Meteorites that crashed onto Earth billions of years ago may have provided the phosphorous essential to the biological systems of terrestrial life.
The meteorites are believed to have contained a phosphorus-bearing mineral called schreibersite, and scientists have recently developed a synthetic version that reacts chemically with organic molecules, showing its potential as a nutrient for life.
Phosphorus is one of life’s most vital components, but it often goes unheralded. It helps form the backbone of the long chains of nucleotides that create RNA and DNA; it is part of the phospholipids in cell membranes; and is a building block of the coenzyme used as an energy carrier in cells, adenosine triphosphate (ATP).
Yet the majority of phosphorus on Earth is found in the form of inert phosphates that are insoluble in water and are generally unable to react with organic molecules. This appears at odds with phosphorus’ ubiquity in biochemistry, so how did phosphorus end up being critical to life?
In 2004, Matthew Pasek, an astrobiologist and geochemist from the University of South Florida, developed the idea that schreibersite [(Fe, Ni)3P], which is found in a range of meteorites from chondrites to stony-iron pallasites, could be the original source of life’s phosphorus. Because the phosphorus within schreibersite is a phosphide, which is a compound containing a phosphorus ion bonded to a metal, it behaves in a more reactive fashion than the phosphate typically found on Earth.
Finding naturally formed schreibersite to use in laboratory experiments can be time-consuming when harvesting from newly fallen meteorites and expensive when buying from private collectors. Instead, it has become easier to produce schreibersite synthetically for use in the laboratory.
Natural schreibersite is an alloy of iron, phosphorous and nickel, but the common form of synthetic schreibersite that has typically been used in experiments is made of just iron and phosphorus, and is easily obtainable as a natural byproduct of iron manufacturing. Previous experiments have indicated it reacts with organics to form chemical bonds with oxygen, the first step toward integrating phosphorous into biological systems.
However, since natural schreibersite also incorporates nickel, some scientific criticism has pointed out that the nickel could potentially alter the chemistry of the mineral, rendering it non-reactive despite the presence of phosphides. If this were the case, it would mean that the experiments with the iron-phosphorous synthetic schreibersite would not represent the behavior of the mineral in nature.
“There was always this criticism that if we did include nickel it might not react as much,” said Pasek.
Pasek and his colleagues have addressed this criticism by developing a synthetic form of schreibersite that includes nickel.
In a recent paper published in the journal Physical Chemistry Chemical Physics, Pasek and lead author and geochemist Nikita La Cruz of the University of Michigan show how a form of synthetic schreibersite that includes nickel reacts when exposed to water. As the water evaporates, it creates phosphorus-oxygen (P-O) bonds on the surface of the schreibersite, making the phosphorus available to life. The findings seem to remove any doubts as to whether meteoritic schreibersite could stimulate organic reactions.
“Biological systems have a phosphorus atom surrounded by four oxygen atoms, so the first step is to put one oxygen atom and one phosphorous atom together in a single P-O bond,” Pasek explained.
Terry Kee, a geochemist at the University of Leeds and president of the Astrobiology Society of Britain, has conducted his own extensive work with schreibersite and, along with Pasek, is one of the original champions of the idea that it could be the source of life’s phosphorus.
“The bottom line of what [La Cruz and Pasek] have done is that it appears that this form of nickel-flavored synthetic schreibersite reacts pretty much the same as the previous synthetic form of schreibersite,” Kee said.
Pasek described how meteors would have fallen into shallow pools of water on ancient Earth. The pools would then have undergone cycles of evaporation and rehydration, a crucial process for chemical reactions to take place. As the surface of the schreibersite dries, it allows molecules to join into longer chains. Then, when the water returns, these chains become mobile, bumping into other chains. When the pool dries out again, the chains bond and build ever larger structures.
“The reactions need to lose water in some way in order to build the molecules that make up life,” said Pasek. “If you have a long enough system with enough complex organics, then, hypothetically, you could build longer and longer polymers to make bigger pieces of RNA. The idea is that at some point you might have enough RNA to begin to catalyze other reactions, starting a chain reaction that builds up to some sort of primitive biochemistry, but there’s still a lot of steps we don’t understand.”
Demonstrating that nickel-flavored schreibersite, of the sort contained in meteorites, can produce phosphorus-based chemistry is exciting. However, Kee said further evidence is needed to show that the raw materials of life on Earth came from space.
“I wouldn’t necessarily say that the meteoric origin of phosphorus is the strongest idea,” he said. “Although it’s certainly one of the more pre-biotically plausible routes.” [Fallen Stars: A Gallery of Famous Meteorites]
Despite having co-developed much of the theory behind schreibersite with Pasek, Kee pointed out that hydrothermal vents could rival the meteoritic model. Deep-sea volcanic vents are already known to produce iron-nickel alloys such as awaruite, and Kee says that the search is now on for the existence of awaruite’s phosphide equivalent in the vents: schreibersite.
“If it could be shown that schreibersite can be produced in the conditions found in vents — and I think those conditions are highly conducive to forming schreibersite — then you’ve got the potential for a lot of interesting phosphorylation chemistry to take place,” said Kee
Pasek agreed that hydrothermal vents could prove a good environment to promote phosphorus chemistry, with the heat driving off the water to allow the P-O bonds to form. “Essentially it’s this driving off of water that you’ve got to look for,” he added.
Pasek and Kee both agreed that it is possible that both mechanisms — the meteorites in the shallow pools and the deep-sea hydrothermal vents — could have been at work during the same time period and provided phosphorus for life on the young Earth. Meanwhile David Deamer, a biologist from the University of California, Santa Cruz, has gone one step further by merging the two models, describing schreibersite reacting in hydrothermal fields of bubbling shallow pools in volcanic locations similar to those found today in locations such as Iceland or Yellowstone National Park.
Certainly, La Cruz and Pasek’s results indicate that schreibersite becomes more reactive as the environment in which it exists gets warmer.
