Ch. 6 – Vagabonds of the Solar System There are several kinds of objects in our Solar System Terrestrial planets Jovian planets “debris” – asteroids, comets and meteoroids and some objects still being classified: Kuiper Belt, Oort cloud

The Inner Solar System (sizes NOT to scale)

Asteroids: three major groups Asteroid belt between the orbits of Mars and Jupiter Trojan Asteroids Near-Earth Objects

Asteroid Icarus comes close to Earth and to the Sun

Asteroids and meteoroids are small “rocky” objects The main difference between the two is size.

Some asteroids have been studied up close. Asteroid Eros

Asteroid Eros was imaged by a spacecraft which then landed on it and sent back data on its composition. NEAR spacecraft site: For a simulation of the trajectory see:

What Killed the Dinosaurs? This is an artistic representation of an asteroid impact in the Yucatan region over 65 million years ago.

Approximate frequency of random impacts

Tunguska Debris, Siberia, 1908

Manicouagan Reservoir: a crater in Canada

Barringer Crater in Arizona – a meteor crater

Near Earth Objects - NEO There is an automated system to scan the sky for near-Earth objects and report them to a computer system. These and other reports are fed into a computer program called the JPL Sentry system: This detected a threat a few years ago, at risk level 2: which is no longer considered a threat, after new calculations were done. For further descriptions: Asteroid 1950 DA may collide with Earth in the year 2880 (1 in 300 chance):

The Asteroid belt contains over 100,000 asteroids, (fact sheet) Ceres (sîr'ēz – link dictionary.com ) ( called a dwarf planet in 2006 ) and Vesta (věs'-tə) ( a minor body link or asteroid ) are currently targeted for detailed study A spacecraft named DAWN was launched in Sept and will arrive in 2011 to begin studying these two objects More on asteroids: sheet link

Comets “Icy snowball” model Two tails may appear: ion tail and dust tail Tails are influenced by the environment as well. Recent news: comet tail blown off by solar wind (called a Coronal Mass Ejection CME) and seen by a spacecraft. Comet Encke was near the Sun when this happened April 20, (shown on separate slide)

Halley’s Comet was last seen in The orbital period is 76 years, so it will be back in 2062.

Comet Tails: ion tail and dust tail Comet Hale-Bopp (1997) had two distinctive tails:

A Comet Trajectory is usually a very narrow ellipse, with eccentricity near 1.0 Some comets appear to come from almost 100,000 A.U. from the Sun, in a region called the Oort cloud.

Comet Reservoirs: the Oort Cloud the Kuiper Belt (pronounced Kye-per)

Halley’s Comet close-up by a passing spacecraft

Comet Encke: ion (or plasma) tail blown completely off by a Coronal Mass Ejection see: APOD 10/3/07 for details linklink

Comet news! Comet Hartley 2 is now visible in the northern sky with binoculars, but moonlight makes it very hard to see. A gallery has been posted online: Dr. Davies observed Hartley 2 last Saturday at about 4:30 a.m., but it was quite hard to see with our large binoculars. Due to the full moon, it will be almost impossible to see this from Oct. 20 until the beginning of November.

Probes of asteroids and comets The NASA Deep Impact mission was sent to collide with a comet on July 4, 2005: Rosetta mission: Lutetia flyby 10 July 2010: (Rosetta also saw evidence of an asteroid collision) EPOXI mission (extended Deep Impact mission, redirected to comet Hartley 2: Amateur photos are shown here:

Meteor Trails in the night sky

Meteor Showers are usually due to old comets. There is definite proof that some are due to known comets. Others are probably fragments of asteroids. List of meteor showers:

Meteorite Samples, stony vs. iron-nickel