RV-sized asteroid will buzz the Earth on Monday

By Phil Plait | June 26, 2011 6:48 am

A rock about 10 meters in size will fly past the Earth Monday at 13:30 UTC (09:30 Eastern US time) 17:01 UTC (13:01 Eastern US time) [Note: the time of closest approach was updated this morning, June 27]. It’ll be a particularly close shave — passing just 12,400 km (7430 miles) from Earth’s surface; a bit less than the diameter of the Earth itself — but it’ll miss for sure.

[Update 2: Images and an animation of the asteroid are now up at the Remanzacco Observatory blog; thanks to NickAstronomer on Twitter for the tip!]

We’re in no danger from the asteroid, named 2011 MD, since there’s essentially zero chance it will hit us. Even if it did, it’s too small to impact the surface, and would instead break apart and burn up in the atmosphere. That would be exciting, and make quite a show, but that’s about it.

Here’s a diagram of the asteroid’s trajectory (note that the size of the Earth is not to scale!):

On this scale, the Earth is actually about half the size shown; it was enlarged on the diagram to make it clear. In this smaller diagram here the trajectory is shown from a different angle (edge-on to the Moon’s orbit) with the Earth to scale, and you can see better that 2011 MD will miss us.

You can really see in those diagrams just how much the Earth’s gravity bends the orbit. At this close an approach the Earth’s gravity is significant, and the path of the object will be significantly altered. Just how much it’s changed is difficult to know until observations are made after the event. However, I’ll note the asteroid will be on the daylit side of Earth after it passes, making observations a bit tricky. I expect radar observations will be made using radio telescopes, which don’t need darkness to work and can provide very accurate measurements of the orbital path.

Speaking of orbits, this one is interesting. 2011 MD’s orbit is quite similar to Earth’s around the Sun, taking 396 days to go around once. The orbit is more elliptical than Earth’s, with a semi-major axis of 1.056 AU.

What does that mean? Well, the major axis is the length of an ellipse across its longest dimension, and the semi-major axis is half that length (that may seem like a funny unit but it’s convenient to do the math). An AU is the average distance of the Earth to the Sun, and again is a convenient unit for astronomers to use. The Earth orbits the Sun in an ellipse that is pretty close to being a perfect circle, and by definition the semi-major axis of our orbit is 1.0.

So 2011 MD’s orbit is a bit more oval and a bit bigger than ours, just barely crossing it. Asteroids like that are called Apollo asteroids, and there are quite a few in that category. As you can see in this diagram, the orbits are so similar it’s hard to distinguish them on the left — look to the right and you’ll see them separate (also shown are the orbits and positions of Mercury, Venus, and Mars for June 27).

It orbits the Sun in 1.085 years, so every 13 years or so (12 of its orbits) we pass it. Some encounters are closer than others, and this is most likely the closest we’ve come in a long time, and most likely will be for some time in the future as well (especially given how much the orbit of 2011 MD will change). In fact, this will be the fifth closest approach of an asteroid on record… and one of those on the list, 2008 TC3, actually impacted us, harmlessly breaking up high over Africa in 2008.

That may be the fate of 2011 MD someday as well… but not today. For now, we get a very good view of this tiny interloper as it zooms past. And it’ll get a good view of us: it’ll pass over the South Atlantic at closest approach, and the Earth will fill half its sky. What a view that would be! Astronomer Pasquale Tricaric put together some very cool animations showing the asteroid’s-eye-view, too.

And I do want to point out one more thing. Since the orbit is very Earth-like, the relative velocity of this rock to us is pretty small. Imagine two cars on a race track, one moving at 200 kph and the other at 210 kph. To someone standing by the track they both scream past at high speed, but to the slower car, the faster one overtakes it at 10 kph — not very fast at all.

The same is true here. Both Earth and 2011 MD orbit the Sun at about 30 km/sec, but the relative speed between the two is small — only about a kilometer/second (except right at closest approach, when the Earth’s gravity speeds it up). That means if we were to launch a rocket at it, it wouldn’t take very much fuel to "catch up" to it. That’s why rocks like these are so very interesting: exploring them is easier in many ways than even getting to the Moon! It’s too late for this particular asteroid this time around, of course… but there are plenty more out there, and their time will come.

And just to be clear once again, since I know some of my readers fret over these things: this rock will miss us for real and for sure.

Orbit diagram credits: NASA/JPL-Caltech

Related posts:

No, 2005 YU55 won’t destroy the Earth
Media fail *again*: HuffPo and Apophis edition
Another tiny rock will whiz past us tomorrow


Comments (81)

  1. Grand Lunar

    A good target for a manned mission, even if it is small.