“Although we see the reaction occurring at room temperature, if you increase the temperature to 60 or 80 degrees Celsius [140 or 176 degrees Fahrenheit], you get increased reactivity,” said Pasek. “So, hypothetically, if you have a warmer Earth, you should get more reactivity.”
One twist to the tale is the possibility that phosphorus could have bonded with oxygen in space, beginning the construction of life’s molecules before ever reaching Earth. Schreibersite-rich grains coated in ice and then heated by shocks in planet-forming disks of gas and dust could potentially have provided conditions suitable for simple biochemistry. While Pasek agreed with that idea in principle, he said he has “a hard time seeing bigger things like RNA or DNA forming in space without fluid to promote them.”
Researchers studied the properties of nearly 9,000 near-Earth objects (NEOs) — asteroids and other bodies that come within 1.3 Earth-sun distances of our planet — to build a model of the overall NEO population.
This model seemed to have a problem, however: It predicted that astronomers should be seeing 10 times more NEOs that closely approach the sun — come within 9 million miles (15 million kilometers) or so of the star — than they actually observe.
The research team spent a year puzzling over this outcome before coming to a surprising conclusion: The missing NEOs are actually being destroyed as they get close to the sun, but long before they actually dive into the star.
“The discovery that asteroids must be breaking up when they approach too close to the sun was surprising, and that’s why we spent so much time verifying our calculations,” study co-author Robert Jedicke, of the University of Hawaii Institute for Astronomy, said in a statement.
The team’s work should help scientists better understand the NEO population in a variety of ways. For example, many meteors that light up Earth’s night skies are pieces of debris shed by parent NEOs on their laps around the sun. Such debris clouds travel on the same orbits as their parent bodies, but astronomers generally have trouble finding these NEOs. The new study suggests that this is because the parent objects have already been destroyed, the researchers said.
In addition, study team members determined that darker NEOs die farther from the sun than brighter ones do, which helps explain something astronomers already knew: Asteroids that approach the sun closely tend to be quite bright.
This finding implies that dark and bright asteroids may differ significantly in structure and composition, the researchers said.
“Perhaps the most intriguing outcome of this study is that it is now possible to test models of asteroid interiors simply by keeping track of their orbits and sizes,” lead author Mikael Granvik, of the University of Helsinki in Finland, said in the same statement. “This is truly remarkable and was completely unexpected when we first started constructing the new NEO model.”
Granvik and his colleagues built their model by studying nearly 100,000 images of NEOs acquired by the Catalina Sky Survey in Arizona over an eight-year period.
To date, scientists have identified and tracked almost 14,000 NEOs, but the overall population is thought to number in the millions. Astronomers think that most of these bodies begin their lives in the main asteroid belt between Mars and Jupiter, and then veer inward after experiencing gravitational nudges by Jupiter and/or Saturn. The new study was published online today (Feb. 17) in the journal Nature.
The mystery of Mars’ missing atmosphere is one big step closer to being solved.
A previous hypothesis had suggested that a significant part of the carbon from Mars’ atmosphere, which is dominated by carbon dioxide, could have been trapped within rocks via chemical processes. However, new research suggests that there’s not enough carbon in deposits on the Red Planet’s surface to account for the huge amounts lost from the air over time.
“The biggest carbonate deposit on Mars has, at most, twice as much carbon in it as the current Mars atmosphere,” study co-author Bethany Ehlmann, of the California Institute of Technology (Caltech) and NASA’s Jet Propulsion Laboratory in Pasadena, California, said in a statement
“Even if you combine all known carbon reservoirs together, it is still nowhere near enough to sequester the thick atmosphere that has been proposed for the time when there were rivers flowing on the Martian surface,” added Ehlmann, who worked with lead author Christopher Edwards, a former Caltech researcher currently with the U.S. Geological Survey.
Although Mars is dry today, scientists think the planet’s surface harbored large amounts of liquid water billions of years ago. Mars must have had a much thicker atmosphere back then, to keep the water from freezing or immediately evaporating, scientists say.
Carbon dioxide can be pulled from the atmosphere via chemical reactions with rocks, forming carbonate minerals. Previous research had suggested that the Red Planet might be covered with significant carbonate deposits, which could have locked up much of Mars’ lost atmosphere.
But Mars orbiters and rovers have found just a few concentrated carbonate deposits. The largest known carbonate-rich deposit on Mars is the Nili Fossae region, an area at least the size of Delaware and potentially as large as Arizona.
Edwards and Ehlmann used data captured by numerous Mars missions — including NASA’s Mars Global Surveyor orbiter, Mars Reconnaissance Orbiter, and Mars Odyssey orbiter — to estimate how much carbon is locked into Nili Fossae. Then, they compared that amount to what would be needed to form a dense, carbon-rich atmosphere that could sustain running water on the surface at the time that flowing rivers are thought to have carved extensive valley networks into the planet’s surface.
The Martian surface has been probed extensively by orbiters and landers, revealing only limited and scattered deposits of carbonate. Therefore, Edwards and Ehlmann deem it unlikely that so many large deposits have been overlooked by past examinations. Although very early deposits could be hidden beneath the Martian crust, their existence wouldn’t solve the mystery behind the atmosphere that existed when the river-carved valleys formed.
So, if the thick atmosphere didn’t become locked in carbonate deposits, what happened to it? One possibility is that it might have been lost to space from the top of the atmosphere — a phenomenon that NASA’s Curiosity rover has found evidence of in the past. Still, scientists aren’t certain how much of that loss occurred before the valleys formed. NASA’s MAVEN (Mars Atmosphere and Volatile Evolution) orbiter may help narrow down the mystery as it studies the Martian atmosphere.
“Maybe the atmosphere wasn’t so thick by the time of valley network formation,” Edwards said. “Instead of Mars that was wet and warm, maybe it was cold and wet with an atmosphere that had already thinned. How warm would it need to have been for the valleys to form? Not ver
“In most locations, you could have had snow and ice instead of rain,” Edwards said. “You just have to nudge above the freezing point to get water to thaw and flow occasionally, and that doesn’t require very much atmosphere.”
The research was published online Aug. 21 in the journal Geology.
