- Jan 17View SourceInteresting post on The Daily Galaxy blog. Life may be possible beneath the surface of a Earthlike planet that could be as far as a billion miles from its sun.Chris
Sent: 1/17/2014 6:28:50 P.M. Eastern Standard Time
Subj: The Daily Galaxy: News from Planet Earth & Beyond
Posted: 16 Jan 2014 08:01 PM PST
Earth-sized planets can support life at least ten times farther away from stars than previously thought, according to researchers at the University of Aberdeen and the University of St Andrews. Many planets previously considered uninhabitable may actually be able to support life beneath the surface. The team challenges the traditional “habitable zone” or “Goldilocks zone” — the area of space around a star that can support life — by taking into consideration life living deep below the ground.The traditional habitable zone is based on the premise that a planet needs to be not too close to its sun but also not too far away for liquid water to persist, rather than boiling or freezing, on the surface, said researcher Sean McMahon. “But that theory fails to take into account life that can exist beneath a planet’s surface. As you get deeper below a planet’s surface, the temperature increases, and once you get down to a temperature where liquid water can exist — life can exist there too.”
The team created a computer model that estimates the temperature below the surface of a planet of a given size, at a given distance from its star. “The deepest known life on Earth is 5.3 km below the surface, but there may well be life even 10 km deep in places on Earth that haven’t yet been drilled. Using our computer model we discovered that the habitable zone for an Earth-like planet orbiting a sun-like star is about three times bigger if we include the top five kilometers below the planet surface.
“The model shows that liquid water, and as such life, could survive 5km below the Earth’s surface even if the Earth was three times further away from the sun than it is just now. If we go deeper, and consider the top 10 km below the Earth’s surface, then the habitable zone for an Earth-like planet is 14 times wider.”
The current habitable zone for our solar system extends out as far as Mars, but this re-drawn habitable zone would see the zone extend out further than Jupiter and Saturn. The findings also suggest that many of the so-called “rogue” planets drifting around in complete darkness could actually be habitable.
“Rocky planets a few times larger than the Earth could support liquid water at about 5 km below the surface even in interstellar space, and even if they have no atmosphere, because the larger the planet, the more heat they generate internally.
“It has been suggested that the planet Gliese 581 d, which is 20 light years away from Earth in the constellation Libra, may be too cold for liquid water at the surface. However, our model suggests that it is very likely to be able to support liquid water less than 2 km below the surface, assuming it is Earth-like.”
“The surfaces of rocky planets and moons that we know of are nothing like Earth. They’re typically cold and barren with no atmosphere or a very thin or even corrosive atmosphere. Going below the surface protects you from a whole host of unpleasant conditions on the surface. So the subsurface habitable zone may turn out to be very important. Earth might even be unusual in having life on the surface.”
NASA’s Kepler team recently reported in Astrophysical Journal on four years of ground-based follow-up observations of the masses, sizes, and orbits of 49 planets orbiting 22 Kepler stars. The study confirmed that the numerous Kepler discoveries are indeed planets and yield mass measurements of these enigmatic worlds that vary between Earth and Neptune in size.
“Kepler’s primary objective is to determine the prevalence of planets of varying sizes and orbits. Of particular interest to the search for life is the prevalence of Earth-sized planets in the habitable zone,” said Natalie Batalha, Kepler mission scientist at NASA’s Ames Research Center in Moffett Field, Calif.
“But the question in the back of our minds is: are all planets the size of Earth rocky? Might some be scaled-down versions of icy Neptunes or steamy water worlds? What fraction are recognizable as kin of our rocky, terrestrial globe?”
Dynamical mass measurements made by Kepler provided a hint: a large fraction of planets smaller than 1.5 times the radius of Earth may be comprised of the silicates, iron, nickel and magnesium that are found in the terrestrial planets here in the solar system, they found. Armed with this type of information, scientists will be able to turn the fraction of stars harboring Earth-sizes planets into the fraction of stars harboring bona-fide rocky planets. And that’s a step closer to finding a habitable environment beyond the solar system — perhaps underground.
Source: Sean McMahon, Jack O’Malley-James, John Parnell, Circumstellar habitable zones for deep terrestrial biospheres, Planetary and Space Science, 2013, DOI: 10.1016/j.pss.2013.07.002
Image creditL http://exep.jpl.nasa.gov/TPF/tpf_earths.cfm
Posted: 17 Jan 2014 07:58 AM PST
"We have shown the first time, that in particular photosynthesis is possible in micro-niches on the surface of Mars," says Jean-Pierre de Vera, a scientist at the German Aerospace Center's Institute of Planetary Research in Berlin, Germany. On Earth, Antarctic lichen has shown itself capable of going beyond survival and adapting to life in simulated Martian conditions.The mere feat of surviving temperatures as low as -51 degrees C and enduring a radiation bombardment during a 34-day experiment might seem like an accomplishment by itself. But the lichen, a symbiotic mass of fungi and algae, also proved it could adapt physiologically to living a normal life in such harsh Martian conditions — as long as the lichen lived under "protected" conditions shielded from much of the radiation within "micro-niches" such as cracks in the Martian soil or rocks.
