Supernovas, the most powerful stellar explosions in the universe, may result from catastrophic nuclear explosions on dead stars, new research shows. Scientists had long theorized that such nuclear events cause some supernovas, but now researchers finally have direct evidence.
A supernova shines brightly enough to briefly outshine all the stars in its galaxy, making it visible from halfway across the universe. Such explosions are rare, only occurring within each galaxy about every 100 years.
For decades, scientists theorized that about one-quarter of all supernovas, a kind known as type Ia supernovas, involved white dwarfs, the remains of stars that cram the mass of the sun into a much smaller volume. White dwarfs are incredibly dense; just a teaspoon of matter from a white dwarf would weigh 5 tons. This gives the stars intense gravitational fields.
Researchers have suggested that when a white dwarf has a companion star, the white dwarf’s gravitational pull can strip matter off the nearby star. This can result in too much extra material on the white dwarf, eventually destabilizing it and setting off a thermonuclear chain reaction that explosively obliterates the white dwarf. However, until now, astronomers did not have direct evidence for this idea.
To search for such evidence and learn more about how type Ia supernovas happen, scientists investigated the supernova SN 2014J, which occurred in January. The explosion happened in a nearby galaxy called M82, located about 11.4 million light-years from Earth.
Until now, type Ia supernovas had exploded too far away for astronomers to detect any gamma rays emitted by the explosions, which made it difficult to probe some of the supernovas’ fundamental properties. However, SN 2014J is the nearest type Ia supernova to Earth detected in at least four decades, and scientists managed to analyze gamma rays from between 50 and 100 days after the explosion occurred, using the European Space Agency satellite INTEGRAL.
Exploding white dwarfs should be full of nickel-56, an unstable isotope of the element. As nickel-56 decays, its byproducts give off specific wavelengths of gamma rays. INTEGRAL detected such radiation, with the levels hinting at an amount of nickel-56 equal to about 200,000 times the mass of the Earth. This is about what scientists expect would be involved with a type Ia supernova.
These findings offer evidence that SN 2014J and other type Ia supernovas do probably originate from thermonuclear explosions on white dwarfs.
This provides an unambiguous proof of the theoretical concept behind supernova type Ias,” said study lead author Eugene Churazov, an astrophysicist at the Max Planck Institute for Astrophysics in Garching, Germany.
However, astronomers have suggested another way type Ia supernovas can happen: when one white dwarf explosively collides with another. The researchers noted their findings cannot rule out the possibility of such a white-dwarf merger for SN 2014J. To confirm which mechanism actually caused SN 2014J, astronomers continue to gather data.
“The search for clues on the progenitor is underway in radio, optical and X-ray bands,” Churazov told Space.com.
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.
ANALYSIS: Supermassive Black Hole Jet Mystery Solved
For any given galaxy, it is estimated that a star will be destroyed by the central supermassive black hole approximately once every 10,000 years. The vast majority of known galaxies are thought to contain at least one supermassive black hole in their cores, having a dramatic effect on galactic and stellar evolution. [Images: Black Holes of the Universe]
As a star drifts too close to a supermassive black hole, intense tidal stresses rip the star to shreds. As this happens, the shredded material will be dragged into the black hole’s accretion disk — a hot disk of gas that is gradually pulled into the black hole’s event horizon, bulking up the black hole’s mass, or blasted as energetic jets from its poles.
Should there be a rapid injection of material — i.e. a star becoming blended and ingested into the accretion disk — powerful X-rays of a specific signature will be generated.
NEWS: Supermassive Black Holes are Not Doughnuts!
In a new study by the Moscow Institute of Physics and Technology and Space Research Institute of the Russian Academy of Sciences, astrophysicists trawled through observations from two space observatories to discover three likely occasions where stars have been eaten by supermassive black holes. Their work has been accepted for publication in the journal Monthly Notices of the Royal Astronomical Society.
Using data from the German ROSAT and European XMM-Newton space observatories, X-ray data from 1990 (to today) could be accessed and three events in different galaxies were positively identified — designated 1RXS J114727.1 + 494302, 1RXS J130547.2 + 641252 and 1RXS J235424.5-102053. Invaluable to this study was the long-duration observations by ROSAT (which operated from 1990 to 1999) and XMM-Newton (launched in 1999) that could detect the moment of stellar death, keeping track of the X-ray emissions over the years as the star’s material was gradually ingested.
NEWS: Intermediate Black Hole Implicated in Star’s Death
No more than two dozen other stellar death event candidates were seen in the observations, but positive identifications probably won’t be available until the launch of the multi-instrument Spectrum-X-Gamma space observatory in 2016.
This work has added some much needed detail to these rare events, indicating that (on average) one star every 30,000 years in any given galaxy will be destroyed by the central supermassive black hole, though the researchers caution that more observations of stars being eaten by supermassive black holes are needed.
