Bad Astronomy
The entire universe in blog form

July 1 2016 9:15 AM

Jupiter Looms Ahead for Juno

On July 5, at 03:18 UTC (July 4 at 11:18 p.m. Eastern U.S. time), the Juno spacecraft will ignite its main engine. It will burn for 35 minutes, and when it’s done, the spacecraft will be doing something a NASA mission hasn’t done in many years: It will be orbiting mighty Jupiter, the biggest planet in the solar system.

Oh my, yes, this is a big deal.


Juno’s mission is to investigate Jupiter, observing its dynamic atmosphere to determine its composition, temperature, and cloud structure. It will measure Jupiter’s ridiculously powerful magnetic and gravitational fields, and reveal what the interior of the giant planet is like. The overarching goal: Find out how Jupiter formed, and how it’s changed in the billions of years since then.

It’ll do this with a fleet of scientific instruments, including particle detectors, a magnetometer, cameras, and many others (SpaceFlight 101 has a great overview of all of them). One instrument, JunoCam, is designed to take color pictures of Jupiter, including its poles, which have never been seen before from above. I was amazed to find out that when Juno is closest to Jupiter (called perijove), JunoCam will have a resolution of 15 kilometers per pixel! Mind you, Jupiter is a staggering 140,000 km across, so we’re talking very high detail shots. We’ll get stunning views of Jupiter’s atmosphere and, hopefully, its aurorae. Emily Lakdawalla has a great write-up of JunoCam on her blog at the Planetary Society.

Before you ask, no, it won’t be getting any pictures of Jupiter’s moons to my knowledge. They’re not the focus of the mission, and besides they’re small and will be far away, so they wouldn’t look like much anyway.

Jupiter in the infrared, taken by the Very Large Telescope. Ground- and space-based telescopes will assist in observing the planet while Juno does its thing.

ESO/L. Fletcher

This is an ambitious mission, made even more difficult by Jupiter’s radiation belt. Jupiter has an incredibly powerful magnetic field, and that’s trapped subatomic particles from the solar wind and emitted from its moon Io. These particles are accelerated to high energy and can damage spacecraft components. Juno’s hardware is hardened against this, but even so it limits the lifetime of the mission. The design is to last for 36 orbits of Jupiter; after that it is planned to do a deorbit burn and fall into the planet itself in 2018.

We’ve sent spacecraft to Jupiter many times, but with one exception they’ve all been flybys, brief but amazing. The exception was Galileo, which orbited Jupiter but suffered a hardware problem with its main antenna that prevented rapid downloading of its data, limiting the goals of the mission. It still worked, and did amazing science, though.

Another pretty cool thing is that the Juno spacecraft is powered by solar panels, which is something that until recently hadn’t been possible for outer planets. Sunlight is weaker out there, and it wasn’t until this mission that solar panels were efficient enough to power a spacecraft; on top of that the instruments are also very efficient with their power, allowing lower energy generation needs.

I’ll be watching the Jupiter Orbital Insertion live and tweeting it. Emily Lakdawalla will as well, and she has a timeline of insertion events on her blog worth keeping bookmarked, too.

It’s been a while since we’ve seen Jupiter up close. This should really be amazing.

June 30 2016 8:30 AM

The GOP’s Denial of Science Primed Them for the Illogic of Trump

Part of the problem with being a vocal advocate for critical thinking is deciding just which facet of nonsense to spend time fighting. The forces of anti-reality present a huge number of fronts, making triage a necessity.

As an astronomer I of course have certain pet projects; I’ve taken on astrology, Moon landing deniers, cosmic doomsday promulgators, and geocentrists. But a background in science allows me to broaden that approach, and I will happily help shoulder the load to debunk the claims of climate change deniers, anti-vaxxers, homeopaths, and young-Earth creationists.


Some of these present a more pressing need than others, of course. Astrology is a minor issue compared with, say, someone who supports abstinence-only education.

But they’re all there, all the time, creating a background buzz of hogwash, an atmosphere of denial of science, evidence, and rational thinking … and that can have devastating consequences.

We are awash in that miasma, where people can say almost anything, no matter how ridiculous, and not be confronted, not be challenged. Many of these purveyors of poppycock wind up surrounding themselves with throngs of people willing and eager to suspend their disbelief and support the foolishness. Cults certainly can form in such an atmosphere … and when the person spouting the nonsense is a politician, that’s when things get very sticky indeed.

