The entire universe in blog form

Nov. 22 2014 7:30 AM

The Art and Politics of an Icy Water World

Well, this is interesting: The folks at the Jet Propulsion Laboratory and SETI Institute have just released a remastered image of Jupiter’s moon Europa, and it’s breathtaking:

Europa
All these worlds are your, including Europa. Attempt landings there.

Photo by NASA/JPL-Caltech/SETI Institute

That’s not even full-res; click it to see it in its splendor.

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Europa is 3120 km (1930 miles) in diameter, a hair smaller than our own Moon. Unlike our Moon, which is rock through and through, Europa has a rocky core covered with water. And by water, I mean liquid water, an undersurface ocean covered with a kilometers-thick shell of ice. The water may be in a layer 100 km thick, and salty, making it a true ocean. In fact, it may have more liquid water than Earth does!

The cracks you see are where ice floes fit together; the brighter areas are nearly pure water ice, but the red/orange regions are cracks, possibly where briny water has been squeezed to the surface, and materials in it chemically affected by the intense radiation environment surrounding Jupiter (caused by its very strong magnetic field interacting with material blasted out by volcanoes on Jupiter’s moon Io).

All of this has made Europa a prime target for exploration for a long time. I was going to write a bit about that, but then saw that JPL made a very informative video explaining it all.

That video is very well-done, and as I watched it I couldn’t help but think it felt like a trailer or promotional video for a new mission in the works. I know a lot of planetary astronomers have wanted to send a dedicated mission to the moon to investigate it far more thoroughly…

… and then I found that, due to the mid-term elections, Rep. John Culberson (R-Tex) is now head of the House's Commerce, Justice, and Science (CJS) appropriations subcommittee. He’s long been an advocate for a Europa mission.

It cannot be coincidence that this new image and video were put out now. The feeling I got while watching it, I suspect, is based on reality. I will not be surprised in the least if, for the next fiscal year budget, NASA asks for a Europa mission, including something as dramatic and unprecedented and as some hardware that can penetrate the ice and take a peek into Europa’s dark, briny depths.

I can’t say I’m opposed to that. There’s a lot of reasons to look around Europa as the video makes clear. You could argue the same for Enceladus, the icy moon of Saturn that has water geysers erupting from its south pole. In many ways Enceladus is a juicier target… but on average Saturn is twice as far from Earth as Jupiter, making the mission longer and more difficult. I figure go close first, learn the lessons, then push the distance boundaries more. As much as I’d like to see what’s under the ice of Enceladus, the shorter trip to Europa makes it an easier goal.

I’ve had my issues with Culberson about NASA, but, depending on how it’s done — extra funding for NASA so that no current or other future missions will get bled of funding, for starters — then an orbiter, lander, and sub-lander to Europa could very well be something I could get behind.

This is something I think NASA should be doing: Pushing the frontier, doing what only a national space agency can do. This would be a huge undertaking, and one that would fire up the public imagination like nothing before it since Apollo. I'd very much like to see that happen.

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Nov. 21 2014 7:30 AM

As the Earth Turns

Last week, I highlighted an amazing video of the Sun taken from space in super-hi-def resolution,  put together from NASA imagery by James Tyrwhitt-Drake.

Today, how about we turn that around, look down, and do the same thing for our fair planet?

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Here’s the Earth, as seen by the Russian Roscosmos’s Elektro-L satellite from May 15–19, 2011, and put together into a video again by Tyrwhitt-Drake. Set it to maximum resolution and make it full screen, and soak up the incredible beauty of home.

Fantastic, isn’t it? But it also takes some explaining.

First, Elektro-L is an Earth-observing weather satellite. It’s in a geosynchronous orbit, meaning it goes around the Earth once every 24 hours, the time it takes the Earth to spin once. From our point of view that means the satellite is fixed in the sky, neither rising nor setting. From the satellite’s point of view the Earth always shows the same face; looking down it always sees the same part of Earth. That’s why a geosynch orbit is so useful for weather. The video makes that obvious, too.

The satellite has cameras sensitive to visible light—the kind we see—and near-infrared. Plants reflect that kind of light very strongly, so places where there’s vegetation show up strongly in the satellite images. Normally those are colored red in pictures, but for this video Tyrwhitt-Drake colored that channel a more natural-looking green. Plants aren't the only thing that reflect IR light, so some places look green that aren't; note Saudi Arabia, for example, and the Sahara, which have a yellow-green tint from sand.

