NASA MESSENGER Captures Images of Ice on Mercury

Nasa's MESSENGER spacecraft

NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft has provided the first optical images of ice and other frozen volatile materials within permanently shadowed craters near Mercury's north pole.

The images not only reveal the morphology of the frozen volatiles, but they also provide insight into when the ices were trapped and how they've evolved, according to an article published in the journal, Geology.

Two decades ago, Earth-based radar images of Mercury revealed the polar deposits, postulated to consist of water ice.

Prokofiev, named in August 2012 for the Russian composer, is the largest crater in Mercury’s north polar region to host radar-bright material.

Credit: NASA /Johns Hopkins University Applied Physics Lab /Carnegie Iinstitution of Washington

That hypothesis was later confirmed by MESSENGER through a combination of neutron spectrometry, thermal modeling, and infrared reflectometry.

"But along with confirming the earlier idea, there is a lot new to be learned by seeing the deposits," said lead author Nancy Chabot, the Instrument Scientist for MESSENGER's Mercury Dual Imaging System (MDIS) and a planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.

Beginning with MESSENGER's first extended mission in 2012, scientists launched an imaging campaign with the broadband clear filter of MDIS's wide-angle camera (WAC).

Mercury Dual Imaging System (MDIS)

Although the polar deposits are in permanent shadow, through many refinements in the imaging, the WAC was able to obtain images of the surfaces of the deposits by leveraging very low levels of light scattered from illuminated crater walls. "It worked in spectacular fashion," said Chabot.

The team zeroed in on Prokofiev, the largest crater in Mercury's north polar region found to host radar-bright material.

"Those images show extensive regions with distinctive reflectance properties," Chabot said.

"A location interpreted as hosting widespread surface water ice exhibits a cratered texture indicating that the ice was emplaced more recently than any of the underlying craters."

In other areas, water ice is present, she said, "but it is covered by a thin layer of dark material inferred to consist of frozen organic-rich compounds." In the images of those areas, the dark deposits display sharp boundaries.

"This result was a little surprising, because sharp boundaries indicate that the volatile deposits at Mercury's poles are geologically young, relative to the time scale for lateral mixing by impacts," said Chabot.

"One of the big questions we've been grappling with is 'When did Mercury's water ice deposits show up?' Are they billions of years old, or were they emplaced only recently?" Chabot said.

"Understanding the age of these deposits has implications for understanding the delivery of water to all the terrestrial planets, including Earth."

Overall, the images indicate that Mercury's polar deposits either were delivered to the planet recently or are regularly restored at the surface through an ongoing process.

The images also reveal a noteworthy distinction between the Moon and Mercury, one that may shed additional light on the age of the frozen deposits.

"The polar regions of Mercury show extensive areas that host water ice, but the Moon's polar regions, which also have areas of permanent shadows and are actually colder, look different," Chabot said.

"One explanation for differences between the Moon and Mercury could be that the volatile polar deposits on Mercury were recently emplaced," according to the paper.

"If Mercury's currently substantial polar volatile inventory is the product of the most recent portion of a longer process, then a considerable mass of volatiles may have been delivered to the inner Solar System throughout its history."

"That's a key question," Chabot said. "Because if you can understand why one body looks one way and another looks different, you gain insight into the process that's behind it, which in turn is tied to the age and distribution of water ice in the Solar System. This will be a very interesting line of inquiry going forward."

NASA Cassini: Titan's Gigantic polar clouds of hydrogen cyanide

Titan's hazy orange globe hangs before the Cassini spacecraft. 

Image credit NASA/JPL/Space Science Institute.

Gigantic polar clouds of hydrogen cyanide roughly four times the area of the UK are part of the impressive atmospheric diversity of Titan, the largest moon of Saturn, a new study led by Leiden Observatory, the Netherlands Institute for Space Research and the University of Bristol has found.

The research is published today in Nature.

Titan is unique in our solar system because of its dense nitrogen-methane atmosphere, which is very similar to Earth's in some ways, but very different in others.

For example, air temperatures are around 200 degrees colder and, in contrast to the warm salt water seas of Earth, frigid hydrocarbon lakes populate Titan's surface.

Titan has seasons just like Earth, only each season lasts over seven years instead of three months due to its ponderous orbit around the Sun.

After equinox in 2009, Titan's south pole entered the perpetual darkness of polar winter. Soon after, instruments on NASA's Cassini spacecraft observed the development of a gigantic polar cloud covering over one million square kilometres, roughly four times the area of the UK.

Bristol researcher and co-author Dr Nick Teanby said: "The cloud was first seen in images from Cassini's cameras taken in 2012."

"It started off quite small but soon grew to cover the entire south polar region. This was totally unexpected and set us puzzling over what the cloud could be made of."

