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Posts Tagged ‘solar system

Android phone goes into orbit

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The mobile-phone space race has ended in a tie: Last month we found out that NASA’s final space shuttle flight was taking a couple of iPhones to the International Space Station, and it turns out that an Android phone was aboard the shuttle Atlantis as well.

The Google-powered Samsung Nexus S phone will be used on the station in a series of experiments aimed at developing free-flying robotic assistants — zero-gravity gizmos that were inspired by the zippy little training sphere that helped Luke Skywalker practice his lightsaber skills in “Star Wars.” These volleyball-sized free-fliers are known as SPHERES — which is short for Synchronized Position Hold, Engage, Reorient Experimental Satellites.

SPHERES prototypes have been in the works for more than a decade. The camera-equipped, thruster-driven devices were developed by students at the Massachusetts Institute of Technology in cooperation with the Defense Department and NASA, for possible use as remote-controlled observers in microgravity environments. You could imagine a spyball floating through far-off modules of a space station to make sure all systems were go, during times when the station’s human crew is otherwise occupied. Future versions of the device could also look over the shoulder of a spacewalker to give Mission Control an up-close video view of the action.

The beauty part is that the SPHERES prototypes have an expansion port for plugging in extra devices or appendages — and the Samsung Nexus S is the first smartphone to be plugged in.

“By connecting a smartphone, we can immediately make SPHERES more intelligent,” D.W. Wheeler, lead engineer in the Intelligent Robotics Group at NASA’s Ames Research Center, said in a NASA news release. “With a smartphone, the SPHERES will have a built-in camera to take pictures and video, sensors to help conduct inspections, a powerful computing unit to make calculations, and a Wi-Fi connection that we will use to transfer data in real time to the space station and Mission Control.”

Neither the Android phones nor the iPhones are being used to make actual phone calls: Space station residents have special satellite-linked Internet phones for that. But today’s smartphones pack so much computing power that they could come in handy as backup navigation devices (in the iPhones’ case) or satellite controllers (in the Android phone’s case).

“We’ll start by simulating a mobile inspection of the station to test how well SPHERES can move around and collect data using the smartphone’s camera and sensors,” said Terry Fong, director of the Intelligent Robotics Group. “This will tell us basic information about the light and sound levels inside various areas of the station. Then we’ll use SPHERES to conduct an interview with a crewmember — a task that usually requires two crew members to complete. We’ll have Mission Control and the smartphone-enhanced SPHERES take the place of the astronaut holding the video camera.”

Just having the phones on the space station serve as status symbols for the companies involved.

“Samsung is proud to have the Nexus S chosen to be aboard NASA’s final space shuttle launch, an event that is historical,” Dale Sohn, president of Samsung Mobile, said in the news release. “The research that is being conducted with SPHERES using the Nexus S will help monitor and communicate from the International Space Station.”

So what about all the other smartphones and tablets that are out there? Because this is the last shuttle flight, future gizmos will have to be certified for flight on other types of space transports, such as the Russian Soyuz or Progress craft, European and Japanese cargo spaceships, or on commercial vehicles that are currently under development.

The future telecom space race may well be a contest to see which company can extend its calling network to the final frontier. I’m sure there are some future space tourists who’d love to flip on their phone while flying on SpaceShipTwo, call down to their pals and say, “Can you hear me now?” What do you think?

 

Via MSNBC

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We May Not Live in a Hologram After All

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Holo-universe

You may remember the hubbub that a Fermilab physicist caused last year when he started to investigate some strange results coming from the GEO600 gravitational wave experiment.

In a nutshell, GEO600 — a mindbogglingly sensitive piece of kit — started to detect what particle physicist Craig Hogan interpreted as quantum “fuzziness.” This fuzziness, or blurriness on the smallest possible scales, could be interpreted as evidence for the “holographic universe” hypothesis.

