Posted on by Nancy Atkinson

Will Asteroid 2011 AG5 Hit Earth in 2040?

The orbit of asteroid 2011 AG5 carries it beyond the orbit of Mars and as close to the sun as halfway between Earth and Venus. Image credit: NASA/JPL/Caltech/NEOPO

[/caption]

You may have heard about an asteroid in the news this week that has a 1 in 625 chance of hitting Earth on Feb. 5, 2040. So, will this asteroid, named 2011 AG5, really hit our planet? The quick answer is, probably not. But astronomers will need more observations of this asteroid to say one way or the other for sure.

“Because of the extreme rarity of an impact by a near-Earth asteroid of this size, I fully expect we will be able to significantly reduce or rule out entirely any impact probability for the foreseeable future,” said Donald Yeomans, head of the Near-Earth Object Observations Program at NASA’s Jet Propulsion Laboratory.

Yeomans classified the chance of impact as “unlikely” and here are some facts that we do know about Asteroid about 2011 AG5:

What is the potential that this asteroid will impact Earth?

Currently astronomers have this asteroid ranked as a “1” on the 1 to 10 Torino Impact Hazard Scale. A “1” means this asteroid will have a pass near the Earth that poses no unusual level of danger. Current calculations show the chance of collision is extremely unlikely with no cause for public attention or public concern. Very likely, subsequent telescopic observations will lead to re-assignment to Level 0. The 1 in 625 chance is what the predictions are for the data that NASA has right now. Further observations will likely decrease the odds, and may even bring it to zero.

How big is this asteroid?

2011 AG5 is a 140-meter-wide (460 feet) space rock. Its composition is not yet known – whether it is a rocky, iron or icy asteroid.

How many Near Earth asteroids are out there?

Asteroid 2011 AG5 is one of 8,744 near-Earth objects that have been discovered so far, as of this week (March 1, 2012). NEOs are objects that come within 1.3 AU of the Sun (with Earth at 1 AU, so it means they pass through our neighborhood.)

1,305 of these NEOs have been classified as Potentially Hazardous Asteroids (PHAs), which are those that are larger than about 150 m (500 ft) and come within 0.05 AU of Earth’s orbit, so 2011 AG5 is right at the edge of that classification.

How was this asteroid discovered?

It was discovered on Jan. 8, 2011, by astronomers using a 60-inch Cassegrain reflector telescope located at the summit of Mount Lemmon in the Catalina Mountains north of Tucson, Arizona.

Where is 2011 AG5 now?

Its orbit carries it as far out as beyond Mars’ orbit and as close to the Sun as halfway between Earth and Venus. See the image above for its approximate current location. Its proximity to the Sun from our vantage point on Earth means astronomers can’t make observations right now.

When will astronomers find out more and be able to make better predictions?

“In September 2013, we have the opportunity to make additional observations of 2011 AG5 when it comes within 91 million miles (147 million kilometers) of Earth,” said Yeomans. “It will be an opportunity to observe this space rock and further refine its orbit.”

Yeomans added that even better observations will be possible in late 2015.

Will this asteroid come close to Earth before 2040?

2011 AG5 will next be near Earth in February of 2023 when it will pass the planet no closer than about 1.2 million miles (1.9 million kilometers). In 2028, the asteroid will again be in the area, coming no closer than about 12.8 million miles (20.6 million kilometers). The Near-Earth Object Program Office says the Earth’s gravitational influence on the space rock during these flybys has the potential to place the space rock on an impact course for Feb. 5, 2040, but this has very unlikely odds of occurring at 1-in-625.

“Again, it is important to note that with additional observations next year the odds will change and we expect them to change in Earth’s favor,” said Yeomans.

Screenshot from the Impact Earth website animation.

If Asteroid 2011 AG5 were to hit Earth, what is the potential for damage to Earth?

