Other Objects in the Solar System PDF

Lesson 9 Other Objects in Our Solar System Copyright © 2020 W. W. Norton & Company Asteroids ▪ Asteroids are generally rocky or metallic objects larger than 100 meters (330 feet) across. ▪ Remains of primitive planetesimals that never coalesced into large bodies or were broken up in collisions ▪...

Lesson 9 Other Objects in Our Solar System Copyright © 2020 W. W. Norton & Company Asteroids ▪ Asteroids are generally rocky or metallic objects larger than 100 meters (330 feet) across. ▪ Remains of primitive planetesimals that never coalesced into large bodies or were broken up in collisions ▪ Found throughout the Solar System, but concentrated into a number of groups, the largest of which is the asteroid belt between Jupiter and Mars. ▪ The largest is Ceres, diameter ~1000 kilometers (dwarf planet) ▪ 150,000 in catalogs, and probably over a million with diameter >1 kilometer. ▪ Small asteroids are more common than large asteroids. ▪ All the asteroids in the solar system wouldn’t add up to even a small terrestrial planet. Figure 22.28a,c Asteroids are cratered and not round. Asteroids with Moons ▪Some large asteroids have their own moon. ▪Asteroid Ida has a tiny moon named Dactyl. Density of Asteroids ▪Measuring the orbit of asteroid’s moon tells us an asteroid’s mass. ▪Mass and size tell us an asteroid’s density. ▪Some asteroids are solid rock; others are just piles of rubble. Asteroid Orbits ▪ Most asteroids orbit in the asteroid belt between Mars and Jupiter. ▪ Trojan asteroids follow Jupiter’s orbit. ▪ Orbits of near-Earth asteroids cross Earth’s orbit. ▪ Nearest Asteroid to Earth was BU-2023 which came 3540 km from Earth in 2022 Thought Question Which explanation for the belt seems the most plausible? A. The belt is where all the asteroids happened to form. B. The belt is the remnant of a large terrestrial planet that used to be between Mars and Jupiter. C. The belt is where all the asteroids happened to survive. Thought Question Which explanation for the belt seems the most plausible? A. The belt is where all the asteroids happened to form. B. The belt is the remnant of a large terrestrial planet that used to be between Mars and Jupiter. C. The belt is where all the asteroids happened to survive. But WHY didn’t they form a planet? Orbital Resonances ▪ Asteroids in orbital resonance with Jupiter experience periodic nudges. ▪ Eventually, those nudges move asteroids out of resonant orbits, leaving gaps in the asteroid belt. ▪ The effect of these meanmotion resonances is a change in the asteroid's orbital elements (particularly semimajor axis) sufficient to create these gaps in semimajor axis space. The ratio is represents the number of Jupiter orbits for the asteroid orbit. If the ratio is 2/5, then Jupiter completes 2 orbits for 5 asteroid orbits. Origin of Asteroid Belt ▪Rocky planetesimals between Mars and Jupiter did not accrete into a planet. ▪Jupiter’s gravity, through influence of orbital resonances, stirred up asteroid orbits and prevented their accretion into a planet. Pluto ▪ Dwarf planet since 2006 ▪ Orbital plane at a 17-degree tilt to the Earth’s orbital plane ▪ Orbit is very eccentric ▪ Located in the Kuiper Belt ▪ Much smaller than the terrestrial or Jovian planets ▪ Not a gas giant like other outer planets ▪ Has an icy composition like a comet ▪ Has a very elliptical, inclined orbit ▪ Has more in common with comets than with the eight major planets ▪ Pluto’s size was overestimated after its discovery in 1930, and nothing of similar size was discovered for several decades. What is Pluto like? ▪ Its moon Charon is nearly as large as Pluto itself (probably made by a major impact). ▪ Pluto is very cold (40 K). ▪ Pluto has a thin nitrogen atmosphere that will refreeze onto the surface as Pluto’s orbit takes it farther from the Sun. Discovery