If Pluto’s subsurface ocean had frozen over completely, it would have formed highly pressurized ice that would have caused the dwarf planet to shrink, according to new research. The canyons and valleys on Pluto seem to have formed as the dwarf planet swelled up, rather than as it shrank, indicating that a liquid ocean most likely sits beneath the thick ice crust today, researchers said in the study.
“Thanks to the incredible data returned by [NASA's New Horizons mission], we were able to observe tectonic features on Pluto’s surface [and] update our thermal evolution model with new data,” Noah Hammond, a graduate student at Brown University, said in a statement from the school. Hammond worked with his advisers — Amy Barr, of the Planetary Science Institute, and Marc Parmentier, also at Brown — to study the likelihood that a liquid ocean hides beneath Pluto’s .
When the New Horizons probe flew past Pluto last July, its images of the dwarf planet’s surface revealed deep faults, or fractures in the surface, hundreds of kilometers long, according to the statement from Brown. The long canyons appeared to form as Pluto’s crust expanded, Hammond said. “A subsurface ocean that was slowly freezing over would cause this kind of expansion,” he said.
It didn’t take long for scientists to conclude that Pluto once housed an ocean, but the question of whether it had already frozen over remained. Using updated measurements of Pluto’s diameter and density, Hammond’s model revealed that a frozen ocean beneath the crust would have changed from conventional water ice to a more compact, crystallized structure known as “ice II.” As the ice changed, the frozen ocean would have shrunk, creating an entirely different type of feature known as compressional fractures, which are not seen on Pluto’s surface.
“We don’t see the things on the surface we’d expect if there had been a global contraction,” Hammond said. “So we conclude that ice II has not formed, and therefore that the ocean hasn’t completely frozen.”
Ice II would have formed only if the dwarf planet’s outer shell were at least 160 miles (260 kilometers) thick, putting sufficient pressure on the underlying ice, the statement said. Under the thinner shell, the ocean could have remained regular ice, not shrinking at all.
Hammond’s model suggests that the shell might be closer to 190 miles (300 km) thick, thanks to high temperatures in the core, according to the paper. The addition of nitrogen and methane ice spotted on the surface of the tiny world may also help keep the water warm.
“Those exotic ices are actually good insulators,” Hammond said.
That means oceans could lie not only inside tiny Pluto but also in other similar worlds in the far reaches of the Kuiper Belt, the sphere of ice and rock at the edge of the solar system.
“That’s amazing to me,” Hammond said. “The possibility that you could have vast liquid water ocean habitats so far from the sun on Pluto — and that the same could also be possible on other Kuiper Belt objects as well — is absolutely incredible.”
The research was published online on June 15 in the journal Geophysical Research Letters.
Researchers studied the properties of nearly 9,000 near-Earth objects (NEOs) — asteroids and other bodies that come within 1.3 Earth-sun distances of our planet — to build a model of the overall NEO population.
This model seemed to have a problem, however: It predicted that astronomers should be seeing 10 times more NEOs that closely approach the sun — come within 9 million miles (15 million kilometers) or so of the star — than they actually observe.
The research team spent a year puzzling over this outcome before coming to a surprising conclusion: The missing NEOs are actually being destroyed as they get close to the sun, but long before they actually dive into the star.
“The discovery that asteroids must be breaking up when they approach too close to the sun was surprising, and that’s why we spent so much time verifying our calculations,” study co-author Robert Jedicke, of the University of Hawaii Institute for Astronomy, said in a statement.
The team’s work should help scientists better understand the NEO population in a variety of ways. For example, many meteors that light up Earth’s night skies are pieces of debris shed by parent NEOs on their laps around the sun. Such debris clouds travel on the same orbits as their parent bodies, but astronomers generally have trouble finding these NEOs. The new study suggests that this is because the parent objects have already been destroyed, the researchers said.
In addition, study team members determined that darker NEOs die farther from the sun than brighter ones do, which helps explain something astronomers already knew: Asteroids that approach the sun closely tend to be quite bright.
This finding implies that dark and bright asteroids may differ significantly in structure and composition, the researchers said.
“Perhaps the most intriguing outcome of this study is that it is now possible to test models of asteroid interiors simply by keeping track of their orbits and sizes,” lead author Mikael Granvik, of the University of Helsinki in Finland, said in the same statement. “This is truly remarkable and was completely unexpected when we first started constructing the new NEO model.”
Granvik and his colleagues built their model by studying nearly 100,000 images of NEOs acquired by the Catalina Sky Survey in Arizona over an eight-year period.
To date, scientists have identified and tracked almost 14,000 NEOs, but the overall population is thought to number in the millions. Astronomers think that most of these bodies begin their lives in the main asteroid belt between Mars and Jupiter, and then veer inward after experiencing gravitational nudges by Jupiter and/or Saturn. The new study was published online today (Feb. 17) in the journal Nature.
Invisible “plasma lenses” shaped like noodles, lasagna sheets or hazelnuts might lurk between stars in the Milky Way, researchers say.
This finding could help solve the longstanding mystery of where a major part of the galaxy’s matter is hiding, the scientists added.
Astronomers first detected clues of these mysterious structures 30 years ago as they monitored quasarsquasars, the brightest objects in the universe. Quasars are the most energetic form of active galactic nuclei, which are supermassive black holes in the centers of distant galaxies that release extraordinarily large amounts of light as they rip apart stars and gobble matter
Previous research found that radio waves from quasars could vary wildly in strength, a phenomenon technically known as an extreme scattering event. Astronomers suggested these events were due to clouds of plasma — that is, electrically charged particles. These clouds are essentially lumps in the thin gas that fills the space between the stars in the Milky Way.
“Lumps in this gas work like lenses, focusing and defocusing the radio waves, making them appear to strengthen and weaken over a period of days, weeks or months,” study lead author Keith Bannister, an astronomer at the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Australia, said in a statement.
Previous research suggested these “plasma lenses” are huge — about 620 million miles (1 billion kilometers) wide, a distance nearly seven times the distance between Earth and the sun. Ones detected so far lie about 3,200 light-years away, nearly 800 times farther than the nearest star to Earth, Proxima Centauri.
Plasma lenses among the stars
Plasma lenses have been difficult to find, so much about them is a mystery. For instance, estimates suggested the pressures within these plasma lenses are about 1,000 times greater than the surrounding interstellar gas. It was uncertain how these structures could form and survive long enough for astronomers to detect as often as they have.
In addition, until now, scientists knew nothing about the shape of these plasma lenses. This made it difficult to figure out what these structures were or what their origins were.
Now astronomers have for the first time successfully detected a lensing event while it was happening. This helped them conduct follow-up analyses that permitted the first estimates of plasma lens shapes.
Researchers used the Australia Telescope Compact Array to scan about 1,000 active galactic nuclei for sudden changes in their radio waves. They detected a lensing event in 2014 that went on for a year in connection with the quasar PKS 1939-315, located in the constellation Sagittarius. Whereas old analyses of lensing events only monitored two radio frequencies, “our new method gave us 9,000 frequencies at once,” Bannister told Space.com. “It was like going from black-and-white TV to color.”
Based on their findings, the researchers suggest this plasma lens could neither be a spherical cloud nor a corrugated or bent sheet.
“We could be looking at a flat sheet, edge on,” study co-author Cormac Reynolds at CSIRO said in a statement. “Or we might be looking down the barrel of a hollow cylinder like a noodle, or at a spherical [hollow] shell like a hazelnut.”
