Bad Astronomy Blog
Aysun Ülger is, like me, someone who loves atmospheric optical phenomena. Halos, glories, aurorae, iridescent clouds … so much so she created a Facebook page where she collects such photos. She just started it, but there are already a few lovely examples there.
And this includes, of course, rainbows. Since I just wrote about that very cool quadruple rainbow in New York, I thought I’d follow up with an example of a fun series of photos Ülger took herself in Izmir, Turkey: a rainbow rising as the Sun set!
Those were all taken on the same day, April 6, 2015, except for the bottom one, which she included in the series to show just how high a rainbow can get. In order (top to bottom), they were taken at 3:41, 3:50, 4:24, 4:50, 5:21, and 6:11 pm. The bottom one was taken at 5:58 pm on March 28. But due to a local time change, it corresponds to 6:58 on the later date.
As I’ve written about many times, rainbows appear in the sky opposite the Sun—to see one, you have to stand with the Sun behind you. That’s because the light from the Sun bends inside the raindrop and is reflected on the drop’s backside, back toward the Sun. But not exactly: The light leaves the drop at an angle of about 138°. Only drops 42° away from the point in the sky directly opposite the Sun send that light toward you (180°–138°).
Also, the colors that make up the Sun’s white light get bent by slightly different amounts, spreading them out across the bow.
Since the arc of the rainbow is centered on the point on the sky directly opposite the Sun, a low Sun means a high rainbow, and a high Sun means a low rainbow. As Ülger waited, the Sun set, so the rainbow got higher. You can even see a double rainbow (called the secondary) and Alexander’s dark band, the darker region between the two bows.
Too bad she couldn’t get a time lapse of this! But she did point me to this one, which shows the increasing (more vertical) angle of the base of a very bright rainbow as the Sun lowers.
We get extremely bright rainbows in Colorado in the spring and summer, once afternoon rain showers clear out. They tend not to last very long, but still, next time I see one I’ll have to try getting a time lapse of it. That’ll be a fun project.
On Thursday, April 23, 2015, the 14th episode of Crash Course Astronomy went live. It’s about our sister planet Venus, and I spent quite a bit of time talking about just how infernally inhospitable it is.
Just as I have with every other episode, I had a lot of fun writing and recording it. A little background: Once we finish getting the footage of me talking, it’s edited and sent around to the team for comments. I then scour the ‘net looking for good images we can use, usually from NASA, ESA, and other public organizations (they have excellent high-resolution images which are free to use). Those images (and sometimes video) are placed in the rough cut, and then it goes off to Thought Café, who does our animations.
Eventually it goes live on YouTube, posted around 3:00 p.m. Mountain Time every Thursday. We promote it, and keep an eye on the YouTube comments for anything useful (did we make a factual error, is the audio good, and so on).
For the Venus episode on April 23 I was in Utah giving a talk at Clark Planetarium. When I got back that evening I checked to make sure the video was up, linked to it for a blog post first thing Friday morning, and then went to bed.
I was out of contact for much of Friday, traveling home. When I landed, though, there was a text from my editor that there was a problem.
If you’ve watched Crash Course Astronomy, you know I like to make jokes, and sometimes I’m the butt of them. The team goes along with it, and it’s usually great. This time, though, we made a mistake without even knowing it.
In one part of the episode, I’m talking about how Venus is really pretty when you look at it from Earth, but up close, it’s an awful place. As I spoke about Venus being pretty, we put up a cute animation of Botticelli’s famous “Birth of Venus”. But then, when I say Venus up close is awful (and say, "Yikes!"), we zoom in on the drawing and it turns out Venus has my face on it.
I thought this was pretty funny, a bit of humor poking fun at me. So we okayed it.
Well, it turns out that wasn’t so OK and funny with a lot of viewers. We got some comments that the joke was transphobic, making fun of transgender people.
That’s why my editor had texted me. I called her, and she told me what had happened. As soon as she told me, I had a forehead-slapping moment. Of course this could be seen as transphobic. In retrospect it was obvious. The good news is that the team felt the same way, and had already re-edited the video to remove that part, and had re-uploaded it before I had even called.
Let me be clear: I apologize for myself and on behalf of the team to anyone offended by the joke. None of us would knowingly make a joke at the expense of a group of people, especially one already marginalized and so often mocked in society. That wasn’t at all the intent, and it didn't occur to us it could be seen that way when we put it together. I hope you forgive us, and we’ll try to do better in the future.
