10 Things to Know About Mercury 1:SMALLEST Mercury is the smallest planet in our solar system—only slightly larger than Earth's Moon.  2: INSIDER It is the closest planet to the Sun at a distance of about 36 million miles (58 million kilometers) or 0.39 AU. 3: LONG DAYS, SHORT YEARS One day on Mercury (the time it takes for Mercury to rotate or spin once with respect to the stars) takes 59 Earth days. One day-night cycle on Mercury takes 175.97 Earth days. Mercury makes a complete orbit around the Sun (a year in Mercury time) in just 88 Earth days. 4:ROUGH SURFACE Mercury is a rocky planet, also known as a terrestrial planet. Mercury has a solid, cratered surface, much like the Earth's moon. 5: CAN'T BREATHE IT Mercury's thin atmosphere, or exosphere, is composed mostly of oxygen (O2), sodium (Na), hydrogen (H2), helium (He), and potassium (K). Atoms that are blasted off the surface by the solar wind and micrometeoroid impacts create Mercury's exosphere. 6: MOONLESS Mercury has no moons.  7: RINGLESS There are no rings around Mercury.  8: TOUGH PLACE TO LIVE No evidence for life has been found on Mercury. Daytime Temperatures can reach 430 degrees Celsius (800 degrees Fahrenheit) and drop to -180 degrees Celsius (-290 degrees Fahrenheit) at night. It is unlikely life (as we know it) could survive on this planet. 9: BIG SUN Standing on Mercury's surface at its closest approach to the Sun, our star would appear more than three times larger than it does on Earth. 10: ROBOTIC VISITORS The two spacecraft of ESA-JAXA's BepiColombo are en route to Mercury. NASA's Mariner 10 was the first mission to explore Mercury. NASA's MESSENGER was the first to orbit the innnermost planet.

10 Things to Know About Venus 1: EARTH-SIZED If the sun were as tall as a typical front door, the Earth and Venus would each be about the size of a nickel.   2: SECOND ROCK Venus orbits our Sun, a star. Venus is the second closest planet to the sun at a distance of about 67 million miles (108 million km). 3:A DAY LONGER THAN A YEAR One day on Venus lasts 243 Earth days because Venus spins backwards, with its sun rising in the west and setting in the east. 4: DIVERSE TERRAIN Venus' solid surface is a volcanic landscape covered with extensive plains featuring high volcanic mountains and vast ridged plateaus. 5: MOONLESS AND RINGLESS Venus has no moons and no rings. 6: GREENHOUSE EFFECT The planet’s surface temperature is about 900 degrees Fahrenheit (465 degrees Celsius)—hot enough to melt lead. 7:WATER ON VENUS Many scientists believe water once existed on the surface. Future Venus explorers will search for evidence of an ancient ocean. 8:MANY VISITORS More than 40 spacecraft have explored Venus. The ‘90s Magellan mission mapped the planet's surface and Akatsuki is currently orbiting Venus. 9:LIFE ON VENUS Venus’ extreme temperatures and acidic clouds make it an unlikely place for life as we know it. 10:SUPER ROTATING ATMOSPHERE While the surface rotates slowly, the winds blow at hurricane force, sending clouds completely around the planet every five days.

Ten Things to Know About Earth 1: MEASURING UP If the Sun were as tall as a typical front door, Earth would be the size of a nickel. 2: THIRD ROCK Earth orbits our Sun, a star. Earth is the third planet from the Sun at a distance of about 93 million miles (150 million km). 3: AS THE WORLD TURNS A day on Earth is 24 hours. Earth makes a complete orbit around the sun (a year in Earth time) in about 365 days. 4: WE'RE ON IT Earth is a rocky planet with a solid and dynamic surface of mountains, canyons, plains and more. Most of our planet is covered in water. 5: BREATHE EASY Earth's atmosphere is 78 percent nitrogen, 21 percent oxygen and 1 percent other ingredients—the perfect balance to breathe and live. 6: OUR COSMIC COMPANION Earth has one moon. 7: RINGLESS Earth has no rings. 8: ORBITAL SCIENCE Many orbiting spacecraft study the Earth from above as a whole system—observing the atmosphere, ocean, glaciers, and the solid earth. 9: HOME, SWEET HOME Earth is the perfect place for life as we know it. 10:PROTECTIVE SHIELD Our atmosphere protects us from incoming meteoroids, most of which break up in our atmosphere before they can strike the surface.

