Bad Astronomy
The entire universe in blog form

Feb. 28 2017 9:54 AM

The Daily Show’s Roy Wood Jr. Knows Exactly How Moonlight Won Best Picture: “Peak Blackness”

“What in the living fuck happened at the Oscars?” A shocked Trevor Noah posed this question to Daily Show correspondent Roy Wood Jr., who provided a simple but convincing explanation. “Peak blackness,” Wood explained, a “rare metaphysical anomaly that can only occur when an amalgam of black excellence comes together at the same societal intersection.” Sunday night’s awards ceremony, he said, was the culmination of Black History Month, Beyoncé’s pregnancy announcement, and the apparent zombification of Frederick Douglass. Of course Moonlight was headed for victory.

But what was the biggest sign of triumph? It’d have to be Gary, the Windy City tourist unwittingly thrust into the center of Hollywood’s biggest night. “You knew Moonlight was winning,” Wood Jr. said. “Because a brother from Chicago was taking selfies and touching people’s trophies.”

Jan. 31 2017 8:45 AM

All Good Things

We’re all stories in the end. Just make it a good one.
          —The Doctor

On Nov. 12, 2012, I posted my first blog article for Slate. This article you are reading right now is my last.


After 1,541 days and more than 3,000 articles, I’m moving on. Starting Wednesday, I will be writing at my new blog home: Syfy Wire.

I know, this may seem like an odd jump, but it actually makes perfect sense. Syfy Wire (formerly Blastr) has always been a news outlet for science fiction, but Syfy has made a solid commitment to expanding its coverage to everything the genre encompasses. And what’s the first word in science fiction, eh? Science, technology, social issues … these are the foundational aspects of great science fiction, and issues about which I’ve been writing for years. Perhaps you’ve noticed. So I’m happy to communicate the real-world aspects that happen to tie into fiction.

I’ve written many times how science fiction has inspired me and so many other scientists. It’s a natural fit for me—and a lovely way of coming full circle—to be able to give back to the genre and tie it together with real life. Much of the science fiction of today is the reality of tomorrow.

If you follow me there you won’t see much change in what I write. I’ll still cover astronomy, space exploration, politics, and the odd goat picture or two. You can still find me all over social media, of course. I keep links to that centralized at

As for Slate, it’s been an amazing 4.22 years—

… holy wow. Writing that out, I just realized: Right now, the light from me sitting at my computer writing my first post on Slate has traveled almost the same distance as Proxima Centauri is from Earth. Sadly, Proxima is in the Southern Hemisphere, so that light cannot reach it (the Earth is in the way), but soon that light will pass many stars in our galactic neighborhood. We know most stars have planets, so I have to posit: If there’s anyone watching on those exoplanets—and they have really big telescopes—they’re about to get an eyeful (or whateverful) of what we humans here on Earth know about the Universe. How about that?

—and I’ve truly enjoyed my tenure here. Slate has supported me pontificating, ranting, researching, writing, and just nerdifying. For that I am very, very grateful.

We part amicably, but part we must. Thank you to my current editor Susan Matthews and Editor-in-Chief Julia Turner for their support, to past editor Laura Helmuth and Editor-in-Chief David Plotz for their encouragement and kindness over the years, and to all those at Slate who are keeping the fires of journalism burning at a time when it’s more important than ever.

Most of all, of course, my thanks to you, Bad Readers, for indulging me all this time. I hope you follow me to Syfy Wire. There’s still so much I have to say, so much I have to show you—the Universe is big, and getting bigger every day. No matter where I am, I’m compelled to share it with you. Come along then.

Jan. 30 2017 8:45 AM

Shaking the Fabric of Reality

Hands down, the biggest science story of 2016 was the detection of gravitational waves. Even the discovery of the planet Proxima Centauri B takes second seat to it.

Gravitational waves are ripples in the very fabric of space-time, created when massive objects are accelerated. The existence of these waves in reality was a natural byproduct of Einstein’s relativity equations, but their detection has been difficult. That’s because the waves are incredibly weak, at least in everyday life. To get waves strong enough to detect, you need truly massive objects undergoing intense acceleration.


The Laser Interferometer Gravitational Wave Observatory, or LIGO, was designed to detect gravitational waves, and in 2016 it finally did. Even then, it took the merging of two enormous black holes (with combined mass of 65 times that of the Sun!) accelerated to a large fraction of the speed of light for LIGO to detect the waves.

It was a feat of extraordinary human achievement. How extraordinary? My friend Derek Muller, creator of the Veritasium science videos, went to LIGO to talk to scientist Rana Adhikari to put it all in perspective (with the help of my friend and fellow Bill Nye Saves the World writer Teagan Wall).

