back to article Moon riven by colossal cracks

Ebb and Flow, the twin spacecraft that comprise NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission, have created a gravity map and other analyses of the moon, and Lunar boffins have used the results to assert that our sole natural satellite is riven by deep cracks. Maria Zuber of the Massachusetts Institute of …

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Misleading title

After such a title, I expected *something* about large cracks on the moon. What we get is a statement in the first paragraph telling there are cracks, and another in the last paragraph hoping no-one falls into said cracks.

In between, nothing. Not even the nice picture reveals "cracks", unless they are on a scale which cannot be easily seen on-screen (in which case, they can't be "colossal").

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Happy

Re: Misleading title

"In between, nothing."

Yup that's a crack then.

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Ru
Paris Hilton

Re: Misleading title

Will dikes do?

Blurb suggests that the cracks in question would only be a pixel or two wide and at most 24 pixels long on a full resolution image of the gravity map. Tricky to show in the one in the article, perhaps.

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Re: Misleading title

"Will dikes do?"

Well they certainly have cracks but I wouldn't want to go there.

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WTF?

"It would be poetic..." (?)

Uh, how? Is this some meme going around I don't know?

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Re: Misleading title

If the crack were filled in, then that would be really something.

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Re: Misleading title

Wasn't denying they existed - just pointing out that for an article whose headline(s) shout about "colossal cracks", there was very little written about said features.

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Anonymous Coward

"thin crust, no cheese"

Still looks like a pizza, though.

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Re: "thin crust, no cheese"

On the contrary, the Wallace and Gromit mission of 1989 proved conclusively that the crust is indeed made of cheese.

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Re: "thin crust, no cheese"

Although analysis failed to identify a terrestrial analogue, which may cast doubt on the theory that the moon was formed from cheese ejected from the Earth.

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Meh

Re: "thin crust, no cheese"

Presumably after a long primordial night passed in interstellar alcohol.

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Coat

It's a very pretty picture...

but it doesn't even show Tycho Magnetic Anomaly 1.

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Joke

Also in the news..

...moon radioactive after repeated blasting with man-made xrays!

While ridiculous, I would not surprised in the slightest if one of the tree hugger sites runs with it...

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Mushroom

Re: Also in the news..

They say the Midwest is in great distress, and that NASA blew up the moon!

(with apologies to Lou Reed)

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Facepalm

Re: Also in the news..

Well they will now there's a reference to it on the Internet that can be quoted out of context! ;-)

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Request for technical information

That looks like a very detailed 'picture' and I'm wondering how they did it. A gravity sensor in orbit would detect a local value of gravity corresponding to the integrated contributions of all lunar matter beneath it (and off to the side, etc).

The only way I can think of to resolve the detailed contribution of small mass regions is to do an enormous number of scanning orbits (all carefully monitored for position), with a massive number of data points and then do some very hairy mathematics on the resulting data set.

Is that what they did or is there a simpler and more elegant way of getting that much detail from a gravity sensor in orbit?

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Ru
Boffin

Re: Request for technical information

It looks like a detailed picture, but when you consier the actual size of the moon, you'll see that this particular map isn't actually that high resolution.

The technique that GRAIL uses is derived from a similar system called GRACE that mapped the Earth... bit more data available on the relevant wiki page, etc, and a bit of searching the interwebs may provide you with similar information from more trustworthy sources. The technique is very neat, though not trival to explain, but basically it involves two spacecraft in the same orbit measuring the changes in their relatative separation over time.

GRACE managed a 200km resolution for its gravity map of Earth, but from a much higher altitude. I can't find actual numbers for GRAIL right now, but they'll likely be of the same order.

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Boffin

Re: Request for technical information

NASA animation blurb suggests that the gravity map resolution ~20km, which is pretty impressive.

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Boffin

Re: Request for technical information

The thing about the Moon is that it has no atmosphere, so you can orbit it at a much lower altitude. Grace's initial altitude was actually 500km (typical for low earth orbit satellites: much lower and you drop out of orbit quite fast). GRAIL orbits at a mere 50km above the moon surface, so it can achieve much better horizontal resolution.

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Re: Request for technical information

I note on the NASA page that the anomalies run in spirals that were not mentioned at any time. No more than the probability of any part of the surface being impacted from an head-on collision (as would be the case with a neat hemispherical crater.)

Come to think of it, if the washing machines were following the same N/S course all the time, wouldn't the craters appear eliptical?

How would they correct for that in an application working in miligals?

(Which if I read the article correctly is 1/1000 of 1/10 of a meter per second per second acceleration.) I mean they cross this bordeline of inches (2.5ish cm multiples) (N0 1D34 what that is in Regespik.) and manage to adjust the loops they are getting so that the craters are corrected for the books.

Is that likely?

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looks like an elevation map

What cracks?

