Bad Astronomy
The entire universe in blog form

May 30 2015 7:30 AM

How to Make a Rubber Ducky Comet

Before we knew what comets and asteroids looked like up close, it was popular (at least in media) to imagine them as roughly spherical, maybe a bit lumpy.

The reality was way stranger. The first comet seen up close, Halley’s, was actually more elongated, like a rock you might find in your back yard. As we sent space probes to more of these celestial flotsam, we found most were oddly shaped, and some downright bizarre: a double-lobed bowling pin shape kept popping up. Hartley 2, Wild 2, Kleopatra (which looks like a cartoon dog bone!), and now, most recently, 67P/Churyumov-Gerasimenko, the new home of the Rosetta probe. The solid part of this comet looks like a rubber ducky, with a large, flattish lobe connected somewhat off-center to a smaller, more rounded chunk.


What gives?

I’ve written about this before. My original thinking was that these shapes are due to a slow collision by two bodies, which manage to stick together. 67P, however, has many features that look more like it was one object that has been eroding away in the middle, creating the double-lobed shape.

Now it looks like the former was more important than the latter. A new study has just been published showing that slow-speed collisions between two objects can create the shapes we see.

The researchers used three-dimensional modeling to determine how this could work, and the video above shows a representative example. A larger and small body collide slightly off-center, causing material from the smaller one to splash on to the bigger one, and slowing their relative speed. Their mutual (weak) gravity draws them together again about a day later, and they wind up sticking to each other, forming the familiar two-lobed morphology.

This also explains a peculiar layering seen in some comets, due to the splashing of material from one object to the other. It’s nice when a single model can explain more than one physical characteristic.

Collisions like this may have been common in the very early solar system, when there were a lot more objects out there; as the giant planets formed after a few tens of millions of years, their powerful gravity wound up eliminating many of those comets and asteroids (either by drawing them in and assimilating them, flinging them away and ejecting them from the solar system, or dropping them down in to the inner solar system in an event called the Late Heavy Bombardment, the scars of which are still visible on the Moon today). A collision like this would be rare now.

If this scenario is correct, then, looking at 67P, I have to think both processes are at work there. It originally formed as a slow speed collision, and then erosive processes have been at work for quite some time since. The cliffs on the smaller lobe appear to be due to cleaving or calving of the comet there, and you wouldn’t expect such large flat features after a collision.

That wouldn’t surprise me at all; a lot of the features we see in astronomical objects in the solar system today are the result of many processes, some of them ongoing. These things have been around a long time, after all, and there have been periods of fairly intense activity since the whole place formed some 4.56 billion years ago. It’s incredibly rare to find an intact, pristine time capsule from that time so long ago, and we have to be aware that, in simple terms, stuff happens. So to speak. 

If this model is true, it means that collisions like this were common (since we see double lobes so often) and that most would’ve happened a long time ago. This may be testable by examining these dog bone/rubber ducky/bowling pin objects and seeing if we can determine just when they may have assumed these shapes. If it happened right after the solar system formed, then great! If not, well, then we’ll have to modify the hypothesis or abandon it.

Such is science. We sometimes have to follow a path to a wrong idea to make sure it’s not right. But even then, it may be salvageable, and at worst we’ve learned something anyway. Science is pretty cool that way.

Video Advertisement

May 29 2015 7:30 AM

Crash Course Astronomy: Uranus and Neptune

I’m not gonna lie to you: This is the best cold open of any episode we’ve done so far. I made myself laugh writing it.

Before you comment, PLEASE READ THE FOOTNOTE ON THIS ARTICLE. And if you still feel the need to comment, remember, neither you nor I is funnier than Futurama.


About that pronunciation, this may help as well.

UPDATE, May 29, 2015: ARG! I made a mistake in the video; I said the rings of Uranus were discovered in 1997, but they were discovered in 1977. It was a typo in the original script and it somehow made its way to the video without any of us noticing. Aggravating. My apologies for any confusion.

I’ve also written about those giant storms that erupted in Uranus’ atmosphere, an odd hypothesis about why the planet is tipped over, and an interesting claim that Herschel may have seen the rings of Uranus!

May 28 2015 7:00 AM

Pluto - 47 Days

In 47 days, the New Horizons spacecraft will zip past Pluto and its moons at a relative speed of 14 kilometers per second. As of right now, there’s more than 50 million km still to go.

