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Planetary Notes
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Mercury is the smallest planet and closest planet to the sun at 0.39 A.U.
Its rotation is 59 earth days and its
orbit takes 88 earth days. Mercury is a terrestrial planet with a rocky cratered surface. It has no moons, no
rings and a thin atmosphere.
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Venus is slightly smaller than earth and 2nd closest to the sun at 0.79 A.U.
A day or rotation on Venus is
actually longer than its year or revolution around the sun. Venus is a terrestrial planet, with no moons or rings.
It is the hottest planet because of the greenhouse effect caused by constant thick clouds of sulfuric acid. Venus
is the only terrestrial planet which spins backwards.

Earth is 1 A.U. from the sun, has 1 moon, no rings and supports life as we know it.
70% of earth’s surface is
covered in water. The atmosphere is 78% nitrogen and 21% oxygen.
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Mars is the 4th planet at 1.52 A.U.
It has 2 small moons, which are Phobos and Deimos. It is terrestrial with no
rings. Mars has a thin atmosphere, mostly carbon dioxide and has a red surface due to rusting iron.

The asteroid belt is between Mars and Jupiter. Asteroids are solid, rocky, irregularly shaped with no
atmospheres. The largest asteroid is Ceres, which is classified as a dwarf planet. All the asteroids combined are
smaller than the earth’s moon.

Jupiter is 5th planet from the sun at 5.2 A.U.
It is a Jovian or gas Giant planet and is the largest in the solar
system. It rotates in only 10 earth hours. Its atmosphere is mostly hydrogen and helium and it has faint rings.
Jupiter’s great red spot is a gigantic storm. Jupiter's four largest moons - Io, Europa, Ganymede, and Callisto were first observed by the astronomer Galileo Galilei in 1610 and are known today as the Galilean satellites.
Ganymede is the largest moon in the solar system and the only moon known to have its own magnetic field; and
a liquid-water ocean with the ingredients for life may lie beneath the frozen crust of Europa,

Saturn is the second largest planet, 6th from the sun at 9.5 A.U.
It is a gas giant with more than 50 moons and
large distinct rings, with an atmosphere mostly of hydrogen and helium. It is the least dense planet, and would
float in water. Its moon, Titan, the 2nd largest in the solar system, is shrouded in a thick, nitrogen-rich
atmosphere that might be similar to what Earth's was like long ago.

Uranus is the 3rd largest planet, 7th from the sun at 19.19 A.U.
It rotates backwards like Venus and rotates on
its side. It has over 20 moons and very faint rings.

Neptune is the 4th largest planet, 8th from the sun at 30.07 A.U.
Made up of water, ammonia and methane. It
has more than 10 moons and 6 rings. The largest moon is Triton. Neptune's winds can be three times stronger
than Jupiter's and nine times stronger than Earth's. Axis tilted 47

Pluto is a dwarf planet.
Most dwarf planets are located in the Kuiper Belt, a region of icy objects beyond the
orbit of Neptune. Dwarf planets are rocky with no rings. Some have moons.

A meteoroid is a little chunk of rock or debris in space.
Meteoroids become meteors -- or shooting stars --
when they interact with a planet's atmosphere and cause a streak of light in the sky. Debris that makes it to the
surface of a planet from meteoroids are called meteorites.

Comets are cosmic snowballs of frozen gases, rock and dust.
A comet warms up as it nears the sun and
develops an atmosphere, or coma. The coma may be hundreds of thousands of kilometers in diameter. Shortperiod comets (comets that orbit the sun in less than 200 years) reside in the icy region known as the Kuiper Belt
beyond the orbit of Neptune from about 30 to 55 AU. Long-period comets (comets with long, unpredictable
orbits) originate in the far-off reaches of the Oort Cloud, which is five thousand to 100 thousand AUs away.

The Oort Cloud is a spherical shell, occupying space at a distance between five thousand and 100 thousand
AU containing known icy worlds and comets that are much smaller than Earth's moon.

Terrestrial planets are the inner 4 - Mercury, Venus, Earth and Mars.

Jovian planets or gas giants are the last 4 – Jupiter, Saturn, Uranus and Pluto.
less than 24 hours, have rings and many moons each.
They are rocky and have no rings.
They are gaseous, rotate in
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