Meteors, NEOs, & PHOs

AS3141 Benda Kecil dalam Tata SuryaProdi Astronomi 2007/2008Budi 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

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

Ries 2004

Ries 2004

Ries 2004

Hazardous Objects

• Comets

• Asteroids (PHAs)

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

Ries 2004

CartoonsNew Yorker

Ries 2004

The Great Chicxulub Impact 65 Myr Ago

Globally Catastrophic ImpactEnd of Cretaceous period

Ries 2004

The Bedout Impact 250 Myr Ago

Becker et al. 2004

Offshore of north-western Australia

Globally Catastrophic ImpactEnd of Permian period

Impact Tsunami:Asteroid Eltanin

Impact Tsunami: Asteroid 1950DA (1)

Ward & Asphaug 2003

Ward & Asphaug 2003

Impact Tsunami: Asteroid 1950DA (2)

Destruction & Fatalities

Source: John Pike

Impact Hazard Scale

Chesley et al. 2002

The Palermo ScalePR

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

The End

NASA

Geologic Timescale