Elements of the Solar System,Exploring Extrosolar PlanetsandEvolution of Planetary Systems FIZ466, İTÜ
The Astronomical Unit (AU) • The appropriate length unit for studying the Solar System is AU • AU is the average distance between the Sun and the Earth • 1 AU = 150 Million km=8 light minutes
Not only the Sun and the Planets • The Sun • Planets (terrestrials and Jovians) • Moons of the planets • Meteorites • Astroid belts • Comets • Oort Cloud • Kuiper Belt • Interplanetary dust
Mass Distribution • Sun: 99.85% • Planets: 0.135% • Comets: 0.01% ? • Satellites: 0.00005% • Minor Planets 0.0000002% ? • Meteoroids: 0.0000001% ? • Interplanetary Medium: 0.0000001% ? • Simply: Sun 99.9 % & 0.1% Jupiter
The Nine Planets • Mercury • Venus • Earth • Mars • Jupiter • Saturn • Uranus • Neptune • Pluto(?) MNEMONIC: My Very Educated Mother Just Sent Us Nine Pizzas
Imagening the distances • Imagine the Solar System being a soccer ground (about 100 m long). • The Sun would be a glaring orange in the centre. • Pluto would encircle the sun at the edge of the soccer ground, having the size of a dust particle. • The Earth would be 1,30m away from the “orange“, having the size of a sesame seed.
Bode’s Relation • a simple rule that gives the distances of the planets from the Sun where N=0, 3, 6, 12, 24…for Mercury, Venus, Earth, Mars, etc.
Planet N Bode’s Law Radii True Orbital Radii Mercury 0 (0+4)/10 = 0.4 AU 0.39 AU Venus 3 (3+4)/10 = 0.7 AU 0.72 AU Earth 6 (6+4)/10 = 1.0 AU 1.00 AU Mars 12 (12+4)/10 = 1.6 AU 1.52 AU ____ 24 (24+4)/10 = 2.8 AU _______ Ceres 24 2.88 AU Jupiter 48 (48+4)/10 = 5.2 AU 5.2 AU Saturn 96 (96+4)/10 = 10.0 AU 9.5 AU Uranus 192 (192+4)/10 = 19.6 AU 19.2 AU Neptune ? ? 30.1 AU Pluto 384 (384+4)/10 = 38.8 AU 39.5 AU
What does Bode’s Law tell us? • Bode's Law predicted that there should be a planet between the orbits of Mars and Jupiter. • The "missing planet" turned out to be the asteroid belt.
Terrestrial Planets • The inner four planets at the center of the solar system: • Mercury, Venus, Earth, Mars • They all are small, rocky, rotate slow, they have small number of moons. • Metal cores.
Jovian Planets • Outer planets of the Solar System • Jupiter, Saturn, Uranus & Neptun • They are made of gas/liquid/ice • No solid surface • Small solid core (rock) • They have rings • Large number of moons
Gas giant planets: Jupiter & Saturn • Dominant composition: • Hydrogen + Helium, like the sun • Surface clouds: ammonia ice, water ice.... • Deep in interior: liquid metallic hydrogen • Even deeper: rocky core of ~ 10...15 M • These are model results which depend on equation of state of hydrogen • For Saturn this is certain (unless models are wrong) • For Jupiter the uncertainty includes Mcore=0
Ice giant planets: Uranus & Neptune • Dominant composition: • Water + Ammonia + Methane ices • Only atmosphere contains H, He (in total only minor) • Uranus: • 25% Iron + Silicates • 60% Methane + Water + Ammonia • 15% Hydrogen + Helium • Neptune: • 20% Iron + Silicates • 70% Methane + Water + Ammonia • 10% Hydrogen + Helium
Thermal emission of Jupiter and Saturn • Jupiter and Saturn emit more radiation than they receive from the sun. • They are not massive enough for nuclear burning (need at least 13 Mjup) • Kelvin-Helmholz cooling time scale much shorter than current age (at least for Saturn) • Possible solution: • Helium slowly sediments to center, releases gravitational energy
Why U+N ice, J+S hydrogen? • Theory: • All four formed at similar location, first forming a rock+ice core by accumulating icy bodies • Somehow U + N were moved outward and did not accrete much gas anymore • J + S remained and accreted large quantities of hydrogen gas
Summary - What do the inner planets look like? • They are all… • rocky and small! • No or few moons • No rings
Summary - The Jovian Planets • They are all… • gaseous and BIG! • Rings • Many moons
What are Moons? • Moons are like little planets that encircle the real planets. • Usually, they are much smaller than planets. • Planets can have no moons (like Mercury and Venus), one moon (like Earth) or up to a very large number of moons (e.g. >63 for Jupiter). • Mars (2), Saturn (>34), Uranus (>27), Neptun (>13), Pluto (1)
Asteroids • Small bodies • planetoid, minor planet • Their mass is not sufficient to make them spherical • Many of the asteroids are part of the asteroid belt between Mars and Jupiter. • Believed to be left over from the early evolution of the solar nebula. • Largest object Ceres is about 1000 km accross
Asteroid Belt • The doughnut-shaped concentration of asteroids orbiting the Sun between Mars and Jupiter • More that 200000 asteroids • Total mass, a few 1024 g, is 1/30 of the Moon. • if the estimated total mass of all asteroids was gathered into a single object, this object would be less than 1,500 kilometers across
The Origin of the Asteroid Belt • The asteroid belt may be material that never coalesced into a planet, perhaps because its mass was too small; the total mass of all the asteroids is only a small fraction of that of our Moon. • A less satisfactory explanation of the origin of the asteroid belt is that it may have once been a planet that was fragmented by a collision with a huge comet.
