Lecture Nine

Question 1

Describe the characteristics of asteroids.

Answer 1

Most are found in the asteroid belt between Mars and Jupiter = Main belt asteroids (over one million found so far).
Some have orbits that bring them close to Earth = Near Earth asteroids, or near Earth objects (NEOs) (over 10,000 found).
Leftovers from a planet that never quite formed.
Different compositions and types and sizes.
Largest is planet-like, as it is rounded = Dwarf Planet.
Others sometimes called minor planets.
Widely spread - on average one asteroid every 3,000km^2.

Question 2

What is Ceres and what are its characteristics?

Answer 2

A dwarf planet. 
Largest things in the asteroid belt. 
Diameter 952.4km. 
1 day = 9.07 hours. 
1 year = 4.6 Earth years. 
About 25% water by weight. 
Water has been detected here, water vapour plumes detected from two areas, Piazzi and Region A. 
Unknown why the plumes are occurring, but may be similar to ones found on Enceladus and Europa.

Question 3

What is Vesta and what are its characteristics?

Answer 3

Not fully rounded - so not a dwarf planet, second largest asteroid.
Basaltic crust over olivine mantle.

Question 4

What are the compositions of asteroids?

Answer 4

The same as the composition of meteorites found so far - stone, stoney-iron and iron, but also water and ice.

Question 5

Describe Pluto and it’s characteristics.

Answer 5

Used to be the ninth planet. 
Now a Dwarf planet. 
Binary planet system with Charon. 
Radius: 1151km. 
0.002 of Earths mass. 
Temperature: 40-50 K. 
Water ice and rock.

Question 6

Why isn’t Pluto a planet any more?

Answer 6

Discoveries of more ‘planets’ keep being made.
A large number of new planets at least one of which is larger than Pluto.
The possibility of hundreds of things being discovered.

Question 7

What is the Kuiper Belt?

Answer 7

More than 70,000 bodies larger then 10km.

Source of short period asteroids and comets.

Question 8

What is the Oort Cloud?

Answer 8

More then 10^12 bodies larger than 1km (50,000-100,000 AU) (AU = distance from Earth to Sun).
Reservoir for long period comets.
Organic chemicals in comets.

Question 9

What are comets?

Answer 9

Dirty snowballs - Ice and dust (C rich).
Orbit the sun, some periodically head into the inner solar system.
Some make it out past the sun again, some don’t, some come back again.
Possible sources for some carbon and some water on early Earth.
As they come close to the sun, the water ice begins to evaporate off, and they lose mass and grow a tail that trails away from the sun.