"Unfortunately, while the images showed that the cloud was very high up, at over 250km above the surface, they did not allow us to figure out what the cloud was actually made of or why it was there."

For the next two years Cassini gathered more data including infrared spectra of the cloudy region.

Lead author Remco de Kok said: "When we looked at the spectra, we saw two large peaks that weren't present in spectra of other places on Titan."

"These peaks coincided exactly with the peaks you'd expect from ice particles of hydrogen cyanide, or 'blauwzuur' (blue acid) as it's known in the Netherlands, which is highly toxic."

"This was very surprising to us, since we did not expect HCN ice to be able to form so high in Titan's atmosphere."

This new research suggests that Titan's south pole must be extremely cold to allow hydrogen cyanide to condense.

In fact, the upper atmosphere must have cooled by over 50 degrees in less than a year to reach a blisteringly cold -150C.

Remco de Kok concluded: "This is a very rapid change given Titan's long annual cycle and is much colder than previously thought possible."

"It suggests that once the pole is in shadow the upper atmosphere acts as a very efficient radiator of heat, perhaps due to the high abundance of exotic hydrocarbon and nitrogen based compounds, which emit strongly in the infrared."

"Cassini is set to continue observing Titan until it takes a dive into Saturn at the end of its mission in 2017. It will be fascinating to see how the cloud will develop."

More information: HCN ice in Titan's high-altitude southern polar cloud, Nature, dx.doi.org/10.1038/nature13789

The Arctic ice is melting into Nordic Seas but the Gulf Stream remains

Mosaic of images of the Arctic by MODIS on the Aqua satellite. 

Credit: NASA

The melting ice in the Arctic is not the source of reduced saline in Nordic Seas.

It is the Gulf Stream that has provided less salt.

A new study published Sunday in Nature Geoscience claims; the source of fresher Nordic Seas, since 1950, is rooted in the saline Atlantic, as opposed to an influx of Arctic freshwater, dispelling the common inference.

"This is an important finding as it shows that the Gulf Stream is not about to short circuit. A halting Gulf Stream has been a concern with ongoing climate change; its collapse was taken to the extreme in the Hollywood blockbuster The Day After Tomorrow," says Tor Eldevik, professor in oceanography at the University of Bergen and the Bjerknes Centre.

Reversing the chain of events
The Nordic Seas have freshened substantially since 1950. At the same time, there has been observed an increased river runoff and net ice melting in the Arctic.

The concurrence of a less saline ocean and Arctic freshwater input has given the climate research community reason for concern.

"It has been a concern that a layer of Arctic freshwater could impede the Gulf Stream's Arctic branch."

"Going back in time, into and through the ice ages, such a freshwater lid has been understood to reduce ocean circulation and thus the Gulf Stream's poleward heat transport," says Tor Eldevik.

Eldevik is co-author of the study where Mirjam Glessmer and colleagues at the Bjerknes Centre in Bergen, Norway, show that change in the Nordic Seas is at the receiving end of change in the more global climate system.

Southern freshwater
The researchers from the Bjerknes Centre have analysed the available observations back to 1950 and conclude that the changing salt content in the Nordic Seas is explained by the variable salinity of the Gulf Stream's Arctic branch entering the seas from the south.

The mode of operation is also realised in a numerical ocean model forced by the observed stated of the atmosphere during the period in question.

Although not part of the present study, it appears to be several reasons for the freshening of the Atlantic source waters.

A dominant explanation is a general increase in net precipitation over the North Atlantic Ocean (which may very well relate to global climate change).

The contribution is spread over the Gulf Stream system, and accordingly transported further northward.

The analysis of Glessmer and colleagues further shows, and in line with the above, that the salt deficit in the Nordic Seas is not related to a surface layer of freshwater.

The low-salinity anomaly since 1950 is distributed throughout the water column following the Gulf Stream's northern overturning from warm surface flow to cold deep water.

Potential for climate prediction
The study has important practical implications.

The Bjerknes Centre is presently developing the Norwegian Climate Prediction Model, with the aim of establishing a Norwegian operational system for climate prediction on seasonal to decadal time scale.

"Our study documents how large-scale changes in our marine climate propagate with the extension of the Gulf Stream into the Nordic Seas."

"This suggests that the marine climate could be predictable on the time scale that a climate signal is travelling north," concludes Tor Eldevik.

More information: Glessmer, M.S., T. Eldevik, K. Våge, J.E.Ø. Nilsen, and E. Behrens, 2014: "Atlantic origin of observed and modelled freshwater anomalies in the Nordic Seas." Advance online publication Nature Geoscience, dx.doi.org/10.1038/ngeo2259

Jupiter's Moon, Europa mimics Earth tectonics

False-colour image of Europa’s trailing northern hemisphere, where subduction zones are hypothesised (?) to exist. 

