LCROSS didn't destroy the Moon. Whaddya know?

By Phil Plait | October 20, 2009 8:00 am

Note: I had an error in the original calculation for the Sun’s energy output (I blew it converting from ergs to Joules, if you’re curious). I fixed the error in the text below. I usually like to keep my mistakes open, but striking through the text in this case would make it confusing to read, so instead I simply fixed it and admit my error here. Anyway, the change isn’t a big deal; although the numbers changed, it doesn’t change the fact that the impact was teeny tiny compared to anything else the Moon goes through.

On October 9, a Centaur rocket booster, watched and followed by the Lunar Crater Observation and Sensing Satellite, impacted the Moon at several kilometers per second. Slamming into a crater near the lunar south pole, the hope was that the impacts would excavate water frozen permanently under the surface, eject plumes kilometers high, and give us our best evidence yet of ice on the Moon.

NASA played up the event, saying the plume might be visible from Earth. I didn’t think the flash would be visible from Earth (though the rocket booster impact was seen by LCROSS); from here we can’t see the floor of Cabeus crater where the impacts occurred, but I had hopes about the plume. Unfortunately, none of the fleet of terrestrially moribund telescopes detected the plume. A lot of people (bloggers, web commenters, twitterers) expressed disappointment.

Some people were a little more, um, well… crazy.

Now, that’s not too surprising. First off, most people understandably don’t have a great grasp of the scale of the Earth and Moon, and so may have been expecting a lot more out of this event. Others, also lacking that sense of scale, thought that disaster would befall the Moon. Still others in this group think that humans polluting the Moon is a tragedy.

All of them were and are wrong. Why? Let’s see.

1) Smackdown

First off, let’s talk about the initial flash from the impact. Our view from Earth was blocked, but if it were bright enough it might have illuminated the walls of the crater. Is it realistic to see the flash from a backyard telescope? Before the event I wondered about that, so I calculated about how bright it would be. Since I went to the trouble, I’ll subject you to it too. Plus, the math is fun.

This has to do with energy. When something smacks into something else, the energy in its motion is converted into other types of energy. When you clap your hands, for example, it’s sound. But at very high speeds, a lot of that energy is converted into heat and light. The amount of light you get out depends on lots of things, but mostly on the energy of the moving object, its kinetic energy.

That’s easy to calculate: the kinetic energy of an object is 1/2 x its mass x its velocity squared. The Centaur had a mass of about 2000 kilograms (a little over two standard tons) and was moving at 2.5 km/sec when it hit the Moon. Doing the math, that means it had a kinetic energy of a little over 6 billion Joules, equivalent to the energy release of blowing up about 1.5 tons of TNT.

That sounds like a lot! But that’s the total kinetic energy of the booster, and while it was released upon impact, not all of it turned into light. Some of it went into heating up the ground, some into vaporizing the metal in the rocket, some into displacing the ground — digging a crater and ejecting a plume — and so on.

But let’s be optimistic for a moment, and assume all the energy was converted into visible light. How bright would it have been from Earth?

The easiest way is compare the energy and distance of the impact to the energy and distance of the Sun. We know how bright the Sun is, so by setting up a ratio we can calculate the maximum brightness of the Centaur event.

The distance to the Sun is 150 million km, and it gives off 4 x 1026 Joules every second. The Moon is 400,000 km away, and the Centaur impact had an energy of 6 x 109 Joules. Brightness scales with distance squared, so the ratio of the two brightnesses is

(Energy of Centaur / Energy of Sun) x (Distance of Sun / Distance of Moon)2

So let’s see… divide that there, multiply by this, carry the two… and we get that the ratio of the brightness of the Centaur impact as seen from Earth is about 2 x 10-12. In other words, the Sun is 500 billion times brighter! Wow!

But how bright does that make Centaur? Astronomers measure brightness in magnitudes, and I won’t bore you with the details this time, but knowing the brightness of the Sun and the ratio, that means that the Centaur impact — assuming all the energy went into visible light — would have shone at a magnitude of about 3 or 4, visible to the unaided eye but not glaringly obvious.

So it’s not like you’d have to squint and turn away from the glare. Standing on the Earth looking at the Moon, you’d barely have seen it at all, and the brightness of the Moon itself would have washed it out.

And that’s a best case. In reality we know that the energy doesn’t go into a visible flash; most of it is turned into heat. That means infrared energy, the kind that was easily detected by LCROSS when the Centaur booster hit the Moon. But even then the amount of kinetic energy converted to light is very low; I was quoted a figure of about 1/100th of a percent by an expert some years ago. That means that the flash — even in infrared — would have been at a magnitude of about 13 or 14, which is pushing the limits of small telescopes. And the visible flash would have been smaller yet.

That’s why I wasn’t expecting ground-based telescopes to see the flash. I had hopes, but no such luck.

2) The Big Mo

What about momentum? I read a few places where people were concerned that the impact might change the Moon’s orbit.

When you think about it a little, you’ll see this isn’t a concern. The Centaur was a cylindrical hunk of metal 13 meters high and 3 in diameter. The Moon is a ball of solid rock over 3400 kilometers across! So it’s like a flea hitting a freight train. But let’s make sure.

Momentum is simply the mass of an object times its velocity, and any momentum the Centaur had was given to the Moon. Let’s assume the Moon is standing still (that is, has velocity = 0) and then ask how fast the Moon would move after the booster hit it. That’s easy: we set the two momenta equal, divide the momentum of Centaur by that of the Moon, and solve for the Moon’s velocity:

mass x velocity of Centaur = mass x velocity of the Moon, so the Moon’s velocity after impact = (mass x velocity of Centaur)/ (mass of Moon)

Doing the math, (2000 kg x 2500 m/sec) / 7.4 x 1022 kg = 7 x 10-17 m/s.

