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terça-feira, 28 de fevereiro de 2017

NASA WEB-Mid-infrared Of Saturn's Rings Shows Bright Cassini Division

Mid-infrared Of Saturn's Rings Shows Bright Cassini Division

©NATIONAL INSTITUTES OF NATURAL SCIENCES
Saturn View in The Mid-infrared
A team of researchers has succeeded in measuring the brightnesses and temperatures of Saturn's rings using the mid-infrared images taken by the Subaru Telescope in 2008.
The images are the highest resolution ground-based views ever made. They reveal that, at that time, the Cassini Division and the C ring were brighter than the other rings in the mid-infrared light and that the brightness contrast appeared to be the inverse of that seen in the visible light (Figure 1). The data give important insights into the nature of Saturn's rings.
The beautiful appearance of Saturn and its rings has always fascinated people. The rings consist of countless numbers of ice particles orbiting above Saturn's equator. However, their detailed origin and nature remain unknown. Spacecraft- and ground-based telescopes have tackled that mystery with many observations at various wavelengths and methods. The international Cassini mission led by NASA has been observing Saturn and its rings for more than 10 years, and has released a huge number of beautiful images.
Subaru Views Saturn
The Subaru Telescope also has observed Saturn several times over the years. Dr. Hideaki Fujiwara, Subaru Public Information Officer/Scientist, analyzed data taken in January 2008 using the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on the telescope to produce a beautiful image of Saturn for public information purposes. During the analysis, he noticed that the appearance of Saturn's rings in the mid-infrared part of the spectrum was totally different from what is seen in the visible light
Saturn's main rings consist of the C, B, and A rings, each with different populations of particles. The Cassini Division separates the B and A rings. The 2008 image shows that the Cassini Division and the C ring are brighter in the mid-infrared wavelengths than the B and A rings appear to be (Figure 1). This brightness contrast is the inverse of how they appear in the visible light, where the B and A rings are always brighter than the Cassini Division and the C ring (Figure 2).
"Thermal emission" from ring particles is observed in the mid-infrared, where warmer particles are brighter. The team measured the temperatures of the rings from the images, which revealed that the Cassini Division and the C ring are warmer than the B and A rings. The team concluded that this was because the particles in the Cassini Division and C ring are more easily heated by solar light due to their sparser populations and darker surfaces.
On the other hand, in the visible light, observers see sunlight being reflected by the ring particles. Therefore, the B and A rings, with their dense populations of particles, always seem bright in the visible wavelengths, while the Cassini Division and the C ring appear faint. The difference in the emission process explains the inverse brightnesses of Saturn's rings between the mid-infrared and the visible-light views.
Changing Angles Change the Brightnesses
It turns out that the Cassini Division and the C ring are not always brighter than the B and A rings, even in the mid-infrared. The team investigated images of Saturn's rings taken in April 2005 with COMICS, and found that the Cassini Division and the C ring were fainter than the B and A rings at that time, which is the same contrast to what was seen in the visible light (Figure 3).
The team concluded that the "inversion" of the brightness of Saturn's rings between 2005 and 2008 was caused by the seasonal change in the ring opening angle to the Sun and Earth. Since the rotation axis of Saturn inclines compared to its orbital plane around the Sun, the ring opening angle to the Sun changes over a 15-year cycle. This makes a seasonal variation in the solar heating of the ring particles. The change in the opening angle viewed from the Earth affects the apparent filling factor of the particles in the rings. These two variations - the temperature and the observed filling factor of the particles - led to the change in the mid-infrared appearance of Saturn's rings.
The data taken with the Subaru Telescope revealed that the Cassini Division and the C ring are sometimes bright in the mid-infrared though they are always faint in visible light. "I am so happy that the public information activities of the Subaru Telescope, of which I am in charge, led to this scientific finding," said Dr. Fujiwara. "We are going to observe Saturn again in May 2017 and hope to investigate the nature of Saturn's rings further by taking advantages of observations with space missions and ground-based telescopes."