    And it’s RV sized? Maybe it’s really Lone Starr, and his side-kick Puke….er, Barf.

  2. Cam

    Whats the over/ under on doomsday articles written?

  3. t-storm

    so is it possible that it’ll perturb one of our satellites?

  4. @T-storm

    I had the same thought. Or even take out a few.

  5. Joseph

    She didn’t look drewish!

  6. JohnDoe

    This would be a great target, not for a manned misson, but to capture so that we can finally have more than just one moon. Then we could send a manned mission to the “new moon”.

  7. Nadim

    Will it be possible to get a photo of it on a camera? Or will it be way too small, and be suitable only for the Hubble?

  8. panini

    Right, why haven’t we planned a mission to “explore” one of these asteroids yet? If not manned, a small sample return capsule or stationary robot at least.

  9. Chris Winter

    “Even if it did, it’s too small to impact the surface, and would instead break apart and burn up in the atmosphere.”

    Even if it’s a nickel-iron body?

  10. Tom

    Is this asteroid passing close enough to Earth that it’ll be ripped apart by tidal forces?

  11. DLC

    “It’s Coming Right at us! ” he yelled and then dove out the window. . . into the open air of a 3 story fall. . .
    Lesson? Panic can often be more dangerous than what you’re panicking over.

  12. Anchor

    There seems to be a common misperception about orbital mechanics afoot here which I’ve encountered frequently elsewhere. Just because an asteroid passes close to Earth doesn’t necesarily make it an easy target for a manned mission: proximity isn’t everything. The relative change in velocity (and therefore fuel expenditure) required to rendesvous with one AND return to Earth is the actual problem. Even with an asteroid like 2011 MD, one would need to achieve greater than Earth escape velocity just to sidle up to it. That’s already most of the energy required to reach Mars.

  13. Chip

    Here’s a few questions – not necessarily applying to this asteroid:
    Is it possible to calculate the trajectory of objects that miss the Earth shortly after they’ve missed the Earth or do they have to be tracked for a long time and is there much of a danger of an object’s course being altered so as to hit us later?

  14. Bramblyspam

    Hmm, a thought just occurred to me. Does this mean Earth isn’t a planet, since it hasn’t cleared its orbit?

  15. Vasha

    I also have a question tangentially related to this asteroid. As the moon gradually gets farther away, the earth’s influence on it weakens, right? and the chances grow that perturbations could cause it to drift right out of orbit? Right now, that’s not going to happen; it would take a hell of a big object (planet-size?) passing by to pull the moon out of its orbit. But how long is it going to take for that to change? How long until say, a close encounter with a 1-km rock could do it?

  16. Kim

    I’m just trying to find a scientific reason to put a relay on such an asteroid. You know, going up there, catching up with this rock and deploying a stuff that will beep us back is a kind of awesome I can’t describe, even if it’s useless. It will be like fishing a cosmic whale with a space harpoon, but willing to stay alongside it forever.

  17. Jonathan Latimer

    With its similar orbit — is it possible that this asteroid is left over from the event that created Earth’s Moon? Or is it more likely that it is flotsam from the same stuff that created the planets in the first place?

  18. mihirchander

    It’s high time to get rid of narrow minded and outdated ideas like countries,nationalism and patriotism.These NEO asteroids are a good reminder.

  19. Wil

    If the composition of the asteroid was worth the expense of a vehicle, it could be captured and taken into a high orbit for mining.



    Is this asteroid passing close enough to Earth that it’ll be ripped apart by tidal forces?

    Negative. Assuming that the asteroid in question is spherical, with a density of 3000 kg/m^3 for a rocky asteroid, then the Roche limit – the distance from the primary mass at which a satellite will disintegrate due to tidal forces exceeding the satellite’s own gravity – can be easily be calculated according to the formula:

    d = R[2(P_M/P_m)]^{1/3},

    where d is the distance from the primary, R is the radius of the primary, P_M is the density of the primary, and P_m is the density of the secondary (satellite).

    So, given that the Earth’s density is 5,513 kg/m^3 and its radius is 6,378.137 km, we then have:

    d = 6,378.137×[2×(5,513÷3,000)]^{1/3}

    Therefore: d = 9,842.968 km

    So the asteroid 2011 MD will be well outside that limit at 12,400 km.

  21. SaddieN

    If the orbit of this rock is going to be changed so dramatically, will it still have an orbit around the sun, one that still resembles the one of earth?

