‘Drumbeat is getting louder’ for mission to Europa after water geyser hints at life under oceans of ice
NASAJupiter's
moon Europa is one of the most interesting places in the solar system
because it's covered with ice and is one of the key locations where life
could exist.
Water and organic chemicals make Jupiter’s tiny moon the most exciting destination in the solar system, says Michael Hanlon.
Where there is water, there might be life. That is the mantra that has guided NASA’s astrobiology programme ever since it became respectable to talk about little green men, or rather microbes, back in the Nineties. If we want to find out whether we are alone, we need to find somewhere with an ocean.
Water is a perfect solvent (just about everything, even gold, dissolves in water to some extent), allowing the complex suite of biochemical reactions that drive living processes. Other liquids have been proposed as the basis of life, but most biologists believe that water-plus-carbon is the most likely scenario for life outside Earth.
The trouble is, liquid water is a rare commodity in the Solar System. Frozen water is everywhere. Comets are mostly made of water ice. Mars is covered with the stuff. The outer planets and their moons are rich in water. But large quantities of the liquid stuff are rare.
Which is why scientists are so excited about Europa, the second of Jupiter’s large Galilean moons, which has just become the new hot destination in the solar system.
New images from the Hubble space telescope, released at a conference in the U.S. last month, showed a cloud of water vapour — in effect a huge geyser — erupting from Europa’s south pole. And new analysis of old data showed that the Europan surface is rich in organic compounds. According to Kevin Hand, a scientist at NASA’s Jet Propulsion Laboratories in Pasadena, the “drumbeat is getting louder” for a mission to Europa.
So why is Europa so exciting and why might it be home to life? Europa
is about the same size as our moon. Before the Voyager probes arrived
at Jupiter in the Eighties, it was thought that it would look like our
moon as well.
But it didn’t. Instead the images showed a place that looked like a huge white billiard ball — gleaming, smooth and almost no craters at all. Analysis showed that the surface was made of almost pure water ice and this fact, plus the lack of craters, started decades of feverish speculation.
Craters are used by astronomers as a dating tool. Everything big in the Solar System gets hit from time to time. The number of craters we see is a good marker of how old the terrain we are looking at is.
There are hardly any large, obvious craters on Earth’s surface, not because we don’t get hit, but because Earth’s surface is, in geological terms, young.
Earth itself is ancient, but its surface is constantly being modelled by plate tectonics and erosion. The big object which hit the Mexican coast 65 million years ago left a crater the size of Wales, but within a few tens of thousands of years it had been filled in with mud and clay from the sea, its edges eroded. Today the Chicxulub crater is invisible from the surface.
The Moon’s surface, on the other hand, is ancient. Nothing much has happened there for four billion years, so the ancient impact craters dating from the Moon’s youth are still there.
Mars has fewer craters than the Moon but far more than the Earth,
suggesting that its surface lies between the two extremes in terms of
age. Venus has a “young” surface, a hint that extensive volcanism may be
constantly or episodically remodelling the crust.
But Europa’s surface looks like it was formed last week. Hal Levison, a scientist in the Southwestern Research Institute in Texas, has calculated that Europa should get hit by something big every million years or so. We see only a dozen craters on the surface, indicating that its surface is, on average, only 12 million years old, and in places no craters at all, meaning much younger again. How could this be, in a place with no air and where it is so cold (-160C) that liquid water is an impossibility?
Scientists eagerly awaited the arrival of the NASA Galileo space probe at the Jovian system. The pictures sent back in June 1996 astonished the scientists. Over the next couple of years a landscape of tumbled ice blocks, “icebergs” apparently frozen into the sea, grooves and enormous rifts poured into NASA’s computers. Europa was an active world, whose frozen surface covered a huge secret.
But how are these oceans possible? To melt ice that far from the sun, you need a source of heat, and on Europa there are two. One is volcanoes — Europa’s neighbour, another (ice-free) moon called Io, is the most volcanically active object in the solar system. And another is tidal heating. Europa is kneaded like putty by the gravitational forces of Jupiter and the other moons. This squeezing generates heat — maybe enough to melt the ice under the surface crust.
