The Solar System

Venus

Mars

Saturn

Neptune

Mnemonic: My Very Educated Mother Just Served Us Noodles.

The Sun is about 150 million km away.

Venus. Its thick carbon dioxide atmosphere traps heat (a runaway greenhouse effect).

The asteroid belt, between Mars and Jupiter.

Jupiter

1 astronomical unit (AU)

Mercury

Inner (Mercury to Mars): small, rocky, dense, few or no moons. Outer (Jupiter to Neptune): large, made mostly of gas and ice, low density, rings and many moons.

Close to the young Sun it was too hot for ices to freeze, so only rock and metal formed solids. Beyond the frost line, ices helped build large cores that pulled in hydrogen and helium gas.

About 4.6 billion years.

About 73% hydrogen and 25% helium by mass. It fuses hydrogen into helium in its core.

Earth's axial tilt of about 23.5°, which changes the angle and length of daylight through the year.

Kepler's second law: a planet sweeps out equal areas in equal times, so it moves fastest when closest to the Sun.

T^2 = a^3 , with the orbital period T in Earth years and the average distance a in AU.

Iron oxide (rust) in the dust covering its surface.

The largest volcano in the solar system, a shield volcano on Mars.

A giant, centuries-old storm on Jupiter, wider than Earth.

Io, Europa, Ganymede and Callisto. Ganymede is the largest moon in the solar system.

Saturn, about 0.7 g/cm³, less dense than water.

Titan, Saturn's largest moon.

Both appear to have liquid water oceans beneath icy crusts, making them candidates for life.

Uranus, tilted about 98°, probably from a giant collision long ago.

Venus. (Uranus also counts as retrograde because of its extreme tilt.)

Methane in their atmospheres absorbs red light and reflects blue.

The IAU said a planet must clear its orbital neighborhood. Pluto shares its region with many other Kuiper Belt objects.

Ceres, Pluto, Haumea, Makemake and Eris.

A disk of icy bodies beyond Neptune (about 30–50 AU), including Pluto; the source of many short-period comets.

A distant, roughly spherical shell of icy bodies thought to surround the solar system; the source of long-period comets.

Asteroid: rocky or metallic body, mostly in the asteroid belt. Comet: icy body that forms a glowing coma and tails near the Sun. Meteoroid: small rock in space; meteor: its streak of light in the atmosphere; meteorite: the piece that reaches the ground.

Away from the Sun, pushed by the solar wind and sunlight, no matter which way the comet is moving.