Egads. That means the Moon gained a velocity of 0.00000000000000007 meters per second from the impact. In other words, if you waited, say, 460,000,000 years you’d see the Moon will have moved a meter.

In other other words, a flea hitting a freight train. The concerns over the Moon plummeting to Earth or being blasted out of orbit a la Space:1999 were a tad unfounded.

In fact, the Moon is hit by meteorites all the time, and is probably smacked by something with the same momentum as the Centaur several times per year. Since the Moon is still there, we can safely assume the Centaur impact had essentially zero effect.

3) Extra-terrestrial eco-terrorism

OK, so we couldn’t see the flash, and the Moon remained unmoved after the impact. But what about humans being fined for cosmic littering?

I heard from several people personally who felt that we shouldn’t impact our stuff on the Moon because it’s polluting the surface. Some felt that it was just wrong in a vague way, but couldn’t clearly express why. Others felt it was just a dumb macho stunt.

First, it was not a stunt. High-speed impacts are a legitimate way — really the only one we have right now — to see if water lurks beneath the permanently shadowed floors of polar craters. You can accuse NASA of being macho jerks, but I don’t think that sticks. It’s really just a silly accusation.

As for littering, I think that’s a sense of scale. The Moon has a surface area of 37 million square kilometers, and the Centaur dug a crater about 20 meters across. Saying that has any real impact on the Moon is like arresting someone for mowing their back yard*

And remember, the Moon is constantly bombarded from space. Roughly a ton of material hits the Moon every day, so the Centaur is a blip on top of that. And I’ll add that the Moon is essentially a giant rock in space, with no forests, no ecosystems, no delicate climate to knock out of whack. As a scientist I don’t want us defacing the Moon any more than necessary; it’s always best to study objects like it in situ. But I also know the Moon is very, very large, our impact doing this very, very small, and the outcome could be scientifically pretty huge.

One point to be made, of course, is that if we do find water, it makes it far more likely we’ll build colonies on the Moon that could do large scale mining and such, and that really will have an impact. That’s true, but again the Moon is a giant barren rock in space. I challenge anyone who worries that we will hurt the Moon somehow to first tell me exactly how what we’re doing is a bad thing (other than a vague discomfort with it), and also to turn around and defend how they live in a house or apartment or wherever. That has a much larger impact on the Earth, where we know things are in a pretty delicate condition. Plus, we live here and depend on the Earth.

Conclusion

I certainly understand why people might be concerned over what we’re doing on and to the Moon, but it’s a concern borne out of not understanding the scale of the Moon and what we’re doing with it. Think of it this way: when you stand outside and gaze at the Moon with your unaided eye, the smallest crater you can see is about 100 kilometers across. That means you could hit the Moon with an asteroid a mile across, and once the smoke cleared the crater would be too small to see without a telescope!

That’s the scale we’re talking about here. In the meantime, there is real science to be done and real challenges to overcome in going to the Moon. In my opinion, these small efforts to understand it are well worth the effort. And I would bet the bank that in 100 years, if we do boldly go and colonize our nearest cosmic neighbor, they will look back at this era fondly, though with a small bit of chagrin as they wonder, "What took us so long?"



* Yes, I know that lawn mowers pollute the air, and that some places make it illegal to mow in times of really bad air quality. But that’s because hundreds of thousands or millions of people mow their lawns. When NASA launches a million spacecraft to hit the Moon, then we’ll talk.

CATEGORIZED UNDER: Astronomy, NASA, Piece of mind, Science
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Comments (85)

  1. Pete

    “fleet of terrestrially moribund telescopes” ???

    Are they really all dying on Earth?

    Seriously, though, a good article. I was unaware that anyone was loony (lunie?) enought to think the LCROSS impact would be big enough to alter the Moon in any significant wat.

  2. Nick

    So how big a crater does a 1 mile diameter asteroid make?

    Nick

  3. The moon may not have been destroyed, but were its feelings hurt?

  4. The flea hitting a train got me thinking and I had some time to spare, so I did some calculations. I got a value of 0.08704g for a flea’s weight and 1m/s for a flea’s takeoff speed. I also got a value of 5,500 tons (4,989,516,070g) for the average freight train. Doing all of the calculations leads to the train’s velocity being 1.7 x 10^-11 m/s. This is actually much more than the Centaur impact. Now my Googled values might be off a bit, but it is interesting to think that a flea hitting a freight train would actually have about 250,000 times the effect that LCROSS had on the moon!

  5. Derek

    >> When NASA launches a million spacecraft to hit the Moon, then we’ll talk.

    Say… Now that WOULD be an interesting experiment.

  6. @Todd W,

    I have it on good authority that the moon is now angry with us and isn’t talking to us. (Then again, if you talk with the moon on a regular basis, perhaps you need to seek psychiatric assistance.)

  7. markogts

    IMHO, your assumption that the Sun energy to compare is that one of one second of its emission, is a bit arbitrary. We should take in account the energy the Sun releases in a time of the same duration of the supposed flash, some thousanths of a second. Moreover, the spectral distribution o the flash is not necessarily the same as the Sun’s one.

    Of course, from an astronomical POW, this is just hair-splitting.

  8. What’s all this math and science? We all just know this stuff based on a feeling. We don’t need that fancy science stuff, it just messes up our … aura … or something…

  9. rob

    according to homeopathic astronomilogical collision theory, when a small rocket booster succusses the moon and mixes with water present in the lunar regolith, the resulting 10,000C mixture of booster and water should give off phased plasma in the 40W range. because it didn’t, and homeopathic astronomical collision theory is 103% correct, it must mean that the moon has no water. any claims that NASA makes concerning water on the moon MUST be a hoax. it’s probably from a leaky drinking fountain on the soundstage where the collison was faked.

