Bad Astronomy
The entire universe in blog form

May 28 2016 9:00 AM

Come See Me at Star Trek: Mission New York

On Sept. 8, 1966, NBC aired the first regular episode of a new TV show called Star Trek. It had a bit of a rocky beginning, and had a rocky end three years later. But like Spock himself it would be resurrected and go on to become a major force in popular culture.

I don’t need to give you details; if you read my blog, you probably know them as well as I do. This year marks the 50th anniversary of Trek, with more than 700 episodes and a dozen movies covering that time span.

Advertisement

Holy cripes. That’s a lot of Trek! But hey, it’s well-loved, including by me. And that’s why I’m as happy as a tribble in an overhead bin of quadrotriticale to let y’all know that I’ll be at the Star Trek: Mission New York convention to celebrate the show’s golden anniversary.

The con is kind of a big deal. Actors from all the series will be there; just look at the guest list: William Shatner, Kate Mulgrew, Michael Dorn, Terry Farrell, Jonathan Frakes, Marina Sirtis, and lots more … including me.

Writing that is strange but also good.

Star Trek guests
One of these things is not like the others.

Star Trek Missions

The con will be from Sept. 2–4 at the Javits Center in Midtown Manhattan. We haven’t ironed out the details of what I’ll be doing just yet, but I expect it’ll include talks about science and astronomy (Trek related? Count on it!) and panels as well. I’m hoping to do something with some of the actors, too, but all that is TBD.

Given that this is part of the huge 50th anniversary celebration, I’d urge you to get tickets early if you want to go.*

I’ve got some other things I’m doing for the big anniversary as well, and I’ll let you know here and on the usual venues when those come up. I’m terribly excited about all this. Trek really was a big inspiration for me (proof), and now to be able to be a part of it in some small way is just a dream come true. My sincere thanks go to my friend Holly Amos for making this all possible, too.

P.S. If you're wondering about the picture of me, it's a crop from this. The full story is pretty cool

* Boldly, of course.

May 27 2016 8:30 AM

A Physics Outsider Says NASA Asteroid Scientists Are All Wrong. Is He Right? (Spoiler: No)

People love a good “David versus Goliath” story, especially when David is an outsider, a lone voice against a big government agency that he’s accusing of being incompetent and wasting money.

The problem with that narrative is that sometimes David is wrong.

Advertisement

Nathan Myhrvold is a billionaire, the former chief technology officer at Microsoft, and holds a Ph.D. in physics. He has a scientific background, obviously, and recently became interested in the search for near-Earth asteroids, the kind that get close enough to our home planet to be a threat.

After doing some of his own research, he thinks that a team of scientists at NASA/JPL and Caltech have made serious errors in measuring the properties of asteroids. And he’s gone farther than that: He’s accused them of making “colossal error[s],” and made hints of fraud.

That’s an extremely serious accusation. It’s also, in my opinion, grossly wrong (NASA also issued a response backing up the scientists). After considering his research, I have concluded that the team is not in error, Myhrvold is.

The team of scientists is working on a potential NASA mission called NEOCam—the Near-Earth Object Camera—to map out the locations, orbits, and physical characteristics of near-Earth asteroids as a way to systematically determine what threat they pose to our fair planet. To do this, the scientists need to understand how their telescope operates; that is, if it sees an asteroid, how do you convert that brightness measured to a diameter? The size of the asteroid is a critical factor; without that it’s very difficult to understand much else about it. Over time, the team has published several papers showing how they make this calculation, using methods used before for earlier satellites, including NEOWISE, the predecessor of NEOCam.

Myhrvold, wanting to explore this topic himself, set about trying to replicate their results on his own. What he found, though, was that his numbers for asteroid diameters disagreed with the results from the team of scientists, sometimes by a huge margin.

One of them was wrong. Which one?

WISE observation of asteroid
A composite showing a rather typical NEOWISE discovery; the 650-meter wide near-Earth asteroid 2013 YP139 (circled in red, plus a close-up inset at the bottom), the first such rock discovered by NEOWISE.

NASA/JPL-Caltech

Myhrvold contacted the team, including Amy Mainzer, the NEOCam principal investigator, who has a long history of publishing scientific papers in the asteroid discipline, in order to discuss his ideas. (Full disclosure: I have known Amy for many years and consider her a friend. I talked with her about Myhrvold’s claims, and she was very helpful in pointing out references and explaining some of the physics and mathematics involved.)