Planetary Resources deployed its first spacecraft from the International Space Station last month, and the Washington-based asteroid-mining company aims to launch a series of increasingly ambitious and capable probes over the next few years.
The goal is to begin transforming asteroid water into rocket fuel within a decade, and eventually to harvest valuable and useful platinum-group metals from space rocks.
“We have every expectation that delivering water from asteroids and creating an in-space refueling economy is something that we’ll see in the next 10 years — even in the first half of the 2020s,” said Chris Lewicki, Planetary Resources president and chief engineer Chris Lewicki.
“After that, I think it’s going to be how the market develops,” Lewicki told Space.com, referring to the timeline for going after asteroid metals.
“If there’s one thing that we’ve seen repeat throughout history, it’s, you tend to overpredict what’ll happen in the next year, but you tend to vastly underpredict what will happen in the next 10 years,” he added. “We’re moving very fast, and the world is changing very quickly around us, so I think those things will come to us sooner than we might think.”
Planetary Resources and another company, Deep Space Industries, aim to help humanity extend its footprint out into the solar system by tapping asteroid resources. (Both outfits also hope to make a tidy profit along the way, of course.)
This ambitious plan begins with water, which is plentiful in a type of space rock known as carbonaceous chondrites. Asteroid-derived water could do far more than simply slake astronauts’ thirst, mining advocates say; it could also help shield them from dangerous radiation and, when split into its constituent hydrogen and oxygen, allow voyaging spaceships to fill up their fuel tanks on the go.
The technology to detect and extract asteroid water is not particularly challenging or expensive to implement, Lewicki said. Scientific spacecraft routinely identify the substance on celestial bodies, and getting water out of an asteroid could simply involve bagging up the space rock and letting the sun heat it up.
Carbonaceous chondrites also commonly contain metals such as iron, nickel and cobalt, so targeting these asteroids could allow miners to start building things off Earth as well. That’s the logical next step beyond exploiting water, Lewicki said.
The “gold at the end of the rainbow,” he added, is the extraction and exploitation of platinum-group metals, which are rare here on Earth but are extremely important in the manufacture of electronics and other high-tech goods.
“Ultimately, what we want to do is create a space-based business that is an economic engine that really opens up space to the rest of the economy,” Lewicki said.
Developing off-Earth resources should have the effect of opening up the final frontier, he added.
“Every frontier that we’ve opened up on planet Earth has either been in the pursuit of resources, or we’ve been able to stay in that frontier because of the local resources that were available to us,” Lewicki said. “There’s no reason to think that space will be any different.”
Planetary Resources isn’t mining asteroids yet, but it does have some hardware in space. The company’s Arkyd-3R cubesat deployed into Earth orbit from the International Space Station last month, embarking on a 90-day mission to test avionics, software and other key technology.
Incidentally, the “R” in “Arkyd-3R” stands for “reflight.” The first version of the probe was destroyed when Orbital ATK’s Antares rocket exploded in October 2014; the 3R made it to the space station aboard SpaceX’s robotic Dragon cargo capsule in April. [Antares Rocket Explosion in Pictures]
Planetary Resources is now working on its next spacecraft, which is a 6U cubesat called Arkyd-6. (One “U,” or “unit,” is the basic cubesat building block — a cube measuring 4 inches, or 10 centimeters, on a side. The Arkyd-3R is a 3U cubesat.)
The Arkyd-6, which is scheduled to launch to orbit in December aboard SpaceX’s Falcon 9 rocket, features advanced avionics and electronics, as well as a “selfie cam” that was funded by a wildly successful Kickstarter project several years ago. The cubesat will also carry an instrument designed to detect water and water-bearing minerals, Lewicki said.
The next step is the Arkyd 100, which is twice as big as the Arkyd-6 and will hunt for potential mining targets from low-Earth orbit. Planetary Resources aims to launch the Arkyd-100 in late 2016, Lewicki said.
After the Arkyd 100 will come the Arkyd 200 and Arkyd 300 probes. These latter two spacecraft, also known as “interceptors” and “rendezvous prospectors,” respectively, will be capable of performing up-close inspections of promising near-Earth asteroids in deep space.
If all goes according to plan, the first Arkyd 200 will launch to Earth orbit for testing in 2017 or 2018, and an Arkyd 300 will launch toward a target asteroid — which has yet to be selected — by late 2018 or early 2019, Lewicki said.
“It is an ambitious schedule,” he said. But such rapid progress is feasible, he added, because each new entrant in the Arkyd series builds off technology that has already been demonstrated — and because Planetary Resources is building almost everything in-house.
“When something doesn’t work so well, we don’t have a vendor to blame — we have ourselves,” Lewicki said. “But we also don’t have to work across a contractural interface and NDAs [non-disclosure agreements] and those sorts of things, so that we can really find a problem with a design within a week or two and fix it and move forward.”
For its part, Deep Space Industries is also designing and building spacecraft and aims to launch its first resource-harvesting mission before 2020, company representatives have said.
Extracting and selling asteroid resources is in full compliance with the Outer Space Treaty of 1967, Lewicki said.
But there’s still some confusion in the wider world about the nascent industry and the rights of its players, so he’s happy that the U.S. Congress is taking up the asteroid-mining issue. (The House of Representatives recently passed a bill recognizing asteroid miners’ property rights, and the Senate is currently considering the legislation as well.)
“I think it’s more of a protection issue than it is an actual legal issue,” Lewicki said. “From a lawyer’s interpretation, I think the landscape is clear enough. But from an international aspect, and some investors — I think they would like to see more certainty.”
Now researchers have found that silica-rich rock much like the continental crust on Earth may be widespread at the site where Curiosity landed on Mars in August 2012.
“Mars is supposed to be a basalt-covered world,” study lead author Violaine Sautter, a planetary scientist at France’s Museum of Natural History in Paris, told Space.com. The findings are “quite a surprise,” she added.
