APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

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Expand view Topic review: APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

Re: APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

by stephen63 » Wed Apr 03, 2013 4:25 pm

Perhaps there was no Theia at all.
Alternative hypothesis: http://www.lpi.usra.edu/meetings/lpsc2012/pdf/1738.pdf

Re: APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

by neufer » Wed Apr 03, 2013 12:44 pm

Murphy wrote:
A simple question: If a major object collided with the earth which broke off the moon from the earth, it seems logical that some of the object that hit the earth should still be present. Do we have any physical evidence? Is the composition different from the earth? Or, is it now impossible to differentiate?
Computer simulations suggest that Earth rocks & Moon rocks should be somewhat different amalgamations of the mantle of that object [i.e., Theia] and of the original Earth. However there is little evidence that Moon rocks & Earth rocks significantly differ.
http://en.wikipedia.org/wiki/Giant_impact_hypothesis#Modified_hypothesis wrote:
<<Theia is thought to have struck the Earth at an oblique angle when the latter was nearly fully formed. Computer simulations of this "late-impact" scenario suggest an impact angle of about 45° and an initial impactor velocity below 4 km/s. Theia's iron core would have sunk into the young Earth's core, and most of Theia's mantle accreted onto the Earth's mantle, however, a significant portion of the mantle material from both Theia and the Earth would have been ejected into orbit around the Earth. This material quickly coalesced into the Moon (possibly within less than a month, but in no more than a century). Estimates based on computer simulations of such an event suggest that some twenty percent of the original mass of Theia would have ended up as an orbiting ring of debris, and about half of this matter coalesced into the Moon.

The Giant impact hypothesis does not explain well the similar composition of Earth and the Moon. Especially, the indistinguishable relation of oxygen isotopes cannot be explained by the classical form of this hypothesis. According to research on the subject that is based on new simulations at the ETH Zürich by physicist Andreas Reufer [no relation - Neufer] and his colleagues, Theia collided directly with Earth instead of barely swiping it. The collision speed may have been higher than originally assumed, and this higher velocity may have totally destroyed Theia. According to this modification, the composition of Theia is not so restricted, making also a composition of up to 50% water ice possible.>>

Re: APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

by Murphy » Wed Apr 03, 2013 6:54 am

A simple question: If a major object collided with the earth which broke off the moon from the earth, it seems logical that some of the object that hit the earth should still be present. Do we have any physical evidence? Is the composition different from the earth? Or, is it now impossible to differentiate?

Re: APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

by FLPhotoCatcher » Fri Mar 22, 2013 4:02 am

Using the GRAIL data, a scientist called Wieczorek calculated that the average density of the lunar crust is 2550 kilograms per cubic meter. "This is much, much lower than what has been assumed for lunar crust; in fact, it's lower than the density of granite. We know what the highlands crust is made of, we have samples of it: the density of the minerals that makes up the crust is around 2800-2900 kilograms per cubic meter. For the Moon's density to be so low, Wieczorek says, it must be very porous, fractured and busted up to give it about 12% void space, to a depth of several kilometers below the surface." However, I read somewhere that moonquakes traveled around the moon several times, ringing it like a bell. They said that meant the moons rock (including the crust) had fewer cracks and faults than earth. That would make Wieczorek's conclusion wrong. Maybe it is made of green cheese after all...

Re: Cuyte stuff goes here; you have been warned!

by Chris Peterson » Thu Mar 21, 2013 11:41 pm

neufer wrote:As my daughter Andrea found out...that sort of depends on how much you care for Guinea pig
Cuy is really good, especially barbequed. They have some interesting sauces, as well. I'd compare it to rabbit, and nothing like chicken.

Cuyte stuff goes here; you have been warned!

by neufer » Thu Mar 21, 2013 9:11 pm

Quigley wrote:
I had always wondered if I would instantly "lose weight" if I went to Equador.
As my daughter Andrea found out...that sort of depends on how much you care for Guinea pig:
http://en.wikipedia.org/wiki/Guinea_pig#South_America wrote:
[img3="Dish from Ecuador called "Cuy""]http://upload.wikimedia.org/wikipedia/c ... ish_SG.jpg[/img3]

<<Guinea pigs (called cuy, cuye, curí) were originally domesticated for their meat in the Andes. Traditionally, the animal was reserved for ceremonial meals by indigenous people in the Andean highlands, but since the 1960s it has become more socially acceptable for consumption by all people. It continues to be a major part of the diet in Peru and Bolivia, particularly in the Andes Mountains highlands; it is also eaten in some areas of Ecuador (mainly in the Sierra) and Colombia. Because guinea pigs require much less room than traditional livestock and reproduce extremely quickly, they are a more profitable source of food and income than many traditional stock animals, such as pigs and cows; moreover, they can be raised in an urban environment. Both rural and urban families raise guinea pigs for supplementary income, and the animals are commonly bought and sold at local markets and large-scale municipal fairs. Guinea pig meat is high in protein and low in fat and cholesterol, and is described as being similar to rabbit and the dark meat of chicken. The animal may be served fried (chactado or frito), broiled (asado), or roasted (al horno), and in urban restaurants may also be served in a casserole or a fricassee. Ecuadorians commonly consume sopa or locro de cuy, a soup dish. Pachamanca or huatia, a process similar to barbecueing, is also popular, and is usually served with corn beer (chicha) in traditional settings.

