NASA’s planet-hunting Kepler space telescope continues to zero in on the first “alien Earth” despite being hobbled by a malfunction more than two years ago.
Last Thursday (July 23), mission scientists announced the discovery of Kepler-452b, which they and NASA officials described as the most Earth-like exoplanet yet found. Kepler-452b circles a sunlike star at about the same distance Earth orbits the sun, but the alien world is about 60 percent wider than our home planet, so it’s not a true “Earth twin.”
Kepler-452b “is the closest thing that we have to another place that somebody else might call home,” Jon Jenkins, Kepler data analysis lead at NASA’s Ames Research Center in Moffett Field, California, said during a news conference Thursday. [Exoplanet Kepler 452b: Closest Earth Twin in Pictures]
While the discovery of Kepler-452b is new, the observations that led to it are several years old. The planet was dug out of data Kepler gathered during the first four years of its original planet hunt, which came to an end in 2013.
The main goal of the $600 million Kepler mission is to determine how common Earth-like planets are across the Milky Way galaxy.
During its original round of operations, the Kepler spacecraft stared at more than 150,000 stars continuously and simultaneously, watching for tiny brightness dips that could betray the presence of a planet crossing, or “transiting,” its host star’s face. This work required extremely precise pointing, an ability Kepler lost when the second of its four orientation-maintaining reaction wheels failed in May 2013.
Kepler generally needs to observe multiple transits to detect a planet, so it can take a while for the observatory to spot a potentially habitable world. (Earth, after all, would transit the sun from a hypothetical alien Kepler’s perspective just once a year.) Small, rocky planets also present a signal-to-noise issue that can be mitigated by observing multiple transits.
Kepler team members have therefore long maintained that the most interesting Kepler finds should come at relatively late stages in the mission. So, while Kepler observed beyond the 3.5 years prescribed by the prime mission plan, the failure of the second reaction wheel was initially “crushing,” Jenkins said.
But only initially, for Kepler scientists have gotten better and better at analyzing the observatory’s huge dataset and pulling out intriguing finds from the original planet hunt, team members said.
For example, the discovery of Kepler-452b was announced along with 521 newfound planet “candidates,” bringing Kepler’s total tally of potential planets to 4,696. Just 1,030 of these worlds have been confirmed by follow-up observations or analysis, but about 90 percent of them should end up being the real deal, mission scientists have said. [10 Exoplanets That Could Host Alien Life]
Furthermore, 11 of the newly detected 521 candidates are similar to Kepler-452b: They’re less than twice Earth’s diameter and reside in their host stars’ “habitable zone,” that just-right range of distances in which liquid water could exist on a planet’s surface.
Such detections were made with the aid of new software that automated some parts of the data-analysis process that had previously been done manually, said Kepler research scientist Jeff Coughlin, of the Search for Extraterrestrial Intelligence (SETI) Institute in Mountain View, California.
Continued improvements in software and analysis techniques should result in more discoveries down the road, Coughlin added. Indeed, he said, the team plans to release another “catalog” of Kepler finds next year.
“We’re really optimistic that we’re going to continue to discover even more small, habitable-zone planets,” Coughlin said during Thursday’s news conference.
Kepler’s enormous dataset is publicly archived, so it should give academics and citizen scientists plenty to chew on far into the future, he added.
“I really expect that discoveries will be coming from Kepler for the next several decades,” Coughlin said.
Regardless of what happens in the future, Kepler’s discoveries have already revolutionized exoplanet research. The spacecraft’s finds suggest, among other things, that every Milky Way star hosts at least one planet on average; that rocky planets are extremely common throughout the galaxy; and that about 20 percent of all stars in the Milky Way host a roughly Earth-size planet in their habitable zones.
And while team members pore over data from the original mission, Kepler continues to gather data during a new mission called K2. The observatory’s handlers figured out a way to improve its pointing abilities using sunlight pressure as a sort of ersatz reaction wheel, and Kepler is now studying a variety of cosmic objects and phenomena, from distant supernova explosions to comets and asteroids in our own solar system.
The K2 plan also calls for continued exoplanet hunting, though on a much lesser scale than Kepler used to perform. (NASA announced the new mission’s first alien-planet discovery this past December.)
The failure of the second reaction wheel “is kind of the best worst thing that could’ve ever happened to Kepler,” Jenkins said. “It really broadens the field of exoplanets. It broadens the science that we can do with this phenomenal spacecraft.”
NASA announced that it is collaborating with Microsoft to enable astronauts onboard the orbiting space station to use the company’s virtual reality headset.
Two pairs of Microsoft’s HoloLens computerized eyeglasses are scheduled to be sent to the space station when SpaceX launches its seventh commercial resupply mission on June 28.
“HoloLens and other virtual and mixed reality devices are cutting edge technologies that could help drive future exploration and provide new capabilities to the men and women conducting critical science on the International Space Station,” Sam Scimemi, NASA’s director of the space station program, said in a statement. “This new technology could also empower future explorers requiring greater autonomy on the journey to Mars.”
Microsoft unveiled HoloLens in January at a Windows 10 event where CEO Satya Nadella said the device will be the world’s first holographic computing platform. The device is designed to allow users to see high-definition holograms with surround sound. They’re also built to understand voice commands and hand gestures.
The project that NASA and Microsoft are teaming up on has been dubbed Sidekick and is focused on helping astronauts who need to perform various tasks off-Earth.
By using HoloLens, which look much like a pair of wrap-around sunglasses and are expected to ship on July 29 along with Windows 10, the astronauts should be able to perform some on-station tasks with less training and be more efficient in the work they’re doing.
NASA already has tested the devices on board NASA’s Weightless Wonder C9 jet to make sure they work as expected in gravity-free environment.
Alien worlds with helium skies might be fairly common throughout the universe, researchers say.
One such helium-rich exoplanet might have already been discovered about 33 light-years from Earth, scientists added.
In the past two decades or so, astronomers have confirmed the existence of more than 1,800 extrasolar planets. Among these exoplanets are strange worlds called warm Neptunes — planets that, at 10 to 20 times the mass of Earth, are about the mass of “cold Neptunes” such as Uranus and, naturally, Neptune, but are as close, or closer, to their stars than Mercury is to our sun.
These warm Neptunes can reach scorching temperatures of more than 1,340 degrees Fahrenheit (725 degrees Celsius), and complete orbits around their stars in as little as one or two days. [The Strangest Alien Planets (Gallery)]
Astronomers had assumed that Neptune-size exoplanets would possess rocky or liquid cores wrapped in atmospheres dominated by hydrogen and helium, much like the giant planets in our own solar system. However, planetary scientist Renyu Hu at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, and his colleagues reasoned that warm Neptunes are so close to their stars that stellar radiation may have dramatically altered their atmospheres.
The researchers discovered that warm Neptunes could often have atmospheres enriched with helium. “They could be fairly common,” Hu told Space.com.