"There were no studies on adaptation to Martian conditions before," said de Vera"Adaptation is very important to be investigated, because it tells you more about the interactions of life in relation to its environment."
Previous Mars simulation experiments focused on simply measuring the survival of organisms at the end of a given time period. By contrast, de Vera and his group of German and U.S. colleagues measured the lichen's activities throughout the experiment that was detailed in the Sept. issue of the journal Planetary and Space Science. They wanted to see whether the lichen had continued its normal activities rather than simply clinging to life in a dormant state.
Two groups of lichen samples were placed inside a Mars simulation chamber about the size of a big pressure cooker, which itself sat within a fridge about the size of an armoire. That allowed researchers to simulate almost everything about Martian conditions such as atmospheric chemistry, pressure, temperatures, humidity and solar radiation — the lone exceptions being Martian gravity and the added contribution of galactic radiation.
Institute of Planetary Research One of the lichen samples in the Mars chamber was exposed to the full brunt of radiation expected on the Martian surface, while the second set of samples received a radiation dose almost 24 times lower to simulate life in the "protected" condition. A third group of lichen samples sat outside the chamber as a control.
Both lichen sample groups survived their month-long period under Martian conditions. But the heavier dose of radiation from a Xenon lamp simulating the surface radiation conditions kept the unprotected sample group from doing much beyond clinging to survival.
Only the "protected" lichen carried on normal activities such as using photosynthesis to turn sunlight into chemical energy for itself. The protected lichen recovered quickly after an initial "shock" period by adapting well enough to steadily ramp up its photosynthetic activities all the way until the end of the experiment.
"We have shown the first time, that in particular photosynthesis is possible in micro-niches on the surface of Mars," de Vera explained.
The lichen chosen for the experiment, called P. chlorophanum, has proven itself a survival champion even before the Mars simulation. Researchers removed lichen samples for testing from its home atop the rocky Black Ridge in Antarctica's North Victoria Land — a frozen, dry landscape not unlike that of many places on Mars.
The latest Mars simulation experiment did not try to simulate the Martian dust storms that can blanket the entire planet for a month. But de Vera points out that lichen can survive in a resting state for thousands of years on Earth while covered with dust, snow or ice.
Lichen don't exist alone as possible Earth survivors on Mars. Other studies conducted by de Vera have suggested that methane-producing bacteria, known as methanogens, could also manage a Martian existence.
"There are important indices that Earth life can survive, to be metabolically active and adapt physiologically to live on Mars during the time periods which have been investigated," de Vera said.
The experiment's results have huge implications for ongoing robotic missions searching for evidence of life on Mars. First, they confirm that such missions would do well to focus on searching for possible Martian life within the "micro-niche" environments beneath the soil or within rocks protected from surface radiation. Second, they lend hope to the idea that Martian life — if at all similar to Earth life — could have indeed survived up until today.
The lichen's remarkable adaptation to Martian conditions suggests a third, equally important lesson — it justifies the ongoing caution of NASA and other space agencies in ensuring that Earth organisms don't accidentally hitchhike a ride to Mars. Such planetary protection measures seem likely to continue until the possible day that humanity decides to colonize Mars and perhaps change the planet's landscape in the process.
Because the surface of Mars today is bone-dry and frozen all year round, it’s difficult to find any place on Earth onside a lab simulation that is truly Mars-like. But two locations, Antarctica’s Upper Dry Valleys and the hyper-arid core of Chile’s Atacama Desert (below), come close. They have become prime destinations for scientists who want to understand the extreme limits of life on Earth and the prospects for life on Mars.
Jocelyne DiRuggiero, an associate professor of biology at Johns Hopkins University in Baltimore, Maryland, studies samples from both locations. She’s interested in the similarities and the differences between the microbial communities that live in these two extreme desert regions. In both places, very little liquid water is present. In the core of the Atacama, years can go by between one rainfall and the next, but it is warm, so when there is precipitation, a significant amount of liquid water is available for a very short time.
In University Valley, one of Antarctica’s Upper Dry Valleys, the availability of liquid water is limited in a different way. University Valley receives more regular precipitation than the Atacama, but it’s so cold there that any precipitation falls in the form of snow and remains frozen.
Antarctica's Dry Valley is an ideal place for scientists to study how the Earth's plumbing was formed; its current landscape was eroded in to existence millions of years ago, and has undergone very little subsequent erosion since. Researchers have labeled the Dry Valleys region a “relic landscape” as it is the only known location on Earth which is the same now as it was millions of years ago.
Johns Hopkins University geologist Bruce Marsh found the Dry Valleys in 1993, what he calls a walk-in “museum” and “the one place on earth where the plumbing system is exposed in this way. You can stand on shelves of solidified lava that were deposited by magmatic activity 180 million years ago,” he said. “It’s awe inspiring.”