Unfortunately, there’s more. In the comments to the (re-uploaded) video, some people are complaining that we are under the thumb of the PC crowd, and the phrase “social justice warrior” is used derisively. Let me address those commenters now:
You’re wrong. First, it’s not up to you to decide what offends or does not offend a group of people you are not a part of. You may feel that this was not an offensive joke, and you are welcome to that opinion; certainly the joke wasn’t intended that way.
But what you don’t get to decide is what offends others, especially in a group you’re not a part of. You may think that offense is undeserved, or that they are overreacting. You have the right to think that, but you cannot dictate it to those others.
Even if there was no harm meant in the joke, people may still take offense at it, and that’s their right. In this case, I can easily see where transgender folks would be put off by it, even angered.
And here’s the important bit: Apologizing and changing it does no harm, and in fact does some good; it helps a group of people see that we can be sensitive to their needs.
There are times when I think people are too sensitive, and times I think others aren’t sensitive enough. I tend to judge these on a case by case basis. But with a group that is historically marginalized and “othered”, well, a little (extra) empathy does a soul good.
And for the other bit, people derisively calling us “social justice warriors”? They may use it as a derogatory term, thinking of SJWs as shrill and overbearing, but to me it’s a term that refers to people willing to go to bat for others who don’t have as big a soapbox. I might prefer the term “ally”, but SJW fits fine, too. This world could use a lot more social justice. I’ll be happy to fight for it when I can.
So to them I say: “Thanks!”
There but for the grace of physics goes us: Venus, second rock from the Sun, could be said to be Earth’s twin… but it’s the evil one.
Find out why on this week’s episode of Crash Course Astronomy!
I love the fact that you can learn all about Venus in this week’s episode, and then go outside after sunset and see it for yourself, shining brilliantly in the west. It’ll be close and bright for the next few months, actually, so you’ll have plenty of chances to see it. And in July it’ll start to show its crescent phase even in binoculars. That’s really something, and I hope y’all go out and take a look.
Let’s start this off by being very clear: Vaccines don’t cause autism.
They just don’t. Perhaps I should be scientific, careful, technical, and say that no connection between vaccines and autism has ever been found. That’s technically true, because, after all, there is some incredibly small chance that eventually perhaps some connection might possibly be found. But when study after study after study show no such connection whatsoever, at some point it’s probably OK to close the door on this.
Now it’s time to slam it shut. A new study, reported in the prestigious Journal of the American Medical Association, looked at a group of over 95,000 children and found no connection between the Measles-Mumps-Rubella vaccine and incidence of autism.
Specifically, they looked at children who had older siblings, looking at the rate of diagnoses of autism spectrum disorder and vaccination. The study is pretty interesting, and I suggest you read it, but the results are pretty clear, as the researchers themselves write: “MMR vaccine receipt was not associated with an increased risk of ASD at any age.”
Emphasis mine, but c’mon. That’s emphatic.
Mind you, younger siblings who have an older sibling diagnosed with ASD are themselves at a higher risk for it (likely due to genetic factors). Despite this, the researchers conclude:These findings indicate no harmful association between MMR vaccine receipt and ASD even among children already at higher risk for ASD.
In other words, the MMR vaccine is not associated with autism.
Mind you, the entire modern anti-vax movement is based on the idea that the MMR vaccine somehow causes autism; that was the conclusion drawn by Andrew Wakefield in a paper published in the British journal the Lancet… a paper that was retracted, that had several of Wakefield’s team members asking to have their names removed from it, that established a clear conflict of interest for Wakefield who stood to make hundreds of millions of dollars replacing an MMR vaccine with his own alternative, and which prompted the BMJ to call Wakefield’s methods “fraudulent”.
Yeah, that paper.
This new study is getting some press, which is nice, but I’m seeing here and there some folks hoping this will be the last nail in the anti-vax movement. It won’t be. That’s because the anti-vaxxers are not basing their decisions on science, they’re basing them on emotion. We’ve seen this over and again; as I pointed out before, this isn’t the first study showing no link between vaccines and autism.