The high levels of extreme ultraviolet radiation that warm Neptunes would receive from their stars would cause their hydrogen to waft away.
“Hydrogen is four times lighter than helium, so it would slowly disappear from the planets’ atmospheres, causing them to become more concentrated with helium over time,” Hu said in a statement.
A warm Neptune with a fairly small atmosphere could become helium-dominated over the course of up to 10 billion years, Hu said. (For comparison, Earth is about 4.5 billion years old.)
One way to detect such a planet would be to note the color of its sky. Neptune is a brilliant azure blue because of methane. However, the scarcity of hydrogen on helium-atmosphere worlds would mean that methane, which is composed of one carbon atom and four hydrogen atoms, would be rare, while carbon monoxide and carbon dioxide, which are composed of carbon and oxygen, would be far more common. As such, a helium-sky planet would probably appear grey or white, researchers said.
One warm Neptune called GJ 436b that is peculiarly low in methane might be such a helium-rich planet. NASA’s Spitzer Space Telescope found that GJ 436b, which is located about 33 light-years from Earth, is also rich in carbon monoxide.
A number of other features would also help set helium-sky worlds apart. For instance, an atmosphere rich in helium would be puffier than one made of carbon dioxide or nitrogen because helium is lighter than either of those two gases, “and this feature makes the helium atmosphere more observable,” Hu said.
In addition, because helium is easier to heat than hydrogen, a helium-rich planet is more likely to have a hot spot facing its star than a hydrogen-rich world.
Future research could use NASA’s Hubble Space Telescope to look for more warm Neptunes with carbon monoxide and carbon dioxide in their atmospheres, and NASA’s upcoming James Webb Space Telescope might one day directly detect helium in the skies of these planets.
“Any planet one can imagine probably exists, out there, somewhere, as long as it fits within the laws of physics and chemistry,” study co-author Sara Seager of MIT said in the same statement. “Planets are so incredibly diverse in their masses, sizes and orbits that we expect this to extend to exoplanet atmospheres.”
Hu, Seager and their colleague Yuk Yung of JPL detailed their findings in a paper that will appear today (June 24) in the Astrophysical Journal.
Where can scientists find clues to help them locate and understand life beyond Earth? According to speakers at the 2015 Astrobiology Science Conference, the hunt begins in many locations, from planets beyond our solar system to the ground beneath our feet.
At a news briefing hosted by NASA, three speakers discussed a wide range of ways that scientists are assisting in the search for life elsewhere in the universe. Those efforts include studies of extreme life-forms on Earth, photographs of the sun glinting off Earth’s ocean, and studies in Antarctica that will assist a mission to one of Jupiter’s icy moons.
John Grunsfeld, associate administrator for science at NASA, opened the panel discussion with remarks about his own passion and enthusiasm for the search for life, and how it fits into NASA’s overall mission to “innovate, explore, discover and inspire.”
Alexis Templeton, an associate professor of geological sciences at the University of Colorado-Boulder, discussed the NASA-funded “Rock-Powered Life Team,” for which she is principal investigator.
“[We're] quite interested in the capability of rocks to store energy within them to be used to power biological systems,” Templeton said. “Essentially, there’s a fundamental understanding that rocks have within them, depending on their chemistry, the ability to release electrons or components that can fuel and power different systems essentially much like fuel cells do. And one of the big questions at the moment is how we can couple the energy that’s stored within rocks into biological systems.”
If rocks can serve as an energy source for life, it might opened up new possibilities for where life could thrive in the universe. In particular, it could mean that organisms don’t need direct exposure to sunlight, but could live in subsurface environments.
Templeton said the group is investigating life-forms found in the deserts of Oman, where rocks formed in the Earth’s mantle have come to the surface. Prolonged contact between the rocks and pools of water has “changed the water chemistry progressively,” Templeton said, making it highly alkaline — a “rare type of water to find on Earth.” Life-forms discovered in these pools are not only surviving in the alkali environments, but are optimized for them.
“This is, then, very exciting to start to imagine that there’s biological life-forms that may be well adapted in the subsurface environment to be sustained by the reactions between these rocks and water,” Templeton said.
Britney Schmidt, an assistant professor of earth and atmospheric sciences at the Georgia Institute of Technology, discussed the search for life in sub-surface oceans such as those found on Jupiter’s icy moons and other icy worlds.
“We think a lot about Mars in the search for life in the solar system, but there’s a whole host of ice-rich worlds that harbor subsurface oceans,” Schmidt said. “And these are important places to think about in the search for life, even within our own solar system.”
NASA recently announced a suite of instruments that the agency selected to go aboard a planned satellite mission to Europa, one of Jupiter’s moons. Scientists say its possible life could exist beneath the icy surface of Europa, in the immense ocean that lies below.
Currently, Schmidt is principal investigator for the NASA-funded project Sub-Ice Marine and Planetary Analog Ecosystems, or SIMPLE, a project that Schmidt says will assist future missions to icy worlds.
“[We] work with a number of different vehicles, a number of different remote sensing and in-situ sensing platforms, to study our ocean the same way we’d want to study the ocean of [Jupiter's moons] Europa or Enceladus,” Schmidt said.
The project includes a vehicle called “Icefin,” which is exploring the ocean below the Antarctic ice. Another instrument, called “Artemis,” will perform long-range exploration under the ice; another project will conduct ice-penetrating radar studies of the ice shelves of the Antarctic, all of which are “perfect analogs” for the work that is set to be done by radar instruments flying over Europa. [Photos: Europa, Mysterious Icy Moon of Jupiter]
A glimmer of life
Vikki Meadows, a professor of astronomy and principal investigator at the University of Washington’s Virtual Planetary Laboratory in Seattle, spoke last about studies that could assist in identifying signs of life through direct observations of exoplanets.
She presented an image taken by the LCROSS satellite (before it crashed into the moon in 2009) of the Earth as a partially illuminated crescent. The curved sliver of light was not uniform — it featured a slightly brighter section right near its midpoint. That, said Meadows, was a glint of sunlight reflecting off the ocean.
Alien Planet Quiz: Are You an Exoplanet Expert?
This “glint effect,” Meadows said, is something that scientists theorized might reveal the presence of an ocean on a distant exoplanet. But the images taken by LCROSS are the first “glint” data ever collected.
“By comparing our models and that data, we were able to confirm that in fact our models are accurate,” Meadows said. “We have more confidence now about predicting the type of signals we might be able to detect from extrasolar planets when we go for the gold and actually try to detect an ocean on another planet.”
Meadows’ team has also done work to help narrow down what kind of elements and molecules in a planet’s atmosphere might indicate the presence of life — in particular, what the presence of oxygen says about the presence or absence of life — and how to spot false positives.