And now here we are, with Donald Trump the nearly inevitable champion of the Republican Party.

This is no coincidence. An interesting if infuriating article in New Republic very clearly lays out how the GOP has spent decades paving the road for Trump by attacking the science that goes against their prejudicial ideology. I strongly urge you to read it, but one section jumped out at me in particular:

There’s another factor at work here: The anti-intellectualism that has been a mainstay of the conservative movement for decades also makes its members easy marks. After all, if you are taught to believe that the reigning scientific consensuses on evolution and climate change are lies, then you will lack the elementary logical skills that will set your alarm bells ringing when you hear a flim-flam artist like Trump. The Republican “war on science” is also a war on the intellectual habits needed to detect lies.

Yes, precisely. This is exactly what I have been saying for years now. When we erode away at people’s ability to reason their way through a situation, then unreason will rule. And not just abut scientific topics, but any topics. We see nonsense passed off as fact all the time by politicians, including attacks by Rep. Lamar Smith, R-Texas, on theNational Oceanic and Atmospheric Administration, claims by Sen. Ted Cruz, R-Texas, that there’s been a pause in global warming, the GOP attacks on Planned Parenthood, and more. People will still believe what these politicians say, long, long after the claims have been shown to be completely false.

Months ago, early on in the presidential campaign, I made light of Trump, saying that his particular candidacy would crash and burn when he inevitably said or did something so outrageous and horrific that people would flee his side.

I was wrong. I underestimated just how thoroughly the GOP had salted the Earth. Philosophical party planks of climate change denial, anti-evolution, anti-intellectualism, intolerance, and more have made it such that Trump can literally say almost anything, and it hardly affects his popularity.

The good news is that even the party elders are terrified to support him, and many seem to be accepting what looks like the inevitable wave coming this November, and instead are hoping to recoup in 2020.

Perhaps that will come to be. Trump’s numbers are certainly slumping, and I see no way he will be able to pivot toward anything resembling reality, no way for him to gather more middle-of-the-road votes. His racist, bigoted, misogynistic, xenophobic narcissism is too firmly entrenched for it to be otherwise.

The GOP isn’t to blame for Trump existing—we can lay that at his own feet—but the path he’s taking was certainly smoothed by them.

The fact is, this is the candidate the Republicans have sown, and so shall they reap. My hope is that the majority of the electorate will see through the nonsense, the distortions, the lies, and use their critical thinking skills on Nov. 8. Reality doesn’t give a damn about our beliefs, and so we must instead give a damn about reality.

Want to know more about how to think critically? I have some thoughts on that:

Tip of the candle in the dark to Zack Kopplin.

June 29 2016 9:30 AM

Using the Most Violent Explosions in the Universe to Measure Its Size

One of the most difficult aspects of astronomy is distance. Even the Earth’s Moon is 380,000 kilometers away, a four-day trip by rocket, and that’s the closest object in the Universe to us!

Remote galaxies are a hundred million billion times farther away than that. That’s a soul-crushing distance, almost beyond human grasp.


Almost. We’re pretty clever, we humans, and we’ve found ways to figure out how far away cosmic objects are. One powerful tool we’ve found are “standard candles”: bright objects that all shine at the same luminosity. Think of it this way: Take two light bulbs you know are the same brightness (say, 100 Watt bulbs) and place them at different distances. The more distant one will be fainter, of course. But if you can measure how much fainter it is, you can calculate their relative distances. If you can measure the distance to the nearer one, you automatically know how much farther away the second one is.

We have various types of standard candles at our disposal. Supernovae are good ones; there’s a special kind of exploding star (called a Type Ia) that all explode with more or less the same energy. These are very bright and can be seen to tremendous distances. It turns out they have their quirks, so they’re not perfect candles, but we could adjust for inconsistencies. Once that was done, they allowed astronomers to measure distances all the way across the Universe, and even determine that the universal expansion is accelerating.

Still, it would be nice to have more than one ruler. Waiting around for a supernova takes a while, and even then they’re so faint we need huge telescopes to spot them. And while they let us see out to about 11 billion light-years—a very long way—that still falls short of the roughly 14 billion light-year distance to the edge of the observable Universe.

