 made this new high-resolution map of the moon's gravity field.)
GRAVITY'S RAINBOW: NASA's Gravity Recovery and Interior Laboratory (GRAIL) made this new high-resolution map of the moon's gravity field.
Image: NASA/JPL-Caltech/MIT/GSFC
SAN FRANCISCO — The moon and other rocky bodies in the inner solar system were pounded by long-ago impacts far more violently than previously thought, two NASA spacecraft have found.
NASA's twin Grail probes have created an ultra-precise gravity map of the moon, revealing that its crust is almost completely pulverized. The surprising find suggests that Earth, Mercury, Venus and Mars endured a similar beating billions of years ago, researchers said.
The discovery "really opens a window to this early stage of just what a violent place the surfaces of all terrestrial planets were early in their history," Grail principal investigator Maria Zuber of MIT said during a press conference here Dec. 5 at the annual fall meeting of the American Geophyiscal Union.
The new results shed light on how the moon formed, and they may help scientists better understand where life might be found today on Mars, if it ever existed, Zuber added. [Graphic: How the Grail Probes Work]
Formation flying
The $496 milion Grail mission launched in September 2011 to map the moon's gravity field with unprecedented precision.
The twin probes, named Ebb and Flow, fly in formation around the moon, detecting the tiny changes in the distance between them caused by lunar mountains, craters and subsurface mass concentrations.
The Grail team has used such measurements to create a new lunar gravity map, which researchers say is the highest-resolution map of this kind ever generated for a celestial body. And it revealed some interesting information about the moon.
For starters, the lunar crust is incredibly porous, suggesting it was fractured by countless impacts long ago. The crust is also thinner than previously thought — just 21 to 27 miles (34 to 43 kilometers), compared to earlier estimates ranging from 30 to 40 miles (48 to 64 km).
Support for the Giant Impact theory
Ebb and Flow also spotted many large, linear structures under the moon's surface that can run for up to 300 miles (480 km). These subsurface "dikes" of solidified magma are covered by craters, suggesting that they predate most of the moon's violent impacts.
The dikes could only have formed if the moon's crust were extending, making room for the magma, researchers said. This would happen if the moon's interior were heating up and expanding, as predicted by the leading theory for the moon's origin — the Giant Impact hypothesis.
This idea posits that a Mars-size body smashed into Earth about 4.5 billion years ago, and the moon coalesced from pieces of our planet that were blasted into space.
"The process of building a moon out of that debris should result in a situation where the moon is cooler on the inside and warmer on the outside," said Grail guest scientist Jeff Andrews-Hanna of the Colorado School of Mines. "And then what naturally happens is that the interior will warm up and expand during that first billion years."
"This had been predicted theoretically a long time ago, but there was no direct observational evidence to support this period of early lunar expansion until this Grail data," Andrews-Hanna added.
Martian life deep underground?
Grail's revelations about the violent early history of the inner solar system suggest that the upper crusts of its rocky planets are highly and deeply fractured, Zuber said.
See what we're tweeting about
14 Comments
Add CommentRe: "...[T]he Giant Impact hypothesis...posits that a Mars-size body smashed into Earth about 4.5 billion years ago, and the moon coalesced from pieces of our planet that were blasted into space."
Reply | Report Abuse | Link to thisIf the information available to me is correct, an explosion (which is what seems to result from an impact), does not generate order. Rather, as in the case of the detonation of an explosive device (i.e., a bomb), those who detonate it are counting on the destruction of the existing order. Yet, we're being told repeatedly that explosions generate order (i.e., a "big-bang" or an impact event).
Clicking on the hyperlink "Giant Impact hypothesis," leads to the web page,
http://www.space.com/18106-moon-formation-earth-giant-impact.html,
where clicking on the hyperlink, "giant impact theory," leads to the web page,
http://www.space.com/9926-moon-life.html.
Activation of the video, provided the following commentary by planetary scientist Jay Melosh (3:20 ff.):
"Even though a mars-sized body struck the Earth, probably at 12 km/sec., the mass of Earth is so great, and the gravitational (binding?) energy so large, that the Earth actually maintained its integrity. In fact, what it did is swallow up the impactor; they merged together and formed the new planet. Only a tiny fraction actually blew off; something like 1/100th of the mass of the impactor, which is the mass of the moon"
What is the evidence for the claim that the moon exists as a result of impact?
