# Asteroid Passes Within 7500 Miles Of Us? **URL:** \ **Category:** Miscellaneous and Personal Stuff I Must Share\ **Created:** [June 27, 2011, 11:08pm UTC](https://boards.straightdope.com/t/asteroid-passes-within-7500-miles-of-us/587072 "2011-06-27T23:08:07Z")\ **Posts on this page:** 17\ **Page:** 3
**Author:** ![levdrakon](https://avatars.discourse-cdn.com/v4/letter/l/49beb7/32.png) [@levdrakon](https://boards.straightdope.com/u/levdrakon)\ **Post date:** [June 29, 2011, 4:05pm UTC](https://boards.straightdope.com/t/asteroid-passes-within-7500-miles-of-us/587072/41 "2011-06-29T16:05:45Z")
> [@greg charles](#): > > small 1x power binoculars … Your eyes? lol. 🙂 ---
**Author:** ![Malacandra](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@Malacandra](https://boards.straightdope.com/u/Malacandra)\ **Post date:** [June 29, 2011, 4:32pm UTC](https://boards.straightdope.com/t/asteroid-passes-within-7500-miles-of-us/587072/42 "2011-06-29T16:32:50Z")
> [@Greg\_Charles](#): > > Small 1x power binoculars … your eyes? No reason not to use 1x binoculars for star-gazing - just by gathering more light they’d help you see things. The Andromeda Galaxy, for instance, is a much [bigger](http://apod.nasa.gov/apod/image/0612/m31abtpmoon.jpg) naked-eye object than the full Moon, but it’s so dim that even its bright centre is only marginally visible. Since even a 20-mile asteroid would be about a millionth of the Moon’s mass, I wouldn’t expect one to have a drastic effect on its orbit. ---
**Author:** ![Candyman74](https://avatars.discourse-cdn.com/v4/letter/c/ad7895/32.png) [@Candyman74](https://boards.straightdope.com/u/Candyman74)\ **Post date:** [June 29, 2011, 5:00pm UTC](https://boards.straightdope.com/t/asteroid-passes-within-7500-miles-of-us/587072/43 "2011-06-29T17:00:25Z")
> [@Who\_me\_1](#): > > According to that article there was never any chance of it hitting us, and even if it had it would have burned up in the atmosphere. Not much of a bullet! I’m so proud to have started a mini-meme! 🙂 ---
**Author:** ![Daylate](https://avatars.discourse-cdn.com/v4/letter/d/9dc877/32.png) [@Daylate](https://boards.straightdope.com/u/Daylate)\ **Post date:** [June 29, 2011, 8:11pm UTC](https://boards.straightdope.com/t/asteroid-passes-within-7500-miles-of-us/587072/44 "2011-06-29T20:11:14Z")
> [@](#): > > No reason not to use 1x binoculars for star-gazing - just by gathering more light they’d help you see things. I don’t think 1X binoculars are a reasonable light gathering aid. If they had a 50mm objective lens, then the exit pupil (the bundle of rays coming out of the eyepiece into your eyes) would also be 50mm in diameter. So, as the nighttime diameter of the pupil of your eye is only around 7mm, all the rest of that light would be wasted. The diameter of the bundle of rays coming out of the eyepiece is calculated by dividing the diameter of the object lens by the power of the lens system. This is why the best night vision binoculars are 7 X 50 (7 power with a 50mm objective lens). 50mm divided by 7 = just a shade over 7mm, just the size that will fit into a normal person’s pupil. A lower power than 7 would just be wasting the light. Things wouldn’t look any brighter than with the naked eye. ---
**Author:** ![bup](https://avatars.discourse-cdn.com/v4/letter/b/6bbea6/32.png) [@bup](https://boards.straightdope.com/u/bup)\ **Post date:** [June 29, 2011, 8:16pm UTC](https://boards.straightdope.com/t/asteroid-passes-within-7500-miles-of-us/587072/45 "2011-06-29T20:16:01Z")
1xmagnification was intended as a joke, people. ---
**Author:** ![billfish678](https://avatars.discourse-cdn.com/v4/letter/b/7bcc69/32.png) [@billfish678](https://boards.straightdope.com/u/billfish678)\ **Post date:** [June 29, 2011, 8:18pm UTC](https://boards.straightdope.com/t/asteroid-passes-within-7500-miles-of-us/587072/46 "2011-06-29T20:18:43Z")
> [@bup](#): > > 1xmagnification was intended as a joke, people. Take heart. I could almost see what you did there. ---
**Author:** ![a35362](https://avatars.discourse-cdn.com/v4/letter/a/3da27b/32.png) [@a35362](https://boards.straightdope.com/u/a35362)\ **Post date:** [June 30, 2011, 5:05pm UTC](https://boards.straightdope.com/t/asteroid-passes-within-7500-miles-of-us/587072/47 "2011-06-30T17:05:43Z")
Here is a [simulation](http://www.todaysbigthing.com/2008/09/09) of a 500 kilometer asteroid (about 311 miles) hitting the Earth. Owie! ☹ ---
