News Article | April 17, 2017
Mars has electrically charged metal atoms (ions) high in its atmosphere, according to new results from NASA's MAVEN spacecraft. The metal ions can reveal previously invisible activity in the mysterious electrically charged upper atmosphere (ionosphere) of Mars. "MAVEN has made the first direct detection of the permanent presence of metal ions in the ionosphere of a planet other than Earth," said Joseph Grebowsky of NASA's Goddard Space Flight Center in Greenbelt, Maryland. "Because metallic ions have long lifetimes and are transported far from their region of origin by neutral winds and electric fields, they can be used to infer motion in the ionosphere, similar to the way we use a lofted leaf to reveal which way the wind is blowing." Grebowsky is lead author of a paper on this research appearing April 10 in Geophysical Research Letters. MAVEN (Mars Atmosphere and Volatile Evolution Mission) is exploring the Martian upper atmosphere to understand how the planet lost most of its air, transforming from a world that could have supported life billions of years ago into a cold desert planet today. Understanding ionospheric activity is shedding light on how the Martian atmosphere is being lost to space, according to the team. The metal comes from a constant rain of tiny meteoroids onto the Red Planet. When a high-speed meteoroid hits the Martian atmosphere, it vaporizes. Metal atoms in the vapor trail get some of their electrons torn away by other charged atoms and molecules in the ionosphere, transforming the metal atoms into electrically charged ions. MAVEN has detected iron, magnesium, and sodium ions in the upper atmosphere of Mars over the last two years using its Neutral Gas and Ion Mass Spectrometer instrument, giving the team confidence that the metal ions are a permanent feature. "We detected metal ions associated with the close passage of Comet Siding Spring in 2014, but that was a unique event and it didn't tell us about the long-term presence of the ions," said Grebowsky. The interplanetary dust that causes the meteor showers is common throughout our solar system, so it's likely that all solar system planets and moons with substantial atmospheres have metal ions, according to the team. Sounding rockets, radar and satellite measurements have detected metal ion layers high in the atmosphere above Earth. There's also been indirect evidence for metal ions above other planets in our solar system. When spacecraft are exploring these worlds from orbit, sometimes their radio signals pass through the planet's atmosphere on the way to Earth, and sometimes portions of the signal have been blocked. This has been interpreted as interference from electrons in the ionosphere, some of which are thought to be associated with metal ions. However, long-term direct detection of the metal ions by MAVEN is the first conclusive evidence that these ions exist on another planet and that they are a permanent feature there. The team found that the metal ions behaved differently on Mars than on Earth. Earth is surrounded by a global magnetic field generated in its interior, and this magnetic field together with ionospheric winds forces the metal ions into layers. However, Mars has only local magnetic fields fossilized in certain regions of its crust, and the team only saw the layers near these areas. "Elsewhere, the metal ion distributions are totally unlike those observed at Earth," said Grebowsky. The research has other applications as well. For example it is unclear if the metal ions can affect the formation or behavior of high-altitude clouds. Also, detailed understanding of the meteoritic ions in the totally different Earth and Mars environments will be useful for better predicting consequences of interplanetary dust impacts in other yet-unexplored solar system atmospheres. "Observing metal ions on another planet gives us something to compare and contrast with Earth to understand the ionosphere and atmospheric chemistry better," said Grebowsky. The research was funded by the MAVEN mission. MAVEN's principal investigator is based at the University of Colorado's Laboratory for Atmospheric and Space Physics, Boulder. The university provided two science instruments and leads science operations, as well as education and public outreach, for the mission. NASA Goddard manages the MAVEN project and provided two science instruments for the mission. The University of California at Berkeley's Space Sciences Laboratory also provided four science instruments for the mission. Lockheed Martin built the spacecraft and is responsible for mission operations. NASA's Jet Propulsion Laboratory in Pasadena, California, provides navigation and Deep Space Network support, as well as the Electra telecommunications relay hardware and operations.