According to calculations from the Impact Earth website, an object of this size would begin to break up in Earth’s atmosphere at an altitude of 65500 meters (215,000 ft). Some of the larger pieces would reach the ground, with the pieces hitting Earth’s surface (ground) at a velocity Of 2.64 km/s (1.64 miles/s). The impact energy would be 7.52 x 10^15 Joules, or 1.8 MegaTons.

This would not cause any global problems, as the planet as a whole would not be strongly disturbed by the impact.

The broken projectile fragments would strike the ground in an ellipse about 1.17 km by 0.824 km in diameter, and the result of the impact is a crater field, not a single crater. The largest crater would be about 400 meters in diameter (1,310 feet). The impact would create a Richter Scale Magnitude-like event of 4.8.

If you were 1-10 km away from the impact area, you would feel a sensation like a heavy truck striking building. Standing cars would be rocked noticeably. Indoors, dishes and windows, might be disturbed and walls might make a cracking sound. An air blast at speeds of 26.3 m/s = 58.9 mph would arrive approximately 10 – 30 seconds after impact.

If this impactor hit in an ocean, the impact-generated tsunami wave would arrive approximately 6.18 minutes after impact if you were 10 km away, with a wave amplitude is between: 4.78 and 9.55 meters (15.7 feet and 31.3 feet).

How often do asteroids hit the Earth?

Yeomans said that every day, Earth is pummeled by more than 100 tons of material that spewed off asteroids and comets. Fortunately the vast majority of this “spillover” is just dust and very small particles. “We sometimes see these sand-sized particles brighten the sky, creating meteors, or shooting stars, as they burn up upon entry into Earth’s atmosphere,” Yeomans said in his “Top Ten Asteroid Factoids” article. “Roughly once a day, a basketball-sized object strikes Earth’s atmosphere and burns up. A few times each year, a fragment the size of a small car hits Earth’s atmosphere. These larger fragments cause impressive fireballs as they burn through the atmosphere. Very rarely, sizable fragments survive their fiery passage through Earth’s atmosphere and hit the surface, becoming meteorites.”

More info:
Catalina Sky Survey
Minor Planet Center
Asteroid and Comet Impact Hazards website from NASA
NASA’s Near Earth Object Program
Impact Earth website

Posted on by Nancy Atkinson

Thierry Legault: Astrophotography is an ‘Adrenaline Rush’

Thierry Legault with the equipment he uses for satellite images. Images courtesy of Thierry Legault.

[/caption]

During one of the final space shuttle missions, photographer Thierry Legault traveled nearly 4,000 km across various locations in Europe to try and capture the shuttle docked to the International Space Station as the two spacecraft transited across the surface of the Sun.

“Essentially, I was trying to catch the clear sky so I could take images of an event that would last less than a second,” Legault said from his home in France.

This type of dedication to his craft, along with his attention to detail and quality has earned Legault the reputation as one of the top amateur astrophotographers in the world.

Amazingly, he started his astrophotography hobby — and his specialty of imaging objects in front of the Sun — just by chance. And now Legault has been shooting breathtaking images of spacecraft in orbit and astronomical objects and events for nearly 20 years.

“I began in 1993 with one of the first CCD cameras, the first year that CCD cameras were available for amateurs,” Legault said. “It was a wonderful time, because it was a time of pioneers, and it was a revolution after film.”

An Airplane in Front of the Sun Credit & Copyright: Thierry Legault

Intrigued by what could be done with digital equipment, he experimented by taking planetary and deep sky pictures and has now amassed a prolific portfolio of stunning images. In 2001 he took the first of the type of images he has become renown for.

“I took a picture of a plane in front of the Sun,” Legault recalled, “and it was published on APOD (Astronomy Picture of the Day), and so now I have taken many images of things in front of the Sun.”

Image of the solar transit of the International Space Station (ISS) and Space Shuttle Atlantis, 50 minutes after undocking from the ISS, before return to Earth, taken from the area of Mamers, Normandie, France on September 17, 2006. Credit and copyright, Thierry Legault

In 2006 he took pictures of the space station and space shuttle side by side just as the shuttle undocked. It was published by newspapers around the world, including a double page in the Guardian, was shown on CNN and other news shows, and was everywhere on the internet.