“What we do in those environments is try to understand who is there, what those organisms might be doing, how they are distributed,” says DiRuggiero, and whether the organisms are “really active metabolically,” or if instead they’re “just sitting there, because they’ve been brought by the wind.”
DiRuggiero’s primary tool is DNA sequencing. Working with soil samples that weigh one- to two-tenths of a gram each (about a teaspoonful), she extracts the DNA from any microbes present in each sample. She then sends the DNA off to a lab for sequencing.
Sample preparation is a difficult process because there aren’t many microbes in her samples. Each gram of soil contains perhaps one hundred to one thousand, an extremely low number. The same size sample of ordinary soil typically contains ten million to a billion organisms.
Because the microbial populations she’s working with are so small, contamination is a serious problem. She has to be careful not to let skin cells or hair fall into her samples. Sneezing or coughing on them could pollute them. So DiRuggiero does her work under a special hood that prevents contact with outside air. And even then she has problems, because some of the silica filters she uses to extract DNA from her samples arrive from the manufacturer with microbial cells clinging to them.
Although she has had more time to work with samples from the Atacama, DiRuggiero says the University Valley samples are particularly interesting. Because University Valley is both near the South Pole and more than a mile above sea level, the ground there stays frozen even in summer. There are few places in the world where this is true. “It’s about 40 degrees Celsius colder than the Atacama soil,” she says. That’s about 70 degrees Fahrenheit colder.
That temperature difference results in a significant difference in habitability. There are more microbes in University Valley soil than in Atacama soil.
“Right now the only parameter. . .we have measured that differentiates the populations, Antarctica and the Atacama, is the temperature,” DiRuggiero says. In both locations, “the soils are very dry, the soils are very low in organics, they contain a fair amount of salt. The big difference is the temperature. We don’t really know what it means yet.”
It may seem odd that microbes are happier in sub-freezing conditions than in a warm desert. “This is counter to human experience but makes sense for microbes,” Chris McKay, a planetary scientist at NASA Ames Research Center in Moffett Field, California, wrote in an email. “Cold allows them to sleep, which is a good survival mechanism,” he explained, adding that “this result bodes well for life in the cold deserts of Mars.” McKay heads the NASA-funded IceBite team, which is testing a prototype coring drill for possible use on a future Mars mission. The IceBite team obtained the University Valley samples that DiRuggiero studies.
So far DiRuggiero has been working with University Valley samples collected during the IceBite team’s first season in the field, in 2009. She’s looking forward to getting her hands on more-extensive samples collected at the end of 2010, samples that are still making their way back from Antarctica.
Beneath the dry soil layer in University Valley is “what we call ice-cemented ground, which is basically frozen mud. And that mud has been frozen for thousands and thousands of years,” says DiRuggiero. “So the question is, Is there any water available for the micro-organisms, and do we see a difference in the microbial community between the soil above and this ice-cemented ground right underneath?”
There is some evidence, based on climate data collected last year by the IceBite team, that at the interface between the dry soil and the frozen mud, “there might be some melting in the summer,” says DiRuggiero. “There might be water available at least part of the time” and microbes might be “actively growing and metabolizing at least during a small portion of the year.”
“Melting,” in this case, doesn’t mean the soil gets soggy or muddy, or that the temperature gets above freezing. Rather, it means that thin layers of liquid water can form between the sand grains that make up the soil and the ice below it. But that’s plenty of water for microbes. They’re small. They don’t need a lot of water.
“At temperatures above -20ºC (-4ºF) there is a layer of unfrozen water between the sand grains and the ice. These layers can support microbial life at least [down] to -15ºC (5ºF),” McKay explained.
“On Mars today the temperatures of the ground ice are much too cold for this effect to be useful,” he wrote. But Mars wobbles. At present Mars is tilted on its axis at about the same angle as Earth’s.
Five million years ago, however, Mars leaned over at an angle of about 45º, and for nearly half of each martian year (equivalent to about one Earth year), the polar regions received constant sunlight. Back then “the ground ice at the polar regions,” like the site where NASA’s Phoenix spacecraft landed in 2008, “would have been much warmer. We think it would have been in the range of -15ºC to -20ºC. So liquid water layers” in the past were “a possibility.”
The question then is this: If life ever took hold on Mars, back when the planet was warmer and wetter, did a few hardy microbes evolve a survival strategy that let them go into a deep sleep, and then every 10 or 20 million years, when the ground warmed up to -20ºC or so, wake up and put on a little growth spurt?
The answer will have to wait until a follow-up mission to the martian polar regions can dig deeper than Phoenix did. It is just such deep polar drilling that McKay’s IceBite project is working to make possible.
The Daily Galaxy via NASA/Astrobio.net
Image credits: NASA/JPL and http://www.atacamaphoto.com/