New meteor shower points to a future close encounter

By Phil Plait | July 28, 2011 7:00 am

A pair of astronomers monitoring an all-sky camera got a surprise (PDF) when they checked data from last February: a half dozen meteors all seemed to come from the same spot in the sky, indicating they all had a common origin. After doing some calculations, they found that they probably come from a parent comet with an orbit that’s at least 53 years long. Moreover, the orbit of this comet crosses that of the Earth, meaning we may have a close encounter with this object sometime in the future.

And because I can sense the oncoming panic on the web over this news, let me break it down for you. I’ll give you the science (which is cool), how we know this unseen comet may be potentially, um, interesting, then the reason you don’t need to run around in circles screaming (spoiler: it’s rude to others nearby, but also unnecessary).

But just to be up front: should you panic? Nope. We know there are objects out there that could hit us in the future sometime. This comet is in many ways just another one. As I’ll point out below, we pass through lots of meteor streams, so there are plenty of other comets that could hit us. I know, I know, that doesn’t sound reassuring, but think about it: how often is the Earth hit by a comet? Not very often, despite having a few on the list of Potentially Hazardous Objects. So having one more we know about out there isn’t great, but in reality doesn’t really make things any worse for us.


Meatier showers

That picture above is one of the meteors in question. You can see the streak as the tiny bit of rock (probably the size of a grain of sand) glowing as it rammed through the Earth’s atmosphere at about 35 km/sec (22 miles/sec, or nearly 80,000 mph). If you go out on any dark night, you’re bound to see the random meteor or five. But meteor showers are when we see lots of them in a short time, and they occur when the Earth passes through the dust debris left behind by a comet.

Most comets are dirty snowballs: dust, pebbles, and boulders held together by ice (water ice, but also frozen carbon dioxide and other things we normally think of as gases). This makes comets the litter bugs of the solar system, shedding material when the Sun warms them up and turns the ice into gas. The vapor blows off, and the looser material forms a ribbon or stream that stays more or less along the same orbit as the comet.

If the path of the comet intersects the orbit of the Earth, we plow through that material at the same time every year. Think of it this way: imagine a racetrack, and you are driving around it. Now also imagine a long line of gnats flying across the racetrack. You would drive through that line of bugs at the same point on the racetrack every time, right? OK, replace you with the Earth, the racetrack with the Earth’s orbit, and the bugs with debris shed off a comet. Since the Earth returns to the same point in its orbit every year, if there is cometary debris there, we’ll smack into it at roughly the same calendar day every year.

This loose stuff from the comet burns up in our atmosphere, and we get a meteor shower. Due to perspective, we see them all radiating away from a single point in the sky, called the radiant. Going back to the car analogy, imagine driving through a tunnel with lights on the side. As you drive, the lights pass you on the left and right, but all seem to be coming from a spot up ahead. That’s the radiant. The image here [click to embiggen] shows the annual Leonids meteor shower as seen from the Modra Observatory in Slovakia, and you can see how they all point to the same spot in the sky.

In fact, meteor showers are named after the point in the sky from which they radiate. We get the Perseids in August (which stream away from the constellation Perseus), the Leonids in November (from Leo, like in that picture above), and the Geminids (Gemini, duh) in December. This new shower appears to come from a point near the star Eta Draconis in February, so these are now called the February Eta Draconids (to distinguish them from another shower, the Eta Draconids which appear in April [Note: these two meteor showers seem to have a lot of characteristics in common, which is interesting. I’m investigating that now.]


Knowing the path is not the same as walking the path

The meteors in question were caught by the Cameras for Allsky Meteor Surveillance, or CAMS. Five were seen for sure, and there may have been a dozen more. All seemed to come from that same spot in the sky, and all had similar brightnesses, speeds, and orbital characteristics (determined by backtracking the paths they made across the sky). Using these data, the astronomers determined that the parent comet — which has never been seen — is most likely one that takes a long time to circle the Sun, at least 53 years, and possibly more. The orbit of the comet is highly tilted to that of the Earth, and it goes just inside our planet’s orbit by a few million kilometers.

This means that the comet’s path crosses ours, and in general that’s not a good thing. But is it really a big danger? Remember, there are dozens of meteor showers every year, so really we cross paths with lots of comets. But comet impacts are exceptionally rare! Put it this way: how many people do you know who have been killed by comets hitting the Earth?