At this point, the accounts diverge. Myhrvold says the team was not cooperative about their work and gave him “cryptic” answers to his questions.

Mainzer told me a very different story. She said she worked with Myhrvold multiple times, trying to show him where some of his ideas were either incorrect or not applicable to the work they were doing, but he remained defiant. She pointed out specific errors, but despite that the errors remain his work.

The errors she mentioned are various, including his confusing diameter with radius in his calculations and using a model that incorrectly determines diameters. For his part he says their model doesn’t include some basic physics, and that some of their numbers are suspicious.

So what’s going on? Other articles cover some of the basic claims (see "further reading" at the end of this article), but I want to take on some of the science claims.

The Light and the Heat

Myhrvold claims that the physical model of asteroids the team uses doesn’t work and that they ignore “basic physics.” Now, setting aside the rather bizarre idea that an entire team of professional scientists at JPL and Caltech might not understand undergraduate-level physics, his claim that their model doesn’t work is simply wrong. Worse, it’s his own model that falls short.

The basic goal here is to determine the diameters of asteroids. How do you do that? The idea behind NEOCam is that it will use very sensitive detectors to measure the amount of infrared light the asteroids emit. Anything warm emits infrared light, and the amount of light an asteroid gives off depends in part on its size. By measuring different colors of infrared, complicating factors (like reflectivity) can be accounted for, and the diameter found.

radar image of an asteroid
The asteroid 2015 TB145 was imaged using radar when it passed the Earth in 2015 by less than 500,000 kilometers. Measurements indicated it is about 600 meters across.

Arecibo Observatory

To make sure they’re doing it right, the NEOCam team looked at asteroids for which the diameters were previously known (that part’s important). There are quite a few with accurately measured diameters; for example, some have been pinged with radar, which yields very good results for asteroids that get near the Earth. Others have had their sizes measured using occultations: Sometimes an asteroid will pass directly in front of a star, blocking its light as seen from Earth. Knowing the velocity at which the asteroid moves around the Sun together with the length of time it blocks the star gives you its size.

NEOWISE (the earlier satellite) observed these asteroids. The team then used the known diameters to create a model (a mathematical equation) of how the light is emitted. That way, they can then observe other asteroids with unknown diameters and use their brightness to measure their sizes. This is the model they’re using for NEOCam.

This is the model Myhrvold claims is wrong. However, the asteroid diameters found by the NEOWISE team agree very well with previous satellite measurements. NEOWISE looked at many of the same asteroids as an earlier mission called IRAS—a couple of thousand of the same asteroids—and found that the diameters calculated for those asteroids matched the measurements using IRAS to about 10 percent. Not only that, measurements using a Japanese satellite called Akari also yielded similar results, and all three agree well with the radar and occultation measurements.

That’s a very good indication the NEOCam team is doing things right.

Despite this, Myhrvold disagrees. He says the team is ignoring basic physics, and the diameters they are getting are wrong.

Myhrvold has written a paper with his results, and when I read it, it became clear to me that this accusation is based on a false premise. He is trying to calculate asteroid diameters starting with basic physics (from the ground up, so to speak), while the NEOCam team is doing it empirically, based on observations (so, from the top down). In the latter case the physics is built in to the way the model is generated.

Here’s an analogy: Imagine a quarterback trying to throw a football into a receiver’s hands. An accomplished quarterback has thrown the ball thousands of times, and already knows by feel and muscle memory how to throw the ball, giving it the right speed, direction, and spin to complete the pass.

What Myhrvold is trying to do is start with the physics of motion, trigonometry, momentum transfer, air drag, and so on and then telling the quarterback how to throw the ball.

But the physics is built in to the quarterback’s experience. The passer doesn’t need to calculate all the physics to complete the pass. If we humans had to do the calculus every time we wanted to move, we’d be frozen stiff. So Myhrvold’s accusation that the NEOCam’s team ignores basic physics is incorrect.

Asteroid 295 Theresia size measurement
Myhrvold used NEOWISE data to calculate the size range of the asteroid 295 Theresia. The problem: His result is way, way too big.