People simply don’t make decisions based on facts. That’s not how we’re wired. Fear is an incredibly strong motivator, and many of the anti-vax groups use it to their advantage. Look at the truly atrocious Australian Vaccination Skeptic Network, who actually and truly compare vaccination to sexual assault (and seriously, survivors of such assaults may want to have a care clicking that link; the AVSN graphic is abhorrent and brutal).
And look no further than someone like Robert F. Kennedy Jr., who believes that vaccines cause autism, and compared this to the Holocaust. Yes, the Holocaust. He backed off that analogy when called out on it, yet few seem to remember this isn’t the first time he’s made this despicable claim. I’ve written about Kennedy before, taking him to task on his unfounded claims, and wrote a follow-up after he doubled down on it.
So yeah. The folks who beat the drums about vaccines and autism will never stop. My hope is that they will eventually be marginalized, like Moon Hoax believers.
The good news is that action is being taken. California is looking at stricter rules for parents who want to opt out of vaccinating their children, for example, and in Australia, the religious exemption is being removed.
And of course the forces of good are still at work, promoting vaccination. The Bill and Melinda Gates Foundation has put out a lovely campaign using art to show how important vaccines are. Called The Art of Saving a Life, it features works of film, literature, music, photography, and more.
As someone who loves classical music, especially Debussy, one video in particular struck me. Called Afternoon of a Faun, it’s a powerful piece about Tanaquil LeClercq, principal dancer at the New York City ballet. Before a European tour in 1956, she declined getting a polio vaccine. She contracted polio in Copenhagen, and became paralyzed. She never danced again. Chinese pianist Lang Lang performs the pas de deux from Debussy’s Afternoon of a Faun, with images of LeClercq in the background.
I would like to personally thank Mr. and Mrs. Gates for supporting this project. It is extraordinarily difficult to discuss this topic with people who lean towards being against vaccinations, and it’s all too easy to reinforce their beliefs. I think that by continually putting forth a positive message, together with presenting the facts, we can get vaccination rates in this country up to where they need to be to protect us all.
As a father myself, and with an immunocompromised family member, I know how important this is. When you get vaccinated, the life you save may be your own, and it may also be someone you know and love. But it may very well be someone you don’t know, but who is loved by others.
To those of you who vaccinate: I thank you too.
On April 25, 1990, the world—the Universe—changed.
That was the day the crew of STS-31 deployed the Hubble Space Telescope into orbit. This magnificent observatory has a special place in my heart. When it launched I was in graduate school in astronomy, and had just received my master’s degree. I was looking for Ph.D. research, and my adviser mentioned he was on a project to use Hubble to observe exploding stars … and now, 25 years later this week, Hubble is still going strong, doing astronomy.
And in my way, I am too.
I worked on Hubble one way or another for a decade, including being on a team that built one of the cameras that was installed on Hubble in 1997. I’ve written so much about Hubble over the past 2½ decades I don’t think there’s much more I can say about it. At the bottom of this post there are links to some of my favorite articles.
But I can still show you pictures.
The sheer amount of science Hubble has done is stunning, but of course most people know it because of the gorgeous imagery it’s provided for a quarter-century. That’s no shock, and that’s just fine in my book. People need to know more about the Universe in which they live, and if Hubble is that gateway, who am I to complain?
So let me show you what Hubble’s best at: spectacular, mind-expanding and brain-melting pictures. I was going to choose 25, but I feared Slate’s servers would burst into flame, so instead I picked 12½. Why that? Well, it’s 25 / 2, and it turns out I have a picture that kinda sorta qualifies as the ½. You’ll see.
So here, let your eyes soak up the majesty of the Universe, and fill your brain with the joy of astronomical discovery.
Heavenly Chess Piece
Just below Orion’s belt is the star Sigma Orionis, well over 1,000 light-years from Earth. It’s actually a pentuple star, a five-star system, blasting out as much light as 75,000 Suns! It illuminates and heats a ridge of hydrogen gas nearby, and the famous Horsehead Nebula is a thick cloud of colder gas and dust silhouetted against it, deep black in normal images.
But using infrared cameras, Hubble sees light coming from inside the dust cloud, bringing out details within it. All those towers pointing up—and even the head of the horse itself—are illuminated from above by Sigma Ori, and in fact are being dissolved by its intense radiation. Like so many things in the Universe, we’re getting a snapshot of a beautiful object that is ephemeral; this too shall pass. However, the Horsehead is the site of ongoing star formation, so while the cocoon will eventually dissolve, the stars will live on for millions and even billion of years.