NASA WEB-NASA JPL latest news release Martian Winds Carve Mountains, Move Dust, Raise Dust

NASA JPL latest news release
Martian Winds Carve Mountains, Move Dust, Raise Dust
Fast Facts:
› Wind is a dominant force shaping landscapes on Mars, despite the thin air.
› A recent study supports the idea that a mountain that is oddly in the middle of a Martian crater was formed by wind subtracting other material after the crater had been filled to the brim with sediments.
› Modern winds in the crater show effects such as dusty whirlwinds, shifting sand and active dunes.
› NASA's Mars rover Curiosity has begun investigating linear-shaped dunes during the crater's windy summer season.
On Mars, wind rules. Wind has been shaping the Red Planet's landscapes for billions of years and continues to do so today. Studies using both a NASA orbiter and a rover reveal its effects on scales grand to tiny on the strangely structured landscapes within Gale Crater.
NASA's Curiosity Mars rover, on the lower slope of Mount Sharp -- a layered mountain inside the crater -- has begun a second campaign of investigating active sand dunes on the mountain's northwestern flank. The rover also has been observing whirlwinds carrying dust and checking how far the wind moves grains of sand in a single day's time.
Gale Crater observations by NASA's Mars Reconnaissance Orbiter have confirmed long-term patterns and rates of wind erosion that help explain the oddity of having a layered mountain in the middle of an impact crater.
"The orbiter perspective gives us the bigger picture -- on all sides of Mount Sharp and the regional context for Gale Crater. We combine that with the local detail and ground-truth we get from the rover," said Mackenzie Day of the University of Texas, Austin, lead author of a research report in the journal Icarus about wind's dominant role at Gale.
The combined observations show that wind patterns in the crater today differ from when winds from the north removed the material that once filled the space between Mount Sharp and the crater rim. Now, Mount Sharp itself has become a major factor in determining local wind directions. Wind shaped the mountain; now the mountain shapes the wind.
The Martian atmosphere is about a hundred times thinner than Earth's, so winds on Mars exert much less force than winds on Earth. Time is the factor that makes Martian winds so dominant in shaping the landscape. Most forces that shape Earth's landscapes -- water that erodes and moves sediments, tectonic activity that builds mountains and recycles the planet's crust, active volcanism -- haven't influenced Mars much for billions of years. Sand transported by wind, even if infrequent, can whittle away Martian landscapes over that much time.
How to Make a Layered Mountain
Gale Crater was born when the impact of an asteroid or comet more than 3.6 billion years ago excavated a basin nearly 100 miles (160 kilometers) wide. Sediments including rocks, sand and silt later filled the basin, some delivered by rivers that flowed in from higher ground surrounding Gale. Curiosity has found evidence of that wet era from more than 3 billion years ago. A turning point in Gale's history -- when net accumulation of sediments flipped to net removal by wind erosion -- may have coincided with a key turning point in the planet's climate as Mars became drier, Day noted.
Scientists first proposed in 2000 that the mound at the center of Gale Crater is a remnant from wind eroding what had been a totally filled basin. The new work calculates that the vast volume of material removed -- about 15,000 cubic miles (64,000 cubic kilometers) -- is consistent with orbital observations of winds' effects in and around the crater, when multiplied by a billion or more years.
Other new research, using Curiosity, focuses on modern wind activity in Gale.
