According to the most widely-accepted theory, the Moon formed roughly 4.5 billion years ago when a Mars-sized object named Theia collided with Earth (aka. the Giant Impact Hypothesis). This impact threw up considerable amounts of debris which gradually coalesced to form Earth’s only natural satellite. One of the most compelling proofs for this theory is the fact that the Earth and the Moon are remarkably similar in terms of composition.
However, previous studies involving computer simulations have shown that if the Moon were created by a giant impact, it should have retained more material from the impactor itself. But according to a new study conducted by a team from the University of New Mexico, it is possible that the Earth and the Moon are not as similar as previously thought.
When it comes to the study of planets, moons, and stars, magnetic fields are kind of a big deal. Believed to be the result of convection in a planet, these fields can be the difference between a planet giving rise to life or becoming a lifeless ball of rock. For some time, scientists have known that has a Earth’s magnetic field, which is powered by a dynamo effect created by convection in its liquid, outer core.
Scientists have also long held that the Moon once had a magnetic field, which was also powered by convection in its core. Previously, it was believed that this field disappeared roughly 1 billion years after the Moon formed (ca. 3 to 3.5 billion years ago). But according to a new study from the Massachusetts Institute of Technology (MIT), it now appears that the Moon’s magnetic field continued to exist for another billion years.
The study, titled “A two-billion-year history for the lunar dynamo“, recently appeared in the journal Science Advances. Led by Dr. Sonia Tikoo, an Assistant Professor at Rutger’s University and a former researcher at MIT, the team analyzed ancient lunar rocks collected by NASA’s Apollo 15 mission. What they found was that the rock showed signs of a being in magnetic field when it was formed between 1 and 2.5 billion years ago.
The age of this rock sample means that it is significantly younger than others returned by the Apollo missions. Using a technique they developed, the team examined the sample’s glassy composition with a magnometer to determine its magnetic properties. They then exposed the sample to a lab-generated magnetic field and other conditions that were similar to those that existed on the Moon when the rock would have formed.
This was done by placing the rocks into a specially-designed oxygen-deprived oven, which was built with the help of Clement Suavet and Timothy Grove – two researchers from MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS) and co-authors on the study. The team then exposed the rocks to a tenuous, oxygen-free environment and heated them to extreme temperatures.
As Benjamin Weiss – a professor of planetary sciences at EAPS – explained:
“You see how magnetized it gets from getting heated in that known magnetic field, then you compare that field to the natural magnetic field you measured beforehand, and from that you can figure out what the ancient field strength was… In this way, we finally have gotten an accurate measurement of the lunar field.”
From this, they determined the lunar rock became magnetized in a field with a strength of about 5 microtesla. That’s many times weaker than Earth’s magnetic field when measured from the surface (25 – 65 microteslas), and two orders of magnitude weaker than what it was 3 to 4 billion years ago. These findings were quite significant, since they may help to resolve an enduring mystery about the Moon.
Previously, scientists suspected that the Moon’s magnetic field died out 1.5 billion years after the Moon formed (ca. 3 billion years ago). However, they were unsure if this process happened rapidly, or if the Moon’s magnetic field endured, but in a weakened state. The results of this study indicate that the magnetic field did in fact linger for an additional billion years, dissipating about 2.5 billion years ago.
As Weiss indicated, this study raises new questions about the Moon’s geological history:
“The concept of a planetary magnetic field produced by moving liquid metal is an idea that is really only a few decades old. What powers this motion on Earth and other bodies, particularly on the moon, is not well-understood. We can figure this out by knowing the lifetime of the lunar dynamo.”
In other words, this new timeline of the Moon casts some doubt on the theory that a lunar dynamo alone is what powered its magnetic field in the past. Basically, it is now seen as a distinct possibility that the Moon’s magnetic field was powered by two mechanisms. Whereas one allowed for a dynamo in the core that powered its magnetic field for a good billion years after the Moon’s formation, a second one kept it going afterwards.
In the past, scientists have proposed that the Moon’s dynamo was powered by Earth’s gravitational pull, which would have caused tidal flexing in the Moon’s interior (much in the same way that Jupiter and Saturn’s powerful gravity drives geological activity in their moons interiors). In addition, the Moon once orbited much closer to Earth, which may have been enough to power its once-stronger magnetic field.