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Detecting more of these plasma lenses could reveal their shapes, which could in turn shed light on their origins. Previous research suggested two potential origins for these plasma lenses. One involves plasma sheets, perhaps the remains of shock waves from supernovas, Bannister said. Another involves cold clouds pulled together by the force of their own gravity.
If the plasma lenses are shaped like sheets, they may be plasma sheets. If they are spherical hollow shells, then they may be cold clouds held together by their own gravity. If they are hollow tubes, they may be flux tubes, structures formed by magnetic fields in the interstellar medium, Bannister said.
If the plasma lenses are made up of cold clouds, that suggests that cold clouds must make up a substantial fraction of the Milky Way, Bannister said. If so, they could help solve the so-called “missing baryon problem.”
Normal matter is made up mostly of particles known as baryons, which include protons and neutrons found in the atoms making up planets, stars and galaxies. Normal matter only makes up about one-sixth of all matter in the universe, with the rest consisting of dark matter, a mysterious invisible substance detectable via its gravitational influence on normal matter.
However, even normal matter presents a puzzle, since theories of the formation and evolution of the universe predict there should be about two times more baryons than astronomers see. Cold clouds might help solve the missing baryon problem, but “proving that is still a long way off though,” Bannister said.
In the future, the Australian Square Kilometre Array Pathfinder (ASKAP) should find plasma lenses “in droves,” Bannister said. This may help solve the mystery of what these structures are, he noted.
The scientists detailed their findings in the Jan. 22 issue of the journal Science.
A previously unidentified highway of dust extends across the Milky Way, between the sun and the central bulge of the galaxy, scientists have found.
Called the “Great Dark Lane” by the astronomers who announced it, the dusty road twists in front of the bulge of the galaxy.
“For the first time, we could map this dust lane at large scales, because our new infrared maps cover the whole central region of the Milky Way,” Dante Minniti, a researcher at Universidad Andres Bello in Chile and lead author of a study describing the findings, told Space.com by email.
Mapping the Milky Way
The center of a spiral galaxy contains a collection of stars that bulge above and below the flatter spirals, much like an egg yolk. The arms that give the galaxies their classification twist around the bulge, often in a beautiful spiral (although sometimes they are more elongated). Lanes of dust often lie between these arms, which present a particular challenge to map out.
“It is very difficult to mapthe structure of our galaxy because we are inside, and it is very large and covered with dust clouds that are opaque in the optical,” Minniti said.
Working with a team of astronomers, Minniti used the European Space Observatory’s Vista Variables in the Via Lactea Survey (VVV), a project to scan the Milky Way using the VISTA telescope in Chile, to study the galaxy in the near-infrared. At this wavelength, telescopes are able to peer through the clouds of dust to a group of objects known as red clump (RC) stars lying within the bulge.
Red clump stars have helium-burning cores that generate a similar brightness no matter what their age or composition is. This makes them reliable distance indicators for astronomers.
Based on the measurement of 157 million stars, Minniti and his team found that the RC stars of the Milky Way’s bulgewere split into two colors — a difference they determined was caused by dust between the stars and the observers. The astronomers could see a sharp transition between the two distinct groups — the dusty Great Dark Lane dividing them.
The Great Dark Lane extends approximately 20 degrees across the sky, reaching both above and below the plane of the galaxy. It sits roughly 15,000 light-yearsfrom the solar system, although the team is still working to refine the distance. It lies outside of the bulge rather than being contained within it, they said.
If the dust passed through the bulge itself, the red clump stars of the center would have a patchier distribution, rather than a clean break, as some of the stars at a certain height above the plane would be in front of the dust and others would be behind it, the researchers said. Instead, all of the red clump stars contained within the bulge lie behind the dust, according to the study.
“Detailed maps and modeling are needed in order to test this important galactic feature,” the researchers wrote in their paper, which appeared in the journal Astronomy & Astrophysics last year.
When the monster back hole at the center of the Milky Way galaxy belched out an exceptionally high number of powerful X-ray flares last year, it made astronomers wonder — is this a sign that the beast chowed down on a passing gas cloud, or is this lack of cosmic etiquette typical for black holes?
The black hole at the center of the Milky Way, known as Sagittarius A* (Sgr A* for short), is typically very quiet – it doesn’t eat a lot of material, and there is relatively little light that radiates from the region around it. Which is why the apparent uptick in bright X-ray flares came as a surprise to scientists.
Could the bright flares seen in August 2014 have been caused by a gas cloud that passed too close to the black hole, and become an unsuspecting snack? And if that is the case, what does it tell scientists about what exactly happens to material that falls into a black hole? Alternatively, are these types of flare clusters typical of black holes, and an example of scientists’ limited understanding of these mighty beasts? Upcoming observations may shed some light on these dark objects. [Images: Milky Way's Monster Black Hole Shreds … Something]
Bright flare activity increases
Packing a double punch of observational power, NASA’s Chandra X-ray Observatory and the European Space Agency’s XMM-Newton space telescope have been observing Sgr A* (pronounced “Sagittarius A-star”) on and off since 1999. In the last three years, the total coverage time has increased thanks to a series of dedicated observation campaigns.
For long stretches, Chandra’s detectors would see only “quiescent” X-ray activity from Sgr A*, and then, suddenly, a bright flare would appear. The center of the Milky Way is one of the most densely populated regions of the galaxy, and the view between Earth and Sgr A* is blocked by stars and gas clouds. The Chandra scientists cherished the light that managed to make its way to their detectors, according to Daryl Haggard, an astrophysicist at McGill University in Montreal, who studies the black hole using Chandra data.
Haggard is a co-author on a new study suggesting there was a two- to threefold increase in the number of bright flares emitted by Sgr A* beginning in August 2014 and extending through November 2014 (the paper does not show an overall increase in the flare rate). In one particularly active period, five bright X-ray flares burst forth from Sgr A* in a time frame that would typically see only one. One of the flares, seen in September, was three times brighter than any other flare detected from that region. The new paper looked at 15 years of Chandra and XMM-Newton data, as well as data from the SWIFT space telescope, in an effort to show that the increase was not merely a result of greater observation time.
What was happening to cause the increase? According to the new research, there are two leading ideas.
G2, the mystery object
The first hypothesis involves a controversial object called G2. In 2011, a group of astronomers using the Very Large Telescope in Chile announced that this cosmic daredevil was going to make a very tight swing around Sgr A*. What would happen during this close approach was a subject of hot debate, because scientists couldn’t say for sure what G2 was – a pure dust cloud or a compact object surrounded by a dust cloud.
If G2 is a solid object, then it should have swung around Sgr A* without being pulled past the event horizon, beyond which nothing, not even light, can escape. But if it is pure gas, scientists predicted that the gravity of the black hole would smear it like a wisp of smoke, and a sizable amount of material would become lunch for Sgr A*. That would, theoretically, produce an increase in the light emitted from the region around the black hole, because when material falls into a black hole it accelerates rapidly, causing it to radiate light.
That means that if G2 is a dust cloud, it could have provided scientists with the first real-time, short-term observation of a black hole eating. To watch one of the most monstrous cosmic creatures in the universe devour a meal right in our own backyard would be an unrivaled opportunity for scientists. It would tell them about how black holes grow over their lifetimes, and provide new insights into the strange physics that takes place near the edge of these extreme gravity wells. Imagine a scientist who is trying to study lions in the wild, but never getting to see them hunt and devour their prey — G2 might finally let scientists watch Sgr A* in action.
The excitement was a palpable lead-up to G2′s close approach to Sgr A*. Andrea Ghez, an astrophysicist at the University of California at Los Angeles and one of the scientists who confirmed the existence of Sgr A*, said it was one of the “most watched events in astronomy in my career.”