The rover this month is investigating a type of sand dune that differs in shape from dunes the mission investigated in late 2015 and early 2016. Crescent-shaped dunes were the feature of the earlier campaign -- the first ever up-close study of active sand dunes anywhere other than Earth. The mission's second dune campaign is at a group of ribbon-shaped linear dunes.
"In these linear dunes, the sand is transported along the ribbon pathway, while the ribbon can oscillate back and forth, side to side," said Nathan Bridges, a Curiosity science team member at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.
The season at Gale Crater is now summer, the windiest time of year. That's the other chief difference from the first dune campaign, conducted during less-windy Martian winter.
"We're keeping Curiosity busy in an area with lots of sand at a season when there's plenty of wind blowing it around," said Curiosity Project Scientist Ashwin Vasavada of NASA's Jet Propulsion Laboratory, Pasadena, California. "One aspect we want to learn more about is the wind's effect on sorting sand grains with different composition. That helps us interpret modern dunes as well as ancient sandstones."
Before Curiosity heads farther up Mount Sharp, the mission will assess movement of sand particles at the linear dunes, examine ripple shapes on the surface of the dunes, and determine the composition mixture of the dune material.
Shifting Sand and 'Dust Devils'
Images taken one day apart of the same piece of ground, including some recent pairs from the downward-looking camera that recorded the rover's landing-day descent, show small ripples of sand moving about an inch (2.5 centimeters) downwind.
Meanwhile, whirlwinds called "dust devils" have been recorded moving across terrain in the crater, in sequences of afternoon images taken several seconds apart.
After completing the planned dune observations and measurements, Curiosity will proceed southward and uphill toward a ridge where the mineral hematite has been identified from Mars Reconnaissance Orbiter observations. The Curiosity science team has decided to call this noteworthy feature the "Vera Rubin Ridge," commemorating Vera Cooper Rubin (1928-2016), whose astronomical observations provided evidence for the existence of the universe's dark matter.
As Curiosity focuses on the sand dunes, rover engineers are analyzing results of diagnostic tests on the drill feed mechanism, which drives the drill bit in and out during the process of collecting sample material from a rock. One possible cause of an intermittent issue with the mechanism is that a plate for braking the movement may be obstructed, perhaps due to a small piece of debris, resisting release of the brake. The diagnostic tests are designed to be useful in planning the best way to resume use of the drill.
The rover team is also investigating why the lens cover on Curiosity's arm-mounted Mars Hand Lens Imager (MAHLI) did not fully open in response to commands on Feb. 24. The arm has been raised to minimize risk of windborne sand reaching the lens while the cover is partially open. Diagnostic tests of the lens cover are planned this week.
During the first year after Curiosity's 2012 landing in Gale Crater, the mission fulfilled its main goal byfinding that the region once offered environmental conditions favorable for microbial life. Theconditions in long-lived ancient freshwater Martian lake environments included all of the key chemical elements needed for life as we know it, plus a chemical source of energy that is used by many microbes on Earth. The extended mission is investigating how and when the habitable ancient conditions evolved into conditions drier and less favorable for life. For more information about 