  10. LOL @ rob! 😀

    By the way, an interesting astronomical perspective: If you took ALL the material in the asteroid belt, it would equal aproximately 4% of the moon. Eithere there isn’t much in the asteroid belt, we have a big moon, or some combination of the two. :)

  11. markogts

    Oh, BTW, on Paolo Attivissimo’s blog, we compared this energy to the one of the Saturn IVb impacts, and it looks like forty years ago we did much more damage, some ten times more energy.

    http://complottilunari.blogspot.com/2009/10/apollo-14-rifotografato-il-cratere.html

    According to the LCROSS site, the energy of the impact was 6 billion Joules, while here they say the Saturn IVb impact released 55 billion Joules.

  12. Nigel Depledge

    The BA said:

    The Centaur had a mass of about 2000 kilograms (a little over two standard tons) . . .

    I beg to differ.

    2000 kg is 2 (metric) tonnes, which is a bit less than 2 standard tons (each of which is 20 cwt, or 160 stone or 2240 lb).

    I think instead you refer to the “short ton” (2000 lb), which may be standard in the USA but ain’t standard anywhere else.

    I think what I’m trying to say is just to remember that your audience is international, and that what you might consider to be standard may not be.

  13. mike burkhart

    Litering the moon? what about all the junk from the space probes and the apllo missions all of its still on the moons surface I don’t hear these people saying we should go there and clean up our mess we’ve left behind maybe they are worried about the cost or just were we would put all of junk if we did bring it back

  14. Travis

    Littering is relative. Alien visitors to Earth would think a Human landfill was wonderful in the same way we love it when we stumble upon a beaver dam or a termite mound. “Evidence of the natural inhabitants.” Discovering the stuff on the Moon would be even more exciting since it would be like finding an elephant tusk in the middle of Australia.

  15. Cheyenne

    @Nigel – I don’t think it’s that big of a deal. It’s not like we’ve ever lost a NASA mission because they messed up in confusing English and Metric units. Oh wait a sec…..(Mars Climate Orbiter – $125 million)

    The US should catch up to the rest of the world and go metric (btw- I actually have no idea if a short ton and a regular ton are metric/English differences, but I’m sticking with the gist of what I wrote!).

  16. gopher65

    @Nigel Depledge:

    Short tons aren’t standard anywhere:P. Both 2240 and 2000 are used in the US, depending on exactly what is being measured, and where it is being shipped. Just like 1 gallon equals both 3.78 litres and 4 litres, depending on where it is being shipped. They really need to standardize metric use in most fields* to stop my head from exploding;).

    *there are a few fields where imperial measurements have to be used in some situations, such as baking. 1 cup != 250 ml. It’s close, but when you’re baking you can’t just mix and match approximations like that. Having a recipe that calls for 12 cups and converting that to 3 litres is a baaaaad idea. Baking is a science, not an art (unlike cooking, which is an art).

  17. Petrolonfire

    Some people were a little more, um, well… crazy.

    Some people always are. Sadly, they’ll be the ones to get the publicity & attention. :roll:

    Sanity is the exception.

  18. @markogts, I spotted Phil’s deliberate schoolboy error, too. However, I think (based on Deep Impact, where a bright plume was photographed several minutes after impact), that the duration of the flash would be a lot longer than a second, making it fainter on average.

    Of course, most of the energy might go into an initial spike of less than a second, followed by a longer glow.

    I’m not sure one can ever demonstrate that someone is wrong to think something is a tragedy. If I choose to consider a small amount of Centaur debris on the Moon a tragedy, that’s a matter of my values, and you can’t really say I’m wrong. How I live is irrelevant: plenty of people from Noah on down to Q have considered pretty well everything about the human race to be tragedy.

    Self-loathing: a much underrated concept.

  19. Andrew

    I think that some people were just afraid that Space 1999 would become real.

  20. Obviously we must increase NASA’s budget so we can establish a permanent lunar base, which can then clean up the litter.

  21. Gary Ansorge

    Note that the “short ton” is an IMPERIAL measurement and is 2000 lbs WEIGHT, which only applies on the surface of the earth, whereas the term “tonne” is 1000 kg MASS, which applies everywhere in the universe and is a measure of MASS. The only place that mass and weight are equal is under one Gravity(9.8 m/sec^2) acceleration.

    I agree, we(USA) REALLY need to get with the international standard. We’ve been trying for a half century but we’re kinda slow.

    GAry 7

  22. Aerimus

    @gopher65:

    Well, actually, you could make the conversion in baking, you’d just need to adjust the quantity of all the ingredients to match, similar to cutting or doubling the recipe to decrease/increase the batch yield. But given that so much baking involves tradition (such as the pound cake recipe that is generations old in my wife’s family), I wouldn’t expect to see too many bakers making the change anytime soon.

  23. StevoR

    A letter texted in to the South Aussie Sunday Mail newspaper (2009 Oct. 18th) says – & I quote verbatim – :

    Are NASA insane? Bombing our moon that controls our weather, tidal changes and atmospheric pressure? It won’t be man that causes his own destruction it will be those silly scientists. – A.E. Swain, Semaphore.

    *Facepalm*

    *Headdesk*

    Teh stoopid it burns! :roll:

    That’s what we’re up against here. That’s the level of utter ignorance and tripe that’s getting published in a respectable (okay semi-respectable) Australian paper. Sigh. :-(

    Think about it – not only does this letter writer have no idea about LCROSS, not only hasn’t he heard of – d’uh! – Craters he thinks the Moon controls our *weather* and *atmospheric pressure* for pity’s sake! Plus he sems to imply that scientists aren’t even human or as AE sexist~ally (not a word? It is now!) put it “man”. Depressing really.