Note: Before watching, I recommend you read my article about the observation of the first gravitational waves, and a follow-up when LIGO detected its second merging black hole pair; they’ll give you background on how this works.

He uses the word absurd, and it really does fit. The technical aspects of this experiment are so sophisticated and sensitive that it almost sounds like Star Trek tech. Yet here we are, doing it. And we’re not done yet: More detectors are coming online, and soon we may have them in space as well, increasing our sensitivity to these waves by huge leaps. It’s possible we may eventually be able to detect literally every binary black hole system in the Universe. And the cosmos is swimming in a background of gravitational waves coming from all directions; my pal Chiara Mingarelli is working on a ridiculously sophisticated system to detect that noisy background, too.

We receive a lot of information from space, but it comes in only a few flavors: light waves, meteorites, subatomic particles. With the discovery of gravitational waves, an entirely new way to view the Universe has come online. It was astonishingly difficult to get to this point, but human curiosity is an immensely powerful force. It accelerates our minds. Maybe Newton and Einstein never put equations to that, but it’s a fact of science nonetheless.

Jan. 27 2017 10:46 AM

In a Week of Space Tragedy Anniversaries, We Must Continue to Venture Onward

Creaters on the Moon named for Challenger astronauts
Seven craters on the Moon were named for the Challenger astronauts. They all sit in a vast basin named Apollo.

NASA/GSFC/Arizona State University

Friday is the 50th anniversary of the Apollo 1 fire that killed three astronauts. I wrote the following article a few years ago, but my feelings have not changed at all. Space calls to us, and we must answer, even when we know we will lose people along the way. We can minimize this loss, but we cannot eradicate it. If you ask any astronaut, I expect they would agree.

Today marks the second in a week of three tragic anniversaries in space exploration. On Jan. 27, 1967, we lost three astronauts in the Apollo 1 fire. On Feb. 1, 2003, seven astronauts died when Columbia broke apart upon re-entering Earth’s atmosphere. And Jan. 28, 1986, is when the Space Shuttle Challenger exploded, killing all seven astronauts on board.


All three of these events were horrible. All three were the results of unlikely chains of events that seemed inevitable afterward. All three sparked immense debate over the dangers and value of exploring space.

And all three should show us how important it is that we carry on that exploration.

There are two ways to look at why slipping loose the surly bonds of Earth is so critical. One is practical. Going into space has given us tremendous advantages in life. Global communication. Weather forecasting. Technology spinoffs that have generated vast economies. The list goes on and on. How many dangerous regimes have collapsed because we can directly see and talk to those being oppressed? How many lives have been saved by advance knowledge of crippling weather events? How much have our lives improved due to the wonderful technology generated? The money spent on space exploration has literally paid us back manifold.

That argument alone is more than enough to support both automated and crewed space exploration. But there’s more.

We are a species of explorers. It’s in our blood, in our makeup. We crave to see what’s around the next corner, what’s over that hill, what’s next in our adventure. Sometimes we learn something massively important, and sometimes we don’t. Sometimes we come home to tell the tale, and sometimes we don’t. Exploration has fantastic rewards, and grave dangers. But fulfilling our need to explore is its own goal.

The practical benefits of exploration are our sustenance, but the adventure itself is the flavor. The price we pay for this, sometimes, is counted in human lives. And it’s a terrible price. But we must continue to explore because it’s a part of us.

The very fact that so many people are so deeply affected by these events shows just how profoundly space exploration reaches into us. Any event involving large multiple deaths in a single, searing moment is going to resonate with us, and certainly watching it live on television will magnify that feeling. But in this case, we hold astronauts to a higher level. Like with any dangerous occupation that makes life better for others, risking their lives is part of the job requirement.

At first, it feels like this makes these losses cut even more. But it’s ironic: The astronauts themselves knew the risks and downplayed the significance of them potentially being killed. They thought it was worth the risk, or else they wouldn’t have done what they did. That doesn’t make their loss any easier, but it shows us that we must carry on—who could convey that message better than the ones who themselves sit on top of those rockets?

There are many reasons we lose lives exploring space. It’s inherently difficult and dangerous, a hostile environment that takes supreme and envelope-pushing effort even to reach. And there will always be human errors, those caused by carelessness, rush, politics, greed, and simple mistakes. We can minimize these risks in many ways, but over time, the odds of these mistakes leading to tragedy become inevitable.

The only way to absolutely minimize these risks is to stop exploring. And that’s unacceptable. Ships are safe in the harbor, but that’s not what ships are for.

I hope that we have learned from your experience, I hope that we have become better through your experience, and that, while we will never forget what happened to you, we will also remember what you were trying to do, and what you did do.

Per ardua ad astra.

Some parts of this post are based on articles I have written in the past about these events.

