The Solar System
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Transcript of The Solar System
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