Archive for the ‘Bacteria’ Category


Plants that were frozen during the “Little Ice Age” centuries ago have been observed sprouting new growth, scientists say. Samples of 400-year-old plants known as bryophytes have flourished under laboratory conditions. Researchers say this back-from-the-dead trick has implications for how ecosystems recover from the planet’s cyclic long periods of ice coverage. The findings appear in Proceedings of the National Academy of Sciences.

They come from a group from the University of Alberta, who were exploring an area around the Teardrop Glacier, high in the Canadian Arctic. The glaciers in the region have been receding at rates that have sharply accelerated since 2004, at about 3-4m per year. That is exposing land that has not seen light of day since the so-called Little Ice Age, a widespread climatic cooling that ran roughly from AD 1550 to AD 1850.

“We ended up walking along the edge of the glacier margin and we saw these huge populations coming out from underneath the glacier that seemed to have a greenish tint,” said Catherine La Farge, lead author of the study.

Bryophytes are different from the land plants that we know best, in that they do not have vascular tissue that helps pump fluids around different parts of the organism. They can survive being completely desiccated in long Arctic winters, returning to growth in warmer times, but Dr La Farge was surprised by an emergence of bryophytes that had been buried under ice for so long.

“When we looked at them in detail and brought them to the lab, I could see some of the stems actually had new growth of green lateral branches, and that said to me that these guys are regenerating in the field, and that blew my mind,” she told BBC News. “If you think of ice sheets covering the landscape, we’ve always thought that plants have to come in from refugia around the margins of an ice system, never considering land plants as coming out from underneath a glacier.”

But the retreating ice at Sverdrup Pass, where the Teardrop Glacier is located, is uncovering an array of life, including cyanobacteria and green terrestrial algae. Many of the species spotted there are entirely new to science.

“It’s a whole world of what’s coming out from underneath the glaciers that really needs to be studied,” Dr La Farge said.

“The glaciers are disappearing pretty fast – they’re going to expose all this terrestrial vegetation, and that’s going to have a big impact.”


Two studies have found that depression and the use of certain antidepressants are both associated with increased risk for Clostridium difficile infection, an increasingly common cause of diarrhea that in the worst cases can be fatal.

Researchers studied 16,781 men and women, average age 68, using hospital records and interviews to record cases of the infection, often called C. diff, and diagnoses of depression. The interviews were conducted biennially from 1991 to 2007 to gather self-reports of feelings of sadness and other emotional problems. There were 404 cases of C. difficile infection. After adjusting for other variables, the researchers found that the risk of C. diff infection among people with a history of depression or depressive symptoms was 36 to 47 percent greater than among people without depression.

A second study, involving 4,047 hospitalized patients, average age 58, found a similar association of infection with depression. In addition, it found an association of some antidepressants — Remeron, Prozac and trazodone — with C. diff infection. There was no association with other antidepressants. “We have known for a long time that depression is associated with changes in the gastrointestinal system,” said the lead author, Mary A.M. Rogers, a research assistant professor at the University of Michigan, “and this interaction between the brain and the gut deserves more study.”

Both reports appeared in the journal BMC Medicine.

Radioactive iron may be first fossil imprint of a nearby cosmic explosion.

by Alexandra Witze

Sediment in a deep-sea core may hold radioactive iron spewed by a distant supernova 2.2 million years ago and preserved in the fossilized remains of iron-loving bacteria. If confirmed, the iron traces would be the first biological signature of a specific exploding star.

Shawn Bishop, a physicist at the Technical University of Munich in Germany, reported preliminary findings on 14 April at a meeting of the American Physical Society in Denver, Colorado.

In 2004, scientists reported finding the isotope iron-60, which does not form on Earth, in a piece of sea floor from the Pacific Ocean. They calculated how long ago this radioactive isotope had arrived by using the rate at which it decays over time. The culprit, they concluded, was a supernova in the cosmic neighbourhood.

Bishop wondered if he could find signs of that explosion in the fossil record on Earth. Some natural candidates are certain species of bacteria that gather iron from their environment to create 100-nanometre-wide magnetic crystals, which the microbes use to orient themselves within Earth’s magnetic field so that they can navigate to their preferred conditions. These ‘magnetotactic’ bacteria live in sea-floor sediments.