Now, with new forensic data gathered by NASA telescopes, scientists say they have a better idea about what caused the star explosion in the nearby Messier 82 galaxy.
At 12 million light-years away, the Type Ia supernova first spotted on Jan. 21 was the closest to Earth in years. There are two primary explanations for how Type Ia supernovas are triggered: Either a small dense star core known as a white dwarf takes on too much mass from its companion star, or two white dwarfs merge. Both result in a spectacular explosion. But that first scenario should enshroud the white dwarf in a cloud of gas that produces a significant amount of X-rays after the explosion. The second would leave little or no X-rays behind.
A group of astronomers looked for an X-ray source around the supernova in Messier 82, also known as the Cigar Galaxy, using NASA’s Swift telescope and Chandra X-ray Observatory. But their search turned up quite empty. Compared with older data gathered around the region, there were no new X-rays present after the supernova.
“While it may sound a bit odd, we actually learned a great deal about this supernova by detecting absolutely nothing,” study leader Raffaella Margutti of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts, said in a statement from NASA. “Now we can essentially rule out that the explosion was caused by a white dwarf continuously pulling material from a companion star.”
Margutti and colleagues say more work is still needed to confirm how the supernova named SN 2014J was triggered.
Black holes do indeed come in three sizes: small, medium and extra large, a new study suggests.
Astronomers have studied many black holes at either size extreme — “stellar-mass” black holes, which are a few dozen times as weighty as the sun, and supermassive black holes, which can contain millions or billions of times the mass of the sun and lurk at the heart of most, if not all, galaxies.
Researchers have spotted hints of much rarer medium-size black holes, which harbor between 100 and several hundred thousand solar masses. But it’s tough to weigh these objects definitively — so tough that their existence has been a matter of debate.
But that debate can now be put to rest, says a research team that has measured an intermediate black hole’s mass with unprecedented precision. A black hole in the nearby galaxy M82 weighs in at 428 solar masses, give or take a hundred suns or so, they report today (Aug. 17) in the journal Nature.
“Objects in this range are the least expected of all black holes,” study co-author Richard Mushotzky, an astronomy professor at the University of Maryland, said in a statement. “Astronomers have been asking, ‘Do these objects exist, or do they not exist? What are their properties?’ Until now, we have not had the data to answer these questions.”
Patterns in the light
Black holes famously gobble up anything that gets too close, including light. But that doesn’t mean astronomers can’t see them; bright X-ray light streams from the superhot disk of material spiraling into a black hole’s mouth.
About 15 years ago, NASA’s Chandra X-ray Observatory spacecraft spotted such emissions coming from a source in the galaxy M82, which lies about 12 million light-years away from Earth. For a long time, Mushotzky and some other scientists suspected that the object, called M82 X-1, was a medium-size black hole. But those suspicions were tough to confirm.
“For reasons that are very hard to understand, these objects have resisted standard measurement techniques,” Mushotzky said.
In the new study, a team led by University of Maryland doctoral student Dheeraj Pasham took a closer look at M82 X-1. They studied observations made from 2004 to 2010 by NASA’s Rossi X-ray Timing Explorer (RXTE) satellite, which ceased operations in 2012.
The RXTE data revealed a pair of repeating oscillations in M82 X-1′s X-ray emissions. These oscillations occurred 5.1 times per second and 3.3 times per second, respectively — a ratio of three to two. This fact allowed the team to determine the black hole’s mass.
“In essence, [the] frequency of these 3:2 ratio oscillations scales inverse[ly] with black hole mass,” Pasham told Space.com via email. “Simply put, if the black hole is small, the orbital periods at the innermost circular orbit are shorter, but if the black hole is big, the orbital periods are longer (smaller frequencies).”
The researchers calculated M82 X-1′s mass at 428 suns, plus or minus 105 solar masses.
“In our opinion, and as the paper’s referees seem to agree, this is the most accurate mass measurement of an intermediate-mass black hole to date,” Pasham said.
Learning about black-hole growth
Confirming the existence of intermediate black holes could help researchers better understand the supermassive monsters at the cores of galaxies.
Such behemoths apparently first formed in the universe’s very early days, just a few hundred million years after the Big Bang. They could not have grown so big so fast if their “seeds” were small stellar-mass black holes (which result from the collapse of giant stars), Pasham said.
“Many theories, therefore, have suggested that these initial seed black holes had to have been a few 100 -1,000 times our sun,” he said. “But we did not have firm evidence for such intermediate-mass black holes.”
Stellar-mass black holes also often feature paired X-ray oscillations that occur in a 3:2 frequency ratio. Therefore, the new observations suggest that medium-size black holes may behave like scaled-up versions of stellar-mass black hole systems, Pasham added.
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.
The agency’s Nuclear Spectroscopic Telescope Arrayprobe, or NuSTAR, looked on as a mysterious X-ray source, called a corona, moved closer to a supermassive black hole. The black hole’s immense gravity pulled harder on the corona the closer it came, stretching and blurring the X-ray light in the process, researchers said.
