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Slide 2 Slide 3 Asteroids, Comets, and Meteoroids Asteroids are small, rocky objects. The name asteroid actually means star-like bodies. Slide 4 The largest known asteroid is Ceres. Ceres is 940 km across. There were 4000 known asteroids by the mid-1990s. Slide 5 Slide 6 Slide 7 Slide 8 Slide 9 The total mass of all these asteroids is less than 1/10 the mass of our Moon. Asteroids generally have very eccentric orbits between the orbits of Mars and Jupiter. Slide 10 Asteroids were first discovered when astronomers were looking for a planet that fit the Titius- Bode law. Slide 11 Giuseppe Piazzi first detected Ceres in 1801 at an orbit 2.8 A.U.s from the Sun. This distance was perfect for the expected location of a planet by the T-B law. Slide 12 Soon thereafter, three more asteroids were discovered: Orbit Diameter Pallas2.8 A.U.580 km Juno2.7 A.U.320 km Vesta3.4 A.U.540 km Slide 13 Slide 14 Slide 15 Slide 16 Slide 17 Most of the asteroids are confined to the asteroid belt, between 2.1 and 3.3 A.U. from the Sun. Slide 18 Slide 19 Slide 20 The asteroids may have been a planet at one time, or they may have never formed a planet due to the gravitational pulls of Jupiter (probably the latter). Slide 21 Slide 22 Slide 23 Slide 24 Most asteroids always stay between the orbits of Mars and Jupiter. Some stray inside Earths orbit, the Apollo Asteroids. The Amor Asteroids cross Mars orbit. Slide 25 In 1968, the asteroid Icarus missed Earth by 6 million km. In 1989, asteroid 1989FC passed Earth at a distance of 800,000 km (2 times the distance to the Moon). Slide 26 In 1991, 1991BA missed by less than half the distance to the Moon at 170,000 km. Slide 27 The possibility of a collision with an asteroid is a real concern; however, there is not much we could do about such an occurrence. Slide 28 Statistically, over a million year period there should be 3 Apollo asteroid collisions. Slide 29 Most Apollo asteroids are about 1 km in size, but one is 10 km. Slide 30 Collision with even a 1 km asteroid would be catastrophic. It would devastate an area 100 km in diameter. Slide 31 The impact would be equal to one million 1-megaton nuclear bombs (this is 100 times ALL the nuclear weapons now on Earth). It would also produce a fatal blast wave. Slide 32 Spaceguard is a systematic search to try and predict potential collisions with Apollo asteroids. The entire staff of Spaceguard is less than the number of employees at the local McDonalds. Slide 33 Asteroid 3753 follows the yellow path while also orbiting the Sun. Each orbit the yellow path shifts, taking 385 years to complete one cycle. Asteroid 3753s orbit is inclined to Earths, so they can never collide. Slide 34 Slide 35 Slide 36 Slide 37 There are families of asteroids called Hirayama Families. Each family contains 5 to 10 members that all have similar orbits. Slide 38 They are probably the remains of a single asteroid that broke up after a collision with another asteroid. The remnants then spread out along the orbit. Slide 39 There are also binary asteroids: two asteroids that orbit each other in addition to orbiting the Sun. Slide 40 Slide 41 Trojan Asteroids are asteroids that orbit in Jupiters orbit. They are locked at LaGrange points with Jupiter (60) as a result of the synchronism of gravity with the Sun and Jupiter. Slide 42 Slide 43 The main asteroid belt has gaps called Kirkwood Gaps. These are produced by gravitational resonances with planets (much as Saturns moons produce gaps in the rings). Slide 44 There are two basic types of asteroids: C-type asteroids and S-type asteroids. Slide 45 The C-type asteroids contain lots of carbon (C stands for carbonaceous). They are the least reflective asteroids with albedos around 0.05. Slide 46 The S-type (S means silicon) are made up more of rocky materials. Containing less carbon, they are more reflective with albedos of 0.15 to 0.25. Slide 47 The asteroids at the edge of the asteroid belt that is closest to the Sun are primarily S-type. The asteroids transition gradually to being more C-type as you move out further from the Sun. Slide 48 The size of asteroids is estimated by the amount of light reflected and the amount of heat radiated. Rare stellar occultations aid in determining size. Slide 49 Larger asteroids are roughly spherical, while the smaller ones can be highly irregular in shape. Slide 50 Slide 51 The Jupiter probe Galileo passed through the asteroid belt twice. It passed close to and took pictures of Gaspra in 1991. Slide 52 Slide 53 Slide 54 Slide 55 Gaspra is irregularly shaped, has a maximum diameter of 20 km, is pitted with craters up to 2 km across, and has a regolith (dust) layer. Slide 56 Slide 57 Slide 58 On Feb 14, 2000 the NEAR spacecraft became the first artificial satellite of an asteroid when it moved into orbit around the asteroid Eros, a 20 mile long asteroid with a 3 mile crater. Slide 59 Slide 60 Slide 61 Slide 62 Slide 63 Slide 64 Slide 65 Slide 66 Slide 67 Slide 68 Slide 69 Slide 70 Slide 71 Slide 72 Slide 73 Slide 74 Slide 75 Slide 76 The NEAR spacecraft arrived at Eros (the goddess of love) on February 14, 2000, so here is your valentine!! Slide 77 Slide 78 Eros is a large, S-type near-earth asteroid that is too small to have enough gravity to form it into a sphere. By comparison, Eros has less than a thousandth Earth's gravity, so a 100 pound object on Earth would weigh about 1 ounce on Eros. A baseball thrown at 22 miles per hour would completely escape into space! Slide 79 Slide 80 Slide 81 Slide 82 Slide 83 Slide 84 Slide 85 Slide 86 Slide 87 Slide 88 Slide 89 Slide 90 Slide 91 Slide 92 Slide 93 Slide 94 Slide 95 Slide 96 Slide 97 Slide 98 Other spacecraft have been sent to research asteroids as seen in the next slide. Slide 99 Slide 100