quarta-feira, 22 de fevereiro de 2017

NASA WEB-CBS-Stunning space discovery: 7 Earth-size planets found orbiting dwarf star

Stunning space discovery: 7 Earth-size planets found orbiting dwarf star

Imagine standing on the surface of the exoplanet TRAPPIST-1. This artist’s concept is one interpretation of what it could look like.
 
 NASA/JPL-CALTECH
Last Updated Feb 22, 2017 2:12 PM EST
Astronomers have discovered seven roughly Earth-size planets very close to a cool dwarf star some 39 light years from Earth, including three orbiting in the star’s habitable zone where liquid water, a key ingredient for life as it’s known on Earth, could be present, researchers announced Wednesday.
The record-setting star system is the first to feature three Earth analogues in the so-called “Goldilocks” zone of their parent star and the first to include seven such worlds overall. The discovery was announced Wednesday in the journal Nature.
“Finding a second Earth is not just a matter of if, but when,” said Thomas Zurbuchen, associate administrator of science at NASA Headquarters. “Just imagine how many worlds are out there that have a shot at becoming a habitable system that we could explore.”
The intriguing star system was first studied by Belgium’s Transiting Planets and Planetesimals Small Telescope, or TRAPPIST, observatory in Chile where observations in 2016 indicated the presence of two and possibly three planets.
NASA’s infrared-sensitive Spitzer Space Telescope, working with the European Southern Observatory’s Very Large Telescope, then spent 500 hours studying the star, confirming the existence of two planets and discovering five more, boosting the total to seven.
“Not one, not two, but seven Earth-size planets,” marveled Michael Gillon, an astronomer at the University of Liege in Belgium who led the study. “This is is the first time that so many Earth-size planets were found around the same star. Furthermore, with three of them in the habitable zone.
“The star itself is what is called an ultra-cool dwarf, which is the least massive kind of star that exists,” he told reporters. “These stars are much smaller, much cooler than our sun and still, they are very frequent at the scale of our galaxy, more frequent than solar-type stars.”
For comparison, he said, if Earth’s sun was the size of a basketball, TRAPPIST-1 would be roughly equivalent to a golf ball.
exoplanets2.jpg
This artist's conception shows what the TRAPPIST-1 planetary system may look like, based on available data about their diameters, masses and distances from the host star.
 NASA/JPL-CALTECH
Some 229 trillion miles from Earth in the constellation Aquarius, the TRAPPIST-1 star is “so cool that liquid water could survive on planets orbiting very close to it, closer than is possible on planets in our solar system,” NASA said in a statement. “All seven of the TRAPPIST-1 planetary orbits are closer to their host star than Mercury is to our sun.”
The innermost habitable zone planet is roughly the size of Earth and receives about the same amount of light, possibly resulting in surface temperatures very similar to our planet’s. The middle planet in the habitable zone receives about the same amount of light that Mars does, orbiting TRAPPIST-1 every nine days. The outermost planet receives the level of sunlight one would experience somewhere between Mars and the asteroid belt.
The planets may be “tidally locked” to their star, gravitationally held in place so only one side of the worlds face their sun. If so, the planets could host truly alien weather patterns, with strong winds and extreme changes in temperature.
The planets also are very close together. Researchers said an observer standing on one world likely could discern clouds and other features on neighboring worlds, which could appear larger in the sky than Earth’s moon.
But it is not yet known whether any of the planets host an atmosphere or liquid water and additional observations are planned, along with expanded studies to look for planets around other dwarf stars.
exoplanets.jpg
The TRAPPIST-1 star, an ultra-cool dwarf, has seven Earth-size planets orbiting it.
 NASA/JPL-CALTECH
Spitzer detected the planets indirectly by studying how light from TRAPPIST-1 periodically dimmed as the worlds repeatedly passed in front of the star.
Using that data and others, astronomers were able to measure the sizes of the planets, allowing them to roughly calculate their masses, densities and orbital periods. It appears they likely are rocky planets, but additional observations are needed to determine if any have detectable atmospheres or liquid water.
“We’ve made a giant, accelerated leap forward in a search for habitable worlds and life on other worlds, potentially speaking,” said Sara Seager, professor of planetary science and physics at Massachusetts Institute of Technology. “With this amazing system, we know there must be many more potentially life-bearing worlds out there just waiting to be found.”
exoplanets-solar-system-comp.jpg
This chart shows, on the top row, artist conceptions of the seven planets of TRAPPIST-1 with their orbital periods, distances from their star, radii and masses as compared to those of Earth. The bottom row shows data about Mercury, Venus, Earth and Mars.
 NASA/JPL-CALTECH
Additional observations are planned by Spitzer and the Hubble Space Telescope, which will focus on four of the seven planets, including the three now known to orbit within the habitable zone of TRAPPIST-1. Hubble observed the two innermost planets earlier, but found no evidence of the sort of hydrogen-dominated atmospheres that define worlds like Jupiter, Saturn, Uranus and Neptune in Earth’s solar system.
NASA’s Kepler space telescope, which was built to look for transiting exoplanets, also is studying the TRAPPIST-1 system, collecting high-precision data that will help researchers refine their knowledge of the worlds discovered so far while being on the lookout for additional planets.
And NASA’s James Webb Space Telescope, the $8.6 billion follow-on to Hubble that is scheduled for launch in 2018, also will study the TRAPPIST-1 system, spectroscopically studying atmospheric constituents and looking for telltale signs of biological indicators such as oxygen, methane and other chemicals.

