Transcript Chapter 2 - The Solar System

Chapter 2
The Solar System
Part 3
Asteroids (Minor Planets)


Objects in the solar system smaller than a planet
that are made of rock.
The first asteroid in space, named Ceres, was
discovered in 1801. Since then over 250,000
asteroids have been discovered and that
number continues to rapidly increase every year.
This despite that probably many asteroids are
too small to be seen from Earth.
Asteroids


Ceres is still by far the largest known asteroid
with a diameter of 623 miles. Only 26 have been
discovered larger than 120 miles. Most are
smaller than a mile across.
Asteroids are referred to by a number and its
name. The number represents the order in
which it was discovered. For example, Ceres is
referred by 1 Ceres since it was the first one
discovered.
Asteroids


The space probe Galileo provided the first close images
of an asteroid when it passed near and photographed
951 Gaspra and 243 Ida in the Main Asteroid Belt.
Galileo’s pictures revealed that Ida has a natural
satellite, Dactyl. Ida is about 35 miles long and 15 miles
in diameter. Its tiny moon is about a mile in diameter and
orbits about 60 miles above Ida. Since then several
other asteroids have been found to have companions,
leading astronomers to believe that it may not be
uncommon.
Asteroids

Most asteroids reside in the Main Asteroid
Belt between Mars and Jupiter. It is
hypothesized that they are bits of
primordial solar system material that was
unable to form a planet due to Jupiter’s
large gravitational influence.
Near Earth Asteroids


Gravitational perturbations mostly from Jupiter cause
asteroids to occasionally leave the Main Asteroid Belt
and wander the solar system. Those that come near
Earth are called Near Earth Asteroids.
Asteroid collisions with Earth are known to be common
in its history. Until the 1990s though, it was not
recognized that they could significantly change
conditions on Earth. This was brought about by the
theory that an asteroid impact 65 million years ago was
responsible for the extinction of some 85% of all
species, including all of the dinosaurs.
Near Earth Asteroids

There are currently 3168 discovered near earth
asteroids. They are classified into 3 categories:
 Apollo – Asteroids that cross the orbits of both Earth
and Mars.
 Amors – Asteroids that cross the orbit of Mars but not
Earth.
 Atens – Asteroids that cross the orbit of Earth but not
Mars.
 The last close encounter happened last year when
the peanut-shaped 3-mile long asteroid named 4179
Toutatis passed within a million miles of Earth.
NEAR (Near Earth Asteroid
Rendezvous)-Shoemaker



Mission launched in February 1996 to study
near earth asteroids 253 Mathilde and 433 Eros.
First attempt to insert NEAR-Shoemaker into
Eros’ orbit failed in 1998. The second attempt in
2000 was successful though.
NEAR-Shoemaker conducted the first long-term
close-up study of an asteroid: mass, structure,
geology, composition, and gravity.
NEAR-Shoemaker


Near-Shoemaker discovered that Eros has an
ancient surface covered with craters, grooves,
layers, house-sized boulders, and other complex
features. It also seems to be a fragment of a
larger body.
In February 2001, the NEAR spacecraft landed
on asteroid Eros, after transmitting 69 close-up
images of the surface during its final descent.
Asteroid Collision Prevention


Efforts to find near earth asteroids stepped up in
1998 with highly efficient automated systems
that consist of cameras and computers directly
connected to telescopes. Since then a large
majority of the asteroids have been discovered
by such automated systems .
Several theories exist as to how to prevent a
collision with an asteroid. The most popular is
the one to deflect the asteroid such that it
misses Earth. How to exactly accomplish this is
not exactly known.
Comets


Unlike the other small bodies in the solar
system, comets have been known since
antiquity. There are Chinese records of Comet
Halley going back to at least 240 BC.
Comets are sometimes called dirty snowballs.
They are a mixture of ices (both water and
frozen gases) and dust that for some reason
didn't get incorporated into planets when the
solar system was formed. This makes them very
interesting as samples of the early history of the
solar system.
Comets








Comet Machholz
Comet Hale-Bopp
Comet C 2003 K Linear
Comet Neat
Comet Bradfield
Comet Halley
Comet Wild 2
Comet Shoemaker-Levi 9
Comets

Comets have several distinct parts:
 nucleus: relatively solid and stable, mostly
ice and gas with a small amount of dust and
other solids.
 coma: dense cloud of water, carbon dioxide
and other neutral gases sublimed from the
nucleus;
 hydrogen cloud: large but very sparse
envelope of hydrogen surrounding the comet
and sometimes trailing it;
Comets


dust tail: very long white tail composed of
smoke-sized dust particles driven off the
nucleus by escaping gases; this is the most
prominent part of a comet to the unaided eye;
ion tail: very long bluish tail composed of
ionized gas caused by interactions with the
solar wind. It always points away from the
Sun.
Comets


Since both the coma and the tails are composed
of material driven off the nucleus by solar
heating, comets are invisible except when they
are near the Sun.
Most comets have highly eccentric orbits which
take them far beyond the orbit of Pluto; these
are seen once and then disappear for millennia.
Only the short- and intermediate-period comets
(like Comet Halley), stay within the orbit of Pluto
for a significant fraction of their orbits.
Comets


Short-period comets are believed to originate in the
Kuiper Belt. Other comets are theorized to come from
the Oort cloud or perhaps from outside our solar system.
After 500 or so passes near the Sun off most of a
comet's ice and gas is lost leaving a rocky object very
much like an asteroid in appearance. (Many of the nearEarth asteroids may be "dead" comets.) A comet whose
orbit takes it near the Sun is also likely to either impact
one of the planets or the Sun or to be ejected out of the
solar system by a close encounter (esp. with Jupiter).
Meteor Showers

A meteor shower sometimes occurs when
the Earth passes through the orbit of a
comet. Some occur with great regularity:
the Perseid meteor shower occurs every
year between August 9 and 13 when the
Earth passes thru the orbit of Comet
Swift-Tuttle. Comet Halley is the source
of the Orionid shower in October.
Comet Machholz

Good views of Comet Machholz are in store for
northern hemisphere comet watchers in
January. Now making its closest approach to
planet Earth, the comet passed near the
Pleiades star cluster on January 7th and the
double star cluster in Perseus on January 27th
as Machholz moves relatively quickly through
the evening sky. Currently just visible to the
unaided eye from dark locations, the comet
should be an easy target in binoculars or a small
telescope.