This hypothesis describes the 3-dimensional universe we live in as a projection from a 2-dimensional “shell” at the very edge of the universe. As with any projection, the projected “pixels” will become fuzzy the closer you zoom in on them. The quantum fuzziness GEO600 seemed to detect could be evidence for this projection effect. The Universe is therefore a hologram, so the idea goes.

Spurred on by the GEO600 results, Hogan is currently working on a project to build a “Holometer” at Fermilab to probe these quantum scales, hopefully shedding some light on what this fuzziness could be.

However, as announced this week, a space-borne European satellite that should be able to measure these small scales too, doesn’t appear to be registering any quantum fuzziness. In fact, it has yet to detect anything quantum, indicating that spacetime’s “graininess” is composed of quanta that a lot smaller than predicted — and in my view, puts a question mark over the interpretation of the GEO600 results.

Gamma-Ray Bursts and Grains of Quanta

The European Space Agency’s Integral gamma-ray observatory can make very precise measurements of the gamma-rays emitted by energetic (and often mysterious) gamma-ray bursts (GRBs).

GRBs are thought to be caused by the collapse of massive stars as they reach the end of their lives, explode and form neutron stars or black holes. As they explode, they blast a high-energy pulse of gamma-ray radiation from their poles, outshining entire galaxies. If correctly aligned with Earth, we can detect GRBs as a bright, transient flash.

As the gamma-rays — high-energy photons that exist at the extreme end of the electromagnetic spectrum — travel through space, their polarization (or “twist”) is affected by the spacetime they travel through.

If spacetime is composed of tiny quantum “grains,” the gamma-ray photons’ polarization should change from random polarization (at the GRB source) to biased toward a certain polarization when received by the Integral spacecraft.

Also, high-energy gamma-rays should be more twisted than lower energy gamma-rays; the difference in the polarization can therefore be used to estimate the size of the quantum grains.

What’s the Polarization?

If spacetime was smooth and continuous (as Einstein viewed the Universe), the polarization will remain random, and there will be no difference between high- and low energy photons no matter how far the gamma-rays travel. But if spacetime is composed of grains (as quantum mechanics predicts), the further the gamma-rays travel, the greater the polarization difference.

So, Philippe Laurent of CEA Saclay and his collaborators analyzed the polarization of gamma-rays from a very energetic gamma-ray burst. GRB 041219A occurred on Dec. 19, 2004, and it was immediately recognized as being in the top one percent of GRBs for brightness.

Also, due to its distance — 300 million light-years away — data from this explosion should have also revealed a measurable difference in the polarization between low- and high-energy gamma-ray photons.

Alas, no polarization difference was detected.

Some theories predict the quantum graininess should manifest itself at scales of around 10-35 meters — a scale known as the Planck length, the fundamental scale for quantum dynamics. Through the precise nature of its polarization measurements, Integral hasn’t found any quantum graininess down to a scale of 10-48 meters; that’s 10,000,000,000,000 times smaller than the “fundamental” Planck length.

So, if quantum predictions are correct, the spacetime quanta must be made from grains that are 10-48 meters in scale or less.

What does this mean?

Holographic Universe… or Not?

For Hogan’s interpretation of the GEO600 results to be correct, this graininess should be measurable over larger scales. In fact, GEO600 started to detect quantum fuzziness at scales of around 10-16 meters — that’s 10,000,000,000,000,000,000 times largerthan the Planck length.

At first glance, the Integral results appear to contradict the GEO600 interpretation, therefore disputing the holographic universe hypothesis all together. If these “fuzzy” 10-16 meter scales aren’t detected through Integral’s polarization measurements of gamma-rays, perhaps the GEO600 quantum fuzziness is an effect of overlooked instrumental error.

However, all may not be lost.

The Integral polarization results depend on spacetime being constructed from discrete quanta that behave in a way that fits with quantum theory. The holographic universe hypothesis goes one step further, constructing 3-dimensional spacetime from projections of a 2-dimensional “shell” — perhaps gamma-ray photons behave differently in this fuzzy, projected, quantum world, and this could be why no polarization difference between gamma-ray photons are detected.