**Author:** ![Sailboat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sailboat/32/461_2.png) [@Sailboat](https://boards.straightdope.com/u/Sailboat)\ **Post date:** [June 30, 2011, 6:46pm UTC](https://boards.straightdope.com/t/asteroid-passes-within-7500-miles-of-us/587072/48 "2011-06-30T18:46:50Z")
> [@tdn](#): > > Damn, and I could have been out there in my little triangular space ship shooting it to little pieces! The pieces would have just re-entered the other side of the screen and been as much a threat as before. ---
**Author:** ![Suburban\_Plankton](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/suburban_plankton/32/219_2.png) [@Suburban\_Plankton](https://boards.straightdope.com/u/Suburban_Plankton)\ **Post date:** [June 30, 2011, 6:56pm UTC](https://boards.straightdope.com/t/asteroid-passes-within-7500-miles-of-us/587072/49 "2011-06-30T18:56:02Z")
> [@CalMeacham](#): > > What would a good comet strike look like? Try to imagine the Earth getting hit by a cubic mile of hot fudge sundae… ---
**Author:** ![Damfino](https://avatars.discourse-cdn.com/v4/letter/d/f9ae1b/32.png) [@Damfino](https://boards.straightdope.com/u/Damfino)\ **Post date:** [June 30, 2011, 7:27pm UTC](https://boards.straightdope.com/t/asteroid-passes-within-7500-miles-of-us/587072/50 "2011-06-30T19:27:39Z")
Where’s Spaceguard? ---
**Author:** ![Winston\_Bongo](https://avatars.discourse-cdn.com/v4/letter/w/a9adbd/32.png) [@Winston\_Bongo](https://boards.straightdope.com/u/Winston_Bongo)\ **Post date:** [June 30, 2011, 9:09pm UTC](https://boards.straightdope.com/t/asteroid-passes-within-7500-miles-of-us/587072/51 "2011-06-30T21:09:05Z")
> [@Suburban\_Plankton](#): > > Try to imagine the Earth getting hit by a cubic mile of hot fudge sundae… According to that article there was never any chance of a hot fudge sundae hitting the earth, and even if it had it would have melted in the atmosphere. Not much of a bullet! ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [June 30, 2011, 9:30pm UTC](https://boards.straightdope.com/t/asteroid-passes-within-7500-miles-of-us/587072/52 "2011-06-30T21:30:46Z")
> [@TruCelt](#): > > Does anyone know how much impact energy would be reuired to alter the moon’s orbit? For the Earth-Luna system, the specific orbital energy is the sum of the standard gravitational parameters of the Earth and Luna, divided by twice the semi-major axis. That gives about 524 KJ/kg. Luna masses 7.3477 × 10[SUP]22[/SUP] kg, so making a 1% change in orbital energy (and corresponding change in tidal energy) would require 0.01 \* 524 \* 7.35 x 10[sup]22[sup] KJ = 3.85 \* 10[sup]23[/sup]. Using maximum estimates for the size and density of 2011 MD (45 m diameter, a Fe/Ni composition with 7.7 g/cm[sup]2[/sup]) gives a mass of 367\*10[sup]3[/sup] tonnes. This would have to be moving 4580000 km/s, or about 1.5% of _c_ in order to make this change. I’d be less worried about this than the infinitesimal chance of knocking a DirecTV satellite out of service. Stranger ---
**Author:** ![Gray\_Ghost](https://avatars.discourse-cdn.com/v4/letter/g/c0e974/32.png) [@Gray\_Ghost](https://boards.straightdope.com/u/Gray_Ghost)\ **Post date:** [June 30, 2011, 10:39pm UTC](https://boards.straightdope.com/t/asteroid-passes-within-7500-miles-of-us/587072/53 "2011-06-30T22:39:00Z")
> [@Suburban\_Plankton](#): > > Try to imagine the Earth getting hit by a cubic mile of hot fudge sundae… > [@Winston\_Bongo](#): > > According to that article there was never any chance of a hot fudge sundae hitting the earth, and even if it had it would have melted in the atmosphere. Not much of a bullet! Well, we can ignore the nuts, at least… The real question is whether the sundae could run on a treadmill long enough to burn itself up. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [June 30, 2011, 11:00pm UTC](https://boards.straightdope.com/t/asteroid-passes-within-7500-miles-of-us/587072/54 "2011-06-30T23:00:48Z")