  22. I’m sad I wasn’t able to make the first Spaceballs joke…

  23. Idlewild

    What’s the chance that the earth could pull in a passing asteroid and make it into a moon?

  24. Keith Bowden

    “Look out, it’s coming right for us!”
    blam blam blam blam!!

    (I’ve been watching too much South Park. Hey, it’s in Colorado, too…)

  25. Smitty

    lets capture it, load it with nukes, and shoot it deep into space. some alien planet is gona have a rough week

  26. Re: 20:
    Most asteroids are substantially less dense that 3000 kg/m3. See, for example, this list:


    @Lab Lemming,

    That’s why said “Assuming…”!

  28. chris j.

    regrettably, there won’t be much to see. according to sky&telescope, it will get no brighter than magnitude 11, and even then only for south africa and south america.


    ADDENDUM: The given distance for d, above, is from the centre of the Earth, not from its surface; therefore, the Roche limit distance from the Earth’s surface for the specified asteroid would be: 9,842.968 km (d) – 6,378.137 km (Earth’s radius) = 3,464.831 km

  30. Pete Jackson

    Police: What happened?

    Victim: I got run over by an RV!

    Police: Did you get a description?

    Victim: Just the tag number: MD 2011

  31. Tom



    If I’ve done the math right, then for an object to break up at a distance of 12,400 km from Earth, the mean density would have to be about 430 kg/m^3. If I’ve read the paper that Lab Lemming (@27) mentioned correctly, this is well below the density of any known asteroid.

  32. Pete Jackson

    An interesting special case would be a ‘contact binary’ asteroid whereby two masses are stuck together only by their own gravity, looking like a dumbbell. An example is Toutatis. That should be easier to separate.

  33. Joseph G

    @16 Kim:
    ♬”We’re whalers on the moon, we carry a harpoon…”♬


  34. Ken

    “2011 MD’s orbit is quite similar to Earth’s around the Sun, taking 396 days to go around once. The orbit is more elliptical than Earth’s, with a semi-major axis of 1.056 AU. “

    From the look of those two orbital tracks, after June 28 this sentence will have to be rewritten in the past tense. That’s some serious deflection.

  35. On a more serious note, I think at a point where one of these less significant near-earth objects comes along, we should use it as a test case for deflection. Of course the logistics of this and the fact that it will require money will do more to deflect any government from participating and when the time comes for us to actually do this for survival or general safety, we’ll be using untested technology for one of those cool all-or-nothing scenarios we as humans like to try.


    @Tom (#32) – Yep, that’s correct!

  37. MoteInGodsEye

    I wonder if one were to be standing on the asteroid what we would feel as “G’s” as the earth’s gravity increasingly bends it’s trajectory?


    Hey! I have just noticed that some bastard has pinched the “I” in my comment above at #28!

  39. un malpaso

    DAMN! Missed again! That cosmic game of pool is dragging on and on…

  40. I wonder about the comment made about the satellites. If it will have an affect on them, like possibly hit one. I wonder if we could see this thing. Probably not.

  41. Zara

    It appears to be the outline of a… Winnebago.

  42. Dutch Railroader

    To be clear, a priori the change in 2011 MD’s orbit is neutral with regards to when it will impact the earth, which it certainly will do eventually. Its orbit will remain earth-crossing, and given its new period (which will be longer than it is now, given that it’s crossing behind the earth) one can quickly calculate how long it will be before we have another close encounter.

  43. Dave

    Because @8. panini billionaires needed another tax break! and we don’t count hiding money off shore as economic treason.

  44. Sam42

    Hey guys, I’ve a question: Just supposing we came across an asteroid that was going to hit us, with what degree of certainty could we predict where it would hit? Would it just be a matter of which ‘side’, or is there a way of working it out more accurately, if at all?

  45. Garrett

    Love how the interaction between the asteroid and the Earth resembles a coulomb elastic collision between charged particles.

  46. Pete Jackson

    @40 IVAN: Sorry, I thought no one would notice :-(

    Here it is back.


  47. ShavenYak

    Mote, #39: You would not feel any G forces, because you and the asteroid would be in freefall.

  48. Garrett

    ShavenYak, #50. That doesn’t sound right. In orbit you are in freefall, but the asteroid will not be in orbit around the Earth. So I would expect some g-forces to be felt by an observer standing on the asteroid (positive or negative, depending on what side of the asteroid you are standing).

  49. Gus Snarp

    So the question of whether it could hit one of our satellites got me thinking about just what the odds are of striking a satellite. In this case the asteroid would only get a limited swath of potential satellites, those orbiting higher then 12,000km, but lets say we launched a rocket from a random spot on the earth at a random time, past the altitude of the highest satellite. What are the odds it would hit a man made satellite?