    I’m writing a response to hopefully go in the paper too but we’ll have to wait & see if that gets published.

    PS. I second the notion that the USA finally joins the rest of the world and adopts the metric system. You’ll quickly get used to it and find it actually makes heaps more sense than your current measures. While you’re on with it – you’d be well-advised to change from measuring temperatures in Fahrenheit to Celsius degrees too. 😉

  24. The Moon may not have been destroyed, but it wreaked havoc with my horoscope!

    #18, Naked Bunny With A Whip:
    No, the reason we must increase NASAs budget is so we can build bigger Moon bombs! I say, go big, or go home!

  25. Jar Jya Binks Killer

    LCROSS didn’t destroy the Moon.

    No, but our Moon sure destroyed LCROSS! 😉

    (Maybe the crazies just misheard and got that backwards somehow? 😉 )

  26. @MichaelL: We can bomb the litter right off the Moon. Science!

  27. @StevoR,

    Sometimes I wonder just how stupid a theory has to be before even people like that won’t believe it. Sometimes I even consider coming up with an obviously ridiculous theory just to see if it gets quoted as fact. Something like:

    “The Moon and the Earth are actually part of a cosmic Newton’s Cradle. The LCROSS impact might make the Moon swing out, then swing back and impact the Earth. Then we would swing out, swing back and impact the Moon. The repeated swinging and crashing will wipe out all like on the Earth!!!”

    I wonder if that letter writer would buy the “Cosmic Newton’s Cradle” theory. 😉

  28. I scribbled down some calculations and worked out that the impact was roughly equivalent to:
    – the HMS Queen Elizabeth being pummeled by a dust speck
    – a head-on collision between a Mack truck and an E coli bacterium
    – a person being gored by a chicken pox virion

  29. Asimov Fan

    @ 16. Vagueofgodalming Says:

    “I’m not sure one can ever demonstrate that someone is wrong to think something is a tragedy.”

    Au contraire!

    Shakespeare’s ‘MacBeth’ is a tragedy. Sophocles ‘Antigone’ and ‘Oedipus Rex are tragedies but Shakespeares ‘Taming of the Shrew’ and Heller’s ‘Catch-22’ are both comedies! No doubt about it.

    Well okay, you could describe the latter as a farce – which is a kind of comedy – I guess. 😉

    Seriously, while you may be technically correct, there are some situations in which most reasonable people would have to say :

    “Anyone calling that (situation X) tragic is just being ridiculous and very stupid. Sometimes offensively so.”*

    Calling the “littering” of the Moon by the crater left by LCROSS is, I think such a case. There is absolutely nothing tragic about a successful (well successful~ish albiet literally not as spectacular as hoped) space exploration mission.

    A tragedy is an innocent child being killed or a good man going bad or a magnificent work of art being destroyed or .. stuff like that. Oh, & there’s the artistic form eg. plays too of course!

    But calling events like this “tragedy” is, I think, just absurd – and, yes, totally wrong.

    * One example that often annoys me is when a sports team loses at a ball game & this is termed “tragic” by the teams supporters. Now that loss isn’t “tragic” – just part of the sport – and when you compare such a “tragedy” to a real tragedy with the associated real pain and suffering, to massive loss of life or property, and put it in perspective it gets quite irritating. A car crash that kills a family is tragedy. An earthquake that destroys a village is a tragedy. A team losing a sorting event or, worse, yet an individual player being injured breifly and missing a game is nothing like that. At all. :-(

  30. StevoR

    @ 25. TechyDad Says:

    I wonder if that letter writer would buy the “Cosmic Newton’s Cradle” theory.

    Y’know, it really wouldn’t surprise me. :roll:

    The sheer ignorance of some people – & their unwillingness to let their complete ignorance stop them talking rubbish – is just breath-taking sometimes.

  31. I thought of another way to visualize the scale of the moon:

    Imagine the surface of both North and South America wrapped up into a sphere, and stitched together like the covering on a baseball. The result would be a bit bigger (~12%*) than the surface of the moon.

    So you could roughly imagine Centaur as a decent size truck smashing somewhere into the landmass of N. and S. America at twice the speed of a bullet. Is that going to make a hell of a noise and a crater? Sure. Is it going to move continents? Uh, no.

    (Note: N. America + Antarctica actually comes very close to the surface area of the moon, but it’s harder to visualize those wrapping up in a ball. Got my numbers from Wikipedia.)
    (*although the diff. in radius would only be ~100 km, or 6%)

  32. Ca n´Internet

    It´s still a bit of a new moon, so we can still stir up a hornets nest by telling people the moon is gone.

  33. StevoR

    Hmm .. Given # 30 Ca n’Internet’s comment there :

    Maybe they should’ve scheduled the LCROSS impact for April’s Fools day? 😉

    (Yeah, I know, it probably wouldn’t have been new Moon then. Still I’m sure we could’ve fooled some of the suckers out there!)

  34. Spectroscope

    @ 27 Asimov fan:

    Agreed. ‘Tragedy’ is an overused word and one that is frequently wrongly applied to situations that no reasonable person would consider tragic.

    If anyone considers the impact of LCROSS into the Lunar surface constitutes a genuine “tragedy” then I’d argue they’ve lost all sense of perspective and need to take a very long hard look at themselves.

  35. I was trying to identify this magical substance the Centaur was made of that is twice as dense as gold before I realised that by “3 in diameter” Phil means 3 metres diameter and not 3″ diameter.

    I suppose I’m just used to Phil using crazy imperial units rather than proper units.

