AST Lecture 17: Asteroids and Dwarf Planets

What Are Asteroids?

• Orbit the sun

• Made mainly of rock and metal

• 25 million larger than 100 diameter

• 600 larger than 50km diameter

What shape is the orbit of an asteroid?

• They are elliptical

• Time of an orbit depends on semi-major axis

Ceres

• Dwarf planet

• Largest object in the asteroid belt

• Covered with craters

• Studied by dawn Space probe 2015-2018

• Has salt deposits from cryo-volcano (ice-volcano)

• Still active after a meteor strike

• Has a 4km mountain (Ahuna Mons)

• Landslides on crater wall

• Layers

  • Rocky center

  • Liquid brine (extremely salty water)

  • Icy crust

  • Dark crust on surface

• Large enough that the strength of gravity is stronger than the strength of the rock/ice it is made of

• Orbits the sun

• Not massive enough that it mostly clears out its orbit

Vesta

• Largest Asteroid is Vesta

• Around half the size of Ceres

• At one point Vesta was hot enough for interior to become liquid

• Vesta experienced differentiation

  • Has a nickel/iron core

Eros

• Gravity measures that its homogenous

• Has catering (very old surface)

• 50% chance of striking Earth in the next billion years or so

Osiris-Rex (Satellite)

• Observed small objects flying off of asteroids

• Tracking these particles and the spacecraft were used to probe Bennu’s interior

• It is low density

Bennu

• Orbit crosses the Earth

• Orbit continuously perturbed by the planets and is not stable

• It has a 1 in 2700 chance of Striking that the Earth before 2199 CE

Pluto

• Craters

• Old surface

• Nitrogen ice plains

  • Made of frozen nitrogen air

  • Might get warm enough to melt and get nitrogen lakes

• Water ice mountains 

• 248 Orbital years

• Orbit is inclined

• Crosses Neptune's Orbit

• 3:2 resonance with Neptune

Charon (Moon of Pluto)

• Compared to pluto Charion is a very large for a moon

• Surface has more craters than Pluto

• Surface is mainly water ice

Comets

• Appear rarely in the night sky

• Are visible for days

• Have tails pointing roughly away from the Sun

• Often come back on a fixed period (decades to millennia)

Comet Orbit

• Gas tail

• Gets warmer close to the sun

• Sun heats up the comet and ice melts and boils away

Comet Tails

• Gas/plasma is pushed directly away from the sun by high energy particles called the Solar wind

• Dust is accelerated (less) by light from the Sun

• So it points a little behind the Gas/Plasma tail

• Larger chunks that come off don’t get affected much by the sun and so lie along the orbit (Roughly following or leading the comet)

Oort Cloud

• Outside the Kuiper is a huge spherical cloud of comets called the oort Cloud

• Comets in it were formed near Jupiter but kicked out by Gravitataional interactions

• Contains trillions of objects

Meteors

• Every night millions of object strike Earth

• Most are very small (size of grain of sand) and burn up in the atmosphere

Meteorites

• When objects hit the surface of the Earth

• Large ones could be destruction

• 50 KYA a 50m object made a big ass crater

Cretaceous-Paleogene Extinction event:

• 66 ish million years ago

• Asteroid or comet around 30 km across struck Earth

• Corresponds with extinction of most dinosaurs