When Galaxies Collide
In the 1960s, astronomer Halton Arp catalogued more than 300 oddly shaped galaxies, many of which are interacting pairs, behemoths distorting each other through their mutual gravity. Many are physically colliding, dancing an eons-long performance that will end with them merging into one much larger galaxy.
Arp 273 is just such a pair, 300 million light-years from Earth. The smaller one may have actually passed through the larger one, suffering tremendous distortion as it did so; gas clouds slamming into each other has triggered a burst of star formation in it. The bigger of the pair was also affected; the spiral arms are off-kilter and asymmetric, a common reaction to the violent encounter.
Both have retained their overall spiral shape, but if they fall back together, that may be lost. But for now, and the next few million years at least, they provide this lovely sight.
Ring Around the Supernova
As I mentioned, I used Hubble for my Ph.D. work. Specifically, I studied the star Sanduleak -69 202, which exploded and became Supernova 1987A. To be honest, I studied the ring of gas surrounding the star, lit up by the explosion. To me, the supernova was just the Universe’s biggest flashbulb, illuminating the stuff I really wanted to see.
At the time, no other ring like it has ever been seen. The formation mechanism is still a mystery (though we’re learning more about it all the time). The two outer rings are much thinner and an even bigger mystery. This image was taken in December 2006, when the shock wave from the explosion was finally starting to hit the clumpy inner ring. Knots of denser material lit up, making it look like a string of luminescent pearls. You can even see the expanding debris from the supernova inside the ring, elongated into a fishlike shape. That material, moving at several thousand kilometers per second, will eventually slam into the ring as well … and then we’ll see some real fireworks.
Going Very, Very Deep
Hubble isn’t a particularly large telescope, with a 2.4 meter mirror. What makes it special is that it’s in orbit, above our atmosphere that glows faintly (hiding faint objects) and blurs out smaller details. So when you take Hubble and point it at one patch of sky accumulating photons, what you get is sheer awesomeness: the Hubble Extreme Deep Field, a stunning mosaic made up of 2,000 separate images for a total exposure time of 2 million seconds, over three weeks!
Gaze upon that picture, let your eyes wander. With only a few exceptions, every single object in that field is an entire galaxy, a mighty collection of billions or hundreds of billions of stars! Thousands can be seen here, yet this patch of sky is so tiny you could easily cover it many times over with the tip of your pinky at arm’s length. The Universe is vast and terrifying and magnificent beyond our ability to properly express.
Some of those galaxies are more than 10 billion light-years away, and you see them as they were when the Universe was young. This image is a huge boon to astronomers studying the nature of the cosmos, but you don’t need to be a professional scientist to be overawed by it. If this doesn’t give you a chill, check your pulse. You may be dead.
Of all the images Hubble has taken in 25 years, I sometimes think that V838 Monocerotis is the oddest. This star underwent an epic eruption, blasting out a huge cloud of dust that has expanded visibly over the years. It’s thought that the cause was the merger of two stars orbiting each other; they spiraled in and then physically consumed each other, forming a single (highly unstable) star, which then erupted.
The cloud expanded so rapidly the change can be seen over just a few years, and this time-lapse shows that happening (with some interpolation between images to make the expansion smoother).
Incredible; we usually don’t get to see change on such short time scales in astronomy, but happily Hubble has revealed it in this case … with the help of expert astrophotographer Robert Colombari, who remastered this amazing shot.
When I was young, hauling my telescope to the end of the driveway to observe the heavens, one of my favorite targets was M15, a globular cluster: A more-or-less spherical cloud of stars about 30,000 light-years away in the constellation of Pegasus. I could easily see hundreds of stars in it … but it has a hundred thousand stars in it, as this Hubble image gloriously reveals.
It’s more than 12 billion years old, an ancient stellar city, and many of its stars have exploded or faded away in old age. There’s even a planetary nebula in it (see the Ring Nebula and NGC 6302 entries below), which you can see as a blue glow to the left of center; that’s a dying star casting off its outer layers, much as the Sun will do six or seven billion years from now.
The Wings of a Butterfly
When stars die, they do not go gently into that good night. Some explode, like Supernova 87A, while stars more like the Sun blow off their outer layers in episodic winds. When these winds of gas collide, they light up, creating breathtaking planetary nebulae. NGC 6302 is a lovely example of such a beast.