Jan. 26 2017 8:45 AM

The Broad Strokes of Jupiter

This post is what Boing Boing calls a “unicorn chaser,” a bit of eye candy to cleanse the brain after a particularly off-putting article. So, after Wednesday’s distressing news, here’s something to make your cerebrum a bit happier.

A new image of Jupiter taken by the Juno spacecraft reveals a fantastic vista that looks like an impressionistic painting. When it took the frames making up this image, Juno was looking down on Jupiter from about 17,000 kilometers above the cloud tops, when the spacecraft was above Jupiter’s northern latitudes.


You can see the intricate play between winds at different latitudes, interacting to create magnificent swirls, vortices, and turbulence in a view wholly different than what we’re used to from Earth. It’s hard to even see the usual banding in the clouds!

To the bottom left is a massive storm, technically called NN-LRS-1 (the North North Temperature Zone Little Red Spot 1). The size of the Earth(!!!), it’s been nicknamed the Little Red Spot—not a bad name, though it’s one of the largest storms on the largest planet in the solar system.

This image was taken on Dec. 11, when Juno was at Perijove 3 (the third time while orbiting Jupiter that it passed close to the planet). The raw data from Juno are available online, and two “citizen scientists,” Gerald Eichstaedt and John Rogers, processed these images to create the lovely shot.

LRS-1 is an anti-cyclone, a region of high pressure with gas swirling around it at speeds faster than a whopping 600 kph. Since it’s in the northern hemisphere (around 40° north latitude) it rotates clockwise—anti-cyclones in the southern hemisphere spin the other way due to the Coriolis effect. It’s not clear why it’s brownish in color, but it’s changed hue over the years, from reddish to brown to off-white. In visible light, like this image, it can sometimes be hard to see against the similarly colored surroundings. It’s actually very bright when observed using a near-infrared filter; this is due to methane clouds capping the storm at high altitudes. Methane preferentially reflects light in the near infrared.

Some jovian storms come and go, forming, growing, then dissipating. Some last far longer. The iconic Great Red Spot (which is in the southern hemisphere, along with its pal Oval BA) is at least 400 years old. We’ve only been observing Jupiter for that long, so for all we know the GRS is millennia old, or maybe even more ancient. The LRS is younger; it was first spotted in 1993. It grows by absorbing other storms; in 1998 it merged with three smaller systems that had been observed since the 1930s!

Jupiter is weird. But that’s one reason we keep an eye on it. It’s very different than Earth, but like everything else in the Universe it obeys the same set of physical rules. It spins rapidly, it’s mostly gas, it has immense gravity, it’s cold … all of these come together through the mathematics of physics to make it understandable. And then, by contrast, we understand the Earth better. Our own planet is complex, subtle, robust, delicate … and these all come together to form an environment we must understand. For now, and for the foreseeable future, it’s the only planet we’ve got that we can live on. It’s only by observing Earth and the other planets we have nearby that we can hope to understand our home world well enough to make sure that foreseeable future lasts a long, long time.

Jan. 25 2017 8:45 AM

Make America Gagged Again

Welcome to our new, terrifying reality: According to reports, President Donald Trump’s administration has ordered a media blackout of people who work at the Environmental Protection Agency and the United States Department of Agriculture.

It gets worse: According to Reuters, Trump has also ordered the EPA to remove its climate change pages.


I want to be very careful here. The EPA and USDA media blackouts might be due simply to Trump’s transition team trying to minimize confusion during the changeover to the new administration; Maggie Koerth-Baker at FiveThirtyEight makes this case.

This may be true. BuzzFeed and the Associated Press, however, obtained internal emails from the EPA and USDA that indicate the new administration is gagging people at the two government agencies, forbidding them from tweeting, going on any social media, or issuing press releases about their science. The only news they are allowed to issue must be vetted first. Also, in the case of the EPA, a Trump administration order has frozen grants and any new business. Note that the EPA has been under heavy attack by the GOP for years.

For what it’s worth, the USDA has disavowed the order … kind of. They say, “This internal email was released without Departmental direction, and prior to Departmental guidance being issued. ARS [Agricultural Research Service] will be providing updated direction to its staff." So they’re not saying it wasn’t true or wasn’t issued, they’re just saying that it wasn’t issued officially. We’ll see soon how this will play out. Update, Jan. 25, 2017, at 16:30 UTC: After the public outcry, the USDA has rescinded the gag order. BuzzFeed has the story.