of Pluto by Clyde Tombaugh on February 18, 1930. The object moved, the background stars did not. Lick Observatory images are 1 day apart Pluto (diameter ~ 2320 km; surface T = - 390° F) and its moon Charon imaged by the Hubble Space Telescope Charon was discovered in 1978 and is ~ 1,200 km in diameter Pat Rawlings conception of the Pluto-Charon binary-planet system (left-front = Charon; right-back = Pluto) Relative sizes of Pluto, Charon, and the US. Pluto is 2,320 km and Charon ~ 1,200 km in diameter Pluto’s unusual orbit It is steeply inclined (17°) and highly eccentric (0.25). At times, Pluto’s orbit reaches inside that of Neptune The New Horizons Mission – the race to catch the atmosphere of Pluto before it freezes in ~2015 Launch January 19, 2006 (Jupiter fly-by February 2007) Pluto encounter in July 2015 Pluto’s Surface ▪ Close-ups of Pluto’s surface from New Horizons 2015 flyby reveal icy mountains and fractured plains. Figure 22.29a PLUTO AND THE KUIPER BELT ▪ Beyond Neptune, the most distant major planet, are a large number of smaller objects, all of which currently known are smaller than the smallest major planet, Mercury. ▪ These objects, which include the first observed and named, Pluto, also have eccentric orbits in comparison to the inner eight planets. ▪ Although Pluto was discovered in 1930, no other objects of comparable size and greater distance were detected until the 1990s and later. ▪ Pluto has a very eccentric (and tilted) orbit in comparison to the inner planets, and in a portion of its orbit, it can be closer to the Sun than is Neptune. ▪ Most of the other objects discovered in the Kuiper Belt in recent years have been smaller in size than Pluto, as well as more distant from the Sun. ▪ Most recently, an object has been discovered which is at least equal, and probably larger, in size than Pluto, and is also the most distant such object discovered as yet. Pluto’s Moons ▪ Pluto has several moons including the largest Charon that was discovered in 1978. ▪ Note the relatively low number of impact craters on the surface. Figure 22.29b Satellites of Pluto Discovered by HST THE NEW HORIZONS MISSION TO PLUTO ▪ Pluto is the last of the original 9 planets of our solar system which has not been visited by spacecraft. ▪ On January 19, 2006 the New Horizons spacecraft was launched by NASA on a mission which did a fly by of Jupiter on February, 2007 and reached Pluto in July, 2015. ▪ It also explored Pluto’s satellite Charon, and other members of the Kuiper Belt zone beyond the orbit of Neptune, to the extent possible. New Horizons Mission Objectives • Map surface composition of Pluto and Charon • • • • • • Characterize geology and morphology ("the look") of Pluto and Charon Characterize the neutral atmosphere of Pluto and its escape rate Search for an atmosphere around Charon Map surface temperatures on Pluto and Charon Search for rings and additional satellites around Pluto Conduct similar investigations of one or more Kuiper Belt Objects NEW HORIZONS SCIENTIFIC INSTRUMENTS ▪ ALICE – Ultraviolet Mapping Spectrometer ▪ LORRI – Long-Range Reconnaissance Imager ▪ RALPH MVIC – Multispectral Visible Imaging Camera ▪ RALPH LEISA – Linear Etalon Imaging Spectral Array (Infrared Spectrometer) ▪ REX – Radio Experiment (also transmits all science data from the spacecraft) ▪ SWAP – Solar Wind Analyzer Around Pluto ▪ SDC – Student Dust Counter Artist’s Concept of New Horizons Mission Spacecraft at Pluto and Charon THE KUIPER BELT ▪ The Kuiper belt, named after astronomer Gerard Kuiper, is a relatively new designation for the region of the outer solar system beyond the orbit of Neptune (whose largest known member, by this designation, has (until recently) been Pluto). ▪ The Kuiper Belt is also believed to be the primary home of most of the long-period comets. ▪ In recent years, a significant