The Solar System Figure Courtesy NASA/JPL-Caltech

The Sun Luminosity 3.9 x W Mass 1.99 x Kg Radius 6.96 x 10 8 m Temperature 5800 K Distance 1.50 x m (1 AU) AU = Astronomical unit

Sun and the planets Mass distribution %Sun %Planets %Comets, Kulper Belt Objects, Planetary Satellites, Minor Planets, Meteorids, Interplanetary Medium Major portion of angular momentum in planets

The Eight Planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune Elliptical orbits with Sun at one focus Orbits nearly circular – Mercury maximum eccentricity Orbits nearly coplanar – Mercury inclined at 7 degrees Other than Mercury and Venus, all are known to have Planetary satellites Pluto?

Orbit Parameters (J2000) PlanetSemi-major axis (au) Eccentricity eInclination Mercury Venus EM Binary Mars Jupiter Saturn Uranus Neptune

Physical Parameters PlanetMean Radius (km) Mass (x kg) Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune

Physical Parameters PlanetSidereal Orbit Period (y) Sidereal Rotation Period (d) Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune

Inner Planets 10 January 2010 Revolve conter-clockwise Looking down at Earth’s N-pole Terrestrial Planets composed of rock and metals relatively high densities slow rotation solid surfaces no rings and few satellites Small Mass Solar System Live Portion of orbit in blue is above the plane of the ecliptic; in green is below the plane of the ecliptic. Orbits to scale not planet sizes

Outer Planets Four Giant Planets - low densities, rapid rotation, rings and lots of satellites, strong magnetic filed Jupiter and Saturn largest and second largest Mainly Hydrogen and Helium Gas Giants Neptune and Uranus Mainly ice (fluid)– water, rocks – silicate and metal condensates ammonia and methane Ice Giants

Rotation Courtesy: Venus and Uranus Retrograde rotation Rest Direct Rotation Angle relative to orbital axis

Origin of the Solar System Coplanar orbits – ecliptic plane Rotation axis of nearly all planets and Sun normal to ecliptic Alignment of angular momentum suggests that the Solar System formed by the fragmentation of a spinning disk made of gas and dust 4.5 billion years ago

Nebular Hypothesis Cloud (nebula) of gas and dust collapses under its own gravity, possibly triggered by an external disturbance eg. Supernova blast wave Figure courtesy by Bill Arnett

Spinning DIsk Conservation of angular momentum Nebula forms a disk Figure courtesy by Bill Arnett

Protosun and protoplanets Figure courtesy by Bill Arnett

Inner Solar System (Revisited) 1 January 2010 Asteroids (Yellow dots), Comets (sunward-pointing wedges). Vernal Equinox to right along +x axis of right figure

Outer Solar System (Revisited) Positions of asteroids and comets with semi-major axis (a) greater than 5 AU (orbital periods greater than ~11 years) on 2010 January 1. The orbits and positions of Earth, Jupiter, Saturn, Uranus, Neptune, Pluto, and comets Halley and Hale-Bopp are also shown.

Distant Solar System Objects with semi-major axes (a) greater than 6 AU (orbital periods greater than ~15 years) on 2010 January 1. Jupiter, Saturn, Uranus, Neptune, Pluto, Eriss, Sedna, and comets Halley and Hale-Bopp are shown. The brighter color is used for the portion of the orbit above the ecliptic plane. Trans-Neptunian objects larger than about 700 km in diameter are shown as white diamonds,

Distant Solar System

Pluto is no longer a planet IAU resolution in 2006 (1)A planet is a celestial body that: a. is in orbit about the sun b. has sufficient mass for its self-gravity to overcomeits rigid body forces so that it assumes a hydrostaticequilibrium (nearly round) shape, c. has cleared the neighbourhood around its orbit.

Pluto is a dwarf planet (2) A dwarf planet is a celestial body that a. is in orbit about the sun b. has sufficient mass for its self-gravity to overcome its rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and c. has not cleared the neighbourhood around its orbit, and d. is not a satellite (3) All other objects, except satellites, orbiting the sun shall be referred to collectively as Small Solar- System Bodies.

Dwarf Planets Pluto is a “dwarf planet” by the above definition and isrecognized as the prototype of a new category of trans-Neptunian objects. Designated Dwarf Planets 1 Ceres, Pluto, and Eris

Asteroids Small rocky bodies Those observed range in diameter from 948 km (1Ceres) to a few meters. Primarily in orbit between Jupiter and Mars (i.e. main-belt). Near-Earth asteroids (NEAs) are a subset of asteroids whose orbits approach and/or cross the Earth's orbit.

Asteroids Includes Trojans - bodies captured in Jupiter's 4th and 5 th Lagrange points Centaurs - bodies in orbit between Jupiter and Neptune Trans-Neptunian objects - orbiting beyond Neptune Minor Planets

Lagrange Points Two masses in nearly circular orbit Test particle has equilibriun points L1, L2, L3 Unstable L4, L5 stable

Comets Small icy bodies (water and dust) Few km (~1 km) in extent Formed in Outer Solar System – Cold Orbits are disturbed by massive planets Approach the Sun (few AU) Vapourised Atmosphere – upto few hundred thousands of km

Comets Reflected light Atmosphere glows – fluorescence Tail pointing away from Sun Gas – pushed by Solar wind Dust – radiation pressure

Comet Halley 76 year period – small changes e a AU

Comet Halley

Hale Bopp Hale-Bopp 1997 Time period 2520 yr

Comets Short period < 200 yrs lie in ecliptic Possibly originate in trans-Neptune region Disturbed by outer planets Orbit often in ecliptic Long period > 200 to millions of years Orbit generally not in ecliptic Possibly scattered from between Uranus and Neptune to Oort Cloud

Oort Cloud Comets – not from interstellar space Apohelion around 50,000 AU No preferred direction Comets reside in a cloud at peripheryy of Solar Susyem Maybe as many as a trillion Come into Solar System due to disturbance- long period Comets

Trans-Neptunian Objects Several Scientists have proposes the existence of small objects in the Solar System beyond Neptune’s orbit – source of Short Period Comets Leonard (1930), Edgeworth (1945), Kuiper (1951) KuiperBelt between 30 to 50 Au from Sun Short period Comets – scattered disk Beyond Kuiper belt

Edgeworth-Kuiper belt First EKBO 1992 (Jewitt and Luu) Around 1000 EKBOs known ~70,000 predicted larger than 100 km Ice – frozen volatides (methane, ammonia and water) Temperature ~50 K Pluto, Makemake, Humea dwarf planets Pluto largest EKBO

Scattered DIsk