Update, Jan. 25, 2017, at 22:00 UTC: The Trump administration has told EPA employees to "stand down" and not take down the climate change pages. This is potentially great news, but I will take it with a grain of salt: Doug Ericksen, a Washington state senator and climate change denier, is part of the transition team for the EPA and has been quoted as saying, "We’re looking at scrubbing [the climate section of the EPA site] up a bit, putting a little freshener on it, and getting it back up to the public." Given that Erickson doubts climate change even exists, that statement fills me with little confidence.

On their own, under different circumstances, I’d wager Koerth-Baker is right, and these emails indicate the normal sort of transitional time where it’s best to make sure everyone is on the same page before talking to the media. But the context here is important. The EPA has had its grants frozen, and it seems that Trump has indeed ordered them to take down their climate pages.

This also comes just days after the National Park Service Twitter feed posted a side-by-side comparison of Trump’s inaugural gathering versus President Obama’s; shortly thereafter the entire Department of the Interior Twitter feed went dark, allegedly on the order of “the new administration.” It’s well-known how fragile Trump’s ego is, and it’s being reported that he was apoplectic over media coverage of the low attendance at his inauguration and the much larger Women’s March the next day (full disclosure: I marched in Denver).

Also, while Obama’s White House website talked about climate change, that part of the site is now gone (it currently only exists in archival form). The new website makes no mention of it at all, except to talk about Trump’s policy of opening up as much oil drilling in the United States as he can.

Given all this, it provides background into the EPA and USDA emails that is chilling. It appears that Trump wants to keep these groups under the thumb of the White House, and to make sure the only news that gets out aligns with what the new administration approves.

If true, this is no media blackout. It’s censorship.

Again, this seems like an extreme conclusion, but we now live in a time of extreme circumstances. Just days ago we saw Press Secretary Sean Spicer’s first press meeting, where he blatantly lied about the size of Trump’s inauguration audience, then abruptly left without taking questions. Then Trump spokeswoman Kellyanne Conway dismissed criticism of Spicer, saying he was presenting “alternative facts.”

Right. This forehead-slapping revelation prompted me to tweet:

To be clear, what Conway and Spicer were doing was lying.

The trend here is clear. Trump has been lying and saying provably false things since the early days of his campaign; his entire rise to the top of the GOP presidential candidate heap was based on his birtherism. He has also fervently denied any science that goes against his ideology, picking and choosing what he wishes to believe (or disbelieve). Hence his denial of the reality of human-induced climate change and his courting of the worst of the anti-vaccination promoters like RFK Jr. and Andrew Wakefield—the latter is the father of the modern anti-vax movement, even though he has been struck off the U.K. General Medical Council’s register and his original findings have been retracted and branded as fraudulent.

Ordering the EPA to take down its climate change pages is appalling. As Reuters says,

The page includes links to the EPA's inventory of greenhouse gas emissions, which contains emissions data from individual industrial facilities as well as the multiagency Climate Change Indicators report, which describes trends related to the causes and effects of climate change.
The Trump administration's recently appointed team to guide the post-Obama transition has drawn heavily from the energy industry lobby and pro-drilling think tanks, according to a list of the newly introduced 10-member team.

So yeah, that’s very, very worrisome.

As bad as this is, I have no doubt whatsoever it will get worse. The National Oceanic and Atmospheric Administration—our chief scientific agency tracking climate change—has been under constant attack for years, including McCarthy-esque fishing expeditions by the GOP-controlled House Committee on Space, Science, and Technology.* NASA is also one of the strongest and most important scientific voices we have discussing climate change, and senior Trump adviser Bob Walker has already said they plan to curtail NASA’s Earth science research.

How long will it be before Trump makes it official, gagging NOAA and NASA scientists as well?

We’ve seen this happen before in recent times; when Stephen Harper became Canada’s prime minister, his anti-science right-wing administration did much the same thing, gagging scientists, including climate scientists, from talking to the media or public. Scientists rebelled and created their own site where they could announce their results, but the gag order wasn’t rescinded until Harper’s party was voted out of power. Besides it being a national embarrassment, the gag order meant that news articles about scientific research could report it incorrectly and the scientists could not issue corrections. It also allowed Harper to prevent the public knowing about research that went against his own anti-climate agenda.

Don’t think it can happen here? It already has, back in the George W. Bush administration, when for just one example a PR flack was put in place at NASA who meddled with their science communication efforts.

And now, it seems, it’s happening here once again.

This is extremely worrying. In the absence of scientific autonomy and open discussion, the administration is free to make up whatever reality serves it best. Given that Trump signed an executive order making it easier to build the Dakota Access Pipeline—a colossal conflict of interest, since Trump has stock in the company that would build it—we can see very clearly what reality that will be. Massive corruption, suppression of free speech and the freedom of the press, oppression of minorities, the complete reversal of women’s rights, and the literal sickening of America.