Credit: NASA /JPL /University of Arizona

Jupiter's icy moon Europa may have active tectonic plates similar to those that shape the Earth, which had long been thought unique in this respect, scientists said Sunday.

They used images captured by NASA's Galileo spacecraft, which orbited Jupiter and its moons from 1995 to 2003, to study the criss-cross of ridges and fractures on Europa's ice shell.

The moon, slightly smaller than the one orbitting Earth, has one of the youngest surfaces in the Solar System, implying "rapid recycling", said the team.

They found evidence that a piece of the surface had disappeared along a boundary between two ice plates, possibly when one sunk under the other.

They took this as evidence of surface material being recycled into the moon's interior, similar to parts of Earth's crust which sink into the underlying mantle at so-called subduction zones where tectonic plates converge.

This conceptual illustration of the subduction process (where one plate is forced under another) shows how a cold, brittle, outer portion of Europa’s 20-30 kilometer (roughly 10-20 mile) thick ice shell moved into the warmer shell interior and was ultimately subsumed. 

A low-relief subsumption band was created at the surface in the overriding plate, alongside which cryolavas may have erupted.

Image Credit: Noah Kroese, I.NK

The team studied an area of 134,000 square kilometres (51,700 square miles), using the images and a reconstruction of geological features.

They found that a 20,000 km2-portion of surface was missing.

"We propose that Europa's ice shell has a brittle, mobile, plate-like system above convecting warmer ice," they wrote in the journal Nature Geoscience.

"Hence, Europa may be the only Solar System body other than Earth to exhibit a system of plate tectonics."

Europa is one of the four largest moons of Jupiter, the fifth planet from the Sun and the largest in our Solar System.

Close-up view of a proposed zone of mid-ocean-ridge-like plate spreading on Europa (unrelated to the region studied in this work). 

This dilational band called Phaidra Linea, located in Europa’s trailing hemisphere near Argadnel Regio, shows internal striations related to spreading and bilateral symmetry about a central axis. Older geological features can be matched perfectly to either side of the spreading zone. 

The black strip in the center of the image is a narrow region where the images overlap and there is no image coverage. 

Credit: NASA/JPL

More information: Nature Geoscience, dx.doi.org/10.1038/ngeo2245

Meteorite impact: Nicaragua government report - Video

"A mysterious explosion that rocked Nicaragua's crowded capital Managua, creating a large crater, appears to have been caused by a meteorite, officials said Sunday.

Amazingly, in a sprawling city of 1.2 million people, the impact near the international airport did not cause any known injuries, but it did leave a crater measuring 12 meters (39 feet) across.

"We are convinced that this was a meteorite. We have seen the crater from the impact," said Wilfredo Strauss of the Seismic Institute.

The meteorite appeared to have hurtled into a wooded area near the airport around midnight Saturday, its thunderous impact felt across the capital.

The hit was so large that it registered on the instruments Strauss's organization uses to size up earthquakes."

In this Sunday Sept. 7, 2014, publicly distributed handout photo provided by the Nicaraguan Army shows an impact crater made by a small meteorite in a wooded area near Managua's international airport and an air force base. 

Nicaraguan government spokeswoman Rosario Murillo said Sunday that a loud boom heard overnight by residents of the capital was a "relatively small" meteorite that "appears to have come off an asteroid that was passing close to Earth." 

Credit: AP Photo/Nicaraguan Army

Nicaragua's government said Sunday that a mysterious boom heard overnight in the capital was made by a small meteorite that left a crater in a wooded area near Managua's airport.

Government spokeswoman Rosario Murillo said a committee formed by the government to study the event determined it was a "relatively small" meteorite that "appears to have come off an asteroid that was passing close to Earth."

Murillo said Nicaragua will ask international experts to help local scientists in understanding what happened.

The crater left by the meteorite had a radius of 12 meters (39 feet) and a depth of 5 meters (16 feet), said Humberto Saballos, a volcanologist with the Nicaraguan Institute of Territorial Studies who was on the committee. He said it is still not clear if the meteorite disintegrated or was buried.

Humberto Garcia, of the Astronomy Center at the National Autonomous University of Nicaragua, said the meteorite could be related to an asteroid that was forecast to pass by the planet Saturday night.

"We have to study it more because it could be ice or rock," he said.

Wilfried Strauch, an adviser to the Institute of Territorial Studies, said it was "very strange that no one reported a streak of light. We have to ask if anyone has a photo or something."

Local residents reported hearing a loud boom Saturday night, but said they didn't see anything strange in the sky.

"I was sitting on my porch and I saw nothing, then all of a sudden I heard a large blast. We thought it was a bomb because we felt an expansive wave," Jorge Santamaria told The Associated Press.

The site of the crater is near Managua's international airport and an air force base. Only journalists from state media were allowed to visit it.