This slide is not essential for the exam and can be skipped Kirkwood Gaps • If you plot the radius of the orbits of the asteroids you do not get a smooth `bell-curve' shape. There are concentric gaps in the asteroid belt known as Kirkwood gaps. • These gaps are orbital radii where the gravitational forces from Jupiter do not let asteroids orbit (they would be pulled into Jupiter). • For example, an orbit in which an asteroid orbited the Sun exactly three times for each Jovian orbit would experience great gravitational forces each orbit, and would soon be pulled out of that orbit. • There is a gap at 3.28 AU (which corresponds to 1/2 of Jupiter's period), another at 2.50 AU (which corresponds to 1/3 of Jupiter's period), etc. The Kirkwood gaps are named for Daniel Kirkwood who discovered them in 1866. This is an example of resonance. This resonance phenomenon has Jupiter passing by any asteroid in the Kirkwood gaps every two or three asteroid years, depending on which gap. The repeated tugging induces an asteroid into larger, longer orbits closer to Jupiter. Eventually, however, an asteroid's resonance with Jupiter disappears as its orbit increases.
Comets • A comet consists of a tiny nucleus with diameter less than 10 km. The nucleus is made up of frozen gases and dust. • Eccentric orbit around the Sun. • Most comets spend most of their time at vast distances from the Sun. • When they approach the Sun, some gases will be vaporized and an extended coma will then be produced (of size 100000 km). • The tail can be up to 1AU long. • Orbits of a comet may be open or close. A comet with an open orbit will only visit the Sun once. However, a comet with a closed orbit (actually it is elliptical) will visit the Sun again and again. Perhaps, the most famous one is the Comet Halley, it has a closed orbit with a period of 76 years. a white dust tail and a blue gas (ion) tail.
Comet Tails • When a comet moves close to the Sun, the solar wind (charged particles ejected from the Sun) and the Sun's radiation pressure push the dust and gases of the comets away, this will result in a beautiful long tail. • From this, we know why the comet tail is always pointing away from the Sun. The dust trail is made of particles that are the size of sand grains and pebbles. They are large enough that they are not affected much by the Sun's light and solar wind. The gas tail, on the other hand, is made of grains the size of cigarette-smoke particles. These grains are blown out of the dust coma near the comet nucleus by the Sun's light.
Meteoroids, Meteors and Meteorites • When asteroids collide with one another they can produce small fragments known as meteoroids. • If a meteoroid enters the atmosphere of the Earth, it glows due to heat generated by friction. These are called meteors. • If the rock survives the trip through the atmosphere and strikes the surface of the Earth, the remnant is called a meteorite. • Only 2 documented cases in which a person is hit by a meteorite.
Two documented Cases This slide is not essential for the exam and can be skipped • Annie Hodges of Sylacauga, Alabamawas napping on her couch on November 30, 1954 when an eight-pound meteorite crashed through the roof. It bounced off a large console radio and hit her in the arm and then in the leg, leaving her bruised but okay. • On the afternooon of June 21, 1994, Jose Martin and his wife, Vicenta Cors, were driving in Spain from Madrid to Marbella. As they zoomed past the town of Getafe, a three-pound meteorite smashed through their windshield on the driver’s side, ricocheted off the dashboard, and bent the steering wheel, breaking the little finger on Martin’s right hand. It then flew between the couple’s heads and landed on the back seat. Other than the broken little finger, they were okay.
Meteor Shower • Comets exposed to the heat of the inner solar system slowly disintegrate • This is another source of meteoritic material • When the Earth passes through the debris left in a comet’s orbit, the result is a metor shower of micrometeorites.
Perseid Meteor Shower • Usually the best meteor shower of the year. • It starts in August 10 and peaks the following 2 days • Specs of rock that have broken off the comet Swift-Tuttle. August 10, 1998
Kuiper Belt & Oort Cloud • Kuiper Belt is a "junkyard" of countless icy bodies left over from the solar system's formation. • Kuiper Belt is shaped like a disk. • The Kuiper Belt extends from inside Pluto's orbit to the edge of the solar system. • Kuiper Belt was discovered in 1992 • There are at least 70,000 "trans-Neptunians" with diameters larger than 100 km in the radial zone extending outwards from the orbit of Neptune (at 30 AU) to 50 AU. • The Oort Cloud, which is much further (50000 AU), is a vast spherical shell of billions of comets.
When is a planet not a planet? Recently, the International Astronomical Union (IAU) had a fierce to try to iron out the definition of a planet. They decided that a planet: • Is in orbit around the Sun. • Has sufficient mass for their self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape. • Has cleared the neighbourhood around its orbit. Objects that pass the first two tests, but fail the third, and which are not themselves satellites of other planets, are now called dwarfplanets.
Quaoar and Sedna: new planets? Quaoar is a Kuiper belt object discovered by Trujillo and Brown in 2002 with the Palomar Telescope. It orbits outside Pluto and was the largest Solar System object discovered since Pluto in 1930. Its diameter is about 1300km (half the size of Pluto), and it is on a very circular orbit currently one billion miles outside Pluto. Sedna is a similar object that is even further away, and takes over 10,000 years to orbit the Sun. It was discovered in 2004 by the same astronomers.
Xena and its moon Gabrielle, imaged by the Keck telescope. 2003UB313, aka Xena In 2003, a Kuiper-belt object was found which is bigger than Pluto. It even has its own moon! Its orbital period is 560 years on a highly-inclined orbit. Although colloquially known as Xena, it is called 2003UB313 until an official name is decided.