  36. @Vagueofgodalming actually, a flash from such impact is so short in duration that it would be invisible to the naked eye (almost) regardless of the brightness! For comparison, see this video (gif animation actually) of a meteoroid impact in the area of Mare Nubium (Sea of Clouds) recorded by MSFC engineers Heather McNamara and Danielle Moser on May 2, 2006:
    lunar impact video

    From NASA website: The video plays in 7x slow motion; otherwise the explosion would be nearly invisible to the human eye. “The duration of the fireball was only four-tenths of a second,” says Cooke. “A student member of our team, Nick Hollon of Villanova University, spotted the flash.”

  37. … anyways, my most favorite argument went along the lines of, quote: “the conspiracy to cover up the presence of an extraterrestrial civilizations on the Moon, reported in witnessed statements by astronauts Buzz Aldrin and Neil Armstrong, and in witnessed statements to NSA (National Security Agency) photos and documents regarding an extraterrestrial base on the dark side of the Moon” – and I’m not even talking about the fact that there is NO such thing as the “dark” side of the Moon …

    I was like WTF, are you serious?

  38. Chip

    Looking at it from another direction, suppose a comet loaded with water or a NASA experimental tank of water impacts the Moon. The H2O is vaporized of course but what becomes of it at the impact site on the molecular scale? In other words if you quickly returned to the impact site and investigated with the right equipment, would you find evidence of higher water content embedded in the crater and surrounding regolith?

  39. !astralProjectile

    (More unit confusion)
    Daniel Pope:
    Did you use International inches1 or US survey inches2 in your calculation?

    1) 39.33 inches per meter
    2) 2.54 cm per inch.

    😉

  40. PaleGreenPantsWithNobodyInsideThem

    Phil, in your energy calculation, you neglected to add in the LCROSS rest mass energy. So it could have been a lot higher if the entire mass of the spacecraft was annihilated into pure energy.

  41. PaleGreenPantsWithNobodyInsideThem

    Oh, and the potential energy (mgh) as measured from the earth is enormous.

    /gotta think like a crazy, Phil.

  42. Cheyenne

    I think LCROSS has bigger implications for NASA than most people realize. It didn’t destroy the moon but it might have just wiped out the idea of a long duration moon base in our lifetimes. If the upcoming full data analysis shows that there is no usable water resource then that plan is DOA for now. And if that is a no fly idea then….well….I won’t say anymore.

  43. LightPhoenix

    I have a question regarding your point on momentum. I’m not a physicist, but wouldn’t there also be a certain degree of “course correction,” so to speak, due to the effects of the gravity of the Earth pulling the Moon into a stable orbit? Obviously it wouldn’t be the case with an object of large mass, as the momentum would shove it right out of orbit. However, with such a minimal change it would seem to me that the Moon would “fall back” into a stable orbit.

  44. Michelle

    Electric lawnmowers, Phil. Electric lawnmowers.

    I never understood why people use gas lawnmowers in the first place… What’s with the idea of shoving gas in everything when you can just plug the thing in?

    Though I THINK someone tried or did pass a law against lawnmowing on sunday mornings in my area because of the NOISE…

  45. Nemo

    I think that some people were just afraid that Space 1999 would become real.

    Keith Olbermann cited the 2002 version of The Time Machine, in which the use of nukes to excavate tunnels on the Moon (!) somehow shifts it in its orbit, with disastrous consequences. Of course he was being humorous, but IMHO this kind of joke is only funny to people who don’t understand the scale of the Moon. Which seems to be most of them, sadly.

    Coincidentally, I watched that movie again a few days later. It’s another anti-science, “we went too far” piece of crap adaptation that has nothing to do with the source material. The sad thing is that the 2030 of the movie looked glorious.

    Of course my own number-free estimate is that we couldn’t measurably shift the Moon’s orbit with the entire nuclear arsenal of the world.

  46. I know there are underground lakes here on Earth that have unique ecosystems. Scientists don’t even want to breach them for fear of destroying unique species. Let’s transpose that to the moon. What if in that crater there was indeed an underground lake with a delicate ecosystem. We’d find water, woohoo, but we’d destroy that delicate and unique ecosystem forever, boohoo.

  47. DeepField

    I have never really believed there will be water, or at least that the crashes will be able to find it, because I think that at all temperatures the water evaporates (or sublimates), and given enough time all ice will eventually disappear.

    On the other hand, since those satellites are no longer useful, crashing them against the Moon is about the coolest thing to do with them.

    On the other hand, are all the terrestrial telescopes really “moribund”?

  48. Gary

    @ #43 Olberman may have been humorous in referencing the 2002 version of The Time Machine, but in one conversation I was told that the moon could break up excactly as shown in that movie. She was also quite distraught about LCROSS messing with horoscopes. There are also some Youtube videos that use the scene of Jupiter becoming a star in the movie 2010 to show how NASA is planning to do exactly that to Saturn with the Cassini probe. Followers of woo frequently mention The Matrix as evidence of how “they” distort our reality. Some 9/11 twoofers even believe that holograms were used to make it look like planes hit the WTC. I swear some of these folks are just psychotic.

  49. Jim A.

    Well the Moon IS big, but if water IS present, it is likely to be a fairly scarce resource. There’s some logic to the idea that we might want to prospect for it in a way that didn’t vaporize a large amount of it. And of course the Ocean is big, but we’ve managed to pollute and overfish a large proportion of it.

  50. Kevin F.

    LCROSS didn’t destroy the Moon. Whaddya know?

    Well I don’t see it in the sky right now, so it MUST have been! 😀

  51. Chip

    @ Cheyenne wrote: “I think LCROSS … might have just wiped out the idea of a long duration moon base in our lifetimes.”

    Maybe, if the moon is devoid of usable water it makes a very large scale lunar colony much more difficult to maintain, but not impossible. Lack of usable water does not make a more modest latter-day lunar “Little America” station (i.e. Admiral Byrd) impossible.