    @Pete Jackson (#49),

    OK, but don’t do it again! 😉

  51. Here’s an image I shot of it this morning, 5 hours before closest approach:


  52. Pete Jackson

    @57: Beautiful image, Marco. How long is the trail in arcseconds?

    No obvious sign of rotational modulation, but you wouldn’t expect that in 30 seconds (but who knows).

    Thanks for posting!

  53. So, did we all die or what?

  54. Pete Jackson

    @39, 50: The question of g forces relates to IVAN3MAN_AT_LARGE’s estimates of whether the asteroid might break up at closest approach. Normally, on the asteroid, you would feel a g force of about one-millionth of Earth’s surface gravitational acceleration. Now, at closest approach to the Earth, the g force on the side facing the earth will be somewhat less, mainly:

    g force from asteroid – (g force from Earth on side of asteroid nearest earth – g force from Earth at center of asteroid)

    The g force on the side of the asteroid away from Earth will be the essentially identical:

    g force from asteroid – (g force from Earth at center of asteroid – g force from Earth at side of asteroid farthest from Earth).

    According to IVAN’s calculations, the differences in the parentheses will be less than the g force from the asteroid, so the astronaut will experience a reduction of the g force from the asteroid, but he will not float away!

    Note that, considered separately, the g forces from the Earth will be about 250,000 times greater than the g force from the asteroid, but since we are in an orbit, it is only the differences that count.

  55. Darren

    @51, the asteroid is not in orbit, but it is in freefall (there are no non-gravitational forces acting on it). Other than tidal differences, the forces on the asteroid and the observer would be identical. So no forces from the earth would be felt.

    If gravity were a tractor beam affecting the asteroid and not the observer, then there would be forces between the two that could be measured/felt

  56. mike burkhart

    So there is nothing to worry about? Good I think we sould have a color coded system for Asteroids that cross the earths orbit. This sould be the system: Green Alert: Asteroid has no effect on Earth or the Moon Blue Alert:Asteroid will collide with the Moon. Yellow Alert: Asteroid will fragment some fragments will colllide with Earth Red Alert: Asteroid will collide with the Earth. These are the main dangers I see maybe some of you can think of others and expand the warning system.

  57. Gary Ansorge

    10 meteres? That’s about the right size for a H.O.M.E.(high orbital mini earth). I could retire there,,,

    Now, if I just had access,,,

    Gary 7

  58. Sparky

    Does anyone know when the pretty radar images will be released?

  59. Wallace Neslund

    If the closing speed of the asteroid is only about a kilometer/sec, that’s about 3600kl/hr, or about 2232/mph. Since the closest approach is 7430 miles from Earth, why doesn’t it go into orbit around Earth or just get sucked into Earth’s atmosphere? The orbital velocity of the Space Shuttle and the ISS is about 17,500/mph at about 150 miles above Earth. Even the geostationary satellites at 22,236 miles up have an orbital velocity of 6878/mph. Since the asteroid will be both closer and slower than a geostationary satallite, it should be either pulled into orbit around Earth or down into a collision with Earth’s atmosphere. The only possible reason why it wouldn’t be is if the “speed up” at close approach is so great that it exceeds the orbital velocity at the distance it passes by the Earth. Exactly how much is this speed up that it can go from 2232/mph to well over 6878/mph?

  60. Pete Jackson

    @71Wallace: You are confusing closing velocity and total velocity. At closest approach, the closing velocity is zero, but the total velocity relative to the earth will still be somewhat greater than needed for escape from the Earth’s gravity and return to interplanetary space.

  61. I SAW IT! It was blue/white/orange bright light. It felt like it was going down here :O

  62. Wallace Neslund

    @ Pete Jackson: No I’m not confusing closing velocity and total velocity. Do you even know what “closing velocity” even is? Closing velocity is the velocity of the asteroid as it approches the Earth. It increases as it get closer to the Earth until it reaches the closest approach, then it switches to receding velocity, which is decreasing as it moves away from the Earth against Earth’s gravitational pull. Obviously at closest approach there is no approaching or receding velocity since for that single instant, the asteroid is neither approaching or receding from the Earth, but that has absolutely nothing to do with what I said. I have no idea why you even mentioned that.