“It was an incredible success, which was very surprising. This type of imaging is very fun for me, as I like the challenge,” Legault said. “But it is interesting how taking a picture of a spaceship in front of the Sun is really something for non-astronomers, but yet I never received so much interest for all the other astronomy images I have taken.”

Legault said he has received emails and letters from people around the world expressing how much they enjoy his transit images.

One of the setups Legault uses for solar imaging. Image courtesy Thierry Legault

Living in the suburbs of Paris means there are plenty of lights to interfere with his astrophotography.

“Where I live is not a problem for taking pictures of some satellites, the Sun, the Moon and planets,” he said. “For deep space imaging and for the space station, I have to put everything in the van and drive 20-30 kilometers and go to the country; also for solar or lunar transits I have to go to the place where the transit is visible.”

This is the first image ever taken from the ground, of an astronaut in extravehicular activity (EVA1). Steve Bowen, attached to the end of the ISS robotic arm (MSS), was working on a defective ammonia pump. The pump was hooked to the ISS mobile base system (MBS). All major elements of the robotic arm are visible, including the structures of the motorized joints and some elements along the arms (smaller than the astronaut). Credit and copyright, Thierry Legault.

For the STS-131 mission in May of 2010, Legault traveled to Spain, Switzerland, various parts of France, and for the STS-133 mission in February 2011, where he took the first-ever ground-based image of astronaut in spacewalk he drove to Germany, and to both the south and north of France, and between 3,000 and 4,000 kilometers.

All this driving and weeks of preparation is for an event that he never sees live with his own eyes, and usually lasts about a half a second. He uses CalSky.com to calculate the exact moment and exact location he will need to be to capture an event.

“For transits I have to calculate the place, and considering the width of the visibility path is usually between 5-10 kilometers, but I have to be close to the center of this path,” Legault explained, “because if I am at the edge, it is just like a solar eclipse where the transit is shorter and shorter. And the edge of visibility line of the transit lasts very short. So the precision of where I have to be is within one kilometer.”

Legault studies maps, and has a radio synchronized watch to know very accurately when the transit event will happen.

“My camera has a continuous shuttering for 4 seconds, so I begin the sequence 2 seconds before the calculated time,” he said. “I don’t look through the camera – I never see the space station when it appears, I am just looking at my watch!”

Atlantis during the STS-135 mission docked to the International Space Station, July 15, 2011. Credit: Thierry Legault.

For a transit event, he gets get a total of 16 images – 4 images every second, and only after he enlarges the images will he know if he succeeded or not.

“There is a kind of feeling that is short and intense — an adrenaline rush!” Legault said. “I suppose it is much like participating in a sport, but the feeling is addictive. I did it with a friend two years ago and now he is addicted too.”

Legault added that when he succeeds, it is a very satisfying feeling.

But Legault is not keeping the adrenaline rushes all to himself; he willingly shares his knowhow and techniques.

His website provides a wealth of knowledge about his techniques and equipment

In 2005 he wrote a book (in French) called Astrophotographie, that has sold over 6,000 copies, and he is working on getting it published in English. The book provides information on how to image constellations, stars, comets, eclipses, the Moon, planets, sun, and deep-sky objects, in accessible, nontechnical language. Legault also gives practical advice on equipment and technique, with answers to problems faced by every beginner. He also co-authored another book, “New Atlas of the Moon” with Serge Brunier, and in the March 2012 issue of Sky and Telescope, Legault wrote a detailed article on how to take detailed, ground-based images of the ISS.

Tomorrow on Universe Today, Legault will share his advice for avoiding “bad” astrophotography.

