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Astronomy 311
Professor Lee Carkner
Lecture 15
Temperature of Mars
Temp of Mars from radiation balance
TM = [RS/(2 DS)]½ TS
TM = [6.96X108 / (2)(1.5)(1.496X1011)]½ (5778)
TM = 227.7 K
TF = 1.8TK -460 = (1.8)(227.7)-460 = -50.1 F
How good is this estimate?
Principle source of error is that we have ignored the
effects of Mars’s atmosphere
Since atmosphere is very thin, error is small
How hot must Sun be for liquid water on Mars?
 TM = [RS/(2 DS)]½ TS
TS = TM /{[RS/(2 DS)]½}
TS =(273) / {[6.96X108 / (2)(1.5)(1.496X1011)]½}
TS= 6926.2 K
Rocks in Space
Asteroid --
Meteoroid -- a small piece of rock in space
Meteor -caused by friction
Meteorite -- a meteoroid that hits the
Types of Meteorites
Two major types are iron and chondrite
Chondrites are composed of silicates (rock)
Chondrites are the most common type of
But, irons are much easier to find
Chondrites look a lot like normal Earth rocks
What are the properties of chondrites and
irons and how can you identify them?
Iron Meteorites
Composed of iron and nickel
Called regmaglypts
These are a particular type of crystal that forms
only by very slow cooling (millions of years)
Helps to distinguish true meteorites from
terrestrial rocks
Widmanstatten Patterns
Chondrite (Stony) Meteorites
One distinguishing feature is a fusion crust
where the outer layers are heated by friction
with the atmosphere
Origin uncertain, but indicate that chondrites
have never been strongly heated
Carbonaceous chondrites also contain
volatiles (water and carbon compounds) and
thus represent unprocessed material from the
very early solar nebula
The Missing Planet
In 1801 G. Piazzi found a faint moving
star in the gap
Ceres was too small to be the missing
planet, but soon many more smaller
objects were found
This is the asteroid belt
The Asteroid Belt
Asteroid Myths
Are the asteroids debris from a planet
that exploded?
Is the asteroid belt dangerous to travel
There is on average about one million
kilometers between asteroids
Asteroid Facts
Size: Ceres (918 km), Pallas (544 km),
Vesta (529 km), about 200 larger than
100 km, most are less than 1 km
Description: very small, irregularly
shaped, cratered
Formation of the Asteroid Belt
Jupiter’s gravity:
Ejected most near-by planetesimals
Alters the orbits of the remaining asteroids
Studying Asteroids
Several asteroids have been observed at
close range
In 2005 the Japanese mission Hayabusa
studied asteroid Itokawa and tried to
collect a sample for return to Earth
Scheduled to move to Ceres in 2015
Asteroid Types
S Type
M type
C Type
composed of carbonaceous chondrite material
C type asteroids tend to be found in the outer
asteroid belt where temperatures are lower
Formation of Meteoroids
heavier materials (like iron) sank to the core, while
lighter elements (silicates) formed the crust
decay of radioactive materials provided the heat
Fragments of the core form iron meteoroids
Asteroids that never differentiated formed
 NEO’s can hit the Earth
About 1 big one every few hundred years
 Consequences of impacts
~50 m diameter
~100 m diameter costal hit
Mass extinctions
~1 km diameter
What Use is an Asteroid?
Space Habitats
Put engines on the space colony
Providing Material for Life in Space
Asteroids are small bodies that orbit the Sun
Most are in the asteroid belt between Mars
and Jupiter (2-3.5 AU)
Jupiter’s gravity prevented the asteroids
from forming a planet
Small (most less than 1 km)
Max size is few hundred km
Irregularly shaped
Heavily cratered
Summary: Meteoroids
made of metal
formed from core of
asteroids (M type)
Achondrites (Stony)
made of rock with
no inclusions
made from crust of
asteroids (S type)
Chondrites (Stony)
made of rock with
small inclusions
made from
asteroids (S and C