Is there anything that could fill that gap? The problem is you need hugely energetic events to be bright enough to see from all those billions of light-years away.

The good news is there are such hugely energetic events: gamma-ray bursts (or GRBs). These are ridiculously powerful blasts, so luminous they can even dwarf the brightness of a supernova. They were discovered in the 1960s, and we’ve learned a lot about them since then, including the amazing idea that they are the birth cries of black holes! If you want some background, I have a whole episode of Crash Course Astronomy about GRBs:

There’s a problem, though: No two GRBs appear to be alike. They explode with different energy, they have different brightnesses, they fade differently. Some have explosions that last for seconds, others for hours. There’s an expression in the GRB community: “If you’ve seen one GRB, you’ve seen one GRB.” That makes them terrible standard candles.

maybe. Astronomers have been trying for quite some time to find some way to standardize them, account for their differences, so that they can be used as cosmic metersticks. And it appears that the first solid step toward that has been done: Maria Dainotti and a team of astronomers have just published a paper where it looks like they cracked the GRB code! They found a set of 122 GRBs that, when examined carefully, display a unique set of observable characteristics that allow them to be used to determine their distance.

light curve of a GRB
A "light curve" of a GRB, showing how it fades with time. The scale is logarithmic (2 means 100, 3 means 1,000, and so on). The peak happens rapidly, then it fades, plateauing from about 200–10,000 seconds. The red oval marks the end of the plateau phase.

Dainotti et al.

The GRBs they examined were all of the long variety, with detectable energy that lingers for weeks. Each got very bright and then faded rapidly for minutes. After that they stopped fading, “plateauing” for a few minutes. Then, finally, they begin fading again, this time more slowly. Each of these GRBs also had an independent measurement of its distance (using its redshift; see Crash Course Astronomy Episodes 24 and 42 for more on that), which then allowed for the total energy emitted to be calculated.

What Dainotti and her team found is that when you look at that sample of GRBs and plot three of their characteristics—how luminous they are at their peak, how luminous they are during their plateau stage, and when the plateau phase ends—they all behaved in a nice, orderly way. Instead of being randomly scattered around, they all fall into an obvious pattern. They also found that if they exclude a few subtypes of GRBs the correlation is even tighter.

The beauty of this is what you can do with it. If you observe a distant GRB with these characteristics, all you need to do is plot it against the others, and the distance to it pops right out.

Well, it’s not that easy, but the point is this may be a new way to use GRBs to measure distances across the cosmos (and it’s telling us some physics about the GRBs themselves which is interesting). That’s pretty exciting. This is still new, but it’s a promising step toward being able to use these fickle explosions to probe the conditions of the Universe at much larger distances than we’ve been able to up this point.

I’ll note that this work would not have been possible at all were it not for the existence of Swift, a NASA satellite launched in 2004 designed specifically to rapidly find and observe GRBs. It’s cataloged more than 1,000 bursts now, providing a huge database that allows astronomers to look for trends. And it’s still going strong after all these years. I worked on the education and public outreach for Swift for many years, and seeing it supporting important work like this makes me pretty proud.

We didn’t understand GRBs much at all until the late 1990s, and now we’re close to being able to use them to take the measure of the Universe itself. That’s almost as amazing as GRBs themselves.

June 28 2016 1:24 PM

Small Meteorite Punches Through Roof of House in Thailand

In the early morning of Tuesday, a small rock that is very likely a meteorite fell onto a house in Phitsanulok's Muang district in Thailand, punching a hole in the roof and doing some minor damage inside.

Apparently many people in the area, including the owner of the home, heard a loud explosion some time before, which may have been the shock wave from the meteorite entering the atmosphere.


I don’t speak or read Thai, but there’s a video from the Matichon TV YouTube channel with some pretty interesting footage.

I’ll note that in September 2015 a somewhat larger meteor burned up in the same area and was caught on video, but that’s certainly a coincidence.

The rock from this fall will have to be tested to make sure it’s a meteorite, but it certainly looks like one to my eye; the gray interior is common in stony meteorites, and the outer dark shell may be a “fusion crust,” caused by the few seconds of intense heat as the meteoroid (what the solid piece of rock or metal is called before it hits the ground) passes through the air at high speed.

