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Mars, Venus, and Mercury

from Solar System
560L - 740L

Lexile Levels
560L - 740L 750L - 890L 900L - 1040L

Mars, Venus, and Mercury are the planets most like Earth. They’re spinning balls of rock.

Venus is about the same size as Earth. Mars has seasons and poles topped with ice, just like Earth. And they’re in our neighborhood, not far from the Sun. But the surface of Venus is hot enough to melt lead. Mars has dust storms as strong as hurricanes. Sunrise to sunrise on Mercury takes six Earth months. Scientists learn a lot about Earth by studying these planets. Looking at our neighbors is like asking over and over, “What if Earth were...?”

Mercury

Mercury is the closest planet to the Sun, so it’s the hottest, right? No, Venus is as hot—or hotter. On the side facing the Sun, Mercury is a screaming-hot 800°F. The dark side is a freezing –280°F! That makes Mercury one of the colder planets! The reason for that has to do with atmosphere. Venus has a superthick atmosphere that holds in heat. Mercury hardly has any atmosphere at all, so heat goes out into space very quickly. ▶

Venus

How hot is Venus?
• Lead, tin, and zinc would easily melt.
• Mercury (the metal, not the planet) would boil.
• About 85 percent of Venus is covered with flowing lava. The planet has tens of thousands of volcanoes. ▶

Surface of Venus showing craters and valleys.

◀ Mountains and other surface features on Venus are named for women or goddesses. Just like the planet itself! Venus was the Roman goddess of love and beauty.

Check It Out!

Planets near the Sun are rocky. But planets far away from the Sun are mostly gas. Why?

Here’s a guess. At first, rocky planets had hydrogen and helium atmospheres, like the gas giants do. But they’re closer to the Sun. So the Sun’s strong solar wind blew away the gases. The atmospheres these planets have now came from gases in their cores.

Solar System Mystery

In 2015, scientists announced that the planet-hunting Kepler telescope had found eight new exoplanets. Those are planets that orbit a star other than the Sun. At least three of them are in the “habitable zone” of their star. That’s the area where temperatures are just right for liquid water to form. And also maybe life?

Earth

Earth is far from the Sun, but it’s a little warmer than it should be. Because of the greenhouse effect, carbon dioxide and other gases keep heat from escaping. If they didn’t, our planet would be freezing. It would be about 60°F colder! On Venus, the greenhouse effect rules. The atmosphere is 97 percent carbon dioxide—a greenhouse gas. Heat can’t escape, so the whole surface is about 900°F. Even the poles are superhot! ▶

Cartoon showing the planet Earth with a face and thermometer in its mouth.

Mars

We know Earth supports life, because here we are! After Earth, Mars is the planet most likely to support life.
• Need balmy weather? On a summer day, the temperature is about 72°F at the equator. Too bad Martian nights drop down to –94°F. It’s even colder at the poles!
• Need oxygen? Then you’re out of luck. The thin atmosphere of Mars is mostly made of carbon dioxide.

The surface of Mars showing hills, valleys, and craters.

Image of a hill on the surface of Mars showing dark streaks that indicate liquid water.

▲ Don’t go looking for little green men, but there may be life on Mars. In September 2015, scientists said they were sure there’s water on Mars. They figured it out with new photos. The Mars Reconnaissance Orbiter has been sending pictures of the red planet for a while. In this image, you can see dark streaks on canyon walls and hillsides. How did they get there? In warm months, supersalty water melts and runs downhill. Then, scientists believe, it makes these streaks. Water on Mars isn’t news: We’ve known there’s frozen water in its north and south poles for a while. But flowing water could mean there’s actual life on Mars. It’s probably just tiny microbes.

The rocky surface of the Martian surface.

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Like Venus, the atmosphere of Mars is mostly carbon dioxide. That’s a greenhouse gas. So why isn’t Mars superhot like Venus?

The atmosphere on Mars is very thin. That means the greenhouse effect isn’t nearly as strong.

Olympus Mons on Mars is the biggest known volcano. It’s more than twice as tall as Mauna Kea. That’s Earth’s tallest volcano. But Olympus Mons is extinct. That means it doesn’t erupt anymore. As far as we know, only Venus, Earth, and some moons of Jupiter, Saturn, and Neptune have volcanoes that still work. ▼

Crater Creations

A crater is a hole in the Earth made by a falling meteorite. Not all craters are created equal! What they’re like depends on the meteorite’s mass, speed, and angle. The type of surface makes a difference, too.