    If we have some really good reasons and motivation, it is also not impossible to create an enormous complex on the moon with a relatively small human crew but lots of automation and specialized robots. The small staff of people will need imported water while the robots go for some occasional oil. 😉

    There is also the possibility that ice on the moon is still there but not easy to find.

  52. mike burkhart

    On 2nd thought the apollo 11 landing site should be left alone and declared a historical site maybe some of these people watched The empire strikes back to munch where the empires star destoryers dump ther garbage before going into hyperspace you can’t expect Palpatine and Darth vader would care about useing space as a garbage dump .this must be the efect of the dark side of the force

  53. In other other words, a flea hitting a freight train.

    I imagined ‘using a penny to derail a train’… which reminds me, I don’t have any of my ‘flattened pennies’ anymore IIRC.

    21. Andrew Says:

    I think that some people were just afraid that Space 1999 would become real.

    I’d prefer UFO, with the purple haired women in tinfoil outfits.

    47. Nemo Says:

    Coincidentally, I watched that movie [Time Machine remake]again a few days later. It’s another anti-science, “we went too far” piece of crap adaptation that has nothing to do with the source material.

    As I refer to that attitude: there are things, Doctor Frankenstein, Man was not meant to know.

    J/P=?

  54. Nemo

    @ #43 Olberman may have been humorous in referencing the 2002 version of The Time Machine, but in one conversation I was told that the moon could break up excactly as shown in that movie.

    In fairness to the movie, I should add that it explicitly says the nukes only shifted the orbit, with the implication that it was tidal forces that then caused the breakup.

  55. Mike

    Re: Note: I’ve been informed there is a math error in here that propagates through my calculations, but is small overall and doesn’t change my conclusion (I have the Sun’s luminosity ten times too high, which is a big mistake (stupid conversion error) but the effect is so weak anyway it doesn’t matter except to be pedantically accurate). I’ll fix it later, since I have to go give a talk in a few minutes.

    Peer review in action. I dig it. 😉

  56. gss_000

    @Cheyenne

    Unfortunately you’re extrapolating a bit too much here. First, the results from Chandraayan-1 already have shown there is a lot more water than a lot of people thought. Sure it’s not concentrated in one location, but that it found water not at the poles and not in shadowed craters makes missions a lot more viable.

    Second, you’re making a common fallacy that looking at one spot on the moon automatically means we know everything about it. A point location does not equal global coverage. Sure, it was the most likely spot according to models and calculations, but they can be wrong or missing some key factor.

    Does that mean you’re incorrect in the end? Not necessarily. But while a positive result will really boost the case, I think a negative result here is not as game changing as you imply.

    PS. IIRC, NASA in trying to calm people about the moon being destroyed put out some figures that stated that the moon gets hit by an LCROSS event four times a month.

  57. Pete

    @Michelle re: electric lawnmowers

    They’re nice, until you mow over the damn cord…..ZZZZZap!

  58. Steve Paluch

    Nice post, Phil. Nail on the head once again.

  59. I'd rather be fishin'

    @ Michelle “I never understood why people use gas lawnmowers in the first place… What’s with the idea of shoving gas in everything when you can just plug the thing in?”

    Worked well on my small rectangular yard. My new large yard needed a 100 foot extension cord, then there was the &$^$%^ ing trees my dear wife made me plant which meant a 160 ft cord and more care to not run over an orange cord on a green lawn. I love being colour blind. Or I could buy a 5 gallon gas can (Imperial gallons that is, don’t know how many Yankee gallons that converts to). SI rulez!

  60. Owen

    “When you clap your hands, for example, it’s sound. But at very high speeds, a lot of that energy is converted into heat and light.”

    So the question is: just how hard would I have to clap my hands to convert that energy into a really cool flash? (Ouch!)

  61. Jar Jya Binks Killer

    @ 20. Vagueofgodalming Says:

    @markogts, I spotted Phil’s deliberate schoolboy error, too. However, I think (based on Deep Impact, where a bright plume was photographed several minutes after impact), that the duration of the flash would be a lot longer than a second, making it fainter on average.

    Would that be referring to the space mission or the disaster movie? 😉

  62. Joe

    Great post, dr. Plait! My girlfriend’s 13-year-old brother expressed concern to me a few weeks ago about the moon being knocked out of orbit or worse, destroyed by the the LCROSS impact. I sat down with him and explained some astronomy to him, reading multiple passages of “Death from the Skies” out loud.

  63. Ode to NASA’s LCROSS Mission

    At Cabeus did NASA geeks,
    A swifty Centaur rocket hurl,
    Where dust, and mayhap water reeks,
    ‘Pon craters numberless, and peaks,
    Under the cosmic whirl.

    Sent twice two tons of massy metal,
    To feel out lunar soil’s fettle.
    And also careful cameras set,
    To record impact on lunar rill,
    Ensure the wants of public met,
    Make time long record of the thrill,
    Assure sunny days for budget till.

    But, oh! When stopwatch ended countdown,
    To indicate the mighty crashdown,
    Appeared no hint of fiery flash down,
    There on Selene’s apparition.

    Were the cameras to be faulted,
    For missing flash on Moon assaulted?

    Or had some Lunar Politician,
    Told Ace, a junior lab technician,
    “Strip down that leftover techy thing,
    From building that new Saturn ring,
    Set a force field strong and watchful,
    To stop this arrogant man sent missile. ”

    “Include a grokking gizmo, Ace,
    To do that thing of the Martian race.
    Twist that racing Terran thing,
    Clear outa this here four D space.
    Enough of taking human guff!
    Teach those Earthlings right enough,
    That they’re not really red hot stuff!”