NASA ER-2: Melt ponds shine in MABEL laser altimeter flight images

Engineers installed a new camera system on MABEL for its summer 2014 campaign, so scientists could better understand what it measured during flights. 

A key goal of the Alaska-based campaign was to measure glacial melt ponds like this one, photographed July 16. 

Credit: NASA

Even from 65,000 feet above Earth, aquamarine melt ponds in the Arctic stand out against the white sea ice and ice sheets. These ponds form every summer, as snow that built up on the ice melts, creating crystal clear pools.

On July 16 and July 17, NASA's ER-2 aircraft flew above Alaskan glaciers and to the North Pole, carrying an instrument called the Multiple Altimeter Beam Experimental Lidar (MABEL).

MABEL is a laser altimeter, measuring the elevation of glaciers, mountains, forests and other topography below.

Scientists will use those measurements to design analysis software, or algorithms, for the upcoming Ice, Cloud and land Elevation Satellite-2 (ICESat-2) mission.

The 2014 MABEL campaign continued through July and was launched, in part, to capture melt ponds and other features of summer ice.

After nine science flights out of Fairbanks, Alaska, the ER-2 and MABEL returned to California on Aug. 1, gathering additional data along the way.

For this campaign, engineers added a new camera system to allow the team to match the MABEL measurements with a visual glimpse of the ground.

The digital camera takes a picture every 3 seconds, each frame capturing an area about 2.5 by 1.5 kilometers (1.6 by 0.9 miles).

Some of these first images downloaded were just what the MABEL team wanted to see, said Thorsten Markus, ICESat-2 project scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

They want to understand how the MABEL data collected over a melt pond differs from data collected over open water, ice and more, and the images indicate there will be good measurements to analyze.

From the ER-2’s cruising altitude of 65,000 feet, the camera system snaps images of an area about 2.5 by 1.5 kilometers (1.6 by 0.9 miles). 

These melt ponds, formed by snowmelt on Alaskan glaciers, can range in size and shape. 

Credit: NASA

"We have clear open water, then we see melt ponds and then we see open water again," Markus said of a shot taken on the way to the North Pole.

"For algorithm development, this is perfect."

On a July 17 flight to the North Pole and back, the ER-2 aircraft carrying the MABEL instrument flew over fractured sea ice, dotted with melt ponds and marked by ridges formed by the dynamic ice. 

Credit: NASA

NASA Mars MRO HiRise Image: A Pedestal Crater

Credit: Nasa /JPL /University of Arizona

This HiRISE image shows what is termed a pedestal crater, so-called because the level of the surface adjacent to the crater is elevated relative to the surface of the surrounding terrain.

The raised surface has patterns and a general outline resembling what ejecta would look like after being thrown out from the crater by the impact.

This impact probably occurred at a time when the surface of the whole scene was at the level of the raised surface.

The ejecta landed on the part of this surface close to the crater. Erosion then removed material in the rest of the scene while the impact ejecta shielded the area around the crater, protecting the ground under it from eroding and keeping it high.

The eroded, or “missing”, terrain in the rest of the scene may have contained ice. Lobe shapes at the base of the raised ejecta and polygons (visible when zoomed in) on the surface both suggest the pedestal material may have, or may still, contain ice.

The pattern of ejecta is asymmetric around the crater, suggesting the impactor may have hit the ground traveling from the north-east.

NASA Mars MRO HiRise Image: Late winter on south-facing slopes

Image Credit: NASA MRO.

An image of Mars taken by the HiRISE instrument on NASA's Mars Reconnaissance Orbiter shows frost or ice (white areas) persisting in late winter only on south-facing slopes that have not received much direct sunlight.

Ridges between gully alcoves receiving more light appear reddish and mostly free of frost. New gully activity is not readily detectible in this image.

In some years, the frost (up to roughly 3.3 feet or 1 meter thick) triggers avalanches, although not in most years.

The frost here consists of mostly carbon dioxide (dry ice), but also contains small amounts of water ice.

NASA Cassini: The geyser basin of Saturn's moon Enceladus

This view looks across the geyser basin of Saturn's moon Enceladus, along fractures spewing water vapour and ice particles into space. 

Cassini scientists have pinpointed the source locations of about 100 geysers and gained new insights into what powers them. 

Credit: NASA/JPL-Caltech/SSI

Scientists using mission data from NASA's Cassini spacecraft have identified 101 distinct geysers erupting on Saturn's icy moon Enceladus.

Their analysis suggests it is possible for liquid water to reach from the moon's underground sea all the way to its surface.

These findings, and clues to what powers the geyser eruptions, are presented in two articles published in the current online edition of the Astronomical Journal.

