jeudi 19 octobre 2017

Final Spacewalk Preps Before November Cygnus Launch

ISS - Expedition 53 Mission patch.

October 19, 2017

Four Expedition 53 crewmates huddled together and made final preparations the day before the third and final spacewalk planned for October. Meanwhile, NASA’s commercial partner Orbital ATK has announced Nov. 11 as the new launch date for its Cygnus cargo carrier to the International Space Station.

Commander Randy Bresnik and Flight Engineer Joe Acaba are reviewing procedures and configuring tools before their spacewalk set for Friday at 8:05 a.m. EDT. NASA astronaut Mark Vande Hei and Paolo Nespoli from the European Space Agency will assist the spacewalkers in and out of their spacesuits and guide the duo as they work outside.

Image above: Astronaut Joe Acaba (foreground) assisted crewmates Randy Bresnik (right) and Mark Vande Hei before they began a spacewalk on Oct. 10. Image Credit: NASA.

The spacewalk was originally set for Wednesday before mission managers replanned a new set of tasks due to a camera light failure. Bresnik and Acaba will now replace the camera light assembly on the Canadarm2’s newly installed Latching End Effector and install an HD camera on the starboard truss. The duo will also replace a fuse on Dextre’s payload platform and remove thermal insulation on two electrical spare parts housed on stowage platforms.

Orbital ATK is targeting the launch of its eighth Cygnus resupply mission to the station for Nov. 11. Cygnus will make a nine-minute ascent to space after launch, then begin a two-day trek to the station where it will be installed for a month-long stay after its capture by the Canadarm2.

Related links:

Orbital ATK:

Expedition 53:

Space Station Research and Technology:

International Space Station (ISS):

Image (mentioned), Text, Credits: NASA/Mark Garcia.

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New NASA Study Improves Search for Habitable Worlds

NASA - Goddard Space Flight Center logo.

Oct. 19, 2017

New NASA research is helping to refine our understanding of candidate planets beyond our solar system that might support life.

“Using a model that more realistically simulates atmospheric conditions, we discovered a new process that controls the habitability of exoplanets and will guide us in identifying candidates for further study,” said Yuka Fujii of NASA’s Goddard Institute for Space Studies (GISS), New York, New York and the Earth-Life Science Institute at the Tokyo Institute of Technology, Japan, lead author of a paper on the research published in the Astrophysical Journal Oct. 17.

Image above: This illustration shows a star's light illuminating the atmosphere of a planet. Image Credits: NASA Goddard Space Flight Center.

Previous models simulated atmospheric conditions along one dimension, the vertical. Like some other recent habitability studies, the new research used a model that calculates conditions in all three dimensions, allowing the team to simulate the circulation of the atmosphere and the special features of that circulation, which one-dimensional models cannot do. The new work will help astronomers allocate scarce observing time to the most promising candidates for habitability.

Liquid water is necessary for life as we know it, so the surface of an alien world (e.g. an exoplanet) is considered potentially habitable if its temperature allows liquid water to be present for sufficient time (billions of years) to allow life to thrive. If the exoplanet is too far from its parent star, it will be too cold, and its oceans will freeze. If the exoplanet is too close, light from the star will be too intense, and its oceans will eventually evaporate and be lost to space. This happens when water vapor rises to a layer in the upper atmosphere called the stratosphere and gets broken into its elemental components (hydrogen and oxygen) by ultraviolet light from the star. The extremely light hydrogen atoms can then escape to space. Planets in the process of losing their oceans this way are said to have entered a “moist greenhouse” state because of their humid stratospheres.

In order for water vapor to rise to the stratosphere, previous models predicted that long-term surface temperatures had to be greater than anything experienced on Earth – over 150 degrees Fahrenheit (66 degrees Celsius). These temperatures would power intense convective storms; however, it turns out that these storms aren’t the reason water reaches the stratosphere for slowly rotating planets entering a moist greenhouse state.

“We found an important role for the type of radiation a star emits and the effect it has on the atmospheric circulation of an exoplanet in making the moist greenhouse state,” said Fujii. For exoplanets orbiting close to their parent stars, a star’s gravity will be strong enough to slow a planet’s rotation. This may cause it to become tidally locked, with one side always facing the star – giving it eternal day – and one side always facing away –giving it eternal night.

