What a Comet Looks Like … From 9 Meters Away!
The European Space Agency has just released some fantastic close-up images taken by the Philae lander of the comet 67P/Churyumov-Gerasimenko. This release came out along with a passel of scientific papers (in Science magazine behind a paywall; here’s a summary) about results from the Rosetta probe’s lander, too.
When I saw these images the hair on the back of my neck stood up. These photos may not look like much at first, but when you realize you’re seeing the surface of a comet hundreds of millions of kilometers from Earth, and can see objects as small as a centimeter across … well, I hope your brain gets that same electric shock mine did.
Here’s the story.
On Nov. 12, 2014, at 15:34:06.471 (± 1 second), the Philae lander made contact with the surface of the comet 67P/Churyumov-Gerasimenko.
The first time. Two malfunctions (a cold-gas jet system designed to push the lander down onto the comet’s surface didn’t fire, and neither did the harpoons meant to anchor Philae to the comet) occurred, and instead of landing and staying secured to the surface, Philae bounced high into space, only to land again, bounce again, and finally skid (that is, make multiple shallow, short bounces) to a stop many hours later, and many hundreds of meters from its intended destination.
It fell to rest on its side, shadowed by an overhang of ice and rock. Contact became intermittent, and a few days later the battery fell below levels needed to keep the probe awake. It went into hibernation.
Then, months later, it woke up! The solar panels had collected enough energy to turn the lander back on. Contact was again intermittent, and the future of the lander’s lifespan is still unclear. But it performed like a champ, taking images, spectra, and other measurements that have returned unprecedented knowledge about the comet back to us on Earth.
This shot was taken when the lander was a mere 9 meters—30 feet—from the surface of the comet. The area you’re seeing is 9.7 meters across, about the size of one half of a tennis court. It shows that the surface is covered in a coarse regolith (loose material that hasn’t consolidated into a solid mass; we see similar surfaces on airless bodies like the Moon), and rocks of various sizes, ranging from centimeters to meters across. You can also see material of different darkness; some are quite dark while others are reflective.
Some of the rocks are smooth, and some sharp. In one of the papers published (Mottola et al.) they analyze the images, speculating that the smooth rocks may have once been embedded in ice or boulders, and then freed after the material they were embedded in disaggregated. The rougher ones with flat faces may be from bigger rocks that fell and shattered. Some of these chunks are partially buried in the regolith; are they being buried as the looser stuff piles up or being exhumed as the material moves away? Static pictures make that difficult to discern.
From higher up there’s more of an overview; the shot above was taken when Philae was still 48.5 meters from first impact. The area seen is about 50 meters across, half the length of a football field. The big rock, nicknamed Cheops, is about 5 meters in size. It may be an individual piece, or an outcropping of bedrock below. What’s very interesting about it is the arrowhead-shaped depression is sits in (the point is to the right), and the fine-grained material piled up on its left. That’s a wind-blown feature! Material immediately upwind of a rock gets picked up and blown around the rock, leaving behind an arc-shaped moat, and a pile of finer grains on the rock’s downwind side.
What could cause this? My first thought was ice turning into a gas (sublimating) as the comet warms up on its approach closer to the Sun. But I didn’t think this could be right; that gas would expand so rapidly that it wouldn’t have much effective pressure very far from the vent. It turns out that may be right; Mottola and his co-authors note that as well and wonder if perhaps this is caused by temporary gusts of material from impacts as the comet moves through space. I like this idea, though it seems that this would take a long time, and a comet’s surface doesn’t last long as the ice beneath it sublimates. However, it would also explain some of the erosion features seen as well. Hopefully as time goes on we’ll see more work in this area. Remember, these are first, initial results!
I love the image above (from Biele et al.): It was taken by the Rosetta probe itself and is a before-and-after picture of where Philae initially hit the comet. The left image was taken 15 minutes before impact, and the one on the right 25 minutes later, about 10 minutes after Philae bounced. You can see the impact craters from the lander! The two pits marked B and C are from the lander, and are 10 and 20 centimeters deep, respectively (the feature marked A is probably just a coincidental small undulation in the surface, casting a shadow that makes it look like a crater). This shows the regolith on the surface is at least 20 centimeters deep, too.