So Bishop and his colleagues acquired parts of a sediment core from the eastern equatorial Pacific Ocean, dating to between about 1.7 million and 3.3 million years ago. They took sediment samples from strata corresponding to periods roughly 100,000 years apart, and treated them with a chemical technique that extracts iron-60 but not iron from nonbiological sources, such as soil washing off the continents. The scientists then ran the samples through a mass spectrometer to see if any iron-60 was present.

And it was. “It looks like there’s something there,” Bishop told reporters at the Denver meeting. The levels of iron-60 are minuscule, but the only place they seem to appear is in layers dated to around 2.2 million years ago. This apparent signal of iron-60, Bishop said, could be the remains of magnetite (Fe3O4) chains formed by bacteria on the sea floor as radioactive supernova debris showered on them from the atmosphere, after crossing inter-stellar space at nearly the speed of light.

No one is sure what particular star might have exploded at this time, although one paper points to suspects in the Scorpius–Centaurus stellar association, at a distance of about 130 parsecs (424 light years) from the Sun3.

“I’m really excited about this,” says Brian Thomas, an astrophysicist at Washburn University in Topeka, Kansas, who was not involved in the work. “The nice thing is that it’s directly tied to a specific event.”

“For me, philosophically, the charm is that this is sitting in the fossil record of our planet,” Bishop says. He and his team are now working on a second core, also from the Pacific, to see if it too holds the iron-60 signal.


Hollywood director James Cameron found little evidence of life when he descended nearly 11,000 metres to the deepest point in the world’s oceans last year. If only he had taken a microscope and looked just a few centimetres deeper.

Ronnie Glud at the University of Southern Denmark in Odense, and his colleagues, have discovered unusually high levels of microbial activity in the sediments at the site of Cameron’s dive – Challenger Deep at the bottom of the western Pacific’s Mariana Trench.

Glud’s team dispatched autonomous sensors and sample collectors into the trench to measure microbial activity in the top 20 centimetres of sediment on the sea bed. The pressure there is almost 1100 times greater than at the surface. Finding food, however, is an even greater challenge than surviving high pressures for anything calling the trench home.

Any nourishment must come in the form of detritus falling from the surface ocean, most of which is consumed by other organisms on the way down. Only 1 per cent of the organic matter generated at the surface reaches the sea floor’s abyssal plains, 3000 to 6000 metres below sea level. So what are the chances of organic matter making it even deeper, into the trenches that form when one tectonic plate ploughs beneath another?

Surprisingly, the odds seem high. Glud’s team compared sediment samples taken from Challenger Deep and a reference site on the nearby abyssal plain. The bacteria at Challenger Deep were around 10 times as abundant as those on the abyssal plain, with every cubic centimetre of sediment containing 10 million microbes. The deep microbes were also twice as active as their shallower kin.

These figures make sense, says Glud, because ocean trenches are particularly good at capturing sediment. They are broad as well as deep, with a steep slope down to the deepest point, so any sediment falling on their flanks quickly cascades down to the bottom in muddy avalanches. Although the sediment may contain no more than 1 per cent organic matter, so much of it ends up at Challenger Deep that the level of microbial activity shoots up.

“There is much more than meets the eye at the bottom of the sea,” says Hans Røy, at Aarhus University in Denmark. Last year, he studied seafloor sediments below the north Pacific gyre – an area that, unlike Challenger Deep, is almost devoid of nutrients. Remarkably, though, even here Røy found living microbes.

“With the exception of temperatures much above boiling, bacteria seem to cope with everything this planet can throw at them,” he says.

Journal reference: Nature Geoscience, DOI: 10.1038/ngeo1773|NSNS|2012-GLOBAL|online-news


Each year, hundreds of millions of metric tons of dust, water, and humanmade pollutants make their way into the atmosphere, often traveling between continents on jet streams. Now a new study confirms that some microbes make the trip with them, seeding the skies with billions of bacteria and other organisms—and potentially affecting the weather. What’s more, some of these high-flying organisms may actually be able to feed while traveling through the clouds, forming an active ecosystem high above the surface of the Earth.