When this happens, thick clouds form on the dayside of the planet and act like a sun umbrella to shield the surface from much of the starlight. While this could keep the planet cool and prevent water vapor from rising, the team found that the amount of near-Infrared radiation (NIR) from a star could provide the heat needed to cause a planet to enter the moist greenhouse state. NIR is a type of light invisible to the human eye. Water as vapor in air and water droplets or ice crystals in clouds strongly absorbs NIR light, warming the air. As the air warms, it rises, carrying the water up into the stratosphere where it creates the moist greenhouse.

This process is especially relevant for planets around low-mass stars that are cooler and much dimmer than the Sun. To be habitable, planets must be much closer to these stars than our Earth is to the Sun. At such close range, these planets likely experience strong tides from their star, making them rotate slowly. Also, the cooler a star is, the more NIR it emits. The new model demonstrated that since these stars emit the bulk of their light at NIR wavelengths, a moist greenhouse state will result even in conditions comparable to or somewhat warmer than Earth's tropics. For exoplanets closer to their stars, the team found that the NIR-driven process increased moisture in the stratosphere gradually. So, it’s possible, contrary to old model predictions, that an exoplanet closer to its parent star could remain habitable.

This is an important observation for astronomers searching for habitable worlds, since low-mass stars are the most common in the galaxy. Their sheer numbers increase the odds that a habitable world may be found among them, and their small size increases the chance to detect planetary signals.

The new work will help astronomers screen the most promising candidates in the search for planets that could support life. “As long as we know the temperature of the star, we can estimate whether planets close to their stars have the potential to be in the moist greenhouse state,” said Anthony Del Genio of GISS, a co-author of the paper. “Current technology will be pushed to the limit to detect small amounts of water vapor in an exoplanet’s atmosphere. If there is enough water to be detected, it probably means that planet is in the moist greenhouse state.”

In this study, researchers assumed a planet with an atmosphere like Earth, but entirely covered by oceans. These assumptions allowed the team to clearly see how changing the orbital distance and type of stellar radiation affected the amount of water vapor in the stratosphere. In the future, the team plans to vary planetary characteristics such as gravity, size, atmospheric composition, and surface pressure to see how they affect water vapor circulation and habitability.

Image above: This is a plot of what the sea ice distribution could look like on a synchronously rotating ocean world. The star is off to the right, blue is where there is open ocean, and white is where there is sea ice. Image Credits: Anthony Del Genio/GISS/NASA.

The research was funded by the NASA Astrobiology Program through the Nexus for Exoplanet System Science; the NASA Postdoctoral Program, administered by Oak Ridge Affiliated Universities, Oak Ridge, Tennessee, and Universities Space Research Association, Columbia, Maryland; and a Grant-in-Aid from the Japan Society for the Promotion of Science, Tokyo, Japan (No.15K17605).

Related links:

Tokyo Institute of Technology, Japan, paper:

Astrobiology, Exoplanets:

Images (mentioned), Text, Credits: NASA Goddard Space Flight Center/Bill Steigerwald.


Dawn Mission Extended at Ceres

NASA - DAWN Mission patch.

Oct. 19, 2017

NASA has authorized a second extension of the Dawn mission at Ceres, the largest object in the asteroid belt between Mars and Jupiter. During this extension, the spacecraft will descend to lower altitudes than ever before at the dwarf planet, which it has been orbiting since March 2015. The spacecraft will continue at Ceres for the remainder of its science investigation and will remain in a stable orbit indefinitely after its hydrazine fuel runs out.

The Dawn flight team is studying ways to maneuver Dawn into a new elliptical orbit, which may take the spacecraft to less than 120 miles (200 kilometers) from the surface of Ceres at closest approach. Previously, Dawn's lowest altitude was 240 miles (385 kilometers).

Image above: This artist concept shows NASA's Dawn spacecraft above dwarf planet Ceres, as seen in images from the mission. Image Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.

A priority of the second Ceres mission extension is collecting data with Dawn's gamma ray and neutron spectrometer, which measures the number and energy of gamma rays and neutrons. This information is important for understanding the composition of Ceres' uppermost layer and how much ice it contains.

The spacecraft also will take visible-light images of Ceres' surface geology with its camera, as well as measurements of Ceres’ mineralogy with its visible and infrared mapping spectrometer.