Bill, using your reasoning crystals can't form in volcanic eruptions, but we know they do. You can even buy "Mt. St. Helens crystals" online for an example that likely happened during your lifetime
Reply | Report Abuse | Link to thisYou need to review the laws of thermodynamics better. Energy moving around can create islands of order - a big splattery impact onto proto-Earth by a Mars-sized object would create a huge amount of orbiting debris which would naturally coalesce into a moon due to gravity. Due to gravity, this object would become spherical.
I don't know that the big-impact hypothesis is true, but a misreading of the laws of thermodynamics is not the way to disprove it.
If the moon and interior planets were battered early in their history, what does it has to do with gravity?
Reply | Report Abuse | Link to thisIf the gravity depends on the mass, and we can consider the mass concentrated in the center, what connection does it have with the hits the moon (and inner planets) received?
Why does it mean the crust is thin? Do we have molten rock in the center of the moon?
Do gravity magnitude change from place to place? Isn't it fixed all around the planet and only depends on distance from the center of the planet?
I do not think (without deep study of the subject matter) the moon originated form an impact of a Mars size object on Earth.
Probably at the beginning the Earth was rotating too fast and it was liquid metal. Part of it dis-attached from Earth.
Probably what we need is courses of physics to study things in depth.
Anyway, very interesting!
Probably the mass within the planet is not uniformly distributed. This causes the gravity to change from place to place.
Reply | Report Abuse | Link to thisObviously on Earth the gravity on the poles is not the same than the gravity on the Ecuador. the distance to the center is different that obviously also counts.
The fact that the crust in the moon is thin does not mean the center of the moon is molten. It was probably(some time ago) molten, but not any more.
Yes, gravity changes from place to place.We need to take into account distance from the center and distribution of mass.
All these seems very elementary.
what is important here is the capacity to go over there and measure with such precision these, that could be subtle changes, not that easy to detect.
and then to introduce these facts into theories about the formation of the moon.
It is OK.
SteveO (comment 3),
Reply | Report Abuse | Link to thisIt's unclear to me why "my reasoning" (which, in fact, is not my reasoning, but that of the sources consulted in research) prevents crystals from forming in volcanic eruptions.
Re: "...a big splattery impact onto proto-Earth by a Mars-sized object would create a huge amount of orbiting debris which would naturally coalesce into a moon due to gravity."
Presumably you'll agree that there was no human observer present for the alleged proto-Earth event. Where, in the scientific literature, is the report(s) of the results of testing this assertion?
Bill,
Reply | Report Abuse | Link to thisYou assert that explosions don't generate order. (As an aside, this is an extension of an argument made by the creationist crowd who willfully misunderstand the laws of thermodynamics.) An explosion of some sort is the release of some sort of energy - perhaps chemical energy from TNT, atomic energy from a nuclear bomb, or kinetic energy from an asteroid. The total energy (enthalpy) of the closed system (the universe) doesn't change - it just moves from various forms to other forms: chemical potential energy to kinetic and heat energy(which is just another way to say atomic kinetic energy), nuclear potential energy to kinetic and heat energy (along with different elements and particles) and gravitational and kinetic energy into heat and kinetic energy, respectively.
To a person, an explosion looks like going from order to disorder, and it is true that thermodynamically the universe as a whole moves from order to disorder (entropy). But that is as a whole. Local regions can, with an input of energy (and an overall increase in entropy) create islands of order from disorder. So if I increase the entropy of the universe by heating up some sugar in water, and then further increase the entropy by allowing it to cool and evaporate, I can form islands of very high order - sugar crystals.
So yes, order can (in fact must) come from disorder and yes, order (crystals) can form from explosions. It is a misunderstanding of thermodynamics that would lead you to any other conclusion.
Similarly, a Mars-size impactor splatting into the proto-Earth would merge into the mass we know and love (and live on) plus ejecting huge amounts of mass. A lot of that would fall back down to the planet, some of it would fly off, perhaps to become a meteorite on some other planet, or just to orbit the Sun. But a lot of it would fall together pulled by their own gravity. Once that starts, a small proto-Moon gathers more to itself, and with greater gravity, gathers more and more.