The discovery came about when a team of scientists based at the Georgia Institute of Technology in Atlanta hitched a ride on nine NASA airplane flights aimed at studying hurricanes. Previous studies carried out at the tops of mountains hinted that researchers were likely to find microorganisms at high altitudes, but no one had ever attempted to catalog the microscopic life floating above the oceans—let alone during raging tropical storms. After all, it isn’t easy to take air samples while your plane is flying through a hurricane.

Despite the technical challenges, the researchers managed to collect thousands upon thousands of airborne microorganisms floating in the troposphere about 10 kilometers over the Caribbean, as well as the continental United States and the coast of California. Studying their genes back on Earth, the scientists counted an average of 5100 bacterial cells per cubic meter of air, they report in the Proceedings of the National Academy of Sciences. Although the researchers also captured various types of fungal cells, the bacteria were over two orders of magnitude more abundant in their samples. Well over 60% of all the microbes collected were still alive.

The researchers cataloged a total of 314 different families of bacteria in their samples. Because the type of genetic analysis they used didn’t allow them to identify precise species, it’s not clear if any of the bugs they found are pathogens. Still, the scientists offer the somewhat reassuring news that bacteria associated with human and animal feces only showed up in the air samples taken after Hurricanes Karl and Earl. In fact, these storms seemed to kick up a wide variety of microbes, especially from populated areas, that don’t normally make it to the troposphere.

This uptick in aerial microbial diversity after hurricanes supports the idea that the storms “serve as an atmospheric escalator,” plucking dirt, dust, seawater, and, now, microbes off Earth’s surface and carrying them high into the sky, says Dale Griffin, an environmental and public health microbiologist with the U.S. Geological Survey in St. Petersburg, Florida, who was not involved in the study.

Although many of the organisms borne aloft are likely occasional visitors to the upper troposphere, 17 types of bacteria turned up in every sample. Researchers like environmental microbiologist and co-author Kostas Konstantinidis suspect that these microbes may have evolved to survive for weeks in the sky, perhaps as a way to travel from place to place and spread their genes across the globe. “Not everybody makes it up there,” he says. “It’s only a few that have something unique about their cells” that allows them survive the trip.

The scientists point out that two of the 17 most common families of bacteria in the upper troposphere feed on oxalic acid, one of the most abundant chemical compounds in the sky. This observation raises the question of whether the traveling bacteria might be eating, growing, and perhaps even reproducing 10 kilometers above the surface of Earth. “That’s a big question in the field right now,” Griffin says. “Can you view [the atmosphere] as an ecosystem?”

David Smith, a microbiologist at NASA’s Kennedy Space Center in Florida, warns against jumping to such dramatic conclusions. He also observed a wide variety of microbes in the air above Oregon’s Mount Bachelor in a separate study, but he believes they must hibernate for the duration of their long, cold trips between far-flung terrestrial ecosystems. “While it’s really exciting to think about microorganisms in the atmosphere that are potentially making a living, there’s no evidence of that so far.”

Even if microbes spend their atmospheric travels in dormancy, that doesn’t mean they don’t have a job to do up there. Many microbial cells are the perfect size and texture to cause water vapor to condense or even form ice around them, meaning that they may be able to seed clouds. If these microorganisms are causing clouds to form, they could be having a substantial impact on the weather. By continuing to study the sky’s microbiome, Konstantinidis and his team hope to soon be able to incorporate its effects into atmospheric models.


Mythical King Midas was ultimately doomed because everything he touched turned to gold. Now, the reverse has been found in bacteria that owe their survival to a natural Midas touch.

Delftia acidovorans lives in sticky biofilms that form on top of gold deposits, but exposure to dissolved gold ions can kill it. That’s because although metallic gold is unreactive, the ions are toxic.

To protect itself, the bacterium has evolved a chemical that detoxifies gold ions by turning them into harmless gold nanoparticles. These accumulate safely outside the bacterial cells.

“This could have potential for gold extraction,” says Nathan Magarvey of McMaster University in Hamilton, Ontario, who led the team that uncovered the bugs’ protective trick. “You could use the bug, or the molecules they secrete.”

