Astronomy 101 The Solar System Tuesday, Thursday 2:30-3:45 pm Hasbrouck 20. Tom Burbine

Transcription

1 Astronomy 101 The Solar System Tuesday, Thursday 2:30-3:45 pm Hasbrouck 20 Tom Burbine

2 Course Course Website: Textbook: Pathways to Astronomy (2nd Edition) by Stephen Schneider and Thomas Arny. You also will need a calculator.

3 Office Hours Mine Tuesday, Thursday - 1:15-2:15pm Lederle Graduate Research Tower C 632 Neil Tuesday, Thursday - 11 am-noon Lederle Graduate Research Tower B 619-O

4 Homework We will use Spark owebct Homework will be due approximately twice a week

5 Class Averages For people who took all 4 tests: Class average is 81 Grades range from a 98.5 to a 55.4 Scores will go up when the lowest exam grade is dropped after the final

6 A ( ) A- ( ) B+ ( ) B ( ) B- ( ) C+ ( ) C ( ) C- ( ) D ( ) F (below 59.49)

7 Final Cumulative Monday - 12/14 4:00 pm Hasbrouck 20 Review Session Sunday -12/13 3:00 pm Hasbrouck 134

8 Formulas you may need to know p 2 = a 3 F = GMm/r 2 F = ma a = GM/r 2 Escape velocity = sqrt(2gm/r) T (K) = T ( o C) c = f*λ E = h*f KE = 1/2mv 2 E = mc 2 Density = mass/volume Volume = 4/3πr 3

9 More Formulas Power emitted per unit surface area = σt 4 λ max (nm) = (2,900,000 nm*k)/t Apparent brightness = Luminosity 4π x (distance) 2

10 Intelligent Life Intelligent life that we can detect is usually defined as life that can build a radio telescope

11 Radio Transmitting information over radio waves is very cheap uses equipment that is easy to build has the information-carrying capacity necessary for the task The information also travels at the speed of light.

12 Where are they? Fermi s Paradox

13 Fermi s Paradox Why have we not observed alien civilizations even though simple arguments would suggest that some of these civilizations ought to have spread throughout the galaxy by now?

14 Reason for question Straightforward calculations show that a technological race capable of interstellar travel at (a modest) one tenth the speed of light ought to be able to colonize the entire Galaxy within a period of one to 10 million years.

15 Explanation Interested in us but do not want us (yet) to be aware of their presence (sentinel hypothesis or zoo hypothesis)

16 Explanation Not interested in us because they are by nature xenophobic or not curious

17 Explanation Not interested in us because they are so much further ahead of us

18 Explanation Prone to annihilation before they achieve a significant level of interstellar colonization, because: (a) they self-destruct (b) are destroyed by external effects, such as: (i) the collision of an asteroid or comet with their home world (ii) a galaxy-wide sterilization phenomenon (e.g. a gamma-ray burster (iii) cultural or technological stagnation

19 Explanation Capable of only interplanetary or limited interstellar travel because of fundamental physical, biological, or economic restraints

20 Fermi s paradox The Fermi paradox is the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilizations and the lack of evidence for, or contact with, such civilizations.

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22 Jupiter Largest planet Mass kg (317.8 Earths) Jupiter is 2.5 times more massive than all the other planets combined Mean density g/cm 3 Equatorial diameter - 142,984 km ( Earths)

23 Probes to Jupiter Pioneer Pioneer Voyager Voyager Ulysses Galileo Orbiter Cassini

24 Jupiter Jupiter's atmosphere is composed of ~81% hydrogen and ~18% helium. Jupiter probably has a core of rocky material amounting to something like 10 to 15 Earth-masses. Above the core lies the main bulk of the planet in the form of liquid metallic hydrogen. This exotic form of the most common of elements is possible only at pressures exceeding 4 million bars 1 bar standard atmospheric pressure at sea level on Earth.