News Article | April 17, 2017
It vanished into thin air. Around 90 per cent of the Red Planet’s atmosphere was probably lost to space over just a few hundred million years, according to a key measurement from NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. Today Mars is a freezing, arid desert with an atmosphere 1 per cent as dense as Earth’s and its water mostly locked up in polar ice caps. But most planetary scientists think it was not always so. Certain Mars soils contain minerals that on Earth are produced in the presence of water, and some Martian features seem to point towards ancient lakebeds and even fast-flowing rivers. To have retained this liquid water, the planet’s carbon dioxide-dominated atmosphere must once have been much thicker to limit surface evaporation. MAVEN has been orbiting Mars since 2014 on a quest to find out where all that CO went. It could have gone into the ice caps, into the rocks as carbonate minerals or it could have been lost to space. “People have spent decades looking for the carbonate minerals that would be the repository of CO and they haven’t found them,” says MAVEN team leader Bruce Jakosky at the Laboratory for Atmospheric and Space Physics in Boulder, Colorado. “That’s what has pushed the community into considering the role of escape to space.” The orbiter tracked two isotopes of argon in the atmosphere, argon-36 and argon-38. Because argon is unreactive, the only way it can leave Mars is when an ion smacks into one of its atoms and boots it off into space like a billiard ball, a process called sputtering. The heavier isotopes are harder to remove this way so, over time, Mars has ended up with more argon-38 than argon-36 in its atmosphere. Measuring the ratio of these two isotopes can tell us exactly how much argon the planet has lost. Assuming that the initial ratio was the same as on Earth and elsewhere in the solar system today – and accounting for other sources of argon like volcanic eruptions or incoming meteorites that would have returned some to the atmosphere – the MAVEN team worked out that about 66 per cent of the argon-36 that was ever in the Martin atmosphere has been sputtered away. From that, they calculated that 10 to 20 per cent of CO – equivalent to at least half a bar of atmospheric pressure – vanished through sputtering. And this is only a lower limit as other processes can remove carbon dioxide but leave argon unaffected, Jakosky says. Also considering these, he estimates that 80 to 90 per cent of the CO atmosphere was lost. It would have happened relatively quickly, too. Around 4.1 billion years ago, Mars’s magnetic field switched off for reasons we don’t understand. Without this field helping to hold it in place, the atmosphere became more vulnerable to sputtering from incoming charged particles from the solar wind. It may have taken just a few hundred million years for most of the atmosphere to be stripped away, the researchers say. “I think this is the explanation of why Mars went from a planet that is habitable by microbes at the surface, with warm temperatures and liquid water, to the cold, dry planet we see today,” Jakosky says.
News Article | August 12, 2016
Here's a wonderful feature about my favorite constellation and the galaxy's most awesome telescope (at least one of them!) from NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. Like cosmic ballet dancers, the stars of the Pleiades cluster are spinning. But these celestial dancers are all twirling at different speeds. Astronomers have long wondered what determines the rotation rates of these stars. By watching these stellar dancers, NASA's Kepler space telescope during its K2 mission has helped amass the most complete catalog of rotation periods for stars in a cluster. This information can help astronomers gain insight into where and how planets form around these stars, and how such stars evolve. "We hope that by comparing our results to other star clusters, we will learn more about the relationship between a star’s mass, its age, and even the history of its solar system," said Luisa Rebull, a research scientist at the Infrared Processing and Analysis Center at Caltech in Pasadena, California. She is the lead author of two new papers and a co-author on a third paper about these findings, all being published in the Astronomical Journal. The Pleiades star cluster is one of the closest and most easily seen star clusters, residing just 445 light-years away from Earth, on average. At about 125 million years old, these stars -- known individually as Pleiads -- have reached stellar "young adulthood." In this stage of their lives, the stars are likely spinning the fastest they ever will. As a typical star moves further along into adulthood, it loses some zip due to the copious