We the people need to make sure our voices are heard, and that this cannot stand. There are many ways to do this, including supporting the American Civil Liberties Union, whose sole purpose is to make sure no one tramples on the First Amendment. Also, call your senators and representative! That really can make a difference, even in heavily red or blue districts.

Make your voice heard. Suppressing science must not stand. At the very least, despite Trump’s slogan of wanting to make America great again, this will hobble our country’s ability to perform first-class scientific research. At worst it will set back our ability to monitor our nation’s health, the quality of its products, and will also delay for years the critical need to invest in alternative energy sources (this time, the term alternative, unlike Conway’s claims, is actually real and beneficial) and do what we can to slow climate change.

This is a clear and present threat to our nation’s and our planet’s health. Don’t let it go unchallenged.

*Correction, Jan. 25, 2017: This post originally misidentified the National Oceanic and Atmospheric Administration as the National Oceanographic and Atmospheric Administration.

Jan. 24 2017 8:45 AM

Juno Makes Another Pass at Jupiter

On July 5, Jupiter acquired a new moon: NASA’s Juno spacecraft. Launched in 2011, Juno passed by the Earth in October 2013 to pick up some energy and fling itself to Jupiter. Once it arrived, it burned its main engine for over a half hour, slowing enough to place itself into a highly elongated orbit that took it over Jupiter’s poles.

The orbital burn went perfectly, but a potentially serious problem arose. In October, after two complete orbits (each about 54 days apiece), the main engine was scheduled to fire once again. It was supposed to change Juno’s orbit from the initial looping trajectory that took it as close as 4,200 kilometers over Jupiter’s poles to over eight million kilometers out, to the new “science orbit” that was supposed to be only 14 days long.


However, just before the burn, telemetry indicated that a pair of valves had failed to work properly. The orbit reduction maneuver was at first postponed until Dec. 11, but then it was decided to postpone it again until at least the next perijove (closest approach to Jupiter), which is in February 2017. The spacecraft is working, and collecting good data, so engineers decided it would be better to work the problem longer to make as sure as they can that the maneuver will be performed properly.

The image above is from a few hours after the last pass in December, called Perijove 3 (counting the Jupiter orbital insertion in July as 0, the dip over the pole in August Perijove 1, and October Perijove 2). It shows the south pole of Jupiter to the bottom, and from this vantage we’re looking “up” at the Great Red Spot (which is located at a latitude of about 22° south of Jupiter’s equator). The smaller red storm to the lower right is called Oval BA (no relation), but it’s hardly small: It’s about the same diameter as Earth! It formed in 2000 when three smaller storms merged.

The image was processed by master planetary photographer Damian Peach, and it’s so, well, odd. Jupiter orbits the Sun in roughly the same plane as Earth, and its rotational axis is pretty much perpendicular to that plane. That means, from Earth, we tend to be looking down on Jupiter’s equator, with the belts and zones stretching across horizontally. From this angle everything is tilty; it’s a view we cannot get from Earth. If you want to see Jupiter this way, you have to go there.

Which is another reason Juno is so cool. Another Juno image Peach put together from the raw data graced the Astronomy Picture of the Day site recently as well.

This last pass of Jupiter by Juno was the first to take gravity data. One of the main purposes of the Juno mission is to map the interior of Jupiter. As it passes very close to the planet, the layers of material beneath the surface of the planet pull on the spacecraft differently, affecting its orbital trajectory minutely. These changes can be used to determine the density of those layers, which in turn reveals the internal structure of Jupiter.

Weirdly, it’s not clear if Jupiter has a distinct core or not; different physical models for how it formed yield different results. Juno may be able to help scientists determine which is correct. In the meantime, Juno will pass through Jupiter’s intense magnetic field, returning information about that as well.

Hopefully, over the next few weeks scientists and engineers will be more confident they can put Juno into the correct science orbit. Until then, it’s still doing good work, and we can enjoy the literally unearthly view.

Jan. 23 2017 8:45 AM

Curiosity Finds An(other) Alien Visitor on Mars

The Curiosity rover has been on Mars since Aug. 6, 2012. In the more than four years it’s been there, it’s seen wonders beyond our Earthly reckoning: evidence of ancient flowing water, evidence of ancient standing water, methane in the atmosphere now, carbon in the rocks, dark basaltic sand dunes, weird lumpy moons circling a dusty red planet.

Mars is indeed an alien world. But even with all that, sometimes Curiosity still manages to find things on Mars that are able to surprise and delight: The photo above shows a meteorite sitting on the planet’s surface.


How cool is that?

The picture was taken on Jan. 12—the 1,577th Martian day, or “sol,” after Curiosity landed—when the rover was investigating sedimentary rocks in the Murray Formation, a large deposit along the flanks of Aeolis Mons (also called Mount Sharp), which itself is the central peak in Gale Crater. Since landing, Curiosity has been inside Gale Crater, heading toward that central mountain.

