My pal Veronica Belmont hosts a show on TechFeed called Fact or Fictional, where she investigates the science of a movie based on viewer suggestions. She recently took on the
wonderful fantastic gawd-awful piece of festering offal "Armageddon", talking to scientist Joe Hanson, who writes the terrific It’s OK to Be Smart blog.
Let’s just say they agree with me about the movie:
If you want to learn how we’d really prevent an asteroid impact, and why we need to take this seriously, I gave a TEDxBoulder talk about it. It’s a real threat, but one we can prevent if we choose to do so.
Mars is weird. Right? I mean, it’s a whole other planet. So you expect it to be weird.
But then I see pictures like this one from the Mars Reconnaissance Orbiter’s HiRISE camera, and I am reminded just how weird it is:
[Click to chicxulubenate.]
Most craters you see are pretty simple: something impacts the ground at high speed, BOOM!, and you get a crater like a dish tossed into soft sand. But this one has two rings, one inside the other. That can happen with huge impacts producing craters hundreds of kilometers across, but this one is small, only 230 meters from side to side – an American football stadium would just fit inside this crater.
The most likely explanation for the double ring is that the Martian landscape here is layered. There’s rock and sand on the surface, but underneath that is a layer of ice. The big rim is from the displaced rock, and the inner, smaller ring is from the impactor plowing through the ice. Each layer has a different strength – rock is harder than ice – so it’s as if two craters were formed, one inside the other. Radar observations of Mars from orbit have indicated there’s ice under the surface in this region, so that fits.
Similar double-ringed craters have been seen on Mars – though the structure and history is by no means well understood! – and some have been found on the Earth’s Moon as well. Those tend to be big, as I mentioned, though they don’t have to be.
By the way, the image above is color enhanced to show details. The blue may be from carbon dioxide frost, which can be seen in similar color-enhanced HiRISE images. The ripples in the center are sand dunes, sculpted into parallel waves by the ceaseless Martian wind.
Craters this small on Earth are extremely unlikely to form; the impactor would be maybe 20 meters or so across, and objects that size tend to break up when they ram through our thick atmosphere at high speed. Mars has much thinner air, so rocks that size can hit intact. Studying craters on Mars is a chance to see what these hypervelocity impacts are like under very different conditions, which helps us understand them. The physics of extremely high-speed collisions is hard to study experimentally – accelerating large objects to that kind of speed is both difficult and more than slightly dangerous – so it’s nice to have a lab like Mars where we can observe these effects.
Tip o’ the lens cap to HiRISE on Twitter. Image credit: NASA/JPL/University of Arizona.
By now you’ve probably heard that on September 10, Jupiter got whacked by an asteroid or comet again. It was seen directly by amateur astronomer Dan Peterson, and video was taken by George Hall, who kindly posted a fairly awesome a four-second clip on Flickr:
[You may need to refresh this page to see it.]
You can read more about it at Scientific American.
I tweeted about this shortly after it happened (I was returning from the UK and didn’t have time to write about it here), and got a lot of people wondering how big the flash was. On the video it looks like it’s thousands of kilometers across! But that’s not real; the size you see is due mostly to the optics of the telescope and video camera Hall used (plus other factors like atmospheric blurring). Given the brightness I guessed the object was a kilometer or so across, but I heard a radio interview the other day (I missed the guest’s name; sorry) where an astronomer said it may have been only 10 meters across – the size of a large truck.
I was surprised at first when he said that, but then realized something critical: Jupiter is a lot bigger than Earth.
The energy released by an asteroid upon impact depends primarily on two things: how big it is and how fast it’s moving. For a given asteroid, that means it’ll explode with far more energy if it hits Jupiter, because Jupiter’s gravity is much stronger than Earth’s, and pulls the rock in faster. Simply because of this, impacts on Jupiter can be greater than 20 times more energetic than on Earth. There are other factors (like orbital speeds, what direction the asteroid was moving, and so on), but in general and pound for pound Jupiter impacts are bigger than on Earth.
A 10-meter rock hitting the Earth will release roughly as much energy as a 0.1 megaton bomb, whereas on Jupiter that same rock will release about 2 megatons. A rock twice that size will have 8 times the mass (volume increases with the cube of the radius) so even if it were 20 meters across, the explosion could’ve been in the 15 – 20 megaton range, which is starting to get to the size of the largest nuclear weapons ever detonated on Earth.
So yeah, that’s a lot of power. It doesn’t take a big rock to make a bright flash when you’ve got Jupiter pulling the strings.
