Oh No! NASA’s LCROSS Is Going to Hit the Moon! Run!

 Posted by DrJeff on October 8th, 2009

 Copyright 2009  |  About this blog



This is a supplement to my earlier post NASA LCROSS to Slam into Moon October 9, 2009.

This is crossposted at the Huffington Post HERE.



We’re slamming this thing into the Moon?! Hasn’t anybody thought this through?! The Moon’s going to be forced from its orbit! Giant tides will wash around the Earth! Buildings will topple! The Man in the Moon will be mad at us! Do we really need another catastrophe?!

An hour after I put up my NASA LCROSS to Slam into Moon post to help teachers make this a Teachable Moment on the Moon in classrooms, my good Twitter friend Heather Good at FoundonMars.com tells me there are actually folks out there thinking about impending doom (check out the comments at this recent HuffPost article.) She asked me to come up with something that can put everyone’s mind at ease. There was tension, anxiety, scared people … shades of Orson Welles War of the Worlds radio broadcast that had folks running from their homes. Cool (not the running thing. The “can you come up with something to calm folks” thing.)




Okay, first, the target for the impact is the crater Cabeus. The operative word is CRATER. All those large craters on the Moon are from massive things hitting the Moon—far more massive than an Atlas V Centaur upper stage vehicle heading moonward. Yet we’re still here.


What? You think that virtually all were from impacts long ago, and “who knows what effect they had on Earth back then?” OK, I knew that was coming (since I wrote it). The Atlas V Centaur upper stage has the equivalent mass of a meteoroid less than 2 feet (1/2 meter) across. Believe it or not, Moon and Earth are struck regularly by meteoroids of this size—and we’re still here.


You want more?


The Atlas V Centaur upper stage has a mass of 2,000 kg (the more massive of the two vehicles impacting the Moon). It will be moving at 5,600 mph (9,000 km/hr.) BAM! By comparison, the Moon is orbiting the Earth at the measely speed of 2,300 mph (3.700 km/hr). On the other hand, the Moon is just a tad bit more massive (heavy sarcasm aside—UNBELIEVABLY MORE MASSIVE) than the human-built specks on a collision course with it.


So let’s say we wanted to change the Moon’s speed by JUST 1 MPH (1.6 km/hr)—which is less than 1/2,000th its orbital speed—and we were going to do it by hurling Atlas V Centaur upper stages at the Moon. How many would we have to hurl its way? HEY, let’s give every person on planet Earth an opportunity to hurl one. Would that do it? Uh … nope. Every person on Earth (all nearly 7 billion of us) would each need to hurl 1 MILLION Atlas V Centaur upper stages at the Moon. I’d rather just hurl one and not worry about it. Rest easy, sleep well, and let’s see if we can find water on the Moon at the South Pole.


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5 Responses to “Oh No! NASA’s LCROSS Is Going to Hit the Moon! Run!”

  1. Steven Says:
    October 8th, 2009 at 3:00 pm

    Wouldn’t 7 billion people hurling 1 million 2000kg stages each at the moon have a measurable REACTION on the earth’s orbit? Just sayin’

  2. DrJeff Says:
    October 8th, 2009 at 3:23 pm

    Cratermoon- well yeah. But less of an effect than on the Moon since the Earth is 81 times more massive than the Moon. And where are you going to get all those rockets anyway, not to mention everyone needs a pitching arm that can hurl about a ton at 5,600 mph (1,000,000 times)?

  3. Mitchell Says:
    October 8th, 2009 at 11:11 pm

    Perhaps point out we’ve done this several times already? Six discarded Apollo lunar module ascent stages – similar mass, similar impact energy. The Ranger missions.

    I wonder if there are recent high-res photos of the known LM or Ranger impact sites? “That tiny shadow over there…”

    Perhaps mention that “!! 5,600 mph !!” is 10x slower than most of the cruft that usually hits us (Moon and Earth) – 2 km/s vs a more typical 20+ km/s.

    How often is the Moon hit by something of similar mass? Given the low speed, how often is there an impact of similar energy? Maybe something very vaguely like yearly and daily?

    The whole point isn’t about creating a collision – those happen all the time. It’s just about having one that you know about ahead of time, in a place you can see well, so you can arrange to watch closely.

    I’m reminded of NASA getting a note of concern from a fisherman somewhere, that if Apollo 11 brought back some Moon rocks, the Moon would become less bright and he would net less fish.

    Perhaps this is a teachable moment for the concept that people have no sense of scale? “It’s very hard to have a sense of what is reasonable, and not, about very unfamiliar objects.[...] Worrying about this is like worrying about a single raindrop hitting an aircraft carrier.” “Joey!!! Don’t let your little brother drop that goldfish, it’s hitting the floor will destroy the building!!!”

    For some, perhaps this is a teachable moment for “You were confident this was something to be concerned about. You see now it very very isn’t. Perhaps you might remember this possibility of being confident, but completely wrong, when deciding what to be concerned about in future”.

    Might be worth mentioning the ton per hour(?) of rock the Earth gets every day.

    I wonder what (tiny) portion of that is ejecta from recent lunar impacts. Can we hope for an extra microscopic grain of dust from LCROSS? An extra few molecules? Hmm, a half-moon, so solar wind isn’t helping. Oh well.

  4. Mitchell Says:
    October 9th, 2009 at 12:45 am

    How big will the crater be? The basement of a family restaurant.

  5. Mitchell Says:
    October 17th, 2009 at 12:19 am

    At the risk of excessive posting[1], a correction – my post #3 misses some key points.

    Without some concept of the Moon as a gravitationally contained puddle (for instance, from stories of Moon formation or splashing from very large impactors), it is then not unreasonable for people to think “but what if the Moon has a flaw, like a vase? then even a gentle tap might break it”.

    And without some feel for long-term orbital dynamics and stability, it’s not unreasonable to think “but what if the nudge were to ‘unhook’ the Moon, so it doesn’t hang in quite the same place anymore?”.

    Neither are really taught, even to the tiny portion of people who take an introductory astronomy course.

    Physics Education Research has the concept of surveying misconceptions, and crafting material to address them directly. Rather than the false hope of “figure it out, say it clearly, and everything will work out”. Perhaps the same thing could be done with science journalism, given a collaborative environment with which to spread cost and create synergy.

    [1] http://en.wikinews.org/ might be a forum for such discussion, but this story doesn’t seem to have been covered. Perhaps wikinews might be nudged towards greater coverage of science stories. And might provide a collaborative environment in which quality coverage can be created.