Earth Science 22.8 and 22.17

22.8 Inner vs. Outer Planets
22.17 Exoplanets

Satellites

• Man-made satellites orbit all of the inner planets (Mercury, Venus, Earth, Mars) and some outer planets (Jupiter, Saturn).

• Satellites capture photos and collect important data.

• This allows us to study these planets from the comfort of Earth—no field trip needed!

The Inner Planets

• The four inner planets:

  • Mercury, Venus, Earth, and Mars.

  • Also called terrestrial planets because they are similar to Earth.

• Characteristics of inner planets:

  • Solid, dense, rocky composition.

  • No rings, smaller in size, and shorter orbits.

  • Slow spin; Venus spins backward.

The Inner Planets: Relative Sizes

• The inner planets are shown here to scale, from Mercury to Mars.

• All are made of cooled igneous rock with inner iron cores.

• Earth has one moon, while Mars has two small moons.

• Mercury and Venus have no moons.

The Outer Planets

• The four outer planets:

  • Jupiter, Saturn, Uranus, and Neptune.

  • Also called gas giants because they are mostly made of gases (hydrogen and helium).

• Characteristics of outer planets:

  • Larger, longer orbits, and faster spins than inner planets.

  • All have numerous moons and planetary rings.

Gas Giants and Their Composition

• The outer planets are mostly made of hydrogen and helium.

• The Sun and outer planets were able to keep these light gases due to their stronger gravity.

• The inner planets, with weaker gravity, lost their hydrogen and helium.

Moons and Rings

• All of the outer planets have many moons.

• They also have rings made of dust and particles.

• Only Saturn's rings are easily visible from Earth.

Summary

• Inner planets:

  • Shorter orbits, slower spins, made of rock and metal, no rings.

• Outer planets:

  • Longer orbits, faster spins, made of gases, have rings and numerous moons.

• Outer planets are called gas giants because they are mostly made of hydrogen and helium.

The Discovery of Exoplanets

• Exoplanets are planets outside our solar system.

• First exoplanet discovered: Tadmor (Gamma Cephei Ab)

  • First detected in 1988, confirmed in 2002.

• As of 2022, over 5,000 exoplanets have been confirmed!

Artist's Depiction of Gliese 436

• Gliese 436: A dwarf star, reddish due to its cool temperature.

• The recently discovered planet orbiting Gliese 436 is the size of Neptune and orbits every 2.6 days.

How Exoplanets Are Found

• Exoplanets are difficult to see directly because they are:

  • Far away and tiny.

• How we detect them:

  • Slight motion of a star due to the planet’s gravitational pull.

  • Dimming of a star’s light when a planet passes in front of it.

The Search for Life on Exoplanets

• If life exists elsewhere, it’s most likely on an Earth-like exoplanet.

• Kepler-22b:

  • Found in the Earth-zone of a Sun-like star.

  • Potential for liquid water, a key ingredient for life.

• Fun fact: The Milky Way galaxy likely contains around 100 million planets!

Summary

• Exoplanets are planets that orbit stars outside our solar system.

• As detection methods improve, the number of confirmed exoplanets is increasing rapidly.

• If life exists elsewhere, it may be found on Earth-like exoplanets like Kepler-22b.