number of new solar system objects have been discovered in this region, some at considerably greater distance than Pluto at its greatest distance from the Sun (but, until very recently, none as large or larger). ▪ Two of these, known as Quaoar and (more recently) 2004 DW (Orcus), are comparable in size to Pluto’s satellite, Charon. ▪ The most distant of these, is the object named Sedna, discovered at a distance of about 13.4 billion km (89 AU), and also comparable in size to Quaoar, 2004 DW, and Charon. ▪ Sedna has a highly eccentric orbit, which is estimated to extend from 76 AU to as far as 950 AU! UB313 was renamed Eris Orbit of the newly discovered object, 2003 UB313, compared to those of Pluto and the giant outer planets. Note, the orbits of Pluto and UB313, in red, are tilted relative to the plane of the inner giant planet orbits. KUIPER BELT MEMBERS DISCOVERED TO DATE KUIPER BELT MEMBERS DISCOVERED TO DATE 2007 OR10 has been renamed Gonggong Comets ▪ Highly elliptical orbits (right) ▪ Loosely bound aggregates of rock and ice traditionally referred to as “dirty snowballs” ▪ Composed of nucleus and tail ▪ Formed beyond the frost line, comets are icy counterparts to asteroids. ▪ Nucleus of comet is the “dirty snowball.” ▪ Most comets do not have tails. ▪ Most comets remain perpetually frozen in the outer solar system. ▪ Only comets that enter the inner solar system grow tails. ▪ Tail appears as material melts/outgases as it comes nearer the Sun (left, Hale-Bopp) Figure 22.30 Comet Nucleus ▪ Nucleus is composed of loosely bound ice (frozen water, methane, carbon dioxide, and ammonia) and rock Figure 22.31a Nucleus of Comet ▪A “dirty snowball” ▪Source of material for comet’s tail Deep Impact ▪Mission to study nucleus of Comet Tempel 1 ▪Projectile hit surface on July 4, 2005. ▪Many telescopes studied aftermath of impact. Comet Tail ▪ A comet has two tails • The ion tail always points straight away from the Sun. • The dust tail curves slightly, though still away from the Sun because it contains charges and the sun’s magnetic field affects the motion of these particles. • The comet shown on the right is Hale-Bopp. Figure 22.32 Anatomy of a Comet ▪A coma is the atmosphere that comes from a comet’s heated nucleus. ▪A plasma tail is gas escaping from coma, pushed by the solar wind. ▪A dust tail is pushed by pressure of photons. Growth of Tail ▪ Comets eject small particles that follow the comet around in its orbit and cause meteor showers when Earth crosses the comet’s orbit. ▪ Comet 109P/Swift–Tuttle has been known to be the cause of the Perseids meteor shower (August) ▪ Comet Tempel-Tuttle responsible for Leonids (November) ▪ Comet Encke responsible for Taurids (November) Where do comets come from? Only a tiny number of comets enter the inner solar system. Most stay far from the Sun. Oort cloud: on random orbits extending to about 50,000 AU Kuiper belt: on orderly orbits from 30–50 AU in disk of solar system How did they get there? ▪ Kuiper belt comets formed in the Kuiper belt: flat plane, aligned with the plane of planetary orbits, orbiting in the same direction as the planets ▪ Oort cloud comets were once closer to the Sun, but they were kicked out there by gravitational interactions with Jovian planets: spherical distribution, orbits in any direction Meteoroids, Meteors, and Meteorites—1 ▪ Smaller objects (less than 1 meter across) referred to as meteoroids ▪ Meteoroids whose paths cross the Earth’s orbit may collide with the Earth. ▪ A meteoroid that enters the atmosphere generates immense heat, which causes some or all of the meteoroid to vaporize and produce a blazing streak across the sky called a meteor. Figure 22.33b Meteoroids, Meteors, and Meteorites—2 ▪ During a meteor shower, observer can see from ten to a hundred meteors/hour (top). ▪ If a meteoroid makes it to the ground, it