Knowing how deep the craters are and how dense the material is, scientists estimate about 180 kilograms of material was ejected at impact, which is more than the mass of the lander itself (100 kilograms). That’s interesting. All the data from the first impact indicate the material must be incredibly soft, like talcum powder. However, the surface there probably doesn’t have extremely fine-grain stuff in it, so whatever it is must be very loosely packed to have such weak compression strength.
This is very different from where the lander eventually wound up, where the surface is more like solid rock. A comet’s surface varies considerably from place to place. Interestingly, another experiment on Philae (which sent electromagnetic signals through the comet) indicates the interior of the comet’s small lobe is actually homogeneous over all.
[Animation of the lander's descent images. Photo by ESA/Rosetta/Philae/ROLIS/DLR]
And what’s the comet made of? A chemical analysis experiment on Philae (called Cometary Sampling and Composition) was going to drill and sample the comet, but it obviously couldn’t. However, the impact did excavate material from under the surface, and some of this flew into the sampling tubes of the experiment (they call this “sniffing mode”).
It found water, methane, HCN, CO, methylamine, and 11 other types of molecules, many of them organic (that is, containing carbon; don’t confuse this with output from biological processes!). These were probably built up from simpler molecules by ultraviolet light from the Sun and subatomic particle impacts, which break up simple molecules and allow them to build up more complex chemistry. The nitrogen probably came from ammonia, which has been depleted to create these more complicated molecules.
Many of these chemicals are pre-biotic, not biological themselves but necessary ingredients for life. They are used to build sugars, amino acids, and even nucleobases (the building blocks of RNA and DNA). That’s fascinating! It doesn’t mean that these chemicals were brought to Earth by comets necessarily, but it does mean they are not terribly hard to manufacture via natural processes. We knew this before, really, but it’s good to see it confirmed from measurements taken right there at a comet.
One thing I was excited to see in one of the papers (Kofman et al.) is that the likely landing site of Philae has been narrowed down to an area of just 21 x 34 meters! This was done using measurements by the Comet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT) experiment. The rough position was triangulated along a strip about 150 meters long, and then narrowed down to this area by using signals from the lander that passed through the comet itself. Images taken from Rosetta have not been able to nail down the position of the lander unambiguously, so hopefully these results will allow that.
I’m glad we’re finally seeing so much of the science from Philae; most of it has been under wraps for months as the scientists poked through it (and a lot of it still is, awaiting more data to come down to make a complete set so that context can be gleaned).
And as much as we’ll eventually learn from studying 67P, one thing that’s important to remember is that every comet is different! We’ve visited quite a few now, and their diversity is amazing. Some have lots of water ice, some very little. Some are active, some quiet, with different structures, different compositions, and more. As I read the papers and looked at the data, I was struck by how much information we now have on 67P … and how much we still have to learn about comets as a population.
If you ever wonder why I love living in Colorado, well, maybe this’ll help.
That video was shot by Daniel Lowe as he drove through western Colorado and eastern Utah. Where I live, there’s substantial light pollution, but out by Gunnison the skies get dark (one of the many reasons my wife and I held a Science Getaways there), and the stars are magnificent.
And the geology! Some of it is lifted up, some of it eroded down, but there’s a billion years of history tucked away in the American Southwest. This is an astonishing place to live.
And that spillway/waterfall at 01:20? Lowe told me that’s south of Ouray on U.S. Highway 550. That’s a bit of a haul from my neck of the woods, but if I’m ever out that way, I’ll have to stop and see. This planet is a source of unending delights.
The Latest Crash Course Astronomy Will Be Delayed
My apologies, everyone: After we put up this week’s episode of Crash Course Astronomy (about exoplanets), we found an error in one of the animations that got past us.
In some cases where a mistake is found we can simply annotate the video and move on. However, in this case the animation was explaining an important concept that couldn’t simply be corrected in the video itself. Faced with this we decided to take it down, fix the animation, and re-upload the video. Given the time that will take, we also decided to simply wait until next Thursday to re-release it, to keep the episode order on track.