emission of charged particles known as a stellar wind (in our solar system, we call this the solar wind). The charged particles are carried along the star’s magnetic fields, which overall exerts a braking effect on the rotation rate of the star. Rebull and colleagues sought to delve deeper into these dynamics of stellar spin with Kepler. Given its field of view on the sky, Kepler observed approximately 1,000 stellar members of the Pleiades over the course of 72 days. The telescope measured the rotation rates of more than 750 stars in the Pleiades, including about 500 of the lowest-mass, tiniest, and dimmest cluster members, whose rotations could not previously be detected from ground-based instruments. Kepler measurements of starlight infer the spin rate of a star by picking up small changes in its brightness. These changes result from "starspots" which, like the more-familiar sunspots on our sun, form when magnetic field concentrations prevent the normal release of energy at a star’s surface. The affected regions become cooler than their surroundings and appear dark in comparison. As stars rotate, their starspots come in and out of Kepler’s view, offering a way to determine spin rate. Unlike the tiny, sunspot blemishes on our middle-aged sun, starspots can be gargantuan in stars as young as those in the Pleiades because stellar youth is associated with greater turbulence and magnetic activity. These starspots trigger larger brightness decreases, and make spin rate measurements easier to obtain. During its observations of the Pleiades, a clear pattern emerged in the data: More massive stars tended to rotate slowly, while less massive stars tended to rotate rapidly. The big-and-slow stars' periods ranged from one to as many as 11 Earth-days. Many low-mass stars, however, took less than a day to complete a pirouette. (For comparison, our sedate sun revolves fully just once every 26 days.) The population of slow-rotating stars includes some ranging from a bit larger, hotter and more massive than our sun, down to other stars that are somewhat smaller, cooler and less massive. On the far end, the fast-rotating, fleet-footed, lowest-mass stars possess as little as a tenth of our sun’s mass. "In the 'ballet' of the Pleiades, we see that slow rotators tend to be more massive, whereas the fastest rotators tend to be very light stars," said Rebull. The main source of these differing spin rates is the internal structure of the stars, Rebull and colleagues suggest. Larger stars have a huge core enveloped in a thin layer of stellar material undergoing a process called convection, familiar to us from the circular motion of boiling water. Small stars, on the other hand, consist almost entirely of convective, roiling regions. As stars mature, the braking mechanism from magnetic fields more easily slows the spin rate of the thin, outermost layer of big stars than the comparatively thick, turbulent bulk of small stars. Thanks to the Pleiades’ proximity, researchers think it should be possible to untangle the complex relationships between stars’ spin rates and other stellar properties. Those stellar properties, in turn, can influence the climates and habitability of a star’s hosted exoplanets. For instance, as spinning slows, so too does starspot generation, and the solar storms associated with starspots. Fewer solar storms means less intense, harmful radiation blasting into space and irradiating nearby planets and their potentially emerging biospheres. "The Pleiades star cluster provides an anchor for theoretical models of stellar rotation going both directions, younger and older," said Rebull. "We still have a lot we want to learn about how, when and why stars slow their spin rates and hang up their 'dance shoes,' so to speak." Rebull and colleagues are now analyzing K2 mission data from an older star cluster, Praesepe, popularly known as the Beehive Cluster, to further explore this phenomenon in stellar structure and evolution. "We’re really excited that K2 data of star clusters, such as the Pleiades, have provided astronomers with a bounty of new information and helped advance our knowledge of how stars rotate throughout their lives," said Steve Howell, project scientist for the K2 mission at NASA’s Ames Research Center in Moffett Field, California. The K2 mission’s approach to studying stars employs the Kepler spacecraft's ability to precisely observe miniscule changes in starlight. Kepler’s primary mission ended in 2013, but more exoplanet and astrophysics observations continue with the K2 mission, which began in 2014. Ames manages the Kepler and K2 missions for NASA's Science Mission Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corporation operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado at Boulder.