quinta-feira, 16 de fevereiro de 2017

NASA WEB-NASA-funded Website Lets the Public Search for New Nearby Worlds

NASA JPL latest news release
NASA-funded Website Lets the Public Search for New Nearby WorldsNASA is inviting the public to help search for possible undiscovered worlds in the outer reaches of our solar system and in neighboring interstellar space. A new website, called Backyard Worlds: Planet 9, lets everyone participate in the search by viewing brief movies made from images captured by NASA's Wide-field Infrared Survey Explorer (WISE) mission. The movies highlight objects that have gradually moved across the sky.
"There are just over four light-years between Neptune and Proxima Centauri, the nearest star, and much of this vast territory is unexplored," said lead researcher Marc Kuchner, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "Because there's so little sunlight, even large objects in that region barely shine in visible light. But by looking in the infrared, WISE may have imaged objects we otherwise would have missed."
WISE scanned the entire sky between 2010 and 2011, producing the most comprehensive survey at mid-infrared wavelengths currently available. With the completion of its primary mission, WISE was shut down in 2011. It was then reactivated in 2013 and given a new mission assisting NASA's efforts to identify potentially hazardous near-Earth objects (NEOs), which are asteroids and comets on orbits that bring them into the vicinity of Earth's orbit. The mission was renamed the Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE).
The new website uses the data to search for unknown objects in and beyond our own solar system. In 2016, astronomers at Caltech, in Pasadena, California, showed that several distant solar system objects possessed orbital features indicating they were affected by the gravity of an as-yet-undetected planet, which the researchers nicknamed "Planet Nine." If Planet Nine -- also known asPlanet X -- exists and is as bright as some predictions, it could show up in WISE data.
The search also may discover more-distant objects like brown dwarfs, sometimes called failed stars, in nearby interstellar space.
"Brown dwarfs form like stars but evolve like planets, and the coldest ones are much like Jupiter," said team member Jackie Faherty, an astronomer at the American Museum of Natural History in New York. "By using Backyard Worlds: Planet 9, the public can help us discover more of these strange rogue worlds."
Unlike more distant objects, those in or closer to the solar system appear to move across the sky at different rates. The best way to discover them is through a systematic search of moving objects in WISE images. While parts of this search can be done by computers, machines are often overwhelmed by image artifacts, especially in crowded parts of the sky. These include brightness spikes associated with star images and blurry blobs caused by light scattered inside WISE's instruments.
Backyard Worlds: Planet 9 relies on human eyes because we easily recognize the important moving objects while ignoring the artifacts. It's a 21st-century version of the technique astronomer Clyde Tombaugh used to find Pluto in 1930, a discovery made 87 years ago this week.
On the website, people around the world can work their way through millions of "flipbooks," which are brief animations showing how small patches of the sky changed over several years. Moving objects flagged by participants will be prioritized by the science team for follow-up observations by professional astronomers. Participants will share credit for their discoveries in any scientific publications that result from the project.
"Backyard Worlds: Planet 9 has the potential to unlock once-in-a-century discoveries, and it's exciting to think they could be spotted first by a citizen scientist," said team member Aaron Meisner, a postdoctoral researcher at the University of California, Berkeley, who specializes in analyzing WISE images.
Backyard Worlds: Planet 9 is a collaboration among NASA, UC Berkeley, the American Museum of Natural History in New York, Arizona State University in Tempe, the Space Telescope Science Institute in Baltimore, and Zooniverse, a collaboration of scientists, software developers and educators who collectively develop and manage citizen science projects on the internet.
NASA's Jet Propulsion Laboratory in Pasadena manages and operates WISE for NASA's Science Mission Directorate. The WISE mission was selected competitively under NASA's Explorers Program managed by the agency's Goddard Space Flight Center. The science instrument was built by the Space Dynamics Laboratory in Logan, Utah. The spacecraft was built by Ball Aerospace & Technologies Corp. in Boulder, Colorado. Science operations and data processing take place at IPAC at Caltech, which manages JPL for NASA.
For more information about Backyard Worlds: Planet 9

quarta-feira, 15 de fevereiro de 2017

NASA WEB-Lasers Could Give Space Research its 'Broadband' Moment

Lasers Could Give Space Research its 'Broadband' Moment


Several upcoming NASA missions will use lasers to increase data transmission from space.

