Want to stay on top of all the space news? Follow @universetoday on TwitterA hydrosphere in physical geography describes the combined mass of water found on, under, and over the surface of a planet. The total mass of the Earth’s hydrosphere is about 1.4 × 1024 grams, which is about 0.023% of the Earth’s total mass. Around 2 × 1019 grams of this is the Earth’s atmosphere. In addition, 71% of the Earth’s surface, an area of 361 million square kilometers, is covered by ocean.
Having liquid water makes the Earth a special place. Our planet has a very nice temperature range that allows water to remain in its liquid state. If we were a colder object like Pluto, it would not matter how much water there was on the planet; it would all be frozen. On the other hand, if we were on a very hot planet, all of the water would be in a gaseous state. Water vapor and solid water are useless to the living organisms found on Earth.
The world’s oceans contain 97% of the water in the hydrosphere, most of which is salt water. Ice caps, like that found covering Antarctica, and glaciers that occupy high alpine locations, compose a little less than 2% of all water found on earth. Although that is a small amount, the water stored as ice in glaciers would have a great impact on the environment if it were to melt into a liquid. Some people fear that global warming will cause the melting and collapse of large ice sheets resulting in sea level rise. Rising sea levels could devastate coastal cities, displace millions of people, and wreak havoc on freshwater systems and habitats.
The Earth is not the only solar body that is thought to have a hydrosphere. A thick hydrosphere is thought to exist around the Jovian moon Europa. The outer layer of this hydrosphere is almost entirely frozen, but current models predict that there is an ocean up to 100 km in depth underneath the ice. This ocean remains in a liquid form due to the tidal flexing of the moon in its orbit around Jupiter. The volume of Europa’s hydrosphere is 3×1018 meters cubed, which is about 2.3 times that of the Earths’ hydrosphere. It has been theorized that the Jovian moon Ganymede and the Saturn moon Enceladus may also possess sub-surface oceans.
The hydrosphere is a delicate aspect of the Earth. Many things have to remain in balance in order for it to remain in stasis. There needs to be more study to extrapolate a definite cause and effect between the hydrosphere and global warming.
There is a great article on Universe Today that shows the possibility of a hydrosphere on Mars and another on the effects of cosmic rays on the Earth’s hydrosphere. Astronomy Cast offers a solid episode on terra-forming Mars which would require creating a hydrosphere.