Posted on by Nancy Atkinson

Timelapse: Return to the Night Sky at Joshua Tree

Gavin Heffernan’s latest timelapse is a stunning look at the night sky over Joshua Tree National Park in California. You’ll be transported from Earth to space and back to Earth again, seeing the Milky Way in all its glory, plus meteors and a satellite pass or two. This is Gavin’s second visit to Joshua Tree (see the first video here) and was shot with a Canon EOD 7D with a EF-S18-135mm Zoom Lens 3.5, and a Canon EOS 5D Mk II with a Canon Prime 24mm f1.4 L-Series.

Posted on by Jason Major

Warp Drives May Come With a Killer Downside

Dropping out of warp speed could have deadly results. (Image: Paramount Pictures/CBS Studios)

[/caption]

Planning a little space travel to see some friends on Kepler 22b? Thinking of trying out your newly-installed FTL3000 Alcubierre Warp Drive to get you there in no time? Better not make it a surprise visit — your arrival may end up disintegrating anyone there when you show up.

“Warp” technology and faster-than-light (FTL) space travel has been a staple of science fiction for decades. The distances in space are just so vast and planetary systems — even within a single galaxy — are spaced so far apart, such a concept is needed to make casual human exploration feasible (and fit within the comforts of people’s imagination as well… nobody wants to think about Kirk and Spock bravely going to some alien planet while everyone they’ve ever known dies of old age!)

While many factors involving FTL travel are purely theoretical — and may remain in the realm of imagination for a very long time, if not ever — there are some concepts that play well with currently-accepted physics.

Warp field according to the Alcubierre drive. (AllenMcC.)

The Alcubierre warp drive is one of those concepts.

Proposed by Mexican theoretical physicist Miguel Alcubierre in 1994, the drive would propel a ship at superluminal speeds by creating a bubble of negative energy around it, expanding space (and time) behind the ship while compressing space in front of it. In much the same way that a surfer rides a wave, the bubble of space containing the ship and its passengers would be pushed at velocities not limited to the speed of light toward a destination.

Of course, when the ship reaches its destination it has to stop. And that’s when all hell breaks loose.

Researchers from the University of Sydney have done some advanced crunching of numbers regarding the effects of FTL space travel via Alcubierre drive, taking into consideration the many types of cosmic particles that would be encountered along the way. Space is not just an empty void between point A and point B… rather, it’s full of particles that have mass (as well as some that do not.) What the research team — led by Brendan McMonigal, Geraint Lewis, and Philip O’Byrne — has found is that these particles can get “swept up” into the warp bubble and focused into regions before and behind the ship, as well as within the warp bubble itself.

When the Alcubierre-driven ship decelerates from superluminal speed, the particles its bubble has gathered are released in energetic outbursts. In the case of forward-facing particles the outburst can be very energetic — enough to destroy anyone at the destination directly in front of the ship.

“Any people at the destination,” the team’s paper concludes, “would be gamma ray and high energy particle blasted into oblivion due to the extreme blueshifts for [forward] region particles.”

In other words, don’t expect much of a welcome party.

Another thing the team found is that the amount of energy released is dependent on the length of the superluminal journey, but there is potentially no limit on its intensity.

“Interestingly, the energy burst released upon arriving at the destination does not have an upper limit,” McMonigal told Universe Today in an email. “You can just keep on traveling for longer and longer distances to increase the energy that will be released as much as you like, one of the odd effects of General Relativity. Unfortunately, even for very short journeys the energy released is so large that you would completely obliterate anything in front of you.”

So how to avoid disintegrating your port of call? It may be as simple as just aiming your vessel a bit off to the side… or, it may not. The research only focused on the planar space in front of and behind the warp bubble; deadly postwarp particle beams could end up blown in all directions!

Luckily for Vulcans, Tatooinians and any acquaintances on Kepler 22b, the Alcubierre warp drive is still very much theoretical. While the mechanics work with Einstein’s General Theory of Relativity, the creation of negative energy densities is an as-of-yet unknown technology — and may be impossible.

Which could be a very good thing for us, should someone out there be planning a surprise visit our way!