He says the discovery could be used to dissolve gold out of water carrying it, or to design sensors that would identify gold-rich streams and rivers.

The protective chemical is a protein dubbed delftibactin A. The bugs secrete it into the surroundings when they sense gold ions, and it chemically changes the ions into particles of gold 25 to 50 nanometres across. The particles accumulate wherever the bugs grow, creating patches of gold.

But don’t go scanning streams for golden shimmers: the nanoparticle patches do not reflect light in the same way as bigger chunks of the metal – giving them a deep purple colour.

When Magarvey deliberately snipped out the gene that makes delftibactin A, the bacteria died or struggled to survive exposure to gold chloride. Adding the protein to the petri dish rescued them.

The bacterium Magarvey investigated is one of two species that thrive on gold, both identified a decade or so ago by Frank Reith of the University of Adelaide in Australia. In 2009 Reith discovered that the other species, Cupriavidus metallidurans, survives using the slightly riskier strategy of changing gold ions into gold inside its cells.

“If delftibactin is selective for gold, it might be useful for gold recovery or as a biosensor,” says Reith. “But how much dissolved gold is out there is difficult to say.”

Journal reference: Nature Chemical Biology, DOI: 10.1038/NCHEMBIO.1179|NSNS|2012-GLOBAL|online-news

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The search continues for life in subglacial Lake Whillans, 2,600 feet below the surface of the West Antarctic Ice Sheet—but a thrilling preliminary result has detected signs of life.

At 6:20am on January 28, four people in sterile white Tyvek suits tended to a wench winding cable onto the drill platform. One person knocked frost off the cable as it emerged from the ice borehole a few feet below. The object of their attention finally rose into sight: a gray plastic vessel, as long as a baseball bat, filled with water from Lake Whillans, half a mile below.

The bottle was hurried into a 40-foot cargo container outfitted as a laboratory on skis. Some of the lake water was squirted into bottles of media in order to grow whatever microbes might inhabit the lake. Those cultures could require weeks to produce results. But one test has already produced an interesting preliminary finding. When lake water was viewed under a microscope, cells were seen: their tiny bodies glowed green in response to DNA-sensitive dye. It was the first evidence of life in an Antarctic subglacial lake.

(A Russian team has reported that two types of bacteria were found in water from subglacial Lake Vostok, but DNA sequences matched those of bacteria that are known to live inside kerosene—causing the scientists to conclude that those bacteria came from kerosene drilling fluid used to bore the hole, and not from Lake Vostok itself.)

In order to conclusively demonstrate that Lake Whillans harbors life, the researchers will need to complete more time-consuming experiments showing that the cells actually grow—since dead cells can sometimes show up under a microscope with DNA-sensitive staining. And weeks or months will pass before it is known whether these cells represent known types of microbes, or something never seen before. But a couple of things seem likely. Most of those microbes probably subsist by chewing on rocks. And despite being sealed beneath 2,600 feet of ice, they probably have a steady supply of oxygen.

The oxygen comes from water melting off the base of the ice sheet—maybe a few penny thicknesses of ice per year. “When you melt ice, you’re liberating the air bubbles [trapped in that ice],” says Mark Skidmore, a geomicrobiologist at Montana State University who is part of the Whillans drilling, or WISSARD, project. “That’s 20 percent oxygen,” he says. “It’s being supplied to the bed of the glacier.”

In one possible scenario, lake bacteria could live on commonly occurring pyrite minerals that contain iron and sulfur. The bacteria would obtain energy by using oxygen to essentially “burn” that iron and sulfur (analogous to the way that animals use oxygen to slowly burn sugars and fats). Small amounts of sulfuric acid would seep out as a byproduct; that acid would attack other minerals in the sands and sediments of the lake—leaching out sodium, potassium, calcium, and other materials that would accumulate in the water.

This process, called weathering, breaks down billions of tons of minerals across the Earth’s surface each year. Researchers working on the National Science Foundation-funded WISSARD project hope to learn whether something like this also happens under the massive ice sheets covering Antarctica and Greenland. They’ve already seen one tantalizing sign.

