earthsky.org
By in
| Space on Mar 24, 2014
Image via New Scientist

A collection of 10 unexpected and intriguing facts about our solar system – our sun and its family of planets – you probably did not know!

Remember those styrofoam models of the solar system we made in elementary school? The solar system is even cooler than that! Here are 10 things you might not know.

The hottest planet isn’t closest to the sun.

Pluto is smaller than the USA.

George Lucas doesn’t know much about “asteroid fields.”

You can make volcanos using water as magma.

The edge of the solar system is 1,000 times farther away than Pluto.

Almost everything on Earth is a rare element.

There are Mars rocks on Earth (and we didn’t bring here).

Jupiter has the biggest ocean of any planet.

Even really small bodies can have moons.

We live inside the sun.

This artist's concept puts solar system distances in perspective. The scale bar is in astronomical units, with each set distance beyond 1 AU representing 10 times the previous distance. One AU is the distance from the sun to the Earth, which is about 93 million miles or 150 million kilometers.  NASA's Voyager 1, humankind's most distant spacecraft, is around 125 AU.  Image via NASA/JPL-Caltech

This artist’s concept puts solar system distances in perspective. The scale bar is in astronomical units, with each set distance beyond 1 AU representing 10 times the previous distance. One AU is the distance from the sun to the Earth, which is about 93 million miles or 150 million kilometers. NASA’s Voyager 1, humankind’s most distant spacecraft, is around 125 AU. Image via NASA/JPL-Caltech.

1. The hottest planet isn’t closest to the sun. Many people know that Mercury is the closest planet to the sun, well less than half of the Earth’s distance. It is no mystery, therefore, why people would assume that Mercury is the hottest planet. We know that Venus, the second planet away from the sun, is on the average 30 million miles farther from the sun than Mercury. The natural assumption is that being farther away, it must be cooler. But assumptions can be dangerous. For practical consideration, Mercury has no atmosphere, no warming blanket to help it maintain the sun’s heat. Venus, on the other hand, is shrouded by an unexpectedly thick atmosphere, about 100 times thicker than our own on Earth. This in itself would normally serve to prevent some of the sun’s energy from escaping back into space and thus raise the overall temperature of the planet. But in addition to the atmosphere’s thickness, it is composed almost entirely of carbon dioxide, a potent greenhouse gas. The carbon dioxide freely lets solar energy in, but is far less transparent to the longer wavelength radiation emitted by the heated surface. Thus the temperature rises to a level far above what would be expected, making it the hottest planet. In fact the average temperature on Venus is about 875 degrees F, hot enough to melt tin and lead. The maximum temperature on Mercury, the planet closer to the sun, is about 800 degrees F. In addition, the lack of atmosphere causes Mercury’s surface temperature to vary by hundreds of degrees, whereas the thick mantle of carbon dioxide keeps the surface temperature of Venus steady, hardly varying at all, anywhere on the planet or any time of day or night!

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