Nathan Myhrvold (from his paper)

Worse, Myhrvold’s model is wrong. He published his results in his paper, and the numbers he gets are way off. For example, in Figure 21, he uses his model to calculate the diameter of the asteroid 295 Theresia. The known diameter of that asteroid is about 28 kilometers. Myhrvold gets a diameter of 660 kilometers, more than 20 times too big (if he were correct, it would be the second largest asteroid known)! Other examples with similar erroneous diameters can be found. It’s worth noting that other groups have used the NEOWISE data to compute their own models and have had no problems.

Let me be clear here: If you are accusing scientists of messing up the single most important thing they’re trying to measure—an asteroid’s diameter—you’d better get that right yourself. Myhrvold didn’t.

There’s more. For example, Mainzer told me that he confused radius for diameter in several places in his work—which she pointed out—but those errors remained even as he updated his paper. She also told me he based some of his numbers on an old paper about IRAS that had a systematic error in it, one that overestimates the sizes of asteroids.

Despite his own errors, he is accusing the NEOCam team of being wrong.

But it gets worse.

Cut and Paste

Myhrvold wrote what’s called a “white paper,” an overview of the situation as he sees it using simpler language. In it, he notes that some of the diameters for asteroids the NEOCam team calculated are exactly the same as found by an earlier mission. Like, exactly, to several decimal places. Because the chances of this are essentially zero, Myhrvold speculates that the NEOCam team may have had a bug in their code that copied the diameters from the earlier results and propagated it to subsequent results.

Or, he goes further: He speculates that maybe this is due to fraud.

Yes, fraud, as in knowingly faking these numbers. This is a stunningly serious accusation. But there’s a much simpler explanation about the duplicate numbers. I asked Mainzer about this specifically. She told me the numbers are the same because they are copied, but it’s not due to fraud. The mathematical model they use does indeed calculate the diameter, as well as several other important variables that are initially unknown (for example, how reflective the asteroid is in visible light and infrared light). However, if the diameter has already been accurately measured in other ways (radar, occultations or from previous satellite measurements), they can use that number to better calculate the other variables.

This technique is discussed in a paper published in 2011. Myhrvold acknowledges that but then says this is never mentioned in subsequent papers. If true, that would make it seem like the team, in those subsequent papers, is claiming the diameters were calculated using their model, and were not actually from previous measurements. Hence his suspicion of fraud; in fact in his white paper he goes on at length about this. However, as just one example, in this subsequent paper by the team (in Section 3, first paragraph), they clearly reference the first paper describing the method they use, including using measured diameters if available to better nail down the other variables.

In other words, Myhrvold is wrong. They do in fact discuss how they got the diameters in later papers. He may have simply missed this in the later paper. But either way he should have been more diligent in discussing this with the NEOCam team, especially given the seriousness of his accusations.

If you mention fraud, even as a possibility, you’d better have solid data to back it up. From what I’ve seen, Myhrvold’s claims don’t even come close.

asteroid Lutetia
Another way to get a good asteroid diameter: Send a spacecraft there. This is asteroid Lutetia, imaged by the Rosetta spacecraft when it passed in 2010. Lutetia is quite big, about 120 km across.

ESA 2010 MPS for OSIRIS Team MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA & Emily Lakdawalla

There’s one final thing, and it’s important: Myhrvold’s paper has not yet been peer reviewed. This is a critical step in the scientific process: Other scientists look over the paper and make sure it has the proper methodology, it doesn’t have errors, it’s relevant, and more. They make suggestions to the author, who then rewrites the paper (or redoes the research if necessary), and resubmits it. If the reviewers approve, it gets published in a journal.

The peer review process is absolutely necessary to vet work from start to finish, but Myhrvold’s paper has not yet gone through this process. It may not be foolproof, but it’s at least likely to catch errors that are hard for the author to see (like his own erroneous asteroid diameter calculations). An outsider’s opinion can sometimes be valuable.

Despite that, he issued a press release, which is unconventional to say the least. This is sometimes done when a team wants the general community to contribute and comment, but that’s not what Myhrvold is doing. He’s using it as a platform to make accusations that have not been thoroughly checked. It lends a bad smell to what he’s done.

I know this is a complicated issue, but it’s an important one. Questioning results is fine, if it’s done in good faith and by someone who is well-versed in the subject. Myhrvold has cast himself as the outsider with a unique perspective, as David. But in this case, there’s a reason Goliath is, well, Goliath. The NEOCam team has the data, they’ve been open about their methods, and everything they’ve done is online and available for scrutiny.