Over a period of almost seven years, Cassini's cameras surveyed the south polar terrain of the small moon, a unique geological basin renowned for its four prominent "tiger stripe" fractures and the geysers of tiny icy particles and water vapour first sighted there nearly 10 years ago.

The result of the survey is a map of 101 geysers, each erupting from one of the tiger stripe fractures, and the discovery that individual geysers are coincident with small hot spots.

These relationships pointed the way to the geysers' origin.

After the first sighting of the geysers in 2005, scientists suspected that repeated flexing of Enceladus by Saturn's tides as the moon orbits the planet had something to do with their behaviour.

One suggestion included the back-and-forth rubbing of opposing walls of the fractures generating frictional heat that turned ice into geyser-forming vapour and liquid.

Alternate views held that the opening and closing of the fractures allowed water vapor from below to reach the surface.

This artist's rendering shows a cross-section of the ice shell immediately beneath one of Enceladus' geyser-active fractures, illustrating the physical and thermal structure and the processes ongoing below and at the surface.

Image Credit: NASA/JPL-Caltech/Space Science Institute

Before this new study, it was not clear which process was the dominating influence.

Nor was it certain whether excess heat emitted by Enceladus was everywhere correlated with geyser activity.

To determine the surface locations of the geysers, researchers employed the same process of triangulation used historically to survey geological features on Earth, such as mountains.

When the researchers compared the geysers' locations with low-resolution maps of thermal emission, it became apparent the greatest geyser activity coincided with the greatest thermal radiation.

Comparisons between the geysers and tidal stresses revealed similar connections. However, these correlations alone were insufficient to answer the question, "What produces what?"

The answer to this mystery came from comparison of the survey results with high-resolution data collected in 2010 by Cassini's heat-sensing instruments.

Individual geysers were found to coincide with small-scale hot spots, only a few dozen feet (or tens of meters) across, which were too small to be produced by frictional heating, but the right size to be the result of condensation of vapor on the near-surface walls of the fractures.

This immediately implicated the hot spots as the signature of the geysering process.

"Once we had these results in hand, we knew right away heat was not causing the geysers, but vice versa," said Carolyn Porco, leader of the Cassini imaging team from the Space Science Institute in Boulder, Colorado, and lead author of the first paper.

"It also told us the geysers are not a near-surface phenomenon, but have much deeper roots."

Thanks to recent analysis of Cassini gravity data, the researchers concluded the only plausible source of the material forming the geysers is the sea now known to exist beneath the ice shell.

They also found that narrow pathways through the ice shell can remain open from the sea all the way to the surface, if filled with liquid water.

In the companion paper, the authors report the brightness of the plume formed by all the geysers, as seen with Cassini's high-resolution cameras, changes periodically as Enceladus orbits Saturn.

Armed with the conclusion that the opening and closing of the fractures modulates the venting, the authors compared the observations with the expected venting schedule due to tides.

They found the simplest model of tidal flexing provides a good match for the brightness variations Cassini observes, but it does not predict the time when the plume begins to brighten.

Some other important effect is present and the authors considered several in the course of their work.

More information: "Tidally Modulated Eruptions on Enceladus: Cassini ISS Observations and Models." Francis Nimmo et al. 2014, Astronomical Journal 148 46. DOI: 10.1088/0004-6256/148/3/46

Laboratory models suggest that stretching forces shaped Ganymede's surface

An image of a tabletop-size analogue model (left) shows details of fault systems created by extension that visually match an image by spacecraft Galileo of faulted terrain on Ganymede (right). 

Credit: Left Image: Courtesy of Southwest Research Institute; 

Right Image: Courtesy of NASA/JPL SSI

Processes that shaped the ridges and troughs on the surface of Jupiter's icy moon Ganymede are likely similar to tectonic processes seen on Earth, according to a team of researchers led by Southwest Research Institute (SwRI).

To arrive at this conclusion, the team subjected physical models made of clay to stretching forces that simulate tectonic action. The results were published in Geophysical Research Letters.

Physical analogue models simulate geologic structures in laboratory settings so that the developmental sequence of various phenomena can be studied as they occur.

The team, including researchers from SwRI, Wheaton College, NASA's Jet Propulsion Laboratory and NuStar Energy LP, created complex patterns of faults in their models, similar to the ridge and trough features seen in some regions of Ganymede.

The models consisted of a "wet clay cake" material possessing brittle characteristics to simulate how the icy moon's lithosphere, the outermost solid shell, responds to stresses by cracking.

The laboratory models suggest that characteristic patterns of ridges and troughs, called grooved terrain on Ganymede, result from its surface being stretched.

"The physical models showed a marked similarity to the surface features observed on Ganymede," said co-author Dr. Danielle Wyrick, a senior research scientist in the SwRI Space Science and Engineering Division.

