In ours Solar System, astronomers regularly divide the planets right into two teams — the inner planets and also the external planets. The inside planets space closer come the Sun and also are smaller and rockier. The outer planets are additional away, larger and made up mainly of gas.

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The inner planets (in bespeak of distance from the sun, closest come furthest) room Mercury, Venus, Earth and Mars. After an asteroid belt come the external planets, Jupiter, Saturn, Uranus and Neptune. The exciting thing is, in some various other planetary solution discovered, the gas giants space actually quite close come the sun.

This renders predicting how our Solar System created an exciting exercise because that astronomers. Typical wisdom is that the young sunlight blew the gases right into the outer fringes of the Solar System and that is why there space such big gas giants there. However, part extrasolar systems have “hot Jupiters” that orbit nearby to your Sun.


The within Planets:

The four inner planets are dubbed terrestrial planets since their surfaces room solid (and, together the name implies, somewhat comparable to planet — although the term have the right to be misleading because each the the 4 has vastly various environments). They’re made up mostly of heavy metals such as iron and nickel, and also have either no moons or few moons. Below are short descriptions of each of these planets based on this info from NASA.

Mercury: Mercury is the smallest world in our Solar device and likewise the closest. The rotates progressively (59 earth days) loved one to the time it takes come rotate about the sunlight (88 days). The planet has actually no moons, but has a tenuous environment (exosphere) include oxygen, sodium, hydrogen, helium and potassium. The NASA MESSENGER (MErcury Surface, space ENvironment, GEochemistry, and also Ranging) spacecraft is currently orbiting the planet.

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The terrestrial planets of our Solar mechanism at approximately relative sizes. Native left, Mercury, Venus, Earth and Mars. Credit: Lunar and also Planetary Institute

Venus: Venus was once taken into consideration a twin world to Earth, till astronomers discovered its surface ar is in ~ a lead-melting temperature the 900 levels Fahrenheit (480 degrees Celsius). The earth is additionally a slow-moving rotator, through a 243-day lengthy Venusian day and also an orbit roughly the sunlight at 225 days. Its environment is thick and also contains carbon dioxide and nitrogen. The planet has no rings or moons and also is right now being visited by the European space Agency’s Venus refer spacecraft.


Earth: Earth is the just planet with life as we recognize it, yet astronomers have discovered some practically Earth-sized planets exterior of ours solar device in what could be habitable regions of their respective stars. It consists of an setting of nitrogen and also oxygen, and also has one moon and also no rings. Plenty of spacecraft circle our planet to provide telecommunications, weather information and other services.

Mars: Mars is a planet under extreme study due to the fact that it shows indications of fluid water flow on its surface in the ancient past. Today, however, its setting is a wispy mix the carbon dioxide, nitrogen and also argon. It has actually two tiny moons (Phobos and also Deimos) and also no rings. A Mars job is slightly longer than 24 earth hours and it bring away the planet around 687 earth days come circle the Sun. There’s a little fleet that orbiters and rovers in ~ Mars right now, including the big NASA Curiosity rover that landed in 2012.

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The outer planets of our Solar device at roughly relative sizes. Native left, Jupiter, Saturn, Uranus and also Neptune. Credit: Lunar and Planetary Institute

The outer Planets:

The external planets (sometimes referred to as Jovian planets or gas giants) are huge planets swaddled in gas. Castle all have actually rings and every one of plenty that moons each. In spite of their size, just two the them are visible without telescopes: Jupiter and Saturn. Uranus and also Neptune to be the very first planets discovered since antiquity, and also showed astronomers the solar device was larger than formerly thought. Below are short descriptions of every of these planets based on this details from NASA.


Jupiter: Jupiter is the biggest planet in our Solar System and also spins an extremely rapidly (10 planet hours) family member to that orbit that the sunlight (12 planet years). The thick environment is mostly consisted of of hydrogen and also helium, perhaps surrounding a terrestrial core that is around Earth’s size. The planet has actually dozens of moons, part faint rings and a great Red point out — a raging storm happening because that the previous 400 years at least (since we were may be to see it with telescopes). NASA’s Juno spacecraft is en route and will visit over there in 2016.

Saturn: Saturn is ideal known for its significant ring system — seven recognized rings with well-defined divisions and gaps between them. Exactly how the rings got there is one topic under investigation. It likewise has dozens that moons. Its environment is greatly hydrogen and also helium, and it also rotates easily (10.7 planet hours) relative to that is time to circle the sun (29 earth years). Saturn is right now being went to by the Cassini spacecraft, which will fly closer come the planet’s rings in the coming years.

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Near-infrared views of Uranus reveal its otherwise pass out ring system, highlighting the level to which it is tilted. Credit: Lawrence Sromovsky, (Univ. Wisconsin-Madison), Keck Observatory.

Uranus: Uranus was an initial discovered by wilhelm Herschel in 1781. The planet’s work takes about 17 earth hours and also one orbit roughly the sun takes 84 planet years. That mass consists of water, methane, ammonia, hydrogen and also helium bordering a rocky core. It has actually dozens of moons and a pass out ring system. There are no spacecraft slated come visit Uranus right now; the last visitor to be Voyager 2 in 1986.


Neptune: Neptune is a far-off planet that consists of water, ammmonia, methane, hydrogen and helium and a feasible Earth-sized core. The has an ext than a dozen moons and also six rings. The just spacecraft to ever visit it was NASA’s Voyager 2 in 1989.

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To learn an ext about the planets and also missions, inspect out these links:

Solar device Exploration: Planets (NASA)NASA Photojournal (NASA)Missions (NASA)Space science (European space Agency)USGS Astrogeology (U.S. Geology Survey)The Solar System and also Its Planets (European an are Agency)


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CategoriesAstronomy, guide to room TagsEarth, inner planets, Jupiter, Mars, Mercury, Neptune, external planets, Saturn, Uranus, Venus

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