If it runs out of mass early, then you get an asymmetrical shape like many asteroids. If you get enough, the compression of the total mass heats up the interior, which becomes plastic. And since we all know the one shape that minimizes surface area for a given volume is the sphere, you end up with a sphere.
You can perform a similar experiment: look at a falling raindrop. It is spherical, not due to gravity but to surface tension, but it is the same idea.
This theory of moon formation has been tested with computer models: http://www.youtube.com/watch?v=2sr-MriOCzw
That is not to say that the big impactor theory is complete or true, by the way.
Reply | Report Abuse | Link to thisAnd the Big Bang was not really an explosion in the way we think about it, but it was going from a point of infinite order (all mass-energy of the universe in one geometric point) to very great disorder with islands of order (what we see around us now).
Be careful of conflating human language and motivation ("destruction of order") with scientific terms and processes.
If you google "large impact hypothesis" you will find numerous papers on it, and criticisms of it.
Enjoy!
As a novice observer, I see order in the making when I admire the beautiful image of a galaxy dramatically drawn about its black whole. Is entropy truly irreversible?
Reply | Report Abuse | Link to thisIs entropy truly irreversible?
Reply | Report Abuse | Link to thisGood question indeed.
Moon protects its mother Earth, by hunting the comets; so that instead of impacting Earth, they impact Moon.
Reply | Report Abuse | Link to thisTherefore, the surface of Moon is battered with such numerous craters.
http://quran-ayat.com/huda/showthread.php?492-The-role-of-the-Moon-in-protecting-the-Earth
Overall, no, entropy always increases. As a black hole "evaporates" over the lifetime of the universe, it emits particles which (depending on who you believe) do or do not carry out information about what is in the black hole. But either way, those particles also decay, so assuming we don't have enough mass for a "Big Crunch" everything in the universe ends up, after a very long while, as random atomic motion. The final triumph of entropy.
Reply | Report Abuse | Link to thisThat always makes me sad to think about...
SteveO,
Reply | Report Abuse | Link to thisRe: "Local regions can, with an input of energy (and an overall increase in entropy) create islands of order from disorder."
It seems to me the qualifier in that statement is, "...an input of energy..." There is a cost in obtaining a small amount of order from disorder.
Re: "...a Mars-size impactor splatting into the proto-Earth would merge into the mass we know and love (and live on)..."
That's an assertion which requires evidence.
Re: "the Big Bang was not really an explosion..."
The only alternative, in my research experience, is the brane-collision assertion. That simply pushes the problem back to square one. What is the origin of the "branes?"
Re: "This theory of moon formation has been tested with computer models"
Computer models will always be affected by input bias. That doesn't seem to me a good substitute for evidence.
It seems to me that the final triumph of entropy is unthinkable, unbelievable, and probably impossible.
Reply | Report Abuse | Link to thisBut we jump into the field of philosophy.
For all practical purposes we say entropy is always increasing.
That helps us to solve problems and understand how thing are at present.
It is beautiful and worthwhile to study at depth. It helps us to understand a lot of things.
In Chemistry it probably can help us understand at what point a reaction reaches equilibrium, to what extent we may get mechanical (kinetic) energy from combustion in a close chamber, and very probably etc., etc.
We are not at odds with the concept of entropy, and from a practical point of view (and with our probably limited capacity to understand what happens under the skin)we say it increases.
We can transform kinetic energy to heat, but form that heat we can not obtain the same amount of kinetic energy we started with. Heat is chaos, is entropy.
It is perfect, it is a fact. As far as what we know today there is not much we can do about it.
But somehow the question "Is entropy irreversible?" makes sense .
The entire galaxy may be devoured by a black hole. I do not know if that has been observed.
I we do not know what is going on inside the black hole.
We will never be inside a black hole. We may send a ship into a black hole. It may measure something.
Or with pure theoretical reasoning we may one day understand what happens inside a black hole.
Probably there is enough mass (or whatever that may be)in the universe for a "Big Crunch". And the cycle starts all over again.
It is just not possible for this to end up in total chaos. There should be a reversal to entropy.
So do not be sad.
But we need to recognize. that at this point in our understanding, if we discuss that, we enter inevitably into philosophy or religion.
I do not not if there are a couple of persons in the world capable of understanding this matter more profoundely. Very probably there are.
I dont know how we made it this far, so Please have a care. for our gyroscope, our jewel, our sibling.
Reply | Report Abuse | Link to this