So the odds are pretty low. But, to be honest, they aren’t zero, so this is something we should take seriously. If we wait long enough — centuries, or millennia — something out there will have our name on it. It might be much sooner, or it might be much later. In my opinion, based on my understanding of astronomy and statistics, this is something we should prepare for, but not panic over. We have the technology to push something out of the way, whether it’s a comet or an asteroid. If we get enough warning, we can ram it with a spaceship and alter its path, hopefully enough to miss. After that there are techniques to finesse the orbit of the object into something we know is safe (you can read more about that here as well).


Site unseen

There’s more, too. If this comet has a period of a few decades, it’s a little weird we’ve never seen it before. That makes me suspect the orbit may be longer, making a pass more rare. And we can only collide with it if it happens to be at the spot in space where our orbits intersect at the same time the Earth is there (in February). If the comet happens to be there in August, we’d be on the other side of the Sun, and quite safe.

We’re also a pretty small target. Sure, the Earth seems big, but it’s about 13,000 km (8000 miles) across. Judging from the speed of the meteors seen, the comet would be tearing along at 35 km/sec when it passes. That means it could cross the entire disk of our planet in 6 minutes or so. That’s a pretty small window; 360 seconds out of the decades it takes the comet to circle the Sun once.

So again, it’s not something I’ll lie awake night fretting over.


For science!

Still and all, this is a pretty interesting observation. It’s amazing that a handful of tiny grains of rock burning up in our atmosphere can tell us so much about an object we’ve never even seen! The whole purpose of the CAMS is to have multiple eyes on the sky, so meteor paths can be triangulated, backtracked, and calculated. There may be as many as 300 meteor showers every year, but only a few are verified. CAMS may very well increase that number significantly.

Right now, we know of no object out there, comet or asteroid, that will hit the Earth any time soon. That doesn’t mean there aren’t any out there, of course. The sky is wide and deep, and we’ve only been at this a short time. But the more we know, the better. The key here is lead time: the longer in advance we find a potential impactor, the better our odds of pushing it out of the way. The CAMS project is one piece of that, and we also have a fleet of telescopes scanning the heavens looking for them as well.

The time will come when we really will see one that will cross paths with us, being at the wrong place at the wrong time. I hope that by talking about this, raising our awareness of it, more people will demand that we do something about it.

Because we can. We have that choice, when the dinosaurs didn’t. We’re here, and they’re not. Make of that what you will.

But this time I think we’re OK for now. So, to anyone who is still worried to the point of distraction over this as-yet-undiscovered comet, I’ll just leave you with this:

Image credit: SETI CAMS project/Peter Jenniskens; Wikipedia/Modra Observatory


Related posts:

No, 2005 YU55 won’t destroy the Earth
RV-sized asteroid will buzz the Earth on Monday
Are we in danger from a rogue planet?
Repeat after me: Apophis is not a danger!

Comments (39)

  1. Hey, it’s the hippopotamus asteroid again!

    <moonhoaxer>How come, if they all come from the same place, the lines aren’t parallel?</moonhoaxer> :-)

    Though I’m still curious how, from 5 little streaks in the sky, they can even begin to plot an orbit. I mean, if they actually saw the comet itself, how many observations, spread out over how much time, would they need for such calculations? Certainly not one night’s observations?

  2. astronomynut

    I have to agree with Ken B. Just because the gnats hit my windshield doesn’t mean I know which direction they were traveling. Left, Right, Up, Down? I see how we can determine their relative speed and one point in their orbit, but beyond that I don’t see how we can glean any more.

  3. Uh…ahem. Am I the only one who…koff!…super secretly sorta kinda wants to see a comet smack into the earth? Just a little one…maybe. Sometime. Because, you know, it might be…um, kind of neat. In a “gosh, what would happen if I stuck my finger in that light socket” way.

  4. So, how do we know that the meteor in question hasn’t already hit us? It seems like for all we know this could have been the one that wiped out the dinosaurs, and we’re just seeing the remnant debris trail from a long-gone interceptor. Yet one more reason not to panic …

  5. chris j.

    a more scientifically interesting question would be whether the predicted orbit intersects with jupiter, which is far more likely to have interacted with the comet in question by altering its orbit, flinging it out of the solar system, or consuming it like shoemaker-levy.

  6. Chief

    I sense that you have been thinking of Futurama when you picked the headline of Meatier Showers. Please direct all queries and complants to the Matsuto Corporation.

    #4’s comment on it being a trail left from an impactor in the past was something I didn’t think of but is a great question. How would we go about figuring this out.

  7. Thomas Siefert

    I’m with you on that kuhnigget, morbid curiosity is human.
    Also I would like to see who is throwing those snowballs, only bullies throw dirty ones with rocks in them.