Chandra saw nothing, nor did any of the other telescopes observing at the time.
Stefan Gillessen, a researcher at the Max Planck Institute for Extraterrestrial Physics in Germany and one of the lead proponents of the gas cloud theory, argued that G2 might still be a pure gas cloud, but that the dynamics of how and when it would be pulled into Sgr A* were different than originally predicted. Scientists don’t fully understand how material might behave around a black hole.
The new suggestion that Sgr A* released an increased number of bright flares in late 2014 could be the missing light show, according to Gabriel Ponti, a research fellow with the Max Planck group and the lead author on the new paper. Perhaps the material from G2 took longer than expected to fall toward the black hole and radiate.
“A year or so ago, we thought [G2] had absolutely no effect on Sgr A*, but our new data raise the possibility that that might not be the case,” Ponti said in a statement from Chandra.
A cluster of flares
Ponti cautions that the new research cannot confirm the connection between the flare activity and G2 — there’s no evidence to show that it isn’t just a coincidence. Plus, the paper points out that observations in infrared light seem to show that G2 has survived its trip around Sgr A*, suggesting it is not a pure gas cloud.
This doesn’t rule out the possibility that some of the gas from G2 was pulled into the black hole, but it means scientists would have to have a new model for how much gas could be syphoned from G2. And that raises the question of how quickly material moves through the region around a black hole, and around Sgr A* in particular. Does it flow down to the black hole’s gaping maw in a smooth, quickly moving stream, like cream moving through coffee? Or is it slow, like molasses across asphalt? If this burst of flare activity is due to G2 passing by, it would suggest that material falls very quickly, according to Haggard. In fact, it would suggest that material is basically in free- fall as it gets closer to the black hole’s event horizon. [The Strangest Black Holes in Space]
The likelihood of a G2 connection to the increased flare activity “seems tenuous to me,” Haggard told Space.com. She prefers an alternative possibility — that black holes normally exhibit “flare clustering,” or bursts of activity that vary from the “average” behavior they exhibit most of the time.
Ponti writes in his blog post for the Chandra website that other black holes that accrete matter at a similar rate to Sgr A* (but which are millions of times less massive) also show “long-term modulation in their flaring properties.” (Another factor to consider is that an object called G1, spotted before G2 and with a similar physical appearance, approached Sgr A* at a similar distance in 2001, but there was “no particular evidence for anything unusual happening as a result of G1′s passage.” However, he also notes that “the X-ray monitoring was much sparser” at the time.)
Illuminating a black hole
Scientists are still trying to understand why black holes like Sgr A* might release flares in periodic clusters, rather than evenly over time. It could have to do with how the gravitational pull of the black hole destroys matter that falls toward it, perhaps breaking it up into clumps, like a string of pearls that then fall in one after the other, each creating their own flare. It could also have to do with the magnetic properties of the black hole.
The Event Horizon Telescope, a worldwide network of radio telescopes, is currently dedicated to studying the monstrous beast that lives at the heart of Earth’s galactic home. No data has come out of the project yet, but the collaboration may provide the best-ever images of a black hole.
“At present, we don’t know whether the observed variation has anything to do with G2 or not and we are eager to know what the new data collected in 2015 will tell us,” Ponti wrote in a blog post on Harvard University’s Chandra website.
The object known as G2 may not have provided a snack for Sgr A*, the way so many people hoped it would. But it is nonetheless a fascinating object, potentially something that astronomers have never seen before. Ghez’s group of researchers at UCLA have proposed that it may be two stars that merged into one, and they’re wondering if these types of merged stars are typical around Sgr A*, and why.
Sgr A* is the nearest example we have of one of the most captivating creatures in the universe: An object with a gravitational pull so powerful it can bend light, or stop it from ever escaping. There are black holes in the universe that are brighter than entire galaxies, and others that are almost completely invisible. Scientists still aren’t sure if falling into a black hole would involve being shredded into long strips like spaghetti, or crushed by all the material that ever fell in before. The flares detected by Chandra and XMM provide clues about what happens to those that enter the cosmic lion’s den.
The mystery of Mars’ missing atmosphere is one big step closer to being solved.
A previous hypothesis had suggested that a significant part of the carbon from Mars’ atmosphere, which is dominated by carbon dioxide, could have been trapped within rocks via chemical processes. However, new research suggests that there’s not enough carbon in deposits on the Red Planet’s surface to account for the huge amounts lost from the air over time.
“The biggest carbonate deposit on Mars has, at most, twice as much carbon in it as the current Mars atmosphere,” study co-author Bethany Ehlmann, of the California Institute of Technology (Caltech) and NASA’s Jet Propulsion Laboratory in Pasadena, California, said in a statement
“Even if you combine all known carbon reservoirs together, it is still nowhere near enough to sequester the thick atmosphere that has been proposed for the time when there were rivers flowing on the Martian surface,” added Ehlmann, who worked with lead author Christopher Edwards, a former Caltech researcher currently with the U.S. Geological Survey.
Although Mars is dry today, scientists think the planet’s surface harbored large amounts of liquid water billions of years ago. Mars must have had a much thicker atmosphere back then, to keep the water from freezing or immediately evaporating, scientists say.
Carbon dioxide can be pulled from the atmosphere via chemical reactions with rocks, forming carbonate minerals. Previous research had suggested that the Red Planet might be covered with significant carbonate deposits, which could have locked up much of Mars’ lost atmosphere.
But Mars orbiters and rovers have found just a few concentrated carbonate deposits. The largest known carbonate-rich deposit on Mars is the Nili Fossae region, an area at least the size of Delaware and potentially as large as Arizona.
Edwards and Ehlmann used data captured by numerous Mars missions — including NASA’s Mars Global Surveyor orbiter, Mars Reconnaissance Orbiter, and Mars Odyssey orbiter — to estimate how much carbon is locked into Nili Fossae. Then, they compared that amount to what would be needed to form a dense, carbon-rich atmosphere that could sustain running water on the surface at the time that flowing rivers are thought to have carved extensive valley networks into the planet’s surface.
The Martian surface has been probed extensively by orbiters and landers, revealing only limited and scattered deposits of carbonate. Therefore, Edwards and Ehlmann deem it unlikely that so many large deposits have been overlooked by past examinations. Although very early deposits could be hidden beneath the Martian crust, their existence wouldn’t solve the mystery behind the atmosphere that existed when the river-carved valleys formed.
So, if the thick atmosphere didn’t become locked in carbonate deposits, what happened to it? One possibility is that it might have been lost to space from the top of the atmosphere — a phenomenon that NASA’s Curiosity rover has found evidence of in the past. Still, scientists aren’t certain how much of that loss occurred before the valleys formed. NASA’s MAVEN (Mars Atmosphere and Volatile Evolution) orbiter may help narrow down the mystery as it studies the Martian atmosphere.
“Maybe the atmosphere wasn’t so thick by the time of valley network formation,” Edwards said. “Instead of Mars that was wet and warm, maybe it was cold and wet with an atmosphere that had already thinned. How warm would it need to have been for the valleys to form? Not ver
“In most locations, you could have had snow and ice instead of rain,” Edwards said. “You just have to nudge above the freezing point to get water to thaw and flow occasionally, and that doesn’t require very much atmosphere.”
The research was published online Aug. 21 in the journal Geology.
The brightest nova of the century blasted lithium into space at 1.2 million mph (2 million km/h), new research reveals, cracking a long-standing mystery about the chemical balance of the universe.