And the big planet gets hit a lot. The last one seen was on August 20, 2010, and it got whacked in June 2010 as well as in July 2009 (not to mention the ferocious series of impacts in 1994 from comet Shoemaker-Levy 9). That’s pretty close to one biggish impact seen per year, and remember we only see half of Jupiter at a time, and it’s not observed constantly! So the real rate is probably far higher.
I also got a lot of people asking why we call it an impact when Jupiter has no solid surface. That’s because the rock will still explode as it rams through Jupiter’s dense atmosphere; I wrote an explanation of this for an earlier impact. The 1908 Tunguska event here on Earth was an air blast, as well.
It’s amazing we can see these planetary at all, but that’s due to the digital revolution: amateur astronomers take video of Jupiter and other objects to maximize the number of frames they get, which they then can combine into amazing images. A nice side-effect from this is the collection of rapidly-taken data providing long coverage of the planets, which means significantly increasing the odds of seeing something like this. That is precisely why we’re seeing more impacts now than ever before. They’ve always been happening, we’re just a whole lot better at seeing them.
Which is a sobering thought. The Universe is worth investigating, if only for our own self-interest.
Asteroid 2012 DA 14 was discovered a few weeks ago: a 40-meter wide rock on an orbit that brings it pretty close to Earth. Next year, on February 16, it will pass about 27,000 km from the center of the Earth (roughly 21,000 km from the surface), which is pretty close, but still a clear miss.
I wrote about this asteroid earlier this week, and the comments have been pouring in. People are asking if it will hit (no), if the Earth’s gravity will change the orbit of DA 14 (yes), have astronomers accounted for that (yes), and will it ever hit us sometime in the future (we don’t know; see below). One commenter, Chris Laurel, created a wonderful photo-realistic animation of the pass of the asteroid using software called Cosmographia, and, well, I think it will answer most people’s questions and fears:
Isn’t that cool? I did some spot checking using the JPL numbers and diagrams, and this looks pretty accurate to me. You can see how it approaches and misses us, and then he backs out a bit to show that the asteroid’s path is warped significantly by Earth’s gravity. So, to be very clear: next year, in February, this rock will miss us.
However, the amount the orbit is changed by Earth depends on precisely how close it comes, and we can’t measure the orbit that accurately just yet, even though we know it well enough to know it will miss. So what we really need are as many telescopes watching this event next year as possible for as long as possible. That will greatly reduce the uncertainty in the asteroid’s position over time, and allow for a good measurement of the orbit. It’s overwhelmingly most likely that the Earth’s gravity will put the asteroid into an orbit where it will miss us again for some time to come, but the only way to be sure is to really nail down its orbit.
I’m sure there will be an organized campaign with observers all over the world to do this. I’ll post more about that when I hear more, probably in the next few months.
- No, asteroid 2012 DA14 will not hit us next year
- Asteroid 2011 AG5: a football-stadium-sized rock to watch carefully
- My asteroid impact talk is now on TED!
- Just to be clear: asteroid YU55 is no danger to Earth
- Media FAIL *again* (HuffPo and Apophis edition)
- Debunking doomsday
Over the weekend, I posted about asteroid 2012 DA14, which is not the threat some people are claiming it is (at least not right away). And now I have to tell you about an asteroid that might be a threat in the year 2040. Most likely it won’t be, but it’s something we need to look at carefully.
There’s some background I have to give you so this all makes sense, but let me sum up here: the odds of an impact from asteroid 2011 AG5 are low, but not easily dismissed. If it passes us at just the right distance in 2023, it’ll swing back again and impact the Earth in 2040. We don’t know the orbit of it well enough to say either way just yet, and it may be late 2013 before we can be sure. An asteroid expert at NASA says waiting until next year for more observations is not a problem, but another asteroid expert is saying that waiting that long is a bad idea: we should start analyzing a possible deflection campaign for this rock now. I’m personally leaning toward the idea that getting moving on the initial analysis now is not such a bad idea. If you prefer, I have a list of bullet points at the conclusion of this post with summarized information.
[In the interest of full disclosure: Below, I will be talking about Rusty Schweickart and Don Yeomans. I've known Rusty for several years, and Don and I will be on a panel together talking about asteroid impacts at SXSW next week. I honestly like both Rusty and Don. They're good men, very intelligent and honest, and I have a lot of respect for both of them.
Also, because of the length and nature of this post, I strongly urge everyone to read the whole thing, carefully, before commenting. Thank you.]
