Closest to the Sun, yet not the hottest. Scarred by impacts, yet hiding ice. Rotate the planet and tap the glowing points to find out why.
Mercury sits closest to the Sun. Does that make it the hottest planet in the Solar System?
Mercury is the smallest planet in the Solar System, and the one that orbits closest to the Sun. It's a rocky world — no rings, no thick clouds, no oceans. Just a heavily cratered grey surface, baked by sunlight on one side and frozen on the other.
Because it's so close to the Sun, Mercury is hard to see from Earth — it's usually lost in the Sun's glare. For centuries, people only knew it existed because it sometimes appeared briefly at sunrise or sunset. It wasn't until spacecraft — NASA's Mariner 10 in the 1970s, and later MESSENGER — actually flew past and orbited Mercury that we got a clear look at its surface.
Mercury has no moons and, unlike Earth, almost no atmosphere. That single fact — barely any air — explains most of what makes Mercury so extreme: no wind, no weather, no protection from impacts, and no way to hold on to heat once the Sun goes down.
Mercury has no single "discoverer" — it's bright enough to see with the naked eye, so ancient astronomers in Babylon, Greece, and China were already tracking it thousands of years ago. They just didn't know much about it: it moves so fast across the sky (hence the name, after the swift messenger god) and stays so close to the Sun's glare that studying it properly stayed almost impossible for centuries.
The real breakthrough came from space. In 1974–75, NASA's Mariner 10 became the first spacecraft to fly past Mercury, mapping about 45% of its surface. It took another 30 years before MESSENGER arrived in 2011 as the first spacecraft to actually orbit Mercury — spending four years mapping the entire planet, discovering the polar ice, and revealing craters like Caloris in detail. The textures used in this 3D model come from that mission's data.
Mercury orbits about 58 million km from the Sun on average — but distances in space are hard to picture, so here's Mercury next to its neighbours:
Mercury's distance from Earth changes a lot because both planets are constantly moving in their own orbits — sometimes they're on the same side of the Sun, sometimes on opposite sides.
Mercury does two things at once: it races around the Sun, and it spins on its own axis — just much more slowly. One trip around the Sun takes only 88 Earth days, making Mercury's "year" the shortest in the Solar System. But one full spin on its axis takes 59 Earth days — so slow that, combined with its fast orbit, something strange happens: a single Mercury day (sunrise to sunrise) lasts 176 Earth days — exactly two Mercury years.
This 3-spins-for-every-2-orbits pattern is called a 3:2 spin-orbit resonance, and Mercury is the only planet in the Solar System that does it. One effect: because the spin and orbit interact this way, an observer standing in the right spot on Mercury could watch the Sun rise, pause, briefly reverse direction, and only then continue across the sky — a "double sunrise" that doesn't happen anywhere else nearby.
Mercury's orbit is also unusually stretched (elliptical) and tilted compared to most planets, bringing it as close as 46 million km to the Sun and as far as 70 million km, all within a single 88-day year.
Mercury's surface looks a lot like our Moon's — grey, dusty, and covered in craters. That's not a coincidence: both worlds have almost no atmosphere and no active weather, so nothing erases the scars of an impact. A crater formed 4 billion years ago on Mercury can look almost as sharp today as the day it formed.
Most of these craters were carved out during the Late Heavy Bombardment, a period roughly 4 billion years ago when the young Solar System was still full of leftover rocky debris slamming into every planet and moon. Mercury, with nothing to protect it, kept every single mark.
Beyond craters, Mercury has a few features found almost nowhere else: long, cliff-like ridges called lobate scarps, some hundreds of kilometers long, formed as the planet's iron core slowly cooled and shrank, wrinkling the surface like a drying grape. Mercury is also surprisingly dense — it has a huge iron core that makes up around 85% of its radius, far more, proportionally, than any other planet.
With barely any atmosphere, Mercury cannot hold on to heat. The same rock that scorches at midday freezes solid by midnight.
No score, no pressure — just see what stuck.
What did scientists find hiding in Mercury's polar craters?
Why does Venus get hotter than Mercury, even though it's farther from the Sun?
Mercury's huge Caloris crater was formed by...
Closest to the Sun, coldest at night, hiding ice, and scarred by one of the Solar System's biggest impacts.