If the motion looks odd to you, that’s because Tyrwhitt-Drake had to interpolate between frames taken every 30 minutes by Elektro-L. (I explain how this is done in a post about a video of the Curiosity Mars rover landing.) It creates an odd flowing effect but is far better than the jerky snap between images taken so long apart.

Also, the video only shows the Northern Hemisphere first, then the southern flipped over (note the shadow line between night and day, called the terminator, moves the other way), and then finally the whole Earth at lower but still spectacular resolution.

Incredibly, the images off the satellite are originally 11K x 11K (each 120 megapixels!), which Tyrwhitt-Drake resized down to 50 percent, presumably so it would take less than a century to render the video. He says his 5,568 x 5,568 pixel video is available upon request. That would be amazing … if I had a monitor with enough resolution to see it! Maybe I could stitch 25 TVs together …

Tip o' the chlorophyll to Fraser Cain.

Nov. 20 2014 7:00 AM

“Happy 10th Anniversary in Space,” He Said Swiftly

Ten years ago today—on Nov. 20, 2004, at 17:16 UTC—a Delta II rocket thundered into the sky. Sitting inside the payload cowling was NASA’s Swift observatory, awaiting its chance to revolutionize astronomy.

Swift was sent into orbit to look for gamma-ray bursts, the most violent bangs in the Universe since The Big One. These explosions are the birth cries of black holes and occur somewhere in the Universe every day.

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They’re so luminous they can be seen clear across the Universe, but so short in duration that in some cases, literally, if you blink you’ll miss them. They made them incredibly hard to study; it was a lucky break when a burst in 1997 was caught by an X-ray satellite called BeppoSax, the first to have its distance accurately determined; it was a whopping 6 billion light-years away! The history of GRBs involves the cold war, nuclear bomb testing, and many, many years of astronomers scratching their heads. It was one of the most enduring mysteries in astronomy,* and Swift helped us understand them better than any observatory before it.

Swift was designed and built to detect GRBs in gamma rays, X-rays, ultraviolet, and optical light—a huge chunk of the electromagnetic spectrum—and rapidly slew over to point at them, sometimes in well under a minute. It was named after the acrobatic bird, which catches huge numbers of insects on the fly.

It turned out to be a good name.

hypernova
Artist's conception of a supermassive star exploding, forming a black hole and a gamma-ray burst.

Artwork by Dana Berry/NASA/SkyWorks Digital

Swift quickly became the go-to observatory for GRB detection. By the end of 2004 it found nine GRBs—averaging about one per week—even before its observational methods had been fine-tuned. As I write this, after 10 years, it’s detected 921 of these cosmic explosions! That’s stunning.

As soon as it detects a burst, it sends the coordinates out via the Gamma-Ray Coordinates Network. Telescopes hooked up to the network can automatically look for the burst within moments of its discovery that way, and hope to catch the rapidly fading afterglow, caused by the initial explosion sending out so much energy and high speed matter that in a few seconds it dwarfs the Sun’s entire energy output over its entire 11 billion year lifetime!

GRBs are awe-inspiring.

Along the way Swift’s also seen a magnetar explosion (one of the very few astronomical events that actually freak me out due to their mind-crushing violence and scale), watched a neutron star get torn apart by a black hole (!!!), observed hundreds of galaxies, exploding stars, asteroids, comets, and more ... including, get this, the single most luminous event ever witnessed by humans up to that time. And Swift is still up there, orbiting the Earth, scanning the skies diligently and patiently, waiting for the next burst. You can even see a map of the sky showing where the latest bursts have been seen.

Although I wasn’t involved with the science of the mission except tangentially, I worked for many years on the education and public outreach part of the mission. I wrote countless articles about Swift, including much of the EPO website. Our team at Sonoma State University designed a lot of activities for kids using Swift science, including brochures, a paper model of the satellite, classroom activities, a planetarium show, and a lot more. I’m still pretty proud of the work we did for Swift.

And I’m proud of the satellite. It was relatively inexpensive (the total mission cost was about $250 million), and it’s performed nearly flawlessly in the ravages of space for a decade. It’s a paragon of international cooperation to study the Universe, and a true achievement for NASA.

Congratulations to the entire Swift team, and happy anniversary. You deserve it.

* I wrote about this for my book Death From the Skies!, and/or you can read more about it here

Nov. 19 2014 7:30 AM

What Exploded Over Russia This Time?