“The corona recently collapsed in toward the black hole, with the result that the black hole’s intense gravity pulled all the light down onto its surrounding disk, where material is spiraling inward,” study lead author Michael Parker, of the Institute of Astronomy in Cambridge, England, said in a statement.
NuSTAR’s observations provide the most detailed look yet at such events, researchers said.
While light cannot escape once it passes the “event horizon” of a black hole, high-energy emissions do stream from the vicinity of these objects — from the corona, for example, and from the superhot disk of material spiraling into a black hole’s maw.
Astronomers think supermassive black holes — which can contain millions or billions of times the mass of the sun — reside at the cores of most, if not all, galaxies. The black hole observed by NuSTAR, called Markarian 335 (Mrk 335), is 10 million times more massive than the sun and lies 324 million light-years away, researchers said.
NASA’s Swift satellite recently observed a change in Mrk 335′s X-ray brightness, so scientists pointed NuSTAR at the supermassive black hole to take a closer look.
NuSTAR’s observations revealed that the black hole’s gravity pulled the coronal X-ray light onto the inner regions of Mrk 335′s accretion disk. Further study has shown that the corona remains close to the black hole, months after it originally moved inward. (This inward migration was rapid, occuring over a period of days rather than weeks or months, researchers said.)
The new study could shed light on the nature of black hole coronas and the extreme conditions near the cores of supermassive black holes, NASA officials said.
“We still don’t understand exactly how the corona is produced or why it changes its shape, but we see it lighting up material around the black hole, enabling us to study the regions so close in that effects described by Einstein’s theory of general relativity become prominent,” said co-author and NuSTAR principal investigator Fiona Harrison, of the California Institute of Technology in Pasadena.
“NuSTAR’s unprecedented capability for observing this and similar events allows us to study the most extreme light-bending effects of general relativity,” she added.
Black holes may have grown incredibly rapidly in the newborn universe, perhaps helping explain why they appear so early in cosmic history, researchers say.
Black holes possess gravitational pulls so powerful that not even light can escape their clutches. They are generally believed to form after massive stars die in gargantuan explosions known as supernovas, which crush the remaining cores into incredibly dense objects.
Supermassive black holes millions to billions of times the mass of the sun occur at the center of most, if not all, galaxies. Such monstrously large black holes have existed since the infancy of the universe, some 800 million years or so after the Big Bang. However, it remains a mystery how these giants could have grown so big in the relatively short amount of time they had to form. [Images: Black Holes of the Universe]
In modern black holes, features called accretion disks limit the speed of growth. These disks of gas and dust that swirl into black holes can prevent black holes from growing rapidly in two different ways, researchers say. First, as matter in an accretion disk gets close to a black hole, traffic jams occur that slow down any other infalling material. Second, as matter collides within these traffic jams, it heats up, generating energetic radiation that drives gas and dust away from the black hole.
“Black holes don’t actively suck in matter — they are not like vacuum cleaners,” said lead study author Tal Alexander, an astrophysicist at the Weizmann Institute of Science in Rehovot, Israel.
“A star or a gas stream can be on a stable orbit around a black hole, exactly as the Earth revolves around the sun, without falling into it,” Alexander told Space.com. “It is actually quite a challenge to think of efficient ways to drive gas into the black hole at a high enough rate that can lead to rapid growth.”
Alexander and his colleague Priyamvada Natarajan may have found a way in which early black holes could have grown to supermassive proportions — in part, by operating without the restrictions of accretion disks. The pair detailed their findings online today (Aug. 7) in the journal Science.
The scientists began with a model of a black hole 10 times the mass of the sun embedded in a cluster of thousands of stars. They fed the simulated black hole continuous flows of dense, cold, opaque gas.
“The early universe was much smaller and hence denser on average than it is today,” Alexander said.
This cold, dense gas would have obscured a substantial amount of the energetic radiation given off by matter falling into the black hole. In addition, the gravitational pull of the many stars around the black hole “causes it to zigzag randomly, and this erratic motion prevents the formation of a slowly draining accretion disk,” Alexander said. This means that matter falls into the black hole from all sides instead of getting forced into a disk around the black hole, from which it would swirl in far more slowly.
The “supra-exponential growth” observed in the model black hole suggests that a black hole 10 times the mass of the sun could have grown to more than 10 billion times the mass of the sun by just 1 billion years after the Big Bang, researchers said.
“This theoretical result shows a plausible route to the formation of supermassive black holes very soon after the Big Bang,” Alexander said.
Future research could examine whether supra-exponential growth of black holes could occur in modern times as well. The high-density and high-mass cold flows seen in the ancient universe may exist “for short times in unstable, dense, star-forming clusters, or in dense accretion disks around already-existing supermassive black holes,” Alexander said.
