By Jon Fern, staff writer for Save The Water™ | September 24, 2014
- Water is a precious resource here on Earth. Although the surface of our planet is 71% water, only a tiny fraction of that is available for human needs, such as drinking, food production, and sanitation. In fact, a massive 97.5% of Earth’s total stock of water is saline, leaving only 2.5% freshwater, and 70% of that freshwater is locked frozen in the polar ice caps.1 From Earth’s perspective, water is scarce.However, water may in fact be prevalent throughout the universe. NASA estimates that the Jovian moon of Europa may hold 2 to 3 times the amount of Earth’s water. Venus and Mars are also thought to have once had liquid surface water. It is possible that Mars may still have liquid surface water, although this is currently under debate.2Since water is widely considered to be a requirement for the existence of life, finding water beyond Earth is of great interest to scientists conducting research in the field of astrobiology, the study of life in space. Finding incontrovertible evidence of extraterrestrial liquid water will bolster the idea that life is widespread throughout the universe.So far, Earth is the only planet known for sure to have stable surface bodies of liquid water. However, water molecules have been detected in the atmospheres of recently discovered extrasolar planets (planets that orbit stars other than the Sun), and there is evidence that Enceladus, one of the moons of Saturn, may have liquid oceans beneath its frozen exterior.3 Our own surface water exists as a result of atmospheric pressure and our stable orbit around the Sun. Other planets would probably have to have similar conditions for liquid surface water to be present.
There are a number of ways to confirm the presence of water vapor and ice on (or in the atmosphere of) other astronomical bodies, the most accurate being absorption spectroscopy and geochemistry. Detecting liquid water is a lot harder, though. To ascertain whether an astronomical body has liquid surface (or subsurface) water, scientists use a toolkit of detection technques, making use of data pertaining to habitability, gravitational pull, tidal theory, planetary differentiation and radiometry.4
Water vapor is sometimes used as an indicator of surface water, with some scientists inferring the presence of liquid oceans from atmospheric water signatures, while others have conjectured that the presence of subsurface water bodies may also be inferred from this; geysers have recently been detected on Enceladus, for instance, throwing out water vapor that may originate in subsurface oceans.
Some planets and moons, therefore, are likely to hold liquid water. But comets can also carry water, albeit most commonly as water ice.5 It is possible that at least some of the water on Earth may have been brought here by collisions with small astronomical bodies such as comets. Dust samples from comet Wild-2 have yielded evidence that liquid water may exist inside some comets. Saturn’s rings also contain large amounts of ice, a percentage of which is ejected there from the geysers on Enceladus.
However, the very existence of water on some planets may be hindering researchers from finding it. A recent paper argues that small, warm planets may commonly develop cloudy atmospheres, which can unfortunately thwart attempts to observe the atmospheres themselves, by scattering light and reducing the ability to measure spectral absorption and thereby identify chemical species.6
Given the amount of water sources already discovered within our own solar system, and the rate at which water vapor is being detected in the atmospheres of newly discovered exoplanets,7 it is likely that the universe is literally awash with water. Perhaps one day, when we have a self-sustaining space economy, we may be able to make use of off-world water sources. Until then, though, water on Earth is a precious commodity, and one which we must protect and conserve.
- Uncredited, 2006. Human Appropriation of the World’s Fresh Water Supply. University of Michigan. http://www.globalchange.umich.edu/globalchange2/current/lectures/freshwater_supply/freshwater.html Accessed 24th September 2014.
- McEwen, A., et al., 2011. Seasonal Flows on Warm Martian Slopes. Science. http://www.sciencemag.org/content/333/6043/740.abstract Accessed 24th September 2014.
- O’Neill, C., et al., 2010. The role of episodic overturn in generating the surface geology and heat flow on Enceladus. Nature Geoscience. http://www.nature.com/ngeo/journal/v3/n2/abs/ngeo731.html Accessed 24th September 2014.
- Feltman, R., 2014. Scientists hit new milestone in search for water on planets outside our solar system. Washington Post. http://www.washingtonpost.com/news/speaking-of-science/wp/2014/09/24/scientists-hit-new-milestone-in-search-for-water-on-planets-outside-our-solar-system/ Accessed 24th September 2014.
- Cyr, K., et al., 2014. Distribution and Evolution of Water Ice in the Solar Nebula: Implications for Solar System Body Formation. Icarus. http://www.sciencedirect.com/science/article/pii/S0019103598959590 Accessed 24th September 2014.
- Fraine, J., et al., 2014. Water vapour absorption in the clear atmosphere of a Neptune-sized exoplanet. Nature. http://www.nature.com/nature/journal/v513/n7519/full/nature13785.html Accessed 24th September 2014.
- Clavin, W. et al., 2014. NASA telescopes find clear skies and water vapor on exoplanet. http://www.jpl.nasa.gov/news/news.php?release=2014-322 Accessed 24th September 2014.