“We now are getting a much more mature view of what we should be looking for and what might fool us,” Meadows said. “We know in particular which targets we should choose preferentially that will help us avoid these false positives for life and also what other things in the planetary spectrum we should look for that might help us figure out what’s going on.”
The panel’s comments reflected just a sampling of the research being presented at the meeting this week, and a small indication of the work that is slowly but steadily moving the scientific community closer to the possibility of identifying life elsewhere in the universe..
“Are we alone? Is there another civilization out there? Is there any other life out there?” Grunsfeld said in his opening remarks. “The fact that we’re here, and the fact that life is so complex on Earth, rocks survive on a tiny bit of chemical energy, to me is convincing that there is a very high probability there’s life elsewhere.”
Scientists using several telescopes, including NASA’s Chandra X-ray Observatory, found evidence that a planet in an ancient cluster of stars on the edge of the Milky Way drifted too close to a white dwarf star and was ripped apart. NASA officials explained the discovery in a video on the planet’s death by white dwarf.
White dwarf stars start out as any normal star about the size of the sun, but eventually swell into red giants while they burn up the hydrogen in their core and fuse it into helium. When all the hydrogen is gone, only the star’s core is left —a dense sphere with a radius about one hundredth the size of the original star, but with almost the same mass.
The dead stars’ density creates a strong gravitational pull, more than 10,000 times stronger than the gravitational force at the surface of the sun, according to NASA officials.
That force, and its associated tides, could have the power to pull apart a planet that passes too close, astronomers said. They estimate the destroyed planet had about a third of the mass of Earth and the white dwarf has approximately 1.4 times the mass of the sun.
Researchers using the European Space Agency’s INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) discovered the possibility that a white dwarf tore a planet apart when they found an unexpected source of X-ray radiation in globular star cluster NGC 6388. They initially thought the radiation was due to hot gas swirling toward an intermediate-mass black hole thought to be at the center of the cluster.
A second look with Chandra X-ray Observatory, however, revealed that the X-rays were actually coming from a point off to the side of the cluster’s possible black hole center. Scientists continued to monitor the radiation for 200 days with the X-ray telescope on board NASA’s Swift gamma-ray burst observatory, an international mission that aims to solve the mystery of what causes brief and intense flashes of gamma-ray radiation in space.
As scientists monitored the X-rays, the radiation dimmed at a rate that agrees with current theories of how a planet ripped apart by the gravitational tidal forces of a white dwarf would react. These theories predict the debris from a planet shredded by a white dwarf would be heated and glow in X-rays as it falls onto the white dwarf.
“While the case for the tidal disruption of a planet is not iron-clad, the argument for it was strengthened when astronomers used data from the multiple telescopes to help eliminate other possible explanations for the detected X-rays,” NASA officials wrote in a statement.
Astronomers have spotted a dead star polluted with heavy elements, suggesting that the star recently chowed down on a water-laced asteroid.
The destructive process hints at how asteroids probably delivered water to Earth billions of years ago. But it also hints at how asteroids likely deliver water to exoplanets in other planetary systems.
“Our research has found that, rather than being unique, water-rich asteroids similar to those found in our solar system appear to be frequent,” lead researcher Roberto Raddi from the University of Warwick, said in a statement. “Accordingly, many planets may have contained a volume of water, comparable to that contained in the Earth.” [Related: In Search for Alien Life, Follow the Water]
Astronomers once thought that white dwarfs — the Earth-size remnants of low-mass stars like our sun — were pristine. Their intense gravity should pull the heaviest elements down into their depths relatively quickly (thousands of years at most). “In old white dwarfs (hundreds of millions of years old), like the one we observed, one would not expect any heavy element to stay in their atmospheres for long,” Raddi told Space.com in an email.
But when the team observed the white dwarf in question (known as SDSS J1242+5226), they saw that it was smothered in oxygen, magnesium, silicon, iron and other heavy elements. Even hydrogen was far more abundant than expected. These elements match what astronomers expect to see in a water-rich asteroid.
It’s likely that the asteroid passed close to the white dwarf, whose intense gravity shredded it into smaller particles. These particles then formed a disk around the dead star, and slowly rained down over time — polluting the star’s surface with its elements. Because those elements are still expected to sink to the center of the star, the destructive event probably happened fairly recently, Raddi said.
The astronomers suspect that the asteroid was initially comparable in size to Ceres, the largest known asteroid in the solar system, Raddi said. And it likely contained enough water to fill 30 percent of the Earth’s oceans.
The result sheds light on how asteroids can deliver water to stars and other orbiting bodies. Geologists don’t think Earth’s water has been here for too long. The moon-forming impact would have melted the Earth’s crust and mantle, vaporizing any water. Instead, asteroids likely delivered water to Earth in the young solar system.
And this research shows that this process was not unique to our solar system. It’s likely occurring throughout planetary systems in the galaxy, scientists said.
“Our work reinforces previous evidence that water-rich asteroids are common in other planetary systems,” Raddi said. “It also confirms that asteroids can deliver their constituents (rocks and ice) onto the surface of planets in the inner parts of the planetary systems orbiting other stars, likely within what is known as the habitable zone.”
The team made their observations on the U.K.-owned William Herschel Telescope in the Canary Islands, Spain. The study was published today (May 7) in the journal Monthly Notices of the Royal Astronomical Society.
The newfound exoplanets, known as HD 7924c and HD 7924d, are “super Earths” with masses about 7.9 and 6.4 times greater, respectively, than that of our home planet, researchers said. The planets orbit the star HD 7924, which lies just 54 light-years from the sun — a mere stone’s throw considering the size of the Milky Way, which is on the order of 100,000 light-years wide.
The discovery brings the number of known planets in the HD 7924 system to three. (Another super Earth, called HD 7924b, was spotted there in 2009.) HD 7924b, HD 7924c and HD 7924d all lie closer to their host star than Mercury does to the sun. They complete one orbit in five, 15 and 24 days, respectively, researchers said. [The Strangest Alien Planets]
“The three planets are unlike anything in our solar system, with masses seven to eight times the mass of Earth and orbits that take them very close to their host star,” study co-author Lauren Weiss, a graduate student at the University of California, Berkeley, said in a statement.
The research team discovered HD 7924c and HD 7924d using three different ground-based facilities — the Automated Planet Finder (APF) Telescope at Lick Observatory in California, the Keck Observatory in Hawaii and the Automatic Photometric Telescope (APT) at Fairborn Observatory in Arizona. (Keck also found HD 7924b in 2009.)
The research team, which was led by University of Hawaii (UH) graduate student BJ Fulton, used the combined observations of the three telescopes to detect tiny wobbles in the star HD 7924 caused by the gravitational pull of the two newfound planets, and then to verify the worlds’ existence.
Starspots, like sunspots on the sun, can momentarily mimic the signatures of small planets,” said co-author Evan Sinukoff, also a UH graduate student. “Repeated observations over many years allowed us to separate the starspot signals from the signatures of these new planets.”