Nova Centauri 2013 materialized in the sky in December 2013, caused by a huge nuclear explosion on a white dwarf star. This formed a new point in the constellation Centaurus, visible to the naked eye. Now, new measurements from the European Southern Observatory’s (ESO) La Silla facility in Chile reveal that the explosion is ejecting the element lithium, the first time that element has been seen in a nova system. This may help explain the topsy-turvy lithium distribution within stars, according to ESO officials.
“Understanding the amounts of lithium observed in stars around us today in the universe has given astronomers headaches,” ESO officials wrote in a statement. “Older stars have less lithium than expected, and some younger ones up to 10 times more.” The amount of lithium ejected from Nova Centauri is small, less than 1 billionth the mass of Earth’s sun. But the element’s presence in the nova supports a hypothesis in astronomy that a particular class of younger stars could have been built partially from lithium shot out of older stars. This would explain the younger bodies’ higher levels of lithium.
“It is a very important step forward,” study co-author Massimo Della Valle, from INAF–Osservatorio Astronomico di Capodimonte, Naples, and ICRANet, Pescara, Italy, said in the statement. “If we imagine the history of the chemical evolution of the Milky Way as a big jigsaw, then lithium from novae was one of the most important and puzzling missing pieces. In addition, any model of the Big Bang can be questioned until the lithium conundrum is understood.”Della Valle and another co-author, Luca Pasquini, an astronomer at University of Bologna in Italy, have been searching for traces of lithium in novas for over 25 years, according to the statement.
The lead scientist, Luca Izzo from Sapienza University of Rome and ICRANet, is excited too, although newer to the chase, he said in the statement: “It is very exciting to find something that was predicted before I was born and then first observed on my birthday in 2013!”
Planetary Resources deployed its first spacecraft from the International Space Station last month, and the Washington-based asteroid-mining company aims to launch a series of increasingly ambitious and capable probes over the next few years.
The goal is to begin transforming asteroid water into rocket fuel within a decade, and eventually to harvest valuable and useful platinum-group metals from space rocks.
“We have every expectation that delivering water from asteroids and creating an in-space refueling economy is something that we’ll see in the next 10 years — even in the first half of the 2020s,” said Chris Lewicki, Planetary Resources president and chief engineer Chris Lewicki.
“After that, I think it’s going to be how the market develops,” Lewicki told Space.com, referring to the timeline for going after asteroid metals.
“If there’s one thing that we’ve seen repeat throughout history, it’s, you tend to overpredict what’ll happen in the next year, but you tend to vastly underpredict what will happen in the next 10 years,” he added. “We’re moving very fast, and the world is changing very quickly around us, so I think those things will come to us sooner than we might think.”
Planetary Resources and another company, Deep Space Industries, aim to help humanity extend its footprint out into the solar system by tapping asteroid resources. (Both outfits also hope to make a tidy profit along the way, of course.)
This ambitious plan begins with water, which is plentiful in a type of space rock known as carbonaceous chondrites. Asteroid-derived water could do far more than simply slake astronauts’ thirst, mining advocates say; it could also help shield them from dangerous radiation and, when split into its constituent hydrogen and oxygen, allow voyaging spaceships to fill up their fuel tanks on the go.
The technology to detect and extract asteroid water is not particularly challenging or expensive to implement, Lewicki said. Scientific spacecraft routinely identify the substance on celestial bodies, and getting water out of an asteroid could simply involve bagging up the space rock and letting the sun heat it up.
Carbonaceous chondrites also commonly contain metals such as iron, nickel and cobalt, so targeting these asteroids could allow miners to start building things off Earth as well. That’s the logical next step beyond exploiting water, Lewicki said.
The “gold at the end of the rainbow,” he added, is the extraction and exploitation of platinum-group metals, which are rare here on Earth but are extremely important in the manufacture of electronics and other high-tech goods.
“Ultimately, what we want to do is create a space-based business that is an economic engine that really opens up space to the rest of the economy,” Lewicki said.
Developing off-Earth resources should have the effect of opening up the final frontier, he added.
“Every frontier that we’ve opened up on planet Earth has either been in the pursuit of resources, or we’ve been able to stay in that frontier because of the local resources that were available to us,” Lewicki said. “There’s no reason to think that space will be any different.”
Planetary Resources isn’t mining asteroids yet, but it does have some hardware in space. The company’s Arkyd-3R cubesat deployed into Earth orbit from the International Space Station last month, embarking on a 90-day mission to test avionics, software and other key technology.
Incidentally, the “R” in “Arkyd-3R” stands for “reflight.” The first version of the probe was destroyed when Orbital ATK’s Antares rocket exploded in October 2014; the 3R made it to the space station aboard SpaceX’s robotic Dragon cargo capsule in April. [Antares Rocket Explosion in Pictures]
Planetary Resources is now working on its next spacecraft, which is a 6U cubesat called Arkyd-6. (One “U,” or “unit,” is the basic cubesat building block — a cube measuring 4 inches, or 10 centimeters, on a side. The Arkyd-3R is a 3U cubesat.)
The Arkyd-6, which is scheduled to launch to orbit in December aboard SpaceX’s Falcon 9 rocket, features advanced avionics and electronics, as well as a “selfie cam” that was funded by a wildly successful Kickstarter project several years ago. The cubesat will also carry an instrument designed to detect water and water-bearing minerals, Lewicki said.
The next step is the Arkyd 100, which is twice as big as the Arkyd-6 and will hunt for potential mining targets from low-Earth orbit. Planetary Resources aims to launch the Arkyd-100 in late 2016, Lewicki said.
After the Arkyd 100 will come the Arkyd 200 and Arkyd 300 probes. These latter two spacecraft, also known as “interceptors” and “rendezvous prospectors,” respectively, will be capable of performing up-close inspections of promising near-Earth asteroids in deep space.
If all goes according to plan, the first Arkyd 200 will launch to Earth orbit for testing in 2017 or 2018, and an Arkyd 300 will launch toward a target asteroid — which has yet to be selected — by late 2018 or early 2019, Lewicki said.
“It is an ambitious schedule,” he said. But such rapid progress is feasible, he added, because each new entrant in the Arkyd series builds off technology that has already been demonstrated — and because Planetary Resources is building almost everything in-house.
“When something doesn’t work so well, we don’t have a vendor to blame — we have ourselves,” Lewicki said. “But we also don’t have to work across a contractural interface and NDAs [non-disclosure agreements] and those sorts of things, so that we can really find a problem with a design within a week or two and fix it and move forward.”
For its part, Deep Space Industries is also designing and building spacecraft and aims to launch its first resource-harvesting mission before 2020, company representatives have said.
Extracting and selling asteroid resources is in full compliance with the Outer Space Treaty of 1967, Lewicki said.
But there’s still some confusion in the wider world about the nascent industry and the rights of its players, so he’s happy that the U.S. Congress is taking up the asteroid-mining issue. (The House of Representatives recently passed a bill recognizing asteroid miners’ property rights, and the Senate is currently considering the legislation as well.)
“I think it’s more of a protection issue than it is an actual legal issue,” Lewicki said. “From a lawyer’s interpretation, I think the landscape is clear enough. But from an international aspect, and some investors — I think they would like to see more certainty.”
Now researchers have found that silica-rich rock much like the continental crust on Earth may be widespread at the site where Curiosity landed on Mars in August 2012.
“Mars is supposed to be a basalt-covered world,” study lead author Violaine Sautter, a planetary scientist at France’s Museum of Natural History in Paris, told Space.com. The findings are “quite a surprise,” she added.