Now scientists think that Europa is a ball of rock overlain by a water ocean possibly a hundred miles deep, in turn covered by an active thin ice crust which periodically breaks up, new ice constantly forming as water gets close to the surface, much like the pack ice at Earth’s poles. This would explain the lack of craters. The question is, how thin is the crust?
The “geysers” spotted by Hubble indicate that in places the Europan
ice may give way to open water. In 1998, one Galileo photo showed a
tantalising glimpse of what may be a “puddle” — a completely smooth area
of very thin ice. If the ice is tens of miles thick then the Europan
ocean will probably be forever hidden to us. But if there are places
where it is only a few feet or even inches to the water then a lander
would be able to penetrate the crust and explore the depths below.
In his novel 2010: Odyssey 2, a follow up to 2001: A Space Odyssey. Arthur C Clarke speculated that Europa’s oceans (technically one big ocean) could be home to life. If the ice is thin then enough sunlight could leak into the ocean’s upper few feet for photosynthesis to be possible. But a more promising source of energy would be undersea volcanoes, which could spew nutrients into the sea and act as oases around which strange lifeforms could thrive. On Earth, this happens around deep-sea hydrothermal vents, where giant worms and strange yellow organisms inhabit a biosphere completely detached from the solar?driven one on the surface.
Clarke speculated that Europa’s oceans could be home to large animals. Most scientists think this unlikely; there may not be enough energy available for anything more complex than microbes. But we don’t know; many scientists say we should send a follow-up mission to Europa to find out.
Ideally we would send a nuclear-powered lander equipped with a drill and a small robot submarine. There isn’t the money for that right now, so the best hope lies with the “Europa Clipper,” a NASA proposal to send a $2 billion probe to fly through any Europan geysers, analyse the water, and take detailed pictures of its surface. New Scientist magazine reported this month on a plan to send a small armada of tiny “CubeSats”, perhaps privately funded, that could do a “quick and dirty” survey of Europa for a fraction of the cost of a big Nasa mission.
In 2010, humanity was instructed by Clarke’s imagined god-like aliens to keep away from Europa: “attempt no landings there.” In the real world the problem is not sinister monoliths but the realities of NASA budget cuts. If the privateers get there first, and find even hints of life, then this still obscure little cue-ball world will become the most prized real estate in the solar system.
Where there is water, there might be life. That is the mantra that has guided NASA’s astrobiology programme ever since it became respectable to talk about little green men, or rather microbes, back in the Nineties. If we want to find out whether we are alone, we need to find somewhere with an ocean.
Water is a perfect solvent (just about everything, even gold, dissolves in water to some extent), allowing the complex suite of biochemical reactions that drive living processes. Other liquids have been proposed as the basis of life, but most biologists believe that water-plus-carbon is the most likely scenario for life outside Earth.
The trouble is, liquid water is a rare commodity in the Solar System. Frozen water is everywhere. Comets are mostly made of water ice. Mars is covered with the stuff. The outer planets and their moons are rich in water. But large quantities of the liquid stuff are rare.
Which is why scientists are so excited about Europa, the second of Jupiter’s large Galilean moons, which has just become the new hot destination in the solar system.
New images from the Hubble space telescope, released at a conference in the U.S. last month, showed a cloud of water vapour — in effect a huge geyser — erupting from Europa’s south pole. And new analysis of old data showed that the Europan surface is rich in organic compounds. According to Kevin Hand, a scientist at NASA’s Jet Propulsion Laboratories in Pasadena, the “drumbeat is getting louder” for a mission to Europa.
AFP/NASA/FileA body of water as big as North America's Great Lakes could lie beneath Europa, a shining enigmatic moon of Jupiter
But it didn’t. Instead the images showed a place that looked like a huge white billiard ball — gleaming, smooth and almost no craters at all. Analysis showed that the surface was made of almost pure water ice and this fact, plus the lack of craters, started decades of feverish speculation.
Craters are used by astronomers as a dating tool. Everything big in the Solar System gets hit from time to time. The number of craters we see is a good marker of how old the terrain we are looking at is.
There are hardly any large, obvious craters on Earth’s surface, not because we don’t get hit, but because Earth’s surface is, in geological terms, young.
