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 %
0.135 %
Sun
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
Pluto?
•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
Orbit Parameters (J2000)
Planet
Semi-major
axis (au)
Eccentricity e
Inclination
Mercury
Venus
0.38709927
0.72333566
0.20563593
0.00677672
7.00497902
3.39467605
EM Binary
Mars
1.00000261
1.52371034
0.01671123
0.09339410
-0.00001531
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 Parameters
Planet
Mean Radius Mass (x 1024
(km)
kg)
Mercury
Venus
2439.7
6051.8
0.330104
4.86732
Earth
6371.00
5.97219
Mars
Jupiter
3389.50
69911
0.641693
1898.13
Saturn
58232
568.319
Uranus
25362
86.8103
Neptune
24622
102.410
Physical Parameters
Planet
Sidereal
Orbit Period (y)
Mercury
0.2408467
Sidereal
Rotation Period
(d)
58.6462
Venus
0.61519726
-243.018
Earth
Mars
1.0000174
1.8808476
0.99726968
1.02595676
Jupiter
Saturn
11.862615
29.447498
0.41354
Uranus
84.016846
Neptune
164.79132
0.44401
-0.71833
-0.71833
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
http://www.fourmilab.ch/cgi-bin/Solar
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
Venus and Uranus
Retrograde rotation
Rest Direct Rotation
Courtesy: http://cseligman.com/text/sky/rotationvsday.htm
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 http://www.nineplanets.org/
by Bill Arnett
Spinning DIsk
Conservation of angular momentum
Nebula 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 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 SolarSystem 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, 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 subset
of 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 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