One part of the story gives me pause, though: The homeowner says the rock was hot to the touch when she picked it up. In general, a meteoroid is only hot for a few seconds as it rams through the air, decelerating from hypersonic speeds down to below the speed of sound. As it slams through the upper atmosphere about 80–100 kilometers above the Earth’s surface, the intense pressure of its passage compresses the air violently, and that heats the air up, which in turn heats up the meteoroid. It gets hot enough to glow (the air glows too) and we call that part the actual meteor.

But it slows in just seconds, falling the rest of the way at a few hundred kilometers per hour, taking a few minutes to fall the rest of the way to Earth. Air is very cold that high up, so many meteorites should be very cold to the touch if they’re found immediately after hitting the ground. Perhaps the homeowner made a mistake, thinking the intense cold was heat (if you’ve ever touched something extremely cold, the sensations are very similar).

roof hole
Light shines through the hole in the roof made by the rock.

Matichon TV, from the video

I’ll be very curious to hear about any tests run on the fragments. The homeowner says she’ll keep it, and that it will bring her good luck. I don’t know about that, but meteorites from known falls that hit objects on the ground can be extremely valuable to collectors. They’re called “hammers,” and this one has a mass of about 300 grams, so it’s easily worth thousands of dollars.

She’s lucky that no one was injured; at a hundred or more kph that would’ve hurt (it weighs twice as much as a baseball and was moving at least as rapidly as a fastball). Still, if I could choose to have one hit my house, I’d probably take that chance! What a story!

The odds are extremely low, of course. The Earth is three-fourths water, and even the land area is mostly uninhabited. Meteorite falls over populated areas are rare, and having them hit objects even rarer. Very few injuries have been reported, and fewer verified (though a woman named Ann Hodges was hit by a meteorite in the 1950s in Sylacauga, Alabama, and that’s well worth your time to read about). It’s not something I worry about, to be honest.

Perhaps more meteorites from this fall will be found, too. That would be nice. A meteorite is in some ways a gift from the Universe to us, a piece of it that we can hold in our hands and examine in our labs, instead of just seeing from some huge distance away. Sometimes the Universe is pretty cool that way.

Want to learn more about meteors? Here's my episode of Crash Course Astronomy about them!

Tip o’ the Whipple Shield to Ron Baalke.

June 28 2016 9:15 AM

Stealthy Black Hole Spotted by Accident

Using a fleet of telescopes both on the ground and orbiting the Earth, astronomers have discovered what is very likely to be a black hole only a few thousand light-years from Earth.

On its own that’s not terribly newsworthy; we know of lots of black holes in the Milky Way galaxy. What makes this one so very interesting is that it has been hiding in plain sight, located in the sky near a gorgeous globular cluster, masquerading as a distant galaxy.


And even that’s not the most interesting thing. The most interesting thing is what this implies for the total number of such black holes in the Milky Way. There could be a lot more than we first thought. A lot more.*

The object has the handy nickname of VLA J213002.08+120904 (a combination of VLA for Very Large Array, the radio observatory that discovered it, and its coordinates on the sky). It’s also called M15 S2, which I find amusing. Let me explain, because this is fun.

Globular clusters are collections of hundreds of thousands of stars in close proximity to each other. M15 is a glorious example of such a beast; about 30,000 light-years away, quite bright and well-studied. In 1996, a group of astronomers scanned the cluster using the VLA, looking for gas flowing into it. By accident they found a point source of radio emission in the outskirts of the cluster, but they weren’t sure what it was. Some astronomers thought it might be a distant galaxy coincidentally aligned in the sky with the cluster.

In 2014, another team of astronomers observed this object (which they designated S2, for the second unidentified point source of radio emission in M15) using a collection of radio telescope across the planet, and using parallax (the object’s apparent motion in the sky which is actually a reflection of the Earth’s motion around the Sun) found it was located about 7,000 light-years away—one-fifth the distance to M15! Clearly this was neither a distant galaxy nor a weird star in the cluster. That distance puts it firmly inside our own galaxy. The plot thickens.

Finally, another team of astronomers looked at observations from a variety of telescopes, hoping to nail down the identification of this thing. They found it in more radio observations from VLA, and interestingly Hubble Space Telescope observations show what looks to be a faint red source at that position. The kicker is that they also looked in data of M15 taken by the orbiting Chandra X-Ray Observatory, and found nothing; whatever it is, it’s too faint to be seen in even a 30-hour observation.

