Skip to main content
U.S. flag

An official website of the United States government

Tour of Water in the Solar System

October 14, 2021

Happy Earth Week! This year, the theme for Earth Week is Water. Let’s take a tour of the solar system and see where else water exists, and why it’s so unique that water exists in the forms that it does here on Earth! 



Like Earth’s Moon, there is water in permanently shadowed craters near Mercury’s poles. However, there’s not much water and it’s all in the form of ice that would disappear very quickly if exposed to the sun since Mercury doesn’t have a protective atmosphere like Earth. 



The atmosphere of Venus has water vapor, just like Earth’s atmosphere. The surface of Venus is harsh and unlikely to contain liquid water, despite being similar in size to Earth. Many scientists believe that Venus had water long ago just like Earth, but that the water was lost to space because Venus does not have a protective magnetic field like Earth. 



Home, sweet home – the only planet with accessible liquid water at the surface at “room temperature” in lakes, oceans, rivers, but also in solid form as ice caps and glaciers. As a bonus, Earth also has underground liquid water and ice and water vapor in the atmosphere. Earth’s Moon also has small amounts of water ice in permanently shadowed craters and is thought to have buried ice deposits at the poles. 



Landsat 8 Image
Landsat 8 image of rapid ice movement of a glacier in the Arctic Ocean in 2013. View other stunning Landsat images in the Earth as Art Gallery, and image credits here. 


Like Earth, Mars also has polar water ice caps and underground ice deposits. There is also a trace amount of water in the atmosphere of Mars, sometimes seen as clouds. Mars used to have liquid water at the surface (at least occasionally) but much of that water is now trapped as ice or has been lost to space. 

Fan-shaped delta deposit in Jezero crater
Oblique view of the fan-shaped delta deposit in Jezero crater on Mars, which is indicative of past water activity. Credit: NASA/MSSS/USGS Astrogeology. 

Asteroid Belt 

Asteroids are at a point in the solar system called the “frost line” where the heat from the sun is low enough that water condenses into ice. Beyond this line, you are less likely to find liquid water unless it’s below a protective layer of ice, contains dissolved salt to keep from freezing, or is under pressure in an atmosphere. The asteroid/dwarf planet Ceres, for example, may contain an outer layer of dust and rock under which there is a deep layer of salty water ice. 



Jupiter doesn’t have a solid surface, but its atmosphere contains water vapor. Jupiter’s moons harbor a lot of ice in many forms. Ganymede has water ice on the surface, and likely has a large ocean of salty liquid water deep in the subsurface. Callisto is thought to have a surface composed of a mixture of water ice and rock and, like Ganymede, a deep underground ocean of salty liquid water. Europa is famous (and the target for future missions) because the water ice surface is thought to be an icy shell beneath which is a liquid (or mostly liquid) water ocean. Check out NASA’s Europa Clipper mission, being built right now to carry many instruments and cameras to Europa to investigate the ice, subsurface ocean, and the potential that this moon could carry life! 

Lineae on the surface of Europa
Close-up of lineae on the surface of Europa, formed by interactions and movements of the ice with the subsurface ocean. Credit: USGS Astrogeology. 


Like Jupiter, Saturn has no surface but has an atmosphere that contains traces of water vapor. Also, Saturn’s spectacular rings are mostly made of water ice. Titan, the largest moon of Saturn, has a surface that is a mix of water ice and other ices made of hydrocarbons. In addition to a surface with water ice, Titan is thought to have a salty subsurface ocean of liquid water and an icy mantle. Saturn’s moon Dione has a mostly water ice surface and may contain a deep subsurface ocean of liquid water. Enceladus is another famous icy moon like Europa – the surface is covered in water ice, and beneath the south pole is a subsurface ocean of liquid water. Plumes of water vapor and ice have been imaged erupting from fractures in the icy crust and the spacecraft Cassini flew through the plumes, detecting water vapor, hydrocarbons, and salts. 



The first “Ice Giant” Uranus  is thought to have an icy mantle beneath its atmosphere. The blue color of Uranus’ atmosphere is caused by methane, not water. The largest moon of Uranus, Titania, has a surface made of water ice and carbon dioxide ice. There may be a layer of liquid water at the boundary of Titania’s core and mantle. Another moon of Uranus, Miranda, has a surface covered in water ice and, based on its density, may be mostly made of water ice. 



A crescent Uranus from Voyager 2
A crescent Uranus from Voyager 2, highlighting the beautiful atmosphere protecting the icy mantle below. Image credit: NASA/JPL/USGS Astrogeology (more info here).


The next Ice Giant, Neptune, is thought to have an icy mantle beneath its atmosphere just like Uranus. Neptune’s largest moon Triton has a mostly water ice crust and may have a large liquid or slushy ocean deep beneath its frozen surface.  


Neptune as it would appear from a spacecraft approaching Triton
Neptune as it would appear from a spacecraft approaching Triton. Notice the different features on the icy surface of Triton – what complex processes may have formed those? Credit: NASA/JPL/USGS Astrogeology (More info here).


Dwarf planet Pluto’s surface is covered by a combination of nitrogen-rich ice and water ice. Pluto is thought to have a subsurface ocean about 100 kilometers deep. The surface of Pluto’s largest moon, Charon, contains a mixture of ices including water ice. Charon has water ice in its subsurface that may have been liquid in the past, and it may have ice geysers today. 



mage of Pluto from NASA's New Horizons spacecraft
Image of Pluto from NASA's New Horizons spacecraft showing different compositions of ices as different colors. Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute. 

What do you notice about the distribution of water in the solar system? Where is most of the water found – in the inner solar system (between the sun and asteroid belt) or in the outer solar system? Do you think we would be able to use the water on every moon and planet? Why or why not?  

Here’s a fun way to find out more about Water in the Solar System – play one of the PLANETS Water in the Solar System card games! This deck of cards explores how water is distributed in the solar system with a series of fun games, developed for kids 8-14 years but fun for kids of all ages!  

Follow our social media pages to learn more about water in the solar system and how future explorers may be using water to advance our understanding of life on Earth! 

Twitter: @USGS_AstroGeo
Facebook: @USGS_Astrogeology 
Instagram: @usgs_astrogeology 

Get Our News

These items are in the RSS feed format (Really Simple Syndication) based on categories such as topics, locations, and more. You can install and RSS reader browser extension, software, or use a third-party service to receive immediate news updates depending on the feed that you have added. If you click the feed links below, they may look strange because they are simply XML code. An RSS reader can easily read this code and push out a notification to you when something new is posted to our site.