"From the experiments, it appears that a process in which the crust breaks into separate blocks by large amounts of extension is the primary mechanism for creating these distinct features."

"Physical analogue modeling allows us to simulate the formation of complex three-dimensional geological structures on Ganymede, without actually going to Ganymede," said co-author Dr. David Ferrill, director of the Earth, Material and Planetary Sciences Department in the SwRI Geosciences and Engineering Division.

"These scaled models are able to reproduce the fine geometric details of geologic processes, such as faulting, and to develop and test hypotheses for landscape evolution on planetary bodies."

SwRI researchers previously have used physical analog models to examine the process by which pit crater chains, a series of linear pits, or depressions, develop on Mars, and how magma in the Martian subsurface deforms the surface of the Red Planet.

More information: The paper, "Physical models of grooved terrain tectonics on Ganymede," by D.W. Sims, D.Y. Wyrick, D.A. Ferrill, A.P. Morris, G.C. Collins, R.T. Pappalardo and S.L. Colton, was published by Geophysical Research Letters, 16 June 2014, Volume 41, Issue 11, pages 3774–3778, DOI: 10.1002/2014GL060359

What is beneath the cracked surface of Pluto's moon Charon?

An artist’s concept of Pluto as viewed from the surface of one its moons. 

Pluto is the large disk at the center of the image. Charon is the smaller disk to the right. 

Credit: NASA, ESA and G. Bacon (STScI)

Is there evidence of an ocean-past or present-waiting to surprise us on Charon?

It isn't impossible. In fact, it might be likely.

What used to be the smallest planet in our solar system has, comparatively, the biggest moon.

Pluto, now classified as a dwarf planet, has a moon, Charon, almost 1/8th its own mass and almost half its physical volume.

Our Moon, by comparison, has about 1% of the Earth's mass and only 2% of its volume.

Charon is so large compared to Pluto that some astronomer's consider the two to be a sort of binary dwarf-planet system, as opposed to a moon-and-planet system.

Both Charon and our Moon are believed to have formed in the same way: when they were knocked off their parent planets.

Enormous collisions liquified parts of the Earth and Pluto. The debris was thrown into orbit where it later cooled.

In the process of cooling into solid bodies around the Earth and Pluto, the Moon and Charon became locked to their parent planets' orbits.

That locking of the planets to moons results in tides: here on Earth, on the Moon, and, we believe, on Pluto and Charon.

An analysis by scientists at Goddard suggests that tides on Pluto and Charon could have been especially high as Charon cooled.

This is because the part of Pluto knocked into orbit didn't get very far. Charon formed incredibly close to Pluto: only 19,000 km (12,000 miles) away.

By comparison, our Moon is currently 384,000 km (238,855 mi) from Earth. Initially, the orbit might not have been very circular, either: it might have been more eccentric or elliptical-shaped.

Eccentrically-moving, close-by Charon would have pulled on Pluto, and Pluto would have pulled back, resulting in heating of both planets and, maybe, an ocean under Charon's ice shell.

Alyssa Rhoden

Depending on exactly how Charon's orbit evolved, particularly if it went through a high-eccentricity phase, there may have been enough heat from tidal deformation to maintain liquid water beneath the surface of Charon for some time," said Alyssa Rhoden of NASA's Goddard Space Flight Center in Greenbelt, Maryland.

"Using plausible interior structure models that include an ocean, we found it wouldn't have taken much eccentricity (less than 0.01) to generate surface fractures like we are seeing on Europa."

Artist impression of the New Horizons spacecraft as it approached Jupiter en route to Pluto. 

Credit: NASA

On icy moons like Europa and Enceladus, tidal forces exerted by their parent planets cause massive surface cracks to form.

Those cracks are easily appreciated by passing spacecraft. According to Rhoden and colleagues' model, Charon's surface should be similarly cracked.

We expect to see evidence of this fractured surface geology as the New Horizons spacecraft approaches Pluto. New Horizons will pass directly over Pluto and Charon, briefly, on July 15th 2015.

Charon was discovered thirty-five years ago, in 1978, but well-photographed for the first time by New Horizons in 2013.

With the 2015 close-up just around the corner, scientists are working swiftly to make best use of surface photographs returned by the spacecraft.

New Horizons will give us the ability to resolve objects as small as a football field on part of the surface of Pluto and Charon.

With pictures of that detail and models such as this one, we may be able to look backwards in time to determine details about both bodies, such as how thick their ice shells were when they formed.

Studying patterns of fractures in Charon's surface is critical to building accurate models of the ice shell and layers beneath.

"Our model predicts different fracture patterns on the surface of Charon depending on the thickness of its surface ice, the structure of the moon's interior and how easily it deforms, and how its orbit evolved," said Rhoden.

"By comparing the actual New Horizons observations of Charon to the various predictions, we can see what fits best and discover if Charon could have had a subsurface ocean in its past, driven by high eccentricity."

