Bad Astronomy
The entire universe in blog form

April 17 2015 11:15 AM

Crash Course Astronomy: Mercury

Quick: What’s the hottest planet in the solar system?

You might think Mercury, because it’s the closest to the Sun. But in fact, it’s not! Venus is hotter due to its runaway greenhouse effect.


But that’s not to say Mercury isn’t loaded with astronomical goodness. It’s got a lot going on: craters, rupes, a swollen iron core, and a frosty surprise in its boreal craters.

So please watch, listen, and enjoy this week’s episode of Crash Course Astronomy: Mercury.

And a side note I can’t help but mention: Right now as I write this, NASA’s MESSENGER probe has but weeks to live. Out of propellant, by the end of April it’s destined to slam into Mercury’s surface after more than 4,000 orbits of service to science.

Crash Course Mercury, indeed.

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April 17 2015 7:00 AM

Ceres Spins Under Dawn

The Dawn spacecraft recently slid ever so gently into the embraced of Ceres, the largest asteroid in the main belt between Mars and Jupiter. It actually flew past Ceres, slowing itself with its ion engine in a long, looping trajectory that kept it over the tiny world’s unilluminated half.

But then, a few days ago, it got close enough and in the right geometry to begin observations of some sunlit real estate on Ceres. It did this by peeking over the north pole of the asteroid, and the result was an amazing animation of Ceres rotating:

The rotation of a distant world.



That’s phenomenal! These images were taken on April 10 from a distance of 33,000 kilometers and are the highest resolution images we’ve seen so far.

Ceres is a mess. It’s heavily battered, as you might expect for the largest airless body in its neighborhood surrounded by a few billion smaller ones. As I wrote about before, a lot of the craters look to have flat floors, which is what you expect on a world where there’s lots of ice under the surface; that stuff can flood in and fill the crater after an impact (materials with lower tensile strength tend to leave flatter floors, but the ice could also melt and flow in as well).

Some of the craters have central peaks, which is also common in larger impacts as material pushed out by the huge energy of the impact rushes back into the center (like a drop of milk or water that splashes up from the center when you pour the liquid into a glass—this is called isostatic rebound).

Soon enough there will be a lot less guesswork, once Dawn settles into its mapping orbit. We’ll see much better images then and get a much better understanding of this weird little world.

April 16 2015 7:00 AM

To Mars

Why is Elon Musk so hellbent on going to Mars?

There are two answers to this. One is the actual answer. The other isn't exactly wrong—it’s technically correct—but it’s incidental. And it turns out that’s not even really the right question.


Bear with me a moment. You need a little background.

I’ve been interested in SpaceX for a while now. Years ago, when Musk announced he was going to launch the first privately funded liquid fuel rocket into orbit, I figured he might be able do it—it’s a daunting but not impossible task. Still, I was pretty skeptical. But he did have a bit of a leg up: He’d been pouring money into SpaceX, a personal fortune made from running earlier companies like PayPal and (and now SolarCity and Tesla).

It takes more than money, of course, to build a successful rocket program. But my doubts were lessened considerably in September 2008, when, after three previous rockets had failed to achieve their mission goals, a Falcon 1 rocket reached orbit around the Earth. Now, years later, with the Falcon 9 proving to be a reliable vehicle and several successful launches to the International Space Station and beyond under its belt, SpaceX has shown it can look even farther.

This was all on my mind when I got a chance recently to take a tour of the SpaceX construction factory and corporate HQ in Hawthorne, California. I had been invited by Musk, who, to my surprise, follows me on Twitter and reads this blog. (Full disclosure: SpaceX paid for the trip.) I was excited by the prospect—duh—and the place did not disappoint.

As I walked in, for a brief moment it felt more like a company office than a factory. But after a short walk from the front door and past the lobby it’s like, seriously, the scene in Willy Wonka when everyone steps off the elevator into the chocolate factory.

Phil Plait and Dragon
The very first Dragon capsule that went to space. Note the scorch marks.

Photo by Phil Plait, with an assist by SpaceX

Hanging from the high ceiling is the actual first Dragon capsule to be sent into orbit, scorch marks from its atmospheric re-entry licking up the sides. Nearby, two other capsules are in various stages of construction. A half dozen Merlin engines are lined up, already tested once under fire, now being retooled and checked out for their next launch. Two enormous Falcon 9 boosters lie side by side in one corner of the factory. From the café on the mezzanine I can see twin enormous nose cones sitting in the next room, waiting to be used on the demo flight of the Falcon Heavy, a huge rocket that is the next generation of SpaceX boosters. And all this is open, on the floor, available to be gawked at.

