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Mars, Venus, and Mercury

from Solar System
900L - 1040L

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

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

Venus is about the same size as Earth, and 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 differences and 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 must also be the hottest, right? Actually, it’s not, because Venus is just as hot—or hotter. On the side of Mercury that faces the Sun, the planet is a furiously hot 800°F, but the dark side of Mercury is a frigid –280°F! That makes Mercury one of the colder planets in the solar system! The reason for that is related to its atmosphere. Venus has a superdense atmosphere that holds in heat, but Mercury hardly has any atmosphere at all. Without an atmosphere to hold it back, heat escapes into space very quickly. ▶

Venus

How hot is Venus? It’s so hot that lead, tin, and zinc would melt very easily, and 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.

◀ The surface features on Venus, such as continents and mountains, are named for women or goddesses, just like the planet. Venus was the Roman goddess of love and beauty.

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

Here’s a guess. At first, rocky planets were surrounded by hydrogen and helium atmospheres, like the gas giants are. But the rocky planets are closer to the Sun, so the Sun’s powerful solar wind blew away the gases. The atmospheres rocky planets currently have came from gases in their cores.

Solar System Mystery

In 2015, scientists announced that the planet-hunting Kepler telescope had found eight new exoplanets (planets that orbit a star other than the Sun). At least three of them 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 its distance from the Sun would indicate. 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 than it is. On Venus, the greenhouse effect rules because 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 could support life. On a summer day, the temperature on Mars is about 72°F at the equator, but the nighttime temperature plunges down to –94°F. The planet’s poles are even colder! And if you need oxygen, you’re out of luck, because the thin atmosphere on Mars is mostly made up 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.

▲ In September 2015, scientists announced they had proof that water had flowed on Mars. They figured it out by looking at photos they had recently received from the Mars Reconnaissance Orbiter. Water must have made the dark streaks on Mars’s canyon walls and hillsides. They think the streaks form as supersalty water flows downhill when it’s warm. We have long known about water frozen in Mars’s north and south poles. But flowing water could mean there’s life on Mars—even if it’s just little microbes.

The rocky surface of the Martian surface.

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Like Venus, Mars has an atmosphere that’s mostly carbon dioxide—a greenhouse gas. So why isn’t Mars superhot like Venus?

Mars’s atmosphere is very thin, so the greenhouse effect isn’t nearly as strong.

Olympus Mons on Mars is the biggest known volcano. It stands more than twice as tall as Earth’s tallest volcano, Mauna Kea. But Olympus Mons is extinct, and it isn’t expected to erupt again. As far as we know, the only active volcanoes in the solar system are on Venus, Earth, and some moons of Jupiter, Saturn, and Neptune. ▼

Crater Creations

A crater is a hole in the Earth produced when a meteorite fell to the ground, but not all craters are created equal! Their characteristics depend on the meteorite’s mass, speed, and angle of impact. The type of surface it hits makes a difference, too.