The oceans of certain icy moons with surface fractures are considered to be places where extraterrestrial life might be found.

Like Charon, Europa and Enceladus are very cold and very distant from the sun. In all three cases, the formation and maintenance of life would depend upon a reliable energy source as well as elements that can participate in the chemistry of life, such as carbon, nitrogen, and phosphorus.

New Horizons Long Range Reconnaissance Imager (LORRI) composite image showing the detection of Pluto’s largest moon, Charon. 

When these images were taken on July 1 and July 3, 2013, the New Horizons spacecraft was still about 550 million miles (880 million kilometers) from Pluto.

On July 14, 2015, the spacecraft is scheduled to pass just 7,750 miles (12,500 kilometers) above Pluto’s surface, where LORRI will be able to spot features about the size of a football field. 

Credit: NASA /Johns Hopkins University Applied Physics Laboratory /Southwest Research Institute (SRI)

It is unknown if a potential ocean on Charon may have harbored these ingredients or if the ocean there existed for long enough for life to form.

The same questions apply to any ancient ocean on any moon in our Solar System or any other. The first step on Charon is to find the fractures, and then go looking for the warmth that liquid water.

"Since it's so easy to get fractures, if we get to Charon and there are none, it puts a very strong constraint on how high the eccentricity could have been and how warm the interior ever could have been," said Rhoden.

"This research gives us a head start on the New Horizons arrival, what should we look for and what can we learn from it. We're going to Pluto and Pluto is fascinating, but Charon is also going to be fascinating."

NASA ICESat-2 satellite Box structure under construction

An engineer checks ICESat-2's box structure, shortly after its arrival in a NASA clean room in May. 

Over the next two years, engineers and technicians will attach electronics, optics, lasers, a telescope and more to the box, testing its function at each step. 

Credit: NASA's Goddard Space Flight Center /Kate Ramsayer

To build a satellite that will measure all the bumps and dips of our dynamic Earth, engineers started with a black box, built of a composite honeycomb material to make it as light as possible.

The structure was precisely manufactured with an opening to allow lasers to beam to Earth, and other windows sized for a telescope that will capture photons that bounce off our planet and return to the satellite.

The box was measured and marked to denote where the assembly of aligned mirrors, electronics, lasers and photon detectors would be attached.

It must be tough enough to handle the rigors of a rocket launch and years in a harsh space environment; here on Earth, the box structure must be hardy enough to withstand tests engineers use to simulate those conditions.


The box structure at the core of the Ice, Cloud and land Elevation Satellite-2 (ICESat-2), instrument was delivered to a clean room at NASA's Goddard Space Flight Center in Greenbelt, Maryland, in May.

A team of 250 engineers, fabricators and scientists has now started the official integration and testing stage of the laser instrument.

"There's lots of activity, we're moving from looking at all the different subsystems, to looking at the overall system coming together."

"It's really exciting to move forward into that realm," said Cathy Richardson, instrument manager with the ICESat-2 mission. The team will have a half-dozen components ready for delivery in June.

"It's not just a drawing. It's an actual, real piece of hardware, that's getting tested and showing that it's meeting requirements."



ATLAS Assembly
ICESat-2's instrument, called the Advanced Topographic Laser Altimeter System (ATLAS), will measure the elevation of Earth's surfaces, from ice sheets to forests to oceans.

Its six beams will generate a more detailed elevation portrait than single beam of original ICESat-2, which flew from 2003 to 2009, and with the beams paired, scientists will be able to measure surface slope and better calculate height changes.

To measure elevation, ATLAS beams light with a green laser that pulses 10,000 times a second. Only a few photons will bounce off the surface and return to the satellite, but an incredibly sensitive detector counts those that do come back.

Using the time of the photons' return trip, the speed of light and some geometry, scientists can determine the distance the photons traveled and, therefore, the height of Earth below the satellite's orbit.

ATLAS will provide scientists with measurements that create a global portrait of Earth's elevation, and will gather data that can precisely track change, including melting glaciers and thinning sea ice.

Credits: Satellite image courtesy of Orbital Earth image illustrating AMSR-E sea ice courtesy of the NASA Scientific Visualization Studio

"ICESat-2 will revolutionize our understanding of ice sheet and sea ice changes and processes," said Thorsten Markus, ICESat-2 project scientist.

"I think it's one of the most exciting missions out there. There's so much opportunity for real discoveries."

The satellite will observe Earth in a new way, he said, which makes it technically challenging. But this also opens the door for discoveries not yet imagined.

After years of calculations and computer models and discussions, Markus said, it's exciting to see the hardware come together.

NASA ISEE-3 (ICE) spacecraft: Private Group Fund Satellite Reboot Project

Artist's concept image of ISEE-3 (ICE) spacecraft.