Sautter and her colleagues analyzed data from 22 rocks probed by Curiosity as the six-wheeled robot wandered ancient terrain near Gale Crater. This 96-mile-wide (154 kilometers) pit formed about 3.6 billion years ago when a meteor slammed into Mars, and the age of the rocks from this area suggests they could help shed light on the earliest period of the Red Planets, scientists said.
The 22 rocks the researchers investigated were light-colored, contrasting with the darker basaltic rock found in younger regions on Mars. They probed these rocks using the rock-zapping laser called ChemCamon Curiosity, which analyzes the light emitted by zapped materials to determine the chemistry of Martian rocks.
The scientists found these light-colored rocks were rich in silica. A number of these were similar in composition to some of Earth’s oldest preserved continental crust.
Sautter noted that recent orbiter and rover missions had also spotted isolated occurrences of silica-rich rock. The researchers suggest these silica-rich rocks might be widespread remnants of an ancient crust on Mars that was analogous to Earth’s early continental crust and is now mostly buried under basalt.
The researchers added that the early geological history of Mars might be much more similar to that of Earth than previously thought. Future research could investigate whether the marked differences between Mars’ smooth northern hemisphere and rough, heavily cratered southern hemisphere might be due to plate tectonics, Sautter said.
The scientists detailed their findings online Monday (July 13) in the journal Nature Geoscience.
A Mars-size planet about 200 light-years from our solar system has turned out to be the lightest known alien world orbiting a normal star, researchers say.
Astronomers made the discovery after measuring the size and mass of the baking-hot planet, named Kepler-138 b, which orbits a red dwarf star called Kepler-138. Mars is only 53 percent the size of the Earth (or just about half the size), so Kepler-138 b is smaller than the Earth.
In the past couple of decades, astronomers have confirmed the existence ofmore than 1,800 exoplanets, or planets orbiting a star other than our sun. However, it’s more difficult for scientists to calculate the masses of small, rocky planets like Mars or Mercury than for large, gaseous worlds such as Jupiter or Saturn. Scientists measure the masses of exoplanets by looking at how strongly their gravitational fields tug on their stars; small planets have small masses, and their weak tugs on their stars are more difficult for astronomers to detect. As such, few Earth-size exoplanets have had their masses measured. [The Smallest Known Alien Planets in Pictures]
In this new study, astronomers investigated Kepler-138, a cold, dim red dwarf star with a mass about half that of the sun. Kepler-138 is located about 200 light-years from Earth, in the constellation Lyra.
Kepler-138 “is more than 10 million times further away from us than our sun,” study lead author Daniel Jontof-Hutter, an astronomer at Pennsylvania State University in University Park, told Space.com.
The star Kepler-138 is home to three exoplanets, prior research has confirmed by detecting the slight dimming of the star’s light that occurs whenever one of these worlds crosses in front of it. Each of these two planets — Kepler-138 c and Kepler-138 d — is about 1.2 times as wide as Earth. The third, Kepler-138 b, is a little more than half as wide as Earth, making it about the size of Mars.
“Kepler-138 b has the same apparent size to us as a golf ball 10 million kilometers [6.2 million miles] away,” Jontof-Hutter said.
These three exoplanets orbit very close to their star. Kepler-138 b takes a little more than 10 days to complete its orbit, Kepler-138 c requires nearly 14 days and Kepler-138 d needs about 23 days.
Using NASA’s Kepler spacecraft, the researchers looked at how the gravitational tug-of-war among these exoplanets influenced the lengths of their orbits. Because the strength of a planet’s gravitational pull is directly related to its mass, the scientists were able to weigh all three of these planets.
The astronomers found that the mass of the Mars-size inner planet, Kepler-138 b, is about one-fifteenth, or 6.7 percent, of Earth’s, making it about two-thirds the mass of Mars.
“Kepler-138 b is the first exoplanet smaller than Earth to have both its size and its mass measured,” Jontof-Hutter said.
The least massive known alien world may be the exoplanet PSR B1257+12 b, which has an estimated mass only about one-fiftieth, or 2 percent, that of Earth. However, that world does not orbit a normal star, but instead circles a pulsar — a dense, rapidly spinning remnant of a supernova explosion.
Knowing the mass and width of Kepler-138 b helped the researchers calculate its density, which they found is about two-thirds that of Mars, suggesting it has a purely rocky composition.
Although Kepler-138 b may be similar in mass and width to Mars, it is so much closer to its star, and thus hotter, meaning it is likely very different from Mars, Jontof-Hutter said. “In fact, all three planets orbiting Kepler-138 are likely too hot to retain liquid water,” Jontof-Hutter said. On the outermost planet, surface temperatures are about 250 degrees Fahrenheit (120 degrees Celsius), while those on the innermost planet are about 610 degrees F (320 degrees C).
Kepler-138 c and Kepler-138 d have masses 197 percent and 64 percent of Earth’s, respectively.
This finding opens up the study of rocky alien planets smaller than Earth, Jontof-Hutter said.
“The enormous variety of exoplanets that have been discovered by Kepler show us that systems like our own solar system are probably not the norm, and we don’t know why,” Jontof-Hutter said. Analyzing more exoplanets “will give us clues about how planets form and enable us to learn how common systems like are own really are.”
The scientists detailed their findings in the June 18 issue of the journal Nature.
Methane, a potential sign of primitive life, has been found in meteorites from Mars, adding weight to the idea that life could live off methane on the Red Planet, researchers say.
This discovery is not evidence that life exists, or has ever existed, on Mars, the researchers cautioned. Still, methane “is an ingredient that could potentially support microbial activity in the Red Planet,” study lead author Nigel Blamey, a geochemist at Brock University in St. Catharines, Ontario, Canada, told Space.com.
Methane is the simplest organic molecule. This colorless, odorless, flammable gas was first discovered in the Martian atmosphere by the European Space Agency’s Mars Express spacecraft in 2003, and NASA’s Curiosity rover discovered a fleeting spike of methane at its landing site last year.
Much of the methane in Earth’s atmosphere is produced by life, such as cattle digesting food. However, there are ways to produce methane without life, such as volcanic activity.
