Astronomy Student Notes

Transcription

1 Astronomy Student Notes The Solar System Name Date 1 Vocabulary: Number and define each term below in a complete sentence on a separate sheet of paper. (Please illustrate the terms that have a *) Solar System Comparative Planetology Density* Jovian Planets* Terrestrial Planets* Asteroid Belt* Asteroids* Protosun M-type asteroids C-types asteroids S-type asteroids Mass Volcanism* Galileo probe binary asteroids NEAR-Shoemaker craft Apollo asteroids* Trojan asteroids* Interstellar Dust Condensation Theory Kirkwood Gaps Comets* Tail Nucleus* Coma* Hydrogen Envelope* Ions Tails* Dust Tails* Short-period comets Kuiper Belt* Oort Cloud* Meteor Meteorite* Meteoroid Meteoroid Swarm Micrometeoroids Meteor Shower Fireballs Interplanetary Matter Accretion* Solar Nebula* Evolutionary Theory Catastrophic Theories Protoplanet The Solar System An Inventory of the Solar System A.Why is comparative planetology important? -To understand better the conditions under which planets form and evolve -Goal is to develop a comprehensive theory of the of our planetary system that explains all, or at least most, of its observed properties B.How many planets could the ancient Greeks see, what else did they observer? -The, the stars, and five planets Mercury, Venus, Mars, -Comets and C.What is Ceres, where is it located -The largest and the first to be sighted, was discovered in D.List all of the contents in the solar system, according to this section: -One star (the Sun), planets, moons (at last count) orbiting those planets - asteroids larger than 300 km in diameter, tens of thousands of smaller (but well-studied) asteroids -A myriad of comets a few kilometers in diameter, and countless meteoroids less than 100 m across. The list will undoubtedly grow as we continue to explore our cosmic neighborhood. Planetary Properties A.How is a mass of an object measured in the solar system? -The masses of planets with may be calculated by application of laws of motion and gravity -Just by observing the moons orbits around the planets, the of those orbits, like the sizes of the planets themselves, are determined by. B.What is one way we determine a planet s rotational period? -Determined simply by watching surface features appear and disappear again as the planet rotates.

2 -Why can this method be difficult for some planets? -Surfaces are hard to see or may even be nonexistent. Mercury s surface features are hard to distinguish, the surface of Venus is completely obscured by, and Jupiter, Saturn, Uranus, and Neptune have no at all C.What is the average density of (use proper units): -Earth- of Earth matter in every cubic meter of Earth volume -Water kg/m3, kg/m3 -Earth s - a few kilograms per cubic meter The Overall Layout of the Solar System A.What is the order of planets outward, how will you remember? - -Mnemonic B.How are all of the planets in the solar system the same? - Their paths are all - All the planets orbit the Sun in the same sense as seen from above Earth s North Pole and in nearly the same plane as Earth (that is, the plane) C.List some properties that make the planets different: -The planetary orbits are not evenly -??? D.The Titius-Bode Law -How does it work? -The spacing of the orbits increases more or less geometrically as we move out from the Sun: At any point in the list, the distance to the next planet out is about to the next planet in. -What s wrong with this rule? - the rule fails for, which lies only 30 A.U. from the Sun. However, if we ignore Neptune, Pluto is in just about the right place! Terrestrial and Jovian Planets A.How are terrestrial planets similar/different? - All lie within about of the Sun, all are small and of relatively low mass, all have generally and solid surfaces -Surface conditions on the four planets are quite distinct from one another, ranging from barren, heavily cratered terrain on Mercury to widespread volcanic activity on. - Earth and Mars spin at roughly the same rate one rotation every 24 (Earth) hours but Mercury and Venus both take to rotate just once, and Venus rotates in the opposite sense from the others. - Earth and Mars have moons, but Mercury and Venus do not B.What makes Terrestrial planets different from Jovian planets (hint: copy table 6.2) Terrestrial Planet Jovian Planets - to the Sun - from the Sun - spaced orbits - spaced orbits -small masses - masses -small radii -large 2