then becomes a meteorite (bottom). ▪ Meteorite: a rock from space that falls through Earth’s atmosphere ▪ Meteor: the bright trail left by a meteorite Figure 22.33a,c Meteorite Impact Chicago, March 26, 2003 Meteorite Types 1) Primitive: unchanged in composition since they first formed 4.6 billion years ago 2) Processed: younger; have experienced processes like volcanism or differentiation Primitive Meteorites Processed Meteorites Meteorites from Moon and Mars ▪ A few meteorites arrive from the Moon and Mars. ▪ Composition differs from the asteroid fragments. ▪ A cheap (but slow) way to acquire Moon rocks and Mars rocks Edge of the Solar System ▪ The heliosphere is the region affected by the solar wind. ▪ The Kuiper belt is a torus of asteroids from about 30– 100 AU. ▪ The Oort cloud is a sphere of material surrounding our Solar System out to 100,000s of AU. Figure 22.34 Comet SL9 caused a string of violent impacts on Jupiter in 1994, reminding us that catastrophic collisions still happen. Tidal forces tore it apart during a previous encounter with Jupiter. An impact plume from a fragment of comet SL9 rises high above Jupiter’s surface. Tidal forces tore it apart during a previous encounter with Jupiter. Did an impact kill the dinosaurs? Mass Extinctions ▪ Fossil record shows occasional large dips in the diversity of species: mass extinctions. ▪ Most recent was 65 million years ago, ending the reign of the dinosaurs. Iridium: Evidence of an Impact ▪ Iridium is very rare in Earth surface rocks but often found in meteorites. ▪ Luis and Walter Alvarez found a worldwide layer containing iridium, laid down 65 million years ago, probably by a meteorite impact. ▪ Dinosaur fossils all lie below this layer. Iridium Layer No dinosaur fossils in upper rock layers Thin layer containing the rare element iridium Dinosaur fossils in lower rock layers Consequences of an Impact ▪ Meteorite 10 kilometers in size would send large amounts of debris into atmosphere. ▪ Debris would reduce sunlight reaching Earth’s surface. ▪ Resulting climate change may have caused mass extinction. Likely Impact Site ▪Geologists have found a large subsurface crater about 65 million years old in Mexico. A comet or asteroid about 10 kilometers in diameter approaches Earth. Is the impact threat a real danger or media hype? Facts about Impacts ▪ Asteroids and comets have hit Earth. ▪ A major impact is only a matter of time: not IF but WHEN. ▪ Major impacts are very rare. ▪ Extinction level events happen millions of years apart. ▪ Major damage happen tens to hundreds of years apart. Tunguska, Siberia: June 30, 1908 A ~40-meter object disintegrated and exploded in the atmosphere. Meteor Crater, Arizona: 50,000 years ago (50-meter object) Frequency of Impacts ▪Small impacts happen almost daily. ▪Impacts large enough to cause mass extinctions happen many millions of years apart. The Asteroid with our name on it ▪ We haven’t seen it yet. ▪ Deflection is more probable with years of advance warning. ▪ Control is critical: Breaking a big asteroid into a bunch of little asteroids is unlikely to help. ▪ We get less advance warning of a killer comet…. How do the Jovian planets affect impact rates and life on Earth? Influence of the Jovian Planets Gravity of a Jovian planet (especially Jupiter) can redirect a comet. Influence of Jovian Planets Jupiter has directed some comets toward Earth but has ejected many more into the Oort cloud. Was Jupiter necessary for life on Earth? Impacts can extinguish life. But were they necessary for “life as we know it”? Class Questions Review Class Question 1 What year did the IAU officially define what a planet in our Solar System is? a. 2006 b. 1992 c. 1976 d. 1957 Class Question 1 Answer What year did the IAU officially define what a planet in our Solar System is? a. 2006 (answer) b. 1992 c. 1976 d. 1957 