Ten Things to Know About Mars 1: SMALL PLANET If the Sun were as tall as a typical front door, Earth would be the size of a nickel, and Mars would be about as big as an aspirin tablet. 2: FOURTH ROCK Mars orbits our Sun, a star. Mars is the fourth planet from the Sun at an average distance of about 228 million km (142 million miles) or 1.52 AU. 3: LONGER DAYS One day on Mars takes a little over 24 hours. Mars makes a complete orbit around the Sun (a year in Martian time) in 687 Earth days. 4: RUGGED TERRAIN Mars is a rocky planet. Its solid surface has been altered by volcanoes, impacts, winds, crustal movement and chemical reactions. 5: BRING A SPACESUIT Mars has a thin atmosphere made up mostly of carbon dioxide (CO2), argon (Ar), nitrogen (N2), and a small amount of oxygen and water vapor. 6: DOUBLE MOONS Mars has two moons named Phobos and Deimos. 7: RINGLESS There are no rings around Mars. 8: MANY MISSIONS Several missions have visited this planet, from flybys and orbiters to rovers on the surface.The first true Mars mission success was the Mariner 4 flyby in 1965. 9: TOUGH PLACE FOR LIFE At this time, Mars' surface cannot support life as we know it. Current missions are determining Mars' past and future potential for life. 10: RUSTY PLANET Mars is known as the Red Planet because iron minerals in the Martian soil oxidize, or rust, causing the soil and atmosphere to look red.

10 Things to Know About Jupiter 1: THE GRANDEST PLANET Eleven Earths could fit across Jupiter’s equator. If Earth were the size of a grape, Jupiter would be the size of a basketball. 2: FIFTH PLANET FROM OUR STAR Jupiter orbits about 484 million miles (778 million kilometers) or 5.2 Astronomical Units (AU) from our Sun (Earth is one AU from the Sun). 3: SHORT DAY/LONG YEAR Jupiter rotates once about every 10 hours (a Jovian day), but takes about 12 Earth years to complete one orbit of the Sun (a Jovian year). 4: WHAT'S INSIDE Jupiter is a gas giant and so lacks an Earth-like surface. If it has a solid inner core at all, it’s likely only about the size of Earth. 5: MASSIVE WORLD, LIGHT ELEMENTS Jupiter's atmosphere is made up mostly of hydrogen (H2) and helium (He). 6: WORLDS GALORE Jupiter has more than 75 moons. 7: RINGED WORLD In 1979 the Voyager mission discovered Jupiter’s faint ring system. All four giant planets in our solar system have ring systems. 8: EXPLORING JUPITER Nine spacecraft have visited Jupiter. Seven flew by and two have orbited the gas giant. Juno, the most recent, arrived at Jupiter in 2016. 9: INGREDIENTS FOR LIFE? Jupiter cannot support life as we know it. But some of Jupiter's moons have oceans beneath their crusts that might support life. 10: SUPER STORM Jupiter's Great Red Spot is a gigantic storm that’s about twice the size of Earth and has raged for over a century.