During the tour I also saw dozens of people working on the various components of the Falcons 9 and Heavy. It was hard not to notice that they all seemed to be in pretty good spirits—smiling, laughing, talking, gesticulating. Looking around, that wasn’t too surprising. A sense of pride and excitement would be natural working in such a place. But there was something else, too, that I couldn’t quite put my finger on.

Before the thought could crystallize, the tour was over. I was brought over to the admin section of the factory to meet with Musk. I’ll spare you the personal details; you can find those all over the Web. What impressed me the most was his matter-of-fact attitude; not surprisingly he is a man who knows what he wants and how to achieve it. With his track record, he’s earned that confidence.

We talked about various topics for a while—the movie Interstellar, the history of SpaceX, terraforming Mars … and that was when I said something dumb.

“I know Mars is a long-term goal for SpaceX,” I started. Then, pretty much as an aside, I said, “because you want to retire on Mars … ”

Musk got a pained look on his face. “No, that’s wrong. That’s not why I want to get to Mars. That quote is from an article in the Guardian. They pushed me for a sound bite, asking if I wanted to retire on Mars. I eventually said yes. When I retire—hopefully before I go senile—and eventually die, then Mars is as good a place to die as any.”

That line made me laugh; it’s far better than anything printed in the Guardian article.

But still, I was taken aback. “OK then, the article wanted a sexy quote and got one. But if that’s not the reason, what is it?”

Musk didn’t hesitate. “Humans need to be a multiplanet species,” he replied.

And pretty much at that moment my thinking reorganized itself. He didn’t need to explain his reasoning; I agree with that statement, and I’ve written about it many times. Exploration has its own varied rewards ... and a single global catastrophe could wipe us out. Space travel is a means to mitigate that, and setting up colonies elsewhere is a good bet. As Konstantin Tsiolkovsky (the father of modern rocketry) said, “The Earth is the cradle of humanity, but one cannot live in the cradle forever.”

Moon and Mars bootprint
From the Moon to Mars.

Photo by NASA

So I hardly needed to mull that over. But what did happen is that two things became clear in my head simultaneously. One was that Musk’s answer was simply stated, plainly obvious to him, but to the public it’s not. It seems like science fiction.

But with his immense factory sitting directly behind me, there was no doubting this was not the wild dream of a sci-fi fan. This is reality. The dichotomy between public perception and what was really happening here was never clearer to me.

The second was the crystallization of what had been nagging me during the tour.

The overall atmosphere in the factory was one of working at a progressive company on an exciting project. Of course: They build rockets. But the feeling I couldn’t put my finger on before suddenly came into focus. The attitude of the people I saw wasn’t just a general pride, as strong as it was, in doing something cool. It was that they were doing something important. And again, not just important in some vague, general way, but critical and quite specific in its endgame: making humans citizens of more than one world. A multiplanet species.

It’s easy to dismiss this statement, think of some snark as a way to minimize it and marginalize it as the thinking of a true believer. But—skeptic that I am—I’ve come to realize this is not minimal. It is not marginal. This is a real, tangible goal, one that is achievable. And SpaceX is making great strides toward achieving it.

That’s when I also realized that the initial question itself was ill-posed. It’s not why Elon Musk wants to get to Mars. It’s why he wants humanity to get there.

I think that's a pretty good idea.

Days later, back home in Colorado, I went out on my porch just after sunset and took a look at the sky to the west. Venus was shining like a beacon, brilliant and beguiling. Just below it, close in the sky but much farther away in reality, was Mars, a duller red in color and far fainter. But of the two, my gaze kept returning to Mars.

How long before we go there? Is the first human to make their bootprint in the ochre dust already leaving footprints here on Earth?

I suspect so. And it may not be all that long before they’re on their way.

Postscript: There’s been some discussion lately among space and science communicators about the way we talk about space exploration and how it relates to different cultures (for example, DNLee has thoughts on this). This took place, coincidentally, around the same time I wrote this article, and it’s an interesting line of discussion, one I’m mulling it over. I’ll have more to say about this in the near future, I think.