News Article | October 27, 2016
Astronomers using observations from NASA's Kepler and Swift missions have discovered a batch of rapidly spinning stars that produce X-rays at more than 100 times the peak levels ever seen from the sun. The stars, which spin so fast they've been squashed into pumpkin-like shapes, are thought to be the result of close binary systems where two sun-like stars merge. "These 18 stars rotate in just a few days on average, while the sun takes nearly a month," said Steve Howell, a senior research scientist at NASA's Ames Research Center in Moffett Field, California, and leader of the team. "The rapid rotation amplifies the same kind of activity we see on the sun, such as sunspots and solar flares, and essentially sends it into overdrive." The most extreme member of the group, a K-type orange giant dubbed KSw 71, is more than 10 times larger than the sun, rotates in just 5.5 days, and produces X-ray emission 4,000 times greater than the sun does at solar maximum. These rare stars were found as part of an X-ray survey of the original Kepler field of view, a patch of the sky comprising parts of the constellations Cygnus and Lyra. From May 2009 to May 2013, Kepler measured the brightness of more than 150,000 stars in this region to detect the regular dimming from planets passing in front of their host stars. The mission was immensely successful, netting more than 2,300 confirmed exoplanets and nearly 5,000 candidates to date. An ongoing extended mission, called K2, continues this work in areas of the sky located along the ecliptic, the plane of Earth's orbit around the sun. "A side benefit of the Kepler mission is that its initial field of view is now one of the best-studied parts of the sky," said team member Padi Boyd, a researcher at NASA's Goddard Space Flight Center in Greenbelt, Maryland, who designed the Swift survey. For example, the entire area was observed in infrared light by NASA's Wide-field Infrared Survey Explorer, and NASA's Galaxy Evolution Explorer observed many parts of it in the ultraviolet. "Our group was looking for variable X-ray sources with optical counterparts seen by Kepler, especially active galaxies, where a central black hole drives the emissions," she explained. Using the X-ray and ultraviolet/optical telescopes aboard Swift, the researchers conducted the Kepler-Swift Active Galaxies and Stars Survey (KSwAGS), imaging about six square degrees, or 12 times the apparent size of a full moon, in the Kepler field. "With KSwAGS we found 93 new X-ray sources, about evenly split between active galaxies and various types of X-ray stars," said team member Krista Lynne Smith, a graduate student at the University of Maryland, College Park who led the analysis of Swift data. "Many of these sources have never been observed before in X-rays or ultraviolet light." For the brightest sources, the team obtained spectra using the 200-inch telescope at Palomar Observatory in California. These spectra provide detailed chemical portraits of the stars and show clear evidence of enhanced stellar activity, particularly strong diagnostic lines of calcium and hydrogen. The researchers used Kepler measurements to determine the rotation periods and sizes for 10 of the stars, which range from 2.9 to 10.5 times larger than the sun. Their surface temperatures range from somewhat hotter to slightly cooler than the sun, mostly spanning spectral types F through K. Astronomers classify the stars as subgiants and giants, which are more advanced evolutionary phases than the sun's caused by greater depletion of their primary fuel source, hydrogen. All of them eventually will become much larger red giant stars. A paper detailing the findings will be published in the Nov. 1 edition of the Astrophysical Journal and is now available online. Forty years ago, Ronald Webbink at the University of Illinois, Urbana-Champaign noted that close binary systems cannot survive once the fuel supply of one star dwindles and it starts to enlarge. The stars coalesce to form a single rapidly spinning star initially residing in a so-called "excretion" disk formed by gas thrown out during the merger. The disk dissipates over the next 100 million years, leaving behind a very active, rapidly spinning star. Howell and his colleagues suggest that their 18 KSwAGS stars formed by this scenario and have only recently dissipated their disks. To identify so many stars passing through such a cosmically brief phase of development is a real boon to stellar astronomers. "Webbink's model suggests we should find about 160 of these stars in the entire Kepler field," said co-author Elena Mason, a researcher at the Italian National Institute for Astrophysics Astronomical Observatory of Trieste. "What we have found is in line with theoretical expectations when we account for the small portion of the field we observed with Swift." The team has already extended their Swift observations to additional fields mapped by the K2 mission. Ames manages the Kepler and K2 missions for NASA's Science Mission Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corp. operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder. Goddard manages the Swift mission in collaboration with Pennsylvania State University in University Park, the Los Alamos National Laboratory in New Mexico and Orbital Sciences Corp. in Dulles, Virginia. Other partners include the University of Leicester and Mullard Space Science Laboratory in the United Kingdom, Brera Observatory and the Italian Space Agency in Italy, with additional collaborators in Germany and Japan.
