Major planets
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune orbit the Sun as the solar system's primary planets.
Planet library
Eight planets, five recognized dwarf planets, one connected system.
The solar system is organized into inner terrestrial planets, outer giants, and officially recognized dwarf planets. This page presents that learning path with original summaries, interactive tools, and deeper field guides.
Recognized dwarf planets
Ceres, Pluto, Haumea, Makemake, and Eris are the currently recognized dwarf planets in this guide.
IAU definition
The IAU definition clarified the difference between planets and dwarf planets, moving Pluto into the dwarf-planet class.
Planet Classes
How the planets are grouped
Inner terrestrial planets
Mercury, Venus, Earth, and Mars are rocky worlds with solid surfaces. They are comparatively small, dense, and close to the Sun.
Outer giant planets
Jupiter and Saturn are gas giants; Uranus and Neptune are ice giants. They lack hard surfaces and carry large atmospheres above deep interiors.
Dwarf planets
Dwarf planets orbit the Sun and are massive enough to be rounded, but they have not cleared their orbital neighborhoods.
Planet sizes
Jupiter is the largest planet, Mercury is the smallest major planet, and scale comparisons reveal why a true-size solar system is hard to draw.
Planet temperatures
Temperature depends on sunlight, atmosphere, albedo, rotation, greenhouse effects, and internal heat, not only distance from the Sun.
Planet X caveat
A hypothetical distant planet is an active research idea, but direct observational evidence has not confirmed another major planet.
All planets
Open a planetary field guide
Each page combines orbital parameters, mission history, exploration issues, and science priorities.
Mercury
The innermost planet is a dense, cratered world with almost no atmosphere and extreme temperature contrast.
- Revolution
- 87.969 days
- Rotation speed
- 0.256 deg/s display
- Temp
- 167 C mean
- Atmosphere
- No stable atmosphere
- Oceans
- No liquid oceans.
- Moons
- 0
Venus
Venus is Earth's near-twin in size but not in habitability: a dense CO2 atmosphere drives a runaway greenhouse surface.
- Revolution
- 224.701 days
- Rotation speed
- 0.062 deg/s display retrograde
- Temp
- 464 C mean surface temperature
- Atmosphere
- Very dense greenhouse atmosphere with global sulfuric-acid cloud decks.
- Oceans
- No present liquid oceans; any early water inventory was largely lost or chemically removed.
- Moons
- 0
Earth
Earth is the benchmark for comparative planetology: liquid water, plate tectonics, life, and a coupled climate system.
- Revolution
- 365.256 days
- Rotation speed
- 15.041 deg/s display
- Temp
- 15 C mean surface temperature
- Atmosphere
- Thick, life-modified nitrogen-oxygen atmosphere with active weather and climate cycles.
- Oceans
- Global liquid-water ocean covers about 71% of the surface; ice sheets, groundwater, lakes, and rivers complete the hydrosphere.
- Moons
- 1
Mars
Mars preserves river valleys, lake deposits, volcanic provinces, polar caps, and a thin CO2 atmosphere.
- Revolution
- 686.98 days
- Rotation speed
- 14.620 deg/s display
- Temp
- -63 C average
- Atmosphere
- Thin carbon-dioxide atmosphere with global dust, clouds, and strong seasonal pressure changes.
- Oceans
- No stable surface ocean today; ancient lakes, river systems, possible northern seas, polar ice, and subsurface ice are key evidence.
- Moons
- 2
Jupiter
Jupiter is a hydrogen-helium giant whose gravity, radiation belts, and moons form a miniature planetary system.
- Revolution
- 4332.59 days
- Rotation speed
- 36.272 deg/s display
- Temp
- -110 C mean cloud-top temperature
- Atmosphere
- Deep giant-planet atmosphere with no solid surface
- Oceans
- No surface ocean on the planet.
- Moons
- 101 confirmed
Saturn
Saturn is a low-density giant with bright icy rings and moons that are laboratories for habitability and geology.
- Revolution
- 10759.22 days
- Rotation speed
- 33.784 deg/s display
- Temp
- -140 C mean cloud-top temperature
- Atmosphere
- Deep hydrogen-helium giant atmosphere with banded clouds, storms, and a low-density interior.
- Oceans
- No planetary surface ocean.
- Moons
- 285 confirmed
Uranus
Uranus rotates on its side and has an offset magnetic field, making it a priority target for ice-giant physics.
- Revolution
- 30688.5 days
- Rotation speed
- 20.882 deg/s display retrograde
- Temp
- -195 C mean cloud-top temperature
- Atmosphere
- Ice-giant atmosphere over a deep interior rich in water, ammonia, and methane compounds.
- Oceans
- No surface ocean.
- Moons
- 29 confirmed
Neptune
Neptune is the wind-sculpted outer planet, with dynamic storms and Triton, a captured Kuiper Belt object.
- Revolution
- 60182.0 days
- Rotation speed
- 22.346 deg/s display
- Temp
- -200 C mean cloud-top temperature
- Atmosphere
- Dynamic ice-giant atmosphere with methane clouds, dark vortices, and powerful winds.