I’ll be very curious to know what happens once Myhrvold’s paper is peer reviewed. I hope he’ll be as public about it then as he has been up to now.

Further Reading

Because this topic is complex, here are few links to other articles about this to help you parse it all:

May 26 2016 9:00 AM

A Silhouette of Cold, Dusty Galactic Fingers 

I’ve said it before, and no doubt I’ll have many opportunities to say it again: If you like big, splashy, gorgeous astronomical photos, it’s hard to beat a ridiculously magnificent grand design spiral galaxy.

And if you like ridiculously magnificent grand design spiral galaxies, it’s hard to beat Messier 81, especially when it’s displayed in all its glory in a mosaic created by astrophotographer Robert Gendler:

See? Told you.

May 25 2016 8:45 AM

Update: Mysterious Martian Plumes May Be From a Solar Storm and Not an Impending Invasion

In early 2012 a mystery literally erupted on Mars. Well, above it.

Amateur astronomers viewing the Red Planet from Earth noticed weird features on the limb of the planet (the edge as seen from Earth) in March and April 2012. They appeared to be clouds or plumes of some sort, but they were huge, and several hundred kilometers above the surface of Mars. No cloud has ever been seen that high, nor is there any obvious way to make one or get one there.

Advertisement

The features were definitely real; others have been seen (including with Hubble). Lots of ideas were considered—volcanic plumes, aurora, and so on (though Martian war machines were ruled out fairly quickly)—but nothing quite fit.

Now though, astronomers analyzing data from the Mars Express orbiter may have found a solution. Mars got hit by a solar storm.

Mind you, this isn’t conclusive, but it’s promising. Here’s what’s what.

A solar storm is when the Sun throws a magnetic tantrum, blasting off huge clouds of subatomic particles. These events carry a great deal of energy, and their own magnetic field. If they hit the Earth and interact with our magnetic field they can cause aurorae, blackouts, and other issues.

Mars doesn’t have a strong magnetic field, but it’s there; it’s only a couple of percent as strong as Earth’s, mostly due to magnetized rocks left over from when Mars did have an actively generated field (which has since shut down). And, in fact, the magnetic field is known to be a bit stronger over the region where the mystery plumes were seen.

A Mars plume spotted on March 20, 2012. Photo by W. Jaeschke.

Mars Express has been orbiting the planet since 2003, and is equipped with an instrument called ASPERA-3 that studies the interaction of particles from the Sun with the Martian magnetic field, and another one called MARSIS that uses radar to study the atmosphere and look for water under the surface. Looking over the data, scientists found that there were large space weather events around the same time both plumes were seen.

They did not see any obvious effects of this in the Martian ionosphere, the high altitude layer of the atmosphere where the molecules are stripped of electrons and become ionized. This is where you’d expect to see the biggest effect, so that’s a little odd, but it’s also known that the ionosphere in that region of Mars is “disturbed” due to the magnetic field there, so it’s hard to identify anything that would make it even more jinky.

Interestingly, Hubble observed a plume like this in 1997, and it turns out there was also a solar storm that might have hit Mars just before that observation was made. It’s not certain, but it’s compelling.

So what causes the plume? We know that the Martian atmosphere is being slowly stripped away by the solar wind, the more or less continuous stream of subatomic particles blowing off the Sun. Although the details are complex, and not fully understood, what may be happening here is that a storm from the Sun accelerates that process, compressing the Martian magnetic field, exposing the upper atmosphere to the direct effects of the storm. This allows more of the atmosphere to leak into space than usual, which we see as the plumes.

Mind you, this is still fairly conjectural; the evidence is indirect and circumstantial, but it does fit the idea that the storms caused the air over Mars to be extra leaky. Storms like this are rare, and detailed observations of Mars from Earth aren’t done around the clock, so they can miss the effects. Even orbiters around Mars itself may be in the wrong place at the wrong time to catch the effects.

The only way to know for sure is to catch one in the act. The best witness for that would be orbiters on the spot, but even observers from Earth can be crucial. Like seeing asteroid impacts on Jupiter, the more people we have observing Mars the better.

It makes sense to me. It’s easy to believe that in the early years of the 21st century that world would be watched keenly and closely; across that gulf of space, intellects vast and warm and sympathetic would regard Mars with curious eyes, and slowly and surely draw their plans to understand it.

War of the Worlds
Maybe next time.

