All About Neptune

Depending on its orbital position, Neptune is often the eighth, sometimes the ninth planet from the sun. The planet Neptune is the smallest of our gas giants, or the planets in our solar system whose mass is primarily made up of gas. It is, like the other gas giants of Saturn, Jupiter and Uranus, without a well defined surface. Therefore, descriptions such as diameter and volume generally refer to the outermost layer.

Although Galileo first spotted Neptune in 1612, Urbain Le Verrier is credited with the official discovery on September 23rd, 1846. While Galileo believed Neptune to be a star, Verrier proved that it was in fact Neptune the planet. It is named after the Roman god of the Sea.

The composition of hydrogen, helium, and methane gives Neptune its unique blue color. It also has faint rings surrounding the planet. For many years, it was believed these rings were not complete. However, when the Voyager 2 reached the Neptune planet on August 25, 1989, their completion was confirmed. Nine moons have been documented in Neptune’s atmosphere, and 4 more are believed to be present.

Because of Pluto's strange orbit, Neptune is sometimes the most distant planet from the Sun. Since 1979, Neptune was the ninth planet from the Sun. On February 11, 1999, it crossed Pluto's path and once again become the eighth planet from the Sun, where will remain for 228 years.

Neptune data (averages):
Diameter: 30,775 miles
Time to rotate: 19 hours, 12 minutes
Orbit: 165 Earth years

Compared to Earth:
Mass: 17.2 times Earth's
Diameter: 3.9 times Earth's
Distance from Sun: 30 times as far

NEPTUNE: ROMAN GOD OF WATER
Historical notes

Neptune was discovered in 1846 after mathematical calculations of Uranus' movements predicted the existence of another large body.

All About Planet Uranus

The mysteriously tilted planet of Uranus is one of the 4 gas giants, or planets whose gas composes the majority of its mass. The planet Uranus is the seventh from the sun. Its 51,117km diameter classifies it as the third largest planet in the solar system. By mass, Uranus is the fourth largest.

Despite not being certain how the planet Uranus inherited its 98° axial tilt; we are able to study the effects of this uneven heating. Hypotheses suggest this unique aspect is due to a major collision during formation.

John Flamsteed first recorded the planet in 1690, but believed it was a star. Almost 100 years later in 1781, Sir William Hershel made the formal discovery. Although originally mistaking it for a comet, Hershel quickly corrected his error and established Uranus as a planet. After much debate about what to call it, Uranus was named after the Greek god of the sky.

Although there are no current plans to physically explore Uranus, the planet was visited in 1986 by the NASA spacecraft, Voyager 2. The surface composed of rock and ice is surrounded by an atmosphere of hydrogen, helium and methane. Uranus’ average temperature is -218°C, or -360° F. So far thirteen rings surrounding Uranus have been found. The planet Uranus has 27 moons, each named after Shakespearean characters.

All About Saturn

Saturn is the second largest planet in our solar system, making it about 95 times larger than the Earth! The sixth planet out from the sun, it takes Saturn about 29.5 years to orbit the sun one time, traveling a distance of roughly 1,426,000,000 kilometers for one single revolution!

Space.com allows you to discover the planet Saturn like you never have before! Check out our comprehensive articles, photos and interactive features to further explore this distant planet famous for its rings and more than 30 discovered moons!

Learn more about the Cassini spacecraft’s findings of liquid water on Saturn’s moon, Enceladus, and see how this revelation changes the range of sustainable environments for living organisms in outer space. Watch an animation of the Cassini Saturn orbital insertion. Study the latest Cassini findings with our amazing satellite photos of craters, cracks, volcanoes and much more on Titan, which is Saturn’s largest moon. Zoom in on the first radio occultation observation of Saturn’s rings and see them unraveled right before your eyes!

Learn more information about Saturn by clicking on any article, photo or other interactive feature below.

All About Jupiter

The planet Jupiter is shown in the adjacent Hubble Space Telescope true-color image (Ref). Jupiter is by far the largest of the planets. It is more than twice as massive as all other planets combined; if it had been only about 100 times more massive at birth (not so much by astronomical standards) it would have become a star instead of a planet. Then the Solar System might be a double star system instead of a single star with a planetary system.

Jupiter has features very different from terrestrial planets. Its composition is more like that of stars, and if it has any solid surface it is hidden deep at its center: Jupiter is apparently almost entirely gas and liquid. It also has an internal energy source and enormous magnetic fields. Finally, the 4 largest moons of Jupiter (the Galilean Moons) are sufficiently interesting in their own right that they are among the most studied objects in the Solar System. We shall devote a separate section to studying their properties.