Hubble images of black hole
Hubble images of the object across the range of visible light (red to blue from left to right) show that it appears faintly in red wavelengths but not bluer ones.

Tetarenko et al., from the paper

All this put together points toward a very peculiar object: a black hole orbiting a tiny red dwarf star. If the black hole has a mass typical of such objects, about 10 times the mass of the Sun, the red dwarf is about 0.1 to 0.2 times the Sun’s mass (also typical). It’s likely the two orbit each other very closely, with an orbital period of roughly one to two hours. That’s close enough together that the star is grossly distorted by the black hole’s gravity, and material is flowing from it to the hole.

When material does this, it tends to form a disk around the black hole called an accretion disk. It piles up there before falling in to the black hole. The disk can be very hot, glowing brightly in X-rays, and also blast out a wind of subatomic particles. In this case though, the disk appears to be very weak and not as hot, which is why it’s not bright in X-rays even though its wind (or possibly other structures called jets) generates radio emission.

Other types of objects can be bright in radio and quiet in X-rays, but each one of these was systematically eliminated from consideration by the astronomers; for example a planetary nebula would show fuzziness in the Hubble images, but none is seen. In the end, the best candidate is indeed a low-mass binary black hole system.

Assuming this truly is as advertised, it’s the first accreting X-ray quiet black hole binary ever seen outside of a globular cluster. It’s also one of the lowest mass black hole binaries known. And that has some very cool implications.

This object was found essentially by accident in a radio observation of a globular cluster. But it’s not in the cluster; it’s much closer and just happens to lie near it in the sky—that’s fortunate, otherwise it may never have been discovered! Given that one of these was found in a very small region of the sky observed, that implies there are a lot of them scattered throughout the galaxy. Using some simple assumptions, the astronomers find that there may be anywhere from 25,000 to 150 million such low-mass black hole binaries in the Milky Way alone!

That’s a lot. It’s a wide range because of a lot of the uncertainties involved, but even on the low end, that’s three times more than predicted by looking at how stars are born and evolve over time (you need a low-mass star orbiting a high-mass one, so that the bigger one blows up and forms a black hole at the end of its life). And on the high end it’s thousands of times the number predicted.

How can the numbers be so far off? That’s a good question, and it’s not clear. Maybe this really was a very lucky observation, and just happened to spot one such object even though the odds were long. Maybe our stellar formation models are off. Either way, it shows us we need to search for more of these objects so we can figure out what’s going on. That’s not easy, as they’re usually found in X-ray surveys of the sky, and they’re X-ray quiet. Looking for the kind of radio emission these types of objects give off specifically will help, as will looking toward the galactic center for them, since they should be more common where there are more stars. A new generation of more sensitive X-ray telescopes coming soon will do well here, too.

I think this is all wonderful. It’s still possible to discover new objects by accident today and use them to learn important characteristics of the galaxy in which we live. And if it means more black holes to study, hooray! Getting a bigger sample of the weirdest objects in the Universe can only be a good thing for science and our understanding of the cosmos.

*Before you freak out, not to worry: Space is big, and even if there are zillions of these things out there, over the entire lifetime of the Universe the chance of any getting near enough to Earth to hurt us is essentially zero.

June 27 2016 9:00 AM

Comets Scoff at Gravity

On Earth, we are keenly aware of gravity. It shapes and modifies everything we do, including our architecture, our behavior, and the landscape around us.

Comets, on the other hand, think of gravity as more of an afterthought.


The image above is from the Rosetta spacecraft, still traveling along with the comet 67P/Churyumov-Gerasimenko as it orbits the Sun. Both were about 474 million kilometers from the Sun and 449 million kilometers from Earth when this shot was taken.

Rosetta was considerably closer to the comet than that, of course. It was just a hair under 30 kilometers from 67P when it snapped this shot, and the resolution on the full-size image is a stunning 0.5 meters per pixel: about 18 inches!

jagged peaks
A closer look at those peaks.


I love the jagged peaks surrounding the flatter plain, towering shards 100 meters high that clearly don’t have to deal with a whole lot of forces like gravity, wind, and the like (another angle on this same region can be seen here). You can see rocks resting comfortably at all sorts of weird angles, partially due to friction with the surface being more than enough to overcome any sliding due to the weak gravity, but also because “down” becomes a complicated topic if you’re standing there. The comet has two big lobes connected by a thin neck, and what you call “down” changes rapidly and strongly with position.