Proving or disproving a holographic universe, of course, isn’t the focus of this Integral study; it is an attempt at revealing the very fabric of spacetime, helping physicists understand what our Universe is made of.

“This is a very important result in fundamental physics and will rule out some string theories and quantum loop gravity theories,” said Laurent in the ESA press release.

“Fundamental physics is a less obvious application for the gamma-ray observatory, Integral,” added Christoph Winkler, ESA’s Integral Project Scientist. “Nevertheless, it has allowed us to take a big step forward in investigating the nature of space itself.”

 

Via Physorg.com

Discovery Adds Mystery to Earth’s Genesis

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Artist's conception of a dusty planet-forming disk orbiting a stellar object known as IRS 46.

Earth and the other rocky planets aren’t made out of the solar system’s original starting material, two new studies reveal.

Scientists examined solar particles snagged in space by NASA’s Genesis probe, whose return capsule crash-landed on Earth in 2004. These salvaged samples show that the sun’s basic building blocks differ significantly from those of Earth, the moon and other denizens of the inner solar system, researchers said.

Nearly 4.6 billion years ago, the results suggest, some process altered many of the tiny pieces that eventually coalesced into the rocky planets, after the sun had already formed.

“From any kind of consensus view, or longer historical view, this is a surprising result,” said Kevin McKeegan of UCLA, lead author of one of the studies. “And it’s just one more example of how the Earth is not the center of everything.”

Salvaging the samples

The Genesis spacecraft launched in 2001 and set up shop about 900,000 miles (1.5 million kilometers) from Earth. It spent more than two years grabbing bits of the solar wind, the million-mph stream of charged particles blowing from the sun.

The idea was to give scientists an in-depth look at the sun’s composition, which in turn could help them better understand the formation and evolution of the solar system.

To that end, Genesis sent its sample-loaded return capsule back to Earth in September 2004. But things didn’t go well; the capsule’s parachute failed to deploy, and it smashed into the Utah dirt at 190 mph (306 kph).

While some of Genesis’ samples were destroyed in the crash, others were salvageable, as the two new studies show. Two different research teams looked at the solar wind particles’ oxygen and nitrogen — the most abundant elements found in Earth’s crust and atmosphere, respectively.

And they did so with a great deal of care, knowing that the crash had limited their supplies of pristine solar material.

“The stakes were raised on the samples that did survive well,” McKeegan told SPACE.com. “There wasn’t as much to go around.”

The Genesis return capsule slammed into the Utah dirt at nearly 200 mph on Sept. 8, 2004 when its parachute failed to deploy.

The Genesis return capsule slammed into the Utah dirt at nearly 200 mph on Sept. 8, 2004 when its parachute failed to deploy.
CREDIT: NASA/JPL

Analzying oxygen

McKeegan and his team measured the abundance of solar wind oxygen isotopes. Isotopes are versions of an element that have different numbers of neutrons in their atomic nuclei. Oxygen has three stable isotopes: oxygen-16 (eight neutrons), oxygen-17 (nine neutrons) and oxygen-18 (ten neutrons).

The researchers found that the sun has significantly more oxygen-16, relative to the other two isotopes, than Earth. Some process enriched the stuff that formed our planet — and the other rocky bodies in the inner solar system — with oxygen-17 and oxygen-18 by about 7 percent.

While scientists don’t yet know for sure how this happened, they have some ideas. The leading contender, McKeegan said, may be a process called “isotopic self-shielding.”

About 4.6 billion years ago, the planets had not yet coalesced out of the solar nebula, a thick cloud of dust and gas. Much of the oxygen in this cloud was probably bound up in gaseous carbon monoxide (CO) molecules.