Thought Café

May 24 2016 9:15 AM

A Cold Ribbon Where Future Stars Are Born

The Universe lights up when you look at it with different eyes. And, in a very real sense, I mean that literally.

Our galaxy, the Milky Way, is more than just a few hundred billion stars. It’s also loaded with gas and dust, the raw materials from which stars are made. And stars are being made: roughly two to four times the Sun’s mass worth of stars are born every year in our galaxy. Usually that means lots of little stars like red dwarfs, but sometimes it means a truly massive star dozens of times heftier than the Sun. But on average, a handful are born every year.

Advertisement

They form in nebulae, clouds of gas and dust, under a variety of circumstances. There are huge cold clouds of dust out there called molecular clouds, and these are key sites of star birth. They can have regions inside them, knots or clumps they’re usually called, where the density of material is pretty high, big enough that gravity is a player. This material can draw itself together, and stars condense out of the resulting collapse.

That material has to be cold, or else its internal heat can prevent the collapse. So, ironically, one of the best places to look for stars about to be born is inside the coldest places in the galaxy.

The image above shows one such place: a ribbon of brutally cold dust and gas, only about 15°C above absolute zero! The image was taken by the ESA Herschel observatory, which is sensitive to light in the far infrared, way way outside what our eyes can see. This sort of light is emitted by very cold objects, such as clouds undergoing collapse.

The ribbon of material, called LDN 914 (or G82.65-2.00 depending on what astronomical catalog you like) is about 50 light-years long and has about 800 times the mass of the Sun in total, plenty of raw material to make stars. Come back in a few million years, and this will look quite different, lit up by the fierce intensity of dozens of newborn stars.

When I saw this image I thought it looked familiar. It turns out I was mistaken; I was thinking of a different ribbon of star-forming nebula I wrote about back in 2013. But that got me wondering what this object looked like in visible light. I had a suspicion I knew, but I wanted to make sure. 

I dug around the ‘net but didn’t find anything at first. Then, on an astronomy forum for astrophotographers, I saw a post by Werner Mehl. He had taken a very deep exposure of the sky in the constellation of Cygnus, and in his shot was a ribbon of dark material he was having difficulty identifying. Here’s his photo:

LDN 914
It looks different this way, doesn't it?

Werner Mehl, used by permission

Gorgeous, isn’t it? I grabbed his picture, rotated and resized it, and bingo! It’s a perfect match to LDN 914. I contacted Mehl to ask his permission to use it, and also let him know the name of his find (if you’re curious, LDN stands for Lynds Dark Nebulae, a catalog of such objects first published in 1962).

But perhaps you’ve noticed something weird: In Mehl’s photo, LDN 914 is dark, but in the Herschel image it’s bright. What’s going on?

In visible light, that cold dust is extremely opaque. It’s very efficient at blocking light from the stars behind it, and so Mehl’s image shows it as black, with very few stars in it (those are certainly foreground stars, closer to us than the nebula and so unblocked by it).

But anything above a temperature of absolute zero emits light, and what kind of light depends mostly on its temperature. The Sun is very hot and glows in visible light. A red dwarf is cooler and emits mostly red or infrared light. Cold dust clouds glow in the far infrared, where Herschel can see them.

And that’s what I meant at the top of this post. When you look at the Universe with different eyes, it literally lights up.

My favorite examples of this are when visible and far infrared images are overlaid; you can really see how something dark in visible light glows brilliantly in longer wavelengths. The best ones I’ve seen are the Cat’s Paw Nebula, IC 5156, and this, M78 in Orion:

M78
A river of cold fire runs through Orion.

ESO/APEX (MPIfR/ESO/OSO)/T. Stanke et al./Igor Chekalin/Digitized Sky Survey 2

The blue part of the image is visible light and has very dark dust lanes running through it. The orange is from APEX, which sees light with submillimeter wavelengths, where cold dust glows. I love how they fit together like puzzle pieces. Amazing. And truly lovely.

See how beautiful something can be when you widen your perspective a little bit? If there’s a life lesson there, feel free to take it.

Post script: And oh yes, the reason LDN 914 looked familiar to me? I was able to crack that one pretty easily

May 23 2016 12:10 PM

These Dunes Are the Pits. Or Vice Versa.

