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Mars, Venus, and Mercury

from Solar System
750L - 890L

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

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

Venus is about the same size as Earth. Mars has seasons and ice-capped poles, just like Earth. Plus, they’re in our neighborhood—not far from the Sun. But Venus has a surface hot enough to melt lead, and hurricane-force dust storms whip around Mars. From sunrise to sunrise on Mercury takes six Earth months. Both the differences and the similarities tell scientists a lot about Earth. Looking at our neighbors is like asking over and over, “What if Earth were...?”

Mercury

Mercury is closer to the Sun than any other planet is, so it’s also the hottest, right? Actually, it’s not. Venus is just as hot—or hotter. On the side facing the Sun, Mercury is a blazing 800°F, but the dark side of Mercury is an icy –280°F! That makes Mercury one of the colder planets! The reason for that has to do with atmosphere. Venus has a superdense atmosphere that holds in heat, but Mercury hardly has any atmosphere at all. Without an atmosphere to keep it in, heat escapes 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, and 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! Venus was the Roman goddess of love and beauty.

Check It Out!

Why are planets near the Sun rocky and planets farther from the Sun mostly gas?

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 powerful solar wind blew away the gases. The atmospheres they currently have came from gases in the planets’ 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 the planets are in the “habitable zone” of their star. That’s a region where temperatures are just right for liquid water to form—and, perhaps, life?

Earth

Earth is slightly warmer than you might expect, given its distance from the Sun. Because of the greenhouse effect, carbon dioxide and other gases keep heat from escaping. If they didn’t, our planet would be freezing—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, even the poles, is about 900°F. ▶

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

Mars

After Earth, Mars is the planet most likely to be able to support life. That doesn’t mean it actually does support life. On a summer day, the temperature is about 72°F at the equator, but the nighttime temperature drops to –94°F. The poles are even colder! And if you need oxygen, you’re out of luck, because Mars’s thin atmosphere is mostly 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.

▲ In September 2015, scientists said they had proof of water on Mars. They figured it out by looking at new photos sent from the Mars Reconnaissance Orbiter. Water made the dark streaks seen on Mars’s canyon walls and hillsides. The streaks are said to form when supersalty water runs downhill in warm months. There’s water frozen in Mars’s north and south poles. That’s old news. But flowing water could mean there’s life on Mars—even if it’s just tiny microbes.

The rocky surface of the Martian surface.

Check It Out!

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 Earth’s tallest volcano, Mauna Kea. But Olympus Mons is extinct, so it doesn’t erupt. The solar system does have some active volcanoes. As far as we know, they’re only on Venus, Earth, and some moons of Jupiter, Saturn, and Neptune. ▼

Crater Creations

A crater is a hole in the Earth produced by the fall of a meteorite, but not all craters are created equal! It depends on the meteorite’s mass, speed, and angle. The type of surface makes a difference, too.