ASTEROIDS

By Melissa Goschie

What is an asteroid?

• Rocky-metallic objects • Range in size from

about the size of pebbles to around 600 miles (~1,000 km) across.

• Much smaller than planets

• Orbit the sun in an area called the Asteroid Belt

http://images.google.com/imgres?imgurl=http://www.indiana.edu/~geol105/images/gaia_chapter_2/asteroids_compare4.jpg&imgrefurl=http://www.indiana.edu/~geol105/images/gaia_chapter_2/comets_and_asteroids.htm&usg=__ncFdDybfM--CIfePpk2Bu9QbSwo=&h=775&w=630&sz=95&hl=en&start=19&tbnid=XkPsagFZggIwcM:&tbnh=142&tbnw=115&prev=/images%3Fq%3Dasteroids%26gbv%3D2%26hl%3Den

History

• January 1801, Giuseppe Piazzi sees an object he first calls a comet. Then calls it a small planet and names it Ceres.

• Ceres is the Sicilian goddess of grain

• Over next few years Pallas, Vesta and Juno are discovered.

image http://upload.wikimedia.org/wikipedia/commons/9/92/Giuseppe_Piazzi.jpghttp://www.enchantedlearning.com/subjects/astronomy/asteroids/composition.shtml

Where can you find them?

• In the Asteroid Belt between Mars and Jupiter.

• There are thousands of known and lots more discovered every year.

• Ceres is the largest with a diameter of 974 km

• All the asteroids put together would not even be half of the moons mass.

http://upload.wikimedia.org/wikipedia/commons/f/f3/InnerSolarSystem-en.png

How did they get there?

• There are a couple of theories about where asteroids come from.

• One is that when the planets were forming there was material that didn’t have enough mass to come together and instead fragmented out.

• Another theory is that material came from a planet that was destroyed from a collision.

• Either theory dates asteroids to the birth of our solar system.

http://www.vredefortstructure.org/engtimeline02.htm

Terms you might want to know• Asteroid – medium-sized rocky

object orbiting the Sun; smaller than a planet and larger than a meteoroid.

• Meteoroid – a small rocky object orbiting the Sun; smaller than an asteroid.

• Meteor – a bright streak of light in the sky caused by the entry into Earth’s atmosphere of a meteoroid or a small icy particle. Very large, bright ones are called fireballs and bolides. (also known as a “shooting star” or “falling star”)

• Meteorite – a rock of extra-terrestrial origin found on Earth

• Comet – a medium-sized icy object orbiting the Sun; smaller than a planet

http://www.cosmosmagazine.com/files/imagecache/news/files/news/comet2.jpg

Classification by Type• C-type, includes more than 75%

of known asteroids: extremely dark (albedo 0.03); similar to carbonaceous chondrite meteorites; approximately the same chemical composition as the Sun minus hydrogen, helium and other volatiles;

• S-type, 17%: relatively bright (albedo .10-.22); metallic nickel-iron mixed with iron- and magnesium-silicates;

• M-type, most of the rest: bright (albedo .10-.18); pure nickel-iron.

• There are also a dozen or so other rare types

http://rocksfromspace.open.ac.uk/images/Asteroids_Sullivan.jpg

Classification by Location

• The Main Belt is located between Mars and Jupiter.

• Near-Earth are ones that closely approach Earth.

• Trojan are near points of Jupiter’s orbit; 60 degrees ahead and behind).

• The gaps between asteroids in the Main Belt are called Kirkwood Gaps. These gaps are mostly empty regions caused from Jupiter’s orbit.

http://keetsa.com/blog/wp-content/uploads/2007/09/asteroid-belt.jpg

Activity 1How do you know if it is a

meteorite?• http://dawn.jpl.nasa.

gov/Meteorite/experiment.asp

http://www.astronomy-blog.com/images/blogs/4-2008/meteorite-impacts.jpg

Comets

http://www.williamjosephgallery.com/Comet%20Hale%20Bopp%20Over%20Mt%20Hood%20Oregon%20Nehl%201997%20color%2096x5.JPG

Is a comet an asteroid?• Comets have large erratic orbits which when they get close to the

sun the ice is melted and this forms the tail.

• When the comet is completely melted, the remnant becomes an asteroid.

• Asteroids are made up of metals and rocky material

• Comets are made up of ice, dust and rocky material.

• Both asteroids and comets were formed early in the history of the solar system about 4.5 billion years ago.

• Asteroids formed much closer to the sun, where it was too warm for ices to remain solid.

• Comets formed farther from the sun where ices would not melt.

• Comets which approach the sun loose material with each orbit because some of their ice melts and vaporizes to form a tail.

Questions to think about

• What prevents the asteroids in the belt from plunging towards the Sun and hitting the inner planets in the process?

Questions to think about

Question: What prevents the asteroids in the belt from

plunging towards the Sun and hitting the inner planets in the process?

Answer: While the Sun gravitationally pulls the asteroids

inward, the gravitational pull of Jupiter is pulling the asteroids outward. Since the belt is closer to Jupiter than it is to the Sun, Jupiter exerts more of an influence on the asteroids. As a result, the asteroids are held in orbit away from the inner planets.

• Do asteroids have moons?

• Do asteroids have moons?

• Yes, asteroids have moons.

• Have any spacecraft ever landed on an asteroid?

• Have any spacecraft ever landed on an asteroid?

• Yes, on February 12, 2001 flight controllers landed NASA's NEAR spacecraft on an asteroid called Eros. NEAR was the first spacecraft to orbit and touchdown on the surface of an asteroid. NEAR began orbiting Eros a year earlier, on February 14, 2000. The spacecraft collected close up photographs and measured the size and shape of Eros before landing. Eros is the largest of the asteroids whose orbits cross the orbit of the Earth.

•

Activity 2Let’s make our own comet!

Credits