Sautter and her colleagues analyzed data from 22 rocks probed by Curiosity as the six-wheeled robot wandered ancient terrain near Gale Crater. This 96-mile-wide (154 kilometers) pit formed about 3.6 billion years ago when a meteor slammed into Mars, and the age of the rocks from this area suggests they could help shed light on the earliest period of the Red Planets, scientists said.
The 22 rocks the researchers investigated were light-colored, contrasting with the darker basaltic rock found in younger regions on Mars. They probed these rocks using the rock-zapping laser called ChemCamon Curiosity, which analyzes the light emitted by zapped materials to determine the chemistry of Martian rocks.
The scientists found these light-colored rocks were rich in silica. A number of these were similar in composition to some of Earth’s oldest preserved continental crust.
Sautter noted that recent orbiter and rover missions had also spotted isolated occurrences of silica-rich rock. The researchers suggest these silica-rich rocks might be widespread remnants of an ancient crust on Mars that was analogous to Earth’s early continental crust and is now mostly buried under basalt.
The researchers added that the early geological history of Mars might be much more similar to that of Earth than previously thought. Future research could investigate whether the marked differences between Mars’ smooth northern hemisphere and rough, heavily cratered southern hemisphere might be due to plate tectonics, Sautter said.
The scientists detailed their findings online Monday (July 13) in the journal Nature Geoscience.
A heavyweight black hole in the heart of a distant galaxy has the mass of 140 million suns, according to new measurements. A vivid video by the National Radio Astronomy Observatory describes how researchers “weighed” the black hole at the center of the barred spiral galaxy NGC 1097.
Many galaxies have huge black holes in their centers, and these objects affect the galaxies’ growth and evolution. The galaxy NGC 1097 is 47 million light-years away from Earth, too far to determine the mass of its central black hole by the movement of the stars around it. But by tracking the movements of two types of molecular gases around the galaxy’s center, researchers using the Atacama Large Millimeter/submillimeter Array in Chile (ALMA) were able to work backward and figure out the black hole’s gravitational pull.
The ALMA telescopes tracked the radiation emitted from the two gases, hydrogen cyanide and formyl cation, as they swirled around the galaxy. The gases don’t interact strongly with environmental conditions within the galaxy, such as ionized gas flowing inward or outward. This means the gases paint an accurate picture of the effects of gravity’s pull alone. With just two hours of observational data, the researchers learned enough about the distribution and velocities of those gases to fit them to a model and calculate the pull of the galaxy’s core black hole.
The mass of a central black hole affects the physical properties of its host galaxy, and recent work has shown that those effects are different for different types of galaxies, study lead author, Kyoko Onishi, a doctoral student at the SOKENDAI (The Graduate University for Advanced Studies) in Japan, said in a statement. To understand those effects, Onishi said it’s important to measure the mass of these central black holes in various galaxy types.
Because of the quick precision measurements, “ALMA will enable us to observe a large number of galaxies in a practical length of time,” added Onishi, who is doing her research at the National Astronomical Observatory of Japan (NAOJ).
A Mars-size planet about 200 light-years from our solar system has turned out to be the lightest known alien world orbiting a normal star, researchers say.
Astronomers made the discovery after measuring the size and mass of the baking-hot planet, named Kepler-138 b, which orbits a red dwarf star called Kepler-138. Mars is only 53 percent the size of the Earth (or just about half the size), so Kepler-138 b is smaller than the Earth.
In the past couple of decades, astronomers have confirmed the existence ofmore than 1,800 exoplanets, or planets orbiting a star other than our sun. However, it’s more difficult for scientists to calculate the masses of small, rocky planets like Mars or Mercury than for large, gaseous worlds such as Jupiter or Saturn. Scientists measure the masses of exoplanets by looking at how strongly their gravitational fields tug on their stars; small planets have small masses, and their weak tugs on their stars are more difficult for astronomers to detect. As such, few Earth-size exoplanets have had their masses measured. [The Smallest Known Alien Planets in Pictures]
In this new study, astronomers investigated Kepler-138, a cold, dim red dwarf star with a mass about half that of the sun. Kepler-138 is located about 200 light-years from Earth, in the constellation Lyra.
Kepler-138 “is more than 10 million times further away from us than our sun,” study lead author Daniel Jontof-Hutter, an astronomer at Pennsylvania State University in University Park, told Space.com.
The star Kepler-138 is home to three exoplanets, prior research has confirmed by detecting the slight dimming of the star’s light that occurs whenever one of these worlds crosses in front of it. Each of these two planets — Kepler-138 c and Kepler-138 d — is about 1.2 times as wide as Earth. The third, Kepler-138 b, is a little more than half as wide as Earth, making it about the size of Mars.
“Kepler-138 b has the same apparent size to us as a golf ball 10 million kilometers [6.2 million miles] away,” Jontof-Hutter said.
These three exoplanets orbit very close to their star. Kepler-138 b takes a little more than 10 days to complete its orbit, Kepler-138 c requires nearly 14 days and Kepler-138 d needs about 23 days.
Using NASA’s Kepler spacecraft, the researchers looked at how the gravitational tug-of-war among these exoplanets influenced the lengths of their orbits. Because the strength of a planet’s gravitational pull is directly related to its mass, the scientists were able to weigh all three of these planets.
The astronomers found that the mass of the Mars-size inner planet, Kepler-138 b, is about one-fifteenth, or 6.7 percent, of Earth’s, making it about two-thirds the mass of Mars.
“Kepler-138 b is the first exoplanet smaller than Earth to have both its size and its mass measured,” Jontof-Hutter said.
The least massive known alien world may be the exoplanet PSR B1257+12 b, which has an estimated mass only about one-fiftieth, or 2 percent, that of Earth. However, that world does not orbit a normal star, but instead circles a pulsar — a dense, rapidly spinning remnant of a supernova explosion.
Knowing the mass and width of Kepler-138 b helped the researchers calculate its density, which they found is about two-thirds that of Mars, suggesting it has a purely rocky composition.
Although Kepler-138 b may be similar in mass and width to Mars, it is so much closer to its star, and thus hotter, meaning it is likely very different from Mars, Jontof-Hutter said. “In fact, all three planets orbiting Kepler-138 are likely too hot to retain liquid water,” Jontof-Hutter said. On the outermost planet, surface temperatures are about 250 degrees Fahrenheit (120 degrees Celsius), while those on the innermost planet are about 610 degrees F (320 degrees C).
Kepler-138 c and Kepler-138 d have masses 197 percent and 64 percent of Earth’s, respectively.
This finding opens up the study of rocky alien planets smaller than Earth, Jontof-Hutter said.
“The enormous variety of exoplanets that have been discovered by Kepler show us that systems like our own solar system are probably not the norm, and we don’t know why,” Jontof-Hutter said. Analyzing more exoplanets “will give us clues about how planets form and enable us to learn how common systems like are own really are.”
The scientists detailed their findings in the June 18 issue of the journal Nature.
Methane, a potential sign of primitive life, has been found in meteorites from Mars, adding weight to the idea that life could live off methane on the Red Planet, researchers say.
This discovery is not evidence that life exists, or has ever existed, on Mars, the researchers cautioned. Still, methane “is an ingredient that could potentially support microbial activity in the Red Planet,” study lead author Nigel Blamey, a geochemist at Brock University in St. Catharines, Ontario, Canada, told Space.com.
Methane is the simplest organic molecule. This colorless, odorless, flammable gas was first discovered in the Martian atmosphere by the European Space Agency’s Mars Express spacecraft in 2003, and NASA’s Curiosity rover discovered a fleeting spike of methane at its landing site last year.