Please see update below; it appears this was a ground blast and not a meteor.

On Nov. 14, 2014, something exploded over the skies of the Sverdlovsk region of Russia, about 1,500 kilometers east of Moscow. I’m not sure what it was, but the videos coming out are pretty dramatic:

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As we learned from Chelyabinsk in 2013, Russian cars commonly have dashboard cameras, so I’m hoping more footage will surface soon. A couple of teenagers managed to catch it on a phone camera:

It’s very cloudy, but the light can be seen through them. The first obvious guess is that this was a bolide, a fireball caused by a chunk of debris entering our atmosphere from space at high speed. These happen pretty often.

The color is odd; the reddish glow, if accurately portrayed in these videos, isn’t something I generally see in bolide videos and photos (or from the few I have seen with my own eye). They tend to be green or blue, or just white. Not always, but just in general. Of course, the clouds may be affecting the color, too.

Also, it’s really hard to tell, but it doesn’t look like the light is moving, as you might expect from a meteor. The videos are both shaky, so it’s not easy to measure that. The movement looks minimal to me, though. That could be geometry: If the meteor is moving across your line of sight then there is a lot of motion, but if it’s headed more or less  toward or away from you as it moves through the air, sideways motion will be low. I’d expect that the two videos would show different geometries, but again they’re so shaky it’s hard to tell.

Update, Nov. 19, 2014, at 14:50 UTC: Another video has surfaced that shows what looks to be an intense burst of light on the ground. Pay attention about 20 seconds in:

It's brief, but it corresponds to the same flash in the sky. This also can apparently be seen in a video at LiveLeak. It looks like this was an explosion on the ground, reflected in the clouds (see the still frame from the video below). That would explain everything seen in the videos above, including lack of apparent motion and the red coloring. I don't know what the explosion or fire was, but I'm pretty satisfied this was some sort of ground blast, and NOT a meteoric event. My thanks to commenter beanfeast and Sasa Andonov for the tips.

sverdlovsk_fireball_groundflare
A flash on the ground can be seen at the same time as the one in the clouds, and a fireball of some kind becomes visible moments later on the ground as well.

Photo by Doble V Channel, from the video

There are some preliminary flashes in the teenagers’ video a few seconds before the big one, and that’s consistent with a meteoroid breaking up as it comes in. As a big rock rams through the air at many times the speed of sound, the pressure breaks the rock up into smaller pieces, creating flashes as the energy of motion is converted into light and heat. There can then be a much larger flash as the smaller rocks all disintegrate rapidly.

If this wasn’t a bolide, what was it? Beats me. It’s a bit odd to think that a biggish rock from interplanetary space is the most mundane and prosaic explanation, but in this case it is! However, I won’t make up my mind until more evidence is in.

Tip o’ the Whipple Shield to NASANeoCAM on Twitter.

Nov. 18 2014 7:30 AM

Distant Horizons

“Ah, but our reach should exceed our grasp, Or what are the heavens for?”
 —with apologies to Robert Browning

We humans have lived on Earth a long time. Hundreds of thousands of years, give or take, depending on what you define as human. And all that time we have yearned to reach the stars, to explore, to find out what exists elsewhere.

We’re just now starting to do just that. We’ve only been able to fly for a little over a century, and the elapsed time since we first left our atmosphere can be counted in decades, less than a human lifetime. We’re taking our first tentative steps.

And yet we have accomplished so much! We’ve sent our spacecraft to every major body in the solar system, and quite a few minor ones besides. We’ve continuously occupied space for years, and we’ve launched observatories into orbit that examine the Universe in every wavelength regime of the electromagnetic spectrum.

And we’ve done even more: We’ve set down on other worlds. Certainly, most have been through our robotic proxies, but given the inhospitable nature of so many of these worlds, that’s not surprising.

And now we can include an entirely new body to that list: a comet, thanks to the Philae lander sitting on the surface of 67P/Churyumov-Gerasimenko.

To celebrate that, Michiel Straathof has updated Mike Malaska’s classic “Distant Horizons” mosaic to show all the worlds that humans have touched.

Nov. 17 2014 1:05 PM

Shirtstorm

Last week, the European Space Agency landed a space probe on a comet. It was big news—historic, even.

But another event caused a stir at the same time, tangentially related to the event. Matt Taylor, the Rosetta mission’s project scientist, went on the air to talk about the successful landing. However, his choice of attire was unfortunate.