    As I clearly said, the relative velocity of the asteroid compared to Earth as stated by the article would only be 2232/mph at a distance of 7430 miles. That is well under the orbital velocity of an object at that distance. It may be true that both Earth and the asteroid are going 30 kl/sec, but that has nothing to do with the Earth and asteroid gravitational interaction. For that two body system, the only pertinent values are the relative motion of the asteroid compared to the Earth. As I also stated, an object in geostationary orbit at 22,236 miles from Earth has an orbital velocity of 6878/mph, that is exactly fast enough to keep it in orbit. The asteroid is much closer and going, relatively, much slower, so at that speed and distance the asteroid would be drawn in by Earth’s gravity and crash into Earth. The only way that wouldn’t happen is if the “speed up” by Earth’s gravity increased the asteroids velocity to greater than orbital speed at that distance. Since we know orbital velocity at 22,236 miles is 6878/mph, then the asteroid must speed up to far greater than 6878/mph since it is far closer to Earth than the geostationary satallites.

    Again, the question I asked of Mr. Plait was how much was this speed up and how fast was the asteroid going when it passed by the Earth. Obviously well over 6878/mph, but how much more?

  63. Messier Tidy Upper

    @57. Marco Langbroek : Congrats – great work & thanks for sharing it with us. :-)

    @20. & #30 IVAN3MAN_AT_LARGE :

    the Roche limit – the distance from the primary mass at which a satellite will disintegrate due to tidal forces exceeding the satellite’s own gravity – can be easily be calculated ..

    Assuming that you’re good at calculating and maths generally which I’m very much *not* – Thanks for that info – good comments. :-)

    @66. Sparky : Does anyone know when the pretty radar images will be released?

    Not sure about RADAR images but space-dot-com has an article with photos of it and more info. on this close encounter which I’ve linked & is ‘awaiting moderation’ currently. :-)

  64. Messier Tidy Upper

    See :


    for latest photos & more via space-dot-com.

    Also see this on-line news item on it here :


    for more.

    @63. mike burkhart :

    So there is nothing to worry about? Good I think we sould have a color coded system for Asteroids that cross the earths orbit. This sould be the system: Green Alert: Asteroid has no effect on Earth or the Moon Blue Alert:Asteroid will collide with the Moon. Yellow Alert: Asteroid will fragment some fragments will colllide with Earth Red Alert: Asteroid will collide with the Earth. These are the main dangers I see maybe some of you can think of others and expand the warning system.

    Well there’s already the Torino scale :


    devised for pretty much just this purpose. :-)

  65. Wallace Neslund

    I got tired of waiting, so I figured it out myself. At a distance of 7430 miles above the surface of the Earth, orbital velocity is about 9530/mph. Therefore, in order for the asteroid to keep going past Earth and not be captured in orbit or pulled in to crash into Earth, the asteroid had to be going faster than 9530/mph at closest approach. So the “speed up” caused by falling into Earth’s gravity well was more than 9530 – 2232 = 7298/mph. That means the “speed up” more than quadrupled the relative speed of the asteroid as it passed the Earth. Of course, the asteroid will lose all this extra velocity as it climbs out of Earth’s gravity well, but it did serve to move the asteroid past the Earth much faster than it would have if not for the Earth’s gravity assist.

  66. mike burkhart

    One more thing asteroids have been a staple of many video games ,the frist to have one was Space War then Atari made the popular Asteriods and Astroids Deluxe where you had to blast em for the Atari 2600 home system ,Star Ship had Asteriods you had to avoid while in Star Raiders, the enemy fled to an Asteroid Belt you could shoot the Asteroids in this game to prevent them from hiting you.On Intlevison Astrosmash had you protecting a planet from a unending barage of asteroids ,you got points for shooting them but if they hit the planet you lost points.Since then most space games have had asteroids.

  67. The article linked to my name here (click my name to visit – via space-dot-com) shows that the fly-by has altered this tinyt asteroids or meteoroids course for good* :

    The asteroid’s flyby of Earth has changed its orbit, according to Yeomans and Chodas. Before its Earth encounter, asteroid 2011 CQ1 was one of the solar system’s so-called Apollo-class asteroids, whose orbits around the sun are mostly outside the orbit of Earth. [5 Reasons to Care About Asteroids] But during the Feb. 4 flyby, Earth’s gravitational pull warped the flight path of 2011 CQ1. Now the asteroid will spend “almost all of its time inside the Earth’s orbit” in what scientists call an Aten-class orbit, ..

    It apparently also makes 2011 CQ1 the the closest non-impacting object in our asteroid catalog to date.

    * Or for evil potentially although really it doesn’t pose any threat. Not unless it hits a satellite or the space station and the odds of that are .. well, super-ultra-mega extreme would probably be an understatement! 😉


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