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Astronomy 101 The Solar System Tuesday, Thursday 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. Final • • • • • • May 7th Friday 4 pm Totman Gym Cumulative Review Session – Hasbrouck 20, 6:15 pm, Wednesday (May 5th) Formulas • • • • • • • • • • p2 = a3 F = GMm/r2 F = ma T (K) = T (oC) + 273.15 c = f* E = h*f KE = 1/2mv2 E = mc2 Density = mass/volume Volume = 4/3r3 HW • Homeworks #21, #22, #23, and #24 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 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 • 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 Triton • Largest moon of Neptune • Has retrograde orbit (orbits the planet in the opposite direction as the planet is rotating) • May be captured Kuiper Belt Object Pluto • • • • Pluto is a Dwarf Planet Smallest planet Diameter = 2306 ± 20 km (18% of Earth) Mass = (1.305±0.007)×1022 kg (0.0021 Earths) • In the late 19th century, astronomers started speculating that Neptune's orbit was being disturbed by another planet. • Pluto was discovered after an extensive search by Clyde Tombaugh at the Lowell Observatory in Arizona in 1930 Pluto • Venetia Burney (born 1919) was the first person to suggest the name Pluto for the 9th planet However • Pluto is far too small to have the effect on Neptune's orbit that initiated the search. • The discrepancies in Neptune's orbit observed by 19th century astronomers were due instead to an inaccurate estimate of Neptune's mass. • Pluto’s orbit is exceptional among the planets – high inclination (>17 °) and eccentricity (~0.25). – Only Mercury's orbit shows a significant inclination (~7°) and eccentricity (~0.2) • Other planets follow quasi-circular, near–ecliptic orbits Density • 2.03 g/cm3 • What does this mean? Satellites • Charon – discovered in 1978 by astronomer James Christy • Two smaller, provisionally designated ones – Nix – Hydra • Barycenter (center of mass) lies above the planet's surface. • Charon is large relative to Pluto – Diameter is half of Pluto • Some astronomers label it a double planet system • Pluto's icy surface is 98% nitrogen (N2). • Methane (CH4) and traces of carbon monoxide (CO) are also present. • The solid methane indicates that Pluto is colder than 70 Kelvin. Pluto Pluto Kuiper Belt • Pluto is thought to be one of the largest Kuiper Belt Objects (KBOs) • Kuiper Belt is a region of the Solar System beyond the planets extending from the orbit of Neptune (at 30 AU) to approximately 55 AU from the Sun • Over 1,000 Kuiper Belt Objects (1,130) are known Eris • It has a moon - Dysnomia • Larger than Pluto Eris New Horizons Mission • Will characterize the global geology and morphology of Pluto and its moon Charon • Map their surface composition and characterize Pluto's neutral atmosphere and its escape rate • Will also photograph the surfaces of Pluto and Charon. Earth • Is the only planet known to have life SETI • Search for Extra-Terrestrial Intelligence • SETI programs tend to survey the sky to detect the existence of transmissions from a civilization on a faraway planet Intelligent Life • You have to be able to build a radio telescope • Of electromagnetic radiation, only radio and gamma can cross the Milky Way Galaxy • It takes far less energy to produce radio waves than gamma rays Europa • Moon of Jupiter • Has an outer layer of ice http://en.wikipedia.org/wiki/Image:Europa-moon.jpg Europa • Is thought to have a liquid ocean beneath an icy surface • Energy source provided by tidal heating (keeps ocean from freezing) • Proposed as possibly as possibly having extraterrestrial life www.physics.brandeis.edu/powerpoint/Charbonneau.ppt The only star we know that has Earth-Like Planets is the Sun • Sun is sometimes called Sol Galactic Habitable Zone • It is the area in the galaxy whose boundaries are set by its calm and safe environment, and access to the chemical materials necessary for building terrestrial planets similar to the Earth. http://astronomy.swin.edu.au/GHZ/ green is habitable zone Habitable Zones • http://en.wikipedia.org/wiki/Image:Habzonethinkquest.gif HabCat • Catalog of Nearby Habitable Systems made by Jill Tarter and Margaret Turnbull • These Sun-like, habitable stars have just the right distance, constancy, and temperature to qualify in a forthcoming enlarged radio search. What do else do you need? • You need “metals” to make planets –Metals are elements heavier in mass than helium For simple life • You need a planet with an atmosphere and some water • Stars must remain nearly constant in brightness over billions of years for complex life to have time to develop. – On Earth, single cells may have developed after only 800 million years or so, but the fossil record indicates that it took another 3 to 4 billion years before multi-cellular life flourished. • The number of HabCat stars, as a function of distance • M-type stars (solid red histogram) • K stars (dark-hatched green histogram) • G stars (light-hatched violet histogram) • F stars (horizontal-lined yellow histogram) • all stars (open blue histogram). http://www.astrobio.net/news/article436.html Drake Equation • The Drake Equation is an attempt to estimate the number of extraterrestrial civilizations in our galaxy with which we might come in contact. • http://www.activemind.com/Mysterious/Topics/SETI/drake_equation.html Number of habitable planets • 100 billion? Fraction of Planets that have life in the Galaxy • ? Fraction of the Life-Bearing Planets in the Galaxy upon which a Civilization capable of interstellar communication has at some time arisen • ? 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. Fraction of all civilizations that have existed in the galaxy that exist now • ? 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 Any Questions? Any Questions?