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He was wearing a bowling shirt covered in pinup-style drawings of scantily clad women.

This upset a lot of people. A lot. It was compounded by his extremely poorly thought-out description of the difficulty of the Rosetta mission: “She’s sexy, but I never said she was easy.”

Yikes. To be clear, I don’t think Taylor is a raging misogynist or anything like that; I think he was just clueless about how his words might sound and his shirt might be interpreted. We all live in an atmosphere steeped in sexism, and we hardly notice it; a fish doesn’t notice the water in which it swims. I’ve lived in that environment my whole life, and I was well into adulthood before I started becoming aware of it and figuring out how to counter it. I’m still learning.

Importantly, the next day, clearly upset he had caused such a fuss, Taylor apologized on air sincerely and graciously for his actions. For the most part, the people who were upset accepted his apology and moved on.

shirt
The shirt.

Photo from the ESA news stream, via @RoseVeleth's Twitter feed

But it doesn’t end there. As you might expect, when people complained about the casual sexism of the shirt and the mission description, a frothing torrent of backlash misogyny swept over social media, another in a long line of demonstrations of Lewis’ law (“Comments on any article about feminism justify feminism.”)

There is much I could say here, but Dr24Hours wrote an excellent summary that aligns fairly well with my thinking. Please go read that right now.

But I have something to add.

If you think this is just women complaining, you’re wrong. Certainly many have, and rightly so. But the fact is, I’m writing about it. I can point you to many men, friends of mine, scientists and science communicators all, who have spoken up about it. It’s important that men speak up, and it’s important that we listen, too.

If you think this is just complaining from wannabes who can’t hold a candle to someone who just landed a probe on a comet, you’re wrong. Talk to my friend, the cosmologist Katie Mack. Or the planetary scientist Sarah Horst. Or geologist Mika McKinnon. Or astrophysicist Catherine Q.* Or planetary geologist Emily Lakdawalla. Or radio astronomer Nicole Gugliucci. Or professor and science communicator extraordinaire Pamela Gay. Or Carolyn Porco, who worked on the Voyager mission and is the leader of the Cassini imaging team, the space probe that’s been orbiting Saturn for over a decade now.

If you think this is just a bunch of prudes, you’re wrong. It’s not about the prurience. It’s about the atmosphere of denigration.

If you think it’s OK to use a misogynistic gender-charged word to insult and demean a woman because she used a generic nongender-charged insult about a man, then you’re really wrong (and that’s one representative tweet from many I saw just like it).

If you think this isn’t a big deal, well, by itself, it’s not a huge one. But it’s not by itself, is it? This event didn’t happen in a vacuum. It comes when there is still a tremendously leaky pipeline for women from undergraduate science classes to professional scientist. It comes when having a female name on an application to do research at a university makes it less likely to get accepted, and have your research paper cited less. It comes when there is still not even close to parity in hiring and retaining women in the sciences.

So yeah, it’s just a shirt.

And it’s just an ad.

It’s just a saying.

It’s just a TV show.

It’s just the Internet.

Yes, but you almost make as much as a man does.

It’s just a catcall.

It’s a compliment!

It’s just that boys will be boys.

It’s just that she’s a slut.

It’s just that your dress is too short.

It’s just that we want to know what you were wearing at the time, ma’am.

It’s just it’s just it’s just.

It’s just a death by a thousand cuts. No one cut does the deed. In the end, they all do.

* Update, Nov. 18, 2014 at 03:00 UTC: I can't believe I forgot to add my friend Catherine Q to the list of scientists who spoke up about all this. She's on that list now.

Correction, Nov. 19, 2014: I originally misstated that having a female name on a paper made it less likely to be published. The research showed that having a female name on a research job application to a university made it less likely to be accepted.

Nov. 17 2014 7:30 AM

Philae Spotted Hopping Away in Photo of Comet

A few days ago, the world watched and cheered as the tiny spaceship Philae landed on the surface of a comet. However, it was quickly determined that the anchoring harpoons didn’t fire, and the lander bounced off the comet. It soared a kilometer high before falling agonizingly slowly back down nearly two hours later, only to take a second, shorter hop, ending up in comet incognita.

