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What’s New on the Planets?
Small Bodies of the Solar System
• Asteroids: within the orbit of Jupiter
• Centaurs: Between Jupiter and Neptune
• Kuiper Belt Objects (KBO’s): Beyond
Neptune
• Scattered Disk: Extreme KBO’s
• Comets: Icy bodies with elongated orbits
• Meteoroids: Small objects
– Meteors: vaporize in Earth’s atmosphere
– Meteorites: survive to reach surface
The
Asteroid
Belt,
2001
The
Asteroid
Belt,
2010
Asteroid Discoveries
Asteroids
Year
1
1801
100
1867
500
1902
1,000
1921
2,000
1942
5,000
1972
10,000
1981
20,000
1993
50,000
1999
100,000
2000
200,000
2003
Recent Progress
• 2010 September 2
– 535789
– 251651
– 16154
Minor planets catalogued
Officially numbered
Named
• 2013 February 1
– 604344
– 353926
– 17698
Minor planets catalogued
Officially numbered
Named
Can we predict impacts?
• Incomplete inventory of objects
– May be a million km-sized objects
• Initial observations don't permit completely
accurate predictions
• Comets vent gases and change orbits
• The meaning of probability of impact
– Planets don’t “wander”
– Observational uncertainty
Example, Measuring A Lot
• You measure the lot 5 times, getting 99.7,
99.9, 100.1, 100.0 and 100.3 feet.
• Average = 100
• Best estimate but might not be true value
• Any random measurement has even odds
of being too high or low
• P All 5 too high or low = (1/2)5 = 1/32
• P 4 too high or low = 5/32
• P 3 too high or low = (5*4/2)/32 = 10/32
Impact Probability
Impact Probability
Meteorite
Peekskill,
NY 1992
Chondrite
Stony-Iron Meteorite
Iron Meteorite
Meteo-Wrongs
• Meteorites Never:
– Have internal cavities
– Have layers
– Have veins
– Flatten on impact
– Mold around objects
– Almost never light in color outside
• If you “think” it’s magnetic, it’s not
magnetic
Nope
Nope
Uh-uh
No Way
Nope
Nope
Nope
Tunguska, 1908
Tunguska, 1908
Sikhote-Alin
Fall,
February 12,
1947
Mass =
100,000 Kg
Sikhote-Alin Crater
Sikhote-Alin Crater
Sikhote-Alin Crater
Near Miss, August 10, 1972
1972 Near Miss
• Object was about
the size of a bus
• Entered Atmosphere
over Utah, travelling
north, exited over
Canada
• Velocity 15 km/sec
• Missed by 58 km
Returning to Space
Carangas, Peru, 2007
Carangas, Peru, 2007
Averting Impact Hazards
• Simplest Strategy: Detection + Diversion
• Destruction too unpredictable
– Can object be destroyed?
– “Cookie crumbs have no calories”
– In real life, the pieces matter
• The longer the lead time, the easier
diversion becomes
• Only need a close miss
• Detection is cheap and off-the shelf
Diversion
“The question is: how to do it? These things must
be done … delicately.”
•
•
•
•
•
•
Nukes?
Thrusters?
Space tug?
Gravitational?
Solar Sail
Laser?
Asteroid Itokawa
Space Tug
What is a Planet?
• Ancient: 7 (including sun and moon)
• Copernicus: Sun and moon out, Earth in
(6)
• Uranus, 1781 (7)
• Ceres 1801 (8); 12 by 1850
• Asteroids Out, back to 7
• Neptune 1846 (8) Pluto 1930 (9)
• Kuiper Belt, 1990’s; Pluto out
• This is not over yet.
What is a Planet?
• Current Definition:
– Hydrostatic Equilibrium
– Clears its vicinity
• Will certainly need adjustment in the future
Hydrostatic Equilibrium
Hydrostatic Equilibrium
Clearing
the
Vicinity
Two Coming Comets
• Comets are like cats; they have tails, and they
do precisely what they want. –David Levy
• PANSTARRS
– March-April 2013
– Near Moon on March 12
– Faintly visible to unaided eye?
• ISON
– 800,000 miles from Sun in November 2013
– May be very bright in December
– January 8, 2014, only 2° from Polaris
Ceres and Vesta
Dawn to Vesta and Ceres
• First Mission to use ion propulsion
• First Mission to main belt asteroids
• First Mission to orbit two different bodies
Getting
There
Vesta’s
Huge
Crater
Rocket Science
Dropping the Heat Shield
Curiosity Landing
Where Things Landed
Mount Sharp
Layeerd Rocks
Conglomerate
Layered Rocks
Self Portrait
Drill Holes
Meteorite from Mercury?
Finding Other Solar Systems
The Sample Bias Problem
The Exoplanet Zoo
• Hot Jupiters
– Must have migrated inward
•
•
•
•
Highly eccentric orbits
Super-Earths
Waterworlds?
861 as of February 19, 2013
Kepler
• Monitor 100,000 stars
continuously for 4+
years
• Views an area about
10 degrees across
• Detects transits
• Star dims by 1/10,000