Pluto, Comets, and Asteroids

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1 Pluto, Comets, and Asteroids


3 Discovery of Pluto By the end of the 19th century, it appeared that Neptune exhibited irregulari>es in its orbit that indicated the presence of a new planet that had not been previously iden>fied. Percival Lowell searched for this planet un>l his death in 1916, but did not find it. The young astronomer Clyde Tombaugh con>nued Lowell s search, eventually discovering Pluto in However, Pluto is far too small to affect the orbit of Neptune. The apparent irregulari>es in Neptune s orbit were not real and were caused by measurement errors.

4 Discovery of Pluto Tombaugh found Pluto by obtaining 2 photographs of a given area of sky a few weeks apart. He then used a device called a blink comparator to flip between the images, and searched for points of light that moved rela>ve to stars, which remained fixed.

5 Discovery of Pluto

6 The View of Pluto Because of its large distance from the Earth and its small size, Pluto is much too faint to see with the naked eye. With telescopes on the Earth, it is visible as only a point of light. Even images from Hubble barely resolve Pluto, and are not capable of detec>ng surface features. Hubble Space Telescope Earth s moon with same resolu>on

7 Basic Proper>es of Pluto Diameter = 0.17 D earth Mass = M earth = 0.2 M Moon Distance from Sun = AU Atmosphere = N 2, CH 4, CO Surface temperature = C (- 387 F) Rota>onal period (its day) = days Orbital period (its year) = 248 years Moons = 5

8 Orbit of Pluto The orbit of Pluto is highly ellip>cal. As a result, its distance from the Sun varies from 30 to 50 AU over the course of its orbit. In fact, for 20 of the 248 years of its orbit, Pluto is closer to the Sun than Neptune. Because Pluto orbits the Sun twice for every three orbits of Neptune, they are never close to each other and will never collide.

9 Orbit of Pluto The orbits of the terrestrial and Jovian planets are nearly in the same plane. However, Pluto s orbit is >lted by 17 rela>ve to their orbital planes. Thus, both the shape and plane of Pluto s orbit are dis>nc>ve from those of the 8 major planets (but similar to Kuiper Belt objects).


11 Size of Pluto Pluto is much smaller than the 8 major planets. In fact, it is smaller than several moons.

12 Moons of Pluto In 1979, astronomers at the U.S. Naval Observatory discovered a moon orbi>ng Pluto. This object, named Charon, has 1/8 the mass of Pluto and 1/2 the diameter of Pluto.

13 Moons of Pluto Between 2005 and 2012, the Hubble Space Telescope has discovered 4 addi>onal moons around Pluto. Pluto and its 5 moons orbit each other in the same plane, indica>ng that they formed from the debris leg behind from a collision of two Pluto- sized bodies.

14 Mission to Pluto The New Horizons spacecrag was launched in It obtained a gravity assist from Jupiter in 2007 and conducted a flyby of Pluto in The spacecrag will also visit an addi>onal Kuiper Belt object beyond Pluto that is near its path as it leaves the solar system.












26 Discovery of Solar System Bodies Jupiter Saturn Mercury, Venus, Earth, Mars, Jupiter, and Saturn are considered the original planets. They have been known since ancient history and their discovery is not ahributed to any one person.

27 Discovery of Solar System Bodies Jupiter Saturn Uranus 1781 Unlike the original planets, the other planets cannot be seen with the naked eye and were not found un>l telescopes were invented. William Herschel discovered the first modern planet, Uranus, in 1781.

28 Discovery of Solar System Bodies Ceres 1801 Jupiter Saturn Uranus 1781 Asteroid Belt The largest asteroid, Ceres, was discovered in For decades, Ceres was called a planet, but ager many addi>onal smaller bodies were discovered in similar orbits, people realized that Ceres was the largest member of a belt of rocky bodies, now known as the Asteroid Belt.

29 Discovery of Solar System Bodies Ceres 1801 Jupiter Saturn Uranus 1781 Neptune 1846 Asteroid Belt At the same >me that the first asteroids were being found, a new planet was discovered in the outer solar system, Neptune, in 1846.

30 Discovery of Solar System Bodies Ceres 1801 Jupiter Saturn Uranus 1781 Neptune 1846 Pluto 1930 Asteroid Belt Kuiper Belt Beyond the gas giants, a very small, icy body was discovered by Clyde Tombaugh in 1930, named Pluto. Since its discovery, many smaller objects have been found near the orbit of Pluto, now called the Kuiper Belt. Like Ceres, Pluto is a large member of a belt of millions of objects rather than a planet.

31 Discovery of Solar System Bodies

32 Discovery of Solar System Bodies Eris

33 Discovery of Solar System Bodies Ceres 1801 Jupiter Saturn Uranus 1781 Neptune 1846 Pluto 1930 Eris 2005 Asteroid Belt Kuiper Belt Although it was known to be a Kuiper Belt object rather than a planet for decades, Pluto was s>ll called a planet for sen>mental reasons. But in 2005, a new member of the Kuiper Belt was discovered that is larger than Pluto, named Eris. This forced a decision: demote Pluto as a planet, or add Eris as the 10th planet.

34 The discovery of a new object larger than Pluto (Eris) prompted the Interna>onal Astronomical Union to examine how planet should be defined. On Aug. 24, 2006, the IAU defined a planet as an object that is not a moon around a larger object orbits the Sun Defini>on of a Planet has enough mass so that it has pulled itself into a round shape has cleared the neighborhood of its orbit of other objects The IAU also defined a new term, dwarf planet, as an object that has the first three proper>es, but that lacks enough mass and gravity to clear its neighborhood, and is not a moon. Because Pluto is a member of the Kuiper Belt, it falls in this category.

