Space Time

Inner Planets

With supporting text below as a natural lead-in to additional content.

Mercury

The smallest planet in our solar system and nearest to the Sun, Mercury is only slightly larger than Earth's Moon. From the surface of Mercury, the Sun would appear more than three times as large as it does when viewed from Earth, and the sunlight would be as much as seven times brighter.

Mercury's surface temperatures are both extremely hot and cold. Because the planet is so close to the Sun, day temperatures can reach highs of 800°F (430°C). Without an atmosphere to retain that heat at night, temperatures can dip as low as -290°F (-180°C). Despite its proximity to the Sun, Mercury is not the hottest planet in our solar system – that title belongs to nearby Venus, thanks to its dense atmosphere. But Mercury is the fastest planet, zipping around the Sun every 88 Earth days.

Namesake

Mercury is appropriately named for the swiftest of the ancient Roman gods.

Potential for Life

Mercury's environment is not conducive to life as we know it. The temperatures and solar radiation that characterize this planet are most likely too extreme for organisms to adapt to.

Venus

Venus is the second planet from the Sun, and our closest planetary neighbor. It's the hottest planet in our solar system, and is sometimes called Earth's twin.

Namesake

Venus is the second planet from the Sun, and Earth's closest planetary neighbor. Venus is the third brightest object in the sky after the Sun and Moon. Venus spins slowly in the opposite direction from most planets. Venus is similar in structure and size to Earth, and is sometimes called Earth's evil twin. Its thick atmosphere traps heat in a runaway greenhouse effect, making it the hottest planet in our solar system with surface temperatures hot enough to melt lead. Below the dense, persistent clouds, the surface has volcanoes and deformed mountains.

Potential for Life

Thirty miles up (about 50 kilometers) from the surface of Venus temperatures range from 86 to 158 Fahrenheit (30 to 70 Celsius). This temperature range could accommodate Earthly life, such as “extremophile” microbes. And atmospheric pressure at that height is similar to what we find on Earth’s surface.

Earth

While Earth is only the fifth largest planet in the solar system, it is the only world in our solar system with liquid water on the surface. Just slightly larger than nearby Venus, Earth is the biggest of the four planets closest to the Sun, all of which are made of rock and metal. Earth is the only planet in the solar system whose English name does not come from Greek or Roman mythology. The name was taken from Old English and Germanic. It simply means "the ground." There are, of course, many names for our planet in the thousands of languages spoken by the people of the third planet from the Sun.

Namesake

The name Earth is at least 1,000 years old. All of the planets, except for Earth, were named after Greek and Roman gods and goddesses. However, the name Earth is a Germanic word, which simply means “the ground.”

Potential for Life

Earth has a very hospitable temperature and mix of chemicals that have made life abundant here. Most notably, Earth is unique in that most of our planet is covered in liquid water, since the temperature allows liquid water to exist for extended periods of time. Earth's vast oceans provided a convenient place for life to begin about 3.8 billion years ago. Some of the features of our planet that make it great for sustaining life are changing due to the ongoing effects of climate change.

Mars

Mars – the fourth planet from the Sun – is a dusty, cold, desert world with a very thin atmosphere. This dynamic planet has seasons, polar ice caps, extinct volcanoes, canyons and weather.

Namesake

Mars was named by the ancient Romans for their god of war because its reddish color was reminiscent of blood. Other civilizations also named the planet for this attribute – for example, the Egyptians called it "Her Desher," meaning "the red one." Even today, it is frequently called the "Red Planet" because iron minerals in the Martian dirt oxidize, or rust, causing the surface to look red.

Potential for Life

Scientists don't expect to find living things currently thriving on Mars. Instead, they're looking for signs of life that existed long ago, when Mars was warmer and covered with water.

Outer Planets

The giant planets in our outer solar system don't have hard surfaces and instead have swirling gases above a core. Jupiter and Saturn are gas giants. Uranus and Neptune are ice giants.