Several upcoming NASA missions will use lasers to increase data transmission from space. Image Credit: NASA's Goddard Space Flight Center/Amber Jacobson, producer
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Thought your Internet speeds were slow? Try being a space scientist for a day.
The vast distances involved will throttle data rates to a trickle. You're lucky if a spacecraft can send more than a few megabits per second (Mbps) -- a pittance even by dial-up standards.
But we might be on the cusp of a change. Just as going from dial-up to broadband revolutionized the Internet and made high-resolution photos and streaming video a given, NASA may be ready to undergo a similar "broadband" moment in coming years.
The key to that data revolution will be lasers. For almost 60 years, the standard way to "talk" to spacecraft has been with radio waves, which are ideal for long distances. But optical communications, in which data is beamed over laser light, can increase that rate by as much as 10 to 100 times.
High data rates will allow researchers to gather science faster, study sudden events like dust storms or spacecraft landings, and even send video from the surface of other planets. The pinpoint precision of laser communications is also well suited to the goals of NASA mission planners, who are looking to send spacecraft farther out into the solar system.
"Laser technology is ideal for boosting downlink communications from deep space," said Abi Biswas, the supervisor of the Optical Communications Systems group at NASA's Jet Propulsion Laboratory, Pasadena, California. "It will eventually allow for applications like giving each astronaut his or her own video feed, or sending back higher-resolution, data-rich images faster."
NASA's space lasers
Past and future NASA projects involving laser communications:
Name: Lunar Laser Communications Demonstration (LLCD)
Led by: Goddard Space Flight Center
Year: 2013
Objective: Was NASA's first system for two-way communication using a laser instead of radio waves. An error-free uplink data rate of 20 Mbps transmitted from a primary ground station in New Mexico to NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE), a spacecraft orbiting the moon. Demonstrated an error-free downlink rate of 622 Mbps -- the equivalent of streaming 30 channels of HDTV from the moon.
Name: Optical Payload for Lasercomm Science (OPALS)
Led by: JPL
Year: 2014
Objective: Testing laser communications from the International Space Station. Beamed a video file every 3.5 seconds for a total of 148 seconds. With traditional downlink methods, sending the 175-megabit video just once would have taken 10 minutes.
Name: Laser Communications Relay Demonstration (LCRD)
Led by: Goddard Space Flight Center
Year: 2019
Objective: Will relay laser signals between telescopes at Table Mountain, California, and in Hawaii through a relay satellite in geostationary orbit during a two-year demonstration period. The system is designed to operate for up to five years to prove the everyday reliability of laser communications for future NASA missions.
Name: Deep Space Optical Communications (DSOC)
Led by JPL
Year: 2023
Objective: To test laser communications from deep space. An upcoming NASA Discovery mission called Psyche will fly to a metallic asteroid starting in 2023. Psyche is planned to host a laser device called DSOC, which would beam data down to a telescope at Palomar Mountain Observatory in California.
Science at the speed of light
Both radio and lasers travel at the speed of light, but lasers travel in a higher-frequency bandwidth. That allows them to carry more information than radio waves, which is crucial when you're collecting massive amounts of data and have narrow windows of time to send it back to Earth.
A good example is NASA's Mars Reconnaissance Orbiter, which sends science data at a blazing maximum of 6 Mbps. Biswas estimated that if the orbiter used laser comms technology with a mass and power usage comparable to its current radio system, it could probably increase the maximum data rate to 250 Mbps.
That might still sound stunningly slow to Internet users. But on Earth, data is sent over far shorter distances and through infrastructure that doesn't exist yet in space, so it travels even faster.
Increasing data rates would allow scientists to spend more of their time on analysis than on spacecraft operations.
"It's perfect when things are happening fast and you want a dense data set," said Dave Pieri, a JPL research scientist and volcanologist. Pieri has led past research on how laser comms could be used to study volcanic eruptions and wildfires in near real-time. "If you have a volcano exploding in front of you, you want to assess its activity level and propensity to keep erupting. The sooner you get and process that data, the better."
That same technology could apply to erupting cryovolcanoes on icy moons around other planets. Pieri noted that compared to radio transmission of events like these, "laser comms would up the ante by an order of magnitude."
Clouding the future of lasers
That's not to say the technology is perfect for every scenario. Lasers are subject to more interference from clouds and other atmospheric conditions than radio waves; pointing and timing are also challenges.
Lasers also require ground infrastructure that doesn't yet exist. NASA's Deep Space Network, a system of antenna arrays located across the globe, is based entirely on radio technology. Ground stations would have to be developed that could receive lasers in locations where skies are reliably clear.
Radio technology won't be going away. It works in rain or shine, and will continue to be effective for low-data uses like providing commands to spacecraft.
Next steps
Two upcoming NASA missions will help engineers understand the technical challenges involved in conducting laser communications in space. What they'll learn will advance lasers toward becoming a common form of space communication in the future.
The Laser Communications Relay Demonstration (LCRD), led by NASA's Goddard Space Flight Center in Greenbelt, Maryland, is due to launch in 2019. LCRD will demonstrate the relay of data using laser and radio frequency technology. It will beam laser signals almost 25,000 miles (40,000 kilometers) from a ground station in California to a satellite in geostationary orbit, then relay that signal to another ground station. JPL is developing one of the ground stations at Table Mountain in southern California. Testing laser communications in geostationary orbit, as LCRD will do, has practical applications for data transfer on Earth.
Deep Space Optical Communications (DSOC), led by JPL, is scheduled to launch in 2023 as part of an upcoming NASA Discovery mission. That mission, Psyche, will fly to a metallic asteroid, testing laser comms from a much greater distance than LCRD.
The Psyche mission has been planned to carry the DSOC laser device onboard the spacecraft. Effectively, the DSOC mission will try to hit a bullseye using a deep space laser -- and because of the planet's rotation, it will hit a moving target, as well.