The asteroid, called 2011 AG5, was discovered in early 2011 by a telescopic survey of the sky designed to look for asteroids that can get near the Earth. Although its exact size is unknown, it’s roughly 140 meters across — the size of a football stadium. As you can see from this diagram, it orbits the Sun on an elliptical path that brings it out past the orbit of Mars and inside the orbit of Earth. It circles the Sun once every 1.7 years.
As it happens, the orbit of AG5 brings it close to Earth every few orbits. In 2023, it will pass us at a distance of about 1.6 million km (1 million miles). That’s a safe distance, with no chance of it hitting us at all. However, you have to appreciate the gravity of this upcoming situation.
When AG5 passes us in February 2023, the Earth’s gravity will bend its orbit a little bit, changing the path the rock takes. If it passes close to the Earth the orbit changes a lot; if it’s too far the orbit changes only a little. But if AG5 passes us at just the right distance, the orbit will change just the right amount to put it on a collision course with Earth. This region of space is called a “keyhole”, and in this case, should AG5 slip through it, it will hit us 17 years later, in 2040. That collision, though not global in scope, would be catastrophic: equal to about a 100 megaton explosion, twice that of the largest nuclear weapon ever detonated.
The problem is, we don’t know the orbit of AG5 well enough to know if it will travel through the keyhole or not. As I pointed out in the article about the asteroid 2012 DA14, it can be tricky to try to predict asteroid orbits too far into the future. The orbit of an asteroid is determined by making measurements of its position over time, and because of various effects (like blurring due to our atmosphere) it is impossible to get exactly precise positions. They can be good enough to get an accurate orbit for the next few years, but the farther into the future you look, the fuzzier that path gets.
In the case of AG5 we know its orbit well enough to know for sure it’ll miss us by a million miles in 2023, but we don’t have the accuracy yet to know if it will thread the eye of this keyhole, which is very roughly 360 km (240 miles) across. It’s like standing by the side of a road and knowing a car driving down it will safely miss you by 10 meters, but you can’t be sure if that exact distance will be 10.004 meters or 9.996 meters. And that’s the sort of accuracy we need for AG5.
At the moment, given the observations we have, the odds of AG5 passing through the keyhole in 2023 are about 1 in 625. For an asteroid impact, that’s actually pretty high as these things go, but still pretty low in realistic terms. Let me be clear: any professional poker player will tell you never to bet on an inside straight, and the odds of getting the card you need in that case are only 1 in 13 or so. The odds of AG5 hitting us are much lower than that!
Moreover, since the orbit of the asteroid is uncertain, as we get better observations the predicted path is likely to change, to move. In that case — which is almost certainly the way things will play out — the predicted orbit will move away from the keyhole and we’ll be safe from a 2040 impact. This sort of thing has happened several times before with asteroids as their positions are observed over time, and the orbital paths clarified.
Still, a 1 in 625 chance is high enough that we need to be sure. So how do we do that?
For the tl;dr crowd, let’s get this out of the way right away: asteroid 2012 DA14 is almost certainly not going to hit the Earth next February. And by "almost certainly", I mean it: the odds of an impact are so low they are essentially zero. This does not rule out an impact at some future date, but for now we’re safe.
So what’s the story?
A small near-Earth asteroid was discovered in late February by astronomers at the Observatorio Astronómico de La Sagra in Spain, less than two weeks ago. Designated 2012 DA14, it’s estimated to be about 45 meters (150 feet) in diameter, and has an orbit that is similar to Earth’s.
Its orbit is an inclined ellipse, tilted a bit compared to Earth’s orbit around the Sun (the positions of Earth and DA14 are shown for August of 2012 — I picked that randomly to make the orbits clear), and it spends most of its time well away from our planet. However, the path of the rock does bring it somewhat close to the Earth twice per orbit, or about every six months. The last time it passed us was on February 16 – two weeks ago — when it was about 2.5 million km (1.5 million miles) away, equal to about 6 times the distance to the Moon. That’s usually about the scale of these encounters — it misses us by quite a margin.
February 2013: a close shave
Next year, on February 15, 2013, DA14 will actually get pretty close to Earth. It will pass us at a distance of about 27,000 km (17,000 miles) — well beneath many of our own orbiting satellites! To the best of my knowledge, this is the closest pass of a decent-sized asteroid ever seen before the actual pass itself.
However, let’s again be very clear: it will miss. In astronomical terms, 27,000 km is pretty close, but in real human terms it’s a clean miss.