Ten Things to Know About Saturn 1:A COLOSSAL PLANET Nine Earths side by side would almost span Saturn’s diameter. That doesn’t include Saturn’s rings. 2: IN DIM LIGHT Saturn is the sixth planet from our Sun (a star) and orbits at a distance of about 886 million miles (1.4 billion kilometers) from the Sun. 3: SHORT DAY, LONG YEAR Saturn takes about 10.7 hours (no one knows precisely) to rotate on its axis once—a Saturn “day”—and 29 Earth years to orbit the sun. 4: GAS GIANT Saturn is a gas-giant planet and therefore does not have a solid surface like Earth’s. But it might have a solid core somewhere in there. 5: HOT AIR Saturn's atmosphere is made up mostly of hydrogen (H2) and helium (He). 6: MINI SOLAR SYSTEM Saturn has 53 known moons with an additional nine moons awaiting confirmation of their discovery—that is a total of 62 moons. 7: GLORIOUS RINGS Saturn has the most spectacular ring system, with seven rings and several gaps and divisions between them. 8: RARE DESTINATION Few missions have visited Saturn: Pioneer 11 and Voyagers 1 and 2 flew by; But Cassini orbited Saturn 294 times from 2004 to 2017. 9: LIFELESS BEHEMOTH Saturn cannot support life as we know it, but some of Saturn's moons have conditions that might support life. 10: ADD A DASH OF EARTH About two tons of Saturn’s mass came from Earth—the Cassini spacecraft was intentionally vaporized in Saturn’s atmosphere in 2017.

Ten Things to Know About Uranus 1: HUGE Uranus is about four times wider than Earth. If Earth were a large apple, Uranus would be the size of a basketball. 2: SEVENTH WANDERER Uranus orbits our Sun, a star, and is the seventh planet from the Sun at a distance of about 1.8 billion miles (2.9 billion kilometers). 3: SHORT-ISH DAY, LONGISH YEAR Uranus takes about 17 hours to rotate once (a Uranian day), and about 84 Earth years to complete an orbit of the Sun (a Uranian year). 4: ICE GIANT Uranus is an ice giant. Most of its mass is a hot, dense fluid of "icy" materials – water, methane and ammonia – above a small rocky core. 5: GASSY Uranus has an atmosphere made mostly of molecular hydrogen and atomic helium, with a small amount of methane. 6: MANY MOONS Uranus has 27 known moons, and they are named after characters from the works of William Shakespeare and Alexander Pope. 7: THE OTHER RINGED WORLD Uranus has 13 known rings. The inner rings are narrow and dark and the outer rings are brightly colored. 8: A BIT LONELY Voyager 2 is the only spacecraft to fly by Uranus. No spacecraft has orbited this distant planet to study it at length and up close. 9: LIFELESS Uranus cannot support life as we know it. 10: ONE COOL FACT Like Venus, Uranus rotates east to west. But Uranus is unique in that it rotates on its side.

Ten Things to Know About Neptune 1: GIANT Neptune is about four times wider than Earth. If Earth were a large apple, Neptune would be the size of a basketball. 2: EIGHTH WANDERER Neptune orbits our Sun, a star, and is the eighth planet from the Sun at a distance of about 2.8 billion miles (4.5 billion kilometers). 3: SHORT DAY, LONG YEAR Neptune takes about 16 hours to rotate once (a Neptunian day), and about 165 Earth years to orbit the sun (a Neptunian year). 4: ICE GIANT Neptune is an ice giant. Most of its mass is a hot, dense fluid of "icy" materials – water, methane and ammonia – above a small rocky core. 5: GASSY Neptune's atmosphere is made up mostly of molecular hydrogen, atomic helium and methane. 6: MANY MOONS Neptune has 13 moons (and one more awaiting confirmation of discovery), which are named after sea gods and nymphs in Greek mythology. 7: FAINT RINGS Neptune has six known rings. 8: ONE VOYAGE THERE Voyager 2 is the only spacecraft to have visited Neptune. No spacecraft has orbited this distant planet to study it at length and up close. 9: LIFELESS Neptune cannot support life as we know it. 10: ONE COOL FACT Because of dwarf planet Pluto’s elliptical orbit, Pluto is sometimes closer to the Sun (and us) than Neptune is.