  64. Bahdum (aka Richard)

    I got to this part: “I read a few places where people were concerned that the impact might change the Moon’s orbit.”

    I was glad I didn’t have tea in my mouth otherwise I’d need a new monitor.

  65. Blizno

    We humaans have exploded many hydrogen fusion bombs above and under the surface of our own planet.
    But we should be worried about crashing a robot into the dead moon orbiting us? When the energy of that crash is infinitesimal compared to the tiniest of the fusion bombs we have already detonated inside or above our own world?

  66. Les

    Someone beat me to it but; “terrestrally-moribund” — near death?

    Terrestrially-bound more likely I think .

    Good article though!

    Best,

    Les D

  67. Phil

    just a little question about the maths there:

    “Momentum is simply the mass of an object times its velocity, (…) Let’s assume the Moon is standing still (that is, has velocity = 0)

    mass x velocity of Centaur = mass x velocity of the Moon”

    shouldn’t the “mass x velocity of the moon” be zero for a still moon according to that definition ?

  68. Phil

    just a little question about the maths there:

    “Momentum is simply the mass of an object times its velocity, (…) Let’s assume the Moon is standing still (that is, has velocity = 0)

    mass x velocity of Centaur = mass x velocity of the Moon”

    shouldn’t the “mass x velocity of the moon” be zero for the moon if its velocity is null ?

  69. Nigel Depledge

    @ AstroLackey (16) –

    But am I wrong?

  70. Nigel Depledge

    Cheyenne (17) said:

    @Nigel – I don’t think it’s that big of a deal. It’s not like we’ve ever lost a NASA mission because they messed up in confusing English and Metric units. Oh wait a sec…..(Mars Climate Orbiter – $125 million)

    LOL!

    The US should catch up to the rest of the world and go metric (btw- I actually have no idea if a short ton and a regular ton are metric/English differences, but I’m sticking with the gist of what I wrote!).

    The “long ton” (2240 lb) is the standard in the Imperial measurement system, but the system as a whole is obsolescent. Bits of it are still used here and there, but the UK is mostly converted to metric units (and someitmes even uses SI units!).

    I have no idea where the “short ton” came from (maybe someone just decided that 2240 was too fiddly a number to do conversions with?), but I have only ever seen it used by people from the USA.

    The metric tonne is 1000 kg (2200 lb, as near as makes no odds). The ton(ne) is not an SI unit, because the SI would have us use the megagramme (Mg) instead.

  71. Nigel Depledge

    Gopher65 (18) said:

    Short tons aren’t standard anywhere:P. Both 2240 and 2000 are used in the US, depending on exactly what is being measured, and where it is being shipped. Just like 1 gallon equals both 3.78 litres and 4 litres, depending on where it is being shipped.

    Ay-yi-yi!

    Here in the UK, a gallon (that’s an Imperial gallon, of course) is about 4.5 L. This is because a gallon is 10 lb of water (a pint of water weighs a pound and a quarter*, and there are 8 pints in a gallon). A pint is 568 mL (so a gallon is more accurately represented as 4.544 L, but that’s probably a lot more precision than most people need).

    So that’s at least three different volumes that can each be called a gallon.

    They really need to standardize metric use in most fields* to stop my head from exploding;).

    *there are a few fields where imperial measurements have to be used in some situations, such as baking. 1 cup != 250 ml. It’s close, but when you’re baking you can’t just mix and match approximations like that. Having a recipe that calls for 12 cups and converting that to 3 litres is a baaaaad idea. Baking is a science, not an art (unlike cooking, which is an art).

    Erm, I may have to leave others to comment on this bit. How big is a “cup”, exactly? Is it like the old metre, that had a platinum standard held in Paris? Is there somewhere a “standard cup”?

    * I have no idea at what temperature this is supposed to apply, but I guess it’s most likely to be about 15 – 20 °C.

  72. Jesper

    On (I think) The Naked Scientists podcast someone asked the question “How many LCROSS impacts would be necessary to move the Moon 1 degree on the sky?”. They did a quick calculation and concluded you’d need 10^19 LCROSS impacts to move the Moon by 1 degree!

  73. Jadehawk

    “*there are a few fields where imperial measurements have to be used in some situations, such as baking. 1 cup != 250 ml. It’s close, but when you’re baking you can’t just mix and match approximations like that. Having a recipe that calls for 12 cups and converting that to 3 litres is a baaaaad idea. Baking is a science, not an art (unlike cooking, which is an art).”

    why would that matter? as long as you’re using all the same proportions, it’ll still work. even if you just use any old cup from the cupboard.

  74. Jadehawk

    also, some of the best crazy came from RR. on their thread discussing this, they were alternately wondering whether this would turn the moon red and thus usher in the End of The World, or whether the moon would break apart like in the movies. one of them actually did say something along the lines of “we’ve had so many movies about this, you’d think the scientists would know better”.

    because scientists should take science advice from Hollywood, of course *facepalm*

  75. gopher65

    @ #24 Aerimus:

    I don’t expect that you’re still reading this post, but that isn’t the way baking works. You can’t simply double or halve batch recipes and expect it work exactly the same way. There are an *enormous* number of variables involved in baking that can change the outcome (air pressure, humidity, bacterial concentrations in the food (and types), type of oven (thermal, convection, induction, microwave, infrared – the size and power output change things drastically as well, as does the exact design used), and even the types of fungus that are common in your area… California sourdough rye bread tastes different than everywhere else because of a type of spore that is common in the air there but isn’t common elsewhere. The fungus changes the taste enough to be noticeable).