 

Read more about Alcubierre warp drives here, and you can download the full University of Sydney team’s research paper here.

Thanks to Brendan McMonigal and Geraint Lewis for the extra information!

Main image © Paramount Pictures and CBS Studios. All rights reserved.

 

Posted on by Fraser Cain

NASA’s New Video, Voiced by Optimus Prime

Okay, NASA’s really just showing off with this video. They dug up every piece of amazing archival footage and had it narrated by Optimus Prime (Peter Cullen). Tell me this doesn’t make you want to fly off into space and explore the unknown. I wonder how much exploring they’re going to be doing with their recently slashed budgets?

Posted on by Paul Scott Anderson

Exciting New ‘Enceladus Explorer’ Mission Proposed to Search for Life

Water vapour geysers erupting from Enceladus' south pole. Credit: NASA/JPL

Water vapour geysers erupting from Enceladus' south pole. Credit: NASA/JPL

Along with Jupiter’s moon Europa, a tiny Saturnian moon, Enceladus, has become one of the most fascinating places in the solar system and a prime target in the search for extraterrestrial life. Its outward appearance is that of a small, frozen orb, but it revealed some surprises when the Cassini spacecraft gave us our first ever close-up look at this little world – huge geysers of water vapour spewing from its south pole. The implications were thought-provoking: Enceladus, like Europa, may have an ocean of liquid water below the surface. Unlike Europa however, the water is apparently able to make it up to the surface via fissures, erupting out into space as giant plumes.

Now, a new project sponsored by the German Aerospace Center, Enceladus Explorer, was launched on February 22, 2012, in an attempt to answer the question of whether there could be life on (or rather, inside) Enceladus. The project lays the groundwork for a new, ambitious mission being proposed for some time in the future.

Cassini was able to sample some of the plumes directly during its closest approaches to the moon, revealing that they contain water vapour, ice particles and organic molecules. If they originate from a reservoir of subsurface liquid water, as now thought by most scientists involved, it would indicate an environment which could be ideal for life to have started. The necessary ingredients for life (as we know it at least) are all there – water, heat and organic material. The fissures themselves generate much more heat relatively than the surrounding surface, suggesting that the conditions below the surface are much warmer. Maybe not “hot” per se, but warm enough, perhaps also with the aid of salts like in Earth’s oceans, to keep the water liquid.

But what is the best way to search for evidence of life there?  Follow-up missions have been proposed, to again sample the plumes, but with instruments able to look for life itself, which Cassini can’t do. This would seem ideal, as the water is being spewed out into space, with no drilling through the ice necessary. But the Enceladus Explorer project is proposing to do just that; the rationale is that any organisms (most likely microscopic) which may be in the water could easily be destroyed by the force of the ejection from the fissure. So then what is the best way to sample the water itself down below?

Enceladus Explorer would place a base station on the surface near one of the fissures; an ice drilling probe, the IceMole, would then melt its way through the ice crust to a depth of 100-200 metres until it reaches a liquid water reservoir. It would obtain samples of the water and examine them in situ for any traces of microorganisms. With no GPS system available, or external reference points to use, the probe would need to function autonomously, finding its own way through the ice to the water below.

The IceMole is already being tested here on Earth, and has successfully melted its way through the ice of the Morteratsch glacier in Switzerland. The next experiment will have it navigate its way through ice in the Antarctic, sampling completely uncontaminated water from a subsurface lake below the ice, much like the conditions found on Enceladus.

There is no timeframe yet for such a mission, especially given current budgets, but the Enceladus Explorer project has already shown that it is certainly technologically feasible and would provide an incredible look at an environment in the outer solar system which is amazingly Earth-like yet utterly alien at the same time.