To shed light on the nature of the methane on Mars, Blamey and his colleagues analyzed rocks blasted off Mars by cosmic impacts that subsequently crash-landed on Earth as meteorites. About 220 pounds (100 kilograms) of Martian meteorites have been found on Earth.
The scientists focused on six meteorites from Mars that serve as examples of volcanic rocks there, collecting samples about one-quarter of a gram from each — a little bigger than a 1-carat diamond. All the samples were taken from the interiors of the meteorites, to avoid terrestrial contamination.
The researchers found that all six released methane and other gases when crushed, probably from small pockets inside.
“The biggest surprise was how large the methane signals were,” Blamey said.
Chemical reactions between volcanic rocks on Mars and the Martian environment could release methane. Although the dry thin air of Mars makes its surface hostile to life, the researchers suggest the Red Planet is probably more habitable under its surface. They noted that if methane is available underground on Mars, microbes could live off it, just as some bacteria do in extreme environments on Earth.
“We have not found life, but we have found methane that could potentially support microbes in the subsurface,” Blamey said.
Blamey now hopes to analyze more Martian meteorites. He and his colleagues detailed their findings online today (June 16) in the journal Nature Communications.
Mars is a large enough planet that astrobiologists looking for life need to narrow the parameters of the search to those environments most conducive to habitability.
NASA’s Mars Curiosity mission is exploring such a spot right now at its landing site around Gale Crater, where the rover has found extensive evidence of past water and is gathering information on methane in the atmosphere, a possible signature of microbial activity.
But where would life most likely gain energy from its surroundings? One possibility is in an environment that includes “green rust,” a partially oxidized iron mineral. A fully oxidized iron “rust” — one exposed to oxidation for long enough — turns orangey-red, similar to the color of Mars’ regolith. When oxidization is incomplete, however, the iron rust is greenish.
This means that there are two different “redox states,” or types of iron with different numbers of electrons in the same mineral. This difference between the two iron redox states could allow the mineral to take in or give up electrons and thus act as a catalyst, said Laurie Barge, a planetary scientist at NASA’s Jet Propulsion Laboratory. She studies hydrothermal vents, an area where chemical contrasts also fuel life.
“From an environmental science perspective, green rust can absorb and concentrate nutrients, and can also accept and donate electrons for life,” said Barge.
She is the lead author of related work that was presented at the American Geophysical Union’s Joint Assembly meeting in May 2015. Funding for this work comes from the Jet Propulsion Laboratory’s Icy Worlds team as part of the NASA Astrobiology Institute (NAI) element of the Astrobiology Program at NASA.
One major challenge in the search for life on Mars is that its surface is highly oxidized. On Earth, green rust generated in Barge’s lab oxidizes quickly when exposed to air, and its composition is changed in only an hour. However, the lack of oxygen on Mars makes this a slower process. It is likely that green rust occurs beneath the oxidized surface, perhaps only a centimeter or half-inch deep as revealed by Curiosity.
There are more probes on the way to Mars that will include drills. One of those will be NASA’s InSight lander, which is set to go to the Red Planet in 2016. Another is the European Space Agency’s ExoMars rover, expected to launch in 2018.
A major focus of current NASA missions on Mars is finding out where water has flowed in the past. NASA’s Curiosity, Opportunity and Spirit rovers have all found rocks that form in the presence of water, such as the red iron oxide mineral hematite, as well as select sulfates and clays. Further, several orbiting spacecraft have seen signs, such as the presence of gullies, in which water is thought to have once flowed on the surface.
Barge knows from her experiments that green rust forms when two contrasting solutions – one containing iron and one containing hydroxide – are mixed. On Earth, green rust has been found in such environments as non-oxygenated wet sediments and steel pipes that corrode in sea water.
Probing by laser
To detect green rust, Barge suggests using laser Raman spectroscopy, a technique which will be included on ESA’s ExoMars and NASA’s Mars 2020 missions. The technique involves directing a laser beam at a sample and then collecting and analyzing the light that is scattered from the spot to identify its molecular composition and structure. The scattered light contains fingerprint spectral features that allow us to determine the molecular makeup and mineralogy of the sample. Barge has teamed up with Pablo Sobron, a research scientist at the SETI Institute, an expert in laser-based spectroscopy applied to Mars exploration, to adapt the Raman technique for the detection and analysis of green rust.
But first, there needs to be a better understanding of where green rust will occur and how it can support habitability. The JPL Icy Worlds team (led by the Jet Propulsion Laboratory’s Isik Kanik) recently received a second five-year NASA Astrobiology Institute grant to study the habitability of icy worlds, including an investigation into how green rust might drive prebiotic chemistry, or chemistry that is a precursor to life.
“There’s a theory proposed by Michael Russell at JPL that green rust could have acted as a proto-enzyme to convert energy currencies on early Earth,” Barge said, referring to how lifeforms convert proton and electron gradients into chemical energy to drive metabolism and, thereby, life.
Green rust is especially interesting in this regard because it is a double layered hydroxide that can sandwich all sorts of interesting components relevant to life in between these layers, Barge added. These include phosphates, DNA, amino acids and proteins.
The white spot on Ceres in a series of new photos taken on Jan. 13 by NASA’s Dawn spacecraft, which is rapidly approaching the round dwarf planet in the asteroid belt between the orbits of Mars and Jupiter. But when the initial photo release on Monday (Jan. 19), the Dawn scientists gave no indication of what the white dot might be.
“Yes, we can confirm that it is something on Ceres that reflects more sunlight, but what that is remains a mystery,” Marc Rayman, mission director and chief engineer for the Dawn mission, told Space.com in an email.
The new images show areas of light and dark on the face of Ceres, which indicate surface features like craters. But at the moment, none of the specific features can be resolved, including the white spot.
“We do not know what the white spot is, but it’s certainly intriguing,” Rayman said. “In fact, it makes you want to send a spacecraft there to find out, and of course that is exactly what we are doing! So as Dawn brings Ceres into sharper focus, we will be able to see with exquisite detail what [the white spot] is.”