Because Pluto is so far away — it orbits the sun at an average distance of 3.65 billion miles (5.87 billion kilometers) — many questions about the dwarf planet’s composition and activity remain unanswered. Researchers hope New Horizons will lay some of those questions to rest when it flies by Pluto on July 15, 2015.
“Many predictions have been made by the science community, including possible rings, geyser eruptions, and even lakes,” Adriana Ocampo, program executive for NASA’s New Frontiers program, said in a statement. “Whatever we find, I believe Pluto and its satellites will surpass all our expectations and surprise us beyond our imagination.” [New Horizons' Flight to Pluto in Pictures]
Orbiting the sun once every 248 years, Pluto lies outside the reach of most visible instruments. The best images from NASA’s famous Hubble Space Telescope simply show Pluto’s spherical shape and reddish color. Changes in the dwarf planet’s color patterns over the years hint that something is happening there, but no one knows exactly what.
By late April 2015, New Horizons will be close enough to Pluto and its moons to capture pictures rivaling those of Hubble. On July 14, 2015, the craft will make a close flyby of the icy world, ultimately zooming within about 6,200 miles (10,000 kilometers) of its surface. If it cruised past Earth at that range, New Horizons would be able to recognize individual buildings and their shapes.
“Because Pluto has never been visited up-close by a spacecraft from Earth, everything we see will be a first,” Ocampo said. “I know this will be an astonishing experience full of history-making moments.”
New Horizons principal investigator Alan Stern, of the Southwest Research Institute in Colorado, likened the upcoming visit to the way Mariner 4revolutionized understanding of Marsin July 1965. At the time, many people thought the Red Planet was a life-friendly world possibly harboring liquid water and even plants. The New Horizons flyby could change perceptions of Pluto just as dramatically, Stern said.
The flight in won’t be without its challenges. Since New Horizons launched in 2006, two new moons have been discovered orbiting Pluto, upping the total known satellite countto five: Charon, Nix, Kerberos, Styxand Hydra. As many as 10 other moonscould still await detection in the system, one study suggested.
According to simulations, meteorites striking Pluto’s moons could send tiny rocks flying into space, where many of them would enter orbit around the dwarf planet. The debris field likely changes with time as it orbits, growing larger as new material is added. As the New Horizons probe gets closer and closer to Pluto, the mission team will need to keep watch on the system in case evasive maneuvers are required.
“The New Horizons team continues to do a magnificent job in keeping the spacecraft healthy and ready for this incredible rendezvous,” said Ocampo. “The spacecraft is in good hands.”
Asteroid and comet impacts can trigger widespread havoc, killing off life on a global scale. Now, one new study reveals that the molten wreckage of these explosions can entomb the remains of life that once dwelt in the blast zones and preserve them for millions of years, while another study hints that these impacts could even create novel habitats where life can flourish.
These findings suggest that impact craters on alien worlds might be good places to look for past and present signs of life, researchers say.
The blazing heat generated by cosmic impacts can heat, melt and even vaporize tons of soil and rock, some of which forms glass as it cools. Impact geologist Peter Schultz at Brown University in Providence, Rhode Island, has explored impact glasses in Argentina for more than 20 years. An area roughly the size of Texas in eastern Argentina (south of Buenos Aires) is littered with impact glass created by at least seven different impacts that occurred between 6,000 years ago and 9.2 million years ago. [5 Bold Claims of Alien Life]
“As we collected these glasses, we could see what appeared to be leaf-like materials trapped inside,” Schultz said.
He and his colleagues detailed their findings online April 15 in the journal Geology.
Plant material was seen in each impact. In two impacts in particular — one from 3 million years ago and the other from 9 million years ago — Schultz and his colleagues discovered centimeter-size leaf fragments, including structures such as papillae, tiny bumps that line leaf surfaces. Bundles of vein-like structures found in several samples are very similar to modern pampas grass, a species common to that region of Argentina.
“Impact glass may actually trap and preserve remnants of past life,” Schultz said.
The fragile plant matter in these glass samples was exquisitely preserved down to the cellular level. Moreover, the glasses at times also preserved organic compounds as well, including remnants of chlorophyll and related pigments.
To understand how this plant material could have survived the scorching conditions that created the impact glass, Schultz and his colleagues attempted to replicate those conditions in the lab. They mixed pulverized impact glass with fragments of pampas grass leaves, heated the mixtures at different temperatures for various amounts of time, and then quickly cooled them.
The experiments revealed that plant material was preserved when the samples were quickly heated to more than 2,730 degrees Fahrenheit (1,500 degrees Celsius). The water in the exterior layers of the leaves apparently protect the inner layers in a way similar to deep frying, in which the food on the outside dries quickly while the inside cooks more slowly.
This glass could yield insights on environmental conditions at the time of these impacts, shedding light on the climate and life of ancient Earth. In addition, if the wreckage of impacts can preserve signs of life on Earth, it may well do so on distant planets such as Mars. Coincidentally, the soil conditions in Argentina that helped preserve these plant samples are not unlike those found on Mars.
