Mercury flits around the sun in 88 days. It resembles our moon in size and appearance. It has no atmosphere, and its surface is heavily cratered. Mercury is hard to spot because it stays close to the horizon even at its greatest elongation.
The MESSENGER spacecraft studied Mercury's magnetic field. Mercury was mapped, and water ice was discovered at its north pole. Mercury was the messenger of the gods in Roman mythology. He is depicted wearing a winged helmet and winged sandals.
Except for size, Venus and Earth have little in common. Venus' atmosphere consists of carbon dioxide and sulfuric acid. Temperatures reach 900 degrees. The pressure is so great that probes are quickly crushed. Venus was impacted and rotates backwards.
The greenhouse effect is the culprit behind Venus' hellish environment. The greenhouse effect occurs when carbon dioxide traps heat from the sun.
Venus comes from behind the sun to be our "evening star." It gets within 26 million miles of Earth.
The Magellan spacecraft arrived at Venus in 1990. Radar mapped the planet. Transits of Venus occurred in 2004 and 2012.
Ours is the third planet from the sun. It formed 4.6 billion years ago, and life evolved in the first billion years. Life is expected to thrive for another billion.
Earth's circumference at the equator is 25,000 miles. Its diameter is 8000 miles. Water covers 70% of the surface. There are almost 8 billion people.
Earth is a water planet, and that makes it unique. Other planets have atmospheres, but only Earth is capable of supporting life.
Earth turns on an imaginary axis running from the North Pole to the South Pole. Earth's axis is tilted. Its Northern and Southern Hemispheres lean toward and away from the sun at different points in its orbit. Varying amounts of sunlight cause the seasons.
Earth's atmosphere is 21% oxygen and 78% nitrogen. Nowhere else in the solar system is there this much oxygen.
Earth's core consists of iron and nickel. Its mantle consists of silicate rocks. Earth's crust floats on the mantle and creates mountain ranges.
Percival Lowell is synonymous with Mars. He built Lowell Observatory in Flagstaff, Arizona, to study the red planet. He thought he saw canals on its surface and that they were made by a dying race to channel water from the polar caps. Of course, there are no inhabitants on Mars, and Lowell's canals were discredited. With the discovery of ancient river beds and evidence that water once flowed, however, Lowell's "optical illusions" may have been these river beds.
Mars polar caps are dry ice, frozen carbon dioxide. Mars has seasons, and its polar caps expand and shrink. The atmosphere is so thin that the caps evaporate rather than melt. No liquid water has been found.
Mars is 35 million miles away at opposition. It is an ideal target, and American, European, Russian & Japanese space agencies have launched missions. Scientists desperately want there to be life on Mars!
Planets move west to east against the background of the stars. As the faster Earth overtakes Mars, Mars seems to stop and back up. All the outer planets exhibit retrograde motion.
Phobos and Deimos are captured asteroids. Because of their small size and weak gravity, they cannot pull themselves into spheres.
Jupiter is the brightest object after the sun, moon & Venus. It is visible 10 months out of the year. Jupiter is huge compared to Earth. It is basically hydrogen and helium, the same stuff that makes up the sun. If Jupiter were more massive, it would be a star. Thermonuclear reactions would begin.
Jupiter's dark belts and white zones are clouds. Rapid rotation causes patterns. The Great Red Spot is a hurricane that has lasted centuries.
Jupiter has 79 moons. Galileo saw Io, Europa, Ganymede & Callisto, and they are called the Galilean moons. They disappear behind the planet. Io has volcanoes. Voyage 1 discovered faint rings.
Jupiter is about half a billion miles from us.
Earth's rapid orbit takes it between Saturn and the sun every year. At opposition, Saturn rises in the east at sunset and sets in the west at sunrise.
If we were looking down on the solar system, we would see Earth pass between Saturn and the sun. Saturn, Earth & the sun would form a straight line. Only planets orbiting beyond Earth reach opposition. Mercury and Venus never do.
What we thought were 3 rings are actually thousands of rings made of ice. Saturn has 82 moons.
Saturn is about a billion miles from us.
When William Herschel discovered Uranus in 1781, people were stunned! For thousands of years, they thought there were 5 planets. These 5 along with the sun and the moon gave us our 7 day week.
Uranus is a gas giant made of hydrogen and helium with traces of methane and ammonia. Methane gives Uranus its green color.
Uranus was knocked on its side, and its seasons last 20 years. The temperature at its cloud tops is -360 degrees.
Uranus' moons are named after Shakespeare's characters. Miranda has a weird landscape. Uranus has 11 rings and 27 moons.
Neptune is Uranus' twin. It was discovered by the German astronomer Johann Galle. We do not hear much about him.
Neptune is the last of the gas giants and takes 165 years to orbit the sun. It has the strongest winds in the solar system, 1200 miles an hour.
Voyager 2 sent pictures of blue Neptune. Triton, the largest moon, is named after Neptune's son.
Clyde Tombaugh discovered Pluto at Lowell Observatory in 1930. It was classified as a planet until the International Astronomical Union reduced its status to that of a dwarf planet. Pluto now belongs to the Kuiper belt.
Tombaugh thought there was nothing beyond Pluto. Astronomers now know of 2300 Trans-Neptunian Objects, among which is the fairly bright Makemake.
Tombaugh's ashes are on board the New Horizons spacecraft. The container reads: "Interred herein are remains of American Clyde W. Tombaugh, discoverer of Pluto and the solar system's "third zone." New Horizons flew by Pluto in July, 2015, taking pictures. Pluto's most distinctive feature is the heart-shaped glacier made of frozen nitrogen.
Pluto has 5 moons: Charon, Hydra, Nix, Styx & Kerberos.