Ceres is a unique object in our solar system. It is the largest object in the asteroid belt and is classified as an asteroid. It is simultaneously classified as a dwarf planet, and at 590 miles across (950 kilometers, or about the size of Texas), Ceres is the smallest known dwarf planet in the solar system.
The $466 million Dawn spacecraft is set to enter into orbit around Ceres on March 6. Dawn left Earth in 2007 and in the summer of 2011, it made a year-long pit stop at the asteroid Vesta, the second largest object in the asteroid belt.
While Vesta shared many properties with our solar system’s inner planets, scientists with the Dawn mission suspect that Ceres has more in common with the outer most planets. 25 percent of Ceres’ mass is thought to be composed of water, which would mean the space rock contains even more fresh water than Earth. Scientists have observed water vapor plumes erupting off the surface of Ceres, which may erupt from volcano-like ice geysers.
The mysterious white spot captured by the Dawn probe is one more curious feature of this already intriguing object.
Asteroids have long been regarded as planetary building blocks. But they may actually be byproducts of planet formation, born when violent collisions smashed an earlier generation of objects apart, a new study suggests.
Asteroid fragments that fall to Earth as meteorites often contain tiny, round pellets called chondrules that formed when molten droplets quickly cooled in space in the solar system’s early years. Chondrules are found in 92 percent of all meteorites, and are often thought to be the building blocks of planets.
Chondrules were part of the protoplanetary disc of gas and dust surrounding the newborn sun that gave birth to Earth and the other planets. A recent study found that chondrules formed about 1 million years after planetesimals — the building blocks of protoplanets — came together.
Prior research had suggested that chondrules in some meteorites were probably born when rocks in space collided at speeds of more than 22,370 mph (36,000 km/h). However, it was uncertain how the majority of chondrules formed.
Now, scientists have found that cosmic impacts could have generated enough chondrules during the first 5 million years or so of planet formation to explain the large quantity of these pellets.
“The most surprising implication of our work is that the meteorites we find on Earth are not actually the building blocks of planets, as has been thought for a long time,” lead study author Brandon Johnson, a planetary scientist at MIT, told Space.com. “Instead, they may be a byproduct of planetary formation.”
Chondrule-bearing meteorites — known as chondrites — may thus not be representative of the objects that built the solar system’s planets, study team members said.
The researchers simulated impacts of varying speeds between protoplanetary objects about 60 to 650 miles (100 to 1,000 kilometers) wide. They found that when collision speeds exceeded 5,590 mph (9,000 km/h), plumes of molten rock that blasted out from these impacts could form millimeter-size droplets that could have cooled into chondrules.
The scientists calculated that cosmic impacts within a typical protoplanetary disc could have generated more than 44 billion trillion lbs. (20 billion trillion kilograms) of chondrules. For comparison, the present asteroid belt currently has a mass of about 6.6 billion trillion lbs. (3 billion trillion kg).
This finding suggests that cosmic impacts could have generated many of the chondrules in the asteroid belt from which nearly all meteorites originate.
“We’ve put together a coherent model for chondrule formation,” Johnson said. “Once we have a proper context for how chondrules formed, we can really understand what was happening in the nascent solar system.”
Johnson noted that the team’s work only investigated vertical impacts. “More realistic impacts may be at an angle,” Johnson said. Still, such oblique impacts “produce more jetted materials, more chondrules,” he added.
A NASA probe is about to get the first up-close look at a potentially habitable alien world.
In March 2015, NASA’s Dawn spacecraft will arrive in orbit around the dwarf planet Ceres, the largest object in the main asteroid belt between Mars and Jupiter. Ceres is a relatively warm and wet body that deserves to be mentioned in the same breath as the Jovian moon Europa and the Saturn satellite Enceladus, both of which may be capable of supporting life as we know it, some researchers say.
“I don’t think Ceres is less interesting in terms of astrobiology than other potentially habitable worlds,” Jian-Yang Li, of the Planetary Science Institute in Tucson, Arizona, said Thursday (Dec. 18) during a talk here at the annual fall meeting of the American Geophysical Union.
Life as we know it requires three main ingredients, Li said: liquid water, an energy source and certain chemical building blocks (namely, carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur).
The dwarf planet Ceres — which is about 590 miles (950 kilometers) wide — is thought to have a lot of water, based on its low overall density (2.09 grams per cubic centimeter; compared to 5.5 g/cubic cm for Earth). Ceres is likely a differentiated body with a rocky core and a mantle comprised of water ice, researchers say, and water-bearing minerals have been detected on its surface.
Indeed, water appears to make up about 40 percent of Ceres’ volume, Li said.
“Ceres is actually the largest water reservoir in the inner solar system other than the Earth,” he said. However, it’s unclear at the moment how much, if any, of this water is liquid, he added.
As far as energy goes, Ceres has access to a decent amount via solar heating, since the dwarf planet lies just 2.8 astronomical units (AU) from the sun, Li said. (One AU is the distance between Earth and the sun — about 93 million miles, or 150 million km). Europa and Enceladus are much farther away from our star — 5.2 and 9 AU, respectively.
Both Europa and Enceladus possess stores of internal heat, which is generated by tidal forces. This heat keeps the ice-covered moons’ subsurface oceans of liquid water from freezing up, and also drives the eruption of water-vapor plumes on Enceladus (and probably Europa as well; researchers announced last year that NASA’s Hubble Space Telescope spotted water vapor erupting from the Jupiter moon in December 2012).
Intriguingly, scientists announced the discovery of water-vapor emission from Ceres — which may also possess a subsurface ocean — earlier this year.
Ceres’ plumes may or may not be evidence of internal heat, Li said. For example, they may result when water ice near Ceres’ surface is heated by sunlight and warms enough to sublimate into space.
“Right now, we just don’t know much about the outgassing on Ceres,” Li said.
Dawn should help bring Ceres into much clearer focus when it reaches the dwarf planet this spring. The spacecraft, which orbited the huge asteroid Vesta from July 2011 through September 2012, will map Ceres’ surface in detail and beam home a great deal of information about the body’s geology and thermal conditions before the scheduled end of its prime mission in July 2015.