    … or are they called “dirty snowballs” because they are leftovers from a very large and embarressingly detailed snowman?

  8. Messier Tidy Upper

    Every time I see that lowermost picture I see the One Ring To Rule Them all from Lord of the Rings somehow encountering our atmosphere – and you’re right BA, NO that’s not how you destroy it and save (middle) Earth! You need the fires of Mt Doom instead. ;-)

    Good article otherwise though. :-)

    a parent comet with an orbit that’s at least 53 years long.

    We should know the orbit and be able to calculate which comet is responsible shouldn’t we?

    53 yeras is a short period comet and so one we should have seen – it’s last pass would’ve been in 1958 if my calculator is correct. :-)

    Do any from that year possibly fit the bill?

  9. Good review of meteor showers. Thanks, Phil.

  10. Bandsaw

    Ramming (or bombing) a rubble pile won’t do you much good. Gravity tractor would work, but that takes a while. Fortunately, all we’d need would be a small deflection.

  11. tphtwpe

    OK, gives me an idea for an interesting experiment. If we can calculate the trajectory of a comet by finding the shower, then CAMS should look for showers occurring on June 30 and if they find one, figure out where they were coming from and back calculate to determine if the Tunguska area was facing that way at the time of the blast in 1908 and you prove once and for all it was a comet that caused that incident…. Q.E.D.

  12. Geri Monsen

    Ken, to calculate the orbit, one only needs the position and velocity of the meteors at a specific time. We obviously know the position of the meteors — they were where the Earth was when the observations were made. Then, from the camera observations, we can get the speed and direction that the meteors were traveling in when they hit the atmosphere. So, with position, velocity, and Newton’s law’s of motion, the astronomers can calculate the orbit with a rough precision. In the paper, the calculated orbits of all five rocks were pretty close, within certain error bars.

  13. “Meatier showers”

    Oh, Phil! XD … :-|

    BTW is it in Earth’s orbital plane?

    /apologies if I missed that part – had to skim kinda fast

  14. Albert911emt

    Phil, you always have a way of spoiling my God given right to laugh as others run around panicking and screaming at the coming apocalypse. Eh, I guess I’ll just go watch TV.

  15. katwagner

    Um, why should we worry about some comet clocking us at some time in the future when there’s a bunch of idiots in DC ready to kill us off in five days? Life as we know it could be over in a week.

  16. @ Katwagner:

    I agree! In fact, best to withdraw all your savings and investments and place them somewhere secure. Might I suggest my wallet?

    See you the week after next.

  17. Chris Winter

    Chief wrote: “I sense that you have been thinking of Futurama when you picked the headline of Meatier Showers. Please direct all queries and complants to the Matsuto Corporation.”

    Not necessarily. He might, as I was, be thinking of a certain jingle in a TV commercial that aired not so long ago — for an automobile called the Mercury Meteor. ;-)

  18. kuhnigget:

    Uh…ahem. Am I the only one who…koff!…super secretly sorta kinda wants to see a comet smack into the earth? Just a little one…maybe. Sometime. Because, you know, it might be…um, kind of neat. In a “gosh, what would happen if I stuck my finger in that light socket” way.

    Why not hit the “near” side of the Moon instead? (With enough lead time so that every telescope on that side of the Earth were to be watching?)

    Sporkley:

    So, how do we know that the meteor in question hasn’t already hit us? It seems like for all we know this could have been the one that wiped out the dinosaurs, and we’re just seeing the remnant debris trail from a long-gone interceptor.

    Because we cross this comet’s path in February, and everyone knows that the one that wiped out the dinosaurs was in October.

  19. QuietDesperation

    Another site has what they think is an image of the object: Link

  20. Messier Tidy Upper:

    Every time I see that lowermost picture I see the One Ring To Rule Them all from Lord of the Rings somehow encountering our atmosphere

    Funnily enough, I just watched the first disk of Fellowship of the Ring with my kids the other day. Of course, they all had to comment <sheldon>you mean this ring?</sheldon>

  21. John

    On the plus side if a comet does strike the earth then it could throw a lot of dust into the air and delay global warming somewhat. I mean climate change.

  22. Ray

    I’m not all that worried about the meteor hitting us. Bruce Willis is still around and NASA has a plan. I saw a documentary about it a few years ago.

  23. Geri Monsen:

    Ken, to calculate the orbit, one only needs the position and velocity of the meteors at a specific time. […] In the paper, the calculated orbits of all five rocks were pretty close, within certain error bars.