But earlier in May, the probe turned its cameras toward Pluto and took a series of images. They’re still pixelated, but wow.


As you can see, surface features are getting easier to discern (note that a different part of Pluto was seen by the probe on each day, so you're seeing different features). It’s not just light and dark patches, but they have some shape to them as well. It actually reminds me a bit of seeing Mars through a small ‘scope. Note that on the May 10 image there appears to be a dark chunk taken out of Pluto’s side; that’s an illusion due to that spot being particularly dark; it blends in with the blackness of space and fools your eye into thinking Pluto’s missing a piece.

These images are considerably better than what we saw in April, too:

April vs. May, and 20 million km closer

Photo by NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

Not bad. As before, the new images have been carefully planned and post-processed to increase their resolution. These shots were taken from 80, 77, and 75 million km away and are already in many ways better than we can get even with Hubble.

So stay tuned. Every day, New Horizons gets more than 1 million kilometers closer to Pluto, and well be getting some amazing views, culminating in the flyby on July 14. What delights and wonders will we see then?

May 27 2015 12:27 PM

All These Worlds Are Yours …

On Tuesday, NASA announced the scientific research instruments that will be installed on board the 2020s mission headed for Jupiter’s moon Europa.

The moon has a thick ice shell covering an undersurface ocean, and there’s a lot of interesting chemistry going on in that water. We don’t know if there’s life there, or even if the ocean is habitable, but it’s an incredibly enticing destination. That’s why the (currently not-yet-named) mission is headed that way.


And it’ll have quite the suite of instruments onboard, too: a camera that will map almost the entire moon with 50 meter resolution (and some spots with 0.5 meter resolution!), radar that can determine the thickness of the ice and ocean, a thermal (heat) mapper, an ultraviolet camera, and much more. You can read about them on the NASA press release and in the Planetary Society blog post by Casey Dreier.

I’m excited about this; the NASA fiscal year 2016 budget has $30 million set aside to develop the mission. If things go well, there will be more in the years to come. Europa is one of the three best places to look for life in the solar system—the other two being Saturn’s moons Titan and Enceladus, and a mission there would take longer, be bigger, and cost more money. As much as I want to see more of those worlds, I think going to Europa is a good first step. And if we do find something biologically intriguing there, we’ll be in a better place to send more missions.

Now pardon me while I take something of a left turn.

I follow quite a few planetary science folks on Twitter, and it was Christmas for a lot of them on Tuesday. My feed was nonstop chatter about the science that’ll be done at Europa. Someone mentioned that of the nine instruments chosen for the mission, three of them have women as principal investigators (the person in charge of the project). I checked, and sure enough, it’s true.

Female PIs are not exactly unheard of in NASA, but they’re certainly not at a 50-50 ratio with men (I worked on the proposal for the NuSTAR mission, the first NASA astrophysics observatory with a woman at the helm, and that launched just three years ago). There is nowhere near parity in the sexes at most scientific institutions, so I like to support and highlight women in the field when I can (for example, Sally Ride’s birthday on Tuesday).

So in the interest of raising a bit of awareness, I tweeted about it:

Seems clear enough. But I got a couple of angry tweets in response; both accused me of being sexist, seeming to think I was somehow amazed that women could actually run NASA science instruments!

Um. I know that we live in an outrage culture, and I also know just how things get misinterpreted on the ‘Net. Even so that struck me as a bit of a stretch.

I followed up the tweet with another one expressing my own bafflement as to how I could be accused of that when I was supporting women (especially given the context of my many tweets and blog posts supporting women in STEM), and then got responses saying those first responses must’ve been from, gasp, feminists.

At that point my desk got up close and personal with my forehead. I think pursuing this line of thought is going to lead to an ever-amplified Möbius strip of hollering Internuttery, so I’ll leave it to you to follow it if you so choose. Tread carefully.

But this whole thing brought up a point that is worth thinking about. As I said, in most sciences there isn’t parity between men and women. Study after study show that this must have some sort of social basis; women are no less or more suited for science than men. I am no expert on the details, and I leave that for those who are doing the research to investigate. But the conclusion remains.

In an ideal world, science would be science, and anyone of whatever sex who does it for the betterment of humanity is fine by me.

