The largest and deepest reservoir of all known never to have seen the mariners. It has no Islands and the coast, the wind raises the waves, the water is not running sun’s glare. This dark ocean you will not find on any map of the Earth — it is more than 500 million kilometers from us, in Europe, one of the 69 known satellites of Jupiter. The data of the spacecraft Galileo, which orbited Europe 11 times from 1995 to 2003, showed that under the icy surface of this smooth moon lies a vast salty ocean. Its depth should be 100 kilometres — eight times deeper than the Pacific at the maximum depth. In this two to three times more water than all the seas and oceans of the Earth.
We know that the universe is full of watery moons and planets. But how do we know if they can support life?
Europe is not one of a kind. At least two more moons of Jupiter — Ganymede and Callisto — hide oceans under the surface. Titan and Mimas, a moon of Jupiter, probably, too. And there is no doubt that another moon of Saturn, Enceladus hides its water under its frozen crust. Amazing and irrefutable evidence of the profound depths of Enceladus appeared in 2005, when the probe “Cassini” captures the geysers spewing water and ice for hundreds of kilometers into space. Cassini even flew through the geysers in October 2015, after swimming 50 kilometers from the lunar surface to take samples of their content.
To say that the abundance of liquid water in the outer Solar system completely changed the idea of scientists — to say nothing. To revelations Cassini, Galileo and other probes General opinion was this: the moons of Jupiter and Saturn will be similar to the moons of Mars — solid, studded with craters, barren rocks, incapable of harboring life.
“Nobody expected that there will be subsurface oceans,” says Seth Shostak, an astronomer at the SETI Institute of mountain view, California. “Our understanding of habitable worlds has expanded and now we expect that can find life where there is no thought of looking for her before. We have always assumed that life needs to be on the planet. But now I know seven places in our Solar system, where there is every reason to seek life — or at least the conditions for it. And most of them satellites.”
With such an abundance of water at our side, we can confidently assert that there are innumerable planets around other stars should also be in the oceans, not to mention their satellites. Astronomers have previously identified a few “water worlds” outside our Solar system — the planets even without sushi.
“It’s amazing,” says Christopher Glein, a scientist of the mission “Cassini” from the southwest Institute in San Antonio, Texas. “It’s like inventing a new field of Oceanography”.
However, the existence of extraterrestrial oceans should not be so much a surprise. Hydrogen makes up 74% of normal matter in the Universe and oxygen is third most abundant element. Connect them — we get water, H2O. Astronomers have observed traces of water ice in craters on the moon and even on mercury is nearest to the Sun planet. Its a lot of interstellar clouds in the dusty disks of nascent planetary systems; even in the atmosphere of some giant exoplanets already found water.
“The study of exoplanets has been explosive,” says Bonnie Manke, NASA scientist working with the space telescope James Webb, who will go into space next year. “Over the last 20 years we have moved several exoplanets to thousands. And we now know that every star in the night sky has at least one planet. I think we can assume that the majority of these planets is, in a sense, and water.”
And where there’s water, maybe life. “Look for water” — an old axiom of astrobiologists. What makes water so essential? A chemical reaction that will fuel the engines of life requires a liquid for the dissolution and transport of molecules across the cell. Water is one of the best known solvents; it remains liquid at a larger range of temperatures than any other substance. It is possible that other liquids will perform the role of water in alien biochemistry — methane lakes, for example, we found on Titan. But while no exceptions to the rule “life needs water” we find.
It turns out the planet is completely covered with this crucial substance should be the perfect abode for life? Recent studies cover these expectations with a copper basin of water on such planets might be too much for the life that she appeared, or began to flourish, given the chance. “More isn’t better,” says Steven Desch, an astrophysicist at Arizona state University. Dash and his colleagues conducted a computer simulation of exotic geophysical and atmospheric environments,
So unless the planet is completely covered with this essential substance won’t be a perfect haven for life? Some recent studies throw a giant wet blanket on such expectations: many worlds can indeed be too much water for life to occur — or thrive, if it started. “More is not necessarily better,” says Steven Desch, an astrophysicist at the University of Arizona. Dash and his colleagues carried out computer modeling of geophysical exotic and atmospheric environments, which can be detected on other worlds. Their goal is to create a sort of field guide for future hunters of exoplanets. Dash calls it “the periodic table of the planet.” It will be types of worlds that are most likely to contain products of life support in the atmosphere — oxygen or methane, for example. More importantly, these gases should be present in large enough quantities to be able to detect the telescopes decades to come. “We need to put the study of such planets in priority, because they can be the best indicators of life.”