News Article | December 15, 2016
"We've found the apparent sweet spot in the sizes of cold planets. Contrary to some theoretical predictions, we infer from current detections that the most numerous have masses similar to Neptune, and there doesn't seem to be the expected increase in number at lower masses," said lead scientist Daisuke Suzuki, a post-doctoral researcher at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and the University of Maryland Baltimore County. "We conclude that Neptune-mass planets in these outer orbits are about 10 times more common than Jupiter-mass planets in Jupiter-like orbits." Gravitational microlensing takes advantage of the light-bending effects of massive objects predicted by Einstein's general theory of relativity. It occurs when a foreground star, the lens, randomly aligns with a distant background star, the source, as seen from Earth. As the lensing star drifts along in its orbit around the galaxy, the alignment shifts over days to weeks, changing the apparent brightness of the source. The precise pattern of these changes provides astronomers with clues about the nature of the lensing star, including any planets it may host. "We mainly determine the mass ratio of the planet to the host star and their separation," said team member David Bennett, an astrophysicist at Goddard. "For about 40 percent of microlensing planets, we can determine the mass of the host star and therefore the mass of the planet." More than 50 exoplanets have been discovered using microlensing compared to thousands detected by other techniques, such as detecting the motion or dimming of a host star caused by the presence of planets. Because the necessary alignments between stars are rare and occur randomly, astronomers must monitor millions of stars for the tell-tale brightness changes that signal a microlensing event. However, microlensing holds great potential. It can detect planets hundreds of times more distant than most other methods, allowing astronomers to investigate a broad swath of our Milky Way galaxy. The technique can locate exoplanets at smaller masses and greater distances from their host stars, and it's sensitive enough to find planets floating through the galaxy on their own, unbound to stars. NASA's Kepler and K2 missions have been extraordinarily successful in finding planets that dim their host stars, with more than 2,500 confirmed discoveries to date. This technique is sensitive to close-in planets but not more distant ones. Microlensing surveys are complementary, best probing the outer parts of planetary systems with less sensitivity to planets closer to their stars. "Combining microlensing with other techniques provides us with a clearer overall picture of the planetary content of our galaxy," said team member Takahiro Sumi at Osaka University in Japan. From 2007 to 2012, the Microlensing Observations in Astrophysics (MOA) group, a collaboration between researchers in Japan and New Zealand, issued 3,300 alerts informing the astronomical community about ongoing microlensing events. Suzuki's team identified 1,474 well-observed microlensing events, with 22 displaying clear planetary signals. This includes four planets that were never previously reported. To study these events in greater detail, the team included data from the other major microlensing project operating over the same period, the Optical Gravitational Lensing Experiment (OGLE), as well as additional observations from other projects designed to follow up on MOA and OGLE alerts. From this information, the researchers determined the frequency of planets compared to the mass ratio of the planet and star as well as the distances between them. For a typical planet-hosting star with about 60 percent the sun's mass, the typical microlensing planet is a world between 10 and 40 times Earth's mass. For comparison, Neptune in our own solar system has the equivalent mass of 17 Earths. The results imply that cold Neptune-mass worlds are likely to be the most common types of planets beyond the so-called snow line, the point where water remained frozen during planetary formation. In the solar system, the snow line is thought to have been located at about 2.7 times Earth's mean distance from the sun, placing it in the middle of the main asteroid belt today. A paper detailing the findings was published in The Astrophysical Journal on Dec. 13. "Beyond the snow line, materials that were gaseous closer to the star condense into solid bodies, increasing the amount of material available to start the planet-building process," said Suzuki. "This is where we think planetary formation was most efficient, and it's also the region where microlensing is most sensitive." NASA's Wide Field Infrared Survey Telescope (WFIRST), slated to launch in the mid-2020s, will conduct an extensive microlensing survey. Astronomers expect it will deliver mass and distance determinations of thousands of planets, completing the work begun by Kepler and providing the first galactic census of planetary properties. NASA's Ames Research Center manages the Kepler and K2 missions for NASA's Science Mission Directorate. The Jet Propulsion Laboratory (JPL) in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corporation operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder. WFIRST is managed at Goddard, with participation by JPL, the Space Telescope Science Institute in Baltimore, the Infrared Processing and Analysis Center, also in Pasadena, and a science team comprising members from U.S. research institutions across the country. More information: "The Exoplanet Mass-ratio Function from the MOA-II Survey: Discovery of a Break and Likely Peak at a Neptune Mass," D. Suzuki et al., 2016 Dec. 20, Astrophysical Journal iopscience.iop.org/article/10.3847/1538-4357/833/2/145 , Arxiv: arxiv.org/abs/1612.03939