“Marsis covered by dust deposits more than 2 kilometers (1.2 miles) thick in some areas,” Schultz said. “In Argentina, similar deposits of loess [windblown sediment] are 200 to 300 meters (650 to 975 feet) thick.”
Impacts on such dust deposits not only have a chance of melting matter in a way that can preserve signs of Martian life that may have lived billions of years ago, but the dust deposits can also serve as a soft cushion to capture such entombed life.
“The strategy would be to find the right type of impact glass that would most likely have trapped materials inside,” Schultz said. [The Search for Life on Mars (A Photo Timeline)]
Schultz cautioned this work does not mean one should expect to find signs of plants on Mars. Rather, scientists might want to look for relics of microbes in Martian impact glass.
“The next step is to understand the limits of preservation, to understand the conditions of trapping better, and to establish criteria for looking for similar materials on Mars,” Schultz said. “I’m very hopeful we can answer these questions with enough time.”
Schultz cautioned that the findings only apply to impact glass that stayed on the planet it was created, not to rocks blasted into space, as might be the case with meteorites originating from Mars.
“These impact glasses are typically pretty fragile and would break up, whether once launched at high speeds into space … or once they hit the surface at high speeds,” he said. “So, there is little bearing of these findings on life being delivered to the Earth, as yet.”
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In another study, researchers discovered the first known trace fossils of microbes unearthed from within an impact crater. These findings suggest that cosmic impacts could generate novel habitats for life in their blast zones.
Haley Sapers, an astrobiologist at the Canadian Astrobiology Training Program at McGill University in Montreal and at Western University in London, Canada, examined nearly 120 samples of impact glass from Nördlinger Ries, a 15-mile-wide (24-kilometer-wide) crater located in Bavaria, Germany. The energy required to create a crater like Ries is estimated to equal the power generated by 1.8 million atomic bombs, enough to melt many cubic miles of rock at this location about 14.6 million years ago.
“Near the center of the crater, there is a little city called Nördlingen, a double-walled medieval city that is about one kilometer (0.6 miles) in diameter, about the size of the impactor that created the crater,” Sapers said.
Sapers and her colleagues discovered unusual tubular features just one to three microns wide in these glasses, or roughly one-hundredth to three-hundredths the average diameter of a human hair. These formed after the glasses did.
Some of these tubes were straight, while others were curvy, wavy or spiraled. The investigators noted conventional mineral-forming processes could not readily explain the shapes and distribution of these tubes. Instead, they suggest these were formed by microbes etching the glass with organic acids.
“I believe they were etching the rock to extract elements they needed for their metabolism, such as iron,” Sapers said. “They were also creating habitats that could be quite protective that other microbes might have lived in.”
Sapers and her colleagues detailed their findings online April 10 in the journal Geology. Sapers emphasized these findings are from Earth microbes that colonized rocks after the impact.
“These aren’t bugs from space — they didn’t come from the meteor,” Sapers said.
The researchers suggest cosmic impacts on Earth may have created areas friendly to the origin of life.
“It’s interesting that 4.2 billion to 3.8 billion years ago, the early Earth experienced a period known as the Late Heavy Bombardment where there were a lot of impacts, including large impacts, and this period also overlaps with the evidence of the earliest life on Earth,” Sapers said. “One might ask why life arose during such an inhospitable part of Earth’s history. Maybe impact cratering had a role in the origin of life.” [Fly Over Earth's Best-Preserved Crater (Video)]
Impacts on a water-rich planet like Earth or even Mars can generate hydrothermal activity — that is, underwater areas boiling with heat. Seafloor hot springs known as hydrothermal vents more than a mile beneath the ocean’s surface can be home to thriving ecosystems on Earth, including giant tube worms 6 feet (2 meters) tall. The impact that created the Ries crater may have generated hydrothermal activity lasting as long as 10,000 years, giving microbes time enough to colonize the area.
Impacts could provide an otherwise cold, dead planet with heat and energy useful for life, Sapers said.
“Impact events occur not only on Earth, but on pretty much every other rocky and icy object in the solar system,” she said. “As far as we know, they’re the only ubiquitous geological process in the solar system.”
By studying impacts on Earth, scientists might get a better view of how life elsewhere might originate and survive.
“When thinking about future missions to Mars, this could suggest that an impact crater with mineral deposits associated with hydrothermal activity could be a very exciting astrobiology target,” Sapers said.
An international team of astronomers has discovered an exoplanet in the star Gliese 832′s “habitable zone” — the just-right range of distances that could allow liquid water to exist on a world’s surface. The planet, known as Gliese 832c, lies just 16 light-years from Earth. (For perspective, the Milky Way galaxy is about 100,000 light-years wide; the closest star to Earth, Proxima Centauri, is 4.2 light-years away.)
