Another tiny rock will whiz past us tomorrow

By Phil Plait | February 8, 2011 10:04 am

On February 9 at around 19:30 UT, a small asteroid the size of a car will cruise past the Earth, missing us by a distance of about 100,000 km (60,000 miles). By astronomical standards that’s pretty close (about a quarter of the way to the Moon) but it’ll miss us for sure.

Called 2011 CA7, it was discovered earlier this month. The short notice is not too surprising, given that it’s at a very faint magnitude of 20 — you’d need a big telescope to be able to see it at all! Even at closest approach it’ll be magnitude 17, less than a ten-thousandth as bright as the faintest star you can see with your unaided eye.

There is some small uncertainty by exactly how much it’ll miss us; the orbit isn’t precisely determined yet. According to the JPL small-body data browser, the minimum distance 2011 CA7 will pass us is 93,000 km (58,000 miles), and the maximum is 114,000 km (71,000 miles), but the most likely distance is 103,000 km (64,000 miles). These numbers may change as time goes on, but the important thing to note is that it will miss us.

Given the brightness of the object, it’s obviously pretty small, probably around 3 meters in diameter, or about 10 feet. That’s a little bit bigger than 2011 CQ11 which blew past us last week, but not significantly so. Even if it were to hit us it would certainly disintegrate high up in the Earth’s atmosphere and at worst rain down a few rocks; that sort of event happens several times a year somewhere on Earth, if that makes you feel any better. In other words, it’s relatively common and presents very little danger. Interestingly, this little guy has probably passed us many times in the past, but this is the closest encounter yet (which makes sense; it’s so small and faint it’s only when it gets close that it can be seen at all).

This is an interesting rock. Its orbit goes from roughly the orbit of Venus out to that of Mars, and that means it spends most of its time in near-Earth space. I imagine over a long period of time, maybe millions of years, an impact is inevitable — but again, something this small will make a pretty light show but present very little real danger. In that picture above you can see the orbit in teal; the Earth and the asteroid are to the lower left. On this scale — hundreds of millions of kilometers across! — the rock looks like it’s right on top of us, but 100,000 kilometers is a long way off in real terms. A miss is a miss.

I haven’t seen any imaging of it yet but I’m keeping my eyes open, and hopefully we’ll get some nice pictures of this. Stay tuned!

Comments (28)

Links to this Post

  1. Asteroid Of The Day - TDW Geeks | February 8, 2011
  2. Un Visitante para el 09 de Febrero del 2011 | Pablo Della Paolera | February 8, 2011
  3. Anonymous | February 16, 2011
  1. Dan I.

    Phil;

    When you say “might rain down a few rocks” do you mean that, were this to enter the atmosphere (which I know won’t happen) that some rocks would actually reach the ground?

    I don’t know if I feel comforted by the fact that rocks rain from the sky randomly a few times a year.

    Sure it won’t be an extinction level event, but the idea of getting conked on the head by a random rock isn’t exactly a happy thought ;-)

  2. Inajira

    I see Phil’s being very careful to reiterate that it won’t be making contact anytime soon. Surely there isn’t anyone out there thinking this is an Armageddon Candidate? Surely….

  3. CB

    For some reason every announcement about how an asteroid isn’t going to hit us makes me think of this comic:

    http://www.angryflower.com/astero.gif

  4. Messier Tidy Upper

    Cool news, interesting rock, thanks. :-)

    I imagine over a long period of time, maybe millions of years, an impact is inevitable

    Ah, yes but on which planet – Earth or Venus or Mars? ;-)

    Does the orbit hint that it may well be a cometary fragment perhaps?

    @1. Dan I. Says:

    Sure it won’t be an extinction level event, but the idea of getting conked on the head by a random rock isn’t exactly a happy thought .

    Well everyone’s got to die of something & there are many, *many* far worse ways to go. Give me death by asteroid any day .. just not tomorrow or the day after or .. well, give me until at least 2015 so I can see what Pluto’s like okay! ;-)

  5. CB

    If living forever (not excepting universal heat death) is out of the question, then having “Killed by a ****ing Meteor” on my tombstone would be a glorious second best.

