Bad Astronomy
The entire universe in blog form

Oct. 9 2015 9:30 AM

Pluto’s Sky Is Blue! Well, Kinda.

A new image of Pluto was sent back to Earth from the far, far distant New Horizons space probe, and it’s a doozy: It shows Pluto from the other side, backlit by the Sun. While we’ve seen pictures like that before, this one is in color.

And it looks like Pluto’s sky is blue.


But is it? Well …

The blue ring around Pluto in the picture is due to what’s called scattering. Teeny tiny particles are suspended in the atmosphere of Pluto, and when sunlight passes by them, the red light gets through, but the blue light hits those particles and caroms off in a different direction. The Sun is not directly behind Pluto in this picture—it’s off to the upper right, which is why the ring is brighter in that direction—so the light we see consists of the blue part of the spectrum, scattered around and sent toward the New Horizons camera.

On Earth we see the same thing, and it’s why our sky is blue. In our case, it’s nitrogen molecules in the air (which, after all, is 78 percent nitrogen) that do the scattering. For Pluto, it’s probably from a haze of stuff created when the Sun’s ultraviolet light breaks up simple molecules, which then recombine to make more complex stuff. It’s not yet understood what molecules are creating the blue ring, though.

So, if you stood on Pluto, would you see a blue sky?

Well, no. Not really. It’s not like Pluto has a lot of air. The atmospheric pressure on its surface is only about 0.00001 times that of Earth’s! Even if it were warm and had oxygen, you’d suffocate just as quickly as if you were standing on the surface of the Moon.

But assuming you had a spacesuit with a really good heater, the sky would look pretty black. However, at Plutonian sunrise or sunset, it’s possible that there’s enough atmosphere to see a thin blue line near the Sun on the horizon. I’m not sure your eyes would pick it up but a camera might. Update, Oct. 9, 2015: I've been talking with my pal and New Horizons team member Tod Lauer, who pointed out that although it would be fainter than on Earth, the haze in Pluto's atmosphere should be visible to the human eye around sunset/sunrise, and might very well give the sky a blue cast there. I'm inclined to agree with him; he pointed out that images of a crescent Pluto show the haze is visible above the surface (and even very softly illuminates the surface), and the human eye should be able to pick it up near the horizon. I'm pretty sure the sky would look black above you fading to blue near the horizon, but it's unclear how that transition occurs. That would be a very interesting calculation.

Thinking about this made me curious: How long would sunset last on Pluto? By this I mean, once the bottom edge of the Sun touches the horizon, how long will it take the full disk to disappear?

On Earth that takes about two minutes (neglecting our atmospheric effects, which make it act like a lens and can mess with the timing).

But Pluto is so far away that the Sun’s disk appears to be only about 1/40th as wide as it is from Earth on average (Pluto’s orbit is highly elliptical, so sometimes the Sun will look much bigger or smaller than average, but let’s go with this).* That by itself will make sunsets faster.

Pluto spins much slower than Earth does, once every 6.4 Earth days, so the Sun will move more slowly across the sky than it does here. But that’s not enough to make up for its tiny disk. Once the bottom of the Sun kisses the horizon, it’s all over about 20 seconds later.

So if you can see any blue to the sky, right around the horizon, you’d only have about that long to appreciate it. Update, Oct. 9, 2015: New Horizons PI Alan Stern sent me a note pointing out that while the Sun might only take 20 seconds to physically cross the horizon, due to the scattering in the atmosphere twilight on Pluto before sunrise and after sunset might last for many hours. This ties in with the conversation I had with Lauer above. And another thing: Lauer pointed out that Pluto is tilted so much that it's nearly north-pole-on to the Sun, so if you're on the terminator, the day/night line, the time it takes the Sun to set can be much longer right now! I was just playing with numbers above and hadn't even thought of that. This is clearly more complicated than I had first supposed, though just how complicated still isn't clear! But it shows that no matter how you slice it, sunset on Pluto would be pretty amazing to watch. 

water ice on Pluto
The blue shows the location of potential skating rinks on Pluto. But you might want to take a deep breath ... and pack a really big thermos of hot chocolate. Click to embiggen.