Class Question 2 Most planets in the Solar System have a. orbital planes that lie within 3 degrees of the ecliptic plane. b. orbital planes that lie within 3 degrees of the Earth’s orbital plane. c. prograde motion. d. all of the above e. a and c Class Question 2 Answer Most planets in the Solar System have a. orbital planes that lie within 3 degrees of the ecliptic plane. b. orbital planes that lie within 3 degrees of the Earth’s orbital plane. c. prograde motion. d. all of the above (answer) e. a and c Class Question 3 Which of the following probes flew by Pluto in 2015? a. Voyager 1 b. Messenger c. Curiosity d. New Horizons e. Cassini Class Question 3 Answer Which of the following probes flew by Pluto in 2015? a. Voyager 1 b. Messenger c. Curiosity d. New Horizons (answer) e. Cassini Class Question 4 Which of the following is considered a terrestrial planet? a. Mercury b. Jupiter c. Saturn d. Pluto e. Ceres Class Question 4 Answer Which of the following is considered a terrestrial planet? a. Mercury (answer) b. Jupiter c. Saturn d. Pluto e. Ceres Class Question 5 Which of the following is considered a giant planet? a. Mars b. Neptune c. Titan d. Pluto e. Ceres Class Question 5 Answer Which of the following is considered a giant planet? a. Mars b. Neptune (answer) c. Titan d. Pluto e. Ceres Class Question 6 What gas makes up most of the atmosphere of Mars? a. nitrogen b. oxygen c. carbon dioxide d. methane Class Question 6 Answer What gas makes up most of the atmosphere of Mars? a. nitrogen b. oxygen c. carbon dioxide (answer) d. methane Class Question 7 The Earth’s Moon a. formed directly from nuclear fusion processes immediately following the formation of the Sun. b. rotates once on its axis in the same time that it takes to revolve once around the Earth. c. has an atmosphere that burns up most meteoroids before they hit its surface. d. all of the above e. b and c Class Question 7 Answer The Earth’s Moon a. formed directly from nuclear fusion processes immediately following the formation of the Sun. b. rotates once on its axis in the same time that it takes to revolve once around the Earth. (answer) c. has an atmosphere that burns up most meteoroids before they hit its surface. d. all of the above e. b and c Class Question 8 Which of the following does not have any moons? a. Mars b. Venus c. Pluto d. Jupiter e. Neptune Class Question 8 Answer Which of the following does not have any moons? a. Mars b. Venus (answer) c. Pluto d. Jupiter e. Neptune Class Question 9 Which of the following planets have rings? a. Jupiter b. Neptune c. Uranus d. all of the above e. none of the above Class Question 9 Answer Which of the following planets have rings? a. Jupiter b. Neptune c. Uranus d. all of the above (answer) e. none of the above Class Question 10 Where in the Solar System is Pluto located? a. just beyond the heliosphere b. between Mars and Jupiter c. in the Kuiper Belt d. in the Oort Cloud e. in the asteroid belt Class Question 10 Answer Where in the Solar System is Pluto located? a. just beyond the heliosphere b. between Mars and Jupiter c. in the Kuiper Belt (answer) d. in the Oort Cloud e. in the asteroid belt Class Question 11 On which of these Moons do we think the conditions might exist for life? a. Phobos b. Io c. Triton d. Europa Class Question 11 Answer On which of these Moons do we think the conditions might exist for life? a. Phobos b. Io c. Triton d. Europa (answer) Class Question 12 The largest volcano in the Solar System is found on a. Io. b. Venus. c. Mercury. d. Mars. Class Question 12 Answer The largest volcano in the Solar System is found on a. Io. b. Venus. c. Mercury. d. Mars. (answer) Think-Pair-Share Question Do you think life exists elsewhere in the Universe? What conditions would be necessary for life as we know it to exist elsewhere? Homework Answer the Questions in D2L