters such a swarm it
intercepts the particles, the more the closer it passes to the orbit of the comet itself
• Size radius: a few tenth mm – a few cm
Samples
Physical Properties of NEAs (2)
Amplitudes & Rotation Rates
Taxonomy
Binzel et al. 2002
Binzel et al. 2002
Spectral Properties
• 25 years ago only 1862 Apollo have spectral properties resembling ordinary-chondrite meteorites
• At presents about 20% NEOs provide a plausible match to ordinary chondrites
Binzel et al. 2002
Continuous Distribution of Spectral Properties(S-type – Meteorites)
A size-dependent trend: smaller NEOs have (on average) younger and fresher surfaces that have not been subjected to possible space-weathering effects
Their spectral properties are most likely to resemble those for meteorites measured in the laboratory
Binzel et al. 2002
I m p a c t s
• Relative cross-section of the Earth: ~110-9
• Increased by gravitational attraction
• With ~1000 km-sized NEAs, we expect one or two impacts each million years
The Great Chicxulub Impact 65 Myr Ago
Globally Catastrophic ImpactEnd of Cretaceous period
The Bedout Impact 250 Myr Ago
Becker et al. 2004
Offshore of north-western Australia
Globally Catastrophic ImpactEnd of Permian period
Impact Tsunami: Asteroid 1950DA (1)
Ward & Asphaug 2003
Ward & Asphaug 2003
99942 Apophis (2004 MN4)
• It would get worse, based on telescopic observations on succeeding nights:– from 1 chance in 200 on Dec. 22, it would go:– to 1 chance in 170 on Dec. 23, – to 1 chance in 60 on Dec. 24 ( TS=4!),– to 1 chance in 40 on Christmas Day, Dec. 25,– to 1 chance in 37 on Dec. 27, and – based on the next night’s data --
would have gone – to 1 chance in 20 on Dec. 28, except that:
• On Dec. 27th, an against-the-odds search for pre-discovery observations of MN4 had an unexpected success:– Marginal, missed, faint images were found on CCD images from the
Spacewatch telescope on March 15th
– We now knew (or did we???): 2004 MN4 would surely miss the Earth in 2029
Preventing Impacts
• Survey and discovery of NEOs
• Accurate orbit determination• Composition and gross
properties• Coordination of astronomical
observations• Studies of impacts and
environmental and social effects
• Mitigation possibilities
New Yorker
PHOs Summary
• Asteroid impacts: rare example of hazard. Low probability but high consequences
• Monitoring observations will significantly improve their encounter distances
• Aware of the efforts supported and operated by international basis for lowering the impact risks
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