Part I : Asteroids and comets

Comet West (1975)

Asteroid 453 Gaspra

I. History

• First Chinese reports in 467 B.C

• Greeks thought it was an atmospheric phenomenon

• Lots of sightings in many different cultures

A. Ancient times

Comets in China 300 B.C

• Comets remains an unpredictable and erratic event

• They are feared • Comets are associated

with starvation, wars and illness.

B. From ancient times to middle age

Halley's comet during the Norman invasion of England

Storms and fires following a comet (1453)

C. First scientific studies

• After Kepler published his famous laws, english scientist Edmond Halley tries to prove them.

• He found the answer in Newton’s new theories of gravitation.

• He convinces Newton to publish his work on universal gravitation (Principia)

Edmond Halley 1656-1742

• Then he applies Kepler’s and Newton’s laws to the comet he observed in 1682.

• He deduces that the comet sighting of 1456, 1531, 1607 and 1682 are related to the same comet.

• Later scientists will call it : Halley’s comet

Halley ’s comet in 1986

• In 1800, he tries to verify the Titus-Bode law :

• According to this laws, a planet should be located somewhere between Mars and Jupiter.

• In 1801, he found this planet : Ceres which is actually the biggest known asteroid.

Ceres and the Moon

II. Definition and description

• Identity : - Size : 1 to 50 km - Composition : Ice, dust

and other volatile elements such as methane.

- Speed : up to 120 000 km/h when it approach the Sun.

A. Comets

Comet Hyakutake (1998)

• Very irregular forms and composition.

• Ice is usually located in the core whereas dust is on the surface

• Average diameter for comets is 10 km

The core

The coma • Due to solar wind and solar radiation, a lot a gas and dust is ejected when the comet passes near the Sun.

• The result of that is the famous comet tails :

- One tail is made of gas and points directly away from the Sun

- The other tail is curved, less affected by solar wind and is left behind comet’s orbit.

• The dust tail can reach a size of 70 000 km (diameter of the Sun)

• The ion/gas tail can reach a size of 150 000 000 km (Earth-Sun distance)

B. Asteroid (minor planet) and meteoroid

• Identity : - Size : 1 cm to 1000 km - Composition :

Different types of rocks (carbon, siliceous and metallic)

- Speed 1000 to 20 000 km/s at Earth’s orbit.

Asteroid 433 Eros

• Number of asteroid decreases as its mass increases

• Small ones have irregular forms, bigger ones tend to be spherical.

Asteroid classification :

• C-type : Carbonaceous -> 75 %• S-type : Silicaceous -> 12 %• L-type : Metallic -> 8 %

III. Origin, location and orbit

• 4,6 billion years ago an matter disk is formed around the Sun

• Birth of planets by the phenomenon of accretion

• Small objects attract each other and stick together to form bigger objects.

• Volatile elements (ice and methane tends to

• Because of the important mass of Jupiter, the planet that should have existed between Mars and Jupiter fails to birth leaving behind an asteroid belt.

• Same thing goes for the Kuiper’s belt and Neptune.

The asteroid belt and its 500 000 known asteroid. Current estimations say there could have up to 10 million bodies.

Kuiper’s belt : 35 000 bodies > 100 km

Oort’s cloud has a size of 1 light year and contains ~ 1000 billion bodies

Orbits

Asteroids crossing earth’s orbitSome comets orbit. Many are not inside the ecliptic plane

• The big gas planets of the system like Jupiter attract many objects coming from the outer solar system• Thanks to them, the number of bodies reaching the inner solar system is reduced.• In 1994, Shoemaker-Levy 9 comet hit Jupiter

Shoemaker-Levy 9 impact on Jupiter