April 15 2015 7:00 AM

Video of the SpaceX Booster Landing ... Kinda

Update, April 15, 2015, at 22:15 UTC: SpaceX has released a full video of the booster landing on the barge! Watch it below. You can see it land, but it appears to have a bit of a tilt when it sets down. There's a small plume coming from the top, an apparent attempt to compensate, but it's not enough. The booster tips over and explodes. You can see debris arcing all over the place. Very dramatic! 

On Tuesday, SpaceX successfully launched a Falcon 9 rocket with a Dragon capsule loaded with supplies for the International Space Station. Astronaut Samantha Cristoforetti will grapple the capsule on Friday and berth it to the ISS.


The launch was also the second try at landing the first stage Falcon 9 booster on a floating barge in the Atlantic. The first attempt in January was almost successful, but the steering fins ran out of hydraulic fluid causing a spectacular crash-and-burn of the booster.

This second attempt nearly made it as well. The booster found the barge, and actually seems to have landed vertically, but came in with a little bit too much sideways motion, tipping it over.

The video stops just short of the booster heeling over and falling.

Mind you, this is still pretty good. Remember, no one has ever tried anything like this before during a launch, and almost everything went correctly. Clearly, of course, there are still a few things to be ironed out.

Elon Musk himself knows this. After the video came out, he tweeted this:

It’s always nice to treat oneself.

April 14 2015 11:15 AM

A Most Unusual Solar Eclipse Photo

Last month, the Moon passed in front of the Sun … if you happened to be in just the right place on our planet.

Not many were, but we still got some lovely photos of the event.

My friend Tunç Tezel was eyewitness to it, and he took a lot of photos. I posted one in the link above, which is a beautiful if straightforward shot of the totally eclipsed Sun. But then a few days ago he sent me a note saying he had a far more unusual one, and I must say: He’s absolutely right. Check this out!

April 14 2015 7:15 AM

What Kind of Object Can Survive a Close Encounter With a Monster Black Hole?

In or around May 2014, a truly remarkable thing happened: An object, dubbed G2, survived a very close encounter with a very large black hole.

The black hole in this case is the supermassive one in the center of our own galaxy, the Milky Way. Our best estimate of its mass is about 4.3 million times the mass of the Sun, so it’s a bruiser.


Using the largest optical and infrared telescopes in the world, astronomers can actually see the movements of stars orbiting the black hole. Its fierce gravity accelerates them so strongly that they have ridiculously high velocities. Over months and years, even from our vast distance of 26,000 light-years—260 quadrillion kilometers—from the black hole we can physically see their movement.

G2 was discovered a few years ago, and it wasn’t—and still isn’t—clear just what it is. It looks like a big cloud of dust, and it was on a trajectory that was predicted to take it only about 30 billion km from the black hole. That’s close enough that tides from the black hole were expected to tear G2 apart.

But it survived! This means it can’t be just a dust cloud; it must have a star embedded in it, and the star’s gravity held the dust cloud together. (In fact it’s more complicated than this; the star may be a binary. I did a BA Video on this very topic.)

New observations have now put some numbers, and a face, to G2. The image above is a composite of observations taken using the Very Large Telescope in Chile. Each blob is actually G2 seen at a different time; the yellow one is form 2006, then 2010, 2012, and the red one, right before peribothron (closest approach to the black hole*) in February 2014.

The last image, in blue, was taken in September 2014. It appears smeared out, but that apparently is not real but an instrumental effect from the telescope; the object itself doesn’t appear significantly extended.

The coloring is significant: It represents how fast G2 was moving away from Earth as it rounded the black hole (the colors were added later to represent red and blue shift). The velocity in February 2014 was away from us at about 2,700 km/sec, just under 1 percent the speed of light! In September it had rounded the black hole and was headed toward us at more than 3,300 km/sec, an incredible speed. I’ll note it’s so far away that even at that speed it would take millennia to reach Earth, and in fact it’s in a closed orbit around the black hole, so it’s not going anywhere anyway.

Here’s a video of the observations showing the movement of G2 around the black hole:

The astronomers were able to determine the orbital characteristics, too. It takes G2 about 260 years to go around the black hole once. The orbit is extremely elongated (for tech-types: the eccentricity is 0.976, nearly a parabola!) and takes it about 0.1 light-years—a trillion kilometers—out from the black hole before it begins its centurylong dive back in.