But we don’t live in an ideal world, and we must be practical. Women are not staying in sciences, they aren’t treated the same as men (and it’s generally in a negative sense, unless you’ve been living somewhere under the crust of the Earth for the past, oh, say, century or two), and they are at a disadvantage in many ways compared with their male colleagues. Not an intellectual disadvantage, not a performance disadvantage, not any intrinsic disadvantage, but a socially-engineered one.

If all things are equal except for the societal thing, then how about we fix the societal thing?

One way to do that is to simply make people aware of it. I’m not exactly the swiftest boat on the lake when it comes to things like this, and it took me a long time, but I’m coming around to the notion that sexism pervades everything in our culture.* If I can figure that out (due to the raising of my own awareness by my friends and colleagues), then so can others, and if I can help, well then I will.

And so I do what I can. There may come a time when parity or a close approximation thereof can be achieved. When that day arrives then we won’t need to note when women make strides toward equality, and an achievement in science will be simply that, rather than segregated by the sex of the achiever. But that day is not yet here.

In the meantime we can all work toward it, and work toward the bigger goals of science at the same time. And when we do, we need to remember the mistakes of the past, so that we don’t repeat them—social equality is a dynamic equilibrium; we need to keep working at it to maintain it, lest the scales tip once again.

There are entire worlds to explore out there, folks. Let’s do what we can so we can all explore them.

*It’s more fair to say that sexism is one of the main biases pervading our culture, along with many others such as racism, homophobia, and a host of other prejudices. That list goes on and on, and it might be easier just to say there’s a bias against anything that isn’t white-cis-Christian-middle-class-male, but I don’t want to lose the main point here.

May 27 2015 7:30 AM

Time-Lapse: Trails End

Randy Halverson is an amazing astrophotographer, whose gorgeous photos and time-lapse animations have graced this blog numerous times.

His time-lapses show landscapes lit by the setting Sun, roaring thunderstorms, and of course the night sky wheeling overhead … and his newest, Trails End, is magnificent. He’s posted a trailer for it, and wow. Make sure this is set to the highest resolution you can handle (it’s filmed in 4K!), make it full screen, and turn the volume up.


If your heart doesn’t pound at 1:30 when that massive thunderstorm rolls in, then I can’t help you.

As I watched, I was amused to see quite a few geosynchronous satellites in the sky sequences. These are satellites in orbits about 40,000 kilometers from the Earth’s center; in such an orbit they take 24 hours to circle the Earth once, so they appear to stay in more-or-less the same spot in the sky relative to the ground. A trick to finding them in the shots is to not focus on any one part of the sky, but let your gaze take in the whole frame. Stars will move, but the geosynch sats won’t.

At 2:48 I noticed something odd, and Halverson confirmed it: He caught a rocket boosting some satellites into orbit. Also, at 3:20, there’s a meteor that leaves behind a persistent train, a glowing vapor trail. The video slows there for a moment to give you a chance to see it. Very very cool.

Remember, this is just the trailer for the much longer version that’s shot in ultra-high def. If you have a high-res monitor (or a 4K TV!), you could do a lot worse than getting this movie

May 26 2015 1:15 PM

Google Doodle Celebrates Sally Ride’s 64th Birthday

Today, American astronaut Sally Ride would have have been 64 years old.

She died in 2012, but her work lives on as an inspiration to young women who want to touch the stars. Ride was indefatigable in promoting education, in promoting the need to explore space, and working to get girls more involved with science, technology, engineering, and mathematics. As the first American woman in space her place in history was secure, but she knew what this implied for her as a role model, and maximized that leverage.


Google has helped promote her message today in a series of lovely Doodles, animated images that come up when you open the home page of the search engine. This one is my favorite.

Rather self-explanatory, isn't it? There are five in total; refresh the Google home page to see them all.

Dr. Ride was immortalized when NASA named the GRAIL spacecraft impact site after her. But her legacy was secured by her own doing, by her actions. And we thank her for them.

May 26 2015 12:13 PM

BA Video: Close-Up on a Comet

In the 1980s, humanity got its first face-to-face view of a comet when a fleet of spacecraft was sent to visit Comet Halley, which was making its first pass into the inner solar system since 1910. We got never-before-seen close-up glimpses of the nucleus of a comet, the inner solid part that creates the gigantic gas cloud and long, beautiful tail.

Over the years more probes were sent to comets like Tempel 1, Hartley 2, and Wild 2. Each is an individual, and each is weird. But all of those missions were flybys—important but brief.