News Article | February 15, 2017
Danger zones in the air where radiation levels surge could pose an unrecognised health hazard. Airliners may have to avoid these in future, just as they do with volcanic ash clouds, to minimise any risk to travellers and crew. We have long known that high-altitude flight exposes us to cosmic rays. The radiation dose on a flight from London to Tokyo is roughly equivalent to a chest X-ray. Now research flights have revealed the existence of “clouds” where radiation levels can be at least double the usual level. They were discovered as a result of the NASA-funded Automated Radiation Measurements for Aerospace Safety (ARMAS) programme, which aims to develop new methods of measuring and monitoring high-altitude radiation. In 265 flights, radiation levels detected generally followed the expected pattern, but in at least six instances they surged, as though the aircraft was flying through a radiation cloud. “We have seen several cases where the exposure is doubled while flying through the cloud,” says ARMAS principal investigator W. Kent Tobiska, of Los Angeles firm Space Environment Technologies. “It is quite variable and can easily be more or less than that.” Even higher levels have been recorded in some cases, but those results remain unpublished while the team considers alternative explanations for the data. Tobiska says the two main sources of radiation, cosmic rays and the solar wind, can’t account for the surges. “Our new measurements show a third component.” The surges coincided with geomagnetic storms. This points the finger at energetic electrons being lost from the outer Van Allen radiation belts, where charged particles mostly from the solar wind are trapped by Earth’s magnetic field. Tobiska believes that such a storm can liberate electrons trapped in the Van Allen belts. “Those electrons are driven into the upper atmosphere, collide with nitrogen and oxygen atoms and molecules, and then create a spray of secondary and tertiary radiation, likely in the form of gamma rays.” This radiation, he thinks, is what the ARMAS flights are detecting across a wide area. Daniel Baker of the University of Colorado’s Laboratory for Atmospheric and Space Physics says this mechanism seems feasible. “It is plausible that the ARMAS results are related to enhanced loss of radiation belt particles from the magnetosphere into the middle and lower atmosphere.” There are no set standards for radiation safety in US aviation at present, but Tobiska says that regulations are likely in the next few years. The absolute risk may be low, as a chest X-ray only increases the risk of a fatal cancer by 1 in 200,000, but these must be balanced against the large number of flights and whether risk is avoidable. “This is mainly for crew members,” says Tobiska, “but would certainly benefit frequent flyers and even fetuses in their first trimester.” ARMAS work using satellite data and airborne sensors may allow the radiation “clouds” to be tracked. Tobiska says that in future, flights may be diverted or directed to a lower altitude to avoid them.
News Article | March 10, 2016
The one-of-a-kind opportunity gave scientists an intimate view of the havoc that the comet's passing wreaked on the magnetic environment, or magnetosphere, around Mars. The effect was temporary but profound. "Comet Siding Spring plunged the magnetic field around Mars into chaos," said Jared Espley, a MAVEN science team member at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "We think the encounter blew away part of Mars' upper atmosphere, much like a strong solar storm would." Unlike Earth, Mars isn't shielded by a strong magnetosphere generated within the planet. The atmosphere of Mars offers some protection, however, by redirecting the solar wind around the planet, like a rock diverting the flow of water in a creek. This happens because at very high altitudes Mars' atmosphere is made up of plasma – a layer of electrically charged particles and gas molecules. Charged particles in the solar wind interact with this plasma, and the mingling and moving around of all these charges produces currents. Just like currents in simple electrical circuits, these moving charges induce a magnetic field, which, in Mars' case, is quite weak. Comet Siding Spring is also surrounded by a magnetic field. This results from the solar wind interacting with the plasma generated in the coma – the envelope of gas flowing from a comet's nucleus as it is heated by the sun. Comet Siding Spring's nucleus – a nugget of ice and rock measuring no more than half a kilometer (about 1/3 mile) – is small, but the coma is expansive, stretching out a million kilometers (more than 600,000 miles) in every direction. The densest part of the coma – the inner region