The APF Telescope was recently revamped to make it fully robotic, and it now searches the skies for exoplanets without human oversight — a key milestone in the ongoing exoplanet hunt, researchers said.
“This level of automation is a game-changer in astronomy,” said co-author Andrew Howard, an astronomer at UH. “It’s a bit like owning a driverless car that goes planet shopping.”
Astronomers first found planets orbiting another star in 1992, and the exoplanet tally has now risen to nearly 2,000. More than half of these alien worlds have been discovered by NASA’s Kepler space telescope, which launched in March 2009.
Water is a polar molecule and a solvent, two properties that are important for certain chemical reactions critical to life, said NASA chief scientist Ellen Stofan.
“We think water is key to life as we know it,” Stofan said Tuesday (April 28) during the Asimov Memorial Debate, an annual event at New York’s American Museum of Natural History that was moderated by Neil deGrasse Tyson, director of the museum’s Hayden Planetarium.
And Earth is certainly not the only world with ample stores of the stuff. Jupiter’s moon Europa is covered with a sheet of ice that very likely sits on top of a global ocean, and Saturn’s moon Enceladus shows evidence of subsurface water as well. Mars, meanwhile, was once a relatively warm and wet world that apparently harbored large amounts of liquid water in the ancient past for a long period of time — perhaps up to a billion years, Stofan said.
Astrobiologists regard Europa and Enceladus as viable candidates to host alien life today. While researchers might not find life on Mars now, it might have existed there once, Stofan said.
“Many of us in the scientific community have a pretty strong belief, based on science, that at some point life was likely to have evolved on the surface of Mars,” Stofan said. “The hard part is going to be finding it.”
Any Martian life that is found is likely to be microbes, not “little green men,” she added.
Participating along with Stofan and Tyson in Tuesday night’s event — which was called, appropriately enough, “Water, Water” — were Kathryn Sullivan, Administrator at the U.S. National Oceanic and Atmospheric Administration (NOAA); retired US Air Force Gen. Charles Wald; hydrologist Tess Russo; and astronomer Heidi Hammel, an expert on comets and other water-bearing bodies in the solar system.
The discussion did not focus solely on the search for alien life. In fact, much of it was about a looming set of crises that fresh water supplies are facing on Earth, and the connection with NASA and space science. Sullivan noted that NOAA and NASA work closely together; NOAA operates a satellite fleet that monitors weather, climate and land use.
Russo said satellite-based studies of water use can and do help farmers understand how to use water more efficiently. Some 2.4 percent of all the water on Earth is fresh water, and humans can use only a fraction of that, about 0.4 percent of the total. Of that, about 70-90 percent is used for agriculture.
Tyson posited that the plans to settle humans on Mars can be connected with how we use water on Earth, and that technologies for recycling might have Earthbound applications. [The Boldest Mars Missions in History]
Stofan agreed that recycling water is key. On the International Space Station, some 85 percent of the water is recycled. To get to Mars, that percentage will have to be even higher. And water, she added, isn’t just for drinking, but for rocket fuel as well.
There isn’t any liquid water on Mars’ surface, and getting at the stuff might not be easy. “Mars is not a ‘live off the land’ kind of place,” Stofan said. The likely route will be to pre-position some kind of water extraction apparatus on Mars before sending humans.
On other worlds, though, water is even harder to access. On the moon, much of it is locked in clathrates, said Hammel. Clathrates are compounds in which water molecules are trapped inside molecular lattices. Getting the water out is not easy. “You have to go through a lot of material,” she said.
As to water crises on Earth, technology – even from NASA — might not be enough to solve them. “One of the difficulties is taking a NASA thing and scaling it up,” Hammel said.
As it is, humans use a lot of water, and not always sensibly.
“In Las Vegas, per capita water use is twice as much as in New York,” Sullivan said. “But it rains 10 times as much here [in New York].” On top of that, 90 percent of the water in Nevada is used for agriculture. Such imbalances are common. It takes three times more water to produce a plastic water bottle than the bottle contains, she added.
Russo said humanity is draining aquifers much faster than they recharge. “We are pumping water that recharged in a previous ice age,” she said. “The time it takes water to go back to the aquifer is much longer than it takes to pump it. “
From a national security perspective, depleting water has serious implications, Wald said. “In Gaza, water is of the essence. They are using so much that in two years they won’t have any more.” Meanwhile the Ethiopian government has plans for a huge dam on the Nile, which will impact the countries downstream. “Water wars will be exacerbated.”
Even within the United States, water conflicts are becoming more serious, as states fight via the courts over water resources. States such as California grow a large portion of the nation’s food. “The California water problem is all of our problem. We’re in a crisis right now,” Stofan said.
Sullivan noted that a lot of water that could be used for drinking is simply wasted watering lawns — and it ends up being drained right to the ocean from treatment plants. On top of that, water is cheap, so there’s not much incentive to cut back use. And more efficient usage might be the only option. Desalination is energy intensive and generates waste.
“When you suck salt out of seawater, what you have left is thick brine,” Sullivan said. “That’s your waste product.”
The panelists generally were not optimistic that anything but a major crisis would change American habits. At the same time, they had hope that future engineers and scientists could help solve some of the problems. And space science, Hammel said, might be key to that.
“We once polled a bunch of engineers,” Hammel said. “They didn’t talk about desalination; they said what inspired them was space… Somewhere there’s a little girl who is interested in science and went to her local library. She didn’t get a book on desalination, she took out a book on black holes.”
Astronomers have detected an exoplanet’s visible-light spectrum directly for the first time ever, a milestone that could help bring many other alien worlds into clearer focus down the road.
The scientists used the HARPS instrument on the European Southern Observatory’s 3.6-meter telescope at the La Silla Observatory in Chile to study the spectrum of visible light reflected off the exoplanet 51 Pegasi b, which lies about 50 light-years from Earth in the constellation Pegasus. You can see a new video of 51 Pegasi b and its environs here on Space.com.
51 Pegasi b, a “hot Jupiter” gas giant that orbits close to its parent star, was spotted in 1995, when it became the first alien world ever discovered around a sunlike star.
Researchers most often study exoplanet atmospheres by analyzing the starlight that passes through them when worlds cross their stars’ faces from Earth’s perspective. This method, known as transit spectroscopy, is restricted to use on systems in which the stars and planets align.
The new strategy used with 51 Pegasi b, on the other hand, does not depend on planetary transits and could thus find broader applicability, researchers said.
The technique offers other scientific advantages as well.
“This type of detection technique is of great scientific importance, as it allows us to measure the planet’s real mass and orbital inclination, which is essential to more fully understand the system,” study lead author Jorge Martins, of the Instituto de Astrofísica e Ciências do Espaço (IA) and the Universidade do Porto in Portugal, said in a statement.