When people say “there was never a risk that it would hit us”, what they really mean is “from the time of its discovery, the best estimate of its orbital parameters have always had it missing us”. But this rock isn’t very different at all from one that _would_ have hit us. And an extra little sobering thought: These things are named by their date of discovery. Notice how both this one and the previous near-miss both have “2011” in their names? Even with as close as they got, we didn’t know about either until less than a year before. Oh, and you can’t say that something would burn up in the atmosphere instead of impacting. Burning up in the atmosphere _is_ an impact. You’re still adding all that energy to the habitable portion of the planet (and the habitable portion is my favorite part, that’s where I keep all my stuff!). ---
**Author:** ![Malacandra](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@Malacandra](https://boards.straightdope.com/u/Malacandra)\ **Post date:** [July 1, 2011, 6:12am UTC](https://boards.straightdope.com/t/asteroid-passes-within-7500-miles-of-us/587072/55 "2011-07-01T06:12:02Z")
Do tell. I’d still rather have a bomb go off forty miles above my house than in my back yard - better to share the energy around a little than have it all in one place, yes? ---
**Author:** ![Sailboat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sailboat/32/461_2.png) [@Sailboat](https://boards.straightdope.com/u/Sailboat)\ **Post date:** [July 1, 2011, 3:26pm UTC](https://boards.straightdope.com/t/asteroid-passes-within-7500-miles-of-us/587072/56 "2011-07-01T15:26:55Z")
> [@Malacandra](#): > > Do tell. I’d still rather have a bomb go off forty miles above my house than in my back yard - better to share the energy around a little than have it all in one place, yes? Yes and no. Air-bursting artillery shells are _more_ effective than shells that burrowed into the ground. It’s been argued that the Nagasaki bomb killed fewer people than expected because it “missed” its aiming point and the blast was partly blocked by terrain. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [July 1, 2011, 5:47pm UTC](https://boards.straightdope.com/t/asteroid-passes-within-7500-miles-of-us/587072/57 "2011-07-01T17:47:23Z")
Indeed. You can see this from the Federation of American Scientists [Nuclear Weapon Effects Calculator](http://www.fas.org/programs/ssp/nukes/nuclear_weapon_effects/nuclearwpneffctcalc.html?formAction=297&contentId=367). A meteor isn’t a nuclear weapon, of course, so the effects aren’t quite the same, but a meteor can incandesce energetically, delivering massive blast effects long before it makes a groundfall, as aptly demonstrated by the Tunguska event. The size range of this meteor is in about the same range as that estimated for a comet that could have caused Tunguska. This leveled an area of forest over 800 square miles; enough to destroy a major metropolitan area or destroy half a million acres of agricultural land. Basically the only way this wouldn’t result in a very bad day for someone is if it landed in broad ocean area far enough away from any continental shelf to not risk causing a small tsunami. And this wouldn’t happen “40 miles up”; because of the logarithmic relationship between atmospheric mass density and altitude, air burst effects will occur at altitudes of around five miles, and for a larger object will result in fragmenting the core into small pieces that retain most of the momentum of the original object, so it delivers both air burst and distributed ground impact effects. As **Chronos** notes, while several observatories have run limited surveys to identify PHOs per the George E. Brown, Jr. Near-Earth Object Survey Act, there is not a comprehensive ongoing program to identify and track all PHOs, nor any effort to develop a practical means of diverting an identified hazard. Furthermore, although it was previously assumed by known impacts that the probability of hazard was fairly rare, increased resolution of observational capability in even the last decade has revealed that there are far more near misses previously assumed, and the hazard probability continues to inch upward. Although such impacts will still be comparatively rare, a single large event cause sufficient destruction to set back industrial society and cause trillions of dollars of damage or kill tens of millions of people. However, because such a “black swan” event has not yet occurred there is little public impetus to protect against it, or even gain knowledge of the true risks. Stranger [Previous page](https://boards.straightdope.com/t/asteroid-passes-within-7500-miles-of-us/587072.md?page=2)