In general, if you were standing on the surface, you’d feel gravity something around 0.0001 times that of Earth. I’d weigh about a quarter ounce, as much a sip of water. A solid jump would fling you away from the comet forever.

The reason behind this is simple: Comets aren’t terribly big—67P is roughly four kilometers across and has a mass considerably less than a typical Rocky Mountain. This makes the force of gravity on the comet pretty weak, barely enough to hold it together.

context shot
Some context on the image; the arrow indicates the flattish plain in the region of the comet named Seth, though the peaks around it are harder to see from this angle. A very large pit (labeled Seth_01 here) can be seen in the lower left corner of the main image, partially cut off.


Even though conditions on the comet seemingly defy the forces we deal with on the surface of our much larger planet, the comet is actually incredibly fragile. It’s made of rock and ice, and when it gets near the Sun on its 6.4 year orbit that ice turns into a gas. This can dislodge rocks, shift surface features, and generally erode things away (and also create the iconic tail of a comet). In a relatively short time (millions of years? Less?) the comet will lose its structural integrity and fall apart. We’ve seen comets do this.

Such will be the fate of 67P as well. But in the meantime, there’s much to learn! Rosetta is still observing the comet, still sending back valuable data, and still helping us understand these bizarre frozen remnants of the solar system’s past.

My thanks to Emily Lakdawalla who helped me find the location of this shot on the comet’s surface. Follow her on Twitter!

June 26 2016 9:00 AM

A Sunday Morning Brain Teaser For You

Hey, I know just you want on a Sunday morning! A physics problem!

If it helps, think of it as a brain teaser. Like many such, it’s deceptively simple, but when you start to think about it a lot of concepts collide and it’s not as obvious as you might suppose at first glance.


Here’s my friend Dianna Cowern, aka Physics Girl, with the brain-stumper. I suggest you do as she recommends, and stop the video to think about it before she gives the answer.

Did you get it right? I will admit it: I did. For the right reason, too, which I almost had to laugh at; many times when I think about a physics problem like this I can argue it both ways depending on what angle I take on the problem. In those cases I know I’ve forgotten something in my deducings.

In this case, I knew that rock is denser than water (as long as it’s not pumice, I suppose), so in the boat the rock was displacing its weight, but in the water it was displacing its volume. If rock is denser than water, its weight in water is larger than its volume in rock, so it displaces less water when it’s actually in the water, and the level goes down.

That kind of reasoning can be hard to follow if you’re not used to doing it. One slip-up loses the chain of logic. I was actually thinking that as I was going through the steps, and a part of my brain whispered to me, “Do an extreme case; it’ll be easier.” Then one minute later Dianna suggested just that, and I did laugh out loud.

Extreme cases may not solve the exact problem you’re facing, but they really help with getting through the logic, because there’s an intuition you get living in the real world about how some physics works. You really do! For example, you may know that if you throw a ball at about a 45° angle it’ll go farther than if you throw it at a higher or lower angle. If you do the physics you find the equations are symmetric around that angle, meaning that really is the best angle to throw a ball for distance.

Extreme cases exploit that knowledge you’ve gained through just existing in a Universe bound by physical laws, giving you an answer that either makes sense or is absurd, allowing you to get a better grip on things. I use them all the time when trying to figure things like this boat puzzle out, and they really do help. Just remember they’re extreme cases and may not represent the actual answer you want. Apply them carefully, and remember they’re a tool, not a solution themselves.

If you liked this problem and the video, Dianna makes lots of them and they’re really good. This one about mirrors is great and generates a lot of interesting discussion (lots of people say the answer is obvious, but it clearly isn’t to a lot of people). I also like this one about hurricanes and soap bubbles.

You can find more on her website, Physics Girl, and on her YouTube channel.

Tip o’ Archimedes’ bathtub to Mental Floss via Jennifer Ouellette.

June 25 2016 11:20 AM

The Stars at Night Are Big and Bright … Deep in the Heart of the Milky Way.

Sometimes you just need to look at pretty stars.