But the oxygen didn’t stay bound up forever. High-energy ultraviolet light from the newly formed sun (or nearby stars) blasted into the cloud, breaking apart the CO. The liberated oxygen quickly glommed onto other atoms, forming molecues that eventually became the rocky building blocks of planets.

Photons of slightly different energy were required to chop up the CO molecules, depending on which oxygen isotope they contained. Oxygen-16 is far more common than either of the other two, so there would have been much more of this substance throughout the solar nebula, researchers said.

The result, the self-shielding theory goes, is that many of the photons needed to break up the oxygen-16 CO were “used up,” or absorbed, on the edges of the solar nebula, leaving much of the stuff in the cloud’s interior intact.

By contrast, relatively more of the photons that could strip out oxygen-17 and oxygen-18 got through to the inner parts of the cloud, freeing these isotopes, which were eventually incorporated into the rocky planets. And that, according to the theory, is why the sun and Earth’s oxygen isotope abundances are so different.

“The result that we’re publishing this week gives support to the self-shielding idea,” McKeegan said. “But we don’t know the answer yet.”

Nitrogen, too

In a separate study, another research team led by Bernard Marty of Nancy University in France analyzed the nitrogen isotopes in Genesis’ samples. (Nitrogen has two stable isotopes: nitrogen-14, which has seven neutrons, and nitrogen-15, which has eight.)

Marty and his colleagues found an even more dramatic difference than McKeegan’s group did: The solar wind has about 40 percent less nitrogen-15 (compared to nitrogen-14) than do samples taken from Earth’s atmosphere.

Previous studies had hinted that the sun’s nitrogen might be very different from that of Earth, Mars and other rocky bodies in the inner solar system, Marty said. But the new study establishes this firmly.

“Before Genesis and the present measurement of the N isotopic composition of the solar wind and by extension of the sun, it was not possible to understand the logic of such variations,” Marty told SPACE.com in an email interview. “Now we understand that the starting composition, the solar nebula, was poor in 15N, so that variations among solar system objects are the result of mixing with a 15N-rich end-member.”

As to how this enrichment of nitrogen-15 could have happened, Marty as well suggests some type of self-shielding as a possible mechanism. But it’s not a certainty.

“This is a scenario that is consistent with present-day observations,” he said. “We cannot eliminate yet the possibility that these 15N-rich compounds were imported from outer space as dust in the solar system.”

The new results also suggest that most nanodiamonds — tiny carbon specks that are a major component of stardust — likely formed in our own solar system, because they share similar nitrogen isotope ratios with the sun. Some scientists have regarded nanodiamonds as being primarily presolar, thinking they were ejected from other stellar systems by supernova explosions.

Both studies appear in the June 23 issue of the journal Science.

Genesis’ legacy

The two new studies should help scientists get a better understanding of the solar system’s early days, researchers said.

And the results should help rehabilitate the reputation of the $264 million Genesis mission, showing that the capsule crash didn’t render it a failure, McKeegan said.

“We managed to accomplish all the science that we set out to do, all the important stuff,” he said. “The enduring image in everybody’s mind — the picture of the crashed spacecraft in the desert — will be more of a footnote instead of the primary thing that people remember. That’s my hope, anyway.”

 

Via Space

Ice spray shooting out of Saturn moon points to a giant ocean lurking beneath its surface

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Scientists have collected the strongest evidence yet that Saturn moon Enceladus has a large saltwater ocean lurking beneath its surface.

Samples of ice spray shooting out of the moon have been collected by the Nasa’s Cassini spacecraft during one of its frequent Saturn fly-bys.

The plumes shooting water vapor and tiny grains of ice into space were originally discovered emanating from Enceladus – one of 19 known moons of Saturn – by the Cassini spacecraft in 2005.