Peruvians consume an estimated 65 million guinea pigs each year, and the animal is so entrenched in the culture that one famous painting of the Last Supper in the main cathedral in Cusco shows Christ and the twelve disciples dining on guinea pig. The animal remains an important aspect of certain religious events in both rural and urban areas of Peru. A religious celebration known as jaca tsariy ("collecting the cuys") is a major festival in many villages in the Antonio Raimondi province of eastern Peru, and is celebrated in smaller ceremonies in Lima. It is a syncretistic event, combining elements of Catholicism and pre-Columbian religious practices, and revolves around the celebration of local patron saints. The exact form that the jaca tsariy takes differs from town to town; in some localities, a sirvinti (servant) is appointed to go from door to door, collecting donations of guinea pigs, while in others, guinea pigs may be brought to a communal area to be released in a mock bullfight. Meals such as cuy chactado are always served as part of these festivities, and the killing and serving of the animal is framed by some communities as a symbolic satire of local politicians or important figures. In the Tungurahua and Cotopaxi provinces of central Ecuador, guinea pigs are employed in the celebrations surrounding the feast of Corpus Christi as part of the Ensayo, which is a community meal, and the Octava, where castillos (greased poles) are erected with prizes tied to the crossbars, from which several guinea pigs may be hung. The Peruvian town of Churin has an annual festival which involves dressing guinea pigs in elaborate costumes for a competition.>>

Re: APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

by Quigley » Thu Mar 21, 2013 7:56 pm

EXTREMELY INTERESTING! I had always wondered if I would instantly "lose weight" if I went to Equador. Thanks for the fascinating APOD.

Re: APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

by Chris Peterson » Wed Mar 20, 2013 2:57 pm

revloren wrote:OK, so how is gravity variable? I thought that gravity was constant to the mass of the entire body. Is this related to the specific densities of the various areas of the moon's crust? :?:
Gravity isn't variable. The gravitational field of the Moon isn't uniform, and that's because the Moon isn't an isotropic or radially symmetric body. Nor is any stony astronomical body.

I live in the middle of a ring of hills, long suspected of being the remnant walls of an old volcanic caldera. However, the local gravity field was mapped, allowing the crustal density variation to be understood, and this demonstrated that this valley is not, in fact, a caldera. As I walk around here, my weight increases or decreases based on the nature of the underlying crust.

Re: APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

by neufer » Wed Mar 20, 2013 1:54 pm

revloren wrote:
OK, so how is gravity variable? I thought that gravity was constant to the mass of the entire body. Is this related to the specific densities of the various areas of the moon's crust? :?:
Primarily:
  • Upwellings of dense basaltic lava produce red mascons.

    Small meteor craters with no upwelling produce blue holes.
Isostasy, gravity, and the Moon: an explainer of the first results of the GRAIL mission
By Emily Lakdawalla, Planetary Society

Re: APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

by revloren » Wed Mar 20, 2013 6:14 am

OK, so how is gravity variable? I thought that gravity was constant to the mass of the entire body. Is this related to the specific densities of the various areas of the moon's crust? :?:

Re: APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

by neufer » Wed Mar 20, 2013 2:02 am

Chris Peterson wrote:
Boomer12k wrote:
So...Practical application...if you want to appear LIGHTER....stay in the BLUE LOCATIONS!!!
Yes, but you don't need to go to the Moon for that.

Image
These ±50 milligal deviations from "the theoretical gravity of an idealized smooth Earth, the so-called earth ellipsoid," are insignificant as compared to the full figured gal size variations from sitting at different points on the Earth's sea level spinning ellipsoid shape.
http://en.wikipedia.org/wiki/Gravity_of_Earth wrote:
<<In combination, the equatorial bulge and the effects of the Earth's inertia mean that sea-level gravitational acceleration increases from about 978.0 cm·s−2 at the Equator to about 983.2 cm·s−2 at the poles, so an object will weigh about 0.5% more at the poles than at the Equator.>>
Go to the top of Mt. Chimborazo (~0.1% further from the Earth's center/axis)
for a maximal feeling of lightness (i.e., an additional ~0.2% / ~2 gal reduction).
http://en.wikipedia.org/wiki/Chimborazo_%28volcano%29 wrote:
<<Until the beginning of the 19th century, it was thought that Chimborazo was the highest mountain on Earth (measured from sea level), and such reputation led to many attempts on its summit during the 17th and 18th centuries. In 1802, during his expedition to South America, Baron Alexander von Humboldt, accompanied by Aimé Bonpland and the Ecuadorian Carlos Montúfar attempted to reach the summit. From his description of the mountain, it seems that before he and his companions had to return suffering from altitude sickness they reached a point at 5,875 m, higher than previously attained by any European in recorded history. In 1831 Jean Baptiste Boussingault and Colonel Hall reached a new "highest point", computed to be 6,006 m. In 1880 Chimborazo's summit was first climbed by Edward Whymper and the brothers Louis and Jean-Antoine Carrel. As there were many critics who doubted that Whymper had reached the summit, later in the same year he climbed to the summit again choosing a different route (Pogyos) with the Ecuadorians David Beltrán and Francisco Campaña.>>

Re: APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

by Canadian Grandma » Tue Mar 19, 2013 9:16 pm

How reassuring to know that I'm light-headed only because I live in the "Great Lakes" area (blue gravity density)!

