ELIXIR OF LIFE: Finding evidence of water in the solar system and beyond is an important signpost for the presence of life. Liquid water is a solvent, a medium and a catalyst for certain types of proteins, and essential to biological processes.
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When NASA announced last month the finding of water ice in several impact craters on Mars, and either water or hydroxyl widely dispersed on the moon's surface, the solar system became a little more familiar because it seemed a tad more hospitable to life as we know it on Earth.
But is that because the rest of the cosmos has much in common with Earth or vice versa? Water, the unique molecule that cradles and nurtures life here, is apparently common and perhaps abundant in the solar system. Observational evidence suggests that water as a solid, liquid or gas is present at the poles of Mercury, within the thick clouds of Venus, on Mars, inside asteroids and comets, and on Jupiter, Saturn, Uranus and Neptune. Scientists also have speculated that Jupiter's moons Europa, Ganymede and Callisto have vast subsurface oceans of liquid water. They have also detected through spectroscopy water frost on Pluto's moon, Charon. Of course, scientists have known that H2O also seems to be ubiquitous beyond the solar system. They've detected it in one form or another in interstellar gas and even in such unlikely places as the atmospheres of stars. Perhaps it shouldn't be such a revelation. After all, hydrogen is the most common element in the universe, followed by helium and oxygen.
"It's not a surprise that the simple (molecules) would show up again and again," says Pamela Conrad, a planetary scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena and part of the science team for the next-generation Mars Science Laboratory headed to the Red Planet in late 2011. "But I think its discovery on specific planets or other bodies in the solar system has a significance beyond whether or not we're surprised that it's there. It gives us permission to speculate on whether or not there is other chemistry that would be relevant to the origin or the sustenance of life."
As scientists continue their search for extraterrestrial water, it's good to be reminded why they're actually looking for it. Just what is it about water, specifically liquid water, that makes it essential for life? The short answer is that life on Earth requires it. Photosynthetic life snatches the hydrogen from water molecules to make sugars. Organisms use water to add rigidity to cells and transport nutrients. If we don't drink it, we die.
But it's the handful of intrinsic—and collectively unique—properties that explains why water is the elixir of life. Sushil Atreya, who studies the formation of planets and the evolution of their atmospheres at the University of Michigan at Ann Arbor's Planetary Science Laboratory, breaks it down this way: "Liquid water acts as a solvent, as a medium and as a catalyst for certain types of proteins, and those are three main things that allow life to flourish," he says.
Liquid water's property as a solvent, in which salts and organic compounds such as amino acids and sugars readily dissolve, is due to its dipole molecular structure. The oxygen atoms in water hold their electrons much more strongly than the hydrogen atoms do, so they accumulate a negative electrical charge. Water's hydrogen atoms, bent on the same side of the water molecule, are positively charged. The resulting structure is the reason why water molecules can break down such a wide variety of chemical species.
"[Water] is just amazing at being able to make friends with some piece of a molecule, or some piece of an ion," JPL's Conrad says. "And that property of water is special, because more things dissolve in it than in other kinds of solvents." As a result, water is a great arbiter of chemistry that allows tremendous diversity. "When you're trying to make life, you want conditions where you can try many things…in the hopes that something will take shape," he says.
Although it's a superior solvent, water also provides an ideal medium in which chemical reactions can occur and nutrients can be easily transported, Atreya says. That includes enzymes, essential to life processes, which need water in order to do their job. "They have to be in a certain shape in order for them to act as catalysts for biochemical reactions…and water allows them to be in a certain shape," he says.
A few other properties make water the ideal medium for life: Water can remain a liquid over a wide range of temperatures, from zero degree Celsius to 100 degrees C—and even wider if dissolved salts and gases, such as ammonia, are added. (The range also varies with pressure.) Also, ice floats. Frozen water is less dense than its liquid form because "when you make a crystal, arranging atoms in an ordered repeating pattern, you just can't stack them very tightly," Conrad says. The difference in density between the solid and liquid states of water means that ice sheets can cover oceans, protecting life below. If ice sank, water would freeze from the bottom up and we'd live in a very different world. (Only a handful of other substances other than water become less dense when frozen. They include silicon, acetic acid and germanium, among others.)
This particular property of water may make life viable in places like Europa, Jupiter's ice-covered moon that scientists suspect holds a liquid water ocean below. Scientists suspect that subsurface liquid water may exist on Mars, and water ice has been seen gushing from beneath the surface of Saturn's moon, Enceladus. Some scientists, meanwhile, suspect that there may be liquid water beneath the surface of Saturn’s moon Titan.
Another property that shouldn't be neglected: water absorbs infrared radiation, so it can store heat and help organisms maintain temperature. Beneath Europa's icy shell, a key heat source may be the moon's rocky mantle energized by tidal forces exerted by Jupiter, which could be warming the bottom of an ocean possibly 100 kilometers deep, says Bob Pappalardo, the principal scientist at JPL for the extended Cassini mission at Saturn who is also preparing for the next robotic exploration of Europa in the mid- to late-2020s.
It is at those places of chemical disequilibrium, where water is in contact with Europa's hot rocky mantle, where life may thrive. Thermal vents at the bottom of Earth's oceans, where strange life forms congregate around "black smokers" that vent nutrient-rich chemicals, may be analogues for what's happening on the Europan ocean floor. Observations of the satellite's fractured sheath of ice and magnetometer readings from the Galileo spacecraft both suggest a salty water ocean hidden from view.