Ground-based instruments should also play a role in unveiling Ceres. For example, the Atacama Large Millimeter/submillimeter Array, or ALMA — a huge system of radio dishes in Chile — has the ability to probe deeper than Dawn, going into Ceres’ subsurface and shedding more light on the dwarf planet’s composition and thermal properties, Li said.
“This is highly complementary to the Dawn mission,” he said.
Ceres’ relative proximity to Earth also makes it an attractive target for future space missions, Li added.
The molecule in question — iso-propyl cyanide (i-C3H7CN) — was spotted in Sagittarius B2, a huge star-making cloud of gas and dust near the center of the Milky Way, about 27,000 light-years from the sun. The discovery suggests that some of the key ingredients for life on Earth could have originated in interstellar space.
A specific molecule emits light at a particular wavelength and in a telltale pattern, or spectrum, which scientists can detect using radio telescopes. For this study, astronomers used the enormous Atacama Large Millimeter/submillimeter Array (ALMA) telescope in the Chilean desert, which went online last year and combines the power of 66 radio antennas. [5 Bold Claims of Alien Life]
Iso-propyl cyanide joins a long list of molecules detected in interstellar space. But what makes this discovery significant is the structure of iso-propyl cyanide. All other organic molecules that have been detected in space so far (including normal-propyl cyanide, the sister of i-C3H7CN) are made of a straight chain with a carbon backbone. Iso-propyl cyanide, however, has a “branched” structure. This same type of branched structure is a key characteristic of amino acids.
“Amino acids are the building blocks of proteins, which are important ingredients of life on Earth,” the study’s lead author, Arnaud Belloche, of the Max Planck Institute for Radio Astronomy, told Space.com in an email. “We are interested in the origin of amino acids in general and their distribution in our galaxy.”
Scientists have previously found amino acids in meteorites that fell to Earth, and the composition of these chemicals suggested they had an interstellar origin. The researchers in this new study did not find amino acids, but their discovery adds an “additional piece of evidence that the amino acids found in meteorites could have been formed in the interstellar medium,” Belloche wrote.
“The detection of a molecule with a branched carbon backbone in interstellar space, in a region where stars are being formed, is interesting because it shows that interstellar chemistry is indeed capable of producing molecules with such a complex, branched structure,” Belloche added.
It was first suggested in the 1980s that branched molecules could form on the surface of dust grains in interstellar space. But this is the first time such compounds have been detected. What’s more, iso-propyl cyanide seemed to be plentiful — it was almost half as abundant of its more common sister variant in Sagittarius B2, the study found. This means that branched molecules could actually be quite ordinary in interstellar space, the researchers said.
The discovery of a complex microbial ecosystem far beneath the Antarctic ice may be exciting, but it doesn’t necessarily mean that life teems on frigid worlds throughout the solar system, researcher’s caution.
Scientists announced today (Aug. 20) in the journal Nature that many different types of microbes live in subglacial Lake Whillans, a body of fresh water entombed beneath 2,600 feet (800 meters) of Antarctic ice. Many of the micro-organisms in these dark depths apparently get their energy from rocks, the researchers report.
The results could have implications for the search for life beyond Earth, notes Martyn Tranter of the University of Bristol in England, who did not participate in the study. [6 Most Likely Places for Alien Life in the Solar System]
“The team has opened a tantalizing window on microbial communities in the bed of the West Antarctic Ice Sheet, and on how they are maintained and self-organize,” Tranter wrote in an accompanying “News and Views” piece in the same issue of Nature. “The authors’ findings even beg the question of whether microbes could eat rock beneath ice sheets on extraterrestrial bodies such as Mars. This idea has more traction now.”
But just how much traction is a matter of debate. For example, astrobiologist Chris McKay of NASA’s Ames Research Center in California doesn’t see much application to Mars or any other alien world.
“First, it is clear that the water sampled is from a system that is flowing through ice and out to the ocean,” said McKay, who also was not part of the study team.
“Second, and related to this, the results are not indicative of an ecosystem that is growing in a dark, nutrient-limited system,” McKay told Space.com via email. “They are consistent with debris from the overlying ice — known to contain micro-organisms — flowing through and out to the ocean. Interesting in its own right, but not a model for an isolated ice-covered ecosystem.”
Isolated, ice-covered oceans exist on some moons of the outer solar system, such as Jupiter’s moon Europa and the Saturn satellite Enceladus — perhaps the two best bets to host life beyond Earth. McKay and other astrobiologists would love to know if these oceans do indeed host life.
It may be possible to find out without even touching down on Europa or Enceladus. Plumes of water vapor spurt into space from the south polar regions of both moons, suggesting that flyby probes could sample their subsurface seas from afar.
And Europa is on the minds of the higher-ups at both NASA and the European Space Agency (ESA). NASA is drawing up plans for a potential Europa mission that could blast off in the mid-2020s, while ESA aims to launch its JUpiter ICy moons Explorer (JUICE) mission —which would study the Jovian satellites Callisto and Ganymede in addition to Europa — in 2022.
These compounds may reveal that extraterrestrials have disastrously altered their planets, scientists added.
To detect biomarkers, or signs of life, on distant worlds, scientists have often focused on molecules such as oxygen, which theoretically disappears quickly from atmospheres unless life is present to provide a constant supply of the gas. By looking at light passing through atmospheres of alien worlds, past studies have suggested future instruments such as NASA’s James Webb Space Telescope could detect telltale traces of oxygen.
But the search for extraterrestrial intelligence (SETI) has mostly concentrated on “technosignatures,” such as radio and other electromagnetic signals that alien civilizations might give off. Now researchers suggest that searches for atmospheric biomarkers could also look for industrial pollutants as potential signs of intelligent aliens.
Astronomers at Harvard University focused on tiny, superdense stars known as white dwarfs. More than 90 percent of all stars in the Milky Way, including our own sun, will one day end up as white dwarfs, which are made up of the dim, fading cores of stars.