Nicknamed the Butterfly Nebula, it has a thick torus of dust around its equator, and two vast lobes of material racing away from the center. Studies of NGC 6302 were able to physically see the gas expanding over the several years that elapsed between subsequent Hubble images, allowing the age of the object: The lobes were ejected rapidly about 2,200 years ago at speeds of hundreds of kilometers per second, while the dusty ring was blown out over a longer period of time that ended shortly before the lobes formed.
It’s odd to think that such beauty is created by the death of a star, but astronomy is loaded with such ironies. Just read about the next object, the Crab Nebula …
The Crab Nebula is one of the most ridiculously fantastic objects in the sky: The rapidly expanding debris from a star that blew itself to bits a millennium ago. Octillions of tons of gas blasted away from the shredded star at an appreciable fraction of the speed of light, and now the remnant (as it’s called) is six light-years across, 600 trillion kilometers.
In this phenomenal Hubble image (using images combined with those from the Very Large Telescope), the different colors represent different elements in the gas. Blue is warm oxygen, red is oxygen that is even warmer (technically, the oxygen is in a higher energy state, what astronomers call “more excited”), and green is sulfur.
Even though it’s 6,500 light-years away, it’s been observed for so long, and the debris expanding so rapidly, that over time the blobs have actually been seen to move. You can use that to calculate the expansion speed of the gas, and even how old it is! For my old job I wrote an educational activity for students to do just that, too.
Pillars of Astronomy
If there is one Hubble picture that stands above the rest, the single most iconic portrait of a celestial object perhaps ever, then it would be the Eagle Nebula, or M 16.
You may know it as the Pillars of Creation.
The name is apt. Each of these three “elephant trunks” is light years long; the biggest is almost 10 light-years stem to stern, nearly 100 trillion kilometers. All three have dense knots of gas and dust at their tips; the ultraviolet light from stars above them are eating away at them, and they protect the material “downstream”, like water flowing around a rock creating a sandbar. The knots are also forming new stars, so again the name is a good one.
The original version of this was taken by my pal Jeff Hester in 1995, and this new version was taken in 2014, after better cameras were installed on Hubble by later Shuttle missions. The detail is stunning, and in fact changes over the two decades (!) between the two images shows the nebula has changed; the material being sculpted by the stars.
And it’s due for a big change: Spitzer Space Telescope data suggest a supernova went off inside the Eagle, and the shock wave will wipe out the Pillars in the next few thousand years. Sic transit gloria aquila.
Jetting Across the Sky
There are times I see a Hubble image and my jaw drops open. This is one of ‘em. This is a shot of a star-forming region in the vast and sprawling Carina Nebula, one of the largest in our galaxy. Like the Pillars of Creation, these are huge towers of gas and dust actively forming stars, the material being blow back by the fierce light of massive stars off the edge of the field of view here.
But in this case we’re a little farther along in the process: the stars at the tips of these pillars have already been born. They still have a disk of material swirling around them, and complex magnetic fields. This all combines to blast material away from the stars along their axes; twin jets of matter that slams into the surrounding material and lights up. As the towers erode—you can see the gas streaming away from them in fine tendrils—they will reveal the newly born stars. The jet phenomenon only lasts a few thousand years, the blink of a cosmic eye, but is revealed in stunning detail by Hubble.
Galaxy on the Edge
I love a sprawling, majestic spiral galaxy, its arms flung wide, dotted with pink clumps of star-forming gas clouds.
But then there’s the Sombrero Galaxy: A very nearly edge-on spiral, located about 30 million light-years away. At this low angle, the dust lanes stand out as its most striking and even its characterizing feature. The patchy spiral arms take on a more subtle appearance, and the huge spherical halo of stars surrounding its core add the final touch to its magical appearance.
Interestingly, it’s smaller than our Milky Way, only 50,000 light-years across (we’re more than twice that broad), yet it’s estimated to have more than three times the mass of our galaxy.
And hmmm … although we see the Sombrero edge-on, from there the Milky Way is seen at about a 45° angle. That would be awe-inspiring. I’m not sure who gets the better part of this deal.