“It also allows us to estimate the planet’s reflectivity, or albedo, which can be used to infer the composition of both the planet’s surface and atmosphere,” Martins added.
The new data suggest that 51 Pegasi b is highly reflective, a bit larger in diameter than Jupiter and about half as massive as our solar system’s biggest planet, researchers said.
The new observations by HARPS (which is short for High Accuracy Radial velocity Planet Searcher) provide a vital proof of concept for the new technique, which could really come into its own when employed with instruments on bigger telescopes, such as the European Southern Observatory’s Very Large Telescope (VLT), researchers said.
“We are now eagerly awaiting first light of the ESPRESSO spectrograph on the VLT so that we can do more detailed studies of this and other planetary systems,” said co-author Nuno Santos, also of the IA and Universidade do Porto.
The new study was published today (April 22) in the journal Astronomy & Astrophysics.
This finding could help explain how Earth’s magnetic field has lasted for billions of years, researchers added.
Scientists think Earth formed at about the same time as the sun and the rest of the solar system about 4.6 billion years ago from a giant, rotating cloud of gas and dust. Earth and the other rocky planets coalesced from smaller asteroid-sized bodies that accreted or stuck together to form ever-larger chunks of rock.
The meteorites that crash into Earth are usually thought to represent the building blocks that the planet grew from. However, Earth’s crust and mantle puzzlingly have a higher proportion of the element samarium to the element neodymium than seen in most meteorites.
New experiments now suggest that the addition of a sulfur-rich Mercury-like body to the early Earth could explain this anomaly. This research could also help solve another mystery — how the Earth’s magnetic field has lasted for billions of years.
“A Mercury-like body added to Earth during accretion would solve two important problems — that is, kill two birds with one stone,” study co-author Bernard Wood, a geochemist at the University of Oxford in England, told Space.com.
Cooking up the Earth’s core
The researchers performed experiments with samples of material under conditions mimicking those at which Earth formed — temperatures between 2,550 and 3,000 degrees Fahrenheit (1,400 and 1,640 degrees Celsius) and pressures of 1.5 gigapascals. For comparison, 1 gigapascal is nearly 10 times greater than the pressure at the bottom of the Mariana Trench, the deepest part of the ocean.
The samples of material the scientists tested contained traces of elements such as samarium, neodymium, and uranium. These elements are normally chemically attracted to silicate rock, which makes up most of the Earth’s crust and mantle. They do not usually dissolve in iron sulfide, which makes up a significant fraction of Earth’s outer core.
The scientists found that if the early Earth incorporated a rocky body like Mercury, which is high in sulfur, this could make samarium and neodymium dissolve better in iron sulfide. This in turn would make samarium and neodymium more likely to sink down toward Earth’s core.
However, samarium is more attracted to silicate rock than neodymium is. This would have made samarium a bit less likely to sink downward, which could explain why there is a greater proportion of samarium to neodymium in Earth’s crust and mantle.
These experiments could also help solve a mystery concerning Earth’s magnetic field.
Prior research suggests that Earth has possessed a magnetic field for at least 3.5 billion years. Earth’s magnetic field results from churning metal in the planet’s outer core, but it was uncertain how Earth’s core could have remained molten for so long.
The new experiments revealed that if the early Earth engulfed a sulfur-rich Mercury-like body, uranium could have dissolved better in iron sulfide. This in turn would help uranium sink toward Earth’s core. Uranium is a radioactive element that generates heat, which could have kept Earth’s core molten.
Wood and study lead author Anke Wohlers at the University of Oxford detailed their findings in the April 15 edition of the journal Nature.
A telescope will soon allow astronomers to probe the atmosphere of Earthlike exoplanets for signs of life. To prepare, astronomer Lisa Kaltenegger and her team are modeling the atmospheric fingerprints for hundreds of potential alien worlds. Here’s how:
The James Webb Space Telescope, set to launch in 2018, will usher a new era in our search for life beyond Earth. With its 6.5-meter mirror, the long-awaited successor to Hubble will be large enough to detect potential biosignatures in the atmosphere of Earthlike planets orbiting nearby stars.
And we may soon find a treasure-trove of such worlds. The forthcoming exoplanet hunter TESS (Transiting Exoplanet Survey Satellite), set to launch in 2017, will scout the entire sky for planetary systems close to ours. (The current Kepler mission focuses on more distant stars, between 600 and 3,000 light-years from Earth.) [The Search for Another Earth (Video)]
While TESS will allow for the brief detection of new planets, the larger James Webb will follow up on select candidates and provide clues about their atmospheric composition. But the work will be difficult and require a lot of telescope time.
“We’re expecting to find thousands of new planets with TESS, so we’ll need to select our best targets for follow-up study with the Webb telescope,” says Lisa Kaltenegger, an astronomer at Cornell University and co-investigator on the TESS team.
To prepare, Kaltenegger and her team at Cornell’s Institute for Pale Blue Dots are building a database of atmospheric fingerprints for hundreds of potential alien worlds. The models will then be used as “ID cards” to guide the study of exoplanet atmospheres with the Webb and other future large telescopes.
Kaltenegger described her approach in a talk for the NASA Astrobiology Institute’s Director Seminar Series last December.
“For the first time in human history, we have the technology to find and characterize other worlds,” she says. “And there’s a lot to learn.”
Detecting life from space
In its 1990 flyby of Earth, the Galileo spacecraft took a spectrum of sunlight filtered through our planet’s atmosphere. In a 1993paper in the journal Nature, astronomer Carl Sagan analyzed that data and found a large amount of oxygen together with methane — a telltale sign of life on Earth. These observations established a control experiment for the search of extraterrestrial life by modern spacecraft.
“The spectrum of a planet is like a chemical fingerprint,” Kaltenegger says. “This gives us the key to explore alien worlds light years away.”
Current telescopes have picked up the spectra of giant, Jupiter-like exoplanets. But the telescopes are not large enough to do so for smaller, Earth-like worlds. The James Webb telescope will be our first shot at studying the atmospheres of these potentially habitable worlds.
Some forthcoming ground-based telescopes — including the Giant Magellan Telescope (GMT), planned for completion in 2020, and the European Extremely Large Telescope (E-ELT), scheduled for first light in 2024 — may also be able to contribute to that task. [The Largest Telescopes on Earth: How They Compare]
And with the expected discovery by TESS of thousands of nearby exoplanets, the James Webb and other large telescopes will have plenty of potential targets to study. Another forthcoming planet hunter, the Planetary Transits and Oscillations of stars (PLATO), a planned European Space Agency mission scheduled for launch around 2022-2024, will contribute even more candidates.
However, observation time for follow-up studies will be costly and limited.
“It will take hundreds of hours of observation to see atmospheric signatures with the Webb telescope,” Kaltenegger says. “So we’ll have to pick our targets carefully.”