Much of the methane in Earth’s atmosphere is produced by life, such as cattle digesting food. However, there are ways to produce methane without life, such as volcanic activity.
To shed light on the nature of the methane on Mars, Blamey and his colleagues analyzed rocks blasted off Mars by cosmic impacts that subsequently crash-landed on Earth as meteorites. About 220 pounds (100 kilograms) of Martian meteorites have been found on Earth.
The scientists focused on six meteorites from Mars that serve as examples of volcanic rocks there, collecting samples about one-quarter of a gram from each — a little bigger than a 1-carat diamond. All the samples were taken from the interiors of the meteorites, to avoid terrestrial contamination.
The researchers found that all six released methane and other gases when crushed, probably from small pockets inside.
“The biggest surprise was how large the methane signals were,” Blamey said.
Chemical reactions between volcanic rocks on Mars and the Martian environment could release methane. Although the dry thin air of Mars makes its surface hostile to life, the researchers suggest the Red Planet is probably more habitable under its surface. They noted that if methane is available underground on Mars, microbes could live off it, just as some bacteria do in extreme environments on Earth.
“We have not found life, but we have found methane that could potentially support microbes in the subsurface,” Blamey said.
Blamey now hopes to analyze more Martian meteorites. He and his colleagues detailed their findings online today (June 16) in the journal Nature Communications.
As NASA’s New Horizons spacecraft glides its way to the cold outer reaches of our solar system to take the first-ever up-close look at Pluto, the time is right to revise the International Astronomical Union (IAU)’s 2006 definition of a planet, which resulted in Pluto’s “demotion” from planet to ambiguous dwarf-planet status.
For those unfamiliar with the issues that led to that highly controversial decision, here’s a quick recap: It started with Pluto itself, discovered on Feb. 18, 1930, by Clyde Tombaugh, a young American astronomer working at Lowell Observatory in Flagstaff, Arizona. Pluto turned out to be rather unlike the other eight large objects orbiting the sun. Pluto is much smaller than Mercury, and only two-thirds the size of Earth’s moon. Its orbit is tilted and eccentric, crossing Neptune’s. No other planet acted like this. In 2000, astronomers found other objects orbiting the sun in the deep outer solar system, with qualities very much like Pluto’s. They were given names like Sedna , Quaoar, Ixion, Varuna, Makemake and Haumea . Many were close (but not quite equal) to Pluto in size. All of them had tilted, eccentric orbits; quite a few of those orbits crossed Neptune’s.
The tipping point came in 2005. California Institute of Technology astronomer Mike Brown, along with Chad Trujillo of Gemini Observatory and David Rabinowitz of Yale University, discovered a new massive body in the solar system. This new body, which astronomers latter dubbed Eris, was particularly noteworthy: Not only did it possess a moon, but at the time, it was estimated to be larger than Pluto. Subsequent observations revealed that Eris and Pluto are nearly identical in size, though Pluto is likely a few kilometers larger. Initially, Brown had named the newly discovered body Xena (after the protagonist of the eponymous TV show, with a sneaky Planet X reference). Although the name Xena didn’t stick, the IAU later officially — and aptly — christened it Eris after the Greek goddess of chaos and discord.
So, it seemed quite clear that if Pluto was our solar system’s ninth planet, then Eris should be its 10th. And if Eris and Pluto were planets, why shouldn’t Makemake and Haumea be considered planets as well? And what if there were even bigger objects out there to be discovered? Why shouldn’t the solar system have 15 planets, or 40? (Can you imagine the mnemonic device that would be required to remember 40 planets in the solar system?!)
For all who were in support of granting planet status to these objects, an equally adamant camp insisted that none of these objects, including Pluto, deserved to be called planets, and that our solar system contained only eight objects worthy of planet status. Neptune would be the last and final.
A worsening problem
With the intention of solving the debate once and for all, members of the IAU met in 2006. They spent days debating how to establish unambiguous definitions for the objects in our solar system. In the end, Resolution 5A was born:
The IAU therefore resolves that planets and other bodies in our solar system, except satellites, be defined into three distinct categories in the following way:
(1) A planet is a celestial body that (a) is in orbit around the sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit.
(2) A dwarf planet is a celestial body that (a) is in orbit around the sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape , (c) has not cleared the neighborhood around its orbit, and (d) is not a satellite.
(3) All other objects, except satellites, orbiting the sun shall be referred to collectively as small solar-system bodies.
These are, to put it bluntly, terrible definitions. Despite its goal of providing unambiguous definitions, Resolution 5A actually contains the kind of ambiguity that most scientific organizations would protest. It adds confusion, resolves little and makes nobody happy.
So how did that become the official definition of a planet? A very strange vote. If you think low voter turnout is limited to politics, consider this: Only about 4 percent of IAU members were present for the vote on Resolution 5A. But it was travel schedules, not apathy, that caused this abysmal turnout. You see, the vote took place on the last day of the IAU meeting, when many people had to leave to catch flights back home — 424 astronomers were present, even though IAU membership in 2006 was just more than 10,000. As a result, Pluto lost the status it had enjoyed for more than 80 years and became a dwarf planet overnight. [Pluto Demoted: No Longer a Planet in Highly Controversial Definition]
The term “dwarf planet” itself causes confusion. You often hear people say Pluto is still a planet but that it just happens to be a dwarf planet now. But despite the name, the IAU does not consider a dwarf planet a planet — unlike a dwarf star, which is still a star, or a dwarf galaxy, which is still a galaxy. So much for eliminating ambiguity! But just the conflicting use of the word planet isn’t the most unclear part of the resolution.
Credit: Made with the Pluto Safari app for iOS and Android.
Picking apart Resolution 5A
Let’s dissect resolution 5A “Definition of ‘planet’”, one of six IAU Resolutions that were passed at the Closing Ceremony of the General Assembly in 2006.
*Nearly round shape. There is an element of something good here. We all intuitively feel that a planet should be round, or nearly so. But what is “nearly”? How lumpy and bumpy must an object be to no longer qualify as a planet or a dwarf planet? How smooth must the “ball” be? The Earth, which we all agree is a planet, is nearly round on some scales, but on others, it’s not. If you’re standing in the bottom of the Grand Canyon, the Earth isn’t even close to nearly round.
*Cleared the neighborhood. I’ve tried to wrap my head around this phrase for years, tried to convince myself that it makes sense — but I just can’t swallow it. The IAU is trying to express that, in addition to being round, a planet should be the dominant gravitational force in its local region of the solar system. That’s not an unreasonable position. Certainly the Earth and Jupiter are the dominant objects in their local regions. Neptune surely is, too. Even though Pluto’s orbit crosses Neptune’s, Neptune forces Pluto into something called a 3:2 resonance (for every three times Neptune goes around the sun, Pluto goes around twice), preventing collision. But have any of these planets actually “cleared the neighborhood” around their orbits? No. Pluto is still clearly in Neptune’s “neighborhood.” For that matter, Jupiter has two well-known groups of asteroids, the Trojans, which lead and follow Jupiter along in its orbit. For that matter, the Earth hasn’t quite “cleared the neighborhood” around its orbit, either, to which anyone who saw the near-Earth asteroids that entered Earth’s atmosphere near Chelyabinsk, Russia, on Feb. 15, 2013, or Tunguska, Siberia, on June 30, 1908, can attest. So are Earth, Jupiter and Neptune the dominant gravitational objects in their local neighborhoods? Yes, clearly. Have they cleared their neighborhoods? No. Not by a long shot.