Our most detailed information concerning Jupiter has come from the space probes Pioneer 10 (1973), Pioneer 11 (1974), Voyager I (March, 1979), Voyager II (July, 1979), and Galileo (1995-present). The first 4 were flyby missions; the Galileo probe was inserted into orbit around Jupiter December, 1995, and launched a probe into the atmosphere that transmitted information before being destroyed. The Galileo orbiter is in a complex orbit that has been examining Jupiter and the Galilean moons.

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All About Mars

Named after the Roman god of war, the planet Mars is located four planets from the Sun. Commonly referred to as “The Red Planet,” Mars tends to give off a reddish hue when viewed from Earth. This is believed to be caused by an abundance of iron oxide on the planet’s surface. Mars is about half the size of the Earth.

Mars has two moons, Phobos and Deimos, both of which are relatively small in size and not shaped in perfect spheres like the Earth’s moon. Mars can be easily seen from Earth without a telescope at a brightness that is only surpassed by the planet Venus, the Moon and the Sun.

Mars has long been considered the most realistic location for life in our solar system, aside from Earth. Many even believe that intelligent life may have once existed on the planet. Scientific exploration of Mars has not produced any evidence of life on the planet. It is believed that the harsh surface environment and extreme solar radiation that saturates the surface of the planet is not capable of sustaining any kind of life.

Currently, the Mars rovers Spirit and Opportunity are close to entering their third year exploring the surface of the Mars, gathering images and information so that we may continue to increase our knowledge and understanding of the Red Planet, as well as the possibility of past or future life on Mars.

About Planet Earth

The Earth, which is located three planets from the Sun, is the only planet in the universe known to support any kind of life. The Earth is estimated to be approximately 4.57 billion years old. The moon followed not long after. The Earth rotates around its own north to south axis once every 23 hours, 56 minutes and 4.091 seconds (one day), and around the Sun once every 365.2564 days (one year).

The Earth formed when the initial molten lava mass cooled and formed a solid outer crust. The Earth’s approximation to the Sun and ability to absorb its solar energy allowed for photosynthesis to occur. This began the accumulation and storage of oxygen in the Earth’s atmosphere and the development of what we now know as the ozone layer. Early eukaryotic life on Earth soon followed.

With the complete formation of the ozone layer, which blocked all harmful ultraviolet radiation from the Sun, multicellular life began to slowly populate the planet. Following several major catastrophic life extinctions, mankind’s first ancestors slowly began to evolve, beginning the early stages of what has lead to the world as we know it today.

For more information about the evolution of planet Earth, including various Earth science topics, simply click on any link or interactive feature on the page below. You may also view a number of incredible images of Earth, and even a satellite image of Earth taken from space!

All About Venus

Named for the Roman goddess of love by the same name, the planet Venus is the second planet from the Sun, at a distance of roughly 108,209,000 kilometers. With an orbital circumference of 680,000,000 kilometers, Venus is just slightly smaller than the Earth and has a very similar chemical composition. For this reason, Venus is commonly referred to as the Earth’s “sister” planet. It takes Venus just under 225 days to orbit the Sun on full time, compared to the 365 day orbital period of the Earth.

Venus actually rotates from east to west, as opposed to west to east which is the common rotating direction of most other planets in space. The atmosphere on the surface of the planet Venus consists mostly of carbon dioxide, with a small trace of nitrogen. The planet Venus has a surface pressure about 90 times that of the Earth, making any life on the planet unsustainable.

Venus is in view to the naked eye from Earth for a period of 2-3 hours before sunrise and 2-3 hours after sunset. Venus is the only other non terrestrial body, besides the moon, that can be seen from Earth during both day and night time hours. At night, Venus is usually the second brightest object in the sky next to the moon.

For more information on Venus, click on any of the Venus articles, Venus pictures, or other interactive Venus features below.

All About Planet Mercury

The planet Mercury is the closest planet to the Sun within the solar system. Mercury was named by the Romans after their god of the same name. Due to its small angular separation from the Sun, which it orbits every 88 days, Mercury is not easily seen from Earth.

At this time, little is known about this comparatively small planet. The only spacecraft to come close to Mercury was Mariner 10 from 1974 to 1975, which was only able to map 40%–45% of the planet's surface.

From the photographs and other information that has been collected, it has been determined that the surface of Mercury is very similar to our own moon, heavily cratered and barren. The magnetic force generated by Mercury’s iron core is only about 1% as strong as that of Earth’s. Temperatures on Mercury can range anywhere from 90 to 700 degrees K!

Discover more about the planet Mercury! Begin by simply clicking on any image gallery, top news article or other interactive features below.