ASTRONOMY 202 Spring 2007: Solar System Exploration

Instructor: Dr. David Alexander Web-site: www.ruf.rice.edu/~dalex/ASTR202_S07

Class 21: Solar System [3/12/07]

� Announcements

� The Solar System

� Comparative Planetology

� Planetary Facts• Planetary patterns

� Dirt rocks and gas giants• Terrestrial and Jovian planets• Asteroids and Comets • Quick tour of the solar system

� Exploring the planets

Chapters 7&8Chapters 7&8

Now Playing:

Announcements

Web Project

Window is open to choose web project – window closes March 26See class web-site for details and some news sites

- science.nasa.gov is a good one for solar system

Observing

This week is lousy but we will try to get a night next week and I will also try to get the solar telescopes working

Test Results and Summary

Avg. Score: 75 Median score: 73 σ = 20

NASA Podcasting

Science@NASA podcast at

http://science.nasa.gov/podcast.xml

Using an iPod or any portable MP3 player, you can explore the Universe while driving, jogging, waiting in line ... just about anywhere. It's easy: tune in to the Science@NASA podcast.

The Solar System

Learning from Other Worlds6 of the Solar System’s 9 planets were known to the ancients:

Mercury, Venus, Earth, Mars, Jupiter, Saturn

Uranus was the first ‘new’ planet discovered in 1781 by William and Caroline Herschel.

Neptunewas predicted by its gravitational influence on Uranus in 1846.

Pluto was erroneously predicted and discovered in 1930 and was recently downsized to a dwarf planet.

Comparative Planetology: learning about the planets by exploring them all.

includes moons, asteroids and comets.

Big success of Space Age science; in the last 35 years we have visited all the planets (but not Pluto), photographed asteroids close-up, passed by planetary moons (Io, Titan), sent a probe through the atmosphere of Titan, landed on our own Moon, collected samples of cometary material for return to Earth, sent probes through Jupiter’s atmosphere and landed robotic rovers on Mars.

Planetary Information

The relative sizes of the planets, their relative ‘daily’ rotation and orbital periods, the inclination of their orbits, and their average temperatures all tell us something about how the solar system came into existence and what forces contributed to their development (both physical and chemical).

Similar inclinations - typically Year longer than day - typically

Patterns in the Planets� All planetary orbits are nearly circular and lie in nearly the same plane.

� All planets orbit the Sun in the same direction, counterclockwise as viewed from above.

� Most planets rotate in the same direction in which they orbit, with fairly small axis tilts.

� Most of the Solar System’s large moons exhibit similar properties in their orbits around their planets.

Terrestrial and Jovian Planets

Hydrogen compounds on gas giants include water (H2O), ammonia (NH3), and methane (CH4)

JupiterSaturnUranusNeptune

MercuryVenusEarthMars

Pluto??

Asteroids and Comets

Most asteroids reside in Asteroid Belt between Mars and Jupiter. Biggest is Ceresat ~900km.Eros

Comets mostly ice(s) rather than rock like asteroids. Comets originate in KuiperBelt (30-100 AU) and OortCloud (30-60,000 AU).

Comets have a plasma tail and a dust tail.

LINEAR

Asteroids and Comets

Orbits inclined at every possible

angle and going in all possible directions

Orbit in same direction and nearly

same plane as planets

Orbit in same direction and nearly

same plane as planets

Orbit at a great distance

Orbit between Neptune and about 100 AU from Sun

Orbit in inner solar system

Made mostly of iceMade mostly of iceMade mostly of rock

Oort Cloud Comets

Kuiper Belt Comets

Asteroids

Summary of the Solar System

PATTERNS OF MOTION TWO TYPES OF PLANETS

ASTEROIDS AND COMETS EXCEPTIONS

Quick TourSun: >1000 more massive than everything else in the Solar System combined.

Primarily influences planetary ‘climates’ (regulating temperature).

Mercury: 420oC →→→→ -150oC

Venus: ~450oC - due to greenhouse effect of dense atmosphere.

Earth: Only planet with abundant surface water to support life.

Mars: Flowing water in past could imply existence of simple lifeforms.

Jupiter: Has over 60 moons. If was 50-100 times bigger would have become a star.

Saturn: >30 moons. Much less dense than Jupiter. Moon Titan has an atmosphere (mostly Nitrogen).

Uranus: Methane gives it a blue-green colour. Planet + rings tipped on its side. “Planet George”.

Neptune: ‘Twin’ of Uranus. Moon Triton seems to show geysers of Nitrogen gas and orbits planet ‘backwards’.

Pluto: Large inclination to ecliptic plane and very eccentric orbit.