The extended mission at Ceres additionally allows Dawn to be in orbit while the dwarf planet goes through perihelion, its closest approach to the Sun, which will occur in April 2018. At closer proximity to the Sun, more ice on Ceres' surface may turn to water vapor, which may in turn contribute to the weak transient atmosphere detected by the European Space Agency's Herschel Space Observatory before Dawn's arrival. Building on Dawn’s findings, the team has hypothesized that water vapor may be produced in part from energetic particles from the Sun interacting with ice in Ceres’ shallow surface.  Scientists will combine data from ground-based observatories with Dawn's observations to further study these phenomena as Ceres approaches perihelion.

The Dawn team is currently refining its plans for this next and final chapter of the mission. Because of its commitment to protect Ceres from Earthly contamination, Dawn will not land or crash into Ceres. Instead, it will carry out as much science as it can in its final planned orbit, where it will stay even after it can no longer communicate with Earth. Mission planners estimate the spacecraft can continue operating until the second half of 2018.

Dawn is the only mission ever to orbit two extraterrestrial targets. It orbited giant asteroid Vesta for 14 months from 2011 to 2012, then continued on to Ceres, where it has been in orbit since March 2015.

The Dawn mission is managed by JPL for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Alabama. UCLA is responsible for overall Dawn mission science. Orbital ATK Inc., in Dulles, Virginia, designed and built the spacecraft. The German Aerospace Center, Max Planck Institute for Solar System Research, Italian Space Agency and Italian National Astrophysical Institute are international partners on the mission team. For a complete list of mission participants, visit:

More information about Dawn is available at the following sites:

Image (mentioned), Text, Credits: NASA/Tony Greicius/JPL/Elizabeth Landau.


Take a Walk on Mars -- in Your Own Living Room

NASA - Mars Science Laboratory (MSL) logo.

Oct. 19, 2017

When NASA scientists want to follow the path of the Curiosity rover on Mars, they can don a mixed-reality headset and virtually explore the Martian landscape.

Animation above: Access Mars allows any member of the public to explore the discoveries of NASA's Curiosity rover. Animation Credits: NASA/JPL-Caltech.

Starting today, everyone can get a taste of what that feels like. NASA's Jet Propulsion Laboratory in Pasadena, California, collaborated with Google to produce Access Mars, a free immersive experience. It's available for use on all desktop and mobile devices and virtual reality/augmented reality (VR/AR) headsets. That includes mobile-based virtual reality devices on Apple and Android.

The experience was adapted from JPL's OnSight software, which assists scientists in planning rover drives and even holding meetings on Mars. Imagery from NASA's Curiosity rover provided the terrain, allowing users to wander the actual dunes and valleys explored by the spacecraft. Since being rolled out to JPL's scientists in 2015, OnSight has made studying Martian geology as intuitive as turning your head and walking around.

Image above: Access Mars lets users visit several sites from the past five years of discoveries made by NASA's Curiosity rover. Image Credits: NASA/JPL-Caltech.

Access Mars lets anyone with an internet connection take a guided tour of what those scientists experience. A simple walkthrough explains what the Curiosity rover does and details its dramatic landing in 2012. Users also can visit four sites that have been critical to NASA's Mars Science Laboratory mission: Curiosity's landing site; Murray Buttes; Marias Pass and Pahrump Hills. Additionally, the rover's latest location on lower Mt. Sharp will be periodically updated to reflect the mission's ongoing progress.

At the first three locations, users can zero in on objects of scientific interest, including rock outcrops and mud cracks. Katie Stack Morgan, a JPL scientist on the MSL mission, will explain the evidence of habitability Curiosity has unearthed.

Image above: Clicking on the floating spheres in Access Mars lets users see actual photos taking by NASA's Curiosity rover that allowed scientists to make new discoveries. Image Credits: NASA/JPL-Caltech.

More than anything, Access Mars offers a visceral impression of what it would be like to walk alongside Curiosity, wandering through the lonely, red desert.

"We've been able to leverage VR and AR technologies to take our scientists to Mars every single day," said Victor Luo, lead project manager at JPL's Ops Lab, which led the collaboration. "With Access Mars, everyone in the world can ride along."

Access Mars was created using data collected by JPL and built on WebVR, an open-source standard, in an effort to expand access to immersive experiences. Google's Creative Labs team was looking for novel uses for VR and encouraged developers to experiment using its tools.