Water worlds, as it turned out, can be the best place to search for life. Team dash has created a computer model resembling the Earth in almost everything and not too cold and not too hot distance from a stable star like the Sun. Then they filled the world with water five to seven times more than the Earth to drown all of her continents. Sinking your virtual world, they have eliminated a vital process that sustains life that we, humans, are generally forgotten: the weathering of exposed rocks.
In the absence of rain or current of water erodes the rock, the sea in the world, created by a team of Desh, contained very little phosphorus, essential element for life. Sea water itself is acidic enough to dissolve the phosphorus as effective as fresh. “Phosphorus is very important,” says Tessa Fisher, a microbial ecologist at Arizona state University. “In addition to RNA and DNA, it also creates ATP, the energy carrying molecule for the known biochemistry. Terrestrial biochemistry, as far as we know, cannot function in the absence of phosphorus”.
Dash and Fischer emphasize that their model does not preclude the existence of life in the water world. The sea, the planets will probably contain a certain amount of phosphorus, but not enough to support life on a large scale and leave a noticeable imprint in the atmosphere. “There will be no atmosphere, 30% consists of oxygen, as on Earth,” says Fisher. “Perhaps a planet completely covered by ocean, is inhabited. Just life there will be so fragmented that we won’t even be able to detect from the Earth.”
Probably, there are worlds with the same amount of water that life would be impossible. According to scientists, the planet is the size of the Earth with 10% of its weight in water will be absolutely lifeless. Such a planet would have the equivalent of 400 of the earth’s oceans; the enormous pressure at the bottom of the sea would create a dense exotic forms of ice known as ice-six or ice-seven. “Water species do not interact, nothing would have life has not turned out,” says Dash.
And as strange as these conditions may seem, these worlds could be more common than the solid planets by the Land type. Water and stone, perhaps, equally common in planetary systems throughout the cosmos. In our own Solar system comets, the moon and some of the frozen inhabitants of the Kuiper belt is believed to contain the same amount of ice and stone. “The outer planets 50% of ice,” says Dash. “It’s okay. Crazy just how much dry Land.”
From our point of view, the Earth seems to be the quintessence of the world ocean — “pale blue dot” covered seas. But all these oceans spread a thin film on the surface of the planet. By mass the Earth is only 0,025% of the water. With existing technologies, astronomers are unable to say whether planets like the Earth in General any water. Astronomers use two basic techniques to determine the composition of exoplanets. First, they estimate the size of the planet, observing how much light it blocks, passing in front of its star. Then they measure the vibrations of a star that causes a planet in its orbit, which gives us the mass of the planet. The division of the mass of the planet to its volume gives the density, and the density allows astronomers estimate approximately the percentage of gas, solids and water on the planet.
“Think about how thin our ocean. It does not alter the radius of the Earth.” Now astronomers say that exoplanets have oceans, only if water will account for about 10% of its weight. And this is equal to 400 earth’s oceans, huge amounts of water, breaking everything alive. So the only water worlds, which we can detect using existing technologies, will be uninhabitable. “This is the situation at the moment,” says Dash. “We have the ability to find water and even see when the water is 10% of the mass of the planet, but it’s too much water”.
Seven of these worlds revolve in orbit Trappist-1, star 49 light years from us, is named in honor of Belgian beer. They are all the size of the Earth, and three are within the potentially habitable zone of the star, at a distance, where the possible existence of water in liquid state. Now this is the most that neither is of concern to us “potential of land”, but they may be too wet or covered with ice that they were nesting life.
