DARK COSMIC
INSIGHTS

Explore the Solar System: Every Planet, Its Moons and Our Guides

Start with Mercury and travel outward. Each stop below shows the planet in a real spacecraft or crew photo, its known moons, and the Dark Cosmic Insights guides that go deeper. Every guide separates what is observed and measured from what is modelled and what is still open, the approach we explain in How We Know.

Row of real spacecraft images of the eight planets and Pluto, from Mercury to Pluto, not to scale
OBSERVATION (composite): real NASA spacecraft and crew images of the eight planets and Pluto, placed side by side by DCI. Not to scale; colors are as each source states (Mercury black and white, Venus false color, Neptune processed color, Pluto enhanced color).

Jump to: At a glance · Mercury · Venus · Earth · Mars · Jupiter · Saturn · Uranus · Neptune · Beyond Neptune

Moon counts are as of November 2026, from NASA JPL, and change as new moons are confirmed. See our dated moon table for the full dated comparison.

The Planets at a Glance

Tap a planet to jump to its section. Diameter is twice the mean radius; year length is the time for one orbit of the Sun (sidereal period). Moons are known moons.

PlanetDiameterYear lengthMoons
Mercury4,879 km
3,032 mi		88 days0
Venus12,104 km
7,521 mi		225 days0
Earth12,742 km
7,918 mi		1 year1
Mars6,779 km
4,212 mi		1.9 years2
Jupiter139,822 km
86,881 mi		11.9 years115
Saturn116,464 km
72,367 mi		29.4 years293
Uranus50,724 km
31,518 mi		84.0 years29
Neptune49,244 km
30,599 mi		164.8 years16
Pluto*2,377 km
1,477 mi		247.9 years5

*Pluto is a dwarf planet, included for comparison. Diameters and orbital periods: DCI arithmetic from NASA JPL planetary physical parameters (km to miles at 1.609344). Moon counts as of November 2026, from NASA JPL.

Mercury

Mercury in black and white from NASA Mariner 10, its cratered sunlit half against black space
OBSERVATION: Mercury photographed in black and white by NASA’s Mariner 10, the first spacecraft to visit it, in 1974 (PIA00437). Credit: NASA/JPL/USGS.

The closest planet to the Sun and the smallest of the eight.

Known moons: 0

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Venus

Venus as a pale cream globe of clouds
OBSERVATION (false color): Venus imaged by NASA’s Mariner 10 in February 1974, a false-color composite of orange and ultraviolet filter images, reprocessed from archived data (PIA23791). Credit: NASA/JPL-Caltech.

Wrapped in a thick carbon-dioxide atmosphere, Venus is the hottest planet, even though Mercury is closer to the Sun.

Known moons: 0

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Earth

Full Earth with Africa, Arabia and the Antarctic ice cap
OBSERVATION: Earth photographed by the Apollo 17 crew on their way to the Moon, December 7, 1972 (AS17-148-22727). Credit: NASA.

Our home planet, and the only world known to host life.

Known moons: 1, the Moon

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Mars

Orange-red globe of Mars with a white polar cap and dark markings
OBSERVATION: Global color view of Mars (PIA00407). Credit: NASA/JPL/USGS.

A cold desert world explored by orbiters and rovers.

Known moons: 2, Phobos and Deimos

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Jupiter

Banded globe of Jupiter with the Great Red Spot and a small moon shadow
OBSERVATION: Jupiter in a true-color simulated view built from four Cassini images taken December 7, 2000; the dark dot is Europa’s shadow (PIA02873). Credit: NASA/JPL/University of Arizona.

The largest planet, a gas giant with storms bigger than Earth.

Known moons: 115

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Saturn

Golden Saturn tilted with its broad rings
OBSERVATION: Saturn and its rings in a natural-color Cassini mosaic from October 2004 (PIA06193). Credit: NASA/JPL/Space Science Institute.

The ringed giant, with the largest known family of moons.

Known moons: 293

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Uranus

Pale blue-green, nearly featureless globe of Uranus
OBSERVATION: Uranus imaged by NASA’s Voyager 2 in 1986 (PIA18182). Credit: NASA/JPL-Caltech.

An ice giant that spins tipped on its side.

Known moons: 29

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Neptune

Neptune in a processed deep-blue Voyager 2 view with a large dark oval storm
OBSERVATION (processed color): Neptune from Voyager 2 green and orange filter images taken in 1989, showing the Great Dark Spot (PIA01492). Like other classic Voyager 2 views of Neptune, its deep blue comes from processing that boosted contrast to show clouds and winds; a 2024 Oxford-led study found Neptune is a pale greenish blue, close to Uranus (RAS summary). Credit: NASA/JPL.

The farthest planet from the Sun, a blue-green ice giant only slightly bluer than Uranus.

Known moons: 16, led by Triton

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Beyond Neptune: Pluto and the Dwarf Planets

Pluto in enhanced color with a large pale heart-shaped region
OBSERVATION: Pluto in enhanced color from NASA’s New Horizons, July 14, 2015 (PIA19952). Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.

Past Neptune lies the Kuiper Belt, home to Pluto, which was reclassified as a dwarf planet in 2006.

Pluto’s known moons: 5

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Questions That Span the Whole Solar System

Want the stars and galaxies beyond? Visit Stars & Galaxies, or browse every Dark Cosmic Insights article.