Where In The Solar System Is There Water?
Our Blue Planet
Clearly, the best place to find water in our solar system is on Earth. Look at our planet from orbit and you can see how little land Is on our surface compared to the water that is present. Even our moon, all gray and devoid of life, has signs of water near its poles. If water can be found on the moon, can it be in other places in the solar system? That I can answer with a definitive yes!
Comets, The Oort Cloud and Asteroids
Also known as dirty snowballs, comets are small objects made of ice and dirt that orbit the Sun and provide a beautiful show as the approach the Sun and sublimate. Most of them reside in what we call the Oort Cloud. This mass of objects exists outside of the Kupier Belt, where many Pluto-like bodies exist. Though we have not directly seen the Oort Cloud, we are confident in its existence because of the numerous comets we have seen as well as the gravitational pull of the outer edges of the solar system.. Retracing the orbits comets puts their far point, or apogee, in the Oort Cloud.
These comets are believed to be remnants from the early formation of the solar system. As the Sun grew, many of the objects that resided close to the Sun were pushed away by competing gravitational forces and also by the solar wind that the Sun as putting out. As the water moved out it froze along with much of the debris surrounding it.
Amazingly, the line that distinguishes asteroids, large rocky bodies, and comets may be thinner than previously thought. New evidence shows that some asteroids give off tails much like comets as they get near the Sun. Analysis of the tails shows some water chemical signatures. And Ceres, the closest dwarf planet to us (and located in the asteroid belt) shows signs of water in the form of ice volcanoes.
Yes, even this stuff contains water. And the coolest part? It collected it. John Bradley (of the Lawrence Livermore Observatory) and his team have shown that interplanetary dust can form water through solar wind interactions. You see, space weathering erodes away the surfaces of objects like asteroids and comets, and the dust left behind gets hit by the solar wind. Through the collision, bonds can be loosened and oxygen and hydrogen in particular can be freed. Once in this state, another similar impact can cause bonding and thus the formation of water. of course, the rate of production though this is so miniscule that it doesn't explain the missing water problem most of the solar system seems to encounter (Rathi).
The Terrestrial Planets
Besides our own planet, other terrestrial planets also contain water. When you look at Mars through a telescope, one may see white areas near the north and south poles of the planet. What you are actually seeing is frozen water and carbon dioxide that resides during the winter. However, because of the low temperatures on Mars as well as pressure differentials, most of the ice goes straight from a solid to a gas. That being said, some evidence does exist for water flowing from high points to low points along rims. Whether the water flows in substantial amounts remains to be seen.
A decade ago, if you said that water was on Mercury then you would have had inconclusive evidence at best. But recently the MESSENGER probe has found water there. How this water could exist so close to the sun is a mystery. Much of it rests near the poles, like the moon, so perhaps whatever mechanism brought water there is also at play with Mercury, potentially solar particles interacting with the soil on the surface.
The Gas Giants
Moving beyond the asteroid belt we find the gas giants. These are planets that are mostly made of light gases and potentially have rocky-iron cores. When probes such as Voyager, Pioneer, Galileo, Cassini, and the like venture out to these planets, they take a look at the chemicals that exist in their atmospheres. Analysis of the chemicals shows that all the gas giants have traces amounts of water, with Neptune and Uranus having higher amounts than does Jupiter and Saturn. They in fact have so much more water that they are given a slight distinction over the larger two gas giants. They are known as the ice giants of the solar system.
The Moons of the Gas Giants
Though this fact is amazing enough, the truly unique sources of water exist in the moons that surrounds these gas giants. When we look at Jupiter, the moon that everyone focuses on is Europa. This moon has a hard icy exterior which is made of ice. But what is even more exciting is that data shows that underneath that crust exists a liquid ocean. Yes, liquid water flows on Europa. And frequently water from below will escape in cracks on the surface due to internal pressure, thus allowing surface material to flow below according to a study of Galileo data by Britney Scmidt (University of Texas at Austin) and her team in a Nov. 2011 issue of Nature. Hubble found evidence of water shooting off the surface in December 2012, with the oxygen and hydrogen plumes varying in strength based on gravitational pulls from Jupiter and the other moons according to a January 18, 2014 issue of Science by Lorenz Hoth (Soutwest Research Institute).. If enough of that surface material make it to the ocean and sufficient temperatures exist, then the possibility of life there exists. Of course two of the other Galilean moons, Calisto and Ganymede, have lots of water on them but in the form of ice (STSci, Kruesi "Europa May", Kruesi "Europa Spews").
Or so scientists used to think. When they looked at the aurora produced by the magnetic field of Ganymede, the UV rays tell how much the moon's field is disturbed by Jupiter's. In total, the shift this causes is just 2 degrees, but theory predicts it should be 6 degrees if the moon is solid. If it were to have say a 60 mile deep ocean then the discrepancy would be resolved (Haynes).
Moving onto Saturn, two of its moons also show signs of water, though until recently those claims were dubious. The moon Phoebe was an oddity, for it wasn't rocky and had an interesting chemical signature. As it turns out, Phoebe is a captured comet that now resides with Saturn. Another oddity was Enceladus. This moon has an icy crust that alone indicated water, but as the Cassini probe orbited Saturn it saw plumes leaving the moon. Water shoots out of Enceladus and into space, meaning that liquid water also exists there. Titan also likely harbors a subsurface ocean of water based on gravity readings from Cassini.
The Kuiper Belt
Beyond the planets lies the Kuiper Belt, whose existence was postulated in the 1940s but was not found until 1992. This is the region where Pluto and many other dwarf planets also exist. In addition to these objects, many smaller ice-rock bodies exist. It is thought that much of the leftovers from the early solar system made their way out here. Much water resides here, frozen on these objects. And many more surprises are surely in store when it comes to water and our solar system.
Name of Object
Amount of Water (E = 366 million trillion gallons)
Hanyes, Korey. "Inner Ocean Hides in Outer Solar System." Astronomy Jul. 2015: 13. Print.
Kruesi, Liz. "Europa May Harbour Subsurface Lakes." Astronomy Mar. 2012: 20. Print.
---. "Europa Spews Water." Astronomy Apr. 2014: 14. Print.
Rathi, Akshat. "Water, Water Everywhere - in Our Solar System." arstechnica.com. Conte Nast., 21 Jan. 2014. Web. 07 Mar. 2016. Web.
Scriber, Brad. "Water's Out There." National Geographic Apr. 2010. Print.
STSci. "Hubble Space Telescope sees evidence of water vapor venting off Europa." Astronomy.com. Kalmbach Publishing Co., 13 Dec. 2013. Web. 14 Nov. 2015.
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© 2014 Leonard Kelley
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