Access Mars Web VR: A Virtual Walk on Mars

Video above: When NASA scientists want to follow the path of the Curiosity rover on Mars, they can don a mixed-reality headset and virtually explore the Martian landscape. Now everyone can get a sense of what that looks and feels like by visiting . NASA's Jet Propulsion Laboratory in Pasadena, California, collaborated with Google to produce "Access Mars," a free immersive experience. It's available for use on all desktop and mobile devices and VR/AR headsets. This includes mobile-based iOS and Android devices. Users can visit four sites that have been critical to NASA's Mars Science Laboratory mission: Curiosity's landing site; Murray Buttes; Marias Pass; and Pahrump Hills. The rover's location on lower Mount Sharp will be periodically updated to reflect the mission's ongoing progress. For more about all of NASA's Mars missions, go to

NASA has collaborated with a number of outside organizations to create immersive experiences that allow people to "travel" to distant destinations. NASA worked with Google Expeditions, a free immersive app, to provide 360 tours of JPL Mars rover sites, the International Space Station and other NASA locations, and to profile the careers of women at NASA.  JPL also teamed with Microsoft to create OnSight for that company’s HoloLens mixed-reality headset. Using JPL's OnSight software, Microsoft collaborated on a public experience called "Destination: Mars" at Kennedy Space Center Visitor Complex in 2016.

"Immersive technology has incredible potential as a tool for scientists and engineers," Luo said. "It also lets us inspire and engage the public in new ways."

Experience Access Mars here:

For more information about the Mars Science Laboratory mission, visit:

Destination Mars:

Careers of women at NASA:

Animation (mentioned), Images (mentioned), Video, Text, Credits: NASA/Martin Perez/JPL/Andrew Good.

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An Atmosphere Around the Moon? NASA Research Suggests Significant Atmosphere in Lunar Past and Possible Source of Lunar Water

NASA - Lunar Reconnaissance Orbiter (LRO) patch / NASA - Lunar CRater Observation and Sensing Satellite (LCROSS) logo.

Oct. 19, 2017

An Atmosphere Around the Moon? Image Credits: NASA/MSFC

Looking up at the Moon at night, Earth’s closest neighbor appears in shades of gray and white; a dry desert in the vacuum of space, inactive and dead for billions of years. Like many things, though, with the Moon, there is so much more than what meets the eye.

Research completed by NASA Marshall Space Flight Center planetary volcanologist Debra Needham in Huntsville, Alabama, and planetary scientist David Kring at the Lunar and Planetary Institute in Houston, Texas, suggests that billions of years ago, the Moon actually had an atmosphere. The ancient lunar atmosphere was thicker than the atmosphere of Mars today and was likely capable of weathering rocks and producing windstorms. Perhaps most importantly, it could be a source for some, if not all, of the water detected on the Moon.

“It just completely changes the way we think of the Moon,” said Needham, a scientist in Marshall’s Science and Technology Office. “It becomes a much more dynamic planetary body to explore.”

Needham will present the research at the annual Geological Society of America conference in Seattle on Oct. 22. The research paper, available online, will be published in the Nov. 15 issue of Earth and Planetary Science Letters.

Images above: A time sequence of lunar mare -- lava plain -- flows in 0.5 billion year time increments, with red areas in each time step denoting the most recently erupted lavas. The timing of the eruptions, along with how much lava was erupted, helped scientists determine that the Moon once had an atmosphere and that the lunar atmosphere was thickest about 3.5 billion years ago. Image Credits: NASA/MSFC/Debra Needham; Lunar and Planetary Science Institute/David Kring.

Discovering the existence, thickness and composition of the atmosphere began with understanding how much lava erupted on the Moon 3.9 to one billion years ago, forming the lava plains we see as the dark areas on the surface of the Moon today. Needham and Kring then used lab analyses of lunar basalts -- iron and magnesium-rich volcanic rocks -- returned to Earth by the Apollo crews to estimate the amounts and composition of gases -- also called volatiles -- released during those volcanic eruptions.

The short-lived atmosphere -- estimated to have lasted approximately 70 million years -- was comprised primarily of carbon monoxide, sulfur and water. As volcanic activity declined, the release of the gases also declined. What atmosphere existed was either lost to space or became part of the surface of the Moon.

The researchers discovered that so much water was released during the eruptions -- potentially three times the amount of water in the Chesapeake Bay -- that if 0.1 percent of the erupted water migrated to the permanently shadowed regions on the Moon, it could account for all of the water detected there.

“We’re suggesting that internally-sourced volatiles might be at least contributing factors to these potential in-situ resource utilization deposits,” Needham said.