Interestingly, when I made the video and wrote about this object a few weeks ago, there was a thought that it used to be a binary star (two stars orbiting each other) that had merged into a single star after encountering the black hole. This would expel a lot of gas and dust, explaining the peculiar properties of the cloud. The astronomers in this newer study model it as a single star that is very young, and still drawing in (accreting) material from the cloud. What they find fits the observations decently well. We’ve gone from being baffled by this object to now having more than one good explanation for what it is! Hopefully, more observations over time will be able to figure out which of these two models is correct … or if neither is. That’s science.

And if you’ll indulge me a moment …

This image is amazing; it made the hairs on the back of my neck stand up. No joke: We are so good at what we do that we have built telescopes and detectors that can directly detect the motions of objects trillions of kilometers away! We can watch as another bizarre object is caught in the clutches of a black hole and forced into a tight orbit that takes it so close that it moves through space at a fraction of the speed of light itself.

This is what we do, we evolved apes. So many people pooh-pooh science for so many reasons, sometimes claiming other or higher sovereignty. But when I think on things like this, what we see and what we do, I can only shake my head and smile ruefully.

If you want to stare into the face of awesome, science is an excellent way to do it.

*Normally, a close encounter with a star or object like it would be called periastron. But this is a black hole, so this term peribothron is used; literally, close to the hole. Brian Koberlein at One Universe at a Time explains.

Correction, April 14, 2015, at 17:00 UTC: I originally misstated that the black hole was 260 trillion kilometers away. It’s actually 1,000 times farther than that: 260 quadrillion kilometers. Sorry if anyone panicked.

April 13 2015 11:30 AM

For Wyoming, Climate Change Is Now

Science itself has many laws, but it doesn’t give a damn about ours.

Those words still echo loudly when it comes to Wyoming. A new research paper has come out showing that snow melt in the northwest region of that state is occurring earlier all the time, exactly as you’d expect with warmer winters and spring.

The scientists used satellite data to measure snow extent over time and found that snow is melting 16 ± 10 days earlier in the 2000s compared with 1972–1999.

snow melt graph
Percent snow cover for a given day for the area in Wyoming studied. Note that in more recent years, snow melted earlier.

Graph via NASA Earth Observatory

This plot shows the amount of snow cover (vertical axis) over the day of year (horizontal). The red line is the average from 1972–1999, and the purple from 2000–2013. The purple line is lower, meaning that at the same time of year, there was less snow in the more recent measurements than there used to be. Snow is melting earlier.

That has profound consequences; state agriculture depends on that melt water. If the melt is happening earlier that implies there’s less time for snow to accumulate on the mountains there.

Less snowpack on mountains west of the Continental Divide means less water for the western states, where there is a monumental drought. If you think global warming and climate change are things that will only happen sometime in the nebulous future, think again. They’re happening now.

Some good news: Happily, the state Legislature in Wyoming managed to reach a compromise that should allow teaching good climate science in their public schools (hopefully). But there is still a provision for them to review specific educational standards, and there's still a passel of climate change deniers in office there. We'll have to see how this plays out.

And not to shock you, but both U.S. senators from Wyoming are Republicans, and both deny the impact of global warming. Mike Enzi confuses climate with weather (he’s not alone in that sort of ridiculous bluster, of course), and John Barrasso has a long list of attacks on the Environmental Protection Agency and the science of climate change.

We can’t make any progress on the real and potentially devastating effects of global warming until we have politicians who understand it and take it seriously. The good news is that more voters, even Republican voters, are saying that global warming is real. The bad news is that they don’t seem to care enough to act on it.

As water disappears from the west, and one heat wave after another settles in on various locations, as storms get worse and wildfires more damaging, it’s long past time we cared enough. Long past.

April 13 2015 7:00 AM

SpaceX Launch Today: Space Station Supplies and Another Booster Landing Attempt

UPDATE (Apr. 13, 2015 at 20:35 UTC): Today's launch was scrubbed due to weather; storm clouds got too close (10 nautical miles) from the launch pad. The next attempt will be tomorrow, Tuesday, April 14, at 20:10 UC (4:10 p.m. Eastern).

SpaceX is scheduled to launch a Falcon 9 rocket today at 20:33 UTC (4:33 p.m. Eastern) from Florida. The primary goal: Send a Dragon capsule loaded with two tons of supplies to the International Space Station. The secondary one: Land the first stage booster on a barge floating in the Atlantic Ocean.


First things first. If you want to watch the launch live, try the SpaceX webcast page, NASA’s Ustream channel, or NASA TV.