The meteorite sticks out like a sore thumb among the rust-colored rocks and darker wind-blown sand. The shape and color just scream “I’m not originally from here!”—just compare it with the mudstone to the upper left, or the flatter rock below it. It’s hard to say exactly, but it’s likely a few centimeters across, perhaps the size of the palm of your hand.

I collect meteorites and have read quite a bit about them, and to my eye this is obviously a metallic nickel-iron specimen. I have some on my bookshelf that look quite a bit like this!

On Earth, meteorites like this one start out as a larger chunk of metal asteroid orbiting the Sun. If it has the bad (for them, good for us!) luck of slamming into our atmosphere at hundreds of thousands of kilometers per hour, the intense pressure fiercely heats the air ahead of it, melting its exterior and causing it and the air to glow. A bigger asteroid (say, the size of an easy chair or a bus) can actually explode as the pressure flattens and disrupts it, sending hundreds or thousands of smaller pieces outward. They can form all kinds of weird, bizarre shapes, folded, twisted and pitted from the huge forces at play.

The atmosphere of Mars is much thinner than Earth’s but is still thick enough to affect an incoming asteroid in similar ways. I don’t know if this meteorite was part of a larger piece or came in on its own, but the sharp edges and odd surface features betray its extramartian origins.

close up of the meteorite
The ChemCam close-up of the meteorite shows the weird folds and contours caused by its atmospheric passage, and the bright, reflective zap marks of the high-powered laser.


I’m almost positive this is metallic; stony meteorites tend to look more like, well, rocks. This is clearly more like sculpted metal. The only way to be sure is to get spectra of it … which Curiosity can do! The ChemCam detector was designed specifically to be used for this. It has a high-powered laser it uses to zap rock samples, heating them very rapidly. The vaporized rock emits light that can be broken up into individual colors; different elements in the sample can then be determined by the different colors of light they emit.

In the ChemCam Remote MicroImager photo above, you can see the odd shape of the meteorite, as well as several small, evenly spaced shiny features. Those are laser zap marks! ChemCam took spectra of the meteorite, so hopefully we’ll find out what it’s made of. Unfortunately the actual data won’t be made public for some time, but I’d bet the value of that meteorite* that they’ll find it’s mostly iron and nickel (and maybe cobalt); those are the main constituents of metallic meteorites here on Earth.

I’ll note that meteorites have been seen on the Martian surface before by both of the Spirit and Opportunity rovers, and have even been used to examine surface conditions on Mars now and in the past.

So there’s scientific value in this. These specimens also tell us about the conditions in the asteroid belt, so this is extra science for free. Not only that, but the shape and structure of meteorites might be helpful in understanding what happens to objects as they fall through Mars’ atmosphere at high speed, which has some value as well; after all, that’s how we get our own hardware down to the surface (though meteoroids tend to be moving more rapidly than spacecraft).

Also, it’s just really, really cool.

I have to admit, seeing this photo is odd. My first reaction was to think, “Whoa! A meteorite! How weird!” How silly is that? After all, these are close up pictures of the surface of another world. Is this not enough for my science-drenched brain to fill it to capacity with wonder?

Apparently not. There is still room to be awed, and I’m OK with that.

My thanks to RidingWithRobots for the original tweet about this, and to planetary scientist Ray Francis for the ChemCam photo link.

*The price for nice metallic meteorites varies a lot but tends to be around a few dollars a gram. Ones from “known falls”—where the meteor event was seen—are more valuable. Given that this one is on freaking Mars its value is beyond price.

Jan. 20 2017 8:30 AM

If You Need Strength Today, Be Like Daphnis

Today is a difficult day. And it’s just the latest in what have been very, very difficult times.

I’ll be honest with you: Over the past few months, in between bouts of fury and incredulity, like so many of you, I have felt real despair. Watching the country I love, the people I care about, and the science to which I have devoted my life come under such attack has been extraordinarily difficult and painful.


It can be hard to find any comfort in situations like these. And I have no desire to utter to you any hollow phrases, any meaningless pablum that sounds deep but is of no actual content.

Instead, please indulge me for a moment.

First, read this article I wrote Thursday about Saturn’s moon Daphnis. It may seem like a non sequitur, but as you'll see it’s quite the opposite.

Saturn's moon Daphnis, a tiny wordlet with a long reach.

NASA/JPL-Caltech/Space Science Institute/Ian Regan

That image of Daphnis I posted Thursday is grayscale, a single picture of the moon taken by the Cassini Saturn probe. The one you see here was crafted by Ian Regan, using two images from Cassini to create a representation of the color. I actually saw his version first, the colors sublime, adding a subtle and delicate touch to the otherworldly vista.