Another interesting image was also released, and it shows the location of water ice on one small part of Pluto’s surface. Pictures alone won’t give that information, but New Horizons has a spectroscope on it, which breaks light up into many individual colors. Different substances have different spectral signatures, so they can be differentiated from one another. That’s how the water ice was mapped.

Interestingly, in this area it’s only seen in those shallow craters near the top, and a few other areas. Very interestingly, all these regions are red. That’s probably due to the presence of tholins, complex organic (carbon-based) compounds that are created in the same way I described above, when sunlight lets molecules rearrange themselves.

Why would water ice be where the tholins are? That’s a good question and the planetary scientists have been asking themselves that same thing. They don’t know. But like everything else in these images, it’s a clue telling us about what Pluto’s doing: what it’s made of, how that material moves around, how it interacts with other material and sunlight, and maybe even hinting at past geological processes.

After all, that smooth region to the right (informally called Sputnik Planum, the left part of the heart-shaped area) doesn’t seem to have any water. It’s thought to be a sheet of nitrogen ice that probably moved glacierlike over the lowlands, stopping where the elevation got higher. At Pluto’s temperature, water ice is harder than solid rock here on Earth, so I wouldn’t necessarily expect it to be there on the plains. It won’t flow! But why is it in the highlands, in spotty areas? No one knows.

Yet. We’re learning more all the time, something new every time a new batch of data is sent back. And even when we get it all, it’ll be years before it’s all analyzed. And also, don’t forget that the spacecraft may fly by a Kuiper Belt object called 2014 MU69 in January 2019—it’s been selected as a new target, but hasn’t been given the official NASA go-ahead yet. But if it is, then we’ll get to do this all over again with a new object.

Well, new to us. It’s actually more than 4 billion years old. What delights await us when we see that up close?

*Correction, Oct. 9, 2015, at 17:00 UTC: I originally misstated that the Sun would look 1/30th as large from Pluto on average than it does from Earth, but it's actually closer to 1/40th. The rest of the math I did is correct. Thanks to my friend and colleague Don Goldsmith for pointing this out to me.

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Oct. 8 2015 9:30 AM

When Denial Attacks: Ted Cruz vs. Reality

It’s like GOP presidential hopeful and Texas Sen. Ted Cruz stepped right out of George Orwell’s 1984

On Tuesday he was on a Senate subcommittee hearing about government regulation. Among the people giving testimony was the president of the Sierra Club, Aaron Mair. I’m a fan of the Sierra Club; my wife and I have donated to them many times over the years.


Toward the end of the hearing, Cruz started grilling Mair on one part of his testimony, where Mair said, “That people of color and low-income communities are disproportionately impacted by pollution, and climate disruption should not be up for debate any more so than the science behind climate change itself.”

That, of course, set Cruz off. In a typical denier fashion, he lights into Mair about this, starting off with this:

I’m curious: Is the Sierra Club, is this a frequent practice to declare areas of science not up for debate, not up for consideration of what the evidence and data show?

This is Denial 101, to make it sound like scientists are closed minded. In fact, the exact opposite is true: It is due to the overwhelming evidence and data that scientists are so sure that global warming is real, and caused by human activity. And it’s the people like Ted Cruz—by the way, Cruz got a $15 million check from the fossil fuel magnates Farris and Dan Wilks earlier this year—who have closed their minds to this evidence and data, instead cherry-picking, misinterpreting, or outright dismissing anything that disagrees with their denial.

Watch for yourself, if you can stomach it.

Cruz makes claims so wrong and so long-debunked that I won’t go into detail giving them the evisceration they deserve. Instead, Inigo Montoya–like, I’ll sum up:

Cruz Climate Claim: “The 97 percent consensus paper has been discredited.”

Reality: Nope. As usual when it comes to denial claims, the discrediting has itself been discredited. In fact, the consensus may even be higher than 97 percent, higher even than 99 percent.

Cruz Climate Claim: “Satellite data shows no significant warming over the past 18 years.”

Reality: Nope. Also, nope, nope, nope, and nope. Even the mildest effort can add a lot more “nopes” to that series.

It’s too bad they don’t make senators swear in before they hold hearings.

The thing is, I expect that sort of execrable dumbosity from Cruz. I mean, come on, this is the guy who went on Seth Meyers’ late night talk show and claimed that—and I really wish I were making this up—because it’s cold somewhere, global warming must be wrong.