segunda-feira, 13 de fevereiro de 2017

NASA WEB-NASA's Curiosity Rover Sharpens Paradox of Ancient Mars

NASA JPL latest news release

Fast Facts:
› Curiosity rover findings add to a puzzle about ancient Mars because the same rocks that indicate a lake was present also indicate there was very little carbon dioxide in the air to help keep a lake unfrozen.
› No carbonate has been found definitively in rock samples analyzed by Curiosity.
› A new study calculates how much carbon dioxide could have been in the ancient atmosphere without resulting in carbonate detectable by the rover: not much.
Mars scientists are wrestling with a problem. Ample evidence says ancient Mars was sometimes wet, with water flowing and pooling on the planet's surface. Yet, the ancient sun was about one-third less warm and climate modelers struggle to produce scenarios that get the surface of Mars warm enough for keeping water unfrozen.
A leading theory is to have a thicker carbon-dioxide atmosphere forming a greenhouse-gas blanket, helping to warm the surface of ancient Mars. However, according to a new analysis of data from NASA's Mars rover Curiosity, Mars had far too little carbon dioxide about 3.5 billion years ago to provide enough greenhouse-effect warming to thaw water ice.
The same Martian bedrock in which Curiosity found sediments from an ancient lake where microbes could have thrived is the source of the evidence adding to the quandary about how such a lake could have existed. Curiosity detected no carbonate minerals in the samples of the bedrock it analyzed. The new analysis concludes that the dearth of carbonates in that bedrock means Mars' atmosphere when the lake existed -- about 3.5 billion years ago -- could not have held much carbon dioxide.
"We've been particularly struck with the absence of carbonate minerals in sedimentary rock the rover has examined," said Thomas Bristow of NASA's Ames Research Center, Moffett Field, California. "It would be really hard to get liquid water even if there were a hundred times more carbon dioxide in the atmosphere than what the mineral evidence in the rock tells us." Bristow is the principal investigator for the Chemistry and Mineralogy (CheMin) instrument on Curiosity and lead author of the study being published this week in the Proceedings of the National Academy of Science.
Curiosity has made no definitive detection of carbonates in any lakebed rocks sampled since it landed in Gale Crater in 2011. CheMin can identify carbonate if it makes up just a few percent of the rock. The new analysis by Bristow and 13 co-authors calculates the maximum amount of carbon dioxide that could have been present, consistent with that dearth of carbonate.
In water, carbon dioxide combines with positively charged ions such as magnesium and ferrous iron to form carbonate minerals. Other minerals in the same rocks indicate those ions were readily available. The other minerals, such as magnetite and clay minerals, also provide evidence that subsequent conditions never became so acidic that carbonates would have dissolved away, as they can in acidic groundwater.
The dilemma has been building for years: Evidence about factors that affect surface temperatures -- mainly the energy received from the young sun and the blanketing provided by the planet's atmosphere -- adds up to a mismatch with widespread evidence for river networks and lakes on ancient Mars. Clues such as isotope ratios in today's Martian atmosphere indicate the planet once held a much denser atmosphere than it does now. Yet theoretical models of the ancient Martian climate struggle to produce conditions that would allow liquid water on the Martian surface for many millions of years. One successful model proposes a thick carbon-dioxide atmosphere that also contains molecular hydrogen. How such an atmosphere would be generated and sustained, however, is controversial.