Credit: NASA

Red tape and a moderate earthquake did not deter a private group from meeting its goal of making contact with ISEE-3, a 36-year-old NASA spacecraft that has been slumbering in deep space since 1997.

Now, members are trying to redirect the path of the vintage International Sun-Earth Explorer 3 (ISSE-3) probe before it's too late.

The engineers, programmers and citizen scientists, working under the name ISEE-3 Reboot Project, "spoke" with the probe Thursday (May 29) using the Arecibo Observatory in Puerto Rico.

This was after a 5.8-magnitude earthquake shook the area earlier this week during testing, temporarily shutting down telescope operations.

Keith Cowing

"It took a lot of preparation and perseverance," said co-leader Keith Cowing, who remained behind in Virginia for co-ordination while other co-lead Dennis Wingo worked at Arecibo.

Wingo's team has at the Arecibo Observatory for two weeks and is expected to leave Friday (May 30).

The team technically had the capability to command the spacecraft last Friday (May 23), but under a Space Act Agreement with NASA had to have the agency's approval before making the move. That approval finally came through Thursday (May 29).

Dennis Wingo

Cowing acknowledged waiting for approval took longer than he hoped, but said given it's the first time a private group wanted to do something like this, he could appreciate the agency's caution.

Luckily for the group, their preparation worked: first contact went off without a hitch, with the spacecraft responding to a tone exactly as expected. "I'm doing my happy dance," Cowing said.

NASA's International Sun-Earth Explorer (ISEE-3) was undergoing testing and evaluation inside Goddard's dynamic test chamber when this photo was taken. 

Working inside a dynamic test chamber, Goddard engineers wear protective "clean room" clothing to prevent microscopic dust particles from damaging the sophisticated instrumentation. 

NASA launched the 16-sided polyhedron, which weighed 1,032 lbs. (469 kg.), from Cape Canaveral, Florida, on August 12, 19 

This illustration shows the trajectory of the ISEE-3-ICE Trajectory spacecraft. 

Credit: NAS 

The ISEE-3 Reboot Crew After Signal Confirmation on USRP Radio

Ganymede harbours layered sandwich of oceans and ice

This artist's concept of Jupiter's moon Ganymede, the largest moon in the solar system, illustrates the layered sandwich model of its interior oceans. 

Credit: NASA /JPL-Caltech

The largest moon in our solar system, a companion to Jupiter named Ganymede, might have ice and oceans stacked up in several layers like a club sandwich, according to new NASA-funded research that models the moon's makeup.

Previously, the moon was thought to harbor a thick ocean sandwiched between just two layers of ice, one on top and one on bottom.

Steve Vance

"Ganymede's ocean might be organized like a layered sandwich," said Steve Vance of NASA's Jet Propulsion Laboratory in Pasadena, Calif., explaining the moon's resemblance to multi-tiered sandwiches.

The study, led by Vance, provides new theoretical evidence for the team's "layered sandwich" model, first proposed last year.

The research appears in the journal Planetary and Space Science.

The results support the idea that primitive life might have possibly arisen on the icy moon.

Scientists say that places where water and rock interact are important for the development of life; for example, it's possible life began on Earth in bubbling vents on our sea floor.

Prior to the new study, Ganymede's rocky sea bottom was thought to be coated with ice, not liquid, a problem for the emergence of life.

The "layered sandwich" findings suggest otherwise: the first layer on top of the rocky core might be salty water.

"This is good news for Ganymede," said Vance. "Its ocean is huge, with enormous pressures, so it was thought that dense ice had to form at the bottom of the ocean."

"When we added salts to our models, we came up with liquids dense enough to sink to the sea floor."

NASA scientists first suspected an ocean in Ganymede in the 1970s, based on models of the large moon, which is bigger than Mercury.

In the 1990s, NASA's Galileo mission flew by Ganymede, confirming the moon's ocean, and showing it extends to depths of hundreds of miles.

The spacecraft also found evidence for salty seas, likely containing the salt magnesium sulphate (Epsom salt).

Previous models of Ganymede's oceans assumed that salt didn't change the properties of liquid very much with pressure.

Vance and his team showed, through laboratory experiments, how much salt really increases the density of liquids under the extreme conditions inside Ganymede and similar moons.

It may seem strange that salt can make the ocean denser, but you can see for yourself how this works by adding plain old table salt to a glass of water.

Rather than increasing in volume, the liquid shrinks and becomes denser. This is because the salt ions attract water molecules.

More information: "Ganymede's Internal Structure Including Thermodynamics of Magnesium Sulfate Oceans in Contact with Ice," Steve Vance et al., Planetary and Space Science, 2014, in press, dx.doi.org/10.1016/j.pss.2014.03.011