05 Solar System.pdf

Lecture 5 Solar System  Gravitationally bound system The Solar System is the gravitationally bound system of the Sun and the objects that orbit it.  Outline Solar System (observation) – Sun – Planets – Moons...

Lecture 5 Solar System  Gravitationally bound system The Solar System is the gravitationally bound system of the Sun and the objects that orbit it.  Outline Solar System (observation) – Sun – Planets – Moons Efbrazil, CC BY-SA 4.0, via Wikimedia Commons  Sun The Sun is at the center of the Solar System. It is a nearly perfect sphere of hot plasma. Roughly ¾ of the Sun’s mass consists of hydrogen; the rest is mostly helium, with much smaller quantities of heavier elements. Matúš Motlo, CC BY-SA 4.0, via Wikimedia Commons  Large mass The Sun is by far the Solar System’s most massive component. Its mass comprises 99.86% of all the mass in the Solar System. CactiStaccingCrane, CC BY-SA 4.0, via Wikimedia Commons  Nuclear fusion of hydrogen into helium Its large mass produces temperatures and densities in its core high enough to sustain nuclear fusion of hydrogen into helium.  Releases an enormous amount of energy This releases an enormous amount of energy, mostly radiated into space as electromagnetic radiation.  Planets The planets in orbit around the Sun lie near the plane of Earth’s orbit. Planets orbit the Sun in the same direction. https://youtu.be/z8aBZZnv6y8  Mercury Mercury is the first planet from the Sun. The surface of Mercury is heavily cratered.  Venus Venus is the second planet from the Sun. Venus is notable for having a dense atmosphere with a thick, global cloud cover. The surface has been mapped in detail by using radar. The ground shows evidence of extensive volcanism.  Earth Earth is the third planet from the Sun. Earth is an ocean world, the only one in the Solar System sustaining liquid surface water. Earth has an atmosphere.  Mars Mars is the fourth planet from the Sun. Its surface is peppered with volcanoes and rift valleys. The polar regions are covered in white ice caps. Mars has a thin atmosphere. Kevin Gill from Los Angeles, CA, United States, CC BY 2.0, via Wikimedia Commons  Terrestrial planets The four terrestrial or inner planets have dense, rocky compositions. The term “terrestrial planet” is derived from Latin word for Earth (Terra), as these planets are, in terms of structure, Earth-like. CactiStaccingCrane, CC BY-SA 4.0, via Wikimedia Commons  Jupiter Jupiter is the fifth planet from the Sun. The outer atmosphere is divided into a series of latitudinal bands, with turbulence and storms along their interacting boundaries; the most obvious result of this is the Great Red Spot, a giant storm. https://youtu.be/rHwkdcppsuo  Saturn Saturn is the sixth planet from the Sun. Saturn’s atmosphere exhibits a banded pattern similar to Jupiter’s, but Saturn’s bands are much fainter. The planet has a bright and extensive system of rings.  Uranus Uranus is the seventh planet from the Sun. It is a gaseous cyan-coloured planet. – The third-most-abundant component of Uranus’ atmosphere is methane. Methane has prominent absorption bands in the red light, making Uranus cyan in colour.  Neptune Neptune is the eighth and farthest known planet from the Sun. In contrast to the featureless atmosphere of Uranus, Neptune’s atmosphere has active and consistently visible weather patterns.  Giant planets The four outer planets are called giant planets. A giant planet is a diverse type of planet much larger than Earth. CactiStaccingCrane, CC BY-SA 4.0, via Wikimedia Commons  Jupiter & Saturn are gas giants Jupiter and Saturn are gas giants. A gas giant is a giant planet composed mainly of hydrogen and helium.  Uranus & Neptune are ice giants Uranus and Neptune are ice giants. An ice giant is a giant planet significantly composed of “ice”. – The term “ice” refers to volatile chemical compounds, such as water, ammonia, or methane. Like the gas giants, the ice giants also have hydrogen and helium envelopes, but these are much smaller.  Summary Solar system (observation) – Sun – Planets  Lecture 5 – Part 2 Solar system (cont.) – Moons (observation) Saturn’s rings – Dwarf planets & small bodies (observation) – Formation Nebular hypothesis Efbrazil, CC BY-SA 4.0, via Wikimedia Commons  Moons Most of the planets in the Solar System have secondary systems of their own, being orbited by natural satellites called moons.  