However, the Moon gradually moved away from Earth, eventually reaching its current orbit about 3 billion years ago. This coincides with the timeline of the Moon’s magnetic field, which began to dissipate at about the same time. This could mean that by about 3 billion years ago, without the gravitational pull of the Earth, the core slowly cooled. One billion years later, the core had solidified to the point that it arrested the Moon;s magnetic field. As Weiss explained:
“As the moon cools, its core acts like a lava lamp – low-density stuff rises because it’s hot or because its composition is different from that of the surrounding fluid. That’s how we think the Earth’s dynamo works, and that’s what we suggest the late lunar dynamo was doing as well… Today the moon’s field is essentially zero. And we now know it turned off somewhere between the formation of this rock and today.”
These findings were made possible thanks in part by the availability of younger lunar rocks. In the future, the researchers are planning on analyzing even younger samples to precisely determine where the Moon’s dynamo died out completely. This will not only serve to validate the findings of this study, but could also lead to a more comprehensive timeline of the Moon’s geological history.
The results of these and other studies that seek to understand how the Moon formed and changed over time will also go a long way towards improving our understanding of how Earth, the Solar System, and extra-solar systems came to be.
When the Apollo astronauts returned to Earth, they came bearing 380.96 kilograms (839.87 lb) of Moon rocks. From the study of these samples, scientists learned a great deal about the Moon’s composition, as well as its history of formation and evolution. For example, the fact that some of these rocks were magnetized revealed that roughly 3 billion years ago, the Moon had a magnetic field.
Much like Earth, this field would have been the result of a dynamo effect in the Moon’s core. But until recently, scientists have been unable to explain how the Moon could maintain such a dynamo effect for so long. But thanks to a new study by a team of scientists from the Astromaterials Research and Exploration Science (ARES) Division at NASA’s Johnson Space Center, we might finally have a answer.
To recap, the Earth’s magnetic core is an integral part of what keeps our planet habitable. Believed to be the result of a liquid outer core that rotates in the opposite direction as the planet, this field protects the surface from much of the Sun’s radiation. It also ensures that our atmosphere is not slowly stripped away by solar wind, which is what happened with Mars.
For the sake of their study, which was recently published in the journal Earth and Planetary Science Letters, the ARES team sought to determine how a molten, churning core could generate a magnetic field on the Moon. While scientists have understood how the Moon’s core could have powered such a field in the past, they have been unclear as to how it could have been maintained it for such a long time.
Towards this end, the ARES team considered multiple lines of geochemical and geophysical evidence to put constraints on the core’s composition. As Kevin Righter, the lead of the JSC’s high pressure experimental petrology lab and the lead author of the study, explained in a NASA press release:
“Our work ties together physical and chemical constraints and helps us understand how the moon acquired and maintained its magnetic field – a difficult problem to tackle for any inner solar system body. We created several synthetic core compositions based on the latest geochemical data from the moon, and equilibrated them at the pressures and temperatures of the lunar interior.”
Specifically, the ARES scientists conducted simulations of how the core would have evolved over time, based on varying levels of nickel, sulfur and carbon content. This consisted of preparing powders or iron, nickel, sulfur and carbon and mixing them in the proper proportions – based on recent analyses of Apollo rock samples.
Once these mixtures were prepared, they subjected them to heat and pressure conditions consistent with what exists at the Moon’s core. They also varied these temperatures and pressures based on the possibility that the Moon underwent changes in temperature during its early and later history – i.e. hotter during its early history and cooler later on.
What they found was that a lunar core composed of iron/nickel that had a small amount of sulfur and carbon – specifically 0.5% sulfur and 0.375% carbon by weight – fit the bill. Such a core would have a high melting point and would have likely started crystallizing early in the Moon’s history, thus providing the necessary heat to drive the dynamo and power a lunar magnetic field.