I suspect most people will be most interested in the booster landing attempt. The Falcon 9 rocket has two stages. Every kilo you send to orbit means you need fuel to lift it, so many rockets use staging to save fuel; the heavy bottom half is jettisoned at some point, carving a lot of weight off the rocket.

Usually the first stage is discarded; dropping into a watery grave in the ocean or burning up on re-entry. But SpaceX wants to save money by reusing that booster stage. The Falcon 9 booster saves just enough fuel to slow down after the initial launch (and the second stage is safely away). It then drops down, deploys fins on the bottom to help steer it, and—should all go well—lands vertically on a floating platform (technically, the autonomous spaceport drone ship; it has onboard computers that allow it to position itself under the returning booster automatically).

SpaceX tried this in January, with, um, less-than-perfect results. That was due to the fins running out of hydraulic fluid while the booster was still aloft, a shortcoming that has been corrected. This second attempt* will hopefully go better. Mind you, in that first attempt the booster slowed and descended correctly, the barge positioned itself, and everything went right except for the one (catastrophic) problem. Fixing that should go a long way to a successful landing.

If it works, it will be the first time in history a booster will have been recovered in this way.

SpaceX platform
Let's hope things go a bit better this time.

Photo by SpaceX

The main mission is to get a Dragon capsule to ISS. This mission, Commercial Resupply Service 6 (or just CRS-6), will deliver cargo and supplies to the crew on the station. One piece of hardware going up in the Dragon is the Arkyd 3 Reflight, a very small satellite by the company Planetary Resources that will test technology that will be used in future asteroid reconnaissance missions.

Right now, the weather for the afternoon is iffy. If the launch is scrubbed, a second attempt will be made Tuesday at 20:10 UTC (4:10 p.m. Eastern).

Incidentally, SpaceX recently released a bunch of super-hi-res footage of launches and landings from previous missions. It’s pretty cool. This should keep you sated until this next launch.

*Kinda sorta second, that is; during a February launch the ocean was too rough to land on the barge, so SpaceX landed the booster vertically in the ocean. I consider that a practice run.

April 12 2015 9:39 AM

The Last Days of MESSENGER

The MESSENGER Mercury probe is in the news again, this time for two somewhat related items. The spacecraft has been orbiting the closest planet to the Sun since March 2011, just over four years ago, and has been returning amazing data ever since.

It achieved a numerical milestone recently: its 4,000th orbit of the little world. In that time it’s sent over a quarter million images of Mercury back to Earth, an astonishing feat. Because Mercury is so close to the Sun, it’s hard to study from Earth, and it’s also difficult to get a spacecraft into orbit. Mariner 10 flew past the planet in the 1970s, but MESSENGER was first to orbit Mercury—after three flybys, and a gravity assist from both Earth (once) and Venus (twice).


And it comes just in time. MESSENGER is doomed. Because Mercury is so close to the Sun (about 58 million kilometers), the Sun’s gravity pokes at MESSENGER, changing its orbit. It uses hydrazine propellant to alter its orbit, but it's out of fuel. The last orbital maneuver on April 6 used up the remaining hydrazine in its tanks. All that's left is helium (used to keep the tanks pressurized); that can be used as a propellant, but it's not terribly efficient. A few more "burns" are planned to raise its minimum distance above the surface, but they will only add a bit of time to MESSENGER's life. It's not clear when exactly, but sometime in late April or early May the probe is expected to crash into the planet’s surface.

This is inevitable, and was understood by the scientists and engineers on the team even during mission planning. They even are taking advantage of it! MESSENGER has been getting as low as 13 to 17 km from the surface, and the adjustments have kept that distance from 39 to as low as an astonishing 5 km above Mercury. The images taken during this time will be the highest resolution of the mission.

It’s been a great four years, filled with exciting new discoveries and gorgeous pictures of Mercury. I’m glad to see that the team is squeezing every last drop of science they can from the mission before the end. 

April 11 2015 7:30 AM

April Is Global Astronomy Month

If you love astronomy, do I have a month for you.

April is Global Astronomy Month, an informal but planetwide celebration put together by Astronomers Without Borders, a wonderful group that promotes astronomy worldwide. Among its many projects it built a science center in Tanzania that will help teach children there about the Universe, set up an artist residency program, developed community programs, and more.


GAM is a way to bring everyone together across the planet and show them the sky. It’s organizing a lot of events, including:

And much more. It put together a nice little introductory video for the month:

I think this is a great idea. The sky belongs to all of us, everywhere, and we’re a part of it. Why not take a few nights this month and help prove it?