One of my favorite kind of Hubble image is where it observes a target with which I’m familiar from my own nights outside with my ‘scope. The Ring Nebula is a staple in any astronomer’s observing; it’s easy to find and a delightful object. It looks like a pale, ghostly smoke ring in the sky.
… until you point a space telescope at it, at least. Then the incredible detail is revealed (caveat: the Hubble images were combined with those of the ground-based Large Binocular Telescope to create this picture). The Ring is another planetary nebula, a collision between winds cast blown off by a dying star. It was always thought to be a spherical shell because it’s so circular, but the Hubble observations proved it isn’t. See the little dark blobs all around the yellow and green parts? If the Ring were a sphere, they’d be distributed throughout, including across the middle. They’re not, which shows we’re looking down the long axis of a barrel-shaped object.
Those radial spikes are real, too: They’re rays of light from the central star that are let through between dark, dense blobs of material, just like rays from the setting Sun!
Hubble’s Day in the Sun
So I promised 12½ pictures, and here you go: That shot above is the last thing you’d ever expect Hubble to photograph: the Sun.
It’s true … kinda (hence the half credit). The kind of digital detectors originally used on Hubble’s main camera would get electrons trapped in them, which needed to be cleaned off. A blast of ultraviolet light does that well, and the Sun is a very bright UV source. Hubble isn’t allowed to point anywhere near the Sun, so the team came up with an unusual solution: Mount a small mirror that stuck up out of the telescope’s main body. Pointing backward, they’d aim Hubble directly away from the Sun, allowing sunlight to pour into the small periscope and into the detectors.
It worked wonderfully, and the images they made were assembled into that mosaic. That’s nuts, but hey, whatever works, right? You can read the whole story at my friend Glenn Schneider’s website. He actually assembled that image.
One last note
Many of the photos you see by Hubble were processed and created by my old friend Zolt Levay, a master at taking the noisy, messy data from the telescope and turning them into artistic masterpieces. He has just published book of Hubble images called Expanding Universe, and it is truly extraordinary. If you love these pictures, you need this book.
- Andromeda (yeah, you really want to click that)
- Why I’m Watching the Hubble Pairs So Intently (my history with Hubble)
- Epic Tantrum Thrown by a 30 Octillion Ton Baby
- Happy 20th Anniversary, Hubble!
- Hubble. Is. Back.
- Bruce Woodgate
- A Story Involving Me, Hubble, and the Late Astronomer Brian Marsden
- Hubble’s 15th Anniversary
- Oh, just search my blog for “Hubble”
I got some folks asking me if it’s real, and my immediate reaction is: Yup. Seriously, this doesn’t look faked to me, because I’ve seen this sort of thing before.
Double rainbows are fairly common (despite the meme). I’ve seen dozens of them; they’re caused when the sunlight hitting raindrops is particularly bright. The primary rainbow (the one you usually see) can be blazing, and you get a fainter but sometimes still quite bright secondary outside it, with the colors reversed. The primary forms when light is reflected inside a water drop once; the double is when the light’s reflected twice in each drop.
So why are there four rainbows? The angle of the weirder, more vertical bows is what gives it away. If the light forming rainbows reflects off a body of water (say, a lake, pond, or even standing water on a road), you get another set of rainbows cast at a different angle. I’ve never seen this myself, but there are plenty of pictures of it online.
So the picture is real! One thing I’ll add is that I think the colors have been enhanced; they’re a bit too garish to be real. But lots of phones do that, and of course people use filters when posting pictures all the time. But physically, yes, it’s real.
There you go. And it proves, once again, that you should heed my advice: Always look up. You never know what’s going on above your head.
In 2008, the nearby star HR 8799 earned a place in the history books: It was the first star orbited by multiple planets directly seen in photographs. This was quite an accomplishment; stars are billions of times brighter than planets, so getting actual direct images of the planets is incredibly difficult. And here, orbiting this star, four have been discovered!
In the years since, the system has been extensively studied, but it’s still difficult. That’s why a team of astronomers created LEECH—the Large Binocular Telescope Exozodi Exoplanet Common Hunt.* This system is optimized to look at the exoplanets around nearby stars and create a base of observations from a single telescope and camera. Most exoplanets are observed by different telescopes, which introduces uncertainties when you try to compare the observations. Using LEECH should reduce that considerably.