near the nucleus – is the part of a comet that's visible to telescopes and cameras as a big fuzzy ball. When comet Siding Spring passed Mars, the two bodies came within about 140,000 kilometers (roughly 87,000 miles) of each other. The comet's coma washed over the planet for several hours, with the dense inner coma reaching, or nearly reaching, the surface. Mars was flooded with an invisible tide of charged particles from the coma, and the powerful magnetic field around the comet temporarily merged with – and overwhelmed – the planet's own weak one. "The main action took place during the comet's closest approach," said Espley, "but the planet's magnetosphere began to feel some effects as soon as it entered the outer edge of the comet's coma." At first, the changes were subtle. As Mars' magnetosphere, which is normally draped neatly over the planet, started to react to the comet's approach, some regions began to realign to point in different directions. With the comet's advance, these effects built in intensity, almost making the planet's magnetic field flap like a curtain in the wind. By the time of closest approach – when the plasma from the comet was densest – Mars' magnetic field was in complete chaos. Even hours after the comet's departure, some disruption continued to be measured. Espley and colleagues think the effects of the plasma tide were similar to those of a strong but short-lived solar storm. And like a solar storm, the comet's close passage likely fueled a temporary surge in the amount of gas escaping from Mars' upper atmosphere. Over time, those storms took their toll on the atmosphere. "With MAVEN, we're trying to understand how the sun and solar wind interact with Mars," said Bruce Jakosky, MAVEN's principal investigator from the University of Colorado's Laboratory for Atmospheric and Space Physics in Boulder. "By looking at how the magnetospheres of the comet and of Mars interact with each other, we're getting a better understanding of the detailed processes that control each one." This research was published in Geophysical Research Letters. More information: For more information about MAVEN, visit www.nasa.gov/maven
News Article | February 10, 2017
A new study on the absence of liquid water on the surface of Mars has suggested that an easy escape route of hydrogen from the high altitude upper atmosphere is one of the major reasons. In the study, researchers at the University of Colorado debunked the earlier assumption of slower loss of water from Mars and argued that the planet lost liquid water at a rapid pace. The new theory refutes earlier models that said Martian hydrogen escaped slowly yet steadily. "Going back to the 1970s, the conventional picture of Martian hydrogen loss has been one of slow, steady escape over long time scales," said Mike Chaffin, lead author of the new study and a research associate at Laboratory for Atmospheric and Space Physics. According to data from Mars Express, one reason for the rapid hydrogen escape was the floating of water molecules at unusually higher altitudes when the Red planet warms up during summers. This is in contrast to "cold trap" mechanism existing on Earth for keeping atmospheric water closer to the ground. When the water molecules pile up in the middle atmosphere, ultraviolet rays break them into oxygen and hydrogen. After this, an easy escape by hydrogen follows by defying the Mars' low gravity. The study has been published in Nature GeoScience. Though consolidating the findings will require more validations from other data, the finding is significant in underscoring that Mars lost water at a differential rate and no uniform time scale existed. Chaffin noted that there was high seasonal variation in the matter of water loss from Mars than thought earlier. Drastic variations in the hydrogen escape were documented by Hubble Telescope of NASA and the Mars Express of ESA way back in 2007. The data said the rate of hydrogen escape became 100 times more than the normal rate when the orbit of Mars came closest to the sun. That makes the old model of slow hydrogen escape from Mars pretty inadequate. Previous models made a case of water molecules in the Martian atmosphere getting "cold trapped" at lower levels as vapor abundance was low at high altitudes. This was the mechanism with regard to water molecules in Earth's atmosphere. However, that process does not work with Mars as shown by Mars Express data. What actually happens is, when the lower atmosphere of Red Planet heats up during southern summer, water molecules keep rising higher than normal in the atmosphere and bypass the cold trap to move into middle altitudes. Ultraviolet light rays split the water molecules to produce atomic oxygen and hydrogen. When hydrogen moves up the higher altitudes thanks to its low weight, the gas escapes the Martian gravity while leaving the heavier oxygen behind. More details on the hydrogen escape may be gauged by the observations Mars Atmosphere and Volatile Evolution spacecraft that is studying the Martian upper atmosphere and Trace Gas Orbiter of ESA that starts Martian studies in 2018. The co-authors of the study included LASP planetary scientists Justin Deighan, Nick Schneider, and Ian Stewart. © 2017 Tech Times, All rights reserved. Do not reproduce without permission.