I love a good coincidence. Especially a series of them. To wit:

Last week I wrote an article about a massively viral optical illusion photo of a brick wall—if you haven’t seen it yet, I won’t spoil it; just go to my post and be amazed.

Advertisement

The very next post I put up after that had images taken by the Dawn spacecraft of the protoplanet Ceres, showing the cratered surface.

The funny thing is I got a few emails and tweets from people saying they were seeing the craters not as depressions in the surface, but as domes popping up out of it.

I had to chuckle about that. That’s another illusion I know very well, usually called the crater illusion. It was a funny (if minor) coincidence that people saw it in the post following a post about an illusion. It was funnier to me because in the brick wall post, I actually (and also coincidentally) linked to one of my favorite examples of the crater illusion, where dunes in the north African desert look like holes in the ground.

The icing on the coincidental cake? The very next day, the European Space Agency posted a photo of the Rub al Khali desert in the Arabian Peninsula, showing this same illusion, also featuring sand dunes!

The photo at the top of this post shows a part of the (much larger) image, taken by the Sentinel-2A satellite in December 2015. To me, the illusion that the dunes are actually pits in the surface is very strong. Does it look that way to you?

The reason for this is that we evolved to interpret scenes assuming the light is coming from above, like sunlight. When we see a photo, our brains assume the sunlight is coming down from the top of the picture. Something popping up out of the surface (like a sand dune) would be illuminated by that source of light, with the upper part of it (the part nearer the top of the photo) bright and the lower part shadowed.

But in the Sentinel photo, the lower parts of the dunes are bright, and the upper parts dark. That’s because the sunlight is coming from more or less the bottom part of the photo. But our brains have a hard time with that, assume the light is coming from above, and think the dunes must actually be pits. To our addled brains, something with its brighter part toward the bottom must be depressions in the surface, not something popping up out of it. So we see the dunes as pits.

Don’t believe me? I flipped the image over. Take a look:

Dunes flipped
Dune better?

ESA

Now that the light looks like it's coming from the top of the image, do they look like dunes to you? They do to me!

I played with the images for a while and found the illusion to be stronger when I shrank it down quite a bit; if I zoomed in on the dunes I saw them as dunes, and not pits. That was odd. I suspect the wavy lines of dunes give clues to my brain that the lighting doesn’t make sense if they’re pits (especially where the dunes make tight Z-shaped jogs in the lines). Those clues are too small to resolve when the image is smaller, so the illusion is stronger.

As always, while fun, there’s an underlying message here too: Your brain is lying to you. All the time. It does not see the world for what it is, but instead interprets it through a vast number of filters and preconceptions.

What you see is not what you get. It’s a pretty important lesson to remember.

May 23 2016 9:00 AM

Jupiter May Be Hit by a Half-Dozen Visible Asteroid Impacts Every Year

In 1994, Jupiter was pummeled by the repeated impacts of the comet Shoemaker-Levy 9. The comet had been caught by the planet’s gravity earlier, torn apart by the tidal force during a close pass, and then each chunk slammed into Jupiter’s upper atmosphere and exploded, one by one, over the course of a week.

These impacts were easily seen from Earth (I saw the dark dust clouds peppering the cloud tops of Jupiter myself through a 15 cm telescope!), the first time any body other than Earth had been unambiguously seen to be hit by a comet or asteroid.

Advertisement

Since that time, five more impacts have been seen: in 2009, June 2010, August 2010, 2012, and 2016. In each case, the events were caught accidentally by amateur astronomers when they were taking video of Jupiter!

This raises the question: How often is Jupiter actually hit by an object big enough to make a flash visible from Earth?

At a workshop held earlier in May to encourage amateur astronomers to observe the planet in support of the upcoming arrival of the Juno mission to Jupiter, astronomers announced they have an estimated answer: Jupiter gets visibly hit by six to seven chunks of cosmic debris every year.

Yegads. That’s a lot!

They determined that number not just by the times amateurs have seen impacts on Jupiter, but also by how much they didn’t. If you happen to look at Jupiter and see an impact, you can’t know if you were just lucky; you have to observe the planet for a long time to see just how much it gets hit. In this case, observations from about 60 amateurs totaling more than 56 days of video were analyzed to look for impacts. None were seen, but that provides a valuable baseline for the impacts that were caught by accident by other amateurs.

