Top 10 Questions Kids Ask About Mercury

#1: Why is Mercury so close to the Sun? (36 million miles away)

Mercury is about 36 million miles from the Sun—closer than any other planet in our solar system. This proximity isn’t a coincidence but the result of how our solar system formed over 4.6 billion years ago. When the Sun was just a young star, a swirling disk of gas and dust surrounded it. Gravity pulled denser materials like iron toward the center, where Mercury eventually formed. Because of this closeness, Mercury experiences extreme heat on its surface, reaching up to 800°F during the day. Interestingly, despite its closeness to the Sun, Mercury isn’t the hottest planet—that title belongs to Venus, thanks to its thick greenhouse gas atmosphere. Ancient civilizations like the Greeks and Romans noticed Mercury’s rapid movement across the sky and named it after their swift-footed messenger god. Even with its small size—about 3,030 miles in diameter, just a bit bigger than the U.S. from coast to coast—Mercury has a huge impact on how we understand planetary formation.

#2: Can anything live on Mercury? (Temperature range: -290°F to 800°F)

The short answer is no—at least not life as we know it. Mercury’s surface experiences the most extreme temperature swings in the solar system, from blistering 800°F during the day to freezing -290°F at night. These harsh conditions, combined with its lack of atmosphere and water, make it nearly impossible for any known organisms to survive. However, scientists are always cautious when ruling out life entirely. One of the most surprising discoveries came in 2012 when NASA’s MESSENGER spacecraft found evidence of water ice in permanently shadowed craters near Mercury’s poles. These dark regions never see sunlight, staying cold enough to trap ice—an exciting find that opens up new questions about how water reached such an inhospitable place. Could comets or asteroids have delivered it? While Mercury may not be teeming with life, it reminds us that our universe still holds many surprises.

#3: How long is a day on Mercury? (1,408 hours)

A day on Mercury—meaning one full rotation on its axis—lasts about 58.6 Earth days, or 1,408 hours. What makes this even stranger is that Mercury takes only 88 Earth days to orbit the Sun. Because of this odd relationship between its rotation and orbit, if you were standing on Mercury, you’d see the Sun rise, stop, go backward, and then set. One full day-night cycle (sunrise to sunrise) on Mercury actually takes 176 Earth days! This weird solar dance is due to a phenomenon called “spin-orbit resonance.” It means that for every two times Mercury rotates on its axis, it orbits the Sun three times. The result is one of the most unusual “days” in our solar system, making it hard to even define time the way we do on Earth.

#4: Does Mercury have air to breathe? (Atmospheric pressure: ~0.00000000003 psi)

Mercury has almost no atmosphere. Instead, it has what’s called an “exosphere”—a very thin layer of atoms blasted off its surface by solar radiation and meteoroid impacts. This exosphere contains tiny traces of oxygen, sodium, hydrogen, helium, and potassium, but it’s about a trillion times thinner than Earth’s atmosphere. If you tried to breathe on Mercury, you’d instantly suffocate. There’s no air pressure to speak of—roughly 0.00000000003 psi, compared to Earth’s 14.7 psi at sea level. Without an atmosphere, Mercury also lacks weather, wind, or clouds. This makes its skies pitch black, even during the day. It’s both eerie and beautiful to imagine: standing on a rocky plain under a dark sky with the blazing Sun three times larger than it appears from Earth.

#5: What does Mercury look like? (Diameter: 3,030 miles)

Mercury looks a lot like Earth’s Moon—gray, cratered, and desolate. Its surface is covered in impact craters left by meteoroids and comets over billions of years. There are cliffs called “scarps” that stretch for hundreds of miles and rise up to a mile high. These cliffs formed as the planet cooled and contracted, kind of like a drying apple skin that wrinkles. One of the largest craters, the Caloris Basin, is about 960 miles wide—nearly the size of Texas. When sunlight hits its surface, Mercury can shine brightly in our sky, often visible near sunrise or sunset. That’s why ancient astronomers called it both a “morning star” and “evening star.” There’s no color on Mercury—no blue skies, green plants, or oceans—but its rugged beauty and untouched surface offer a stark, powerful view of our solar system’s ancient past.