Image above: The color mosaic of the Moon’s north pole gives a small glimpse into the complex, dynamic past of Earth’s nearest celestial neighbor. Image Credits: NASA/JPL/USGS.

Water is one of the keys to living off of the land in space, also called in-situ resource utilization (ISRU). Knowing where the water came from helps scientists and mission planners alike know if the resource is renewable. Ultimately, more research is needed to determine the exact sources.

The first indication of water on the Moon came in 1994 when NASA’s Clementine spacecraft detected potential signatures of water-ice in the lunar poles. In 1998, NASA’s Lunar Prospector mission detected enhanced hydrogen signatures but could not definitely associate them to water. Ten years later, NASA’s Lunar Reconnaissance Orbiter and its partner spacecraft, the Lunar CRater Observation and Sensing Satellite (LCROSS), definitively confirmed the presence of water on the Moon. That same year, in 2008, volcanic glass beads brought back from the Moon by the Apollo 15 and 17 crews were discovered to contain volatiles, including water, leading to the research that indicates the Moon once had a significant atmosphere and was once much different than what we see today.

Casting one’s eyes at the Moon or viewing it through a telescope, the surface of the Moon today gives but a glimpse into its dynamic and complex history. Recent findings that propose Earth’s neighbor once had an atmosphere comparable to Mars’ continue to unravel the lunar past, while prompting scientists and explorers to ask more questions about Earth’s mysterious companion in the solar system.

To learn more about Marshall’s lunar and planetary science research visit:

To learn more about NASA’s research for solar system exploration visit:

Related links:

Nov. 15 issue of Earth and Planetary Science Letters:

Lunar Reconnaissance Orbiter (LRO):

Lunar CRater Observation and Sensing Satellite (LCROSS):

NASA Marshall Space Flight Center:

Images (mentioned), Text, Credits: NASA/Marshall Space Flight Center/William Bryan.


Deep Space Communications via Faraway Photons

NASA - Psyche Mission logo.

October 19, 2017

A spacecraft destined to explore a unique asteroid will also test new communication hardware that uses lasers instead of radio waves.

The Deep Space Optical Communications (DSOC) package aboard NASA's Psyche mission utilizes photons -- the fundamental particle of visible light -- to transmit more data in a given amount of time. The DSOC goal is to increase spacecraft communications performance and efficiency by 10 to 100 times over conventional means, all without increasing the mission burden in mass, volume, power and/or spectrum.

Image above: Artist's concept of the Psyche spacecraft, which will conduct a direct exploration of an asteroid thought to be a stripped planetary core. Image Credits: SSL/ASU/P. Rubin/NASA/JPL-Caltech.

Tapping the advantages offered by laser communications is expected to revolutionize future space endeavors - a major objective of NASA's Space Technology Mission Directorate (STMD).

The DSOC project is developing key technologies that are being integrated into a deep space-worthy Flight Laser Transceiver (FLT), high-tech work that will advance this mode of communications to Technology Readiness Level (TRL) 6. Reaching a TRL 6 level equates to having technology that is a fully functional prototype or representational model.

As a "game changing" technology demonstration, DSOC is exactly that. NASA STMD's Game Changing Development Program funded the technology development phase of DSOC. The flight demonstration is jointly funded by STMD, the Technology Demonstration Mission (TDM) Program and NASA/ HEOMD/Space Communication and Navigation (SCaN).

Work on the laser package is based at NASA's Jet Propulsion Laboratory in Pasadena, California.

"Things are shaping up reasonably and we have a considerable amount of test activity going on," says Abhijit Biswas, DSOC Project Technologist in Flight Communications Systems at JPL. Delivery of DSOC for integration within the Psyche mission is expected in 2021 with the spacecraft launch to occur in the summer of 2022, he explains.

"Think of the DSOC flight laser transceiver onboard Psyche as a telescope," Biswas explains, able to receive and transmit laser light in precisely timed photon bursts.

DSOC architecture is based on transmitting a laser beacon from Earth to assist line­of­sight stabilization to make possible the pointing back of a downlink laser beam. The laser onboard the Psyche spacecraft, Biswas says, is based on a master-oscillator power amplifier that uses optical fibers.

The laser beacon to DSOC will be transmitted from JPL's Table Mountain Facility located near the town of Wrightwood, California, in the Angeles National Forest. DSOC's beaming of data from space will be received at a large aperture ground telescope at Palomar Mountain Observatory in California, near San Diego.

