Transcript The Formation of the Solar System

Solar System Debris
• Asteroids, meteoroids, comets: any small body in the
solar system.
• Important as they offer information about the early
solar system.
• The early solar system cannot generally be
investigated using the planets as the planets have
evolved over time (e.g. geologic activity on Earth,
etc.)
Asteroids
• Asteroids - fragments of rocky material larger than 100 m in
diameter.
• Vast majority found in the “asteroid belt,” located between Mars
and Jupiter.
• All but one orbit the sun in prograde orbits (in same direction as
the planets).
• Trojan asteroids - locked in place in Jupiter’s orbit due to the
balance of Jupiter and the sun’s gravitational forces.
• Asteroids can be deflected into the inner solar system by the
gravitational field of Mars or Jupiter - can cross Earth’s orbit.
More than 3300 Earth-crossing asteroids are known. Most will
eventually collide with Earth.
Asteroid Properties
• Can estimate size by the amount of sunlight they reflect and the
heat they radiate.
• Total mass of all asteroids probably amounts to less than 1/10
the mass of our moon.
• Asteroid compositions are inferred from spectroscopic
observations.
• Darkest (least reflective) asteroids contain water ice and organic
(carbon-rich) compounds - called carbonaceous asteroids.
More common overall and increase in numbers as you move
further out in the solar system.
• The more reflective silicate asteroids are composed primarily of
rocky material. More common in the inner solar system.
• The asteroid Ida has a small moon (Dactyl) which orbits it.
• Some asteroids (like Mathilde) are porous, meaning they are not
solid rock.
Asteroids
(a) Gaspra as seen by Galileo
spacecraft from a distance of 1600
km.
(b) Ida as seen by Galileo spacecraft
from a distance of 3400 km.
(c) Mathilde as seen by NEAR
spacecraft.
Comets
• Comets - icy rather than rocky in composition and typical diameters range
from 1 to 10 km.
• Travel in highly elliptical orbits about the Sun.
• Tails form when comets near the sun (composed of dust or ionized gas).
• Nucleus - main solid body of a comet - only a few km in diameter.
• Coma - forms when comet comes within a few AU of the sun as part of the
icy surface becomes gaseous and evaporates forming a cloud around the
nucleus.
• Tail is largest part, coma is brightest part, and nucleus is more massive
part.
• Tails are directed away from the sun by the solar wind (an invisible stream
of matter and radiation escaping from the sun).
• Most famous comet - Halley’s comet, which appears once every 76 years
(most recently in 1986).
• Comets are often called dirty snowballs (nucleus contains rocky material
and ice, as well as methane, ammonia, and carbon dioxide).
Halley’s Comet
Halley’s Comet Nucleus
Comet Tails
Comet Orbits
• Highly elliptical orbits take them far beyond Pluto, where they spend
most of their time.
• Not confined to a few degrees within the ecliptic, unlike the other
objects in the solar system.
• Roughly uniformly distributed in all directions from the sun.
• Short-period comets originate from the Kuiper belt, where either
comet-comet interactions or the gravity of Neptune kicks them into an
orbit which brings them to the inner solar system.
• Comets that lie outside of Pluto’s orbit form the Oort cloud, which
completely surrounds the sun.
• Oort cloud may be up to 100,000 AU in diameter.
• Oort cloud members rarely venture into the main solar system (closer
than Pluto).
• Since the Oort cloud exists in all directions (rather than in just the
plane of the ecliptic), objects originating from there come from all
directions (unlike objects from the Kuiper belt).
What is a “shooting” or
“falling” star?
A. It’s an actual star that is moving very
quickly in the sky.
B. A rock moving very quickly in space.
C. A rock moving very quickly through the
earth’s atmosphere.
D. There’s no such thing - it doesn’t really
exist.
E. It’s simply an optical illusion.
Meteoroids
• Meteoroids - fragments of rocky material less than 100 m in
diameter.
• Meteor - sudden streak of light in the night sky caused by friction
between air molecules in Earth’s atmosphere and an incoming
piece of asteroid, meteoroid, or comet.
• Meteorite - any piece of interplanetary debris that survives its
fiery passage through our atmosphere and finds its way to the
ground.
• Smallest meteoroids are rocky remains of broken-up comets called micrometeoroids.
• The comet fragments initially travel in a tightly knit group called
a “meteoroid swarm” moving in nearly the same direction as the
parent comet.
• A meteor shower results when Earth’s orbit intersects the orbit of
such a young cluster of meteoroids.
• Meteor showers are named for the constellation from which they
appear to originate.
Meteoroids
• Larger meteoroids (more than a few cm in diameter) are not usually
associated with comets.
• Larger meteoroids are more likely small bodies that have strayed from
the asteroid belt.
• Larger meteoroids are responsible for most of the cratering on the
surfaces of the moon, Mercury, Venus, and Mars.
• A few meteorites have been identified as originating from the moon or
Mars, having been blasted off by some impact on those bodies.
• Meteoroids less than about 1 m across burn up in Earth’s atmosphere.
• Larger meteoroids reach the surface, where they can cause significant
damage.
• Major collisions between Earth and large meteoroids are thought to now
be rare, occurring on average once every few hundred thousand years.
• One of the most recent large impacts was in 1908 in Siberia (meteoroid
was 30 m across - equal to a 10-megaton nuclear detonation).
• Most meteoroids are rocky, although a few are composed of iron and
nickel.
• Almost all meteorites are old. Radioactive dating shows most to be
between 4.43 and 4.6 billion years old.
Barringer Crater (Winslow, AZ)
Manicouagan
Reservoir
(Quebec)
Tunguska Debris (Siberia)