It took a little while, but images taken by the orbiting Rosetta spacecraft mothership (and assembled into a short video) were released by the European Space Agency showing where Philae impacted the first time. The video shows before-and-after images of where Philae smacked down. At the time, my friend/planetary geologist/Planetary Society blogger Emily Lakdawalla speculated that you could actually see Philae and its shadow in the “after” image, but the data were so noisy I was pretty skeptical.

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Turns out, she was right.*

Here is a lovely animated gif showing the two images, with the impact site marked in the first image, and the lander (with shadow) in the second.

Photo by ESA/Rosetta/NAVCAM; pre-processed by Mikel Canania

Amazing! Astrophysicist Eamonn Kerins did this even better: He made a “difference image,” subtracting one from the other to show what’s changed between the two. It really brings out Philae and its shadow:

Boing!
Boing!

Photo by ESA/Rosetta/NAVCAM/Eamonn Kerins

You can see lots of bright pixels—most likely “hot pixels," overactive spots on the camera detector—with dark ones next to them, a product of how the images were processed. Note how the spot labeled as Philae is blurrier, and the shadow is several pixels below it. That’s pretty convincing to me.

I was initially skeptical because the “plume” stretching below and to the right of the impact site looked the same in both images, and was also mimicked by a similar feature to the upper right; both look like ridge shadows.

In the difference image those go away, so most likely they really are shadows, the lower one coincidentally right on top of where the lander bounced. That’s unfortunate, since it steered me away from what was really happening.

Philae
Before and after, in more detail.

Photo by ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Update, Nov. 17, 2014 at 15:30 UTC: Not long after I posted this, the ESA released a mosaic showing Philae before and after impact, seen moving across the face of the comet by the high-def OSIRIS camera on Rosetta! You can see Philae come in from the lower left, then move off to the right after it bounced. Amazing. 

And as a reminder of what you’re seeing: That’s an action shot of a 100 kilogram machine the size of a lounge chair that weighs less than an ounce in the local gravity hitting the surface of a four kilometer-wide dirty snowball almost precisely on target as seen by another spaceship that took 10 years and three planet flybys to achieve its goal of matching the 40,000 kph velocity and entering orbit around a comet … all of which is a first for humanity, ever.

So yeah. Cool.

*At least she was gracious in victory.

Nov. 16 2014 9:46 AM

Epic 4K Sun Video, With Bonus Sunspot Tantrums

Not long ago, the ridiculously huge sunspot called Active Region 2192 ruled the face of the Sun. Bigger than Jupiter, it was easily seen by the (adequately protected) naked eye, and it was a distracting though extremely cool blemish during October’s solar eclipse.

A sunspot that big has a lot of storage space to stuff magnetic fields, and 2192 didn’t disappoint. Sunspots are essentially magnetic phenomena, and as the huge looping magnetic field lines in the spot tangled up, they sometimes violently snapped and reconnected, releasing their energy as solar flares. Dwarfing every nuclear bomb on Earth combined, the flares kept popping off as 2192 marched across the Sun’s disk, swept along with our star’s rotation.

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From space, the Solar Dynamics Observatory keeps a close eye on the Sun, and watched in multiple wavelengths (think of them as colors) as 2192 did its thing. James Tyrwhitt-Drake, who has created interested scientific animations before, took 17,000 SDO images of the Sun in the ultraviolet, spanning Oct. 14–30, 2014, and created an astonishing video that shows 2192 in all its glory. The video is available in 4K resolution, if your bandwidth can choke that down, but it’s worth it to make this full screen:

The sound you hear is not real; it’s made from visible light data by SDO’s Helioseismic and Magnetic Imager, which maps motions on the Sun’s surface, which was then converted into sound by solar astronomer Alexander Kosovichev.

In this view, south is up, so the Sun rotates right to left (I’m used to it the other way, but hey, in space there is no up, so fine). 2192 makes its appearance early on, announcing its presence with towering loops of magnetic energy over 200,000 km high—mind you, the Earth is a mere 13,000 km across—and dominates the view thereafter. It’s incredible.

You can watch as enormous prominences erupt away from it, hot hydrogen gas flowing along otherwise invisible magnetic field lines like beads on a wire. The gravity of the Sun is strong, and pulls the gas with a force nearly 30 times stronger than Earth’s gravity, but the magnetic field is strong, too, and the gas flows back to the Sun along curving, graceful paths. It’s mesmerizing.

