Solar System and Earth 30 Sep: Solar System and Earth 05 Oct: Earth-Moon 07 Oct: Terrestrial Planets 12 Oct: Mars Close-up 14 Oct: Jovian Planets 19 Oct: Asteroids, comets, etc 21 Oct: Planet formation 26 Oct: Extra-Solar Planets ……….. …… ……….. ……
Solar System • 9 planets going around Sun • Other than that the solar system is practically empty. Most of that is near perfect vacuum. • Large: about 12 billion km across
This image shows the sun and 9planets approximately to scale. The order of these bodies are Sun, Mercury, Venus, Earth, Mars, Jupiter , Saturn, Uranus, Neptune, Pluto
Scientific Notation Express numbers in a general form, A × 10n, which is convenient for both large and small numbers.
Question • If something happens at Sun (e.g. Explosion), we know the event (a) immediately (b) about 3 sec after (c) about 8 min after
Answer (c) About 8 min after Note: in only one second, light can circumnavigate the Earth more than seven times
Solar System • Orbits are almost in a plane (within a few degrees) and close to circular. • Mercury and Pluto are most eccentric and have highest inclination.
Masses of 9 Planets ? Earth
Jupiter Sun: 332,946 (Earth Mass) Much heavier!! Saturn Neptune Mercury Pluto Uranus Venus Earth Mars
The nine planets are often further classified as follows Terrestrial Planets (inner 4 planets) Mercury, Venus, Earth and Mars small, high density, low mass, rocky little or no atmosphere Jovian Planets (next 4) Jupiter, Saturn, Uranus and Neptune Massive, low density, gaseous probably no solid surface Pluto: ball of ice and rock, not much the larger than the largest asteroids
Neptune Mars Terrestrial Jovian Gaseous, no solid surface Rocky, no atmosphere
Terrestrial Small, high density Jovian Massive, low density Pluto
Composition • Two ways to find out what the planets are made of (1) Go There! (Mars and Venus) (2) Spectroscopy – either from Earth or from a spacecraft passing by or in the orbit around the planet
Compositions • Terrestrial planets are rocky - silicon, iron compounds • Jovian planets are gaseous – hydrogen, helium, methane, ammonia, carbon monoxide, carbon dioxide, water vapor etc.
Water on Mars! greeting card from my hockey mate at Jerusalem
Other Solar Stuff • Moons: small bodies that orbit Planets • Asteroids: small bodies that orbit Sun. • Comets: dirty snowballs in highly elliptical orbits around Sun
Asteroids • Most of them are between Mars and Jupiter: Asteroid Belt • The composition is similar to that of terrestrial planets (rocks and metals)
Comets (Ices, rocks) • Comets have ices covering them, and these vaporize and produce a gas halo around the comet when it comes close to Sun. • Kuiper belt comets : from extended wedge of asteroids beyond the orbit of pluto, 30-100AU • Oort cloud comets: from very extended halo of comets, probably it extends to 100,000AU.
Question • What is the farthest Planet to the sun? (a) Mars (b) Mercury (c)Earth (d)Moon (e) Pluto
Answer (e) Pluto. Sometimes Neptune is further, but it is not a choice.
Question • Which of these is not a Planet? (a) Mars (b) Mercury (c)Earth (d)Moon (e) Pluto
Answer (d) Moon. Mars is either a planet or a candy bar, Mercury is either a planet or a metal, and Pluto is either a planet or a cartoon dog. Moon most definitely is not a planet.
Question • What is the closest Planet to the Sun? (a) Mars (b) Mercury (c)Earth (d)Moon (e) Pluto
Answer (b) Mercury.
Question • Which of these takes the least time to travel around the Sun? (a) Mars (b) Mercury (c)Earth (d)Moon (e) Pluto
Answer (b) Mercury. Kepler’s Law