This field would have eventually died out after heat flow led the core to cool, thus arresting the dynamo effect. Not only do these results provide an explanation for all the paleomagnetic and seismic data we currently have on the Moon, it is also consistent with everything we know about the Moon’s geochemical and geophysical makeup.
Prior to this, core models tended to place the Moon’s sulfur content much higher. This would mean that it had a much lower melting point, and would have meant crystallization could not have occurred until much more recently in its history. Other theories have been proposed, ranging from sheer forces to impacts providing the necessary heat to power a dynamo.
However, the ARES team’s study provides a much simpler explanation, and one which happens to fit with all that we know about the Moon. Naturally, additional studies will be needed before there is any certainty on the issue. No doubt, this will first require that human beings establish a permanent outpost on the Moon to conduct research.
But it appears that for the time being, one of the deeper mysteries of the Earth-Moon system might be resolved at last.
For decades, scientists have been of the belief that the Moon, Earth’s only natural satellite, was four and a half billion years old. According to this theory, the Moon was created from a fiery cataclysm produced by a collision between the Earth with a Mars-sized object (named Theia) roughly 100 million years after the formation of primordial Earth.
But according to a new study by researchers from UCLA (who re-examined some of the Apollo Moon Rocks), these estimates may have been off by about 40 to 140 million years. Far from simply adjusting our notions of the Moon’s proper age, these findings are also critical to our understanding of the Solar System and the formation and evolution of its rocky planets.
These fragments were of a compound known as zircon, a type of silicate mineral that contains trace amounts of radioactive elements (like uranium, thorium, and lutetium). As Kevin McKeegan, a UCLA professor of geochemistry and cosmochemistry and a co-author of the study, explained, “Zircons are nature’s best clocks. They are the best mineral in preserving geological history and revealing where they originated.”
By examining the radioactive decay of these elements, and correcting for cosmic ray exposure, the research team was able to get highly precise estimates of the zircon fragments ages. Using one of UCLA’s mass spectrometers, they were able to measure the rate at which the deposits of uranium in the zircon turned into lead, and the deposits of lutetium turned into hafnium.
In the end, their data indicated that the Moon formed about 4.51 billion years ago, which places its birth within the first 60 million years of the Solar System or so. Previously, dating Moon rocks proved difficult, mainly because most of them contained fragments of many different kinds of rocks, and these samples were determined to be tainted by the effects of multiple impacts.
However, Barboni and her team were able to examine eight zircons that were in good condition. More importantly, these silicate deposits are believed to have formed shortly after the collision between Earth and Theia, when the Moon was still an unsolidified mass covered in oceans of magma. As these oceans gradually cooled, the Moon’s body became differentiated between its crust, mantle and core.
Because zircon minerals were formed during the initial magma ocean, uranium-lead dating reaches all the way back to a time before the Moon became a solidified mass. As Edward Young, a UCLA professor of geochemistry and cosmochemistry and a co-author of the study, put it, “Mélanie was very clever in figuring out the Moon’s real age dates back to its pre-history before it solidified, not to its solidification.”
These findings have not only determined the age of the Moon with a high degree of accuracy (and for the first time), it also has implications for our understanding of when and how rocky planes formed within the Solar System. By placing accurate dates on when certain bodies formed, we are able to understand the context in which they formed, which also helps to determine what mechanisms were involved.
And this was just the first revelation produced by the research team, which hopes to continue studying the zircon fragments to see what they can learn about the Moon’s early history.
Over the course of the past few decades, our ongoing exploration the Solar System has revealed some surprising discoveries. For example, while we have yet to find life beyond our planet, we have discovered that the elements necessary for life (i.e organic molecules, volatile elements, and water) are a lot more plentiful than previously thought. In the 1960’s, it was theorized that water ice could exist on the Moon; and by the next decade, sample return missions and probes were confirming this.
Since that time, a great deal more water has been discovered, which has led to a debate within the scientific community as to where it all came from. Was it the result of in-situ production, or was it delivered to the surface by water-bearing comets, asteroids and meteorites? According to a recent study produced by a team of scientists from the UK, US and France, the majority of the Moon’s water appears to have come from meteorites that delivered water to Earth and the Moon billions of years ago.