As the Sun rotates, AR 2192 has come around again, returning on or about Nov. 12. But it decayed substantially when it was on the far side of the Sun from the Earth. It’s a shadow, so to speak, of its former self. It doesn’t look like it’ll last much longer. We may not get another spot like it for a long time; it was the biggest seen in decades. But the Sun is a complex beast, and predicting its behavior for things like this is a losing bet. We may not see another like 2192, or another might grow and swell into existence once again. We’ll have to wait and see.

Nov. 15 2014 7:30 AM

Hey, Galileo Was Right!

One of the funny things about being a human is that our intuition can steer us wrong, even on things that should be pretty obvious, things we see literally every day.

For example, if you ask someone what would fall faster, a bowling ball or a marble, I bet a lot of folks would say the heavier bowling ball falls faster. But in fact, if dropped from a meter or so off the ground, they’d fall at the same rate. Gravity accelerates them at the same rate, so they fall at the same rate.

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Part of the reason our intuition is off here is due to air. As objects fall, the air pushes back on them. This depends pretty strongly on their surface area, how big they are, so a lightweight large object will in fact fall more slowly than a heavier, smaller one.

Dropping a bowling ball and a feather will yield results that will satisfy our intuition. But what if you removed all the air from the room and dropped them? What happens then?

My friend and physicist Brian Cox did just this for his new BBC TV series Human Universe. He traveled to NASA’s Space Power Facility at the Glenn Research Center in Ohio to test gravity. What happens when he does is pretty wonderful.

Lovely! With the air removed, the feathers and ball fall at the same rate, just as Galileo predicted and Newton showed mathematically. I assume the bit at the end of the video about Einstein is referring to the Equivalence Principle, which has to do with acceleration due to gravity—if you’re standing on the Earth’s surface, you feel this as your weight, the force due to Earth’s gravity on your mass—and is indistinguishable from acceleration due to some force (like being in a rocket under power). This idea has profound implications, and in part led to Einstein developing the theory of General Relativity. I’d love to see this show and find out how Brian follows that concept farther.

I’ve known Brian for quite some time, and I have to say it’s nice to see him finally get some recognition for his work. The poor guy has been languishing in obscurity for years

Nov. 14 2014 5:06 PM

Rosetta Spots Site of Philae’s First Bounce

Update (Nov. 14, 2014 at 23:00 UTC): Contact with Philae has been re-established! Data taken from the surface (including drill samples) have been sent back to Earth. Not only that, a command was sent to rotate the lander, and that worked as well! It rotated by 35°, enough to point a bigger solar panel up to the Sun. Reports indicate power is flowing, so the life of the mission has at the very least been extended somewhat. This is incredible work by the ESA team!

Update 2 (Nov. 15, 2014 at 00:00 UTC): While the move to rotate the lander was successful, the drain on the battery by the instruments on board was too much. At about half past midnight the voltage dropped below the critical point and the lander put itself into standby mode (no science being done; just communication with the Rosetta orbiter). HOWEVER, the point of the rotation was to get more power available. It's entirely possible that over the next few days, as the comet rotates around, enough sunlight will hit the solar panel to the battery enough charge to restart Philae. As usual, Emily Lakdawalla has more info on this. So Philae is not necessarily dead. It may just be sleeping, hibernating. We could very well hear from it again.

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The European Space Agency just released a great short video showing Rosetta's view on the comet where the Philae lander took its first kilometer-high bounce! [Note: If the video is blank, let it run to the end (it's only 12 sconds long), then hit the "replay" button in the video window. It should play normally then. Sorry about that. We're looking into the problem.]

If I've measured this correctly, the red circle is roughly 15 meters (50 feet) across. The "flight dynamics solution" is where the spot was predicted to be given Philae's trajectory, and as you can see they pretty much nailed it. 

It's hard to interpret exactly what we're seeing in the before and after. The dark streak looks like a plume of material, but I'm not so sure. Just above and to the right you can see another similar dark feature, and I'm leaning toward them both being shadows cast by low ridges as the angle to the Sun changed between the first image and the second. 

These images should prove useful in figuring out just where Philae is; its location is still unknown. As I write this we're still awaiting word that contact between the still-orbiting Rosetta and the lander has been re-established, and the data taken uploaded. Hopefully, samples of the comet have been analyzed by Philae, and we'll get a sense of what materials are on and just below its surface.

This is still very exciting! Certainly, it would've been far better had the lander stayed upright, and able to draw energy from the Sun, but even if that's not to be, it's still done an amazing job.

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