    Thanks. I haven’t read the paper, but I guess that’s why they have those letters after their names. I’m just surprised that the margin of error isn’t like “we think it’s somewhere over in that general area… maybe” as they wave their arms around.

  24. Arthur Maruyama

    @ 8 (Messier Tidy Upper)

    I always see that picture as the One Ring too. :)

    Another possibility is that as a short period comet the parent body might also be an exhausted comet where the volatiles are nearly gone and thus not easily seen from Earth.

    Remember that the debris that creates meteor showers tends to spread along its parent’s orbit, which is why we get the Perseids every year despite the orbit of its parent, Comet Swift-Tuttle, taking 133 years, so we aren’t limited to looking for a comet that last appeared around 1958.
    ?

  25. Whomever1

    Metaphors don’t work in space.

  26. K

    Ok, seriously? I just finished reading, “Lucifer’s Hammer!”

  27. Keith Bowden

    Skeptical Hippo is… skeptical.

    Love it, a nice loooooonnngg post to preemptively refute the potentially forthcoming panic articles. :)

  28. Kurt Kohler

    My first reaction to “meatier showers” was “Cloudy with a Chance of Meatballs.” Before you knock it, any movie with a nerdy girl as a heroine is not to be taken lightly.

  29. Keith Bowden

    @Kuhnigget:
    Ni! Ni, I say! NI!!! :)

  30. Oh, what sad times are these when passing ruffians can say “ni!” at will to old commentators. :(

  31. Nigel Depledge

    @ Kuhnigget (31) –
    Why, even those who make and purvey shrubberies are under considerable economic pressure at this period in history.

  32. JMW

    So if the Phil’s calculations are correct, and the comet takes about 6 minutse to cross Earth’s cross section when it crosses Earth’s orbit, and it orbits the sun once every 53 years (although the orbit was descrbed as “at least every 53 years”)…

    …calculate 6 minutes…
    …times 10 to get an hour…time 24 to get a day…time 365.2442 to get a year…times 53 to get an orbit…

    …then those 6 minutes represent 1 / 4,645,906.224 of the comet’s orbit. So every 53 years, it has that chance to hit us, assuming completely random distribution.

    Which is approximately 3 times the chance of any one ticket winning a 6/49 lottery.

  33. Gary Ansorge

    A good, solid SCIENCE fiction story could be made from a neutron star entering our solar system from above the plane of the ecliptic. When surrounded by a stellar nebula(as most such are) neutron stars can be quite hot from in falling debris however, I expect a “cold” Dark Star such as this(one not encountering such debris) could run astronomers ragged, trying to figure out why our sun and other stellar planets were behaving so oddly when their orbital velocities start changing and there’s nothing visibly causing it,,,(it only needs to be about 12 km in radius)

    Dark Star Crashing,,,sounds like fun.

    Gary 7

  34. rw23

    @Gary #35

    Nice thought, Gary, but as soon as any changes in orbital velocities became measurable we’d be able to narrow down where to look. If there was nothing immediately visible there then I think we’d rapidly come to the conclusion that the object was something like a neutron star or a black hole and start looking for occlusions and gravitational lensing effects.

    Of course, what we could do about the interloper once we’d found it is a different matter…

  35. reidh

    Hell, the bible tells us that someday the earth is going to be hit two times, once by an asteroid, and then by a comet, and people didn’t believe it for 2000 +/- years, and only NOW since astronomers can see them (NEOs) is anybody taking such things as warnings, so what would animate people to unite in fear and preparation? Nothing. And what is the hope that any human device could be manufactered, tested, launched, and then succeed in diverting a collision, within the time frame we will probably have to react.

  36. Questionable

    I’m just a lil sckeptical about our so called pending “DOOM” date in 2012. There are a lot of past cultures from different continents saying the jig is up. That dosen’t really bother me,but being just a layman file their predictions and watch things unfold. Odd that global warming is a project that no one seems to agree on, but then again I read that it’s not just global, but solar system warming. Maybe more to it than just global. The real worry I have is when real events happen that go unrevealed. like a meteor passing through the sun on Dec 21 this year and I hear about it on a talk show. Nasa said that ice and frost was still present upon meteor head when exiting the sun. I find that kinda unlikely to be present after 6,000 degrees, but once again I am a layman. I also read that it had its own moon in it’s orbit,which would put it in a planet class, but I just don’t know how much one reads is true. So I like many will sit back, prepare for what may come idly and smile when most get caught with pants down or just chalk it all up to oops who’s predicting what next year

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