35 Dwarf Planets The IAU classified Ceres, Pluto, and Eris as dwarf planets.

36 Ceres Pluto Eris Moon Largest Asteroid Largest Kuiper Belt Objects

37 Dwarf Planets However, there are about 40 addi>onal objects known beyond the orbit of Neptune that probably sa>sfy the defini>on of dwarf planet, although we don t have enough data for most of them to determine conclusively whether they are round since they are so far away.

38 Problems with the New Defini>ons One problem with dwarf planet is that astronomers already had adequate terms for them: asteroids (Ceres) and Kuiper Belt objects (Pluto and Eris). A new term like dwarf planet seems unnecessary.

39 Comets and Asteroids: Why are they important? Oldest materials in the solar system Possible source of water and organic compounds for the early Earth Occasionally impact the Earth

40 Composi>on of Comets and Asteroids Comets are mostly composed of rocks and ice. They are ogen referred to as dirty snowballs and resemble the icy moons in the outer solar system. Asteroids are mostly made of rocks and metals, and a lihle ice. Thus, they are similar to the terrestrial planets in composi>on. Most comets and asteroids have too lihle mass and gravity to pull themselves into round shapes. As a result, they usually have irregular shapes. Only the largest objects (> km) are spherical.

41 The Asteroid Belt Most asteroids are found in a belt between the orbits of Mars and Jupiter. A small frac>on of asteroids cross the orbit of the Earth known 250,000 known few hundred

42 The Kuiper Belt The Kuiper Belt is a belt of millions of icy bodies (comet nuclei) extending from AU from the Sun, just beyond Neptune s orbit. Pluto and Eris are the largest known members of the Kuiper Belt.

43 The Oort Cloud The Oort Cloud is a spherical shell of billions of icy bodies 50,000 AU from the Sun. Because of it is so far away, we cannot see any of the objects in the Oort Cloud.



46 Seeing Comets If an icy body from the Kuiper Belt or Oort Cloud is deflected into the inner solar system, sunlight can evaporate ice from its surface, forming a huge cloud of gas and dust that can be bright enough to see with the naked eye. hhp://>ve.html




50 Seeing Asteroids Asteroids are much fainter than comets because they have lihle ice, so they don t form the huge clouds found in comets. The first known asteroid, Ceres, needed a telescope to be found. Only one asteroid (Vesta) is visible to the naked eye. However, because most asteroids remain in the inner solar system for the en>re orbits, they are not as faint as the comet nuclei found in the Kuiper Belt and Oort Cloud.

51 Ceres and Vesta Ceres and Vesta are the largest asteroids. Asteroids appear as only points of light through telescopes on the ground because of their small sizes. Even the Hubble Space Telescope is able to detect only a few surface features on the largest asteroids. Ceres Vesta

52 Missions to Comets The European spacecrag Gioho conducted a flyby of Halley s comet in 1986, providing the first close- up images of a comet.

53 Missions to Comets The NASA spacecrag Stardust flew through the coma of the comet Wild 2 in It used a low- density substance known as areogel to collect >ny par>cles of dust from the comet s coma. The spacecrag then returned these samples to Earth in Wild 2 was deflected by Jupiter into the inner solar system rela>vely recently (1974), so it has experienced lihle evapora>on and the samples returned by Stardust should be nearly unchanged since the birth of the solar system.


55 Missions to Comets In 2005, the NASA spacecrag Deep Impact conducted a flyby of the comet Tempel 1 (nucleus diameter = 6 km) and deployed a smaller spacecrag that collided with the comet on July 4. The flyby spacecrag observed the explosion, debris, and crater that resulted from the impact. This mission provided a unique way of studying the interiors of comets.





60 Missions to Comets Roseha is a European spacecrag that was launched in It arrived at the comet 67P/Churyumov- Gerasimenko in August 2014 when it was 5 AU from the Sun. Roseha orbited the comet for 2 years, watching how it changes as it approaches the Sun. The spacecrag also deployed a small lander called Philae onto the surface of the comet nucleus in November 2014.

61 Comet 67P/C- G

62 Roseha spacecrag

63 Philae lander


65 Missions to Asteroids During its journey to Jupiter, the path of the Galileo spacecrag was adjusted slightly so that it would pass near the asteroids Gaspra (1991) and Ida (1993). Galileo provided the first close- up images of asteroids. Both of these objects have irregular shapes and are heavily cratered. A small moon (1.5 km) was found orbi>ng Ida. 20 km 60 km

66 Missions to Asteroids Eros is one of the largest near- Earth asteroids. NEAR Shoemaker arrived at Eros on February 14, It orbited the asteroid for nearly a year, studying its surface, composi>on, and structure. The surface was found to be heavily cratered. At the end if its mission, NEAR Shoemaker landed on the surface of Eros. Although it wasn t designed for a landing, the spacecrag landed intact and con>nued transmiqng for a short >me. 35 km




70 Ceres and Vesta Ceres and Vesta are the largest asteroids. Asteroids appear as only points of light through telescopes on the ground because of their small sizes. Even the Hubble Space Telescope is able to detect only a few surface features on the largest asteroids. Ceres Vesta

71 Mission to Ceres and Vesta The Dawn spacecrag was launched in 2007, orbited Vesta for 1 year in 2011 and 2012, and arrived at Ceres in March Ceres Vesta