But now we have the Rosetta spacecraft orbiting the comet 67P/Chuyurmov-Gerasimenko, studying it in detail and over a great length of time. We’ve learned so much about it, but also opened up a Pandora’s box of even deeper mysteries about comets in general, and this comet in particular.

The big one, in my mind, is why it and so many others are shaped like bowling pins: two separate lobes connected by a relatively thin neck of material. We still don’t know when it comes to 67P, but in this week’s Bad Astronomy Video I go over the evidence we have so far.

The Rosetta mission has a nominal lifespan of a year, following 67P as it nears the Sun and becomes more active. There’s a huge amount left to learn, but a corresponding amount we’ll also discover. And that’s one of my favorite facts about science: It’s a jigsaw puzzle with an infinite number of pieces, so the fun of exploration never ends.

For more information about comets, read my article 10 Things You Don’t Know About Comets.

May 26 2015 7:30 AM

Climate Change Denial Is a Threat to National Security

First, let me be clear about this reality: Planet Earth is warming because of human activity, because of us, and that is profoundly affecting the climate. There is no honest doubt about this; the overwhelming evidence supports it, so much so that 97 percent of climate scientists agree on it.

The effects of climate change are profound. We are already seeing more extreme weather, more powerful tropical storms, more wildfires. As the sea level rises, coastal populations are threatened, including military bases.


I have been saying for a long time that climate change is a threat to our national security, and it’s long past time to call out those who would deny this as abetting that threat.

President Obama did just this last week, in a speech at the U.S. Coast Guard Academy. My Slate colleague Eric Holthaus wrote all about this, and I strongly urge you to read that article. Obama used words like “negligence” and “dereliction of duty”:

After all, isn’t that the true hallmark of leadership? When you’re on deck, standing your watch, you stay vigilant.  You plan for every contingency. And if you see storm clouds gathering, or dangerous shoals ahead, you don't sit back and do nothing. You take action—to protect your ship, to keep your crew safe. Anything less is negligence. It is a dereliction of duty. And so, too, with climate change. Denying it, or refusing to deal with it endangers our national security. It undermines the readiness of our forces.

This sentiment was reinforced in a tweet from the president:

Take a moment and ponder this. The president of the United States of America said that people who deny the reality of climate change are a threat to national security. And he strongly implied that members of Congress who do so are guilty of dereliction of duty.

I agree. And they do so on the basis of what is at best wrong information, and at worst a passel of lies.

The only doubt is manufactured, sole-sourced by the fossil fuel industry. Senators, Congress critters, “think tanks,” sponsored by fossil fuel (and using the same tactics as the tobacco industry)—the doubt they sow is as fake as $3 bill, and just as obvious (and embarrassing). From ridiculous and patently false claims that global warming has slowed, that the world can’t be warming because winter still exists, that (seriously) plants like carbon dioxide so we’re just feeding them; these people’s only purpose is to slow any real progress on fixing the planetary mess we’re in.

And in that way, they are making things far, far worse.

As the latest example, look at an op-ed in Forbes magazine written by Heartland Institute’s James Taylor (yes, that Heartland Institute). Taylor has a history of cherry-picking and distorting results from real climate scientists, and he’s doing the same thing here.

In the op-ed, he claims that global warming has not caused global sea ice retreat. This is a gross distortion of reality. The truth is that in the arctic we’re seeing record low levels of sea ice year after year, including just this year, when in March the North Pole saw the lowest maximum ice extent on record.

Annual Arctic sea ice minima
Arctic sea ice minimum extents since 1979, when satellite measurements were started. This is the 2013 graph that I extended to add 2014's minimum. The blue line is a linear fit to the numbers. Even James Taylor could spot this trend.

Graph by NSIDC

It takes a very twisted view of the world to claim global warming isn’t doing anything to polar ice not two months after that record was broken. And as we know very, very well, Arctic sea ice is on a long, drastic decline that does not show any signs of recovery at all.

But note how Taylor phrases it, using “global” ice. That includes Antarctic sea ice, but as I have written about over and over again, that is really unfair. Antarctic sea ice is very different than at the North Pole; Antarctica is a continent and conditions there are literally polar opposites. The southern sea ice fluctuates quite a bit year to year, and in fact wind-driven snow can be increased by global warming (warmer air can hold more moisture), so glossing over local conditions the way Taylor does is at best misleading.