The new study pins the puzzle to a particular place and time, with an on-the-ground check for carbonates in exactly the same sediments that hold the record of a lake about a billion years after the planet formed.
For the past two decades, researchers have used spectrometers on Mars orbiters to search for carbonate that could have resulted from an early era of more abundant carbon dioxide. They have found far less than anticipated.
"It's been a mystery why there hasn't been much carbonate seen from orbit," Bristow said. "You could get out of the quandary by saying the carbonates may still be there, but we just can't see them from orbit because they're covered by dust, or buried, or we're not looking in the right place. The Curiosity results bring the paradox to a focus. This is the first time we've checked for carbonates on the ground in a rock we know formed from sediments deposited under water."
The new analysis concludes that no more than a few tens of millibars of carbon dioxide could have been present when the lake existed, or it would have produced enough carbonate for Curiosity's CheMin to detect it. A millibar is one one-thousandth of sea-level air pressure on Earth. The current atmosphere of Mars is less than 10 millibars and about 95 percent carbon dioxide.
"This analysis fits with many theoretical studies that the surface of Mars, even that long ago, was not warm enough for water to be liquid," said Robert Haberle, a Mars-climate scientist at NASA Ames and a co-author of the paper. "It's really a puzzle to me."
Researchers are evaluating multiple ideas for how to reconcile the dilemma.
"Some think perhaps the lake wasn't an open body of liquid water. Maybe it was liquid covered with ice," Haberle said. "You could still get some sediments through to accumulate in the lakebed if the ice weren't too thick."
A drawback to that explanation is that the rover team has sought and not found in Gale Crater evidence that would be expected from ice-covered lakes, such as large and deep cracks called ice wedges, or "dropstones," which become embedded in soft lakebed sediments when they penetrate thinning ice.
If the lakes were not frozen, the puzzle is made more challenging by the new analysis of what the lack of a carbonate detection by Curiosity implies about the ancient Martian atmosphere.
"Curiosity's traverse through streambeds, deltas, and hundreds of vertical feet of mud deposited in ancient lakes calls out for a vigorous hydrological system supplying the water and sediment to create the rocks we're finding," said Curiosity Project Scientist Ashwin Vasavada of NASA's Jet Propulsion Laboratory, Pasadena, California. "Carbon dioxide, mixed with other gases like hydrogen, has been the leading candidate for the warming influence needed for such a system. This surprising result would seem to take it out of the running."
When two lines of scientific evidence appear irreconcilable, the scene may be set for an advance in understanding why they are not. The Curiosity mission is continuing to investigate ancient environmental conditions on Mars. It is managed by JPL, a division of Caltech in Pasadena, for NASA's Science Mission Directorate, Washington. Curiosity and other Mars science missions are a key part of NASA's Journey to Mars, building on decades of robotic exploration to send humans to the Red Planet in the 2030s. For more about Curiosity,