So I can’t say I’m surprised by Cruz.

head in the sand
Who knew Congressional hearings had such a big sandbox?

Photo by Shutterstock/alphaspirit

No, what’s so upsetting here is how Mair responded. I’m not sure what he was expecting, or how he and his team readied for the hearing, but he was apparently unprepared for the onslaught of misinformation from Cruz, as well as his persistence.

Watching Cruz grill Mair is like watching a septic tank cleaning truck getting into an accident. You know you’re seeing a lot of crap flying everywhere, but you can’t look away.

If Mair had been in an honest conversation with someone he might have done fine, but he was facing someone who long ago chucked reality out the window. With that sort of disadvantage, all Mair could manage to do was repeat himself several times that the Sierra Club sides with the scientists on the issue. But of course this is red meat to Cruz, who clearly is not a fan of science or scientists. He pressed his advantage over and again, and all Mair could do was flail.

Worse, when Cruz asked him to describe the so-called pause, all Mair could say was that it referred to a slowing of global warming in the 1940s. That’s not even right; the 1940s are arguably when the land and ocean temperatures were much warmer than normal for the first time in decades.

I found myself wishing I were there. I know, it’s easy to be an armchair quarterback, but when Cruz said:

And I assume the Sierra Club would issue a public retraction if confronted with the facts that the data are precisely as I described that over the last 18 years there has been no significant warming and indeed that is why global warming alarmists invented the term “the pause” to explain what they called the pause in global warming because the data demonstrate what you just said, that the Earth is cooking and warming, is not back up by the data.

… all I could think was how I wish I Mair had turned it right back around on him, telling Cruz he was grossly wrong; that the data conclusively and obviously show the Earth has been and still is warming, that “the pause” is just a statistical effect, unreal, and that the clear trend is that the Earth is getting hotter.

The huge irony is this: Imagine Mair had asked Cruz if he would issue a public retraction if he were confronted with the facts. The facts that the Earth is still warming up, that oceans are heating up, that sea levels are rising, that the ice caps are melting, that the greenhouse gas CO2 is being dumped into our air to the tune of 40 billion tons every year, and so much more?

Do you really, honestly think Cruz will ever admit that? Or Inhofe? Or Trump, or Carson, or, or, or?

Here is your modern GOP politician, folks. Deny, deny, deny, and when called on it, deny some more and accuse your opponent of what you yourself are doing.

Orwell couldn’t have written Cruz’s words any more concisely.

Tip o' the thermometer to Evlondo Cooper of the Checks and Balances Project.

Oct. 7 2015 12:03 PM

Relive Our One Giant Leap in an Archive of Thousands of Apollo Photographs

If we can put a man on the Moon, why can’t we put 8,400 hi-res scans of the Apollo mission photographs taken by the astronauts themselves on Flickr?

Oh wait. We can. And Kipp Teague did.


Teague is a network and IT director at Lynchburg College, and he and I have two things in common: We’re both University of Virginia alumni (wahoowa!), and we’re both unabashed fans of the Apollo Moon missions. But where I will sometimes write about the missions and talk about how they’re real, he went way, way farther: He rescanned more than 8,000 original photographs taken by the astronauts using their chest-mounted Hasselblad cameras, creating a huge archive on Flickr showcasing the epic journey to the Moon and back.

Included are shots you’ve seen before, and many I bet you haven’t. I’m pretty familiar with the Apollo images, having spent many hours poring over the Apollo Lunar Surface Journal website, studying the images … but even so there are lots of photos I hadn’t seen before, or at least hadn’t noticed.

For example, look at this gorgeous shot of Goclenius, a 70 kilometer wide impact crater near the Moon’s equator:

Goclenius crater
Goclenius crater, criss-crossed by lava flows.

Photo by NASA/Kipp Teague

WOW. This was taken in 1968 by the Apollo 8 crew, which didn’t land, but instead whipped around the Moon to test out the mission trajectory profile before the actual landing the next year. Look at the detail! The gullies cutting right across the crater on the floor are rilles, carved by flowing lava. The floor of the crater is flat, indicating to me that it was flooded with lava, which pooled inside. The rim of the crater shows slumping, too, landslides causing collapse of material for dozens of kilometers around it.

Pictures like that remind me that the Moon may be dead now, but it wasn’t always. It used to be a place of massive, violent geologic events.