Other scientists have weighed in on the matter. Alan Stern, principal investigator for the New Horizons mission to Pluto, made it clear he disagrees with the IAU resolution. “Any definition that allows a planet in one location but not another is unworkable. Take Earth. Move it to Pluto’s orbit, and it will be instantly disqualified as a planet,” Stern said.
The biggest problem with the IAU’s planet definition is that it replaces an already-ambiguous concept (“What is a planet?”) with three more ambiguous concepts, (“nearly round,” “cleared” and “neighborhood”). Indeed, the only definitive part of the IAU resolution on which everyone can agree is the first part: (1) A planet is in orbit around the sun. It’s why the moon is not a planet. My 6-year-old niece intuitively understands this. It’s the only part of the IAU definition I would keep.
The way out
Let’s look at some other kinds of definitions that are clear and unambiguous.
*International boundaries. It’s well understood that the portion of North America north of 49 degrees, between the Canadian provinces of British Columbia, Alberta, Saskatchewan and Manitoba, and the U.S. states of Washington, Idaho, Montana, North Dakota and Minnesota, is called Canada, and the portion below that latitude is called the United States. There’s no physical demarcation — no river, no mountain range — along the 49th parallel. There’s no subtle change in vegetation or geological structure. But there is a hard, sharp, clearly defined, well-understood boundary that unambiguously answers the question, “What is Canada?” It’s the country north of the 49th parallel. It passes the 6-year-old-niece test.
*Constellation boundaries. Back in 1888, the IAU defined an intricate set of boundary lines in the sky, precisely outlining the groups of stars that were commonly referred to as constellations. It also declared that there would be 88 of these constellations. Lines were chosen carefully, to respect traditional choices about which star might lie in which constellation, and in the end, the definitions were clear. There is no ambiguity about which particular point in the sky falls within which constellation. And, you can tell precisely when a moving celestial object (like Pluto) might cross from one constellation to another. It’s an arbitrarily agreed upon but well-defined system of definitions that has served the astronomical community well for more than 100 years.
*The Karman line that defines the edge of space. Where does the Earth’s atmosphere end and outer space begin? Clearly, there is no physical boundary. There is no bubble holding the atmosphere that one must pierce on one’s way to the International Space Station. The air just gets thinner and thinner until you can ignore it. But in reality, air molecules continue to exist, albeit in smaller numbers, out to an altitude of many thousands of kilometers and beyond — indeed, some of these air molecules may have made it as far as Pluto by now! However, since the early days of manned spaceflight, a near-universally accepted definition is that space begins at an altitude of 100 kilometers (62 miles). In fact, this definition is accepted by the Fédération Aéronautique Internationale (FAI), an international standard-setting body for aeronautics and astronautics. Pilots who’ve flown higher than 100 km have officially earned the title of astronaut. It’s another arbitrary, but widely accepted convention that is clear, unambiguous and easily passes the 6-year-old comprehension test.
What the IAU should have done in 2006, and could easily do moving forward, is to crystallize the definition of the word “planet” as unambiguously as it defined the boundaries of the constellations in 1888. Yes, that definition would have been arbitrary, and yes, the actual physical objects themselves would gradually transition from larger to smaller, and don’t care in the least what we choose to call them. But the IAU could have chosen a definition that resolves the debate in a far more satisfying manner than it actually did.
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The 1,000-km rule
So, what would be a better definition for the objects in the solar system?
(1) A “planet”  is a celestial body that (a) is in orbit around the sun, and (b) has a maximum surface radius greater than 1,000 km (620 miles).
(2) All other objects, except satellites, orbiting the sun shall be referred to collectively as small solar-system bodies.
“But that’s completely unscientific,” you may say. “Why 1,000 km? Why not 1,200, or 750?”
I submit that the precise definition of a planet as an object with a radius of at least 1,000 km is no less scientific than the definition of a kilometer as being a unit of distance equal to 1,000 m, or a degree being 1/360 of a circle.
And there are other reasons why the 1,000-km definition is more scientific than it might seem at first. But let’s put that aside momentarily. Instead, let’s see what would have happened if the IAU had adopted this definition.
Here is a list of the largest known objects orbiting the sun, and their radii in kilometers:
Object Radii (km)
Jupiter: 69,911 km (43,441 miles)
Saturn: 58,232 km (36,184 miles)
Uranus: 25,362 (15,759 miles)
Neptune: 24,622 (15,299 miles)
Earth: 6,378 (3,963 miles)
Venus: 6,052 (3,761 miles)
Mars: 3,390 (2,106 miles)
Mercury: 2,440 (1,516 miles)
Pluto: 1,184 (736 miles)
Eris: 1,163 (723 miles)
Makemake: 715 (444 miles)
Haumea: 620 (385 miles)
Quaoar: 555 (345 miles)
Sedna: 498 (309 miles)
Ceres: 475 (295 miles)
Orcus: 458 (285 miles)
By the 1,000-km definition, all eight classical planets would remain planets. So would Pluto. And we’d add Eris. The solar system would have exactly 10 planets, a number that is deeply satisfying to two-handed, five-fingered humans who’ve been practicing base-10 mathematics for thousands of years. The “Plutophile” camp, fond of keeping Pluto’s planetary status for historical reasons, would retain its dignity. And elevating Eris to a first-class planet would be an honorable nod to the cutting-edge astronomers whose work led to a need for this new definition in the first place.
And finally, the 1,000-km rule, like any good arbitrary rule, actually does a pretty good job of respecting the underlying physical phenomena that it purports to define. Planets are made of physical materials like rock, metal, gas and ice. They may come in different proportions, but those materials all respect the same physical laws. When you put together a lump of rock, metal or ice, in any proportion, certain things start to happen as that lump approaches 1,000 km in radius. The materials will pull together under the force of their own gravity. Solid rock will start to deform. Ice, even frozen hard as granite at the edge of the solar system, will slowly flow. There is no known substance that can resist the force of its own gravity when made into a lump with a 1,000-km radius. Any object, made of any substance, of approximately that size, will eventually flow under action of its own gravity into a shape that is “nearly round” when viewed from far away. The 1,000-km radius just happens to describe something that naturally takes place for objects of a certain size and results in what we all intuitively want a planet to look like.
And for space enthusiasts, there’s one more benefit to my proposed definition. While we’re all looking forward to the New Horizons Pluto flyby, there’s also a certain sadness to knowing that, after Pluto, there will be no more planets in our solar system to explore. If our solar system has 10 planets, that’s no longer true. As far away and difficult as it was to reach Pluto, it will be even more difficult to reach Eris. It’s another frontier, another first and another project to fund. That prospect alone should give the scientific community a reason to rethink and resolve Resolution 5A.
Mars is a large enough planet that astrobiologists looking for life need to narrow the parameters of the search to those environments most conducive to habitability.
NASA’s Mars Curiosity mission is exploring such a spot right now at its landing site around Gale Crater, where the rover has found extensive evidence of past water and is gathering information on methane in the atmosphere, a possible signature of microbial activity.
But where would life most likely gain energy from its surroundings? One possibility is in an environment that includes “green rust,” a partially oxidized iron mineral. A fully oxidized iron “rust” — one exposed to oxidation for long enough — turns orangey-red, similar to the color of Mars’ regolith. When oxidization is incomplete, however, the iron rust is greenish.
This means that there are two different “redox states,” or types of iron with different numbers of electrons in the same mineral. This difference between the two iron redox states could allow the mineral to take in or give up electrons and thus act as a catalyst, said Laurie Barge, a planetary scientist at NASA’s Jet Propulsion Laboratory. She studies hydrothermal vents, an area where chemical contrasts also fuel life.
