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Space Topics: Compare the Planets

Worlds of the Solar System

Our solar system contains roughly a hundred round worlds in a wide range of sizes from gas giants like Jupiter to small rocky worlds like Mars to iceballs like Enceladus. Take a tour of the sizes of bodies in the solar system.

The Solar System at a Scale of 1,000 Kilometers Per Pixel

We begin at a very large scale, taking a distant view of the solar system. This largest scale, of 1,000 kilometers (623 miles) pixel, is the only one at which a tiny piece of the Sun can be fit onto the page. The Sun is vastly more enormous than everything else in the solar system put together. The gas giants Jupiter and Saturn and ice giants Uranus and Neptune dominate the rest of the worlds of the solar system. The rest of the planets are just visible at this scale. Earth, Venus, and Mars come in at 13, 12, and 7 pixels across, respectively. But a few of the giant moons are visible: Jupiter's Ganymede and Saturn's Titan are larger than the planet Mercury, and Jupiter's Callisto is just about as big.

The Sun - 1,391,000 km diameter

		Uranus 51,118 km	Neptune 49,528 km
Jupiter 142,984 km	Saturn 120,536 km (main rings 273,550 km)

Earth 12,756 km	Venus 12,104 km	Mars 6,794 km	Ganymede 5,262 km	Titan 5,150 km	Mercury 4,879 km	Callisto 4,821 km

Now let's zoom in by a factor of 10...

The Solar System at a Scale of 100 Kilometers Per Pixel

Zooming in by a factor of 10 gets us to the scale of the terrestrial planets and the solar system's large moons. The gas and ice giants would be too large to fit on the page at this scale. Earth and Venus are now the standouts, both significantly larger than anything else visible at this scale. Then the smallest planets mix in size with the largest moons: Mars is followed closely in size by Jupiter's Ganymede and Saturn's Titan, both of which are larger than Mercury. Next in size come Jupiter's Callisto and Io, Earth's Moon, Jupiter's Europa, and Neptune's Triton, all of which are larger than Pluto. A jump down in size takes you to the icy moons of the outer solar system: Uranus' Titania, Saturn's Rhea, Uranus' Oberon, Saturn's Iapetus, Pluto's Charon, Uranus' Umbriel and Ariel, and Saturn's Dione and Tethys. Finally, just a bit smaller than these, comes the largest of all the asteroids, Ceres. Several trans-Neptunian objects would appear at this scale but are not included because their sizes are uncertain and no images are available.

		Mars 6,794 km	Ganymede 5,262 km	Titan 5,150 km
Earth 12,756 km	Venus 12,104 km

				Europa 3,122 km	Triton 2,707 km	Pluto 2,390 km
Mercury 4,879 km	Callisto 4,821 km	Io 3,643 km	The Moon 3,476 km

Titania 1,578 km	Rhea 1,528 km	Oberon 1,523 km	Iapetus 1,436 km	Charon 1,186 km	Umbriel 1,169 km	Ariel 1,162 km	Dione 1,162 km	Tethys 1,162 km	Ceres 960 km

Zooming by another factor of 10...

The Solar System at a Scale of 10 Kilometers Per Pixel

Zooming in by a factor of 100 from the orginal view takes us to a scale where the worlds of the solar system begin to deviate from spherical shapes, where mountains and ridges clearly spike above their visible disks. At this size, gravity (which tends to flatten mountains over time) is quite weak, and often is not strong enough to overcome the inherent strength of the rock and ice. At this scale, a spherical shape implies that something happened in the little world's geologic history to heat its interior enough to weaken or even melt the rock or ice and allow gravity to have its way.

We begin with the tribe of sub-2,000-kilometer outer planet moons mentioned above: Titania, Rhea, Oberon, Iapetus, Charon, Umbriel, Ariel, Dione, and Tethys. Next up is the largest asteroid, Ceres. Following Ceres there is a jump in size down to the next largest asteroids, Pallas and Vesta. Pallas is also the first world in this lineup that has not yet been visited by a spacecraft or observed with a powerful enough telescope to produce an image that resolves features on its disk. Lumpy Vesta is followed by the surprisingly spherical moons Enceladus (Saturn) and Miranda (Uranus). Neptune's Proteus and Saturn's Mimas are the last of the bodies to achieve a basically spherical shape. The rest of the moonlets and asteroids for which there are images are definitely lumpy. Unfortunately, no disk-resolved images are available for many of the rest of these bodies, so their shapes are not well known.

Titania 1,578 km	Rhea 1,528 km	Oberon 1,523 km

Iapetus 1,436 km	Charon 1,186 km	Umbriel 1,169 km	Ariel 1,162 km

			--   Pallas 570 km	Vesta 525 km	Enceladus 512 km
Dione 1,162 km	Tethys 1,066 km	Ceres 960 km

				-- Nereid 340 km	Amalthea 262x146 km	-- Juno 240 km
Miranda 480 km	Proteus 440 km	Mimas 418 km	Hyperion 370x280 km

	--	--		--		--	--	--
Phoebe 230x220	Eugenia 226	Kleopatra 217	Larissa 216x168	Galatea 204x184	Janus 194x190	Sycorax 190	Despina 180x148	Puck 162

		--		--	--	--	--	--
Prometheus 148x100	Epimetheus 138x110	Portia 136	Pandora 110x88	Thalassa 108x100	Siwa 103	Caliban 96	Naiad 96x60	Juliet 94

Juno, Eugenia, Kleopatra, and Siwa are asteroids. Amalthea is a moon of Jupiter. Mimas, Hyperion, Phoebe, Janus, Prometheus, Epimetheus, and Pandora are moons of Saturn. Miranda, Sycorax, Puck, Portia, and Caliban are moons of Uranus. Proteus, Nereid, Karissa, Galatea, Despina, Thalassa, and Naiad are moons of Neptune.

Images on this page come from a wide variety of sources, including the Hubble Space Telescope (Mars, Ceres, Vesta), NASA GSFC (Earth, from Terra), the Cassini imaging team (Jupiter, Saturn and its moons), Marc Buie, Lowell Observatory (Pluto and Charon, from Earth-based photometry), Mark Robinson (Mercury, from Mariner 10), Ted Stryk (Uranian and Neptunian moons, from Voyager images), Mattias Malmer (Venus, from Mariner 10), A. Tayfun Öner (Triton, from Voyager), Calvin Hamilton (Titan, from Voyager) and Bill Arnett (the Moon, from his own telescope). The rest are from the Planetary Photojournal at NASA/JPL (Voyager, Galileo, and SOHO images).