Most people will of course be entranced more by the photos of the astronauts themselves. I easily found my favorite Apollo photo of all time: Al Bean standing on the Moon’s surface during Apollo 12, holding a regolith sample container:

Al Bean
A man on the Moon.

Photo by NASA/Kipp Teague

I love the contrast, the glow, of this shot. The streaks on the left are scattered sunlight inside the camera, and you can see the reflection of Pete Conrad, who took this picture, on Bean’s helmet. Note the camera on Bean’s chest; that’s one of the Hasselblads used to take all these incredible photos.

As for why this is my favorite Apollo photo, I described it a few years ago. I had been neck deep in debunking the truly ridiculous claims that the missions were faked and was getting heartburn over it. But going through the lunar photos online I found this one, and something about it—the composition, the artistic qualities of it—caught my eye. And then a realization swept over me, giving me chills and literally raising the hair on the back of my neck:

This is a picture of Al Bean. It's a man in a spacesuit. It's a man in a spacesuit holding a sample container. It's a man in a spacesuit holding a sample container on the Moon. Standing on the Moon. It's a man standing on the freakin' Moon!
Slowly, a wave of awe, joy, and happiness washed over me—a glow of warmth that stays with me to this day. From that moment on I didn't let the conspiracy theorists bug me very much. They were wrong, but even more importantly, they didn't matter. In the long reach of history, they will be forgotten, gnats buzzing around a monumental edifice.

That is the true joy of these photographs. They were taken when we dared to explore beyond the comforts of our home, when we looked skyward and thought, “We can go there.” These photos can inspire the next generation of explorers, those who aren’t afraid to leave safe harbors for worlds beyond.

We did it before. We can do it again.

Oct. 7 2015 9:30 AM

A Lesson in Crewed Language

In many ways, NASA is slow to change. That’s not surprising; it’s a government agency, for one thing, and for another being a tad conservative isn’t such a bad feature when you’re trying to put people into space safely.

But even NASA is ahead of a lot of the curve when it comes to language used when talking about spaceflight. The terms “manned” and “unmanned” have fallen out of favor with the space agency: The NASA History Program Office Style Guide now specifically states that “All references referring to the space program should be non-gender specific.” The only exceptions are for names of buildings and programs; these are—pardon the expression—grandfathered in.*


I think this is great! Words matter. Using more inclusive words is a tacit invitation to people of all flavors, and diversity = strength.

My friend Emily Lakdawalla wrote about this on her blog for the Planetary Society (the comments there are interesting, too, so be sure to check them out as well). The topic came up again when a few science communicators were trying to come up with a good substitute for “manned” and “unmanned.” A lot of us use “crewed,” but as Emily points out (and as I have said many times) it sounds like “crude” when spoken aloud, which can cause momentary confusion for an audience. I’m still not sure what might be best there. “Crewless” works well for “unmanned,” though.

I did a quick search and found that I used the word “crewed” in a post way back in 2007, though it’s unclear if I did that to be more inclusive or just to switch my word usage up a bit. I stopped using the word “manned” a few years ago, though (except when quoting someone, or referring to something like the Manned Maneuvering Unit). I did that when I got into a conversation on this very topic on Twitter with some science communicator friends a while back. I’m a balding, bearded, middle-aged white guy, the very picture of stereotypical science dork. If I figured this out, others can too.

I know a few folks will froth and fume over this change; some people get very hot and bothered when others want to be more inclusive. But things like this cost us very little, and the payoff is large. Even if the cost were higher it wouldn’t matter, because it’s the right thing to do.

Everyone deserves to feel welcome when it comes to math, science, and tech … really everywhere. There’s no way to know from someone’s sex, skin color, or superficial characteristics what they might contribute. We all have brains. What we all need is a chance—and the environment—to participate.

*Space advocate Ariel Waldman points out that this has been in the style guide since 2006!

Oct. 6 2015 12:00 PM

Stephen Ramsden’s Traveling Sun Show

I was puttering around online and happened across something that made me quite happy: CNN put out a short video about my pal Stephen Ramsden. He’s a former air traffic controller who travels around with a very, very impressive array of solar telescopes, teaching kids about the Sun.