Earth’s moon The Moon is Earth’s only natural satellite. The lunar surface is marked by impact craters and, mostly on the near side of the Moon, by dark maria (“seas”), which are plains of cooled magma. These maria were formed when molten lava flowed into ancient impact basins. Gregory H. Revera, CC BY-SA 3.0, via Wikimedia Commons  Jupiter’s moons Jupiter has 95 known moons. The four moons discovered by Galileo Galilei are the largest moons. Io is primarily composed of Jan Sandberg, Attribution, via Wikimedia Commons silicate rock; Europa, Ganymede, and Callisto have a thick coating of ice.  Saturn’s moons This Photo by Unknown Author is licensed under CC BY-SA-NC Saturn has 146 known moons. Seven moons are large enough to have a spherical shape. Titan, Saturn’s largest moon, is the only moon in the Solar System that has a substantial atmosphere. This Photo by Unknown Author is licensed under CC BY  Saturn’s rings The rings of Saturn consist of countless small particles that orbit around Saturn.  Dwarf planets & small bodies The Solar System has dwarf planets and a vast number of small bodies. A dwarf planet is a small body that is large enough to have a spherical shape.  Asteroid belt The asteroid belt is a torus- shaped region, roughly spanning the space between the orbits of Jupiter and Mars. It contains a great many bodies called asteroids.  Asteroids Asteroids are rocky, metallic, or icy bodies. The largest are roughly spherical. The vast majority, however, are much smaller and are irregularly shaped. Kwamikagami, CC BY-SA 4.0, via Wikimedia Commons  Ceres Ceres is smaller than Earth’s moon. It is the largest asteroid and a dwarf planet.  Trans-Neptunian region Beyond the orbit of Neptune lies the area of the “trans- Neptunian region”, with the Kuiper belt and an overlapping disc of scattered objects, which reaches much further out than the Kuiper belt. The entire region is still largely unexplored. It appears to consist overwhelmingly of many thousands of small worlds composed mainly of rock and ice.  Kuiper belt The Kuiper belt is similar to the asteroid belt, but is far larger.  Pluto Pluto is smaller than Earth’s moon. It is a dwarf planet in the Kuiper belt. It is the largest known trans- Neptunian object by volume.  Summary Regions containing many small bodies – Asteroid belt – Kuiper belt  Summary Ceres – Largest body in the asteroid belt Pluto – Largest body in the Kuiper belt  Haumea, Makemake, Quaoar, & Orcus Other objects that astronomers generally accept as dwarf planets are Haumea, Makemake, Quaoar, and Orcus.  Scattered disc The scattered-disc objects have high orbital eccentricities and inclinations. These extreme orbits are thought to be the result of gravitational “scattering” by the gas giants, and the objects continue to be subject to perturbation by the planet Neptune. User: Orionist, CC BY-SA 3.0, via Wikimedia Commons  Eris & Gonggong Eris is the largest known scattered disc object and the most massive of the known dwarf planets. Gonggong is also a dwarf planet.  Extreme trans-Neptunian objects Some objects in the Solar System have a very large orbit. These bodies are called extreme trans-Neptunian objects. Tomruen, CC BY-SA 4.0, via Wikimedia Commons  Sedna Sedna was the first extreme trans-Neptunian object to be discovered. Sedna is classified as a dwarf planet. It is a large object.  Formation of the Solar System Since the 17th century, scientists have been forming hypotheses concerning the origins of our Solar System. In the 20th century, a variety of hypotheses began to build up.  Nebular hypothesis The nebular hypothesis is the most widely accepted model to explain the formation of the Solar System. – The word nebula is derived from the Latin word for ‘cloud’.  Presolar nebula The nebular hypothesis says that the Solar System formed from the gravitational collapse of a giant cloud.  Mass & composition The composition of this region with a mass just over that of the Sun was about the same as that of the Sun today, with hydrogen, along with helium, forming about 98% of its mass. The remaining 2% of the mass consisted of heavier elements.  