Getting a head start
To guide that process, Kaltenegger and her team are putting together a database of atmospheric fingerprints of potential alien worlds. “The models are tools that can teach us how to observe and help us prioritize targets,” she says.
To start, they have modeled the chemical fingerprint of Earth over geological time. Our planet’s atmosphere has evolved over time, with different life forms producing and consuming various gases. These models may give astronomers some insight into a planet’s evolutionary stage.
Other models take into consideration the effects of a host of factors on the chemical signatures — including water, clouds, atmospheric thickness, geological cycles, brightness of the parent star, and even the presence of different extremophiles.
“It’s important to do this wide range of modeling right now,” Kaltenegger said, “so we’re not too startled if we detect something unexpected. A wide parameter space can allow us to figure out if we might have a combination of these environments.”
She added: “It can also help us refine our modeling as fast as possible, and decide if more measurements are needed while the telescope is still in space. It’s basically a stepping-stone, so we don’t have to wait until we get our first measurements to understand what we are seeing. Still, we’ll likely find things we never thought about in the first place.”
A new research center
The spectral database is one of the main projects undertaken at the Institute for Pale Blue Dots, a new interdisciplinary research center founded in 2014 by Kaltenegger. The official inauguration will be held on May 9, 2015.
“The crux of the institute is the characterization of rocky, Earth-like planets in the habitable zone of nearby stars,” Kaltenergger said. “It’s a very interdisciplinary effort with people from astronomy, geology, atmospheric modeling, and hopefully biology.”
She added: “One of the goal is to better understand what makes a planet a life-friendly habitat, and how we can detect that from light years away. We’re on the verge of discovering other pale blue dots. And with Sagan’s legacy, Cornell University is a really great home for an institute like that.”
A new study sheds light on how exoplanets in tightly-packed solar systems interact with each other gravitationally by affecting one another’s climates and their abilities to support alien life.
Because the exoplanets are so close to one another in these compact solar systems, they have tidal influence, much like the Earth and the moon have on each other. The tides modify the spin rates, axial tilts and orbits of these planets over time, and therefore alter their climates.
The study examines two exo-solar systems — Kepler-62 and Kepler-186 — that have made headlines for hosting worlds orbiting in the “habitable zone,” the potentially life-friendly band where water can remain liquid on a planetary surface. The findings show that tidal evolution can profoundly impact a world’s climate
“We wanted to investigate the question of the influence of tidal dynamics on the climate of ‘habitable’ planets,” said lead author Emeline Bolmont, a post-doctoral research scientist at the University of Bordeaux in France at the time when the research was conducted, and now at the University of Namur in Belgium.
The findings can help astrobiologists understand how habitability is affected by the complex gravitational interplay of neighboring planets. The paper were published in March 2015 in the book “Complex Planetary Systems (IAU S310),” a publication of the International Astronomical Union (IAU).
Almost half of the 1,100-plus exoplanetary systems now known contain multiple planets in the manner of our solar system. Because our ability to discover exoplanets is still at an early stage, our instruments are biased towards detecting planets that closely orbit their host stars. As a result, many of these multi-planet systems we know of look like scrunched-up versions of our solar system. These compact solar systems often have several planets whirling around in orbits within the same distance as Mercury is to the sun.
The proximity of these planets causes them to exert tidal influences on each other, modifying their rotations and axial tilts. The moon’s gravity has similarly acted like a brake on Earth’s rotation, slowing it from a primordial six hour day to the just-shy of the 24 hours we set our clocks to in modern times. The moon’s stabilizing mass also helps maintain Earth’s axial tilt of 23.44 degrees, which gives us our seasons and moderates the planet’s overall temperature, much to life’s benefit.
In the solar systems Kepler-62 and Kepler-186, tidal effects from their various planets and host stars similarly impact the planets’ rotation and axial tilt. The general effect is slowed-down planetary spin rates, as well as axial tilts that are regularized in such a way as to spin perpendicular to the plane of their orbits (they have zero axial tilt). The new study evaluated how the gravity of closely interacting exoplanets might modify these two climate-determining parameters over billions of years. The study also briefly assessed the bigger-picture factors of planets’ orbital shapes and distances to see how stable these would remain in compact multi-planet solar systems. Both variables, of course, have a fundamental impact on a planet’s climatic characteristics.
“The presence of liquid water on a planet’s surface depends on many different parameters, some of which are the orbital distance, the shape of the orbit, the direction of the rotation axis of the planet and the rotation period of the planet,” said Bolmont. “All these quantities are influenced by dynamics and in particular by tidal dynamics.”
The study ran computer simulations of the Kepler-62 and Kepler-186 solar systems using to the best data available. Each system’s star is a red dwarf, which is smaller and dimmer than the sun, and hosts at least five planets. The exoplanets Kepler-62e and Kepler-62f, both super-Earths, orbit in the habitable zone. Kepler-186f, meanwhile, is the first approximately Earth-sized exoplanet discovered in a habitable zone. It is therefore widely considered among the best candidates yet spotted for harboring extraterrestrial life.
The computer simulations focused on how the gravitational push-and-pull of the overall system affected these three exoplanets of interest. For the masses of the exoplanets in their models — which determines the planets’ gravitational attraction — Bolmont and her colleagues assumed Earth-like compositions for all five Kepler-62 worlds. For the Kepler-186 system, the researchers played with the compositions to get different masses to see what would happen. The compositions ranged from pure, low-density ice to pure, high-density iron (higher density packs in more mass to the same volume). [Exoplanet Quiz: Test Your Alien Planet Smarts]
An innovative aspect to the computer simulations is a new code developed by Bolmont and colleagues. The code calculates the gravitational interactions between the stars and the planets in Kepler-62 and Kepler-168, computing the resulting orbital evolution of the planets.
The code is more sophisticated physics-wise than those that have powered prior simulations. It adds to the key tidal effects previously discussed, as well as rotational flattening (spinning bodies bulge at their centers, influencing their orbital evolution) and even Einstein’s general relativity, a more accurate description of gravitation than simple Copernican physics, often used in similar simulations.
“We try to take into account the most important dynamical processes for the evolution of a system,” said Bolmont.
The code will be publicly released soon so other scientists can run simulations and tinker with it.
The Bolmont simulations showed that tidal effects in general can help make compact, multi-planet solar systems more stable. The gravitational interplay in simpler runs of the model, without the added-in, relevant physics, worked in setting planets on wild orbits. The system would destabilize, with planets colliding or getting flung right out of the solar system. A destabilization scenario would almost surely be lethal for whatever life might have gotten going in tight, multi-planet systems.
But the addition of tidal effects and the other physics previously mentioned kept the worlds snugly in their respective orbital lanes, at least for the simulation’s duration. The additional gravitational checks and balances help preserve a solar system, it would appear.