"We're pretty sure that the interior of Europa is warm and wet today," Pappalardo says. "I certainly think, when you look at those ingredients for life, that Europa rises right to the top of the places to explore."
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11 Comments
Add CommentIt's good to read some "down to earth" perspectives on the presence of "water", and I use the quotes to differentiate between what is technically water and what we think of as water and its truly amazing properties. Years ago I read very interesting essay by science writer Issac Asimov called "the thalassogens" in which he beautifully laid out the many qualities that water has in particular when at the triple point of its being a gas, liquid and solid at the same temp and pressure. Well worth looking up and reading again and helps to keep this in perspective. Additonally the presence of water suggests we wont have to use expensive rockets to send water to space, which is kinda silly on two counts. First off it would still require expensive and heavy apparatus to collect the water even if it's on the moon and secondly sending stuff to space via cold war era balistic missile technology is a legacy we should be retiring in favor of newer, cleaner and much cheaper systems to deliver bulk payloads of water and fuel and sheilding to space for a few bucks a poud using rail guns and mass drivers, while using Bert Rutan's space taxi for people and delicate apparatus. Old thinking and old ways have conspired to create a box of our own imagination...in the mean time the answers to earth's needs, energy, materials and opportunity, are just beyond our current reach. It's raining soup and we need to design a bucket that can catch it and bring it to us as we expand out into our solar system and beyond, of course.
Reply | Report Abuse | Link to thisNice to read an intelligent and thought generated blog first thing in the morning .We have water here and plenty of it. No "new" water has been created; it's the same stuff recycled over and over since the dawn of time. Improve methods for getting it, keeping it clean and making it available to everyone is feasable and needs to happen ...SOON.
Reply | Report Abuse | Link to thisNon-terrestrial water discovery excites another issue, however. Life comes from water. That our predisposition to find life "out there" is enticed by discoveries of water molecules speaks to our hopes for future discoveries and to our imaginations. Hope and imagination fuel all great discoveries and in fact, along with compassion, may be the truely great qualities of being human. That water indicates the possibility of life makes it the Grand Priz in space exploration.
I have wondered why water was so scarce in the universe and now i have my answer, we simply could not see it. if such a simple molecule, with so many readily usable atoms, could not form I would probably have questioned my faith in science.
Reply | Report Abuse | Link to thisThe Jewish Bible, written down exactly as dictated by God to Moishe (Moses), an occurrence witnessed by 3.5 million people, an infinite amount of information that could not have possibly been written by man, as can be seen by a careful, honest study with the given interpretations and explanations, including the mystical level that clarifies and illuminates the written, says clearly that God separated between the upper waters and lower waters. Thank you for verifying that there are upper waters.
Reply | Report Abuse | Link to thisOh please at least in space leave us alone!
Reply | Report Abuse | Link to thisJust a note to kall4less,, so does the christian bible and the islamic qur'an (in effect,,, all divine books of the Abrahamic Religions). Their concurrence should tell people something...
Reply | Report Abuse | Link to thisThen there is also the obvious; breaking down water provides oxygen to break and fuel to launch us back into space.
Reply | Report Abuse | Link to thisUG, ALL religions got the reality "space" wrong, as with most other things other then human sociology. Though that does not stop the re-interpretation, or re-re-re-re-interpretation of books and teachings, with passages that often are written ambiguously (often on purpose). And doing such effectively allows for just about anything, and is made even more wild with translations through different languages and with words that have more then one meaning . . .all of that effectively invalidates the entire process but tends to keep the religion alive.
Reply | Report Abuse | Link to thisSo, have fun fitting new discoveries into your religious distorted "small world", Most religious books and teachings are designed to allow some flexibility and reinterpretation in the face of real and new knowledge or they would not have survived for too long (though it is fun to watch the periodic "fight back to fundamentals" and how they conveniently gloss over subjects that are no longer viable.. )
I am going to not bother with that rather fruitless task and see the universe as CLEARLY as possible without the religious "glasses" and blinders!
There was a reason God told Moses to take off his shoes,and because of that,anything written in the bible must be taken with a grain of salt.The works of man are not perfect,and the bible being penned by men,thus it is not as well.Although there is some science in the bible it is not a science book.It is a book of history,spiritual guidance,and behavioral control that try's to teach us that we can learn from our mistakes and those made by others in the past.So while we gain in knowlage through trial and error.We must never think we have written,or know it all.
Reply | Report Abuse | Link to thisFunny, I thought this was a science site. Enough of the hijacked BS.
Reply | Report Abuse | Link to thisI think exploration of Europa would be an outstanding mission. I only hope Nasa has the balls to follow through on the requried budget over the years to pull this off.
Water is what we recognize as the foundation of life. Seeing it so abundant elsewhere inspires our imaginations and allows us to feel a much deeper connection as we can start to understand that it is not so hard for life to start. Throw in some radiation shielding and an atmosphere to stabilize the temperature and you have the foundation that you need (atmospheric composition remains up for debate as we need oxygen, but who knows what other life may need).
Of course there are "upper waters". The naivest explanation why there are blue skies and rain, I guess. On the other hand it faces a problem it usually doesn't rain from a blue sky. Seriously, the old cosmologies were based on the idea that the world came from a primordial ocean and that creation consisted in separation. Such a cosmology is not vindicated by the discovery of water molecules on the Moon.
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