I met Steve many years ago and was taken right away with his dedication and enthusiasm for teaching. He’s a natural. That video came out last year, but he’s still out there, going from school to school and showing children sunspots, solar flares, prominences, and more. He’s an inspiration.

Stephen Ramsden
Ramsden setting up for a public Sun viewing in Georgia, his home base state.

Photo by Stephen Ramsden

And not to put too fine a point on it, he takes donations, too (there’s a “donate” button on his Web page). He’s doing a fundraiser right now, and if you donate $100 or more, you’ll get entered to win a Lunt LS80 B1200 solar telescope, and I’ll be honest: I have serious lust for this ‘scope. Happily, I have my own smaller version, so I’m OK. But geez, that’s a sweet machine. And not only that, Ramsden is also raffling off a pair of 8 x 32 Lunt SUNoculars every Friday until Oct. 30 to a donor of any amount.

If you prefer to buy stuff, one of his sponsors, Rainbow Symophony, sells safe solar observing glasses; I have several pair myself and I use them all the time. Stephen doesn't make money from those sales (in fact he gives away glasses for free to anyone who asks if they use them for outreach), but it helps his sponsor so that's agood thing. Come to think of it, I bet such things will be in short supply soon as the Great 2017 Solar Eclipse approaches. You might want to pick up some now. He has other swag, too (again, he doesn't make money for those sales; he does that at cost so others doing outreach can have the same shirts he wears). But donations are best!

He’s doing good work, and I hope he continues to do so for a long, long time.

Correction, Oct. 6, 2015: I originally wrote that the sales of glasses and swag support Stephen, but he sent me a note reflecting the text above.

Oct. 6 2015 9:00 AM

The 20th Anniversary of Exploring Strange, New Worlds

Twenty years ago, on this very date, the field of astronomy underwent a magnificent revolution.

On Oct. 6, 1995, Swiss astronomers Didier Queloz and Michel Mayor announced they had discovered a Jupiter-like planet orbiting a Sun-like star.


This was the very first time a planet was seen orbiting a “normal” star. Planets had previously been discovered around pulsars—the compact and furiously energetic cores of stars that had exploded. But it’s thought that the planets may have formed after the supernova event that created the pulsar, and besides, pulsars are nothing at all like the Sun.

Still, this new planet, called 51 Pegasi b, was a surprise. A big one! While it had about the same mass as Jupiter, it orbited its host star (51 Peg) in just four days, meaning it was on an orbit a mere 8million kilometers from the star. Compare that with Mercury, our solar system’s innermost planet, which never gets closer than about 46 million km from the Sun.

This meant 51 Peg b was hot, cooking away at a temperature of about 1,300° C. No one thought a planet that size could be that close to a star. Did I say the discovery was a surprise? I meant it was a shock, one so profound that it was met with deep skepticism.

As well it should! But its existence was quickly confirmed by team of American astronomers, rivals in the hunt for the first extrasolar planets, as they were once called (we now call them exoplanets).

The planet was found using what’s called the “radial velocity” or reflexive “motion method.” A planet orbits a star due to the star’s gravity. But the planet has gravity, too, so as the planet makes a big circle around the star, the star makes a little circle. In reality both orbit the center of mass of the system, called the barycenter. I describe how this works in my episode of Crash Course Astronomy about the discovery of exoplanets:

As far as we knew at the time, planets like Jupiter had to form far out from their stars, half a billion kilometers or more. Because of this, astronomers who were hunting for exoplanets assumed they would take months or years to make an orbit. They completely missed the presence of 51 Peg b in their data.

Once it became clear these “hot Jupiters” existed, more were found in existing data. Within a few years many more were discovered. It’s now thought they do form far out, but then migrate closer to their star over millions of years. Although they make up only a minority of all exoplanets, these are the easiest to find using reflexive motion; their high mass and close orbit make their signal in the data easiest to see.

Once 51 Peg b was found, the floodgate was opened. HD 209458 b was another hot Jupiter found in 1999, and had an orbit so close to being edge-on that astronomers thought it might actually pass in front of its star, transiting it, dimming its light once per orbit. Careful observations later that same year detected a dip in the star’s brightness (only 1.7 percent!), which gave them the first independent observation of an exoplanet. Any lingering doubts about the existence of these alien worlds evaporated.