For the sake of their study, which appeared recently in Nature Communications, the international research team examined the samples of lunar rock and soil that were returned by the Apollo missions. When these samples were originally examined upon their return to Earth, it was assumed that the trace of amounts of water they contained were the result of contamination from Earth’s atmosphere since the containers in which the Moon rocks were brought home weren’t airtight. The Moon, it was widely believed, was bone dry.
However, that which was discovered on the surface paled in comparison the water that was discovered beneath it. Evidence of water in the interior was first revealed by the ISRO’s Chandrayaan-1 lunar orbiter – which carried the NASA’s Moon Mineralogy Mapper (M3) and delivered it to the surface. Analysis of this and other data has showed that water in the Moon’s interior is up to a million times more abundant than what’s on the surface.
The presence of so much water beneath the surface has begged the question, where did it all come from? Whereas water that exists on the Moon’s surface in lunar regolith appears to be the result of interaction with solar wind, this cannot account for the abundant sources deep underground. A previous study suggested that it came from Earth, as the leading theory for the Moon’s formation is that a large Mars-sized body impacted our nascent planet about 4.5 billion years ago, and the resulting debris formed the Moon. The similarity between water isotopes on both bodies seems to support that theory.
However, according to Dr. David A. Kring, a member of the research team that was led by Jessica Barnes from Open University, this explanation can only account for about a quarter of the water inside the moon. This, apparently, is due to the fact that most of the water would not have survived the processes involved in the formation of the Moon, and keep the same ratio of hydrogen isotopes.
Instead, Kring and his colleagues examined the possibility that water-bearing meteorites delivered water to both (hence the similar isotopes) after the Moon had formed. As Dr. Kring told Universe Today via email:
“The current study utilized analyses of lunar samples that had been collected by the Apollo astronauts, because those samples provide the best measure of the water inside the Moon. We compared those analyses with analyses of meteoritic samples from asteroids and spacecraft analyses of comets.”
By comparing the ratios of hydrogen to deuterium (aka. “heavy hydrogen”) from the Apollo samples and known comets, they determined that a combination of primitive meteorites (carbonaceous chondrite-type) were responsible for the majority of water to be found in the Moon’s interior today. In addition, they concluded that these types of comets played an important role when it comes to the origins of water in the inner Solar System.
For some time, scientists have argued that the abundance of water on Earth may be due in part to impacts from comets, trans-Neptunian objects or water-rich meteoroids. Here too, this was based on the fact that the ratio of the hydrogen isotopes (deuterium and protium) in asteroids like 67P/Churyumov-Gerasimenko revealed a similar percentage of impurities to carbon-rich chondrites that were found in the Earth’s coeans.
But how much of Earth’s water was delivered, how much was produced indigenously, and whether or not the Moon was formed with its water already there, have remained the subject of much scholarly debate. Thank to this latest study, we may now have a better idea of how and when meteorites delivered water to both bodies, thus giving us a better understanding of the origins of water in the inner Solar System.
“Some meteoritic samples of asteroids contain up to 20% water,” said Kring. “That reservoir of material – that is asteroids – are closer to the Earth-Moon system and, logically, have always been a good candidate source for the water in the Earth-Moon system. The current study shows that to be true. That water was apparently delivered 4.5 to 4.3 billion years ago.“
The existence of water on the Moon has always been a source of excitement, particularly to those who hope to see a lunar base established there someday. By knowing the source of that water, we can also come to know more about the history of the Solar System and how it came to be. It will also come in handy when it comes time to search for other sources of water, which will always be a factor when trying to establishing outposts and even colonies throughout the Solar System.
A 74-year-old grandmother was taken into custody after a NASA sting operation to recover a small shard of a Moon rock. In an Associated Press article, Joanna Davis said the Moon rock was given to her husband by Neil Armstrong in the 1970s, and she was trying to sell the item to take care of her sick son. However, any samples from the Moon are considered government property, and so cannot be sold for profit.
But no charges have been filed and NASA is not commenting on the case.
Davis said she was frightened and bruised during the incident that occurred at a Denny’s restaurant
“They grabbed me and pulled me out of the booth,” Davis told the AP.