Posted on by Nancy Atkinson

Life in the Universe, Reflected by the Moon

This view shows the thin crescent Moon setting over ESO’s Paranal Observatory in Chile. Credit: ESO/B. Tafreshi/TWAN

[/caption]

Earthshine – a poetic, fanciful word for the soft, faint glow on the Moon when the light from the Sun is reflected from the Earth’s surface, onto the dark part of the Moon. And as unlikely as it might seem, astronomers have used Earthshine to verify there’s life in the Universe: Us. While we already know about life on our own world, this technique validates that faint light from distant worlds could also be used to find potential alien life.

“We used a trick called earthshine observation to look at the Earth as if it were an exoplanet,” said Michael Sterzik from the European Southern Observatory. “The Sun shines on the Earth and this light is reflected back to the surface of the Moon. The lunar surface acts as a giant mirror and reflects the Earth’s light back to us — and this is what we have observed with the VLT (Very Large Telescope).”

Sterzik and his team said the fingerprints of life, or biosignatures, are hard to find with conventional methods, but they have now pioneered a new approach that is more sensitive. The astronomers used Earth as a benchmark for the future search for life on planets beyond our Solar System. They can analyze the faint planetshine light to look for indicators, such as certain combinations of gases in the atmosphere – as they found looking at earthshine – to find telltale signs of organic life.

Looking at earthshine, they found strong bio-signatures such as molecular oxygen and methane, as well as the presence of a ‘red edge’ caused by surface vegetation.

By observing earthshine astronomers can study the properties of light reflected from Earth as if it were an exoplanet and search for signs of life. The reflected light is also strongly polarised and studying the polarisation as well as the intensity at different colours allows for much more sensitive tests for the presence of life. Credit: ESO/L. Calçada

Instead of just looking at the planet’s reflected light, astronomers can also use spectropolarimetry, which looks at the polarization of the light. Using this approach, the biosignatures in the reflected light from Earth show up very strongly.

“The light from a distant exoplanet is overwhelmed by the glare of the host star, so it’s very difficult to analyze — a bit like trying to study a grain of dust beside a powerful light bulb,” said co-author Stefano Bagnulo from Armagh Observatory in Northern Ireland. “But the light reflected by a planet is polarised, while the light from the host star is not. So polarimetric techniques help us to pick out the faint reflected light of an exoplanet from the dazzling starlight.”

By looking at earthshine, the team was able to deduce that the Earth’s atmosphere is partly cloudy, that part of its surface is covered by oceans and — crucially — that there is vegetation present. They could even detect changes in the cloud cover and amount of vegetation at different times as different parts of the Earth reflected light towards the Moon.

“These observations allow us to determine the fractional contribution of clouds and ocean surface, and are sensitive to Spectropolarimetry unveils strong biosignatures, visible areas of vegetation as small as 10%,” the team wrote in their paper.

“Finding life outside the Solar System depends on two things: whether this life exists in the first place, and having the technical capability to detect it,” said co-author Enric Palle from Instituto de Astrofisica de Canarias, Tenerife, Spain. “This work is an important step towards reaching that capability.”

“Spectropolarimetry may ultimately tell us if simple plant life — based on photosynthetic processes — has emerged elsewhere in the Universe,” said Sterzik. “But we are certainly not looking for little green men or evidence of intelligent life.”

The astronomers said that future telescopes such as the E-ELT (the European Extremely Large Telescope), could provide more detail about the type of life beyond planets that may exists on another world.

Read the team’s paper, (pdf) which was published in Nature.

Source: ESO

Posted on by Nancy Atkinson

Astronomers See Stars Changing Right Before Their Eyes in Orion Nebula

This new view of the Orion nebula highlights fledging stars hidden in the gas and clouds. Image credit: NASA/ESA/JPL-Caltech/IRAM

[/caption]

A gorgeous new image from the tag team effort of the Herschel and Spitzer Space telescopes shows a rainbow of colors within the Orion nebula. The different colors reflect the different wavelengths of infrared light captured by the two space observatories, and by combining their observations, astronomers can get a more complete picture of star formation. And in fact, astronomers have spotted young stars in the Orion nebula changing right before their eyes, over a span of just a few weeks!

