Author: Fraser Cain

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The average circumference of Venus is 38,025 km.

Need some comparison? The average circumference of Earth is 40,041 km. And then if you compare the two numbers, you find that the circumference of Venus is about 95% the circumference of Earth.

If you’ll notice at the top of the article, I specified that we’re talking about the “average circumference”. That’s the number if you average out all the circumference measurements around the planet. This is normally very important when you measure the circumference of planets since they’re often spinning quite rapidly. This rotation causes them to flatten out and bulge around the equator. This means that the equatorial circumference is larger than the circumference if you measure it from pole to pole.

The average (or mean) circumference on Earth is 40,041 km. The equatorial circumference is 40,075 km, and the polar circumference is 40,008 km. So you can see, that’s a pretty big difference, and the average is very important. But here’s the thing. Venus rotates so slowly that it doesn’t bulge at the equator. While the Earth turns once on its axis every 24 hours, Venus takes 243 days to complete a day – that’s even longer than a year on Venus!

Need your numbers in miles? No problem. The circumference of Venus in miles is 23,628 miles.

We have written many articles about Venus for Universe Today. Here’s an article about Venus’ wet, volcanic past, and here’s an article about how Venus might have had continents and oceans in the ancient past.

Want more information on Venus? Here’s a link to Hubblesite’s News Releases about Venus, and here’s NASA’s Solar System Exploration Guide to Venus.

We have recorded a whole episode of Astronomy Cast that’s only about planet Venus. Listen to it here, Episode 50: Venus.

The density of Venus is 5.204 grams per cubic centimeter.

Need some kind of comparison? The density of Earth is 5.515 g/cm³. So Venus is definitely less dense than Earth. And it’s even less dense than Mercury. Of course, it’s much more dense than any of the outer planets, like Jupiter or Saturn.

Scientists think that Venus has an interior structure similar to Earth, with a metal core, rocky mantle, and an outer crust. But these assumptions come purely from the density calculations. Here on Earth, scientists study the interior structure of the planet by using seismographs, and studying how seismic waves from earthquakes travel through the Earth. Since the surface of Venus is hot enough to melt lead, there’s no way to leave scientific equipment on the surface for any period of time to study the interior of the planet.

With its lower density, Venus has a lower mass than Earth. In fact, the mass of Venus is only about 81% the mass of Earth. And it’s also a little smaller than Earth. This means that the surface gravity of Venus is only 90% of what you would experience on Earth.

We have written many articles about Venus for Universe Today. Here’s an article about Venus’ wet, volcanic past, and here’s an article about how Venus might have had continents and oceans in the ancient past.

Want more information on Venus? Here’s a link to Hubblesite’s News Releases about Venus, and here’s NASA’s Solar System Exploration Guide to Venus.

We have recorded a whole episode of Astronomy Cast that’s only about planet Venus. Listen to it here, Episode 50: Venus.

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The axial tilt of Venus is 177.3°. That’s a bit of a confusing number, so let’s figure out what’s going on here. Compare this number to the Earth’s axial tilt of 23.5°. Our tilt gives us such different seasons between summer and winter, so you’d expect that Venus’ much larger tilt would cause more extreme seasons.

Nope. But if you remember your high school geometry, you’ll realize what’s going on. A full circle is 360°. Half a circle is 180°. So if you subtract 177.3° from 180°, you get 2.7°. In other words, Venus is actually only tilted away from the plane of the ecliptic by only 2.7°. Venus is actually completely upside down – almost perfectly upside down.

In fact, Venus is the only planet in the Solar System that rotates backwards compared to the other planets. Seen from above, all the planets are turning in a counter clockwise direction. That’s why Asia sees the Sun first, then Europe, and then the Americas. Mars is the same, and so is Mercury, but Venus is rotating clockwise.

It’s possible that Venus was knocked upside down by a massive impact early in its history. it’s also possible that Venus just slowed down through tidal locking with the Sun, and was somehow spun slowly backwards through its interactions with the other planets.

Here on Earth, the axial tilt is responsible for the seasons. When it’s winter in the northern hemisphere, the north pole is tilted away from the Sun, and less of the Sun’s radiation falls on every square meter of ground. The opposite is true in the summer. Without a significant axial tilt, Venus doesn’t experience seasons like this. The temperature of Venus is a nice even 462°C everywhere on the whole planet.

We have written many articles about Venus for Universe Today. Here’s an article about Venus’ wet, volcanic past, and here’s an article about how Venus might have had continents and oceans in the ancient past.

Want more information on Venus? Here’s a link to Hubblesite’s News Releases about Venus, and here’s NASA’s Solar System Exploration Guide to Venus.

We have recorded a whole episode of Astronomy Cast that’s only about planet Venus. Listen to it here, Episode 50: Venus.

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The geology of Mercury is similar to the geology of the Moon; although, Mercury is a much denser planet with a larger liquid iron core. But when you look at photographs of Mercury, it really looks like you’re looking at the Moon. The surface of Mercury is covered by impact craters and lava plains.

Planetary scientists can judge the age of a planet’s surface by the number and size of impact craters. In the case of Mercury, there are enough craters that scientists think that the surface of Mercury is largely unchanged for billions of years. It’s believed that the surface of Mercury is geologically inactive; although, only 55% of the surface has been mapped in enough detail to see its geology.

Mercury formed with the rest of the Solar System about 4.6 billion years ago. After that was a period of heavy bombardment by asteroids and comets; this lasted until 3.8 billion years ago. All of the planets in the Solar System were beaten up during the Late Heavy Bombardment period, but we can still see the scars on Mercury and the Moon. Some of the largest craters in this period were filled with lava from Mercury’s interior. It’s believed that vulcanism on Mercury ended during its first 700 800 million years.

Craters on Mercury can be small bowl-shaped pockets, or huge impact craters hundreds of kilometers across. The largest crater on Mercury is the Caloris Basin, measuring 1,550 km across. There have been about 15 large impact basins identified on Mercury. Just like the Moon, the larger craters have bright rays of material; it’s brighter because it hasn’t been as weathered by impacts.

One of the unique places on Mercury are the regions around its poles. Astronomers using radar telescopes have detected large deposits of water ice around Mercury’s poles. It’s believed these deposits of ice are located in deep craters near Mercury’s poles where they’re always in shadow. It’s possible these were deposited by comet impacts billions of years ago.

We have written many stories about Mercury here on Universe Today. Here’s an article about a the discovery that Mercury’s core is liquid. And how Mercury is actually less like the Moon than previously believed.

Want more information on Mercury? Here’s a link to NASA’s MESSENGER Misson Page, and here’s NASA’s Solar System Exploration Guide to Mercury.

We have also recorded a whole episode of Astronomy Cast that’s just about planet Mercury. Listen to it here, Episode 49: Mercury.

References:
NASA Solar System Exploration: Mercury
NASA: The Solar System’s Big Bang