So, the exoplanets episode will go back up Thursday, Aug. 6, at 21:00 UTC (5 p.m. ET). Again, I’m sorry about this, but we’d rather be late than keep a fixable mistake in the series! Thank for your patience, and I hope it’s worth the wait.
And in the meantime, we have more than two dozen other episodes online to keep you entertained and learning about our amazing Universe. Have fun!
Arc of Truth
I was out strolling recently on a cloudy day, and—as I always do—I took a quick look around the sky to see if anything interesting was to be seen.
I do so love that habit. This particular time, I was greeted with a most unusual sight: a rainbow segment, just a small arc levitating in the clouds. It was raining in that direction, so there were raindrops in the air, a critical component to make a rainbow.
But the other half of that recipe is sunlight, and that day was almost completely overcast. Almost. In the west there was a small break in the clouds, enough to let a single shaft of sunlight through. That illuminated the suspended raindrops, refracted, and created the partial bow.
What I love about this, though, is that you can see that shaft of light! Haze, raindrops, and other particulates in the air scattered that light, reflected it back to me, lighting up in the path of that sunbeam, contrasted with the storm clouds behind it. And you can tell that the opening in the clouds to the west wasn’t fully open; there must have been a small cloud in the middle to account for the shadow ray piercing through the light shaft and arc.
Mind you, there was no other hint of a rainbow anywhere else in the sky. That was it, the only clear sunlight available. And it was only those raindrops, seen at just the right angle, that allowed me the view of the broken spectral arc. Someone a kilometer away in the wrong direction wouldn’t have seen anything at all. I was at the right place at just the right time.
But even then, it all would’ve been for naught had I not looked up.
Oh, that sky we live under. Wonderful, isn’t it? You should look at it more often.
The Summer of ’82
David: You knew enough to tell Saavik that how we face death is at least as important as how we face life.
Kirk [sadly, resigned]: Just words.
David: But good words! That's where ideas begin.
In June of 1982, I found myself waiting in a long, long line at a mall. I had just graduated high school, and was spending the summer doing what innumerable kids my age had done for decades: eagerly and nervously anticipating going to college in a few months, working at my part-time job (for me, slogging through the brutally humid Virginia weather at 5 a.m. to deliver the Washington Post to more than 100 of my neighbors), hanging out with friends, reading sci-fi books, going to the mall to play video games, and watching movies.
And oh, those movies. The summer of 1982 was magic. Magic! The science-fiction movies that came out in those few short months would change the way movies were made. Think I’m exaggerating? Here are a few of the movies that came out in 1982: Blade Runner. The Thing. Poltergeist. E.T, the Extra-Terrestrial. Tron …
And, of course, one of my favorite movies of all time, Star Trek: The Wrath of Khan. When the first movie (Star Trek: The Motion Picture) came out, we hardcore arrogant and smug fans hated it. It was long, boring, and preachy. It was mocked unceasingly and mercilessly for years. But then Khan came out, and all was forgiven; faster paced, big battles, great tension, and far more personal, Khan was what we had craved.
I’m older, less of an ass, and hopefully wiser now, and appreciate the first movie far more than I did as a hot-headed kid. And yet, Khan still touches something primally Trek in me. The music still sings to me (I had the soundtrack on vinyl, copied it to cassette so I could listen in my Walkman, then on CD, and now digitally; a dynasty that’s lasted for electronic generations), and the scenes in the Mutara nebula still put me on the edge of my seat.
All that was ahead of me, though, as I stood in line at the mall with 100 people ahead of me. Over the course of an hour I was joined by my friends, coincidentally, a chunk of my graduating class wanting to see Khan on opening day. By the time the box office opened there more over a dozen of us (100 people from the front of the line), eagerly chatting away with nervous excitement.
I had no idea at that moment what lay ahead of me in my life: a disastrous first year at college, dropping out because I wasn’t nearly ready for it emotionally, an ego-stomping year of living at home with my parents as I got my act (partially) together, then finishing out college, going to grad school, meeting my future wife, having a daughter, and everything else that life delivers that is simultaneously mundane and glorious.
I’m not sure any of that would’ve registered with me anyway. I was an immature kid, wrapped up in the excitement of seeing Kirk and Spock on the big screen again.
