Xi Zhang E&MS A261 <xiz@ucsc.edu> Planetary Discovery in the era of Spacecraft Exploration Xi Zhang E&MS A261 <xiz@ucsc.edu> TA: Szilard Gyalay <sgyalay@ucsc.edu>

Homework #3 is due this Friday. Homework #4 is online now. Mid-term next Friday (11/03) at 10:40 am.

Outline of this week Overview of solar system Formation of star and planetary system Terrestrial Planets: surface and interior Chap. 7, 8, 9

How do robotic spacecraft work? Flyby: flies by another world only once Orbiter: goes into orbit around another world Probe/Lander: lands on surface Sample return mission: returns a sample of another world's surface to Earth

Earth, as viewed by the Voyager spacecraft

Today’s Outline Overview of solar system Formation of star and planetary system

Overview of Solar System

Main Features There are eight major planets with nearly circular orbits. Planets all orbit in same direction and nearly in same plane. Dwarf planets are smaller than the major planets and some have quite elliptical orbits.

Motion of Large Bodies All large bodies in the solar system orbit in the same direction and in nearly the same plane. Most also rotate in that direction (e.g. Venus does not).

Two Major Planet Types Terrestrial planets are rocky, relatively small, and close to the Sun. Jovian planets are gaseous, larger, and farther from the Sun.

Swarms of Smaller Bodies Many rocky asteroids and icy comets populate the solar system.

Notable Exceptions Several exceptions to the normal patterns need to be explained.

Tilting and Self-Rotation

Sun and planets to scale (size, not orbital distance) Solar system model to scale: https://apod.nasa.gov/apod/ap151225.html

Quiz How does the Earth–Sun distance compare with the Sun's radius? It's about 10 times larger. It's about 50 times larger. It's about 200 times larger. It's about 1000 times larger.

Quiz How does the Earth–Sun distance compare with the Sun's radius? It's about 10 times larger. It's about 50 times larger. It's about 200 times larger. It's about 1000 times larger.

Sun Over 99.9% of solar system's mass Made mostly of H/He gas (plasma) These slides follow the planetary tour pages in Chapter 7. Over 99.9% of solar system's mass Made mostly of H/He gas (plasma) Converts 4 million tons of mass into energy each second

Mercury Made of metal and rock; large iron core Desolate, cratered; long, tall, steep cliffs Very hot, very cold: 425 celsius degree (day), –170 celsius degree (night)

Venus Nearly identical in size to Earth; surface hidden by clouds Hellish conditions due to an extreme greenhouse effect Even hotter than Mercury: 470 celsius degree, day and night

Earth Earth and moon with sizes shown to scale An oasis of life The only surface liquid water in the solar system A surprisingly large moon

Mars Looks almost Earth-like, but don't go without a spacesuit! Giant volcanoes, a huge canyon, polar caps, more Water flowed in distant past; could there have been life?

Mars Curiosity rover landed in August 2012.

Jupiter Much farther from Sun than inner planets Mostly H/He; no solid surface 300 times more massive than Earth Many moons, rings

Jupiter’s moons Jupiter's moons can be as interesting as planets themselves, especially Jupiter's four Galilean moons. Io: active volcanoes all over Europa: possible subsurface ocean Ganymede: largest moon in solar system Callisto: a large, cratered "ice ball"

Saturn Giant and gaseous like Jupiter Spectacular rings Many moons, including Enceladus, and cloudy (hazy) Titan

Saturn’s rings Rings are NOT solid; they are made of countless small chunks of ice and rock, each orbiting like a tiny moon.

Saturn’s moon Titan Cassini spacecraft arrived July 2004 (launched in 1997). The figure on the right shows the Huygens probe separated from the main spacecraft on its descent to Titan.

Uranus Smaller than Jupiter/Saturn; much larger than Earth Made of H/He gas and hydrogen compounds (H2O, NH3, CH4) Extreme axis tilt Moons and rings

Neptune Similar to Uranus (except for axis tilt) Many moons (including Triton)

Neptune-size exoplanets are common from Kepler mission

Dwarf Planets: Pluto, Eris, and more Much smaller than major planets Icy, comet-like composition Pluto's main moon (Charon) is of similar size

Table 7.1 This important summary table may be worth some time in class to make sure students understand how to read it…

What properties of our solar system must a formation theory explain? Patterns of motion of the large bodies Orbit in same direction and plane Existence of two types of planets Terrestrial and jovian Existence of smaller bodies Asteroids and comets Notable exceptions to usual patterns Rotation of Uranus, Earth's Moon, etc.

Today’s Outline Overview of solar system Formation of star and planetary system

Origin of the Universe: The Big Bang The Big Bang produces Hydrogen and Helium