Earth itself is ancient, but its surface is constantly being modelled by plate tectonics and erosion. The big object which hit the Mexican coast 65 million years ago left a crater the size of Wales, but within a few tens of thousands of years it had been filled in with mud and clay from the sea, its edges eroded. Today the Chicxulub crater is invisible from the surface.
The Moon’s surface, on the other hand, is ancient. Nothing much has happened there for four billion years, so the ancient impact craters dating from the Moon’s youth are still there.
NASA/JPL-CaltechBased
on new evidence from Jupiter's moon Europa, astronomers hypothesize
that chloride salts bubble up from the icy moon's global liquid ocean
and reach the frozen surface where they are bombarded with sulfur from
volcanoes on Jupiter's innermost large moon Io. The new findings propose
answers to questions that have been debated since the days of NASA's
Voyager and Galileo missions. This illustration of Europa (foreground),
Jupiter (right) and Io (middle) is an artist's concept
But Europa’s surface looks like it was formed last week. Hal Levison, a scientist in the Southwestern Research Institute in Texas, has calculated that Europa should get hit by something big every million years or so. We see only a dozen craters on the surface, indicating that its surface is, on average, only 12 million years old, and in places no craters at all, meaning much younger again. How could this be, in a place with no air and where it is so cold (-160C) that liquid water is an impossibility?
Scientists eagerly awaited the arrival of the NASA Galileo space probe at the Jovian system. The pictures sent back in June 1996 astonished the scientists. Over the next couple of years a landscape of tumbled ice blocks, “icebergs” apparently frozen into the sea, grooves and enormous rifts poured into NASA’s computers. Europa was an active world, whose frozen surface covered a huge secret.
But how are these oceans possible? To melt ice that far from the sun, you need a source of heat, and on Europa there are two. One is volcanoes — Europa’s neighbour, another (ice-free) moon called Io, is the most volcanically active object in the solar system. And another is tidal heating. Europa is kneaded like putty by the gravitational forces of Jupiter and the other moons. This squeezing generates heat — maybe enough to melt the ice under the surface crust.
Now scientists think that Europa is a ball of rock overlain by a water ocean possibly a hundred miles deep, in turn covered by an active thin ice crust which periodically breaks up, new ice constantly forming as water gets close to the surface, much like the pack ice at Earth’s poles. This would explain the lack of craters. The question is, how thin is the crust?
NASA/JPL-Caltech/University of ArizonaThis
view of Jupiter’s moon Europa features several regional-resolution
mosaics overlaid on a lower resolution global view for context. The
regional views were obtained during several different flybys of the moon
by NASA's Galileo mission, and they stretch from high northern to high
southern latitudes
In his novel 2010: Odyssey 2, a follow up to 2001: A Space Odyssey. Arthur C Clarke speculated that Europa’s oceans (technically one big ocean) could be home to life. If the ice is thin then enough sunlight could leak into the ocean’s upper few feet for photosynthesis to be possible. But a more promising source of energy would be undersea volcanoes, which could spew nutrients into the sea and act as oases around which strange lifeforms could thrive. On Earth, this happens around deep-sea hydrothermal vents, where giant worms and strange yellow organisms inhabit a biosphere completely detached from the solar?driven one on the surface.
Clarke speculated that Europa’s oceans could be home to large animals. Most scientists think this unlikely; there may not be enough energy available for anything more complex than microbes. But we don’t know; many scientists say we should send a follow-up mission to Europa to find out.
Ideally we would send a nuclear-powered lander equipped with a drill and a small robot submarine. There isn’t the money for that right now, so the best hope lies with the “Europa Clipper,” a NASA proposal to send a $2 billion probe to fly through any Europan geysers, analyse the water, and take detailed pictures of its surface. New Scientist magazine reported this month on a plan to send a small armada of tiny “CubeSats”, perhaps privately funded, that could do a “quick and dirty” survey of Europa for a fraction of the cost of a big Nasa mission.
In 2010, humanity was instructed by Clarke’s imagined god-like aliens to keep away from Europa: “attempt no landings there.” In the real world the problem is not sinister monoliths but the realities of NASA budget cuts. If the privateers get there first, and find even hints of life, then this still obscure little cue-ball world will become the most prized real estate in the solar system.
Labels: Astronomy, Exploration, Nature, Science, Space
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