The field matured so quickly that NASA launched the Kepler spacecraft in 2009, designed specifically to stare at 150,000 stars to look for transiting exoplanets around Sun-like stars. As of today, Kepler has more than 1,000 confirmed exoplanets under its belt, and well over 3,000 more waiting confirmation.

We’ve seen planets big and small, hot and cold, orbiting small cool stars, huge hot stars, multiple stars, and even in systems with multiple planets.

When I was a kid—heck, when I was in grad school—the only planets we knew of were the ones in our solar system. Using simple statistics, we now think that planets outnumber stars in the galaxy and that most stars may have planets. There may be tens of billions of Earth-size planets in our galaxy alone!

But we had to start somewhere. Exactly two decades ago, 51 Peg b gave us that start.

51 Peg star chart
The star 51 Peg is just off the Great Square of Pegasus, which is in the east after sunset for northern hemisphere observers. EarthSky has a finding chart for Pegasus, then you can use this image to find the star.

Map by Sky Safari

The host star, 51 Peg, is close by, just 50 or so light-years from us. It’s actually very much like our Sun, just a hair more massive, hotter, and bigger. It’s visible to the naked eye, barely, from a dark site. The constellation of Pegasus is high in the night sky for Northern Hemisphere observers right now, in fact. If it’s clear where you are, and you have a pair of binoculars, why not take a look at it tonight?

I will. The exoplanet is completely invisible to even the largest of telescopes, drowned by the light of its oh-so-close star. But who knows: Maybe a photon or two from the planet itself will pass into your eye as you look at the star, absorbed into your retina.

The sky may be brimming with planets. We stand on one among billions. And if you look, a small spark, literally the tiniest reflection of one, could become a part of you.

Oct. 5 2015 11:00 AM

How to Make a Rubber Ducky Comet: Smash Two Comets Together! Carefully.

Why is the comet 67P Churyumov-Gerasimenko shaped like a rubber ducky?*

It was a bit of a surprise when the Rosetta probe, after a decade of travel around the Sun, approached the comet and sent the first decently resolved pictures of it back to Earth. We knew going in that most asteroids and comets just a few kilometers across are oddly shaped; they lack the gravity needed to make themselves spheres, and after 4 billion years of impacts their shape can be decidedly odd.


We even know of a few bowling pin shaped comets, like Hartley 2 and Wild 2. But 67P just reinforced the weirdness of this all with its two lobes mismatched in size and shape.

So, why? What’s going on? Comets are rock, gravel, and dust all mixed together with various ices holding them together, frozen stuff like water, carbon dioxide, and carbon monoxide. Did these weird, dumbbell-shaped comets start off more round and, for some reason, lost more ice in their midsections, leaving behind the two big lobes? Or were they the result of two interplanetary snowballs that collided and stuck together?

New results from the Rosetta team have finally answered this question. 67P used to be two different comets, but they merged to become the bizarre bit of solar system fluff we now know and love.

How? Well, when two comets love each other very much …

Oh wait, no, that’s not it. Well, actually, kinda. Back in May 2015 astronomers came up with a pretty good scenario on how to form a rubber ducky comet. Two smaller comets collide in a slow-speed, grazing impact. Some material is lost, and the two major pieces separate a bit, but the impact was slow enough that they become gravitationally bound. They fall back together, stick, and voilà!

As for the “how do we know?,” that’s more subtle, and quite clever. Rosetta has been orbiting 67P since August of 2014. Over that time it’s taken a vast number of high-resolution images, revealing details of the surface. Both lobes have flat regions all over them arranged like terraces, and the steps in between the terraces show layering; these probably built up layer by layer over time when the comet(s) first formed billions of years ago.

terraces and layers
A close-up of 67P shows flat terraces (colored green here) and layers (red).

Photo by ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; M. Massironi et al. (2015)

If the comet formed as a single object that has since eroded, you’d expect the terraces and layers on both lobes to align so that their flat sides were perpendicular to the center of the comet, somewhere in the neck, plated around it (something like the individual panels on a soccer ball, which all are perpendicular to the ball’s center, or, of you prefer, more-or-less parallel to the ball’s surface).

If, instead, the two lobes formed individually and later merged, then the terraces on each lobe would be perpendicular to the center of their respective lobe.