Spun faster as it collapsed The nebula spun faster as it collapsed. – It is because of the conservation of angular momentum. https://www.youtube.com/watch?v=64t-dVtDwkQ  Center became increasingly hotter As the material within the nebula condensed, the temperature rose. – The gravitational potential energy was converted into heat. The center, where most of the mass collected, became increasingly hotter than the surrounding.  Protoplanetary disc & protosun The competing forces of gravity and rotation caused the contracting nebula to flatten into a spinning protoplanetary disc and form a hot, dense protosun at the centre. – Centrifugal force is directed radially away from the axis of rotation.  Sun Later, the temperature and density at the core of the Sun became so great that its hydrogen began to fuse, creating an internal source of energy.  Accretion The various planets are thought to have formed from the protoplanetary disc. The currently accepted method by which the planets formed is accretion, in which the planets began as dust grains in orbit around the central protosun.  Planetesimals Through direct contact and self-organization, these grains formed into clumps up, which in turn collided to form larger bodies (planetesimals).  Rocky planetesimals The inner Solar System was too warm for volatile molecules to condense, so the planetesimals that formed there could only form from compounds with high melting points, such as metals and rocky silicates.  Icy planetesimals Beyond the frost line, which is the point between the orbits of Mars and Jupiter, the material is cool enough for volatile icy compounds to remain solid.  Giant planets These icy bodies would become the giant planets. The ices were abundant, allowing the giant planets to grow massive enough to capture hydrogen and helium.  Solar wind The young Sun had a strong solar wind.  Cleared away all the gas and dust The solar wind cleared away all the gas and dust in the protoplanetary disc, blowing it into interstellar space, thus ending the growth of the planets.  Gas giants & ice giants Uranus and Neptune are thought to have formed after Jupiter and Saturn did, when the strong solar wind had blown away much of the disc material. As a result, those planets accumulated little hydrogen and helium.  Protoplanets At the end of the planetary formation epoch the inner Solar System was populated by protoplanets.  Collided & merged These bodies collided and merged.  Terrestrial planets They grew larger until the four terrestrial planets took shape. CactiStaccingCrane, CC BY-SA 4.0, via Wikimedia Commons  Small planets Metals and rocky silicates were quite rare in the presolar nebula, so the terrestrial planets could not grow very large. CactiStaccingCrane, CC BY-SA 4.0, via Wikimedia Commons  Asteroid belt The outer edge of the terrestrial region is the asteroid belt. The asteroid belt formed as a group of planetesimals. Gravitational perturbations from Jupiter disrupted their accretion into a planet.  Ceres Ceres is a surviving protoplanet.  Trans-Neptunian region Beyond Neptune, the Solar System continues into the trans- Neptunian region, a sparse population of icy planetesimals. At its distance from the Sun, initial disc lacked enough mass density to consolidate into a planet.  Pluto, etc. Trans-Neptunian dwarf planets have also been referred to as protoplanets.  Summary Pluto – Trans-Neptunian object (observation) – Protoplanet Nebular hypothesis  Moons The moons that exist around most planets originated by one of a few possible mechanisms.  Earth’s moon Earth’s moon is thought to have formed as a result of a single, large head-on collision. The impact was probably the last in the series of mergers that formed the Earth. The collision kicked into orbit some of the impactor’s mantle, which then coalesced into the Moon. This Photo by Unknown Author is licensed under CC BY-SA  Moons of Jupiter & Saturn Jan Sandberg, Attribution, via Wikimedia Commons The large moons of Jupiter and Saturn may have originated from discs around each giant planet in much the same way that the planets formed from the disc around the Sun. This Photo by Unknown Author is licensed under CC BY-SA-NC  Saturn’s rings There are two main theories regarding the origin of Saturn’s rings. 1. The rings were once a moon of Saturn. This moon disintegrated. 2. The rings are left over from the original nebular material from which Saturn formed.  Summary Solar system – Sun, planets, moons, dwarf planets, small bodies (observation) – Formation Nebular hypothesis Efbrazil, CC BY-SA 4.0, via Wikimedia Commons