Though white dwarfs are quite cold for stars, they would still be warm enough to possess so-called habitable zones — orbits where liquid water can exist on the surfaces of circling planets. These zones are considered potential habitats for life, as there is life virtually everywhere there is liquid water on Earth.
The scientists examined how Earth-size planets in the habitable zones of white dwarfs might look if they possessed industrial pollutants in their atmosphere. They focused on chlorofluorocarbons (CFCs), which are entirely artificial compounds, with no known natural process capable of creating them in atmospheres.
CFCs are nontoxic chemicals that were once used in hairspray and air conditioners, among many other products, before researchers discovered they were causing a hole in Earth’s ozone layer, which protects the planet from dangerous ultraviolet radiation.
“Very hairy extraterrestrials may be a little easier to detect,” joked lead study author Henry Lin, a physicist at Harvard.
CFCs are strong greenhouse gases, meaning they are very effective at absorbing heat. This means that if CFCs are in the atmosphere of a distant Earth-size planet, they could alter a white dwarf’s light when that world passes in front of that star — enough for the $8.8 billion James Webb Space Telescope (JWST), which is due to launch in 2018, to detect them.
In addition, the researchers noted that CFCs are long-lived molecules, capable of lasting up to about 100,000 years in atmospheres. This means they could even serve as markers of long-dead alien civilizationsThe investigators simulated the amount of time it would take JWST to detect the fluorocarbon CF4 and the chlorofluorocarbon CCl3F in the atmosphere of an Earth-size planet in the habitable zone of a white dwarf. They modeled concentrations of these gases 100 times greater than the highs currently seen on Earth.
The scientists found it would take JWST three days of looking at such a white dwarf to detect signs of CF4, and only a day and a half for CCl3F.
“The most exciting aspect of the results is that within the next decade we might be able to search for excessive industrial pollution in the atmospheres of Earth-like planets,” study co-author Abraham Loeb, a theoretical astrophysicist and chair of Harvard’s astronomy department, told Space.com.
Ironically, “aliens are often referred to as green little creatures, but ‘green’ also means ‘environmentally friendly,'” Loeb said. “Detectable CFC-rich civilizations would not be ‘green.'”
The scientists did caution that it would take much longer to detect these industrial pollutants than it would biomarkers such as oxygen, which JWST could find after about three hours of looking at such a planet. Astronomers should only attempt to discover technosignatures such as CFCs if initial searches for fundamental biomarkers like oxygen were successful, the research team suggested.
The astronomers cautioned it would be 100 times more difficult to detect industrial pollutants on planets orbiting yellow dwarf stars like the sun, making such searches beyond the capabilities of JWST. It would also take an unrealistically long time to detect CFC levels on alien planets that match those currently found on Earth, Loeb said.
One potentially sobering future discovery might be of alien worlds that possess long-lived industrial pollutants such as CFCs but no longer have any short-lived biomarkers such as oxygen.
“If we find graveyards of other civilizations, most rational people would likely get engaged in protecting the Earth from a similar catastrophe,” Loeb said.
“We call industrial pollution a biomarker for intelligent life, but perhaps a civilization much more advanced than us with their own exoplanet program will classify industrial pollution as a biomarker for unintelligent life,” Lin said.
However, if astronomers discover a world heavy with CFCs that exists outside the habitable zone of its star, that could mean an extraterrestrial civilization may have intentionally “terraformed” that planet, making it livably warmer “by polluting it with greenhouse gases,” Loeb said. Scientists have previously suggested terraforming Mars by warming and thickening the Red Planet’s atmosphere so that humans can roam its surface without having to wear spacesuits.
Researchers announced their discovery of the deep watery ocean on Enceladus on Thursday (April 3) in the journal Science, confirming suspicions held by many scientists since 2005, when NASA’s Cassini spacecraft spied geysers of ice and water vapor erupting from Enceladus’ south pole.
The discovery vaults Enceladus into the top tier of life-hosting candidates along with Europa, an ice-sheathed moon of Jupiter that also hosts a subterranean ocean. Both frigid satellites bear much closer investigation, researchers say.
“I don’t know which of the two is going to be more likely to have life. It might be both; it could be neither,” study co-author Jonathan Lunine of Cornell University told reporters yesterday (April 2). “I think what this discovery tells us is that we just need to be more aggressive in getting the next generation of spacecraft both to Europa and to the Saturn system once the Cassini mission is over.”
Cassini arrived in orbit around Saturn in 2004 and is currently scheduled to go out in a blaze of glory in September 2017, when it will dive headlong into the giant planet’s thick atmosphere.
Enceladus’ geysers blast material hundreds of miles into space, offering a way to sample the moon’s subsurface ocean from afar. (Researchers think the ocean is feeding the geysers, though they can’t be sure of this at the moment.)
Cassini has already done some of this work with its mass spectrometer, detecting salts and organic compounds — the carbon-based building blocks of life as we know it — in Enceladus’ plumes during flybys of the moon.
But Cassini’s mass spectrometer can detect only relatively light organics. A follow-up mission to Enceladus should sport a more advanced and more sensitive version of this instrument that could spot a wider range of organics, Lunine said.
“You could actually do this by making flybys of Enceladus, the way that Cassini does now,” he said. “I think you could learn quite a bit about the organic inventory in the plume by flying this device.”
Interestingly, astronomers announced in December that they had discovered plumes of water vapor erupting from Europa’s south polar region as well. So that moon’s ocean could be sampled during flybys, too — perhaps by a mission called the Europa Clipper.
NASA is developing the Europa Clipper as a concept mission at the moment. Recent estimates have pegged the mission’s cost at around $2 billion. That’s pretty steep in these tough economic times, so a scaled-down version might have the best chance of getting it off the ground, NASA officials have said.
Enceladus and Europa aren’t the only icy moons that harbor subsurface oceans; Jupiter’s enormous moon Ganymede also has one, for example. But Ganymede’s appears to be sandwiched between layers of ice, while the seas of Enceladus and Europa are in contact with rocky seafloors, making possible all sorts of interesting chemical reactions, researchers say.