It was in the evening when I first saw it, and I was in bed (perhaps ill-advisedly) checking Twitter before going to sleep. I was stunned … and I mean that literally, as in my brain locked up for a moment as the wonder of this image flowed into it.

For just a moment I wasn’t sure what I was seeing, and by that I mean which of Saturn’s panoply of moons and what part of the rings this depicted. Daphnis is so small that it’s only appeared as a barely resolved dot in previous images, and the detail in the surface features threw me. When I saw Regan’s caption identifying the moon, I was stunned anew, since I knew this was by far the highest-resolution photo of Daphnis we’ve ever seen, and likely ever will.

The more I gawked at this photo, the deeper my awe became. The ripples, the structures, the graininess of the rings, the smooth(ish) surface of Daphnis, the ringlets that are so narrow they challenge the ability of Cassini to resolve them, and most of all that gossamer thread of ring pulled away by the feeble gravity of this diminutive moon … all of this was a fantastic delight, a gift literally sent down from the heavens.

As I struggled to tease out the details of what I was seeing, a thought struck me: Daphnis was only discovered in the year 2005. Its presence was first suspected in 2004, when Cassini returned images of waves and spikes in a gap in Saturn’s rings, obviously sculpted by a tiny moon, though its exact location was at the time unknown. Observations were quickly planned to get better images of the gap where the ripples were seen, and in May 2005 astronomers announced they had found it. It was given the name Daphnis the very next year.

And here we are, a dozen years later, with a new and extraordinary view of this odd little satellite. As I lay in bed and mulled over that, a thought struck me. We’ve known about this moon for a decade or so, but how old is it? Millions of years? Billions? How long has this tiny chunk of ice been circling Saturn, carving these marvelous creations out of still tinier chunks of ice?

As I chewed on this, an honest-to-God chill went down my back. This moon has been silently gliding through Saturn’s rings since before humanity existed as a species, and likely far, far longer. It’s done this without notice, without discovery, without supervision, without any sense of purpose or any eyes seeing it.

Daphnis did what it does because it must. It follows the rules of science, dancing to the tune of gravity, and it wasn’t until just a few years ago that we too could read those notes, hear that music, and appreciate its melody.

Daphnis is so small you could circumnavigate it by foot in a few hours, provided you could maintain your traction in its faint whisper of gravity. Yet, in the vastness of Saturn’s rings, almost completely lost among a trillion, trillion particles, it still manages to make waves, to reach out and create an effect, to stir echoes in a system far larger than itself.

And when we ponder the reverberation of those echoes, they engender in us a sense of beauty. Of awe.

All of these thoughts were still ringing in my mind when I happened to see how my friend, astrophysicist Katie Mack, was herself inspired by this image from over a billion kilometers away, and how she captioned it.

This is Daphnis. Daphnis is only 8 km wide, and orbits in a ring gap of 42 km. It uses its tiny gravity to disrupt Saturn's mighty rings and make waves. Daphnis doesn't let being a tiny insignificant speck in a vast uncaring universe stop it. Be like Daphnis.

NASA/JPL-Caltech/Space Science Institute/Katie Mack

Yes, these are trying times, and it is easy to feel overcome, to be overwhelmed by events. And yes, the Universe itself is telling you that you are small. But do you know what else it’s telling you?

You are mighty.

Go out and make a difference. It may be a small one, but its reach may be profound, and extend far beyond what you intend or might perceive.

Go. Be like Daphnis.

Jan. 19 2017 8:45 AM

Saturn’s Moon Daphnis Creates Spectacular Ripples in Saturn’s Rings

When I saw the image above, I literally gasped. It’s an amazing photo, showing the small moon Daphnis inside a gap in Saturn’s rings. The beauty of this shot is apparent, but the science behind it is even cooler.

Allow me to explain.


On Nov. 30, the Cassini spacecraft orbiting Saturn took on a new and risky mission. It began a series of orbits that are taking it over the planet’s north pole and then down just outside the main rings.

In mid-January it dipped through the ring plane on one of these orbits, passing a mere 28,000 kilometers from the tiny moon Daphnis when it took that shot with its narrow-angle (i.e. high-magnification) camera.

That’s the highest-resolution image of Daphnis ever taken; for scale, the flying-saucer-shaped moon is about 8 x 8 x 6 km in size. Measured from sea level, Mount Everest is roughly the same size. You can see some structure to Daphnis; there’s a ridge around its equator that’s probably due to ring particles that have piled up there, and a second ridge at higher latitude. The soft appearance to the moon is probably due to the accumulation of small grains of ice from the rings that have coated it, filling in the craters and other features.