  6. Steve

    Someone needs to tell that rock it’s not 2012 YET! LOL

  7. So, when are we going to get one of these sofa/car/minivan asteroids that actually will enter the atmosphere? Sure, you get some home videos every now and then of a meteor blazing through the sky. But, what would happen if we knew ahead of time about one of these, and turned “real” :-) cameras on it?

    Dan I:

    I don’t know if I feel comforted by the fact that rocks rain from the sky randomly a few times a year.

    Search for “Peekskill meteorite” for info on what can happen.

  8. a different phil

    Ken B, I believe that happened last year.

  9. If my memory serves me right (and all too often there’s a fly in my soup) the meteor that was seen over Austin in February 2009 was said to be “truck-sized”. I think bits did hit the ground and were found in a field around West, Texas. (Not to be confused with west Texas.) It made a pretty show on the way down though: http://www.youtube.com/watch?v=e_eJLcGPWTs

  10. Gary Ansorge

    I’m eagerly anticipating the day we can spot one of these,,,entertaining,,,rocks actually hitting(a priori) and the likely impact zone(by hitting, I mean the atmosphere, not a surface strike).

    I’ll bring the popcorn,,,

    Gary 7

  11. Nemo

    What’s the diagonal line in the picture? Also, why do most of the orbits change color?

  12. MaxyB

    Will passing so close to the earth change CA7’s orbit at all?

  13. a different Phil:

    Ken B, I believe that happened last year.

    Perhaps I wasn’t clear enough. I meant one that is discovered ahead of time, such as 2011 CA7 and 2011 CQ11, so it can be accurately tracked and studied from space to the ground.

    Or did that happen last year, and I didn’t hear about it?

  14. Nemo:

    What’s the diagonal line in the picture? Also, why do most of the orbits change color?

    As an educated guess…

    The diagonal line is the path of the Sun.

    The reason (most of) the orbits change color is because that marks whether it’s “above” or “below” the Ecliptic. Note how the Earth’s orbit is a single color, and note how CA7’s orbit’s color changes right at the point it intersects the Earth’s orbit.

  15. DrFlimmer

    […] a small asteroid the size of a car will cruise past the Earth […]

    So, who’s in charge of the wheel, then?

    Oh yeah, that is Sir Isaac Newton.

  16. fuzzbutt

    “Sure it won’t be an extinction level event, but the idea of getting conked on the head by a random rock isn’t exactly a happy thought”

    Better than getting hit by a toilet seat (Dead Like Me reference)

  17. When 2011 CA7 does its skimmer, its orbit will be perturbed. Oh mama, that’s where the fun is!

  18. un malpaso

    I’m curious, roughly how much damage would a car-size rock do if it hit us? Just break up in the atmosphere, or a couple-kiloton explosion? Either way, I am really impressed that we have the capability to identify orbit-crossing things as small as this. If only we knew about EVERY one out there…

  19. alfaniner

    It would be so cool if the object suddenly made a course shift, directly for Earth.

  20. Messier Tidy Upper

    @19. Uncle Al Says: When 2011 CA7 does its skimmer, its orbit will be perturbed. Oh mama, that’s where the fun is!

    Thinking orbits getting perturbed check out this :

    http://www.planetary.org/blog/article/00002908/

    with the similar encounter with 2011 CQ1 via Emily Lakdawalla’s wonderful blog. :-)

  21. MichaelL

    “On February 9 at around 19:30 UT, a small asteroid the size of a car will cruise past the Earth”.

    Would that be a full-size family sedan, or a basic compact car?

  22. I, too, look forward to the day when we begin tracking all decent sized rocks that WILL enter the earth’s atmosphere and provide us with a great, predictable light show. How far off can that be? If we’re beginning to find the ones that are near misses, then the other variety should start to show up also.

  23. …meaning, of course, that the Drudge Report will headline this news in giant type at the top of the page — IT’S COMING RIGHT FOR US! — with that stupid-assed animated spinning police light at the top.

  24. DrBB

    Dang, I was looking but I missed it. Maybe my UT to Local conversion was off.

  25. Menyambal

    “Its orbit goes from roughly the orbit of Venus out to that of Mars, and that means it spends most of its time in near-Earth space.”

    Well, that depends on how you define “near-Earth space”. Given that sentence, and the diagram, I’d say it spends much of its time out near Mars–most if you want to use the word “most”–another good, but lesser, chunk of time in near Venus, and twice an orbit goes blistering through Earth’s orbit.

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