Terrestrial Planet · Updated May 2026
Mercury.
Mercury is the smallest planet in the solar system and the closest to the Sun, completing an orbit every 88 Earth days at an average distance of 57.9 million km. Its diameter of 4,879 km is barely larger than Earth's Moon. With essentially no atmosphere to retain heat, the dayside reaches 430 °C while the nightside falls below −180 °C — the steepest temperature swing of any planet.
Open Mercury in the viewer →Key facts
A solar day on Mercury (sunrise to sunrise) lasts 176 Earth days — twice its 88-day year. In this viewer's real-time simulation Mercury laps the Sun more than four times every Earth year you watch.
Atmosphere
Mercury has only an exosphere — a wisp of hydrogen, helium, oxygen, sodium and potassium atoms knocked loose by the solar wind and micrometeoroid impacts. There is no weather, no sound, and no greenhouse effect to even out the temperature.
Surface
Heavily cratered and visually similar to Earth's Moon. The Caloris Basin, a 1,550-km impact crater, is one of the largest in the solar system. Long lobate scarps cut across the planet — wrinkles formed as the iron core cooled and the whole planet shrank by an estimated 7 km in radius.
Interior
Mercury has the largest iron core relative to size of any planet — roughly 85% of its radius. That oversized core is why Mercury, alone among the inner planets besides Earth, sustains a global magnetic field, though only about 1% as strong as Earth's.
Formation
Mercury likely formed in roughly its current location 4.5 billion years ago. One leading theory says a giant impact stripped away most of its rocky mantle, leaving the disproportionately huge iron core behind.
Orbit
Mercury's orbit is the most eccentric of any planet (e = 0.205) and tilted 7° from the ecliptic. Its 3:2 spin–orbit resonance — three rotations every two orbits — was only discovered in 1965; before that, astronomers wrongly assumed it was tidally locked.
Notable missions
- Mariner 10 (1974–75 · Past) — First close-up photographs; mapped 45% of the surface during three flybys.
- MESSENGER (2011–15 · Past) — First orbiter; confirmed water ice in permanently shadowed polar craters.
- BepiColombo (2018–2026 · En route) — ESA / JAXA dual-orbiter mission, scheduled to enter Mercury orbit in late 2026.
How to view Mercury in 3D
This page is part of an interactive 3D solar system viewer built with Three.js, WebGL 2.0, and custom GLSL shaders. Mercury orbits the Sun in real time alongside every other planet, with adjustable time speed, scale sliders, and a fly mode that lets you pilot a spacecraft between bodies under realistic gravity.
Fly to Mercury now →Frequently asked questions
Is Mercury the hottest planet?
No — Venus is hotter despite being further from the Sun, because its thick CO₂ atmosphere traps heat. Mercury has no atmosphere to do that.
How long is a year on Mercury?
88 Earth days.
Does Mercury have moons?
No.
Sources & methodology
Numbers cross-referenced with the sources below; surface and atmosphere descriptions reflect findings as of May 2026. Renderings in the 3D viewer use textures based on Solar System Scope and NASA imagery.