That image was taken by the Hubble Space Telescope back in 2009 (but just released recently), using the Advanced Camera for Surveys. It shows a region of the sky very near the center of the Milky Way galaxy, where stars are packed pretty closely together—think of them as city lights, and you see more when you look downtown.

Interestingly, the stars are displayed pretty close to their natural colors. Hubble cameras are equipped with a wide variety of filters that let through light of not just various colors, but also various bandpasses; that is, the range of colors. A narrow bandpass means you’re seeing a very thin slice of colors (say, centered in red), whereas a wide passband lets through light at a bunch of different colors. These filters have various uses; looking at gas clouds, for example, is usually better using narrow bandpasses to isolate the light emitted by specific elements.

June 24 2016 9:00 AM

Neptune Just Got a Little Dark

So Thursday I wrote about Pluto possibly having a liquid water ocean under its surface, which is pretty amazing. But other worlds in the solar system have stuff going on too, y’know.

Like Neptune. It has a new dark spot.


Neptune is what we call an ice giant; bigger than rocky planets like Earth and Mars, but smaller than Jupiter and Saturn. It’s not literally made of frozen stuff; it’s called an ice giant because planetary scientists tend to call things like methane, ammonia, and water ices when dealing with outer worlds.

Neptune orbits pretty far from the Sun, about 4.5 billion kilometers out. That makes it pretty cold, and you might not expect the atmosphere to have much action. For a long time telescopic observations of it didn’t show much (it’s so far away that even though it’s nearly four times wider than Earth, it’s not terribly big in telescopes), but in 1989 the Voyager 2 probe flew past it, revealing a gorgeous deep blue world with a banded atmosphere, and, very surprisingly, a huge dark spot, which was somehow named the Great Dark Spot.

Since then our ‘scopes have gotten better and more of these spots have been found. We now know they’re anticyclones—high pressure systems—in Neptune’s troposphere, the deeper layer of atmosphere under its stratosphere. Since they’re high-pressure systems, we may be peering deeper into Neptune’s atmosphere when we see them.

color view of Neptune
When full color filters are used, the brighter, whiter clouds appear.

NASA, ESA, and M.H. Wong and J. Tollefson (UC Berkeley)

Dark spots on Neptune tend to be associated with bright clouds around their rims, which may be from methane clouds condensing as air blows around and above the dark spots. This happens on Earth …  well, with water instead of methane. Moist air rising up can condense to form clouds; we see this on the windward sides of mountains as the air lifts up to go over the obstacle. In this case, they’re called orographic clouds. With Neptune, the methane freezes, crystallizes, and becomes bright white to form the lovely thin white clouds around the dark spots.

Dark spots come and go. The Great Dark Spot had disappeared by the time Hubble looked for it in 1994, but other ones had appeared in 1995. This new one found is the first one seen in well over a decade. They can last for many years, because they spin in the same direction Neptune does. That sets up a stable feedback system that helps keep the spot rotating (in that case it’s called a vortex). We see this on Jupiter, Saturn, and possibly other places on Neptune, too.

Why is this important? Well, to be frank, atmospheres are complicated. Planets spin, and warm up, and have different stuff in their atmospheres, and sometimes warming or cooling changes the layering and condensation and evaporation rates, and it’s a mess. Understanding them in terms of their physics is really hard.

In some ways the outer planets are simpler than Earth: They’re mostly air. But there are other complications, like gases in abundance we don’t have here (like hydrogen and helium). Also, while the major source of Earth’s heat is the Sun, the outer planets don’t get nearly as much sunlight. Plus, they still have lots of warmth leftover from their formations (yes, they’re still cooling after 4.56 billion years), and for Neptune that’s its major source of heat. So it’s warmed from the inside out, the opposite of Earth.

All these worlds are test cases for our understanding of how atmospheres behave, including our own. Plus, of course, just understanding things is good. Neptune is a huge, massive, complex world, and worthy of our attention just because it exists and is near enough for us to study it.

June 23 2016 9:00 AM

Does Pluto Harbor an Ocean Under All That Ice?

Before the New Horizons space probe zipped past Pluto in July 2015, we weren’t sure what to expect. A lot was known about Pluto in general—given its density, it was likely a mixture of ice and rock, for example—but very little about was known about, say, the surface structure.