25 Jupiter is composed relatively small rocky core surrounded by metallic hydrogen surrounded by liquid hydrogen surrounded by gaseous hydrogen.

26 Clouds clouds of ammonia (NH3), methane (CH4), ammonia hydrosulfide (NH4HS)

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29 zone for the light stripes belt for the dark stripes The differences in colors are caused by slight differences in chemical composition and temperature 13/vjupitr2.mov

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31 Galileo Probe

32 A particularly violent storm, about three times Earth's diameter, is known as the Great Red Spot, and has persisted through more than three centuries of human observation. The spot rotates counterclockwise, once every 7 days. Great Red Spot

33 Jupiter s Rings Jupiter has a faint planetary ring system composed of smoke-like dust particles knocked from its moons by meteor impacts.

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35 Jupiter has four rings

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38 Voyager 1 and 2 Voyager 2 launched first (1977) Then Voyager 1 (1977)

39 Grand Tour Planetary Grand Tour was an ambitious plan to send unmanned probes to the outermost planets of the solar system. Conceived by Gary Flandro of the Jet Propulsion Laboratory, the Grand Tour would have exploited the alignment of Jupiter, Saturn, Uranus, Neptune and Pluto

40 Voyager 2 Went to Jupiter, Saturn, Uranus, and Neptune

41 Voyager 1 Went to Jupiter and Saturn

42 Voyager Golden Record

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44 Pioneer 10 and 11 Plaques (1972)

45 Saturn

46 Saturn Known since prehistoric times Galileo was the first to observe it with a telescope in 1610 In 1659, Christian Huygens correctly inferred the geometry of the rings Saturn is the least dense of the planets; its density (0.7 g/cc) is less than that of water.

47 Rings Very thin 250,000 km or more in diameter they are less than one kilometer thick The ring particles seem to be composed primarily of water ice, but they may also include rocky particles with icy coatings.

48 Roche Limit Rings are either a satellite torn apart by tidal forces or material that was never allowed to condense into moons because of the tidal forces

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50 Cassini-Huygens Visited Saturn and Titan

51 Uranus

52 Uranus Discovered by William Herschel in 1781 In 1977, the first nine rings of Uranus were discovered

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54 Atmosphere The atmosphere of Uranus is composed of 83% hydrogen, 15% helium, 2% methane and small amounts of acetylene and other hydrocarbons. Methane in the upper atmosphere absorbs red light, giving Uranus its blue-green color.

55 Unusual Tipped on its side Why?

56 Due to a collision Probably

57 Uranus Satellites Cordelia Ophelia Bianca Cressida Desdemona Juliet Portia Rosalind 2003U2 Belinda 1986U10 Puck 2003U1 Miranda Ariel Umbriel Titania Oberon 2001U3 Caliban Stephano Trinculo Sycorax 2003U3 Prospero Setebos 2002U2

58 Instead of being named after people from classical mythology, Uranus' moons take their names from the writings of William Shakespeare and Alexander Pope.

59 Neptune

60 Neptune After the discovery of Uranus, it was noticed that its orbit was not as it should be in accordance with Newton's laws. It was therefore predicted that another more distant planet must be perturbing Uranus' orbit. Neptune was first observed by Johan Galle and Heinrich d'arrest on 1846 Sept 23 very near to the locations predicted from theoretical calculations based on the observed positions of Jupiter, Saturn, and Uranus.