[UPDATE: The rt.com article I linked below has changed substantively since I posted my own article here. They have attributed their quotations more clearly, and have taken out most of the more breathless rhetoric. I applaud them for doing so, though I wish they had been more clear in the first place.]
Unsurprisingly, though very irritatingly, I’ve seen a lot of websites writing about this as if the asteroid will hit. For example, rt.com has a very confused article about DA14 claiming it will somehow both miss us and hit us:
The rock’s closest approach to the planet is scheduled for February 15, 2013, when the distance between the planet and space wanderer will be under 27,000 km (16,700 miles). [...] With the asteroid zooming that low, it will be too late to do anything with it besides trying to predict its final destination and the consequences of impact.
Blechh. They write that in a way to make an impact seem likely, but that’s not the case at all! I’ve seen several other websites making similarly contradictory or confused claims (Note:I originally included this SFBay article as an example. It’s not confused, but by using the phrase "potentially fateful day" it struck me as exaggerating the fear). The rt.com article even comes right out and says "NASA confirms… [DA14] has a good chance of colliding with Earth". This is simply not true. I’ll note they don’t actually give a reference to that, so it’s not clear who, if anyone, actually said that, or where they got that information. Either way, it’s wrong.
The fuzzy future
So we’re safe for now. But what about future passes?
That’s harder to say. Predicting where an asteroid will be at some future time depends on a lot of things, including how good the observations are now and how long we’ve been watching it. When we observe an asteroid with a telescope, we can measure its position, but not with perfect accuracy. The Earth’s atmosphere blurs the image a bit, and other factors make it impossible to get an exact measurement. So we observe it many times, over as long a period as possible, to hammer down those uncertainties.
There will always be some small amount of fuzziness to the orbit of an asteroid, though, and the farther ahead in the future you look the bigger that fuzziness gets. For next year, we know the orbit of DA14 well enough to know it’ll miss, but for future orbits it’s harder to say.
As things stand, right now the JPL website lists the next close pass as February 2020, but we don’t know the orbit well enough at this moment to know how close that pass will be*. As things stand, the odds of an impact even then are very, very low (like, 1 in 100,000 — less than your odds of getting hit by lightning in your lifetime). We can’t technically rule it out just yet because, again, the orbit isn’t known well enough to look that far into the future. Of course, astronomers are observing the asteroid right now, and will continue to do so. No doubt we’ll have better orbital information pretty soon.
Keep watching the skies!
So again, because I can’t say this strongly enough: asteroid 2012 DA14 is not an impact threat for February 2013. However, we definitely need to keep our eyes on this guy to see if it poses a threat at some future date. If it does, then you can be sure you’ll be hearing about it from me, and from other websites too. But make sure you find reliable websites. Too many are too ready to breathlessly report this as doomsday when it’s anything but.
So, at least for February 2013, we can safely say:
* I’ll note the European NEO-DyS group uses different mathematical techniques, and they don’t even list that date as a near pass. Instead, they say it’ll be six months later, in September. Again, this shows that given our current observations of DA14, predicting its position that far in the future is very uncertain.
In September 2011, I was honored to be on the speaker roster for TEDxBoulder, which is a local though independently-run version of the much-lauded TED talks. My talk was about saving the Earth from asteroid impacts, something I’ve spent a lot of time thinking and writing about.
The talk is online, and I’ve included it here:
The "We have a space program" line is from science fiction author Larry Niven, so I can’t take credit for it, though I modified it to add the "we can vote" bit. Also, this was the biggest audience I’ve ever spoken to, and it was a great crowd. I was almost last on the roster, but the audience was attentive and clearly enjoying themselves. It was a really fun, energizing, and mind-expanding evening.
The other talks that night are being put online as well. If you ever get a chance to attend a local TEDx conference, you should.
One of the enduring mysteries of our solar system is why Uranus is tilted over on its side. If you measure the angle of a planet’s rotation axis (the location of its north pole) compared to the plane of its orbit, you find that all the planets in the solar system are tipped. Jupiter is only 3°, but Earth is at a healthy 23° angle; Mars is too. Venus is tipped so far over it’s essentially upside-down (we know this because it spins the wrong way).
Uranus, weirdly, is at 98°, like it’s rolling around the outer solar system on its side. The best guess is that it got hit hard by something planet-sized long ago, knocking it over (though there are other, more speculative, ideas). The problem with that is that its moons and rings all orbit around its equator, meaning their orbital planes are tipped as well. It’s hard to see how that might have happened, even if you assume the moons formed in that collision (as, apparently, our Moon formed in an ancient grazing impact with Earth by a Mars-sized body).
