The Solar System

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Chapter 2

• The Solar System
• Part 3

2
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.

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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.

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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.
• Galileos 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.

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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 Jupiters
  large gravitational influence.

6
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.

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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.

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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.

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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.

10
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.

11
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.

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Comets

• Comet Machholz
• Comet Hale-Bopp
• Comet C 2003 K Linear
• Comet Neat
• Comet Bradfield
• Comet Halley
• Comet Wild 2
• Comet Shoemaker-Levi 9

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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

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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.

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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.

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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 near-Earth 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).

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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.

18
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.