    Suffice to say that any given recipe only works in a small region. Once you find a recipe that works for you, you stick with it. Changing that recipe *might* work… or it could destroy it. Trial and error is really the only way to go about finding out (at this time), and you rarely hit it exactly right on the first try. Food manufactures spend billions doing T&E research to create perfect recipes. Individual bakers learn the ins and outs of a precious few recipes over the course of a lifetime, and are never more than mediocre at recipes that they haven’t trial and errored to death. I don’t have that kind of time or money;). Fortunately “mediocre” from a practised baker still tastes pretty darned good.

    Note that none of this applies to cooking. Cooking and baking are two entirely different disciplines,. Cooking is all about experimentation, and making it up as you go along. Not so with baking.

  76. Diego

    The insanity on both ends of the political spectrum drove me nuts. There were far lefters who worried about affecting the Moon goddess or at least that we would knock the moon out of orbit a la Space:1999. I ignored them because they seemed completely insane. But I did have to deal with a friend’s husband who was on Obama’s case for wasting tax dollars “bombing” the moon. They both asked the question of whether anyone actually thought this mission was a good idea. Of course they were being rhetorical because they didn’t want to be confronted with any other opinions, but I went ahead and asked him how far in advance he thought these missions were planned (oh yeah, we launched this probe in a week at Obama’s request, yeah right) because blaming or crediting Obama for NASA’s long-term mission plans was so ludicrous. I told him about practical boons that could derive from the mission and asked him if he had no interest in just learning about the universe even if there were no obvious benefits (that would be a no). All I got back was parroted jokes about drinking bottled water from the Moon and some snide comments followed by him incredulously asking if I REALLY thought we would ever live on the Moon. He thought it was obvious that if I thought that then I was the complete nut job. Then he and his wife ended with a hypocritical comment about how liberals always have to criticize their views and opinions and they never say anything to all the things that daily piss them off. Uh-huh. Anyway, the whole exchange was highly vexing and an exercise in futility for me.

  77. Nigel Depledge

    Deep Field (49) said:

    I have never really believed there will be water, or at least that the crashes will be able to find it, because I think that at all temperatures the water evaporates (or sublimates), and given enough time all ice will eventually disappear.

    Not necessarily.

    If we assume that any water on the moon is delivered there by comet impacts, then all we need is for the rate of accumulation of water to exceed the rate of water loss through sublimation. And the rate of sublimation at any point will depend on the local vapour pressure of the ice, which will depend on temperature. So in a permanently-shadowed crater, the ice will be very very cold and hence will only sublime very very slowly.

  78. StevoR

    @ 65. Sully: Good one – I like it! :-)

    @ 25 (me)

    … not only does this letter writer have no idea about LCROSS, not only hasn’t he (?) heard of – d’uh! – craters; s/he thinks the Moon controls our *weather* and *atmospheric pressure* for pity’s sake! Plus he (?) seems to imply that scientists aren’t even human or, as AE sexist~ally (not a word? It is now!) put it, “man”. Depressing really. :-( I’m writing a response to hopefully go in the paper too but we’ll have to wait & see if that gets published.

    Update :

    It did! Took a while but finally my letter in reply to that anti-science whackjobs ravings was indeed published :

    I’d written :

    ***
    [QUOTE] In a letter texted to the[I] ‘Sunday Mail’ [/I](2009 Oct. 18th) A.E. Swain of Semaphore spouted & I quote verbatim:

    ”Are NASA insane? Bombing our moon that controls our weather, tidal changes and atmospheric pressure? It won’t be man that causes his own destruction it will be those silly scientists.”

    Well A.E. Swain, haven’t you ever heard of craters? Our Moon is naturally covered in them. Hundreds can be observed with a decent telescope and many are visible even through your garden variety binoculars. All these naturally occurring craters are considerably larger than that made by the LCROSS impact – which, by the way, was not a “bomb” but a spaceprobe. There was absolutely never any danger to Earth or of causing any real harm to the lifeless rock which is our Moon. Incidentally, A.E., I think you need to do a lot more research and thinking before you write your next letter because our Moon has nothing whatsoever to do with our planets atmospheric pressure or weather and where you got such silly notions is beyond me. Finally, A.E. Swain, I can assure you that scientists and “man” are not mutually exclusive but the same thing – scientists are men and women too! In fact they are intelligent, compassionate and curious women and men who merely seek to understand and learn from our wonderful cosmos in ways that very often benefit humanity – for instance being responsible for the computers and mobile phones we use to convey these messages! [/QUOTE]

    ***

    This was published albeit in slightly edited & toned down form in last Sunday’s ‘Sunday Mail’ (2009- Nov -8th) “letters”, page 72, second letter down under the header : “Its not rocket science.” (I’d have preferred ‘Hasn’t AE heard of craters?’ & there were a couple of typos of their making too but still quite buzz. :-)

    Just thought I’d let y’all know.

    Noted this on the BAUT too – see :

    http://www.bautforum.com/space-exploration/90153-lcross-lunar-crater-orbiting-sensing-satellite-mission-4.html

  79. TheBlackHole

    Really? A flea hitting a freight train? My analogy was a speck of dust settling on a bowling ball headed for a strike!

  80. david

    What about the people living on the dark side of the moon ?Wont they care if were bombing them,also when did we go to the moon?

  81. Satyendra

    It is strange that all the calculations projected in the article and in the Blog Comments, assume that we would be attempting to detect and image the emission emanating from the energy released by the impact – which admittedly is too small. However, what I feel is that when we try to detect the plume from Earth, what we are attempting is detection of ‘light scattered by dust and gas in the plume – and this light has originated in the Sun”. here a lot would depend on the geometry of the situation – the angle at which the Sun light is falling and the angle at which we are observing etc. and the nature of scattering material – their sizes etc.

    It would be nice to have some discussion on this line of thought to increase our understanding a bit more!!
    Satyendra Bhandari

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