Samples of ice spray shooting out of Saturn moon Enceladus have been collected by Nasa's Cassini spacecraft. Scientists believe it is the strongest evidence yet that Enceladus has a large saltwater ocean lurking beneath its surface

Samples of ice spray shooting out of Saturn moon Enceladus have been collected by Nasa’s Cassini spacecraft. Scientists believe it is the strongest evidence yet that Enceladus has a large saltwater ocean lurking beneath its surface

They were originating from the so-called ‘tiger stripe’ surface fractures at the moon’s south pole and apparently have created the material for the faint E Ring that traces the orbit of Enceladus around Saturn.

During three of Cassini’s passes through the plume in 2008 and 2009, the Cosmic Dust Analyser (CDA) on board measured the composition of freshly ejected plume grains.

The icy particles hit the detector’s target at speeds of up to 11miles-per-second, instantly vaporising them. The CDA separated the constituents of the resulting vapor clouds, allowing scientists to analyse them.

The ice grains found further out from Enceladus are relatively small and mostly ice-poor, closely matching the composition of the E Ring. Closer to the moon, however, the Cassini observations indicate that relatively large, salt-rich grains dominate.

Lead researcher Frank Postberg, of the University of Heidelberg in Germany, said: ‘There currently is no plausible way to produce a steady outflow of salt-rich grains from solid ice across all the tiger stripes other than the salt water under Enceladus’ icy surface.’

Plumes, both large and small, spray water ice from multiple locations along the 'tiger stripes' near the south pole of Enceladus

Plumes, both large and small, spray water ice from multiple locations along the ‘tiger stripes’ near the south pole of Enceladus.

Co-author Sascha Kempf, of the University of Colorado Boulder, added: ‘The study indicates that “salt-poor” particles are being ejected from the underground ocean through cracks in the moon at a much higher speed than the larger, salt-rich particles.

‘The E Ring is made up predominately of such salt-poor grains, although we discovered that 99 per cent of the mass of the particles ejected by the plumes was made up of salt-rich grains, which was an unexpected finding.

‘Since the salt-rich particles were ejected at a lower speed than the salt-poor particles, they fell back onto the moon’s icy surface rather than making it to the E Ring.’

According to the researchers, the salt-rich particles have an ‘ocean-like’ composition that indicates most, if not all, of the expelled ice comes from the evaporation of liquid salt water rather than from the icy surface of the moon.

When salt water freezes slowly the salt is ‘squeezed out’, leaving pure water ice behind. If the plumes were coming from the surface ice, there should be very little salt in them, which was not the case, according to the research team.

Dwarfed: Enceladus can be seen near Saturn's south pole at the bottom of this image

Dwarfed: Enceladus can be seen near Saturn’s south pole at the bottom of this image

 The scientists believe that perhaps 50 miles beneath the surface crust of Enceladus a layer of water exists between the rocky core and the icy mantle that is kept in a liquid state by gravitationally driven tidal forces created by Saturn and several neighboring moons, as well as by heat generated by radioactive decay.

It is thought that roughly 440lbs of water vapor are lost every second from the plumes, along with smaller amounts of ice grains.

Calculations show the liquid ocean must have a sizable evaporating surface or it would easily freeze over, halting the formation of the plumes.

‘This study implies that nearly all of the matter in the Enceladus plumes originates from a saltwater ocean that has a very large evaporating surface,’ said Dr Kempf.

The team’s study is published in the journal Nature.

 

Via DailyMail

Asteroid Heading Near Earth

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asteroid-2011-md-earth-orbit-plane-june-27.jpg

NASA, which is not as busy scheduling space launches anymore, is focusing a great deal of energy on an asteroid about the size of a tour bus that is expected to make an extremely close pass by the Earth on Monday.

On June 27 the asteroid should fly 7,500 miles above the Earth’s surface. The asteroid, named 2011 MD, was discovered last Wednesday by a pair of roboti telescopes in New Mexico that constantly scan the skies. NASA estimates that an object this size comes this close to Earth on an average of every six years.

NASA said for several hours prior to its closest approach, 2011 MD will be visible in moderately large amateur telescopes.