That’s a good sign for life if compressed multi-planet systems can remain together for long periods. Life took several hundred million years to develop on Earth, and a few billion to develop complexity.
Individually, the axial tilts and spin rates of Kepler-62e and Kepler-62f did evolve considerably, and in varying ways, over the course of seven billion years.
“We found that Kepler-62e and f are likely to have different climates,” said Bolmont,
Kepler-62e, according to the simulation, is likely to have a very small axial tilt, thanks to the braking as well as accelerative effects from the other planets in its solar system. Lacking much tilt, Kepler-62e would not experience seasons and its poles would be quite cold. Earth, with its seasons, has cold poles too, of course, when compared to its hot equatorial regions. But the difference in temperature on Kepler-62e between its equator and poles would be far more pronounced.
The exoplanet’s rotation would possibly slow to a day-length equivalent of 125 or so Earth days. A planet’s rotation also contributes to moderating its surface temperatures, like a roast turned on a spit, such that one portion of the meat does not singe black while the rest is merely warmed. In the case of Kepler-62e, with its very slow turning, the side of the planet facing its star heats up considerably more than the night side, plunged into darkness for a third of an Earth-year.
Kepler-62f, on the other hand, is located farther out in the exo-solar system than planet ‘e.’ The gravitational perturbation from the star and inner planets would not be as strong in the outer reaches. Even after seven billion years, Kepler-62f would not have had its axial tilt abolished by the solar system’s other bodies. Kepler-62f should therefore still have an axial tilt, and thus seasons, and a day length perhaps broadly similar to Earth’s.
“Kepler-62f is located farther and wouldn’t have had time to tidally evolve,” said Bolmont.
The case for Kepler-186f is less clear-cut. We know the age of the Kepler-62 solar system, but do not know it yet for Kepler-186. That data is important because the tidal evolution dynamics require long time scales to bring about significant changes in a planet’s parameters. By making some assumptions, though, the Kepler-186 system model can still offer insight.
Assuming that the whole system is older than four billion years, as a separate recent study has suggested, then the four innermost planets in Kepler-186, being located so close to their star, will likely have had any axial tilt to be erased. In the case of Kepler-186f, the outermost planet and the one of interest in its potential habitability, an old solar system would mean it, too, has little to no axial tilt and a day-length of approximately 125 Earth-days.
If the Kepler-186 system is less than a billion years, Kepler-186f might still have a high axial tilt and a fast spin rate, more like Earth’s. The axial tilt might be so high, the models showed, on the order of 80 degrees, that the planet could be spinning on its “side,” as it were, like Uranus in our solar system. (Uranus is thought to have been knocked on its side by a collision at some point in its planetary lifetime. The world is too isolated for the Sun or other planets to tidally “right” the planet back up.) Under that scenario, Kepler-186f would develop a very cold hemisphere that is pointed away from the star, and a possibly too-warm hemisphere facing the star.
Given the holes in the data, the jury is very much still out on how much Kepler-186f’s evolution is tidally influenced.
“We don’t have enough data, such as the age of the system,” said Bolmont.
The overall takeaway from the study is that planets can indeed gravitationally influence each other in compact solar systems in ways that heavily influence climate and therefore habitability. Much more work needs to be done in this area, said Bolmont, to better learn how orbital shapes and distances change over time.
“These are still open questions,” said Bolmont. “There is a lot of diversity in the orbits of the habitable zone planets, and thus in the climate of habitable worlds.”
Scientists searching for signs of intelligent extraterrestrial life in the universe have a new telescope tool to aid them in their hunt for potential alien civilizations.
Called NIROSETI, short for Near-Infrared Optical Search for Extraterrestrial Intelligence, the instrument saw its “first light” this month at the University of California’s Lick Observatory atop Mt. Hamilton east of San Jose. It is built to record levels of light over time so that patterns can be analyzed for potential signals of alien life.
For more than five decades, scientists have been on the lookout for radio signals from other starfolk. But instruments capable of capturing pulses of infrared light have only recently become available. The NIROSETI instrument is attached to the Lick Observatory’s Nickel 1-meter telescope, with months of fine-tuning to follow its first-light observation on March 15
Shelley Wright, an Assistant Professor of Physics at the University of California, San Diego, led the development of NIROSETI while at the University of Toronto’s Dunlap Institute for Astronomy & Astrophysics.
Infrared light penetrates farther through gas and dust than visible light. So this new search will extend to stars thousands rather than merely hundreds of light-years away.
NIROSETI could uncover new information about the physical universe as well – as well as help shape an answer to some big questions: Are we alone? Just how crowded is it out there?
The group making the NIROSETI campaign possible also includes SETI pioneer Frank Drake of the SETI Institute and UC Santa Cruz who serves as a senior advisor to both past and future projects and is an active observer at the telescope.
Regarding use of NIROSETI there is one downside, according to Drake.
“The extraterrestrials would need to be transmitting their signals in our direction,” Drake said in a UC San Diego statement, although he sees a positive side to that limitation. “If we get a signal from someone who’s aiming for us, it could mean there’s altruism in the universe. I like that idea. If they want to be friendly, that’s who we will find.”
Funding for the project comes from the financial support of Bill and Susan Bloomfield.
Astronomers have spotted a fourth star in a planetary system called 30 Ari, bringing the number of known planet-harboring quadruple-sun systems to two. Numerous two- and three-star exoplanets have been identified.
“Star systems come in myriad forms. There can be single stars, binary stars, triple stars, even quintuple star systems,” study lead author Lewis Roberts, of NASA’s Jet Propulsion Laboratory in Pasadena, California, said in a statement. “It’s amazing the way nature puts these things together.”
30 Ari lies 136 light-years from the sun in the constellation Aries. Astronomers discovered a giant planet in the system in 2009; the world is about 10 times more massive than Jupiter and orbits its primary star every 335 days. A second pair of stars lies approximately 1,670 astronomical units (AU) away. (1 AU is the distance between Earth and the sun — about 93 million miles, or 150 million kilometers).
Roberts and his colleagues used the new “Robo-AO” adaptive optics system at the Palomar Observatoryin California to sweep the sky, examining hundreds of stars each evening for signs of multiplicity. This search identified a fourth star in close proximity to 30 Ari’s primary star.
The newfound star circles its companion once every 80 years, at a distance of just 22 AU, but it does not appear to affect the exoplanet’s orbit despite such proximity. This is a surprising result that will require further observations to understand, researchers said.
To a hypothetical observer cruising through the giant planet’s atmosphere, the sky would appear to host one small sun and two bright stars visible in daylight. With a large enough telescope, one of the bright stars could be resolved into a binary pair.
The discovery marks just the second time a planet has been identified in a four-star system. The first four-star planet, PH1b or Kepler-64b, was spotted in 2012 by citizen scientistsusing publicly available data from NASA’s Kepler mission.