The half mile of glacial ice sitting atop Lake Whillans is quite pure—derived from snow that fell onto Antarctica thousands of years ago. It contains only one-hundredth the level of dissolved minerals that are seen in a clear mountain creek, or in tap water from a typical city. But a sensor lowered down the borehole this week showed that dissolved minerals were far more abundant in the lake itself. “The fact that we see high concentrations is suggestive that there’s some interesting water-rock-microbe interaction that’s going on,” says Andrew Mitchell, a microbial geochemist from Aberystwyth University in the UK who is working this month at Lake Whillans.

Microbes, in other words, might well be munching on minerals under the ice sheet. The Whillans team will take months or years to unravel this picture. They will perform experiments to see whether microbes taken from the lake metabolize iron, sulfur, or other components of minerals. And they will analyze the DNA of those microbes to see whether they’re related to rock-chewing bacteria that are already known to science.

Antarctica isn’t the only place in the solar system where water sits concealed in the dark beneath thick ice. Europa and Enceladus (moons of Jupiter and Saturn, respectively) are also thought to harbor oceans of liquid water. What is learned at Lake Whillans could shed light on how best to look for life in these other places.

Thanks to Kebmodee for bringing this to the attention of the It’s Interesting community.


A hardy bacteria common on Earth was surprisingly adaptive to Mars-like low pressure, cold and carbon dioxide-rich atmosphere, a finding that has implications in the search for extraterrestrial life.

The bacteria, known as Serratia liquefaciens, is found in human skin, hair and lungs, as well as in fish, aquatic systems, plant leaves and roots.

“It’s present in a wide range of medium-temperature ecological niches,” said microbiologist Andrew Schuerger, with the University of Florida.

Serratia liquefaciens most likely evolved at sea level, so it was surprising to find it could grow in an experiment chamber that reduced pressure down to a Mars-like 7 millibars, Schuerger said.

Sea-level atmospheric pressure on Earth is about 1,000 millibars or 1 bar.

“It was a really big surprise,” Schuerger said. “We had no reason to believe it was going to be able to grow at 7 millibars. It was just included in the study because we had cultures easily on hand and these species have been recovered from spacecraft.”

In addition to concerns that hitchhiking microbes could inadvertently contaminate Mars, the study opens the door to a wider variety of life forms with the potential to evolve indigenously.

To survive, however, the microbes would need to be shielded from the harsh ultraviolet radiation that blasts the surface of Mars, as well as have access to a source of water, organic carbon and nitrogen.

NASA’s Curiosity Mars rover is five months into a planned two-year mission to look for chemistry and environmental conditions that could have supported and preserved microbial life.

Scientists do not expect to find life at the rover’s landing site – a very dry, ancient impact basin called Gale Crater near the Martian equator. They are however hoping to learn if the planet most like Earth in the solar system has or ever had the ingredients for life by chemically analyzing rocks and soil in layers of sediment.

So far, efforts to find Earth microbes that could live in the harsh conditions of Mars have primarily focused on so-called extremophiles which are found only in extreme cold, dry or acidic environments on Earth. Two extremophiles tested along with the Serratia liquefaciens and 23 other common microbes did not survive the experiment.

A follow-up experiment on about 10,000 other microbes retrieved from boring 12 to 21 meters into the Siberian permafrost found six species that could grow in the simulated Mars chamber, located at the Space Life Sciences Laboratory adjacent to NASA’s Kennedy Space Center in Florida.

The next step is to see how the microbes fare under even more hostile conditions.


Enceladus is little bigger than a lump of rock and has appeared, until recently, as a mere pinprick of light in astronomers’ telescopes. Yet Saturn‘s tiny moon has suddenly become a major attraction for scientists. Many now believe it offers the best hope we have of discovering life on another world inside our solar system.

The idea that a moon a mere 310 miles in diameter, orbiting in deep, cold space,   1bn miles from the sun, could provide a home for alien lifeforms may seem extraordinary. Nevertheless, a growing number of researchers consider this is a real prospect and argue that Enceladus should be rated a top priority for future space missions.