Gliese 832c is a “super-Earth” at least five times as massive as our planet, and it zips around its host star every 36 days. But that host star is a red dwarf that’s much dimmer and cooler than our sun, so Gliese 832c receives about as much stellar energy as Earth does, despite orbiting much closer to its parent, researchers said. [10 Exoplanets That Could Host Alien Life]
Indeed, Gliese 832c is one of the three most Earth-like exoplanets yet discovered according to a commonly used metric, said Abel Mendez Torres, director of the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo.
“The Earth Similarity Index (ESI) of Gliese 832c (ESI = 0.81) is comparable to Gliese 667Cc (ESI = 0.84) and Kepler-62e (ESI = 0.83),” Mendez wrote in a blog post today (June 25). (A perfect “Earth twin” would have an ESI of 1.)
“This makes Gliese 832c one of the top three most Earth-like planets according to the ESI (i.e., with respect to Earth’s stellar flux and mass) and the closest one to Earth of all three — a prime object for follow-up observations,” he added.
A team led by Robert Wittenmyer, of the University of New South Wales in Australia, discovered Gliese 832c by noticing the tiny wobbles the planet’s gravity induces in the motion of its host star.
They spotted these wobbles in data gathered by three separate instruments — the University College London Echelle Spectrograph on the Anglo-Australian Telescope in Australia, the Carnegie Planet Finder Spectrograph on the Magellan II telescope in Chile and the High Accuracy Radial Velocity Planet Searcher (HARPS) spectrograph, which is part of the European Southern Observatory’s 11.8-foot (3.6 meters) telescope at the La Silla Observatory in Chile.
Gliese 832c is the second planet to be discovered around the star Gliese 832. The other one, Gliese 832b, was found in 2009; it’s a gas giant that circles much farther out, taking about nine years to complete one orbit.
“So far, the two planets of Gliese 832 are a scaled-down version of our own solar system, with an inner, potentially Earth-like planet and an outer, Jupiter-like giant planet,” Mendez wrote.
However, it’s unclear at the moment just how much Gliese 832c resembles Earth. Indeed, its discoverers think the newfound world may be more similar to scorching-hot Venus, with a thick atmosphere that has led to a runaway greenhouse effect.
“Given the large mass of the planet, it seems likely that it would possess a massive atmosphere, which may well render the planet inhospitable,” Wittenmyer and his team wrote in their paper, which has been accepted for publication in The Astrophysical Journal. “Indeed, it is perhaps more likely that GJ [Gliese] 832c is a ‘super-Venus,’ featuring significant greenhouse forcing.”
Huge Earth-like planets that have both continents and oceans may be better at harboring extraterrestrial life than those that are water-only worlds. A new study gives hope for the possibility that many super-Earth planets orbiting distant stars have exposed continents rather than just water-covered surfaces.
Super-Earths likely have more stable climates as compared to water worlds, and therefore larger habitable zones where alien life could thrive. In the new study, researchers used the Earth as a starting point for modeling how super-Earths might store their water on the surface and deep underground within the mantle. The work is detailed in a paper titled “Water Cycling Between Ocean and Mantle: Super-Earths Need Not Be Waterworlds” that was published in the January issue of The Astrophysical Journal.
Researchers typically expect super-Earths to exist as water worlds because their strong surface gravity creates relatively flattened surface geography and deep oceans. But the new study found that super-Earths with active tectonics can have exposed continents if their water is less than 0.2 percent of the total planetary mass. [The Strangest Alien Planets (Gallery)]
“A planet could be 10 times wetter than Earth and still have exposed continents,” said Nicolas Cowan, a planetary scientist at Northwestern University and co-author on the new paper. ”That’s important for what the planet looks like and how it ages.”
Cowan and Dorian Abbot, a climate scientist at the University of Chicago, built the model in the study. The model uses Earth as a starting point in defining how a planet’s water distribution could end up balanced in a steady state between the surface oceans and the mantle, which allows the researchers to calculate whether a super-Earth is likely to be a water world or not.
The movement of tectonic plates on Earth transfers water continuously between the surface oceans and the mantle. Ocean water enters the mantle as part of deep-sea rocks when one tectonic plate slides under another and goes down into the mantle.
“Earth is the only known planet with plate tectonics, a deep water cycle, etc., so it’s a good place to start,” Cowan said. “On the other hand, if it turns out that Earth’s deep water cycle is in nowhere near a steady-state, then our conclusions are way off the mark. “
Water in the mantle can re-enter the ocean when volcanic activity splits the planet’s crust at mid-ocean ridges. The loss of the crust causes a drop in pressure that leads the underlying mantle rock to melt and lose volatiles such as water. (An additional twist is that super-Earths with their stronger gravity could have greater seafloor pressure that suppresses the mantle’s loss of water, so that more of the planet’s overall water remains in the mantle.)