Attempt to determine the composition of distant planets across multiple pixels of light, trapped in the telescope, at least will not be accurate. Given these limitations, Dash and his colleagues appreciated that the outer planets Trappist-1 composed of 50% ice; the inner planets consist of 10% of ice and liquid water. “This is more than enough to cover the continents,” says Dash. “You’ll get hundreds or even kilometers squeezed the ice at the bottom of the oceans. This is a dead planet”.
What you need to identify a “living” planet, with the earth mixture of continents and seas, not too wet, not too dry? Given the range of possible worlds, such as our should be plenty. But how to find them? Space telescope James Webb will be king astronomy as soon as will begin its 10 year mission in 2020; it will be able to analyze the atmospheres of giant exoplanets of Neptune-type and maybe even find a few “supertall” — planet 2-10 times more Land mass. However, it will be too shortsighted to see the atmospheres of planets, not to mention the oceans.
“It is hard to look at something so small — about the size of Earth passing in front of a star — and to see the faint glitter of the atmosphere”, says Mance. “There are plans for future telescopes that will be able to do it, and I think I even see it in my lifetime. But Webb will not be able to confirm the presence of water on planet earth-like”.
Telescopes are able to visualize the oceans and the land masses of the other world, probably separated from us for a couple of decades. And even then the resolution will likely be limited to a pixel or two for the entire planet. That might look like one of the most momentous discoveries in the history of science — our first direct look at a world like our own: the color of one pixel is periodically changed from blue to brown, like in the pirouettes, alternately showing land and sea our eyes.
Until that day comes, we can find signs of existence of life in some ecoocean much closer to home. And closest to us such an ocean on Enceladus, plus he has all the conditions necessary for life. When the probe “Cassini”, moving at the speed of almost 30 thousand kilometers per hour, dived through the geyser “Enceladus” in October 2015, registered the hydrogen, carbon dioxide and methane, and therefore, on this satellite is present deep-sea hydrothermal activity on Earth. “We literally tasted the ocean of Enceladus, flying through the plume of a geyser,” says Glen.
The presence of hydrogen, in particular, was a sign that a chemical reaction between the hot rocks and salt water at the bottom of the sea of Enceladus break water into hydrogen and oxygen. Body the size of Enceladus should not normally have appreciable hydrogen content, because this element is very lightweight and small body were to fly into space a long time ago. Therefore, the hydrogen of Enceladus should somehow constantly updated, most likely in the course of reactions of water and hot rocks. Once we find hydrogen, we can conclude that the chemical energy present and a lot of it, and it is the same energy that the organisms in the depths of the Land use for accommodation and food.
The methanogens, a type of ancient bacteria found around hydrothermal vents on Earth — combine the hydrogen with carbon dioxide, and in the process of this reaction releases energy and methane as a byproduct. Simple organisms like these were first inhabited the Earth’s oceans. Even now, after billions of years after its introduction, the methanogens live independently of sunlight and take their place in a strange food chain that sustains the ecosystem of tube worms and giant clams.
Can any form of life more complex than bacteria, to occur on Enceladus, Europe or carefree in the depths of some other lunar seas? “In these subsurface oceans may be life, but sources of energy to sustain life is much more complex organisms, which need more food may not be available,” says Shostak. “We cannot say that this could not happen — companions were there 4.5 billion years old, so multicellular things there may be, but any tuna is unlikely.”
The only way to answer this question is to visit these worlds. NASA has approved the mission, Europa Clipper, which will begin in 2024 and will reach Jupiter in 2030. The spacecraft will travel around Europe 45 times, come to her icy surface to 30 kilometers. Future missions that will actually sit on Europe, Enceladus or Titan, will have to find a complex amino acids and other biomolecules produced by living beings.
Having only one example — our own world — it is impossible to say whether the lives of quite ordinary or incredibly cosmically rare. “Usually I think that because the fossil or chemical evidence of life go as far back in time, life appeared rather quickly,” says Glen. “And people think that if you’re quick, so easy”.
Easy, hard or somewhere in between — doesn’t matter. Now we know one thing: if life needs water, water in bulk in the Universe. This part of the equation to search for life have already been solved finally and irrevocably.
How much water is needed for life elsewhere in the Solar system?
Ilya Hel