This point is endorsed by astrobiologist Professor Charles Cockell of Edinburgh University. “If someone gave me several billion dollars to build whatever space probe I wanted, I would have no hesitation,” he says. “I would construct one that could fly to Saturn and collect samples from Enceladus. I would go there rather than Mars or the icy moons of Jupiter, such as Europa, despite encouraging signs that they could support life. Primitive, bacteria-like lifeforms may indeed exist on these worlds but they are probably buried deep below their surfaces and will be difficult to access. On Enceladus, if there are lifeforms, they will be easy to pick up. They will be pouring into space.”

The cause of this unexpected interest in Enceladus – first observed by William Herschel in 1789 and named after one of the children of the Earth goddess Gaia – stems from a discovery made by the robot spacecraft Cassini, which has been in orbit of Saturn for the past eight years. The $3bn probe has shown that the little moon not only has an atmosphere, but that geysers of water are erupting from its surface into space. Even more astonishing has been its most recent discovery, which has shown that these geysers contain complex organic compounds, including propane, ethane, and acetylene.

“It just about ticks every box you have when it comes to looking for life on another world,” says Nasa astrobiologist Chris McKay. “It has got liquid water, organic material and a source of heat. It is hard to think of anything more enticing short of receiving a radio signal from aliens on Enceladus telling us to come and get them.”

Cassini’s observations suggest Enceladus possesses a subterranean ocean that is kept liquid by the moon’s internal heat. “We are not sure where that energy is coming from,” McKay admits. “The source is producing around 16 gigawatts of power and looks very like the geothermal energy sources we have on Earth – like the deep vents we  see in our ocean beds and which bubble up hot gases.”

At the moon’s south pole, Enceladus’s underground ocean appears to rise close to the surface. At a few sites, cracks have developed and water is bubbling to the surface before being vented into space, along with complex organic chemicals that also appear to have built up in its sea.

Equally remarkable is the impact of this water on Saturn. The planet is famed for its complex system of rings, made of bands of small particles in orbit round the planet. There are seven main rings: A, B, C, D, E, F and G, and the giant E-ring is linked directly with Enceladus. The water the moon vents into space turns into ice crystals and these feed the planet’s E-ring. “If you turned off the geysers of Enceladus, the great E-ring of Saturn would disappear within a few years,” says McKay. “For a little moon, Enceladus has quite an impact.”

Yet the discovery of Enceladus’s strange geology was a fairly tentative affair, says Professor Michele Dougherty of Imperial College London. She was the principal investigator for Cassini’s magnetometer instrument. “Cassini had been in orbit round Saturn for more than six months when it passed relatively close to Enceladus. Our results indicated that Saturn’s magnetic field was being dragged round Enceladus in a way that suggested it had an atmosphere.”

So Dougherty and her colleagues asked the Cassini management to direct the probe to take a much closer look. This was agreed and in July 2005 Cassini moved in for a close-up study. “I didn’t sleep for two nights before that,” says Dougherty. “If Cassini found nothing we would have looked stupid and the management team might not have listened to us again.”

Her fears were groundless. Cassini swept over Enceladus at a height of 173km and showed that it did indeed possess an atmosphere, albeit a thin one consisting of water vapour, carbon dioxide, methane and nitrogen. “It was wonderful,” says Dougherty. “I just thought: wow!”

Subsequent sweeps over the moon then revealed those plumes of water. The only other body in the solar system, apart from Earth, possessing liquid water on its surface had  been revealed. Finally came the discovery of organics, and the little moon went from being merely an interesting world to one that was utterly fascinating.

“Those plumes do not represent a torrent,” cautions McKay. “This is not the Mississippi pouring into space. The output is roughly equivalent to that of the Old Faithful geyser in Yellowstone national park. On the other hand, it would be enough to create a river that you could kayak down.

“The fact that this water is being vented into space and is mixed with organic material is truly remarkable, however. It is an open invitation to go there. The place may as well have a big sign hanging over it saying: ‘Free sample: take one now’.”

Collecting that sample will not be easy, however. At a distance of 1bn miles, Saturn and its moons are a difficult target. Cassini took almost seven years to get there after its launch from Cape Canaveral in  1997.

“A mission to Enceladus would take a similar time,” says McKay. Once there, several years would be needed to make several sweeps over Enceladus to collect samples of water and organics. “Then we would need a further seven years to get those samples back to Earth.”