“From an environmental science perspective, green rust can absorb and concentrate nutrients, and can also accept and donate electrons for life,” said Barge.
She is the lead author of related work that was presented at the American Geophysical Union’s Joint Assembly meeting in May 2015. Funding for this work comes from the Jet Propulsion Laboratory’s Icy Worlds team as part of the NASA Astrobiology Institute (NAI) element of the Astrobiology Program at NASA.
One major challenge in the search for life on Mars is that its surface is highly oxidized. On Earth, green rust generated in Barge’s lab oxidizes quickly when exposed to air, and its composition is changed in only an hour. However, the lack of oxygen on Mars makes this a slower process. It is likely that green rust occurs beneath the oxidized surface, perhaps only a centimeter or half-inch deep as revealed by Curiosity.
There are more probes on the way to Mars that will include drills. One of those will be NASA’s InSight lander, which is set to go to the Red Planet in 2016. Another is the European Space Agency’s ExoMars rover, expected to launch in 2018.
A major focus of current NASA missions on Mars is finding out where water has flowed in the past. NASA’s Curiosity, Opportunity and Spirit rovers have all found rocks that form in the presence of water, such as the red iron oxide mineral hematite, as well as select sulfates and clays. Further, several orbiting spacecraft have seen signs, such as the presence of gullies, in which water is thought to have once flowed on the surface.
Barge knows from her experiments that green rust forms when two contrasting solutions – one containing iron and one containing hydroxide – are mixed. On Earth, green rust has been found in such environments as non-oxygenated wet sediments and steel pipes that corrode in sea water.
Probing by laser
To detect green rust, Barge suggests using laser Raman spectroscopy, a technique which will be included on ESA’s ExoMars and NASA’s Mars 2020 missions. The technique involves directing a laser beam at a sample and then collecting and analyzing the light that is scattered from the spot to identify its molecular composition and structure. The scattered light contains fingerprint spectral features that allow us to determine the molecular makeup and mineralogy of the sample. Barge has teamed up with Pablo Sobron, a research scientist at the SETI Institute, an expert in laser-based spectroscopy applied to Mars exploration, to adapt the Raman technique for the detection and analysis of green rust.
But first, there needs to be a better understanding of where green rust will occur and how it can support habitability. The JPL Icy Worlds team (led by the Jet Propulsion Laboratory’s Isik Kanik) recently received a second five-year NASA Astrobiology Institute grant to study the habitability of icy worlds, including an investigation into how green rust might drive prebiotic chemistry, or chemistry that is a precursor to life.
“There’s a theory proposed by Michael Russell at JPL that green rust could have acted as a proto-enzyme to convert energy currencies on early Earth,” Barge said, referring to how lifeforms convert proton and electron gradients into chemical energy to drive metabolism and, thereby, life.
Green rust is especially interesting in this regard because it is a double layered hydroxide that can sandwich all sorts of interesting components relevant to life in between these layers, Barge added. These include phosphates, DNA, amino acids and proteins.
Dark matter is five times more plentiful in the universe than regular matter, but it does not emit, reflect or absorb light, making it not just dark but entirely transparent. But if dark-matter particles around black holes can produce gamma-rays (high-energy light), such emissions would give scientists a new way to study this mysterious material.
The process responsible for creating the gamma-rays is somewhat counterintuitive, because it seems to defy two common assumptions: that nothing can escape from a black hole and that there’s no such thing as a free lunch.
Jeremy Schnittman is a theoretical astrophysicist at the NASA Goddard Space Flight Center, and he’s beginning a project to look through data from the Fermi Gamma-ray Space telescope for signs of high-energy light around the edge of a black hole that might have been created by dark matter.
“We’re really just getting started on this part of the problem,” Schnittman said. “As a theoretical astrophysicist, I haven’t done a lot of data analysis in my career, so it’s a little bit of a learning curve for me. But fortunately I’m surrounded by people here at Goddard who are real experts at the Fermi data.”
Schnittman’s search for this dark-matter signal began with a computer program that he has been developing for about 10 years. It models in 3D the paths of particles as they zip through space near a black hole, while some of them get close enough to orbit around the black hole or fall in.
Just over a year ago, he decided to adjust the program to model dark-matter particles. The resulting video shows how the subatomic bits get caught up in the gravitational pull of the black hole and swirl around it in a region called the ergosphere (where all particles must orbit in the direction of the black hole’s spin). Some of the particles collide and destroy each other (also known as annihilation), and this produces a pair of gamma-rays.
These particles of light might normally fall into the black hole, helpless against its gravitational pull, were it not for something called the Penrose process.
In 1971, astrophysicist Roger Penrose showed that if two photons are created very close to a black hole, it’s possible for one of them to escape, while the other falls in. This flies counter to the commonly held idea that nothing can escape from a black hole, or at least nothing that goes past the “event horizon” — the point at which the gravitational pull is so strong that nothing, not even light, can ever exert enough force to get away.
According to the Penrose principle, the particles are not created beyond this point of no return, but under normal circumstances, it’s unlikely that either particle would have any means of getting away from the black hole. So the Penrose process still changes the fate of at least one particle, giving it an escape route.
In 2009, a group of researchers showed that the Penrose process could be applied to dark-matter particles that annihilate and form two gamma-rays. If dark-matter particles are annihilating near the surface of a black hole, telescopes on Earth could detect the escaping gamma-rays.
Schnittman’s work using the 3D computer model has shown many more paths that the particles can take, including some that are more likely to produce gamma-rays that can escape the black hole, and with even higher energies than had been previously predicted. A brief description of those results was published in the journal Physical Review Letters last December, and a longer description of the work has been accepted to the Astrophysical Journal.
With those results, Schnittman and his colleagues are now looking for this signal, although they said they expect it to be very dim compared to many other gamma-ray sources. The researchers are creating a list of target galaxies that have few gamma-ray sources and very massive black holes.
“The bigger the black hole, the bigger the signal,” Schnittman said. “It scales in a way that as your black hole [mass] goes up by a factor of 10, the expected signal goes way up, by something like a factor of 1,000.
“The first pass at observing this effect is almost certainly not going to yield an actual detection. But it will provide probably the strongest upper limit on this type of process that has ever been seen before — the idea of high-energy dark-matter particle reactions. Even that is progress.”
The particles that escape the black hole via the Penrose process not only go free, but they also leave with more energy than they started with. In fact, they have more energy than the pair of particles had combined. This, it would seem, is a free lunch.
Since Penrose’s original work, scientists have shown that not only does the escaping particle steal energy from its partner (essentially pushing off the other particle), but it also steals energy from the spinning black hole. Every Penrose particle that escapes slows the spin of the black hole by a very, very tiny amount.
(When he originally proposed the idea, Penrose wrote that this phenomenon could be used by an advanced society as an energy-producing garbage disposal, in which the garbage serves as the particle that falls into the black hole, producing a flux of high energy particles that escapes.)
Schnittman said he is reserved in his hopes for finding a dark-matter signal in the Fermi data. Not only will it be difficult to see such a small signal amid the noise of gamma-rays in the universe, but the existence of the signal also relies on a major unknown: whether or not dark-matter particles create gamma-rays when they annihilate.
The fact is, scientists don’t know what dark matter is made of, and they don’t know if dark-matter particles will annihilate in the way that Schnittman’s model predicts, if they do so at all. So if Schnittman did find a signal, it would mean a major breakthrough in the study of the nature of dark matter.
“That’s Nobel Prize kind of stuff,” Schnittman said. “It’s a long shot, but it would be a tremendous payoff if we found actual confirmation of dark-matter annihilation.”