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Asteroids

Asteroids. Definition . Asteroids: relatively small, predominately rocky objects that revolve around the sun Name means “starlike bodies” Sometimes referred to as minor planets or planetoids. Asteroid Basics. They move on quite eccentric trajectories

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Asteroids

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  1. Asteroids

  2. Definition • Asteroids: relatively small, predominately rocky objects that revolve around the sun • Name means “starlike bodies” • Sometimes referred to as minor planets or planetoids

  3. Asteroid Basics • They move on quite eccentric trajectories • Most are found in the asteroid belt between Mars and Jupiter • Few are larger than 300 km • All the asteroids masses together do not equal the mass of the Earth’s moon

  4. The asteroid Ceres • The largest asteroid, at 940 km (1/10,000th the mass of Earth) • Discovered in 1801 by Guiseppe Piazzi • Has a semimajor axis of 2.8 AU

  5. More Basics • Current number of known asteroids is over 200,000. Hundreds of thousands of others may await discover. • All but one orbit in the same direction as the planets • The asteroids are probably left over material from the solar system’s formation • Jupiter’s gravity keeps the asteroids from combining into a larger body

  6. Physical Properties • There are several different types • C-type (carbonaceous) – darkest in color; found more to the outside of the belt (75 %) • S-type - contains silicate or rocky material; found more to the inside of the belt (15 %) • The largest ones are roughly spherical, but the smaller ones are irregular

  7. The asteroid Vesta • Some Earth meteorites are thought to have originated from Vesta – they are made of basalt. • Unique in that it appears to have undergone volcanism

  8. Two other Asteroids to know • Pallas – 580 km and Juno – 540 km

  9. Asteroid Observations • The Galileo space probe, headed for Jupiter, went through the asteroid belt twice. • In had close encounters with Gaspra and Ida

  10. Gaspra v’s Ida • Both are S-type. • Gaspra is 20 km in size and Ida is 60 km. • Ida is more heavily cratered, because it is in a denser part of the asteroid belt. • Ida is a billion years old, Gaspra just 200 million years old. • Both are thought to be fragments of once large objects.

  11. Gaspra

  12. The neatest thing about Ida… • It has a tiny moon, Dactyl! • Dactyl is just 1.5 km across. • It orbits about 90 km from Ida. • It is also an S-type asteroid.

  13. ` Asteroid Ida and tiny moon asteroid, Dactyl!

  14. Binary Asteroids • Def: two asteroids orbiting one another as they circle the Sun. • May be a result of collisions in the belt. • Less violent collisions may also be responsible for the binary systems. • More violent ones may send asteroids into Earth-crossing orbits.

  15. Binary Asteroid 90 Antiope

  16. The NEAR Spacecraft • Stands for Near Earth Asteroid Rendezvous. • In 1997, visited the C-type asteroid Mathilde and S-type asteroid Eros. • Mathlide was calculated as having a fairly low density, probably a result of being very porous. • It rotates every 17.5 days.

  17. Mathilde, Gaspra and Ida (for size comparision)

  18. The NEAR Spacecraft • NEAR spent a year around Eros. • It was photographed many times. • It was found to be more solid (denser) than Mathilde. • In February of 2001, NEAR landed on Eros, sending back pictures as it did so.

  19. Eros at sunset

  20. Earth-Crossing Asteroids • Most asteroids have a eccentricity of between 0.05 and 0.3. • This means that they stay between Mars and Jupiter. • Those having an eccentricity of 0.4 or more (few) may intersect Earth’s orbit and are known as Earth-crossing asteroids.

  21. Earth-Crossing Asteroids • As of 2004, more than 2600 of these asteroids were known. • More than 600 are listed as “potentially hazardous” – more than 150 m in diameter and come within 0.05 AU of Earth. • 1994 - 2004, more than 850 asteroids passed within 15 million km of Earth. • At least 200 are predicted to pass within that same distance in the next decade.

  22. Earth-Crossing Asteroids • Most will eventually hit Earth. • During a million year period, our Earth gets struck by about 3 asteroids. • On average, 2 will hit water and 1 will hit land. • The Moon, Venus and Mars all show evidence of being hit by asteroids also.

  23. Earth-Crossing Asteroids • Most are about 1 km in diameter. • One 10 km one has been found.

  24. How much of a problem would a 1 km asteroid be if it hit Earth? • Catastrophic! • Would devastate an area 100 km in diameter. • The explosion would be equilvalent to a million megaton nuclear bombs – one hundred times more powerful than all of the nuclear weapons on Earth!

  25. How much of a problem would a 1 km asteroid be if it hit Earth? • The shockwave and possible tsunami would affect an even larger area. • This is believed to have caused the extinction of the dinosaurs. • But, don’t worry! We are watching the skies for “problem” asteroids!

  26. Trojan Asteroids • Orbit at and beyond Jupiter’s orbit. • Several hundred of these are known.

  27. Holes in the main belt? • There are holes in the belt, where fewer asteroid exist, known as Kirkwood gaps (discovered by Daniel Kirkwood, 19th century American astronomor) • These exist because of Jupiter’s gravity.

  28. Red – Near Earth Asteroids Green – other asteroids Blue squares – comets Other blue – Trojan asteroids

  29. Dog-Bone Shaped Asteroid 216 Kleopatra

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