That gap in the rings is real. It’s called the Keeler Gap, and it’s about 30–40 km wide. The width of the gap appears foreshortened because Cassini was just above the ring plane when it took the shot; it’s actually several times wider than the moon is long.

But, oh, those ripples! That, my friends, is the result of gravity. It’s a complicated and intricate dance between moon and rings, but it’s worth learning the moves.

Saturn’s rings are composed of countless tiny particles of ice, each in its own separate orbit around Saturn. They’re tremendously wide—the main rings are 300,000 km across, and would stretch 3/4 of the way from the Earth to our own Moon—but are astonishingly flat. In some places they are only 10 meters high from top to bottom, the height of a three-story house. To scale, this makes them far thinner than a piece of paper.

wide angle shot of Daphnis
Cassini took this wide-angle shot around the same time as the narrow angle one. Note how far the waves go around the rings. Saturn is to the upper right. This is a raw image, so there are some blemishes that aren't real objects.

NASA/JPL-Caltech/Space Science Institute

There are several subdivisions of rings, given letter designations in order of discovery. The broad A ring has distinct two gaps in it, carved by moons orbiting Saturn embedded in the ring. The Encke gap is 325 km wide, and is from the moon Pan. The much narrower Keeler Gap is due to Daphnis.

If you plunk a small moon down in a ring, it will of course carve a gap as it plows through material. Its gravity will attract more material as well, so particles just inside and outside the moon will, over time, fall onto it. The gap grows, but the width of the gap depends on the strength of the moon’s gravity. At some distance, the gravity is too feeble to pull particles all the way out of the ring and onto the moon. Pan has nearly 100 times the mass of Daphnis, so its gravity is stronger, and the gap it carves wider.

What causes those ripples? The orbit of Daphnis is not a perfect circle, but instead is very slightly elliptical. That means it’s sometimes closer to the inner edge of the Keeler gap, and sometimes closer to the outer one. The change is small, only about nine km, but that’s enough. When it’s closer to one edge it pulls on the ring particles a bit harder, creating the wave.

But there’s more to it. The orbit of Daphnis is also tipped a bit to the ring plane, a mere 0.0036° from being exactly aligned. That means it bobs up and down out of the ring plane by about 17 km. When it does it drags the ring particles at the gap edges as well. Those waves you see in the image go in and out of the gap, but also up and down by a kilometer or so.

Perspective makes that hard to see here, but twice every time Saturn orbits the Sun, the rings are edge-on to the Sun, and any vertical excursion can cast long shadows.

Daphnis and rings
In 2009, the Sun shone straight along the rings, so any features out of the ring plane cast long shadows.

NASA/JPL-Caltech/Space Science Institute

That image was taken at Saturn’s northern hemisphere spring equinox in 2009. It’s incredible! You can see Daphnis and the long shadow it casts on the ring. You can also see the vertical waves caused by the moon’s feeble pull. Each wave corresponds to one up-and-down bob of the moon relative to the rings. Eventually, tides from Saturn pull the particles back down, but that takes a while, and the ripples extend for a long way around the ring.

How about that? But wait! There’s more!

Look again at the first picture. You can see the ripple to the left of Daphnis is fuzzier than the others. That may be due to very tiny grains being pulled out (that ripple is on the outside of Daphnis, so was created the last time Daphnis passed those particles). The particles are brighter there than on the ripple right next to Daphnis, which is interesting; that may be due to the Sun’s illumination on the wave.

Daphnis in higher resolution.

NASA/JPL-Caltech/Space Science Institute

That’s a closer look at the top photo. You can see a very thin ribbon of material to the left of Daphnis. That may be due to a clump of material in the ring that was pulled apart by the moon! Note the shape, too; it mimics the ripple but looks like it goes deeper into the gap. Amazing. When I saw that I had to sit back and stare in awe. I don’t think anything like that has ever been seen before.

Also in that shot you can see the rings look grainy. That may very well be a hint of the actual grainy particulate nature of the rings, where material has clumped up! Cassini is getting closer to the rings than it ever has before, so we see them in more resolution. I hope we get even better shots of them over the next few months.

We’d better, because time is running out. Cassini’s end-of-mission is in September of this year, and when it’s done engineers will command it to plunge into Saturn’s atmosphere, where it will burn up and be crushed. This is done to prevent any possible contamination of the moons in case Cassini might impact them in the future after fuel has run out. Instead, the remaining wisps of fuel will be used to send the probe into the planet itself.

I’ll hate to see Cassini go. But images like the ones of Daphnis make me glad we had Cassini for as long as we did. It’s a truly historic mission, and its legacy will live on for a long, long time.

Tip o’ the RTG to Ian Regan.