Astronomers with Herschel mapped this region of the sky once a week for six weeks in the late winter and spring of 2011. Notice the necklace of stars strung across the middle of the image? Over just that short amount of time, a discernible change in the stars took place as they appeared to be rapidly heating up and cooling down. The astronomers wondered if the stars were actually maturing from being star embryos, moving towards becoming full-fledged stars.

To monitor for activity in protostars, Herschel’s Photodetector Array Camera and Spectrometer stared in long infrared wavelengths of light, tracing cold dust particles, while Spitzer took a look at the warmer dust emitting shorter infrared wavelengths. In this data, astronomers noticed that several of the young stars varied in their brightness by more than 20 percent over just a few weeks.

As this twinkling comes from cool material emitting infrared light, the material must be far from the hot center of the young star, likely in the outer disk or surrounding gas envelope. At that distance, it should take years or centuries for material to spiral closer in to the growing starlet, rather than mere weeks.

The astronomers said a couple of scenarios could account for this short span. One possibility is that lumpy filaments of gas funnel from the outer to the central regions of the star, temporarily warming the object as the clumps hit its inner disk. Or, it could be that material occasionally piles up at the inner edge of the disk and casts a shadow on the outer disk.

“Herschel’s exquisite sensitivity opens up new possibilities for astronomers to study star formation, and we are very excited to have witnessed short-term variability in Orion protostars,” said Nicolas Billot, an astronomer at the Institut de Radioastronomie Millimétrique (IRAM) in Grenada, Spain who is preparing a paper on the findings along with his colleagues. “Follow-up observations with Herschel will help us identify the physical processes responsible for the variability.”

Source: NASA

Posted on by Jason Major

Moons Large and Small

[/caption]

It may be one of the best images from Cassini yet this year! Cloud-covered Titan and tiny Prometheus (can you see it just above the rings on the right?) are literally dwarfed by their parent Saturn in an image captured on Jan. 5, 2012.

Prometheus’ pinpoint shadow can also be seen on Saturn’s cloud tops, just inside the thin, outermost F ring shadow at bottom left.

The two moons themselves couldn’t be more different; Titan, 3,200 miles (5,150 km) wide, is wrapped in a nitrogen and methane atmosphere ten times thicker than Earth’s and is covered with vast plains of dark hydrocarbon dunes and crisscrossed by rivers of liquid methane.

Prometheus imaged by Cassini in Dec. 2009.

Prometheus, on the other hand, is a potato-shaped shepherd moon 92 miles long and 53 miles wide (148 x 53 km) that orbits Saturn just inside the narrow, ropy F ring. While it doesn’t have an atmosphere, it does create some impressive effects on the icy material in the ring!

Another moon, Pandora, casts its shadow onto Saturn just outside the F ring shadow at bottom center. 50 miles (80 km) wide, Pandora shepherds the outer edge of the F ring but is itself not visible in this image. Watch an animation here.

This image was featured on the Cassini Imaging Central Laboratory for Operations (CICLOPS) website on Feb. 28, 2012. The view looks toward the southern, unilluminated side of the rings from about 1 degree below the ringplane.

Image credit: NASA / JPL / Space Science Institute.

Posted on by Jason Major

Heads Up: It’s Another Mind-Blowing Aurora Photo

"Forest Storm" by Ole Salomonsen (arcticlightphoto.no)

[/caption]

Photographer Ole Christian Salomonsen is a master at capturing the northern lights in all their glory… as this image once again shows.

Ole describes the story behind this photo:

“Shot at the end of a ‘weak’ aurora night in Muonio, Finland. Took this at outside the cabin I was staying at close to Harriniva. The outburst came from an CME that first started disappointingly weak. I was about to go to bed but thought I should wait just a little more and see. Man am I glad I waited!!”

Man, are we glad too! Thanks for sharing these amazing views with us Ole, and keep up the great (and chilly) work!

Image © Ole Salomonsen. Used with permission. See more of Ole’s work on www.arcticlightphoto.no.