Then the little spacecraft flew by the little world, and our knowledge exploded. The close-up pictures were amazing, both beautiful to behold and tantalizing for the brain. There were lots of surprises, of course, including how diverse the surface was: There are frozen plains of nitrogen, mountains of water ice, dark and bright spots, huge fields of pits on the surface, and much more.


Scattered around the surface are another type of feature: huge cracks, some hundreds of kilometers long and many kilometers deep. They’re pretty interesting, and their presence has led one group of planetary scientists to make an astonishing claim: There may be a liquid water ocean under the surface of Pluto!

If this is true, it’s a very big deal. Pluto is small and extremely cold, so the last thing you’d expect is liquid water anywhere within 3 billion kilometers of it. How can this be?

First, the evidence. The cracks are called extensional tectonic features, meaning you get them when the surface extends, expands. Imagine covering a balloon with mud. Let the mud dry, then inflate the balloon a little bit. What happens? As the balloon expands, it pushes the mud from underneath. Mud isn’t stretchy like rubber, so instead of smoothly expanding it cracks, allowing the pressure underneath to be relieved.

That may be happening on Pluto. The solid crust (mostly water and nitrogen ice) is feeling pressure from underneath, expanding, and cracking. But what could be causing the expansion? Liquid water. And lots of it.

Pluto is mostly ice and rock. However, there is likely to be some amount of radioactive elements in its core. Our own Earth has them, and the heat generated by the decay of these elements is a major source of our planet’s internal heat, even 4.56 billion years after it formed.

Pluto interior
Pluto's layers may include a crust of ice, a liquid ocean under that, and a large core of mostly rock with just enough radioactive material to keep it warm.

Jcpag2012/NASA/Pat Rawlings/Phil Plait

Studies show that even a small amount of such material (including uranium, thorium, and potassium) could produce enough heat inside Pluto to melt some of the water ice. I’ll admit this surprised me; my gut reaction is that Pluto is so small that it would lose heat faster than the radioactive materials could generate it.

The new research just published looks into that. They show that the rocky material inside Pluto insulates it and keeps that heat from leaking away too quickly. The rock acts like a blanket, keeping the heat inside Pluto, and over time it could be enough to not only melt a substantial amount of ice, but keep it liquid even to today.

Well, mostly liquid. Pluto is pretty cold, and some of that water, especially closer to the surface, could start to freeze. When liquid water turns into ice, it expands, and it’s that expansion that’s proposed to cause the crust of Pluto to expand with it, creating the cracks.

How weird is that? Tiny, frigid Pluto, long thought to be a frozen ball of ice, may yet have some spring in its step.

And there’s more. The new research shows that if the ice shell covering Pluto is thick enough—deeper than about 260 km—then the water under the surface could form a strange kind of ice called ice II. It’s still made up of water molecules like regular ice, but under higher pressures (caused by the thicker shell) the molecules realign themselves, forming a different crystal structure than normal ice.

Ice II is denser than regular ice, denser even than liquid water. If it forms, the ocean under the surface would shrink, contracting to a smaller volume. If that happened, you’d expect to see compressional features on the surface of Pluto, like thrust faults.

However, none was found, so it’s unlikely ice II ever formed. That suggests the water under the surface is still liquid, even today. Incidentally, the cracks on Pluto are fresh-looking, with few craters marring them. This indicates relative youth, though it’s hard to know what that means on Pluto. Millions of years? Tens of millions?

Still, this is an intriguing idea. I expect there will be some back-and-forth on this, as the surface of Pluto is examined more closely. For example, there’s a mountain on Pluto that looks like it was pushed up, and then began to subside. If that’s the case, what does that tell us about the thickness of the crust there, and the forces underneath? Also, there are cracks on Pluto’s surface that aren’t linear so much as radial, as if whatever pressure under the surface were greater there than average. Maybe there’s material welling up there, pushing up on the surface.

And of course, there’s another thought. A source of heat, liquid water, and complex chemicals are three ingredients needed for life. Now have a care here: I am in no way saying there’s life under Pluto’s surface! My point is more subtle than that: We wonder if life exists out in the Universe, and the key to that is how commonly the necessary conditions arise. What we’re seeing on Pluto—and on Enceladus, and Europa, and Titan—is that these conditions at least in part appear to pop up quite a bit just in our solar system alone. Even in almost literally the last place you’d expect.

Oh Pluto, will you ever stop surprising us?

I certainly hope not.