Of the thousands of objects discovered by NASA, approximately 827 are asteroids with a diameter of approximately a half-mile or larger. They’re classified as Potential Hazardous Asteroid. NASA is planning to launch a probe to visit one of the dangerous objects before the asteroid makes its way near the Earth.

 

Via BoiseWeekly

Mercury’s origins may differ from sister planets

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Mercury’s origins may be very different from its sister planets, including Earth, based on early findings that show surprisingly rich deposits of sulfur on the ground, scientists said on Thursday.

Early findings from the first spacecraft to orbit Mercury is forcing scientists to rethink how the planet closest to the sun formed and what has happened to it over the past 4 billion years.

NASA’s Mercury Surface, Space Environment, Geochemistry and Ranging spacecraft — nicknamed Messenger — is three months into a planned year-long mission. It has also uncovered evidence of a lopsided magnetic field and regular bursts of electrons jetting through the magnetosphere.

“It’s almost a new planet because we’ve never had this kind of observatory before,” said lead researcher Sean Solomon of the Carnegie Institution of Washington, D.C.

Volcanoes appear to have played a rather large role in shaping Mercury, providing fresh material to fill its cratered face, but also possibly providing an unexpected supply of sulfur to the surface, a finding that suggests Mercury may have had different building blocks than Venus, Earth and Mars.

Scientists expected that Mercury, which is believed to have formed in the hottest, densest part of the original solar nebula, wouldn’t have had the right temperatures to hang on to lighter-weight materials like sulfur.

“Elements like that are usually lost in space,” Solomon said. “The fact that we see sulfur from the surface points strongly that we had sulfur gases coming out.

“All of our simple ideas … a hot planet, easily depleted of volatiles … are not turning out to be the simple story we thought,” Solomon added.

New images from Messenger reveal a massive plain of ancient lava flow, the largest of which spans 400 million square kilometers, about half the size of the continental United States.

Another surprise was the planet’s lopsided magnetic field, which is stronger in the north than the south. Scientists can’t yet account for the asymmetry, but one theory is that the planet’s magnetic field is in the processing of flipping.

Mercury is the only terrestrial body besides Earth that has a magnetic field and one of the prime goals of the Messenger mission is to figure out how Mercury, which sports a massive iron core, was assembled. Scientists believe Mercury’s core, like Earth’s, is responsible for generating its magnetic field

Messenger also has been monitoring regular outbursts of electrons in Mercury’s magnetosphere. Hints of the phenomenon were first detected by NASA’s Mariner 10 probe, which flew past Mercury in 1974.

“We’re seeing these seeing these very dynamic phenomena in the magnetosphere. It’s very surprising and energetic,” Solomon said.

Still to come: measurements to reveal if Mercury hides ice insides its permanently shadowed craters.

 

Via DiscoveryOn

Cassini finally catches Helene

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The Cassini team has had a wretched time trying to get pictures of Helene in the past, but their streak of bad luck is over. Helene is one of the four “co-orbital” moons in the Saturn system, which occupy meta-stable spots in the leading and trailing Lagrangian points on the orbits of Tethys and Dione.

It’s the biggest of the four, but that’s not saying much; it’s only about 36 by 32 by 30 kilometers across, so it’s in the same general size range as Phobos.

It’s proven challenging to predict where it’s going to be with enough accuracy to make sure Cassini can capture it in its camera field of view, with the result that nearly every imaging sequence that Cassini has been commanded to take of Helene has seen the moon wander out of the field of view at one time or another.
Well, Cassini has finally achieved gorgeous global imaging of Helene with a spectacular flyby on Saturday, in which they absolutely nailed the spacecraft’s pointing and got Helene to pose prettily for the camera from beginning to end of the encounter. And what a wacky, wacky world Cassini has revealed Helene to be!!