Biswas anticipates operating DSOC perhaps 60 days after launch, given checkout of the Psyche spacecraft post-liftoff. The test-runs of the laser equipment will occur over distances of 0.1 to 2.5 astronomical units (AU) on the outward-bound probe. One AU is approximately 150 million kilometers-or the distance between the Earth and Sun.

"I am very excited to be on the mission," says Biswas, who has been working on the laser communications technology since the late 1990s. "It's a unique privilege to be working on DSOC."

The Psyche mission was selected for flight in early 2017 under NASA's Discovery Program, a series of lower-cost, highly focused robotic space missions that are exploring the solar system.

The spacecraft will be launched in the summer of 2022 to 16 Psyche, a distinctive metal asteroid about three times farther away from the sun than Earth. The planned arrival of the probe at the main belt asteroid will take place in 2026.

Lindy Elkins-Tanton is Director of the School of Earth and Space Exploration at Arizona State University in Tempe. She is the principal investigator for the Psyche mission.

"I am thrilled that Psyche is getting to fly the Deep Space Optical Communications package," Elkins-Tanton says. "First of all, the technology is mind-blowing and it brings out all my inner geek. Who doesn't want to communicate using lasers, and multiply the amount of data we can send back and forth?"

Elkins-Tanton adds that bringing robotic and human spaceflight closer together is critical for humankind's space future. "Having our robotic mission test technology that we hope will help us eventually communicate with people in deep space is excellent integration of NASA missions and all of our goals," she says.

In designing a simple, high-heritage spacecraft to do the exciting exploration of the metal world Psyche, "I find both the solar electric propulsion and the Deep Space Optical Communications to feel futuristic in the extreme. I'm proud of NASA and of our technical community for making this possible," Elkins-Tanton concludes.

Biswas explains that DSOC is a pathfinder experiment. The future is indeed bright for the technology, he suggests, such as setting up capable telecommunications infrastructure around Mars

Animation above: Laser communications conceptual animation. An animated concept of Deep Space Optical Communications (DSOC) between Mars and Earth. Animation Credit: NASA.

"Doing so would allow the support of astronauts going to and eventually landing on Mars," Biswas said. "Laser communications will augment that capability tremendously. The ability to send back from Mars to Earth lots of information, including the streaming of high definition imagery, is going to be very enabling."

As a "game changing" technology demonstration, DSOC is exactly that. NASA STMD's Game Changing Development program funded the technology development phase of DSOC. The flight demonstration is jointly funded by STMD, the Technology Demonstration Missions (TDM) program and NASA/ HEOMD/Space Communication and Navigation (SCaN). Work on the laser package is based at the Jet Propulsion Laboratory in Pasadena, California.

For more information about NASA's Technology Demonstration Missions program, visit:

For more information about NASA's Space Technology Mission Directorate, visit:

NASA's Psyche mission:

Deep Space Optical Communications (DSOC):

Image (mentioned), Text, Credits: NASA/Gina Anderson/JPL/Andrew Good/Written by Leonard.


mercredi 18 octobre 2017

NASA Team Finds Noxious Ice Cloud on Saturn’s Moon Titan

NASA - Cassini Mission to Saturn patch.

Oct. 18, 2017

Researchers with NASA’s Cassini mission found evidence of a toxic hybrid ice in a wispy cloud high above the south pole of Saturn’s largest moon, Titan.

The finding is a new demonstration of the complex chemistry occurring in Titan’s atmosphere—in this case, cloud formation in the giant moon’s stratosphere—and part of a collection of processes that ultimately helps deliver a smorgasbord of organic molecules to Titan’s surface.

Image above: This view of Saturn’s largest moon, Titan, is among the last images the Cassini spacecraft sent to Earth before it plunged into the giant planet’s atmosphere. Image Credits: NASA/JPL-Caltech/Space Science Institute.

Invisible to the human eye, the cloud was detected at infrared wavelengths by the Composite Infrared Spectrometer, or CIRS, on the Cassini spacecraft. Located at an altitude of about 100 to 130 miles (160 to 210 kilometers), the cloud is far above the methane rain clouds of Titan’s troposphere, or lowest region of the atmosphere. The new cloud covers a large area near the south pole, from about 75 to 85 degrees south latitude.