3 - - -solid surface - - -low density -slow rotation - - -strong magnetic field -few moons - - -many rings C.What percentage of the solar system mass does the Sun make up? 3 Interplanetary Debris A.What is interplanetary matter? - cosmic debris ranging in size from the relatively, through the smaller comets and even smaller meteoroids, down to the smallest that litter our cosmic environment. B.What is the difference between an: - - generally rocky in composition, Their total mass is much less than that of Earth s Moon, so these objects play no important role in the present-day workings of the planets or their moons. - - generally icy rather than rocky in composition (although they do contain some rocky material) and typically have diameters in the 1 10 km range. C. How do we know what material makes up a meteoroid? - they often conveniently deliver themselves right to our doorstep, in the form of allowing us to study them in detail without having to fetch them from space.) D. How do we know what material makes up a comet? - Astronomers can determine a comet s makeup by of the radiation it gives off as it is destroyed E. What can we learn from solar system debris? -Many of these bodies are made of material that has evolved hardly at all since the early days of the solar system, possible origin of solar system and planets,? Solar System Debris Asteroids A.Orbital Properties -Describe an asteroid s orbit, where are they located in the solar system? - majority of these bodies are found in a region of the solar system known as the, located between 2.1 and 3.3 A.U. from the Sun roughly midway between the orbits of (1.5 A.U.) and (5.2 A.U.). -How much of the mass of the solar system is made up of asteroids? - the mass of the Moon, so they do not contribute significantly to the total mass of the solar system. -Where do asteroids come from? -either the fragments of a planet or primal rocks that never managed to accumulate into a genuine planet B.Physical Properties -How are asteroids classified? - by their spectroscopic properties

4 4 - (or carbonaceous) asteroids- darkest, or least reflective, asteroids 75 percent are C-type - asteroids- more reflective contain silicate, or rocky, material 15 percent of all asteroids are S-type asteroids- containing large fractions of nickel and iron ~10 percent -What are the 3 largest asteroids? 1., 940 km (now dwarf planet) 2., 580 km 3., 540 km -What was the purpose of the NEAR-Shoemaker? -For one year, the spacecraft sent back high-resolution images of, and made detailed measurements of its size, shape, gravitational and magnetic fields, composition, and structure. The craft s various sensors revealed Eros to be a body of mass kg and roughly uniform density around 2700 kg/m 3 -February 12, 2001, NEAR-Shoemaker landed on Eros, sending back a series of close-up images as it descended to the surface C.Earth Crossing Asteroids -Describe why an asteroid with an eccentricity interests astronomers? - their paths may intersect Earth s orbit, leading to the possibility of a collision with our planet -What are these asteroids called? - termed (after the first known Earth-crossing asteroid, Apollo -How often is the Earth struck by asteroids? - On average during any given million-year period our planet is struck by about -What kind of effects would an asteroid collision have? - a visit of even a kilometer-sized asteroid to Earth could be catastrophic by human standards. Such an object packs enough energy to devastate an area some in diameter. The explosive power would be equivalent to about a a hundred times more than all the nuclear weapons currently in existence -What has been done to prevent asteroids from colliding with Earth? - Some astronomers take the prospect of an asteroid impact sufficiently seriously that they maintain an " " an effort to catalog and monitor all Earthcrossing asteroids in order to maximize our warning time of any impending collision. -What evidence indicates that an asteroid or comet led to the demise of the dinosaurs? - main geological evidence supporting this theory is a layer of clay enriched with the element. This layer is found in rocky sediments all around our planet. -The abundance of iridium in this one layer of clay is about 10 times greater than in other terrestrial rocks, but it matches closely the abundance of iridium found in -The site of the catastrophic impact has also been tentatively identified near, in the Yucatan Peninsula in Mexico, where evidence of a heavily eroded, but not completely obliterated, crater of just the right size and age has been found. D.Orbital Resonances -What are asteroids?