I wrote about this, and the conclusions about the HR 8799 system found, in my biweekly column for Sen.com. It’s subscription only, but for about the cost of a magazine subscription you get a lot of good stuff. And, of course, there’s a ton of free content on the site as well. You should check it out.
*"Exozodi" refers to zodical light, the glow due to dust orbiting stars. This happens in our own solar system, and can be seen from exceptionally dark sites.
Right now, two planets dominate the sky after sunset: Venus in the west, and Jupiter high to the south. Both are amazingly bright, clearly ruling their areas of the sky. Both planets are also in parts of their orbits where they’re relatively close to Earth, providing excellent viewing opportunities.
Danish “amateur” astronomer (and frequent BA contributor) Emil Kraaikamp took full advantage of this, using his custom-made 40 cm Dobsonian telescope to take images of the planets that are simply and truly jaw-dropping.
First, Jupiter, as seen on April 6, 2015:
Holy wow! The detail is extraordinary. This kind of image is made in a very clever way: using video to maximize the clarity. Our atmosphere roils overhead, blurring out the small details on very short timescales. Taking even a 0.1 second exposure means losing resolution.
But by taking thousands of much faster video frames, the images are sharper. Then, software can pick out the sharpest details in each frame, and assemble them like a jigsaw puzzle to put together a mosaic of the full image. The results are, clearly, stunning!
I was astonished to see the detail on Io, the moon you can see on the right (and that’s casting its shadow on Jupiter’s cloudtops, too). If you look carefully you can see some surface features on the moon, which is pretty amazing considering it’s about the same size as our Moon and was over 700 million km away when this shot was taken!
Kraaikamp also got images of Jupiter’s huge moon Ganymede, and saw amazing detail on it:
On the left is his final video frame stack, and on the right a simulated view using space probe imagery, scaled to the same size. As you can see, quite a bit of detail is discernible. I’ll note that Ganymede is bigger than Mercury (and almost as big as Mars), but that does nothing to mitigate how cool this picture is.
But even then, the most amazing thing he sent me was this picture of Venus he took on the same night. I could scarcely believe it:
Venus is famous for having almost no features visible; the planet is enshrouded in thick, featureless clouds. The only way to see details at all is to look in the ultraviolet… which is what Kraaikamp did.
Material in the clouds absorb ultraviolet instead of just reflecting it all away like they do with visible light. This reveals features in the top of Venus’s ridiculously thick atmosphere, including wind patterns. Kraaikamp has many such images of Venus on his site. Go look, and check out his Jupiter pix, too (especially this animation).
In fact, take a moment and just peruse his whole site. He has a ton of great photos there.
In the Mexican state of Colima there lies an active volcano. Actually, Mexico is lousy with volcanoes, but this one has been doing more than its share of rumbling and grumbling lately.
Photographer César Cantú went to the Colima volcano to photograph it recently, and what he got was way more than he hoped for: Huge lightning discharges blasting through the ash cloud! This type of event is well-known, but not terribly well-understood. I do love a scientific mystery, which is why this event (and a time-lapse Cantú made) is the subject of this week’s Bad Astronomy Video.
A funny note, too: The other day, on Twitter a friend of mine posted a picture of the lightning in the ash cloud. But it was credited to someone else: Hernando Rivera Cervantes! I immediately wondered if there was a bit of picture pilfering going on, so I sent a note to Cantú via his Facebook page. He replied back almost immediately: Cervantes is a fellow photographer, and was in fact standing next to Cantú taking pictures at the same time.
It wasn’t plagiarism. It was essentially the same photo taken by two different people! I wasn’t expecting that. But I’m glad no one was trying to get credit for Cantú’s photo.
Speaking of which, I’ll soon be back at Mauna Kea in Hawaii, very near the lip of the Halema’uma’u vent. While I certainly don’t think we’ll see lightning (it’s venting sulfur dioxide, not ash), I can hope to take some more shots of the lava pit illuminating the plume. Volcanoes don't have to be disastrously dramatic to be exceptionally enthralling.
On September 14 – 20, come to Hawaii to soak up some science at Science Luau 2015!
I’m pretty excited about this. My wife Marcella and I run a company called Science Getaways, where we take normal vacations and make them awesome by adding science. We’ve had many awesome trips over the past few years, and we decided it’s time to up the ante.
And up it we did. Hawaii was the obvious choice; the Big Island has a lot to offer for a week of fun and relaxation, and Science Luau will be equal parts tropical paradise and sciencey goodness.