There are other uncertainties that could make a big difference in the model’s accuracy in predicting a super-Earth’s likelihood of having dry continents. One unknown is the amount of water hidden deep within Earth’s own mantle; Cowan and Abbot cite estimates of one to two oceans’ worth of water. Another factor is whether or not super-Earths have tectonic processes. If the researchers’ assumptions about either factor are wrong, that would change their model’s calculation of the “water world boundary,” which represents the mathematical model’s dividing point between water-worlds and worlds with dry continents.
Cowan and Abbot tried to compensate for the unknowns by drawing conservative conclusions with the results from their mathematical model. But even those conclusions suggest that super-Earths need not be water worlds.
“If some of our input parameters are wildly off, then the actual water world boundary might differ by an order of magnitude,” Cowan said. ”No matter how you cut it, though, the water world boundary is unlikely to be as damning as previously thought.”
The debate over super-Earths will continue until space missions begin collecting hard data on how much water exists on such planets. A space telescope with an interior coronagraph or exterior starshade could block the blinding light of distant stars to get a peek at orbiting planets. But no active space telescopes can currently do the necessary work of mapping the surface of super-Earths.
At the very least, you’d need a space telescope with a mirror a few meters wide, coupled to a starshade tens of thousands of kilometers away,” Cowan explained. “NASA is mooting this idea, but it is not the next priority.”
One space telescope that could fit the bill would be NASA’s Wide-Field Infrared Survey Telescope (WFIRST) — a planned 2.4-meter telescope with an instrument for imaging exoplanets. The $1.6 billion mission remains up in the air until NASA can squeeze it into the budget, but Cowan expects that WFIRST could get off the ground by the mid-2020s or 2030s. If so, that would bring researchers one step closer to understanding whether super-Earths truly work like our own world.
A NASA mission arriving in the Pluto system next year could help scientists figure out if the dwarf planet’s largest moon Charon might have once harbored a subsurface ocean of liquid water.
Researchers think it’s possible that the icy surface of Charon — Pluto’s largest moon — is cracked, which could, in turn, mean that its interior was once warm enough to support an ocean, NASA officials said. Two frigid moons with cracks, Saturn’s Enceladus and Jupiter’s Europa, have underground oceans beneath their icy shells. It’s possible that Charon resembled those two moons sometime in the past.
Charon probably cannot support a liquid ocean today. However, friction created by tidal forces earlier in the solar system’s history could have warmed Charon’s interior. NASA’s New Horizons mission, scheduled to reach Pluto and its moons in 2015, could help scientists learn if Charon was cracked and even wet in its early days.
“Our model predicts different fracture patterns on the surface of Charon depending on the thickness of its surface ice, the structure of the moon’s interior and how easily it deforms, and how its orbit evolved,” Alyssa Rhoden of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said in a statement. “By comparing the actual New Horizons observations of Charon to the various predictions, we can see what fits best and discover if Charon could have had a subsurface ocean in its past, driven by high eccentricity.”
At the moment, Charon is extremely cold like Pluto — the dwarf planet’s surface temperatures are expected to be around minus 380 degrees Fahrenheit (minus 229 degrees Celsius).
Scientists think that the tidal forces that warmed the interior of the moon could have been created if Charon had a very eccentric orbit sometime in the past. The forces would have caused telltale cracks in the moon’s surface.
Charon probably formed after a huge impact blasted pieces of Pluto off into space. Those pieces orbited Pluto, eventually coalescing into the moons, NASA officials said. At the moment, scientists have discovered four other moons orbiting the dwarf planet.
“Initially, there would have been strong tides on both worlds as gravity between Pluto and Charon caused their surfaces to bulge toward each other, generating friction in their interiors,” NASA officials said in a statement. “This friction would have also caused the tides to slightly lag behind their orbital positions. The lag would act like a brake on Pluto, causing its rotation to slow while transferring that rotational energy to Charon, making it speed up and move farther away from Pluto.”
The moon’s orbit around Pluto is very circular now, making it unlikely that Charon is still harboring a liquid ocean, Rhoden said. If Charon does have fractures — surface features that are relatively easy to get, according to Rhoden — it would help scientists learn a little more about the early history of the moon and Pluto’s interactions with it.
“Since it’s so easy to get fractures, if we get to Charon and there are none, it puts a very strong constraint on how high the eccentricity could have been and how warm the interior ever could have been,” Rhoden said. “This research gives us a head start on the New Horizons arrival — what should we look for and what can we learn from it. We’re going to Pluto and Pluto is fascinating, but Charon is also going to be fascinating.”
In 1975, physicist Kip Thorne and astronomer Anna Zytkow proposed the existence of odd objects that are hybrids between red supergiants and neutron stars — the collapsed, superdense remnants of supernova explosions.
These so-called Thorne-Zytkow objects (TZOs) likely form when a red supergiant gobbles up a nearby neutron star, which sinks down into the giant’s core, researchers said. TZOs look like ordinary red supergiants, like the famed star Betelgeuse in the constellation Orion, but differ in their chemical fingerprints, the theory goes.