5 -asteroids that orbit at the distance of Jupiter, either in front or behind the planet -What are and what causes them? - Gaps in the spacings of semi-major axes of orbits of asteroids in the asteroid belt, produced by dynamical resonances with nearby planets, especially Jupiter. Comets -When do comets become brighter, how do they change shape? - comet brightens and develops an extended tail as it. (The name "comet" derives from the Greek word kome, meaning "hair.") -As the comet departs from the Sun s vicinity, diminish until it once again becomes a faint point of light receding into the distance. A.Comet Appearance and Structure -Diagram a comet, include the nucleus, coma, hydrogen envelope and tail: 5 -What are the two types of comet tails? - tails are approximately straight, often made up of glowing, linear streamers - tails are usually broad, diffuse, and gently curved, rich in microscopic dust particles that reflect sunlight, making the tail visible from afar B.Comet Orbits -What is the? - A region in the plane of the solar system outside the orbit of Neptune where most shortperiod comets are thought to originate. - move in roughly circular orbits between about 30 and 100 A.U. from the Sun, never venturing inside the orbits of the -How can we see objects from the Kuiper Belt? - Occasionally, however, a close encounter between two comets, or (more likely) the cumulative gravitational influence of one of the outer planets, "kicks" a Kuiper belt comet into an eccentric orbit that brings it into the inner solar system, and into our view -What is the? - Spherical halo of material surrounding the solar system, out to a distance of about A.U., where most comets originate. C.A Visit to Halley s Comet -Why is Halley s Comet so popular? - In 1705 the British astronomer calculated its path and found that the comet orbited the Sun with a period of. -Halley s successful determination of the comet s trajectory and his prediction of its return was an early triumph of -How did spacecraft study it, what did they learn from these missions? - Halley s comet rounded the Sun in, Soviet craft, Vega 2, traveled through the comet s coma and came within 8000 km of the nucleus - the European Giotto spacecraft was navigated to within 600 km of the nucleus, at km/s the speed of the craft relative to the comet a colliding dust particle becomes a devastating bullet. Debris did in fact damage Giotto s camera, but not before it sent home a wealth of data

6 -What happens to a comet s mass over time? -A comet s mass decreases with time because some material is lost each time the comet rounds the Sun as material from its surface -Comets that travel within an astronomical unit of the Sun, the evaporation rate can reach as high as molecules per second about the comet spends near the Sun -Why will Halley s Comet be destroyed in about 40,000 years? -Loss of material will destroy Halley s comet in about, or 40,000 years D.Physical Properties of Comets -What is the physical makeup of a comet? -Comets are made of dust particles trapped within a mixture of, carbon dioxide, and ordinary water ice, because of this composition, comets are often described as "." E.A Cometary Impact -What happened with the Comet-Shoemaker-Levy 9? - - the collision of a comet (called Shoemaker-Levy 9, after its discoverers) with the planet Jupiter - energy released in each explosion was comparable to a terrestrial nuclear detonations, rivaling in violence the prehistoric impact suspected of causing the extinction of the dinosaurs on Earth 65 million years ago Meteoroids -What is the difference between a: 1. -sudden streak of light in the night sky caused by friction between air molecules in Earth s atmosphere and an incoming piece of interplanetary matter 2. -Before encountering the atmosphere, the piece of debris causing a meteor 3. Any piece of interplanetary debris that survives its fiery passage through our atmosphere and finds its way to the ground -What makes an asteroid different from meteoroid? -Meteoroids are conventionally taken to be less than -What is needed for a meteor shower? - Earth s orbit happens to intersect the orbit of a young cluster of meteoroids, from broken up -What are meteor showers named after? - Meteor showers are usually named for their, the constellation from whose direction they appear to come -What are fireballs? - A few large at such high speed (about 75 km/s) that they either fragment or disperse entirely at high altitudes. -How do meteors make it to the surface of the Earth? - The more massive meteoroids (at least a ton in mass and a meter across) do make it to the surface, producing a crater such as the kilometer-wide -How come there are not more craters on Earth? - Most of the craters are so heavily eroded by weather and distorted by crustal activity that they can be identified only in -What happened in central Siberia in 1908? 6