Why am I thinking of all this now? Lots of reasons, actually. I just got back from Comic-Con, where I saw old friends again, met new ones, and bumped into some of the people who made the stories that so shaped my own life.
The mundanity of the descriptions belies the changes that were about to happen. (This was before the Spoiler Alert, obviously.) Watching that clip from 33 years ago (!!), seeing it as if I were that young once again, catching the 5 o’clock local news, made me smile. It was a great summer.
There’s a lot to be said for the present, too. My daughter somehow caught the Trek bug, and is now a full-fledged Federation dork. I’m bouncing in my seat waiting for her to finish watching the original series so we can see the movies together. I cannot wait to see Khan once again, chewing up the Enterprise as thoroughly as he did the scenery, Kirk’s tactics, Spock’s final (heh) scene.
I wonder how much of the movie I’ll spend sneaking peeks at my daughter’s face, to see how she reacts. Passing down our stories is part of what makes us human, and seeing it with her will, I think, make me feel young, as when the world was new.
The Densest Galaxies Ever Discovered
I think one of the most interesting facts in astronomy is a simple one to state: Galaxies are cannibals. They eat each other.
The Milky Way grew huge this way; our galaxy is in the top tier of spirals in the Universe. (Many are bigger, but the vast majority are far smaller.) It got that way by colliding and merging with smaller galaxies, enlarging its ranks over time. It’s actually in the process of eating several dwarf galaxies right now. Like, literally, at this very moment.
But what of these smaller galaxies? What happens to them?
Some merge completely with the bigger galaxy, a completely digestible meal. But sometimes parts of the smaller galaxy survive. If the center is compact and dense enough, it can make it through the ordeal.
We’ve seen these here and there, but now astronomers have found a new class of such objects: Ultra Compact Dwarfs, or UCDs. And it turns out they’ve been hiding in plain sight.
These galaxies are small and luminous, and incredibly dense with stars. Through ground-based telescopes they’re so small they look like foreground stars, and through Hubble their dense nature but slightly visible fuzzy halos that make them look like distant galaxies. That’s how they avoided discovery for so long: They slipped between the cracks.
These objects are the densest galaxies known. Our Milky Way has hundreds of billions of stars, but they’re spread out over a hundred thousand light-years. One of the new UCDs just discovered has far fewer stars—something like 10 million—but it’s only about 20 light-years across!
That’s really weird. I mean, really weird. It has the size of a typical globular cluster (a spherical cluster containing a hundred thousand stars or so) but is a hundred times denser!
Another UCD found is less extreme but still pretty amazing: It’s about 200 light-years across and has a hundred million stars in it. That’s far larger than a globular cluster, with a lot more stars.
It’s their incredibly compact nature that helped them survive being a galactic snack. This video should help make that clear:
The small galaxy is in a tight orbit around the center of a much larger galaxy. Tides from the big galaxy strip the outer stars off the smaller one; in a sense the gravity they feel from the bigger galaxy is larger, so they get peeled away from the smaller one. Stars closer in to the center of the small galaxy are more tightly bound, and stay together.
After a few passes all the outer stars are ripped away, and what’s left is just the compact nucleus of the smaller galaxy: an ultra compact dwarf. In fact, spectra taken of the UCDs show they resemble the cores of galaxies.
You’d expect to find these objects near bigger galaxies, and sure enough both of the new objects are physically close to much beefier galaxies. Note only that the larger galaxies show signs of recent disturbances (basically, weird overall shapes) indicating they recently underwent a collision and merger.
This work is impressive. It’s not often you find a new kind of astronomical object, especially when examples of them are sitting right in images that have been around for years. But their borderline nature between star clusters and proper galaxies effectively hid them.
I’ve long said that we have to be careful and not let our prejudices blind us to objects that are neither one thing or another (cough cough Pluto cough). In this case, I’m glad this team was able to see these UCDs for what they are.
And I have to add: The astronomers who found them were undergrads, students at San José State University! They combed through archived data taken by several different telescopes to identify potential ultra compact galaxies, then followed up using observations to nail down their characteristics. It’s quite an accomplishment!
And a reminder to not always dismiss something just because it conforms to your own predisposed beliefs. Look around you! What are you missing?