Laboratory experiments were used to find a chemical mixture that matched the cloud’s spectral signature -- the chemical fingerprint measured by the CIRS instrument. The experiments determined that the exotic ice in the cloud is a combination of the simple organic molecule hydrogen cyanide together with the large ring-shaped chemical benzene. The two chemicals appear to have condensed at the same time to form ice particles, rather than one being layered on top of the other.

“This cloud represents a new chemical formula of ice in Titan’s atmosphere,” said Carrie Anderson of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, a CIRS co-investigator. “What’s interesting is that this noxious ice is made of two molecules that condensed together out of a rich mixture of gases at the south pole.”

Previously, CIRS data helped identify hydrogen cyanide ice in clouds over Titan's south pole, as well as other toxic chemicals in the moon's stratosphere.

In Titan’s stratosphere, a global circulation pattern sends a current of warm gases from the hemisphere where it’s summer to the winter pole. This circulation reverses direction when the seasons change, leading to a buildup of clouds at whichever pole is experiencing winter. Shortly after its arrival at Saturn, Cassini found evidence of this phenomenon at Titan’s north pole. Later, near the end of the spacecraft’s 13 years in the Saturn system, a similar cloud buildup was spotted at the south pole.

The simple way to think about the cloud structure is that different types of gas will condense into ice clouds at different altitudes, almost like layers in a parfait dessert. Exactly which cloud condenses where depends on how much vapor is present and on the temperatures, which become colder and colder at lower altitudes in the stratosphere. The reality is more complicated, however, because each type of cloud forms over a range of altitudes, so it’s possible for some ices to condense simultaneously, or co-condense.

Anderson and colleagues use CIRS to sort through the complex set of infrared fingerprints from many molecules in Titan’s atmosphere. The instrument separates infrared light into its component colors, like raindrops creating a rainbow, and measures the strengths of the signal at the different wavelengths.

“CIRS acts as a remote-sensing thermometer and as a chemical probe, picking out the heat radiation emitted by individual gases in an atmosphere,” said F. Michael Flasar, the CIRS principal investigator at Goddard. “And the instrument does it all remotely, while passing by a planet or moon.”

The new cloud, which the researchers call the high-altitude south polar cloud, has a distinctive and very strong chemical signature that showed up in three sets of Titan observations taken from July to November 2015. Because Titan’s seasons last seven Earth years, it was late fall at the south pole the whole time.

The spectral signatures of the ices did not match those of any individual chemical, so the team began laboratory experiments to simultaneously condense mixtures of gases. Using an ice chamber that simulates conditions in Titan’s stratosphere, they tested pairs of chemicals that had infrared fingerprints in the right part of the spectrum.

At first, they let one gas condense before the other. But the best result was achieved by introducing both hydrogen cyanide and benzene into the chamber and allowing them to condense at the same time. By itself, benzene doesn’t have a distinctive far-infrared fingerprint. When it was allowed to co-condense with hydrogen cyanide, however, the far-infrared fingerprint of the co-condensed ice was a close match for the CIRS observations.

Artist's view of Cassini Titan flyby. Image Credits: NASA/JPL-Caltech

Additional studies will be needed to determine the structure of the co-condensed ice particles. The researchers expect them to be lumpy and disorderly, rather than well-defined crystals.

Anderson and colleagues previously found a similar example of co-condensed ice in CIRS data from 2005. Those observations were made near the north pole, about two years after the winter solstice in Titan’s northern hemisphere. That cloud formed at a much lower altitude, below 93 miles (150 kilometers), and had a different chemical composition: hydrogen cyanide and cyanoacetylene, one of the more complex organic molecules found in Titan’s atmosphere.

Anderson attributes the differences in the two clouds to seasonal variations at the north and south poles. The northern cloud was spotted about two years after the northern winter solstice, but the southern cloud was spotted about two years before the southern winter solstice. It’s possible that the mixtures of gases were slightly different in the two cases or that temperatures had warmed up a bit by the time the north polar cloud was spotted, or both.

“One of the advantages of Cassini was that we were able to flyby Titan again and again over the course of the thirteen-year mission to see changes over time,” said Anderson. “This is a big part of the value of a long-term mission.”

The Cassini spacecraft ended its Saturn mission on Sept. 15, 2017.

The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. NASA’s Jet Propulsion Laboratory, a division of Caltech in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington. JPL designed, developed and assembled the Cassini orbiter.

More information about Cassini:

Images (mentioned), Text, Credits: NASA/Karl Hille/Goddard Space Flight Center/Elizabeth Zubritsky.