Using 3-D modeling, the scientists mapped the orientation of the terraces. And what they found is the latter: The terraces align to each lobe individually, not to the center of the comet as a whole. This strongly indicates the lobes formed separately, later merging.

comet map
A 3-D model of the terraces in the comet indicate their orientations, showing the two lobes of 67P formed separately, then later merged.

Photo by ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; M. Massironi et al. (2015)

That is very, very cool. I’ve been curious about this ever since we literally got the first good pictures of the comet. I allowed myself a bit of speculation back then and felt that a low-speed collision between two small comets was unlikely. I guess I was wrong! While space is big, I neglected to consider that time is also long, and over an eon or four collisions may be likely. After all, 67P isn’t the only object like this; we know of quite a few binary and dogbone-shaped asteroids, too.

How about that? The beauty of this, too, is that the answer gives us insight into more than just why the comet is funny-looking. It also tells us about how comets behave, what their formation processes are like, what happens after they form, and, perhaps most interestingly, how often objects in space collide. That in turn helps us understand the history of our solar system in general, as well as how often the Earth itself gets hit by such cosmic debris.

Over time, we do get hit. The rate of such impacts is a good thing to know, so that we can better understand how to prevent them.

After all, we don’t just want to be a … sitting duck.

*Hint: It’s not because it makes bath time so much fun.

Oct. 5 2015 9:00 AM

Ben Carson vs. Ben Carson

Scientist Ben Carson, talking about his own fetal tissue research: "To willfully ignore evidence that you have for some ideological reason is wrong."

Creationist Ben Carson, talking about scientists who understand the Big Bang, evolution, and global warming are real: "I just don't have that much faith," he said. "But they are welcome to believe whatever they want to believe. I'm welcome to believe what I want to believe."


Do politicians ever actually listen to what they say?

Oct. 4 2015 9:30 AM

Marketing Space

I have to admit, I laughed, especially at the “Pluto” part.

Still, I do sometimes worry about the future of NASA marketing. Promoting movies like The Martian is great, but I wonder if this will backfire in the long run. I agree with my friend Joel Achenbach; Congressional squabbling over NASA’s budget and the lack of a clear vision or plan to get to Mars only serves to contrast what NASA promotes versus what it can actually do.


This is not NASA’s fault, mind you. I lay the blame squarely on Congress. They have a clear path ahead of them—fully funding Commercial Crew—but instead keep throwing money at the Space Launch System (which, if built, will cost so much NASA won’t be able to do anything with it) and the Orion capsule, which now may not be able to take humans in it until 2023, a full eight years after Commercial Crew would’ve been able to send humans into space, had Congress funded it.

What a mess. The majority of Americans love NASA, and it’s incredible that NASA can do such amazing feats like send probes to Pluto and Saturn and protoplanets like Vesta and Ceres at all, let alone given the Keystone Kops feel of the Congress members pulling the purse strings. My only hope now is that these folks in Congress get replaced in the 2016 elections.

It’s hard to look to the stars when the people funding you have their heads jammed into pork barrels.

Tip o’ the spacesuit visor to ruimteaart via astronaut André Kuipers.

Oct. 3 2015 9:30 AM

Crash Course Astronomy: Multiple Star Systems

The stars are not as they seem.

The nearest one is tens of trillions of kilometers away, a distance so terrible that the might and power of Alpha Centauri is reduced to a faint spark that can be washed away by the lights of a nearby city.


Distance shrinks details, too. Alpha Centauri is not one star, but two: one very much like the Sun, though slightly larger, orbiting and orbited by another that is somewhat fainter, cooler, and more orange. There’s also a third star, Proxima Centauri, which orbits the pair but is so faint it can’t be seen by the naked eye even though it is in fact the closest known single star to the solar system.

A large fraction of all the stars in the sky are actually multiple stars—binary, trinaries, or even more complex systems. That alone is enough to want to know more about such multiples; but once you look closer you find that such systems become critically important to our understanding of everything in the Universe.

And, contrary to my usual nature, that’s not an overstatement. Find out why in this week’s episode of Crash Course Astronomy: Binary and Multiple Stars.

I’m excited that this phase of Crash Course is airing: We’re traveling farther out into the Universe, even though we haven’t even left our cosmic backyard yet. But there are larger structures to explore, and grander things yet to see. Just you wait.