News Article | February 15, 2017
MARS has a real water shortage. It seems we have either misunderstood what its early years were like – or vast amounts of water are hiding beneath its surface. A lot of evidence points towards Mars being warm and wet early in its history; features that look like rivers, lakes and outflows have been spotted both from orbit and by rovers on the surface, and a lot of the planet’s minerals contain water. So where did all this water go? The Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft was sent to find the answer. Since its arrival at Mars in 2014, it has been measuring how much atmosphere Mars is losing to space. From that, we can figure out how much it had in the past. The orbiter keeps track of both the activity of the sun and the ions streaming away from the planet’s atmosphere to build up an inventory of everything that enters and leaves over time. It also estimates the total loss by measuring the fraction of heavier isotopes of certain atoms versus their lighter counterparts. As the lighter versions are easier to knock out into space with a stray cosmic ray or extra energy from solar photons, a higher fraction of heavy isotopes remaining in Mars’s present-day atmosphere means much of the original atmosphere has been lost. MAVEN focuses on hydrogen and oxygen as ways to trace water and carbon dioxide, and neutral argon as a way to measure the sheer volume of atmosphere loss. Based on measurements of these taken over a full Martian year, the team concludes that about 4 billion years ago, the Red Planet’s atmospheric pressure – currently less than 1 per cent of Earth’s – was up to 1.5 times what Earth’s is today. They also found that it could have had the equivalent of a global ocean between 2 and 40 metres deep in its distant past. “It’s a consistent story,” said team leader Bruce Jakosky at the Laboratory for Atmospheric and Space Physics in Boulder, Colorado, who presented the findings at the American Geophysical Union meeting in San Francisco in December. “Loss of gas to space is likely a major if not the major process for changing the Mars climate through time.” The trouble is, that’s less water than expected. In 2015, James Head at Brown University and Michael Carr at the US Geological Survey estimated that the equivalent of a global ocean a few hundred metres deep was needed to explain all the geological features that look like they were formed by water. “We were counting on their loss rate to explain it,” Head says. “And they didn’t come through.” One possible reason for the discrepancy is that the long-held notion of Mars being like Earth in the past is wrong. One theory has it that the planet was actually cold and dry, and that streams and rivers formed underneath the ice pack instead of via water flowing on the surface. All that would be needed is a slightly denser CO atmosphere – which MAVEN’s measurements suggest you had. “Loss of gas to space is likely a major process for changing the Mars climate through time” The other option is that the water is hidden away somewhere, maybe underground. Dark streaks recently spotted on crater rims that look like they could be liquid water may be fed by underground aquifers, for instance. “Either it’s hidden somewhere, or there wasn’t that much to start with,” says Carr. This article appeared in print under the headline “Where did all the Martian water go?”
Kopp G.,Laboratory for Atmospheric and Space Physics |
Lean J.L.,U.S. Navy
Geophysical Research Letters | Year: 2011
The most accurate value of total solar irradiance during the 2008 solar minimum period is 1360.8± 0.5 W m-2 according to measurements from the Total Irradiance Monitor (TIM) on NASA's Solar Radiation and Climate Experiment (SORCE) and a series of new radiometric laboratory tests. This value is significantly lower than the canonical value of 1365.4± 1.3 W m -2 established in the 1990s, which energy balance calculations and climate models currently use. Scattered light is a primary cause of the higher irradiance values measured by the earlier generation of solar radiometers in which the precision aperture defining the measured solar beam is located behind a larger, view-limiting aperture. In the TIM, the opposite order of these apertures precludes this spurious signal by limiting the light entering the instrument. We assess the accuracy and stability of irradiance measurements made since 1978 and the implications of instrument uncertainties and instabilities for climate research in comparison with the new TIM data. TIM's lower solar irradiance value is not a change in the Sun's output, whose variations it detects with stability comparable or superior to prior measurements; instead, its significance is in advancing the capability of monitoring solar irradiance variations on climate-relevant time scales and in improving estimates of Earth energy balance, which the Sun initiates. Copyright 2011 by the American Geophysical Union.