Sen: Is Kepler-452b Really Earthlike?
I recently wrote about the newly discovered exoplanet Kepler-452b. It’s bigger than Earth, but it orbits its Sunlike star in the habitable zone, where water could ostensibly exist on the planet’s surface.
The planet is actually 1.6 times the Earth’s diameter, and if I were a betting man, I’d wager it’s not Earthlike at all. Given what we think we understand about planets, it’s as likely to have a thick atmosphere like Neptune's as one like Earth's. Maybe more likely. But we just don’t know.
Despite this, a lot of headlines were screaming about an Earthlike planet found, calling it “Earth’s twin.” Feh.
In fact, I feel “feh” so strongly that I wrote all about this for my biweekly column for Sen.com. You can go there to get the details of my “feh”-ness. It’s subscription only, but that includes getting lots of articles by lots of good writers … and there are more to come. You’ll like it.
And to be clear: I am excited about the discovery of this planet, and its implications. I just wish stuff like this weren't overhyped.
Because Comets Aren’t Cool Enough: They Also Have Sinkholes
“No, no. We have already succeeded. I mean, what are the terrors of the Comet? One, the ice venting—no problem. There's a popping sound preceding each; we can avoid that. Two, the sinkhole, which you were clever enough to discover what that looks like, so in the future we can avoid that too.”
—The Dread Astronomer Westley Roberts
The comet 67P/Churyumov-Gerasimenko is heading toward the Sun, and as it does, it slowly dies.
But what a death. Underneath its crusty surface are icy deposits, and as the comet nears the Sun, these warm. The ice turns directly to gas and blows out of vents, forming gorgeous and delicate streamers of water vapor dozens of kilometers long. The picture at the top of the article shows the long-distance view of this; from 177 kilometers away, the Rosetta spacecraft sees quite a few of these jets.
But what do these do to the surface? Some of the vents have been seen in close-up views from Rosetta, and they come from pits that you might mistake for impact craters at first. It’s clear these are the sources of at least some of the jets, but a new study reveals they’re more than that: They’re sinkholes.
Sinkholes on Earth are relatively common; water (for example) can erode away material under the surface, and at some point gravity takes over, and the structural integrity gives way. The surface collapses, sometimes taking cars or even houses with it.
On a comet things are slightly different. For one, the gravity is only a tiny fraction of Earth’s. For another, sinkholes on Earth tend not to jet towers of water vapor out from them.
But the overall idea is the same. Heat from the Sun warms the comet. This heat leaks under the surface (possibly through cracks) and turns the ice into gas, which then leaks out. Eventually a large cavity is formed under the surface, so big that the “roof” of material over it collapses, forming the steep-walled sinkholes.
This allows light to flood in, which can heat the ice rapidly, causing an outburst of jetting from the comet. This has been seen on 67P, too. Eventually, the walls of the hole erode as more ice vaporizes, and the steep pits become more shallow. Quite a few of these are seen on 67P as well. This means the steep pits are young, and the shallow ones old.
While this result doesn’t surprise me—it’s been suspected since the first close-up pictures came back from Rosetta—it’s nice to see the whole story figured out, and an explanation found for the steep pits.
Comets are so cool. And this one has turned out to be a fantastic choice for an extended visit by Rosetta. We’re learning so much about these interplanetary wanderers, and, unsurprisingly, it’s all been really amazing.
Gardasil: Yup, Still Safe
Through an article in Forbes I saw that a new study has been published about the safety of Gardasil, a vaccine for prevention of certain strains of human papillomavirus, or HPV.
HPV is a virus that can lead to genital warts, many types of cancer, and cervical cancer in women, which kills 4,000 women every year in the U.S. alone.
The Gardasil vaccine, on the other hand, caused some people to faint after getting it, and others got mild skin infections—both of which occur somewhat rarely with other vaccines too, as you might expect.
Which sounds worse to you?
The study, published in the Pediatric Infectious Disease Journal, looked at the published data about effects from the vaccine and found that it has a “favorable safety profile.” This study comes after many other previous studies that show essentially the same thing. There is no correlation between getting the Gardasil vaccine and seriously adverse effects such as “autoimmune diseases (including Guillain-Barre Syndrome and multiple sclerosis), anaphylaxis, venous thromboembolism, and stroke.”