Antarctic ice loss
Land ice loss from Antartcica from 2002–2009. Note the scale of the graph on the left: It's in billions of tons.

Diagram by NASA

That doesn’t sound at all like what Taylor is claiming, does it? I guess he doesn’t know (or doesn’t say) that his corporate sponsors are using the ongoing decrease in arctic ice as a reason to explore more drilling sites in north polar waters.

I’ll also note Taylor links to some satellite data from the University of Illinois Polar Research Group to make his claim … and that same group has issued a rebuttal saying Taylor cherry-picked his data and refutes his claim. Oops.

As much as I loathe what Taylor is doing and saying, I reserve my strongest feelings for people like Sen. James Inhofe (R-Oklahaoma); my own senator, Cory Gardner (R-Colorado); and virtually all the GOP presidential candidates, who claim with various degrees of head-in-the-sand-ness that humans aren’t causing global warming.

These people have a sworn duty to protect the people of our nation. What they are doing is the exact opposite in every way. They cut NASA’s funding to investigate climate change. They even cut the Pentagon’s funding to act on it. The Pentagon.

head in the sand
"Maybe if I stay this way until 2016 I can get re-elected."

Photo by Shutterstock/alphaspirit

In the medium to long run these politicians are putting us at greater risk from drought, wildfire, extreme weather, and rising sea levels. In the near run they are cruelly crippling our ability to do the kind of research that has made the United States of America a world leader in scientific innovation.

They claim to love this country. But they sure don’t act that way.

I have written about the reality of global warming and the lies of the deniers so often that to list them all would be counterproductive. Instead, here are some highlights that you can use to counter the denial; check links therein to find even more.

… and, of course, always check Skeptical Science when you hear a claim from someone saying global warming isn’t real. The vast, overwhelming amount of the time, that claim is nitrogen-rich.

May 25 2015 7:15 AM

It’s Crowded Downtown

Funny. I was thinking I want to just post a big, gorgeous, colorful photo showing a bunch of different astronomical objects in one scene, and then I found an old note from Derek Demeter, planetarium director at the Seminole State College of Florida. He’s an accomplished astrophotographer, and took this stunning picture of the galactic center last October:

May 24 2015 7:30 AM

Wait. That’s the Same Comet?

The folks at the European Space Agency released a new picture of comet 67P/Churyumov-Gerasimenko, and I have to admit that it threw me.

Huh. That’s the comet? Where’s the second lobe?


For a second I thought we were just seeing it end-on, so that the bi-lobed rubber ducky shape wasn’t obvious. But then I realized the part we’re seeing is too thin; the big bottom lobe is much wider than seen here. I did a bunch of rotations and such in my head, and quickly concluded there’s simply no angle on the comet that would produce this view.

My brain really jammed at that point, and I had to concede: I didn’t understand the photo. I read the accompanying text to find out what was going on and got a good chuckle. I forgot about the Sun.

Here’s the same photo, with the contrast/brightness wildly stretched:


Photo by ESA/Rosetta/NavCam – CC BY-SA IGO 3.0

Aha! The smaller lobe is there, a barely darker black against the black sky. The reason it can’t be seen is that it’s in the bigger lobe’s shadow. And also, the bottom of the bigger lobe is flattened, shaped more like a river rock than a potato. At this angle it looks foreshortened, so that fooled me as well.

I love puzzles, and I love getting as far as I can before going to the answer key, but this still felt a little like cheating, since I couldn’t figure it out all out by myself. Drat!

But there’s one thing I did see that I do understand. Look to the left, just below the tip of the lobe. See that luminous line dropping down? Care to guess what that is?

Hint: The plumes you see coming from the comet are actually jets of gas, caused by the Sun heating the ice in the comet, turning it directly into a gas.*

Got it now? That vertical line is the shadow of the solid part of the lobe on the gas surrounding the comet. Comets are so weird: They can cast shadows on themselves!

I’ve spent a lot of my life interpreting astronomical images, squeezing the science out of them by analyzing their shapes, contours, brightness, colors, and more. This picture is a good reminder not to take experience for granted, nor to invest too much confidence in it.

Any of us can be fooled at any time. That’s an uncomfortable but necessary piece of information to always keep in mind.

*Also making it useful for the annual Pacific Tech “Smart People on Ice” show. And yes, I did just watch Real Genius for the 300th time the other night. Why do you ask?