Such a mission would therefore involve almost 20 years of space flight – on top of the decade needed to plan it and to construct and launch the probe. “That’s 30 years in all, a large chunk of any scientist’s professional life,” says McKay.

McKay and a group of other Nasa scientists based at the Jet Propulsion Laboratory in Pasadena are undaunted, however. They are now finalising plans for an Enceladus Sample Return mission, which would involve putting a probe in orbit round Saturn. It would then use the gravity of the planet’s biggest moon, Titan, to make sweeps over Enceladus. Plume samples would then be stored in a canister that would eventually be fired back to Earth on a seven-year return journey.

Crucially, McKay and his colleagues believe such a mission could be carried out at a relatively modest cost – as part of Nasa’s Discovery programme, which funds low-budget missions to explore the solar system. Previous probes have included Lunar Prospector, which studied the moon’s geology; Stardust, which returned a sample of material scooped from a comet’s tail; and Mars Pathfinder, which deployed a tiny motorised robot vehicle on the Red Planet in 1997.

“The criteria for inclusion in the Discovery programme demand that any mission must cost less than $500m, though that does not include the price of launch,” says McKay. “We think we can adapt the technology that was developed on the Stardust mission to build an Enceladus Sample Return. If so, we can keep the cost below $500m. We are finalising plans and will announce our proposals in autumn.”

Such a mission is backed by Dougherty. “I think Enceladus is one of the best bets we now have for finding life on another world in our solar system. It is certainly worth visiting but it is not the only hope we have. The icy moons of Jupiter – such as Ganymede, Callisto and Europa – still look a very good prospect as well.”

And there is one problematic issue concerning Enceladus: time. “Conditions for life there are good at present but we do not know how long they have been in existence,” says McKay. “They might be recent or ancient. For life to have evolved, we need the latter to have been the case. At present, we have no idea about their duration, though geologists I have spoken to suggest that water and organics may have been there for a good while. The only way we will find out is to go there.”

The late entry of Enceladus in the race to find extraterrestrial life adds an intriguing new destination for astrobiologists in their hunt for aliens. Before its geysers were discovered, two main targets dominated their research: Mars and the icy moons of Jupiter. The former is the easiest to get to and has already received visits from dozens of probes. On 6 August, the $2.5bn robot rover Curiosity is set to land there and continue the hunt for life on the Red Planet. “For life to evolve you need liquid water, and although it is clear it once flowed on Mars, its continued existence there is debatable,” says Cockell. “By contrast, you can see water pouring off Enceladus along with those organics.”

Many scientists argue that water could exist deep below the Martian surface, supporting bacteria-like lifeforms. However, these reservoirs could be many metres, if not kilometres, below Mars’s surface and it could take decades to find them. Similarly, the oceans under the thick ice that covers Europa – and two other moons of Jupiter, Ganymede and Callisto – could also support life. But again, it will be extremely difficult for a robot probe to drill through the kilometres of ice that cover the oceans of these worlds.

Enceladus, by these standards, is an easy destination – but a distant one that will take a long time to reach. “No matter where we look, it appears it will take two or three decades to get answers to our questions about the existence of life on other worlds in the solar system,” says Cockell. “By that time, telescopes may have spotted signs of life on planets elsewhere in the galaxy. Our studies of extra-solar planets are getting more sophisticated, after all, and one day we may spot the presence of oxygen and water in our spectrographic studies of these distant worlds – an unambiguous indication that living entities exist there.

However, telescopic studies of extra-solar planets won’t reveal the nature of those lifeforms. Only by taking samples from planets in our solar system and returning them to laboratories on Earth, where we can study them, will we be able to reveal their exact nature and mode of replication – if they exist, of course. The little world of Enceladus could then have a lot to teach us.

The caverns of Lechuguilla Cave are some of the strangest on the planet. Its acid-carved passages extend for over 120 miles. Parts of Lechuguilla have been cut off from the surface for four to seven million years, and the life-forms there – mainly bacteria and other microbes – have charted their own evolutionary courses. But Gerry Wright from McMaster University in Canada has found that many of these cave bacteria can resist our antibiotics. They have been living underground for as long as modern humans have existed, but they can fend off our most potent weapons.

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