While this is an estimate (and has not been through the peer-review process), it jibes with the numbers I was coming up with based on the impacts we’ve seen; on the order of once per year (meaning one to 10 times). And that’s only the impacts we can see; we miss half because they hit the far side of Jupiter, facing away from Earth, plus some when they occur within a few weeks of the time Jupiter is behind the Sun as seen from Earth.

Clearly, what we need here is a bigger team of astronomers across the Earth observing Jupiter, so we cover it as much as possible. The folks at the Juno workshop are working on that, as well as improving software that will allow analysis of video taken.

Why video? Well, it gives better time coverage of the planet—a single exposure is generally less than a second (Jupiter is bright through a telescope!), and a video can run for a long time. Also, Earth’s atmosphere boils and seethes, blurring out small details in astronomical targets. Video frames can be very short exposures, helping minimize that blur. Plus, one part of Jupiter might be relatively unaffected in one frame, while a different part of the planet looks better in a different frame. Sections of different video frames can be cropped out and reassembled to create a single, high-resolution shot of the planet. This is a relatively standard technique used by amateurs these days, and was how those more recent impacts were discovered.

As for the science, that part is pretty interesting. The impacts we see (with the exception of Shoemaker-Levy 9) are from pretty small asteroids, probably just a few dozen meters across. Jupiter’s ridiculously strong gravity pulls them in so hard that they are moving five times faster than impacts on Earth on average, making them 25 times brighter (energy released goes as the square of the impact velocity). In that case, even a smaller body can make a bright flash.

Asteroids that small are impossible to see directly from Earth because Jupiter is so far away. So the impacts on Jupiter give us an indirect way to figure out how many such objects are out there. Also, we don’t see too many impacts on other objects (pretty much just the Moon), so the more we see the more we can understand these events. I’m all for that.

As an aside, astronomy is one of the very few fields of science where amateurs* can make valuable contributions. Big professional telescopes are oversubscribed, and can’t afford the time to sit and stare at Jupiter for nights on end. In cases like this (and in many, many others) people with their own ‘scopes really fill a big gap in our understanding.

As someone who considers himself both an amateur and a professional astronomer, I love this. Science should be for everyone, whether you just want to learn more about it, enjoy it yourself, or participate in it directly. Astronomy is a fantastic way to do all of these things.

*Like so many other things in astronomy, there’s no good definition of what an “amateur” is. Someone who isn’t paid? Someone who does it as a hobby, or once a year when they haul a ‘scope out to look at the Moon, or who has done it for so long they know the sky like the back of their hand and write their own software to analyze their observations and create gorgeous images or scientific data? Yes.

May 22 2016 9:30 AM

A Dozen (or So) Ways to Die in Space

Macabre? Sure. But my sense of humor runs dark sometimes, and I love science fiction, so this (very) short animation (very) briefly depicting a bunch of ways hapless space explorers can undergo Death in Space cracked me up.

I could nitpick the science—you won’t explode if you crack your helmet, but it won’t exactly be fun either—but that’s not really in the spirit of the thing. And that’s coming from a guy who literally wrote the book on this subject.

Advertisement

Tip o’ the spacesuit helmet to io9.

May 21 2016 9:00 AM

Now’s a Good Time to Look Up as Mars Looks Back at You With Its Red, Baleful Eye

The other day I was puttering around in the house a couple of hours after sunset and happened to glance out an open window. There, shining over the horizon in the east like a glowering eye, was an intensely bright red-orange “star.” I stopped for a moment, surprised, then realized what was going on: The star was a planet, specifically Mars, and it’s nearing opposition.

If you have a telescope, know someone who does, or live near an astronomy club (click here to find out!) or observatory, now’s the best time all year to see the Red Planet. It’s up all night and about as close as it can get to Earth. On May 30, it’ll be just a hair more than 75 million kilometers away, which as planets go is pretty close.

Advertisement

No, Mars won’t be as big as the Moon in the sky! Mars is only about 6,800 kilometers across, about half the width of Earth, and from 75 million kilometers away it looks pretty small. Still, it’ll be close enough that with a decent ‘scope you’ll see surface features. Maybe not as nice as that Hubble Space Telescope picture at the top of this post, but it’s pretty amazing to be able to see detail on the planet with your own eyes. If you get a chance to use a telescope over the next few weeks and observe Mars, take it! 