7 -June 30, 1908 lack of fragments implies that this Siberian intruder exploded several kilometers, leaving a blasted depression at ground level but no well-formed crater. -Recent calculations suggest that the object in question was a rocky meteoroid about across. The explosion, estimated to have been equal in energy to a 10-megaton nuclear detonation, was heard hundreds of kilometers away and produced measurable increases in atmospheric dust levels all across the. -How are meteors similar/different? - Most meteorites are rocky in composition, although a few percent are composed mainly of -Some meteorites show clear evidence of strong heating at some time in their past, most likely indicating that they originated on a larger body that either experienced some geological activity or was partially melted during the collision, others show no such evidence and probably date from the. - almost all meteorites are old. Direct shows most of them to be between 4.4 and 4.6 billion years old roughly the age of the oldest lunar rocks. Meteorites, along with some lunar rocks, comets, and perhaps the planet Pluto, provide essential clues to the original state of matter in the solar neighborhood. Modeling the Origin of the Solar System A.What are the 9 properties/rules of the solar system? 1. Each planet is in an isolated 2. The orbit of the planets is nearly 3.All orbits are in about the same 4.Sun s direction=planet s rev. direction 5.Most planets mimic rotation of the 6. Most moons revolve in same way 7. Planets are highly 8.Asteroids are very old, don t fit inner or outer 9.Comets do not orbit along ecliptic, have very large The Condensation Theory A.What is the Nebular Theory? -Large cloud of interstellar gas collapsed, becomes to form the Sun at the center- swirling mass is called the B.What caused the Solar System to get its flat shape? -Gravity and rotation speed (like a pizza!), creates rings that eventually become, just like Saturn s rings eventually form moons C.How is the condensation theory different from the nebular theory? -Nebular Theory +, answers old theory s problems= Condensation Theory D.How does accretion create planetestimals? -Accretion is the gradual growth by collisions and sticking and eventually objects grow to thousands of kilometers across= E.How long did heavy meteorites bombardment take place in the Solar System? -The of Solar System formation 7

8 The Differentiation of the Solar System A.What are the 5 most common elements in the Solar System? -Hydrogen,, Carbon, Nitrogen, and B.Why did Jovian planets grow so large compared to terrestrial planets? -More material could due to being far out from the protosun heat, so accretions started earlier C.Where did Earth get its water from? -Two possible ways: Comet bombardment and continuous D.What is the T-tauri phase? -Young star phase when are very intense and blow out any remaining gasonly objects remaining are protoplanets and planetestimals The Role of Catastrophes A.How have possible collisions affected the following planets? - -Collision may have caused two cores to merge creating its large iron-nickel core - -Low rotation rate of 243 days (225 for revolution) result of a collision, also retrograde - - Moon caused by Mars sized object collision - - Late collisions caused loss of atmosphere? - -Tilted rotation its side also retrograde, collision? Its moon Miranda- very bizarre surface terrane, see chapter on Uranus - -Moon- Triton has retrograde motion Planets Beyond the Solar System A.What important discovery occurred in 1995? -The first confirmed planet was discovered due to improvement in telescopes and computing power B.What are two possible ways of detecting extrasolar planets? 1.Looking for the of a star due to gravity from a large planet, the greater the mass of the planet the larger the wobble 2. - if the diameter of a planet is large enough we can see a planet transit a star, just like Mercury does from the Sun C.Why has it been difficult to find Earth-sized planets? -lightweight planets simply don t produce large enough velocity fluctuations to be detectable -Can only find planets with masses the size of but orbit very closely to the star (called Hot Jupiters) 8

9 9 Distance from the Sun Diameter Length of Rotation (Day) Length of Revolution (Year) Composition of Planet Composition of Atmosphere Number of known satellites Sun Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto Ceres