Asteroids

updated july 19, 2009

Titius-Bode Law (1766)

• The distances between the planets gets bigger as you go out.

• Titius & Bode came up with a law that predicted the size of the orbits

• BIG gap between Mars (1.6 AU) & Jupiter (5.2 AU).

• Predict planet at 2.8 AU

Johann Elert Bode (1747 - 1826)

Johann Daniel Titius( 1729 – 1796)

Titius-Bode Law

Mercury

VenusEarth

Mars

Jupiter

Saturn

uranus

y = 0.2387x - 0.6824

R2 = 0.9945

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-0.5

0

0.5

1

1.5

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0 1 2 3 4 5 6 7 8

Lo

g(A

U) Missing Planet

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Ceres Discovered 1801

• First Asteroid discovered by accident by Piazzi 1801

• It’s the biggest, 950 km in diameter (small compared to moon)

• Contains 32% of mass of entire asteroid belt!

• Combined mass of all asteroids is only 4% of earth’s moon

Giuseppe Piazzi.

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Orbit of 1 Ceres4

Structure of Ceres

• Mass determined from perturbations on another asteroid [348 May] which make 3 close approaches between 1891 and 1984.

• Interior is possibly rocky core with icy mantle 60 to 120 km thick (containing about as much as all the fresh water on the earth).

• Dawn Mission (2007) will arrive at Ceres in 2017

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The “Minor Planets”

Name Date Orbit AU

Size (km)

Notes

1 Ceres 1801 2.76 950 Biggest

2 Pallas 1802 2.77 500 Share orbit with Ceres

3 Juno 1804 2.67 235 Stony

4 Vesta 1807 2.36 530 Brightest, Calcium on surface

Sizes determined from occultations of stars by the asteroid

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Vesta probably is DifferentiatedMeteorites with Calcium in them possibly come from Vesta!

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No more found for 38 years

• In 1830 more discovered(1 per year)

• Now several hundred thousand are known between Mars and Jupiter

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•90% of asteroids are in the Asteroid Belt between Mars and Jupiter

•136,000 cataloged

• 13,500 have

official names.

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Jupiter’s gravity helped shape the asteroid belt

• Even today, gravitational perturbations by Jupiter deplete certain orbits within the asteroid belt

• The resulting gaps, called Kirkwood gaps, occur at simple fractions of Jupiter’s orbital period

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Apollo Asteroids

• First Discovered 1932• Cross Orbit of Earth• Icarus goes closer to sun

than Mercury!

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Jupiter’s gravity also captures asteroids in two locations, called Lagrangian points, along Jupiter’s orbit

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Hilda Asteroids

are in a 3/2 resonance with Jupiter

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Several small bodies(asteroids, satellitesof Mars, and a comet nucleus)shown in their relative sizes

Spacecraft have visited a few asteroids.

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Asteroid Ida has its own little moon, Dactyl, which is1.5 km in diameter

Ida is 56 km long

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Gaspra is 18 km long17

Mars’ satellite Phobos

Phobos is cratered, but has an overall smooth surface.

Note the long grooves and chains of craters.

The chains of craters are probably caused by gas coming out of the interior of Phobos.

The other craters are from impacts.

Phobos is probably an asteroid.

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Asteroid #216 Kleopatra, mostly made of metal, mapped by reflection of radar signals (2000) 217x94 km.

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An asteroid mission in progress – the Japanese Hayabusa mission at asteroid 25142 Itokawa

Itokawa is about 500 meters long – it is a Near-Earth asteroid (NEA)

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A landing devicewill grab a sampleof Itokawa andreturn it to Earth.

This will be thefirst asteroid sample-returnmission.

Why aren’t there any impact craterson this asteroid ? (I have no idea !)

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Another Near-Earthasteroid, 433 Eros,was visited by anorbiting spacecraft.

The spacecraft wascalled NEAR (Near Earth AsteroidRendezvous)

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After orbiting 433 Eros for about a year, the spacecraftsettled down onto the surface in a “controlled crash” landing.

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NEAR took pictures all the way down to the surface.This frame shows an area about the size of our classroom.

Boulders in the bottom of adepression on Eros’ surface.

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Asteroids occasionally collide with one another

• Asteroids undergo collisions with each other, causing them to break up into smaller fragments

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Asteroids collide with one another …

In these sketches, an asteroid is shattered by a largeimpact (C). It then reassembles into a broken mass (E), and is again hit by a big impactor (F) and flies apart.

A B C

D E F

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Asteroid fragmentshit the planets andsometimes fall to

the ground as

METEORITES

Meteorites arefree samples

of other worlds.

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The Zodiacal Light

Collisions among the asteroids also produce very fine dust particles. Theseare illuminated by sunlightand form a faint bandacross the sky, visibleat sunrise and sunset.

This is the Zodiacal Light

Milky Way

Horizon

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NEA: Near Earth Asteroids

• The asteroids that have orbits that cross the orbit of the Earth have the possibility to collide with our planet

• The Apollo and Amor family asteroids are most likely to hit Earth

• About 2200 Near-Earth (NEA) asteroids are known• There are more NEAs that have not yet been found

• PHA: Potentially Hazardous Asteroids, 836 known, that come closer to Earth than 0.05 AU and about 100m in

size, i.e. can cause a global catastrophe.

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The 1 mile diameter Barringer Crater (Arizona) was probably created by a 45

meter object, 50,000 years ago.

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Things to do