#6: Has anyone ever gone to Mercury? (Manned missions: 0)

No human has ever set foot on Mercury, and none of our spacecraft have landed there either—yet. So far, only two space missions have visited Mercury. The first was Mariner 10, which flew by in the 1970s and gave us our first close-up images. The second was NASA’s MESSENGER mission, which orbited Mercury from 2011 to 2015, mapping the entire surface and discovering a wealth of new data. Getting to Mercury is incredibly difficult. Because it’s so close to the Sun, spacecraft must fight against the Sun’s massive gravitational pull, requiring a lot of energy and clever maneuvers. Even if we could land, the extreme temperatures and lack of atmosphere make Mercury one of the least hospitable places for human exploration. Still, some scientists dream of sending robotic landers in the future to study those shadowed craters and maybe even sample the ice within.

#7: Why does Mercury have so many craters? (Estimated craters > 400,000)

Mercury has more craters than almost any other planet in our solar system. The reason? It has no atmosphere to burn up incoming meteoroids. Every rock that’s ever collided with Mercury over the last few billion years has left a mark. More than 400,000 craters scar its surface, some as small as a few feet across and others hundreds of miles wide. Because Mercury hasn’t had much volcanic or tectonic activity to resurface or erase these impacts, its landscape is a frozen record of early solar system chaos. It’s like a time capsule, showing us what space was like when the planets were still forming. One fascinating detail is that some of these craters have “hollows”—bright, shallow pits scientists think may be from volatile substances evaporating. Mercury’s craters don’t just tell a story of violence; they offer clues to the planet’s mysterious inner chemistry.

#8: What is Mercury made of? (Core size: 1,100 miles radius)

Mercury is made mostly of metal—its iron core makes up about 85% of the planet’s volume, giving it the highest metal-to-rock ratio of any planet. That’s a bigger core than Earth’s, proportionally. The outer shell is made of silicate rock, similar to the Earth’s crust. Scientists think Mercury might have once been a larger planet whose outer layers were stripped away by a massive collision, leaving mostly metal behind. The core is partly liquid, which was a surprise to scientists, and it helps generate a weak magnetic field—unusual for such a small planet. This magnetic field isn’t strong enough to protect Mercury from the solar wind, but it’s still a puzzle: why does such a small, hot planet have a magnetic field at all? The more we learn about Mercury’s insides, the more it challenges what we thought we knew about how planets form.

#9: Why does Mercury go backward in the sky sometimes? (Retrograde period: 3–4 times per year)

To people watching from Earth, Mercury sometimes appears to move backward in the sky. This is called “retrograde motion,” and it happens about three to four times each year. Of course, Mercury isn’t actually reversing direction—it’s just an optical illusion. Because Mercury orbits the Sun faster than Earth does, it periodically overtakes us in its orbit. As it zips past, it looks like it’s moving backward from our viewpoint. Ancient astronomers found this puzzling and even thought the gods were sending signs. Today, the term “Mercury retrograde” is often used in astrology, blamed for everything from miscommunications to lost keys. Scientifically, it’s a great demonstration of how planetary motion works and how our perspective from Earth shapes what we see in the sky.

#10: Could you walk on Mercury? (Gravity: 0.38 g)

Technically, yes—you could walk on Mercury, assuming you had the right space gear to survive. The gravity is about 38% of Earth’s, so you’d feel lighter—like walking on a trampoline or carrying only a third of your weight. But you’d need a very strong spacesuit to protect you from the extreme heat or cold, not to mention the Sun’s powerful radiation. Mercury’s lack of atmosphere means there’s no weather to kick up dust, so the surface is still and silent. Because of the low gravity, you’d be able to take longer steps and maybe even bounce around like astronauts did on the Moon. Walking on Mercury would be both eerie and awe-inspiring—a reminder of how small we are compared to the Sun dominating the sky just 36 million miles away.

Conclusion

Mercury might be small, but it’s full of surprises. From its giant metallic heart to its icy shadows, from the myths of ancient stargazers to the high-tech eyes of space probes, Mercury continues to spark wonder in young minds. These questions from kids show just how much curiosity this tiny, cratered world can inspire—and they remind us that there’s always more to learn, even about the closest neighbor to our Sun.