Re: APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

by Ernie Wright » Tue Mar 19, 2013 8:23 pm

idoradjr wrote:It would be interesting to see the gravity map overlaid onto the a topographical map to see if there is a correlation between craters and the gravity differences. Are old craters places of higher gravity and newer craters places of lower gravity, or vice versa, or is there no correlation?
Would a side-by-side comparison help? See the SVS web page for several animations, including one with free-air gravity and topography together. They are correlated, but there are still gravity variations after you subtract the effect of surface elevation. What's left is assumed to be the effect of crust thickness.

- Ernie

Re: APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

by Ernie Wright » Tue Mar 19, 2013 8:08 pm

Anthony Barreiro wrote:
neufer wrote:
BobMaller@aol.com wrote:
Am I looking at the Earth side of the moon, the far side of the moon or some combination?
Mostly the right hand (trailing) side of the moon.

The bright red spot on the upper left is Mare Crisium.

The "Colorado C" near the top is the Humboldtianum basin.
Thanks Neufer, I never would have figured this out on my own. I was trying to match the image with surface maps of the near and far sides. I didn't consider that there might be some near and some far side features -- makes me feel like Dr. Watson once Holmes reveals the obvious but previously unrecognized truth.
The image is centered on 101.4 degrees E, so almost exactly half near side (left) and half far side.

- Ernie

Re: APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

by Anthony Barreiro » Tue Mar 19, 2013 6:30 pm

neufer wrote:
BobMaller@aol.com wrote:
Am I looking at the Earth side of the moon, the far side of the moon or some combination?
Mostly the right hand (trailing) side of the moon.

The bright red spot on the upper left is Mare Crisium.

The "Colorado C" near the top is the Humboldtianum basin.
Thanks Neufer, I never would have figured this out on my own. I was trying to match the image with surface maps of the near and far sides. I didn't consider that there might be some near and some far side features -- makes me feel like Dr. Watson once Holmes reveals the obvious but previously unrecognized truth.

Re: APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

by Chris Peterson » Tue Mar 19, 2013 5:08 pm

Boomer12k wrote:So...Practical application...if you want to appear LIGHTER....stay in the BLUE LOCATIONS!!!
Yes, but you don't need to go to the Moon for that.

Image

Re: APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

by Boomer12k » Tue Mar 19, 2013 4:52 pm

So...Practical application...if you want to appear LIGHTER....stay in the BLUE LOCATIONS!!! :D

:---[===] *

Re: APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

by LocalColor » Tue Mar 19, 2013 4:37 pm

Wonderful APOD today and the links to more info are great! Thanks

Re: APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

by idoradjr » Tue Mar 19, 2013 4:35 pm

It would be interesting to see the gravity map overlaid onto the a topographical map to see if there is a correlation between craters and the gravity differences. Are old craters places of higher gravity and newer craters places of lower gravity, or vice versa, or is there no correlation?

Re: APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

by neufer » Tue Mar 19, 2013 2:43 pm

dougettinger wrote:
What does this GRAIL depiction imply for -

Red spots? Blue spots? Blue spots surrounded by red? Blue spots with red spots in the center? I realize the differences in gravity as described, but does anyone have any advanced ideas about the overall implications? I definitely have my own ideas.
Isostasy, gravity, and the Moon: an explainer of the first results of the GRAIL mission
By Emily Lakdawalla, Planetary Society

Re: APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

by neufer » Tue Mar 19, 2013 2:32 pm



BobMaller@aol.com wrote:
Am I looking at the Earth side of the moon, the far side of the moon or some combination?
Mostly the right hand (trailing) side of the moon.
The bright red spot on the upper left is Mare Crisium.

The "Colorado C" near the top is the Humboldtianum basin.

Re: APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

by dougettinger » Tue Mar 19, 2013 1:07 pm

What does this GRAIL depiction imply for -

Red spots? Blue spots? Blue spots surrounded by red? Blue spots with red spots in the center? I realize the differences in gravity as described, but does anyone have any advanced ideas about the overall implications? I definitely have my own ideas.

Doug Ettinger
Pittsburgh, PA

Re: APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

by orin stepanek » Tue Mar 19, 2013 11:24 am

Today's APOD was very interesting with lots of videos! I liked it very much! 8-) Good thing the moon isn't too close! Probably wouldn't be to good if it were too far either! :?

Re: APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

by BobMaller@aol.com » Tue Mar 19, 2013 5:40 am

Am I looking at the Earth side of the moon, the far side of the moon or some combination?

Re: APOD: GRAIL Maps the Moons Gravity (2013 Mar 19)

by bystander » Tue Mar 19, 2013 5:10 am


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