Helene in enhanced color

Helene in enhanced color
Cassini flew within 7,000 kilometers of Helene, Dione’s leading co-orbital satellite, on June 18, 2011. The Saturn-facing hemisphere of the moon is covered with strange gully-like features that probably represent slides of dry material into local topographic lows. Credit: NASA / JPL / SSI / color composite by Gordan Ugarkovic

We saw these gullies on the previous close flyby but this is a much better view. There are two things that are very strange about these gullies. One is to see them at all. Features like this, if seen on Earth or even Mars, would be assumed to have something to do with water, but there is no possibility of liquid water on Helene (though it is likely made mostly of rock-hard water ice). These gullies must form by a dry process in which material — likely very powdery dusty stuff — cascades toward local topographic lows.

The other thing that is very strange is the strong difference in color between the higher-standing stuff and the smooth gully slide areas in between them. Others of Saturn’s moons have some color variations across their surfaces, but really I don’t know of one other than Iapetus where there are such sharp boundaries between one color of material and another. The color differences are most obvious on the right side of the image, where the Sun hits Helene directly and there aren’t many cast shadows; color differences fade as you get toward the lower and lower light near the terminator at the left side of the image. Those color differences are what make this movie version of the flyby images appear to “beat” — every time an image is shot through a short-wavelength ultraviolet filter, the inter-gully ridge areas darken substantially.

 

Cassini’s June 2011 Helene flyby (bounces 3 times)
Cassini got its best-ever view of Saturn’s moon Helene on June 18, 2011, when it approached to within 7,000 kilometers. Helene is a co-orbital moon of Dione. The sunlit face is mostly the side of the moon that always faces Saturn, and is covered with strange gully-like features. The animation “bounces” back and forth to help the viewer see the 3D shape of Helene.

The surface appears to “beat” with contrast changes because Cassini was cycling through different filters to take the images. In short-wavelength filters, the areas between gullies are darker than the smooth gully floors, while there is less contrast between them in the longer-wavelength filters.

To generate this animation, I aligned the frames and rotated them 180 degrees to place north up. Then I used the Photoshop “dust and scratches” filter to remove most of the cosmic ray hits. This also removed a bit of detail from gully areas, unfortunately, but it saved me a lot of time and effort. I cleaned up the worst remaining cosmic ray hits using the clone tool. I adjusted the contrast to push black space to completely black and to bring out some more detail in shadowed areas.

As you watch the animation, try focusing on different areas. Like the massive crater in the north that is partially illuminated in the opening of the animation. Or the faceted shape of the moon, which suddenly brings a huge sunlit face into view. Also try to see if you can see the shadows move across Helene’s face as it rotates; most of the apparent motion is due to Cassini’s motion, but some is Helene rotating on its axis.

Credit: NASA / JPL / SSI / animation by Emily Lakdawalla

There are a couple of dozen little tiny bowl-shaped impact craters scattered across the image, and there are eroded features that are almost certainly older, larger impact craters, but really there are not very many craters considering Helene’s location in the shooting gallery of the Saturn system, so whatever process makes these gullies has also very likely been active recently and has wiped away past smaller craters. This inference becomes even more interesting when you look at the opposite face of Helene, the one that faces out from Saturn, which is heavily cratered as you might expect. Ian Regan put together a really nice comparison of Cassini’s various views of Helene’s two faces:

Cassini's views of Helene through March 2010

 

Cassini’s views of Helene through March 2010
Ian Regan composed this montage of Cassini’s highest resolution views of Dione’s co-orbital moon Helene to attempt to make sense of the positions of its features. The small moon appears very different seen from different angles and under different lighting conditions. The view from the June 18, 2011 flyby is quite similar to the geometry of the Saturnlit view from March 3, 2010 on the lower left of this mini-atlas. Credit: NASA / JPL / SSI / Ian Regan

Why are Helene’s two sides so different? It’s just one of many mysteries that Cassini’s science team still has to solve.

 

Via Planetary