Mind you, all these things and more have been used by people who attack vaccines as an argument against it. And, just like essentially every claim made by the anti-vaccination movement, these arguments are wrong.
It’s very frustrating; mounds of data show these vaccinations are incredibly low-risk, but it only takes a little bit of doubt and fear to make vaccine rates drop. For example, a young girl died tragically not long after getting the vaccine, and it got a lot of press, but it was later found that she died of a completely unrelated cause. This, sadly, is expected; more than 178 million doses of Gardasil have been given worldwide, and given that huge number it’s a statistical certainty that some young people will die not long after getting them. But as the saying goes, correlation is not causation. The vaccines are not to blame here.
Even more frustrating about this vaccine is that it’s being fought by an unusual group of people; while most anti-vax leanings are not affiliated with any particular political persuasion, Gardasil gets attacked additionally by conservatives who think that girls getting it will become more promiscuous, because HPV is a sexually transmitted disease.
However, this has been shown to be false. Worse, these same people tend to promote abstinence-only education, which has been shown conclusively to be the worst possible sex education; kids taught his way tend to have more pregnancies and more STIs than ones who are taught progressive, healthy sex ed.
It’s like Bizarro world, where everything is backward. All the evidence shows Gardasil to be safe and to be effective against a virus that causes horrific illnesses. It also shows that the claims made by anti-vaxxers are wrong, and that people fighting the vaccine because of their own sexual biases are making things far worse.
And yet they dig in. They insist real science is wrong, that their anecdotes are better, that the entire medical industry is on the take (which is silly beyond reason).
But that’s where we are. When it comes to health issues, especially ones tied to sexuality, reason goes out the window and emotions take over.
That’s why I am very, very clear about this: I and my family are all up to date with our vaccinations, and my daughter has had all three stages of the Gardasil vaccine (we’d have done that if she had been a boy, too). As a parent, as someone who knows and loves someone with an autoimmune disorder, and as a person who knows just how truly awful so many diseases are and how easily and safely they can be prevented, I am a strong advocate for vaccinations.
It’s your body, but it affects literally everyone around you. Don’t listen to the anti-vaxxers, who just want to scare you. Get the facts. And please, talk to your board-certified doctor and find out if there are any vaccinations you need.
How many lives will you save when you do?
Tip o’ the virion to the Refutations of Anti-Vaccine Memes group on Facebook.
Journey From the Far Side of the Sun
Studying the Sun from Earth can be frustrating. From 150 million kilometers away, we can only see one side at a time. Sure, the Sun rotates, so we see the whole thing over the course of about a month, but sometimes you want to see it from different angles at the same time, like when it shoots out an explosive flare or coronal mass ejection.
What you want is a stereo view. Or STEREO.
STEREO is the Solar TErrestrial RElations Observatory, a pair of Sun-orbiting satellites; one is in a slightly smaller orbit than Earth so it travels ahead of our planet and the other in a slightly larger one so it lags behind. Over time, they get far enough apart to see the Sun from totally different viewpoints.
Right now, STEREO-A (A for Ahead) is almost directly opposite the Sun from us. In fact, it was behind the Sun for a few days, but even before and after that it was so close to our star that communicating with it was not possible.
The image above, taken in the far ultraviolet, was one of the first to come back from STEREO-A, on July 15 (around the same time New Horizons was sailing past Pluto 15 times farther away from us). At this wavelength, magnetic activity glows fiercely, and you can easily see the towering loops of the Sun’s complex magnetic field piercing the surface and arcing a hundred thousand kilometers above the surface.
STEREO has provided a huge amount of benefit to solar astronomers trying to figure out the ridiculously complicated behavior of our nearest tame nuclear inferno.
Sometimes, though, what it does is just plain cool … like the time it saw the Moon pass in front of the Sun. It’s a solar eclipse like you’ve never seen before.
We learn a vast amount of important, crucial, information from space-based astronomical observatories. But also, they just increase the coolness of our lives.
My apologies to Gerry Anderson for the title of this post.