Meteors, NEOs, & PHOs AS3141 Benda Kecil dalam Tata Surya Prodi Astronomi 2007/2008 Budi Dermawan

Meteor Shower

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

Ries 2004

NEOs & Potentially Hazardous Objects (PHOs)

Near-Earth Asteroids (NEAs)

NEAs Orbital Plots Morbidelli et al. 2002

Physical Properties of NEAs (1)

Physical Properties of NEAs (2) Amplitudes & Rotation Rates Taxonomy 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

Ries 2004

Hazardous Objects Comets Asteroids (PHAs)

I m p a c t s Relative cross-section of the Earth: ~1  Increased by gravitational attraction With ~1000 km-sized NEAs, we expect one or two impacts each million years

Ries 2004

Cartoons New Yorker

Ries 2004

The Great Chicxulub Impact  65 Myr Ago Globally Catastrophic Impact End of Cretaceous period

Ries 2004

The Bedout Impact  250 Myr Ago Becker et al Offshore of north-western Australia Globally Catastrophic Impact End of Permian period

Impact Tsunami: Asteroid Eltanin

Impact Tsunami: Asteroid 1950DA (1) Ward & Asphaug 2003

Impact Tsunami: Asteroid 1950DA (2)

Destruction & Fatalities Source: John Pike

Impact Hazard Scale Chesley et al The Palermo Scale PR

99942 Apophis (2004 MN 4 ) 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. 27 th, 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 15 th –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

The End NASA

Geologic Timescale