So what’s going on? Mars and Earth both orbit the Sun like two cars going around a racetrack at different speeds; the Earth is on the inside track and moves a little faster. When Earth passes Mars on the inside curve, they’re as close together as they can be. When that happens, from Earth, we see Mars on the opposite side of the sky from the Sun—hence the term opposition. Because of that it rises when the Sun sets, and is up all night. It’s a twofer: Mars is as close as it gets, and it’s up at a convenient time to see it.

Things do get a bit complicated in the details. For example, Mars is on a fairly elliptical orbit that takes it as far as about 250 million kilometers from the Sun and as close as 207 million kilometers. That means some oppositions are better than others; the closest approach can range from 100 million to as little as 57 million kilometers from Earth. That means this one is fair to middlin’.

Mars
Hubble's view of Mars over the past few oppositions (displayed to scale) shows how much the planet changes in size.

NASA, ESA, and Z. Levay (STScI)

Because of its elliptical path, it also means opposition and perigee (the time it’s closest to Earth) don’t fall on the same day; opposition is May 22, over the weekend, but perigee is a week later.

Still and all, it’ll be bright and pretty for the next few weeks, so you don’t have to rush out and see it only on May 30! Any time through June and even July will be cool.

And if you want to impress people with your knowledge of Mars as you observe it at a star party, then may I suggest watching my episode of Crash Course Astronomy about the planet? Take notes if you want; there’s no test. The only goal is to understand the Universe around you better and appreciate it a little more.

May 20 2016 8:45 AM

Of Course Trump Chose a Global Warming Denier as His Energy Adviser

Donald Trump has announced his new energy adviser: Rep. Kevin Cramer (R–North Dakota). 

I hope you’re sitting down for this shocker: Cramer is a global warming denier. And to be clear, he’s not just a denier. He’s a crackpot.

Advertisement

First, watch this video put together by the folks here at Slate to get an overview of this guy’s view on science:

Trump’s grave misunderstanding of the difference between weather and climate doesn’t surprise me; he’s a buffoon when it comes to such topics (case in point: he said global warming is a hoax manufactured by the Chinese). Given his history, his choice of a crackpot for energy adviser isn’t terribly surprising.

North Dakota fracking glows at night
If you don't remember any big cities in North Dakota that could glow like that at night, it's because that's not a city. That's the light from huge numbers of fracking sites burning off excess gas.

NASA Earth Observatory/NOAA NGDC

Cramer has a long record of climate change denial (apropos of nothing, over his career Cramer has received more than a half million bucks in funding from the fossil fuel industry, more than twice as much as any other industry). That’s also not surprising given that North Dakota is one of the largest producers of oil and coal in the nation. The burning of excess natural gas fracked in the state is so intense it’s easily visible to satellites in space. Given all that, Cramer denying climate change is de rigeur.

It’s the degree (so to speak) to which he denies it that’s staggering. He’s part of the tiny, tiny head-in-the-sand deniers who won’t even acknowledge the planet’s heating up. That line in the video where he says, “We know the globe is cooling; number one we know that” is from 2012, just a few years ago. We’ve known since long before then the planet is heating up, and the past few years the warming has gone into overdrive; each of the past seven months have been the hottest of those months globally. To actually say out loud that the Earth is cooling would make Orwell blush.

But he wasn’t done; he also added, “… the idea that CO2 is somehow causing global warming is on its face fraudulent.”

Holy. Baloney. He’s not just denying global warming, he’s denying a link between carbon dioxide and the planet’s increasing temperature. For the record, carbon dioxide being a greenhouse gas has been a matter of scientific fact since 1896.

The conservative party really is conservative. When it comes to science, Trump and Cramer want to wind the clock back to the nineteenth century. At least.

Cramer has made it clear that if Trump gets elected, he’ll be no friend to the environment, rolling back regulations and reversing the Clean Power Plan. Trump himself has said he’ll back out of (or “renegotiate”) the Paris climate treaty, a claim he makes based on 100 percent utter nonsense.

It couldn’t be more clear: If Trump does indeed take the White House our planet is, basically, screwed.

So, there you go. Nothing about this is at all surprising from the candidate who put away the dog whistle years ago, bringing out into the open the contempt he has for women, people of color, Muslims, gays, decorum, facts, and science. This is what the modern GOP hath wrought, and come November, hopefully they’ll reap what they’ve sown.

Update, May 20, 2016: Due to a production error, an incomplete version of this post was originally published.

READ MORE STORIES