We’ll go night snorkeling with manta rays, tour a family-owned coffee farm*, hike around the active Kilauea volcano (and stay after dark to watch the lava illuminate the gas plume billowing out of the Halema’uma’u vent — yeah, click that link), and take an optional trip to the Mauna Kea summit to watch the Sun set from over 4,200 meters above the Pacific. After that we’ll drive down to the visitor’s center (at about 3,000 meters) to star gaze, of course! No Science Getaway is complete without that. And my favorite part: We’ll visit a seahorse farm where they’re working to keep the critters from going extinct. You’ll even get to hold one underwater; that’ll be an experience you won’t forget.
We’ll be staying at the luxurious Fairmont Orchid hotel on the west side of the island, right on the Kohala coast. And because we’re doing this during the off-season, the hotel and beaches are likely to be relatively quiet, giving us a cozier feel to the event. We also got very good group rates for the hotel, so if you’ve ever wanted to visit the area this is the way to do it.
Best of all, you’ll be spending a week with like-minded nerds† sharing all this beauty and wonder. We’re always amazed at how many friendships blossom from these Getaways. It’s really wonderful.
For details, go to the Science Luau 2015 page. I hope to see you there! Mahalo!
* Ask any professional: Science runs on coffee.
†I’ll note that Science Luau starts right after HawaiiCon, the island’s only and very fun science fiction convention. I went last year and had a great time; we are not affiliated with each other in any way, but I figure if you’re interested in the Luau, HawaiiCon might geek you out as well.
It’s fun to look out an airplane window at night and try to identify stars above and cities below. But I’ve never had as good a view as this:
That time-lapse video is by Paul Williams, a systems designer based in London. He flies to San Francisco many times a year, and the shortest route takes him over northern Canada (it may not seem like it should at first, but check out the geometry of great circles; this may help too). Armed with a Canon 6D and a small, flexible tripod he can attach to his backpack, he took 1200 photos out the window to create that animation.
He’s done this many times, and I’ve written about his work before. I like this video, too, since it shows a reddish/purple tinge to the light, caused by nitrogen and oxygen molecules in the upper atmosphere getting slammed by subatomic particles from the Sun.
And because why not, here's some footage from "skydivephil" showing the aurorae from Iceland... in real time. It's amazing how quickly they can move. Make sure watch to the very end for a surprise (which was shot in Lapland).
I have a page with tons of links all about what causes aurorae, why they get the colors they do, and more. Lots of fun science there. And of course, watch more of Williams’ videos and check out his Flickr page, too. The aurora season is far from over, so there may be more lights in the sky to come.
And if you’re on a night flight, grab a window seat. Who knows what you’ll see?
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.
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:
That’s phenomenal! These images were taken on April 10 from a distance of 33,000 km, 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.
Why is Elon Musk so hell-bent 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 X.com (and now Solar City 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.
Hanging from the high ceiling is the actual first Dragon capsule to be sent into orbit, scorch marks from its atmospheric reentry 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 lay 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, 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 multi-planet 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.”
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 scifi 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, on 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 multi-planet 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 as 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.
Post Script: 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.
Yesterday (Tuesday, April 14, 2015), 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.
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!
That shot is a mosaic of eight photos taken rapid-fire in just 41 seconds, which he then seamlessly stitched together into a single 360° view.
The Sun is near the bottom, the black circle of the perfectly new Moon blocking it, allowing the Sun’s faint corona to shine through. To the left you can see Venus, and other stars are visible as well.
Tunç was in Longyearbyen, Svalbard (an island technically part of Norway, but substantially north of it at 78° latitude). I can’t even imagine what he went through to get there, set up, and take these shots, but from my warm desk in Colorado, I say, “Thanks!” He has a lot more photos of the sky he's posted on The World At Night website, and I highly recommend you take a look. He's good.
In or around May of 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 trillion 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 2700 km/sec, just under 1 percent the speed of light! In September it had rounded the black hole and was headed toward us at over 3300 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 century-long 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 poopoo 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.
In 2014, I wrote about the Wyoming state Legislature actively moving to suppress real science education when it came to global warming. As I said,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.
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.
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.
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 in reentry. 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—land 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.
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 tomorrow, 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.
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 4000th 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 km), 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.