The Solar System

Figure Courtesy NASA/JPL-Caltech

The Sun

Luminosity 3.9 x 1026 W

Mass 1.99 x 1030 Kg

Radius 6.96 x 108 m

Temperature 5800 K

Distance 1.50 x 1011 m (1 AU)

AU = Astronomical unit

Sun and the planets

Mass distribution

99.85 % Sun

0.135 % Planets

0.015 % 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)Planet Semi-major

axis (au) Eccentricity e Inclination

Mercury 0.38709927 0.20563593 7.00497902

Venus 0.72333566 0.00677672 3.39467605

EM Binary 1.00000261 0.01671123 -0.00001531

Mars 1.52371034 0.09339410 1.84969142

Jupiter 5.20288700 0.04838624 1.30439695

Saturn 9.53667594 0.05386179 2.48599187

Uranus 19.18916464 0.04725744 0.77263783

Neptune 30.06992276 0.00859048 1.77004347

Physical ParametersPlanet Mean Radius

(km)Mass (x 1024 kg)

Mercury 2439.7  0.330104

Venus  6051.8 4.86732

Earth 6371.00 5.97219

Mars 3389.50 0.641693

Jupiter   69911 1898.13

Saturn 58232 568.319

Uranus    25362 86.8103Neptune 24622 102.410

Physical ParametersPlanet Sidereal

Orbit Period (y)SiderealRotation Period (d)

Mercury 0.2408467 58.6462

Venus  0.61519726   -243.018

Earth 1.0000174 0.99726968

Mars 1.8808476 1.02595676

Jupiter   11.862615 0.41354

Saturn 29.447498 0.44401Uranus    84.016846 -0.71833 Neptune 164.79132 -0.71833

Inner Planets10 January 2010Revolve conter-clockwiseLooking down at Earth’s N-pole

Terrestrial Planets composed of rock and metals

relatively high densities slow rotationsolid surfaces no rings and few satellites

Small MassSolar System Livehttp://www.fourmilab.ch/cgi-bin/SolarPortion 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 PlanetsFour Giant Planets - low densities, rapid rotation, rings and lots of satellites, strong magnetic filed

Jupiter and Saturn largest and second largestMainly Hydrogen and Helium Gas Giants

Neptune and Uranus Mainly ice (fluid)– water, rocks – silicate and metal condensatesammonia and methaneIce Giants

Rotation

Courtesy: http://cseligman.com/text/sky/rotationvsday.htm

Venus and UranusRetrograde 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 spinningdisk made of gas and dust

4.5 billion years ago

Nebular HypothesisCloud (nebula) of gas and dust collapses under its own gravity, possibly triggered by an external disturbance eg. Supernova blast wave

Figure courtesy http://www.nineplanets.org/by Bill Arnett

Spinning DIsk

Conservation of angular momentumNebula forms a disk

Figure courtesy http://www.nineplanets.org/by Bill Arnett

Protosun and protoplanets

Figure courtesy http://www.nineplanets.org/by Bill Arnett

Inner Solar System (Revisited)

1 January 2010Asteroids (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 Planets1 Ceres, 134340 Pluto, and 136199 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 subsetof asteroids whose orbits approach and/or cross the Earth's orbit.

Asteroids

•Includes Trojans - bodies captured in Jupiter's 4th and 5th 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 0.967142908462304 a 17.8341442925537 AU

Comet Halley

Hale BoppHale-Bopp

1997

Time period2520 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 diskBeyond 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