Jupiter

Jupiter is a world of extremes. It's the largest planet in our solar system – if it were a hollow shell, 1,000 Earths could fit inside. It's also the oldest planet, forming from the dust and gases left over from the Sun's formation 4.5 billion years ago. But it has the shortest day in the solar system, taking only 10.5 hours to spin around once on its axis.

Jupiter's signature stripes and swirls are actually cold, windy clouds of ammonia and water, floating in an atmosphere of hydrogen and helium. The dark orange stripes are called belts, while the lighter bands are called zones, and they flow east and west in opposite directions. Jupiter’s iconic Great Red Spot is a giant storm bigger than Earth that has raged for hundreds of years. The king of planets was named for Jupiter, king of the gods in Roman mythology. Most of its moons are also named for mythological characters, figures associated with Jupiter or his Greek counterpart, Zeus.

Namesake

Jupiter, being the biggest planet, gets its name from the king of the ancient Roman gods.

Potential for Life

Jupiter’s environment is probably not conducive to life as we know it. The temperatures, pressures, and materials that characterize this planet are most likely too extreme and volatile for organisms to adapt to. While planet Jupiter is an unlikely place for living things to take hold, the same is not true of some of its many moons. Europa is one of the likeliest places to find life elsewhere in our solar system. There is evidence of a vast ocean just beneath its icy crust, where life could possibly be supported.

Saturn

Saturn is the sixth planet from the Sun, and the second-largest planet in our solar system.

Namesake

The farthest planet from Earth discovered by the unaided human eye, Saturn has been known since ancient times. The planet is named for the Roman god of agriculture and wealth, who was also the father of Jupiter.

Potential for Life

Saturn's environment is not conducive to life as we know it. The temperatures, pressures, and materials that characterize this planet are most likely too extreme and volatile for organisms to adapt to. While planet Saturn is an unlikely place for living things to take hold, the same is not true of some of its many moons. Satellites like Enceladus and Titan, home to internal oceans, could possibly support life.

Uranus

Uranus is the seventh planet from the Sun, and it has the third largest diameter of planets in our solar system. Uranus appears to spin sideways.

Uranus is a very cold and windy world. The ice giant is surrounded by 13 faint rings and 28 small moons. Uranus rotates at a nearly 90-degree angle from the plane of its orbit. This unique tilt makes Uranus appear to spin sideways, orbiting the Sun like a rolling ball. Uranus was the first planet found with the aid of a telescope. It was discovered in 1781 by astronomer William Herschel, although he originally thought it was either a comet or a star. It was two years later that the object was universally accepted as a new planet, in part because of observations by astronomer Johann Elert Bode.

Namesake

William Herschel tried unsuccessfully to name his discovery Georgium Sidus after King George III. Instead, the planet was named for Uranus, the Greek god of the sky, as suggested by Johann Bode.

Potential for Life

Uranus' environment is not conducive to life as we know it. The temperatures, pressures, and materials that characterize this planet are most likely too extreme and volatile for organisms to adapt to.

Neptune

Neptune is the eighth and most distant planet in our solar system.

Dark, cold, and whipped by supersonic winds, ice giant Neptune is more than 30 times as far from the Sun as Earth. Neptune is the only planet in our solar system not visible to the naked eye. In 2011 Neptune completed its first 165-year orbit since its discovery in 1846. Neptune is so far from the Sun that high noon on the big blue planet would seem like dim twilight to us. The warm light we see here on our home planet is roughly 900 times as bright as sunlight on Neptune.

Namesake

The ice giant Neptune was the first planet located through mathematical calculations. Using predictions made by Urbain Le Verrier, Johann Galle discovered the planet in 1846. The planet is named after the Roman god of the sea, as suggested by Le Verrier.

Potential for Life

Neptune's environment is not conducive to life as we know it. The temperatures, pressures, and materials that characterize this planet are most likely too extreme, and volatile for organisms to adapt to.