“Studying these objects is exciting because it represents a completely new model of how stellar interiors can work,” study leader Emily Levesque, of the University of Colorado Boulder, said in a statement.
“In these interiors we also have a new way of producing heavy elements in our universe,” she added. “You’ve heard that everything is made of ‘star stuff’ — inside these stars we might now have a new way to make some of it.”
And now Levesque and her team say they have probably found the first TZO — a star called HV 2112 in the Small Magellanic Cloud, a dwarf galaxy that lies about 200,000 light-years away.
The researchers used the 6.5-meter Magellan Clay telescope in Chile to study the light emitted by HV 2112. They found the starlight to be highly enriched in rubidium, lithium and molybdenum, just as theory predicts for TZOs. (Normal red supergiants produce these elements as well, but not in such abundance, scientists said.)
The new data, while suggestive, do not represent a slam-dunk discovery for TZOs quite yet, researchers said.
“We could, of course, be wrong,” co-author Philip Massey, of Lowell Observatory in Flagstaff, Arizona, said in a statement.
“There are some minor inconsistencies between some of the details of what we found and what theory predicts,” he added. “But the theoretical predictions are quite old, and there have been a lot of improvements in the theory since then. Hopefully our discovery will spur additional work on the theoretical side now.”
The find means a lot to Zytkow, who is a co-author of the new study.
“I am extremely happy that observational confirmation of our theoretical prediction has started to emerge,” said Zytkow, who is based at the University of Cambridge in England. “Since Kip Thorne and I proposed our models of stars with neutron cores, people were not able to disprove our work. If theory is sound, experimental confirmation shows up sooner or later. So it was a matter of identification of a promising group of stars, getting telescope time and proceeding with the project.”
The newfound exoplanet candidate Kapteyn b, which lies a mere 13 light-years away, is about 11.5 billion years old, scientists say. That makes it 2.5 times older than Earth, and just 2 billion years or so younger than the universe itself, which burst into existence with the Big Bang 13.8 billion years ago.
“It does make you wonder what kind of life could have evolved on those planets over such a long time,” study lead author Guillem Anglada-Escude, of Queen Mary University of London, said in a statement. [10 Exoplanets That Could Host Alien Life]
Anglada-Escude was referring to Kapteyn b and its newly discovered sister world, Kapteyn c, which both orbit a nearby red dwarf known as Kapteyn’s Star. But only Kapteyn b, a “super-Earth” about five times as massive as our own planet, is thought to be potentially habitable; the larger Kapteyn c is likely too cold, researchers said.
The astronomers spotted both alien planets by noting the tiny wobbles their gravitational tugs induced in the motion of Kapteyn’s Star. These tugs caused shifts in the star’s light, which were first detected using the HARPS spectrometer at the European Southern Observatory’s La Silla Observatory in Chile. Further observations by two other spectrometers — HIRES at the Keck Observatory in Hawaii and the PFS instrument at Chile’s Magellan II Telescope — backed up the finds.
The team didn’t expect to find a possibly habitable world around Kapteyn’s Star, which is one-third as massive as the sun but so close to Earth that it’s visible in amateur telescopes, in the southern constellation of Pictor.
“We were surprised to find planets orbiting Kapteyn’s Star,” Anglada-Escude said. “Previous data showed some moderate excess of variability, so we were looking for very short-period planets when the new signals showed up loud and clear.”
Kapteyn b lies in the star’s habitable zone, the range of distances that could support liquid water — and thus, perhaps, life as we know it — on a world’s surface. The exoplanet completes one orbit every 48 days. The colder Kapteyn c is much farther out, circling the star once every 121 days.
Adding to the intrigue is the strange history of the Kapteyn system. The star originally belonged to a dwarf galaxy that our own Milky Way eventually absorbed and disrupted, researchers said, throwing Kapteyn and its planets into their speedy, elliptical orbit in the galactic “halo” — the region surrouding the Milky Way’s familiar spiral-armed disk.
The remnant of this gobbled-up dwarf galaxy is likely Omega Centauri, a globular cluster about 16,000 light-years away that contains many thousands of stars that are around 11.5 billion years old, researchers said.
“The presence and long-term survival of a planetary system seems a remarkable feat given the peculiar origin and kinematic history of Kapteyn’s star,” the researchers write in the new study, which will be published in the Monthly Notices of the Royal Astronomical Society. “The detection of super-Earth mass planets around halo stars provides important insights into planet-formation processes in the early days of the Milky Way.”
The new discovery is an exciting one that could inform the search for alien life throughout the galaxy, outside researchers said.
It suggests that many potentially habitable worlds will be found in the next years around nearby stars by ground-based and space-based observatories such as ESA’s PLATO mission,” said Richard Nelson of Queen Mary University of London, who was not a part of the study team. “Until we have detected a larger number of them, the properties and possible habitability of the near-most planetary systems will remain mysterious.”