I’m Eric Loberg, director of the Taylor Planetarium here at the Museum of the Rockies. I’m going to discuss the differences of the surface of our innermost planets: Mercury, Venus, Earth, and Mars. Mercury probably looks the most different because it’s full of craters. Mercury is very close to the sun, it’s the smallest of these planets. Lots and lots of craters on Mercury, and not much else, and that’s because in the early heavy bombardment period, everything came in and hit mercury. But, there’s no lava flows, there’s no water to wipe out those craters. There might be a little bit of ice on the very poles of Mercury, and that’s about it. So, when you step on Mercury, it’s going to be very, very hot on the sun side, very, very cold on the away side, on the dark side. And, Mercury’s just going to be full of craters, and that’s about it – a few scrapes and scars where the sun might have shrunk it. Venus, you can’t actually see the surface of, but if we could land there, you’d be crushed, because the surface of Venus is about 90 times the pressure here that we have on Earth. Venus, Earth, and Mars all look sort of the same on the surface, with the exception that Earth has a lot of water, and the other two do not. On Venus, and on Earth, and on Mars, you’ll find mountains, you’ll find riverbeds, you’ll find valleys, you’ll find volcanoes. But, Earth has those valleys, a lot of times, full of water, and the other ones do not. Venus may have the most active volcanoes in the solar system – lots of volcanoes constantly resurfacing the landscape. So, you’ll see some craters, but the craters are sometimes being covered up by the lava flows on Venus – lots of sulfur rain raining on top of you there, clouds that are very, very thick, so we can’t see through except with radar. Earth, of course, has nice oceans, nice climates, nice clouds above us. And so, you’ll get, oh, a kind of a typical landscape that you would expect – water carving out valleys, and you get deep oceans, you get nice mountains. And, we have a very good plate tectonic system that volcanoes release our carbon dioxide, it comes back out into the oceans, and they’re recycled through our plate tectonics. Mars is just a little bit too far away, and we like to talk about Goldilocks – Venus, Earth, and Mars all probably started out similarly. Mars was a little too far away – it couldn’t hold onto its atmosphere, partly because it’s a little bit smaller. I tried to draw them sort of to scale here. Earth and Venus are about the same size. Mercury is just a little bit bigger than Earth’s moon. Mars is about a third the size of Earth, and Mars was a little too small – its atmosphere flew off of the planet, and so did most of its water. Now, we see ice on the polar caps north and south. We think that there’s ice a little deeper in the dirt of Mars, and we’ll discover when this ice left with our new spacecraft heading out to Mars now, MAVEN. Mars has a nice long, long trench, the Valles Marineris, which is longer and deeper than our Grand Canyon. It also has the largest mountain in the solar system, Olympus Mons, an ancient volcano – ancient we think – we haven’t seen any volcanoes go off on Mars. Mars looks a lot like Earth. It looks like a dry riverbed, where there were plains that were cut out by rivers. We see little pebbles that we left on Mars that look like they were smoothed by rivers. We don’t see any running water now, but it certainly looks like there was running water on the past on Mars. And so, these were the differences of the surfaces of the inner planets: Mercury, Venus, Earth, and Mars. I’m Eric Loberg, the director of the Taylor Planetarium here at the Museum of the Rockies.