Well, a team of astronomers have come up with a new idea: maybe Uranus wasn’t hit by one big object. Maybe it was hit by two smaller ones.
The MESSENGER spacecraft, orbiting Mercury for nearly a year now, took this pretty nifty shot of the tiniest planet’s south polar region, showing deep, dark craters in the Goethe basin:
This region is about 300 km (180 miles) from the true south pole of the planet. On Earth that might be a cold spot, but on Mercury, cold spots are hard to come by.
… however, see how dark those craters are? Since they’re near the pole, the Sun never gets far above the horizon for them, and the crater floors are shrouded in perpetual darkness. That does make them cold! Well below the freezing point of water, it’s thought. Interestingly, radar observations of Mercury have indicated something in the crater floors is highly reflective, and water ice fits that bill. It’s not at all confirmed, but it’s entirely possible Mercury — a planet hot enough in the open Sun where zinc can exist as liquid lakes on the surface — might have frozen lakes of ice locked in crater bottoms near its poles!
While gazing idly at this picture, another thought popped into my head. Read More
[Update: It looks like the cause of this was a gas bottle exploding, and not a meteorite. See the update for 21:15 UT below).]
A deadly explosion and fire occurred in Argentina overnight, reportedly killing one woman and injuring several others. Two homes, a store, and several vehicles were destroyed or damaged.
The thing is, while it’s not clear what caused this incident, several people said they saw a ball of fire descend from the sky when it happened.
Neighbors’ accounts describe a ball of fire coming from the sky as the cause of the explosion. The chief of the firefighters, Guillermo Pérez, however, said the "causes remain unknown" and that "gas containers were found intact," ruling out a gas related incident.
Other reports are similar; in that article the ball of fire was described as being blue. I know a lot of folks will think this was caused by a meteor, but it’s a bit early to run with that yet. For one thing, it could’ve been a small plane on fire, for example; this happened very early in the morning (2:00 a.m.), and from the reports I’m seeing it’s not clear if the witnesses were already awake when they saw this or were awakened by it. Eye witness reports are notoriously unreliable, and it can’t help if the witnesses were suddenly woken up.
[Update (17:30 UT): This is looking less like a meteorite to me; this news story has a witness saying he saw the blue fire after hearing the explosion, and after he went outside to see what was what. Thanks to JoseManuelp2 for the link.]
As testament to that, I’m seeing some reports that the ball was red, and a picture was posted to the imaging site yfrog claiming, without any any supporting evidence, to be a shot of it. I include it here; note it’s very dark, out of focus, and very low resolution (from the pixelation). I have no clue what this picture shows, but I have my doubts it’s a fireball. I expect we’ll be seeing lots of rumors and things like this today.
[Update (21:15 UT): The image shown here of the red fireball is a hoax, and the man responsible for it has been arrested. Also reported in that link is that there were gas bottles secretly hooked up to a pizza making stove in a nearby house, and that this may be the cause of the explosion. I expect that is the final straw on this story -- enough evidence is piling up that this was not something form space, or even from the sky; it was some kind of terrestrial event, as expected.]
The explosions and devastation appear to be very real, though. This is the only video I could find on YouTube, and it has no audio, but it shows the aftermath:
I don’t see any obvious airplane wreckage, but it’s hard for me to see that a meteorite impact would’ve done this; for it to have been big enough to cause this much devastation, there would’ve been a big crater as well (like the one that hit in Peru a couple of years back). None is evident, so I’m strongly of the opinion something more terrestrial was to blame here.
I won’t be surprised to hear people asking if this was from the UARS satellite, too. However, that’s pretty much impossible; the satellite came down Friday night, and there couldn’t have been pieces of it still in orbit two days later. Also, again, the type of destruction seen here is unlikely to have been from just a simple impact.
Hopefully we’ll find out soon. If you hear anything please leave a comment below (with a link if you have one), and I’ll post an update when I learn more.
[Update: A grass fire in Texas Saturday night has been reported, and it's claimed to be linked to something falling from the sky. Again, a meteorite is extremely unlikely there, since it would take a big impact to ignite fires. Stuff like this happens all the time, and remember Texas is extremely dry right now. I would guess this was fireworks, but there's not much info on this story either. Thanks to Baron Grim on Twitter for the story.]
Tip o’ the Whipple Shield to Antropomorficah on Twitter. Image credit: screen grab from embedded C5N video.