61 Galileo Galileo's astronomical drawings show that he had first observed Neptune on December 27, 1612, and again on January 27, 1613; on both occasions Galileo had mistaken Neptune for a fixed star

62 Neptune's blue color is largely the result of absorption of red light by methane in the atmosphere

63 Great Dark Spot Thought to be a hole Scooter Small dark spot

64 Great Dark Spot has disappeared

65 Neptune s Rings

66 Shoemaker-Levy 9 Comet that hit Jupiter Discovered in 1993 Hit Jupiter in 1994

67 Roche Limit The smallest distance at which a natural satellite can orbit a celestial body without being torn apart by the larger body's gravitational force. The distance depends on the densities of the two bodies and the orbit of the satellite. If a planet and a satellite have identical densities, then the Roche limit is times the radius of the planet. Jupiter's moon Metis and Saturn's moon Pan are examples of natural satellites that survive despite being within their Roche limits

68 Why is the Roche Limit important? Comet Shoemaker-Levy 9's decaying orbit around Jupiter passed within its Roche limit in July, 1992, causing it to break into a number of smaller pieces. All known planetary rings are located within the Roche limit

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70 The first impact occurred at 20:15 UTC on July 16, 1994 Fragment A of the nucleus slammed into Jupiter's southern hemisphere at a speed of about 60 km/s. Instruments on Galileo detected a fireball which reached a peak temperature of about 24,000 K, compared to the typical Jovian cloudtop temperature of about 130 K, before expanding and cooling rapidly to about 1500 K after 40 s.

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72 Has this happened before? Ganymede

73 Ganymede-Europa

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76 Satellites Jupiter has 63 known satellites The four large Galilean moons plus many more small ones some of which have not yet been named:

77 Simon Marius ( ) In 1614, Marius published his work Mundus Iovialis describing how he had discovered Jupiter s Moons some days before Galileo did The names by which these satellites are known today (Io, Europa, Ganymede and Callisto) are those given them by Marius. But untile the middle of the 20 th century, these satellited were known as "Jupiter I," "Jupiter II," "Jupiter III," and "Jupiter IV" Gan De, a Chinese astronomer, may have discovered the moons in 362 BC

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79 Galileo

80 Galileo spacecraft Launched in 1989 It arrived at Jupiter on December 7, 1995 On September 21, 2003, Galileo's mission ended by crashing into Jupiter's atmosphere to avoid any chance of it contaminating the Galilean moons with bacteria from Earth.

81 Sagan s Criteria for Life (From measurements of Earth by Galileo) Strong absorption of light at the red end of the visible spectrum, caused by absorption by chlorophyll in photosynthesizing plants Absorption bands due to molecular oxygen (O 2 ), which is also a result of plant activity (O 2 in our atmosphere is many orders of magnitude greater than is found on any other planet in the Solar System) Infrared absorption bands caused by methane (CH 4 ) (about 1 part per million in Earth's atmosphere), a gas which must be replenished by either volcanic or biological activity) Modulated narrowband radio wave transmissions uncharacteristic of any known natural source.

82 Densities Io g/cm 3 Europa g/cm 3 Ganymede 1.94 g/cm 3 Callisto (JIV) 1.83 g/cm 3

83 Io

84 Io Io has almost no craters as first seen by Voyager I (1979) What does that mean?

85 It is geologically active Voyager I saw 9 active volcanos

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88 The energy for this activity probably derives from tidal interactions among Io, Jupiter, and two other moons of Jupiter, Europa, and Ganymede.

89 Europa

90 Europa Very smooth surface Its albedo is one of the highest of all moons Lack of craters indicates a young and active surface

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93 Symmetric ridges in the dark bands suggest that the surface crust was separated and filled with darker material, somewhat analogous to spreading centers in the ocean basins of Earth.

94 Spectroscopy suggests that the dark reddish streaks and features on Europa's surface may be rich in salts such as magnesium sulfate (Epsom salt), deposited by evaporating water that emerged from within.

95 Europa It is thought that under the surface there is a layer of liquid water kept warm by tidally generated heat.

96 Ganymede

97 Ganymede Largest Moon of Jupiter Largest Moon in the solar system

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99 Surface is a mix of two types of terrain: very old, highly cratered dark regions somewhat younger (but still ancient) lighter regions marked with an extensive array of grooves and ridges.

100 Galileo Regio

101 Callisto

102 Callisto One of the most heavily cratered objects in the solar system No large mountains

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104 Any Questions?