This looks so much like an elevation map that it would be interesting to see this data subtracted from elevation data. Then perhaps the cracks (and TMA etc) would just jump out at you.

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Linux

Re: looks like an elevation map

"This looks so much like an elevation map that it would be interesting to see this data subtracted from elevation data. " -- It basically is an elevation map. I see it as blue bits are further away from the sensor and exert less gravitational force on the sensor than the red bits which are closer and exert more gravitational force on the sensor.

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Ru
Boffin

Re: looks like an elevation map

If this NASA page is to be believed, this gravity map takes into account surface height variability. You'll note that not all craters have a big gravitational increase in the centre, for example.

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A note on the scale.

I unit is 1 cm/sec^2. The map is in mili's or 0.001 of this. That's 0.001 of those. IE 10 micro metres /sec^2.

In terms of the Earths gravity field that's a variation of 1 micro g.

Which is pretty impressive, and the key to doing things like weighing the ice sheet of Greenland using the GRACE satellite pair.

Note that orbital anomalies in Lunar orbiting satellites since the 1960s pointed to "Mass concentrations" or masscons of above average density. What they would be is unclear.

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Re: A note on the scale.

I love the units - the Galileo. Is that the acceleration of a falling astronomer?

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Facepalm

Re: A note on the scale.

I'm glad you enjoyed the units. I can't say I did.

"Units are milliGalileos where 1 Galileo is 1 centimeter per second squared."

...because we're NASA and just can't bring ourselves to use sane units, ever. When there is no "English" alternative in common use, we'll fall back on CGS and define a new unit of our own that differs by two orders of magnitude from the SI equivalent.

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Re: A note on the scale....can't bring ourselves to use sane units

OK, who wants to suggest an official el Reg unit of gravity?

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Anonymous Coward

Re: A note on the scale....can't bring ourselves to use sane units

Well, my first girlfriend (way back when I was sixteen) had DD bulgarians... while I was bored in a physics class I calculated the gravitational attraction between them when separated by a face-width, i.e. how much force would be squeezing my face without manual-to-mammary assistance. The number was small compared to '1g' nevertheless I think the idea has some merit. So the unit should be called the 'Blubbalubbalub', and as I'm now old and no longer bored I'll leave it to someone else to come up with the calculation.

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Anonymous Coward

All that and not one mention of the word 'mascon', surely one of the most pleasing words in the English language.

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Nah,

Rivulet or Golbdule.

They are the nicest words in our mother tounge.

AND they googlewhack!!! That's the first one I've ever found!!! :D

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Re: Nah,

**** Globdule (sp)

(They still googlewhack though) ;)

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Re: Nah,

...and now that you've posted them, they no longer do. ^_-

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Xrays ??

I don't understand the connection betwen Xrays and gravity measurement?

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Ru
Paris Hilton

Re: Xrays ??

Sounds like it might be sloppy parsing of a press release. Gravity measurements can be used to "x-ray" the moon inasmuch as they reveal details of its internal structure which are otherwise hidden from view. Certainly none of the NASA pages talk about actual x-ray emission, which might be a bit impractical for a couple of little sattelites which are probably solar powered.

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Coat

I read Laboratory as Lavatory...

Made for quite a interesting read.

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Our merkin friends stress both words in a similar manner of course, so you read it pretty much as they would have pronounced it.

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Joke

A moon with a huge crack in it.

As seen in a passing coach window quite regularly.

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Re: A moon with a huge crack in it.

Are you referring to that 'good ole boy' (from the South (of the USA)) plumber whose britches always rode down on him?

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Cracks in the moon, and people still think they didn't go through with the plan to nuke it?

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Is it me...

Or does that imaging map look spookily like the planetary mission screen from The Ur-Quan masters???

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Coat

What kind of unit is that?

"miliGallileos" - try saying that when you're pissed...

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Joke

I see the Irish have abandoned their plans for a moon party, as despite the craic there is no atmosphere.

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Moon Riven

Are the cracks wider than a mile?

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FAIL

"MIT's Maria Zuber of the Massachusetts Institute of Technology"

Do you actually have subeditors?

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Happy

Re: "MIT's Maria Zuber of the Massachusetts Institute of Technology"

Repeating something twice isn't as bad as repeating something twice by repeating something twice.

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Re: "MIT's Maria Zuber of the Massachusetts Institute of Technology"

The sub-editor's salary would have to be financed from whatever you paid to read the content, so probably not.

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Re: The sub-editor's salary

... got blown on the latest el Reg boondoggle Special Projects Bureau tomfoolery. (You know, the one that flew too far, and ended up in the drink.)

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"Neil Armstrong (RIP)

"A small step for (a) man, a gia....FUC*K ME SIDEWAYS"

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Coat

Irish moon mission

They go there for the craic!

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