Astronomy 101 The Solar System Tuesday, Thursday 2:30-3:45 pm Hasbrouck 20 Tom Burbine [email protected] Course • Course Website: – http://blogs.umass.edu/astron101-tburbine/ • Textbook: – Pathways to Astronomy (2nd Edition) by Stephen Schneider and Thomas Arny. • You also will need a calculator. 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 Homework • We will use Spark • https://spark.oit.umass.edu/webct/logonDisplay.d owebct • Homework will be due approximately twice a week 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 • A (92.50 – 100) • A- (89.50 – 92.49) • B+ (87.50 – 89.49) • B (82.50 – 87.49) • B- (79.50 – 82.49) • C+ (77.50 – 79.49) • C (72.50 – 77.49) • C- (69.50 – 72.49) • D (59.50 – 69.49) • F (below 59.49) Final • Cumulative • Monday - 12/14 • 4:00 pm • Hasbrouck 20 • Review Session • Sunday -12/13 • 3:00 pm • Hasbrouck 134 Formulas you may need to know • p2 = a3 • F = GMm/r2 • F = ma • a = GM/r2 • Escape velocity = sqrt(2GM/r) • T (K) = T (oC) + 273.15 • c = f*λ • E = h*f • KE = 1/2mv2 • E = mc2 • Density = mass/volume • Volume = 4/3πr3 More Formulas • Power emitted per unit surface area = σT4 • λmax (nm) = (2,900,000 nm*K)/T • Apparent brightness = Luminosity 4π x (distance)2 Intelligent Life • Intelligent life that we can detect is usually defined as life that can build a radio telescope 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. Fermi’s Paradox • Where are they? 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? 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. Explanation • Interested in us but do not want us (yet) to be aware of their presence (sentinel hypothesis or zoo hypothesis) Explanation • Not interested in us because they are by nature xenophobic or not curious Explanation • Not interested in us because they are so much further ahead of us 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 Explanation • Capable of only interplanetary or limited interstellar travel because of fundamental physical, biological, or economic restraints 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. • http://en.wikipedia.org/wiki/Fermi_paradox Jupiter • Largest planet – Mass - 1.899×1027 kg (317.8 Earths) – Jupiter is 2.5 times more massive than all the other planets combined • Mean density - 1.326 g/cm3 • Equatorial diameter - 142,984 km (11.209 Earths) Probes to Jupiter • Pioneer 10 – 1973 • Pioneer 11 - 1974 • Voyager 1 – 1979 • Voyager 2 - 1979 • Ulysses - 1992 • Galileo – 1995 - Orbiter • Cassini - 2000 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. • Jupiter is composed – relatively small rocky core – surrounded by metallic hydrogen – surrounded by liquid hydrogen – surrounded by gaseous hydrogen. Clouds • clouds of ammonia (NH3), methane (CH4), ammonia hydrosulfide (NH4HS) • zone for the light stripes • belt for the dark stripes • http://en.wikipedia.org/wiki/Cloud_pattern_on_Jupiter • The differences in colors are caused by slight differences in chemical composition and temperature • http://zebu.uoregon.edu/~imamura/121/lecture- 13/vjupitr2.mov Galileo Probe Great Red Spot • 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. Jupiter’s Rings • Jupiter has a faint planetary ring system composed of smoke-like dust particles knocked from its moons by meteor impacts. Jupiter has four rings Voyager 1 and 2 • Voyager 2 launched first (1977) • Then Voyager 1 (1977) 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 Voyager 2 • Went to Jupiter, Saturn, Uranus, and Neptune Voyager 1 • Went to Jupiter and Saturn Voyager Golden Record Pioneer 10 and 11 Plaques (1972) Saturn 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. 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. 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 • http://csep10.phys.utk.edu/astr161/lect/saturn/rings.html Cassini-Huygens • Visited Saturn and Titan Uranus Uranus • Discovered by William Herschel in 1781 • In 1977, the first nine rings of Uranus were discovered 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. Unusual • Tipped on its side • Why? Probably • Due to a collision Uranus’ Satellites • Cordelia • Miranda • Ophelia • Ariel • Bianca • Umbriel • Cressida • Titania • Desdemona • Oberon • Juliet • 2001U3 • Portia • Caliban • Rosalind • Stephano • 2003U2 • Trinculo • Belinda • Sycorax • 1986U10 • 2003U3 • Puck • Prospero • 2003U1 • Setebos • 2002U2 • Instead of being named after people from classical mythology, Uranus' moons take their names from the writings of William Shakespeare and Alexander Pope. Neptune 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. 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 • Neptune's blue color is largely the result of absorption of red light by methane in the atmosphere Great Dark Spot • Thought to be a hole Scooter Small dark spot Great Dark Spot has disappeared Neptune’s Rings Shoemaker-Levy 9 • Comet that hit Jupiter • Discovered in 1993 • Hit Jupiter in 1994 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 2.446 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 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 • 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. Has this happened before? Ganymede Ganymede-Europa Satellites • Jupiter has 63 known satellites • The four large Galilean moons plus many more small ones some of which have not yet been named: Simon Marius (1573-1624) • 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 20th 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 Galileo 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.