Planets with multiple suns have become less of a novelty in recent years, as astronomers have found a number of real worlds that resemble Tatooine, Luke Skywalker’s home planet in the Star Warsfilms.
Indeed, binary stars are more commonthan their singleton counterparts. And the new study suggests that more planetary systems with two pairs of binary stars may be discovered down the road.
“About four percent of solar-type stars are in quadruple systems, which is up from previous estimates because observational techniques are steadily improving,” co-author Andrei Tokovinin, of the Cerro Tololo Inter-American Observatory in Chile, said in the same statement.
In addition to finding a fourth star around 30 Ari, the team also found a third star in a planetary system previously thought to have only two suns.
This system, known as HD 2638, was already known to host a planet with half the mass of Jupiter rushing around its primary star once every 3.4 days, while a second star lies about 44,000 AU, or 0.7 light-years, away. The newly discovered third star sits just 28 AU from the primary star, and it appears to have influenced the orbit of the gaseous planet, researchers said.
The more scientists learn about Mars, the more intriguing the Red Planet becomes as a potential haven for primitive life in the ancient past … and perhaps even the present.
A study released today (March 23) reports that ancient Mars harbored a form of nitrogen that could potentially have been used by microbes, if any existed, to build key molecules such as amino acids. An unrelated study suggests that atmospheric carbon monoxide has been a feasible energy source for microbes throughout the Red Planet’s history. Both papers were published today in the journal Proceedings of the National Academy of Sciences (PNAS).
“It’s more support for this environment that would have had the ingredients that life would have needed,” said Jennifer Stern of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, lead author of the nitrogen study. [The Search for Life on Mars: A Photo Timeline]
All life on Earth requires nitrogen, which is a critical component of amino acids and other biomolecules. But microbes can’t just pull their nitrogen straight out of the air; atmospheric, or molecular, nitrogen (N2) features two atoms of the stuff linked in a tight triple bond, making it relatively inert and inaccessible.
Before life-forms can incorporate nitrogen into their metabolic processes, that bond must be broken; nitrogen must be “fixed” into different, more chemically reactive compounds, such as nitrate (NO3).
That process did indeed occur on Mars, Stern and her team reported in their study, which looked at measurements made by the Sample Analysis at Mars (SAM) instrument aboard NASA’s Mars rover Curiosity.
SAM found significant concentrations of nitrate in soil and rock samples that Curiosity collected at three different spots near its landing site — Rocknest, John Klein and Cumberland.
The John Klein and Cumberland samples, which were drilled from a sedimentary mudstone, had previously allowed rover team members to conclude that, billions of years ago, the area was part of a potentially life-supporting lake-and-stream system. The discovery of fixed nitrogen contributes to this habitability picture.
“Had life been there, it would have been able to use this nitrogen,” Stern told Space.com.
While much of the nitrogen fixation on Earth is biological, Curiosity’s discovery isn’t evidence of Martian life. Nitrogen-nitrogen bonds can also be broken by the thermal shocks caused by lightning and asteroid or comet impacts.
Indeed, the Red Planet’s fixed nitrogen may have been generated primarily by the numerous powerful impacts that occurred (on Mars and other bodies in the inner solar system) about 4 billion years ago, during a period known as the Late Heavy Bombardment, Stern said.
But nitrogen may get fixed on modern Mars as well. In 2005, Europe’s Mars Express orbiter detected nitrogen oxide (NO) high in the Red Planet’s atmosphere. It likely formed after sunlight split apart oxygen, carbon dioxide and molecular nitrogen, Stern and her co-authors said.
“This suggests that N is currently being fixed in the Martian thermosphere, although it is unknown how much, if any, is transported to the lower atmosphere and surface,” the researchers wrote in their PNAS paper.
Curiosity hasn’t been able to get to the bottom of this question so far.
“Right now, our experiment is not targeted to get us a nitrate signal big enough to get, for example, any nitrogen isotope data,” Stern said. (Isotopes are versions of an element that contain different numbers of neutrons in their nuclei.)
“If you had a nitrogen isotope composition of the modern [Martian] atmosphere, which would be very different than the primordial atmosphere, that would tell us about whether it was being formed today or not,” she added. “So it would be great to be able to target an experiment where we could get enough of a signal in the instrument to get that data.”
Energy source for Martian life?
Life as we know it needs certain basic building chemical blocks (such as carbon and fixed nitrogen), liquid water and an energy source. In the other new PNAS paper, Gary King of Louisiana State University suggested that carbon monoxide (CO) could serve as an energy source on Mars, from ancient epochs all the way up to the present day.
While CO is toxic to many organisms, including humans, here on Earth, some microbes use it to drive their metabolism, gaining energy by oxidizing the substance into carbon dioxide (CO2).
Such life-forms are taking advantage of a relatively scarce resource, as Earth’s atmosphere is just 0.3 parts per million (ppm) or so CO by volume. The Martian atmosphere, in comparison, contains 800 ppm CO currently, and concentrations of the stuff may have been much higher in the past. Therefore, CO seems like a plausible candidate for an energy source for Mars life, but the possibility hasn’t drawn much scholarly attention, King wrote in the PNAS paper.
King set out to determine if Earth microbes could indeed utilize CO under conditions approximating those found on the modern Martian surface — low pressure, high CO2 concentrations (CO2 makes up 95 percent of the Red Planet’s atmosphere), low oxygen levels and low to moderate temperatures, among other characteristics.
King specifically targeted the conditions that might prevail at features known as recurring slope lineae (RSL), seasonal dark streaks that have been observed by NASA’s Mars Reconnaissance Orbiter in a number of locales. Some scientists think these streaks are caused by salty water at or near the Red Planet’s surface.
He found that soil samples collected in three different salty systems on Earth — the Big Island of Hawaii, Chile’s Atacama Desert and the Bonneville Salt Flats in Utah — did indeed take up CO under putative RSL conditions.
Other experiments, using the salt-loving (halophilic) microbes Alkalilimnicola ehrlichii MLHE-1 and Halorubrum str. BV1, demonstrated this capacity at the organismal level. A. ehrlichii MLHE-1, in fact, tolerated concentrations of the chemical perchlorate similar to those found in Martian soil.
“These results collectively establish the potential for microbial CO oxidation under conditions that might obtain at local scales (e.g., RSL) on contemporary Mars and at larger spatial scales earlier in Mars’ history,” King wrote in the new study.
King believes his results are also relevant to discussions of the human exploration of Mars. CO-oxidizing organisms such as A. ehrlichii MLHE-1 could be part of an effort to transform the Red Planet into a place more hospitable to humans, he said.
“In order to develop any kind of a soil system that could support anything complex, you would have to have a complex microbial community,” King told Space.com.
“You would need a variety of biosynthetic capabilities. You would need a variety of different elemental transformation capabilities — maybe nitrogen fixers,” he added. “These halophiles would be part of that.”