Reportedly Davis emailed a NASA contractor on May 10, 2011 trying to find a buyer for the rock, as well as a nickel-sized piece of the heat shield that protected the Apollo 11 space capsule as it returned to earth from the Apollo 11 mission to the moon in 1969.
Neil Armstrong has said previously in a written affidavit that he has never given Moon rocks to private citizens.
While Davis’s attorney called the incident “abhorrent behavior by the federal government to steal something from a retiree that was given to her,” according to AP, Davis apparently knew that what she was doing was against the law.
Long-held secrets continue to be unlocked from the Moon. Researchers taking a new look at a rock brought back by the Apollo 17 mission have discovered graphite in the form of tiny whiskers within the lunar sample. Just like the recent finding of water on the Moon, it was previously thought that any carbon present in the Apollo rocks came from terrestrial contamination from the way the lunar samples were collected, processed or stored. Andrew Steele, who led a team from the Carnegie Institution’s Geophysical Laboratory said the graphite could have come from carbonaceous impactors that struck both the Moon and Earth during the Late Heavy Bombardment, approximately 4.1 to 3.8 billion years ago, and if so, could provide a new and important source of information about this period in the solar system’s early history.
“We were really surprised at the discovery of graphite and graphite whiskers,” Steele said. “We were not expecting to see anything like this.”
The tiny graphite whiskers or needles were found in multiple spots within a specific area of lunar sample 722255 from the Mare Serenitatis impact crater in the Taurus-Littrow region, indicating that the minerals are in fact from the Moon and not just contamination.
Steele told Universe Today that he and his team don’t think the graphite originated on the Moon, but haven’t ruled it out completely.
“Our initial thought is that it is from the impactor, as we find it in a very fine grained impact melt breccias,” he said in an email. “I am currently looking in more pristine lunar rocks, i.e. lavas that do not contain evidence of meteorite material, for carbon phases.”
He added that the graphite may have come from the impactor itself, or it may have formed from the condensation of carbon-rich gas released during the impact.
The team used Raman imaging spectroscopy (CRIS) on a thin section of a freshly fractured surface of the rock. This identifies minerals and carbon species and their spatial relationship to each other beneath the surface of a sample. Steele said even though this rock has been on Earth since 1972, new techniques and instruments allowed for the new discovery.
“The analytical spot size is smaller and so we can look at smaller phases,” he said. “The sensitivity is better in the newer instruments and we can use spatially resolved methods that are much more sensitive than in the Apollo era.”
Impact breccias are made up of a jumble of smaller fragments that formed when the moon was struck by an asteroid or other object.
Other previous spectroscopy of the Moon’s surface has also found trace amounts of carbon, but it was thought to have come from the solar wind. However, Steele said he and his team have also ruled that out as the source.
“Several lines of reasoning confirm that the observed graphite and graphite whiskers (GW) are indigenous to the sample,” said the team in their paper. “In particular, all known GW synthesis methods involve deposition from a carbon-containing gas at relatively high temperatures ranging from 1273 to ~3900 K. Thus, the GWs identified in 72255 cannot have been synthesized as a result of sample handling and preparation. Moreover, they could not have been implanted by solar wind, because this carbon is typically too small to identify structurally at the magnifications used. The crystalline graphite grains detected here are likely either intact remnants of graphite and GWs from the Serentatis impactor, or they could have formed from condensation of carbon-rich gas released during impact.”
Steele said their findings indicate that impacts may be another process by which GWs can form in our solar system. Additionally, it appears carbonaceous material from impacts at the time of the Late Heavy Bombardment (LHB), and at a time when life may have been emerging on Earth, does survive on the Moon.
“The Solar System was chaotic with countless colliding objects 3.8 billion years ago,” Steele said in a press release. “Volatiles—compounds like water and elements like carbon were vaporized under that heat and shock. These materials were critical to the creation of life on Earth.”
While the impacts to Earth during that period have since been erased, craters on the Moon are still pristine, so the Moon potentially holds a record of the meteoritic carbon input to the Earth-Moon system, when life was just beginning to emerge on Earth.
The research is published in the July 2, 2010, issue of Science.