- Oceans
- No surface ocean.
- Moons
- 16 confirmed
Atmospheres and oceans
Planet environment matrix
Surface temperature means a rocky-planet surface value; for giant planets it is a cloud-level reference because there is no hard surface.
| Planet | Main atmosphere/gases | Temperature reference | Ocean / liquid status |
|---|---|---|---|
| Mercury | Oxygen, sodium, hydrogen, helium, potassium, calcium, and magnesium atoms in a very thin exosphere. | About -170 to 430 C, with a mean near 167 C because of extreme day-night contrast. | No liquid oceans. Permanently shadowed polar craters can preserve water ice. |
| Venus | About 96.5% carbon dioxide and 3.5% nitrogen, with sulfur dioxide and trace gases. | About 464 C mean surface temperature, hotter than Mercury despite being farther from the Sun. | No present liquid oceans; any early water inventory was largely lost or chemically removed. |
| Earth | About 78% nitrogen, 21% oxygen, 0.93% argon, plus carbon dioxide, water vapor, and trace gases. | About 15 C global mean surface temperature, with large regional and seasonal variation. | Global liquid-water ocean covers about 71% of the surface; ice sheets, groundwater, lakes, and rivers complete the hydrosphere. |
| Mars | About 95% carbon dioxide, 2.7% nitrogen, 1.6% argon, with oxygen, carbon monoxide, and water vapor traces. | About -63 C average, with local surface temperatures from roughly -125 to +20 C. | No stable surface ocean today; ancient lakes, river systems, possible northern seas, polar ice, and subsurface ice are key evidence. |
| Jupiter | Mostly hydrogen and helium, with methane, ammonia, water vapor, hydrogen sulfide, and other trace compounds. | About -110 C near the 1-bar cloud level; temperature rises rapidly with depth. | No surface ocean on the planet. Several moons, especially Europa, Ganymede, and Callisto, are ocean-world candidates. |
| Saturn | Mostly hydrogen with helium, methane, ammonia, phosphine, water vapor, and other trace gases. | About -140 C near the 1-bar cloud level; warmer at depth. | No planetary surface ocean. Enceladus has a subsurface ocean, and Titan has surface methane-ethane lakes and seas. |
| Uranus | Hydrogen and helium dominate; methane absorbs red light and gives the blue-green color. | About -195 C near the cloud-level reference region; Uranus has some of the coldest planetary atmospheric temperatures. | No surface ocean. Interior models include deep water-ammonia-methane fluids or ionic phases under high pressure. |
| Neptune | Mostly hydrogen and helium with methane and trace hydrocarbons. | About -200 C near the cloud-level reference region; deeper layers are much warmer. | No surface ocean. Interior likely contains high-pressure water-ammonia-methane fluids; Triton may host a subsurface ocean. |
Dwarf planets
The five recognized dwarf planets
These objects keep the solar system honest: the boundary between planet, dwarf planet, asteroid, and Kuiper Belt object is a dynamical story.
Ceres
The largest object between Mars and Jupiter and the only officially recognized dwarf planet in the inner solar system.
Region: Main asteroid belt
Pluto
A complex icy dwarf planet once counted as the ninth planet before the IAU reclassification in 2006.
Region: Kuiper Belt
Haumea
An elongated, fast-rotating dwarf planet with moons and a ring system.
Region: Kuiper Belt
Makemake
One of the brightest known Kuiper Belt objects and slightly smaller than Pluto.
Region: Kuiper Belt
Eris
A distant dwarf planet whose discovery helped trigger the formal IAU planet-definition debate.
Region: Scattered disk
Mathematical model
Planet rotation and scale model
Planet meshes are procedural study models: radius, axial tilt, and rotation come from catalog fields, while surface textures are visual aids. The mathematical model does not infer planet shape from a picture.
Rotation phase
\[\theta(t)=\theta_0+\frac{2\pi t}{P_{\mathrm{rot}}}\]
The displayed spin angle advances from the body's rotation period P_rot. Retrograde rotation is represented by the sign of P_rot.
Axial tilt
\[\mathbf{r}_{\mathrm{tilted}}=R_z(\varepsilon)\,\mathbf{r}_{\mathrm{body}}\]
The spin axis is tilted by an explicit obliquity epsilon. The proof is a rigid-body rotation matrix, not an artist-drawn axis.
Scale contract
\[R_{\mathrm{scene}}=k\,R_{\mathrm{catalog}}\]
Scene radius is a scalar multiple of catalog radius unless the user chooses a readability mode. The page states when visual radius is bounded so the model is not mistaken for exact visual scale.
Verification standard: the rendered object must be reproducible from stated equations, catalog parameters, or explicit geometric transforms. Visual reference images may inform presentation only; they are not the source of orbital positions, field vectors, accretion-disk gradients, timing, or engineering layout.
Limitations: browser scenes may use bounded scale, compressed distances, simplified two-body dynamics, schematic transfer curves, or educational approximations where full numerical ephemerides, CFD, finite-element models, or general-relativistic ray tracing are outside the page scope. Those simplifications are part of the model contract, not hidden image-based construction.