Water on Moon and Earth came from same primitive meteorites, analysis shows

May 09, 2013
Backscatter electron image of a lunar melt inclusion from Apollo 17 sample 74220, enclosed within an olivine crystal. The inclusion is 30 µm in diameter. Skeletal crystals within the melt inclusion are a fine mixture of olivine and ilmenite. Dark area in the lower-left is an ion microprobe sputter crater. Credit: John Armstrong, Geophysical Laboratory, Carnegie Institution of Washington

The water found on the moon, like that on Earth, came from small meteorites called carbonaceous chondrites in the first 100 million years or so after the solar system formed, researchers from Brown and Case Western Reserve universities and Carnegie Institution of Washington have found.

Evidence discovered within samples of returned by lunar crews of Apollo 15 and 17 dispels the theory that comets delivered the molecules.

The research is published online in Science Express today.

The discovery's telltale sign is found in the ratio of an isotopic form of hydrogen, called , to standard hydrogen. The ratio in the 's water and in water from specks of trapped in crystals within moon dust match the ratio found in the chondrites. The proportions are far different from those in comet water.

The moon is thought to have formed from a disc of debris left when a giant object hit the Earth 4.5 billion years ago, very early in Earth's history. Scientists have long assumed that the heat from an impact of that size would cause hydrogen and other to boil off into space, meaning the moon must have started off completely dry. But recently, and new research on samples from the have shown that the moon actually has water, both on and beneath its surface.

By showing that water on the moon and Earth came from the same source, this new study offers yet more evidence that the moon's water has been there all along, or nearly so.

"The simplest explanation for what we found is that there was water on the proto-Earth at the time of the giant impact," said Alberto Saal, a at Brown University and the study's lead author. "Some of that water survived the impact, and that's what we see in the moon."

Or, the proto-moon and proto-Earth were showered by the same family of carbonaceous chondrites soon after they separated, said James Van Orman, professor of earth, environmental and planetary sciences at Case Western Reserve, and a co-author.

The other authors are Erik Hauri, of the Carnegie Institution, and Malcolm Rutherford, from Brown.

To find the origin of the moon's water, the researchers looked at the trapped volcanic glass, referred to as a melt inclusion. The surrounding olivine crystals prevent water form escaping during an eruption, providing researchers an idea of what the inside of the moon is like.

Research from 2011, led by Hauri, found that the melt inclusions have plenty of water—as much water, in fact, as lavas forming on the Earth's ocean floor. This study aimed to find the origin of that water. To do that, Saal and his colleagues looked at the isotopic composition of the hydrogen trapped in the inclusions.

Using a Cameca NanoSIMS 50L multicollector ion microprobe at Carnegie, the researchers measured the amount of deuterium in the samples compared to the amount of regular hydrogen. Deuterium has an extra neutron.

Water molecules originating from different places in the solar system have different amounts of deuterium. In general, things formed closer to the sun have less deuterium than things formed further out.

The investigators found that the deuterium/hydrogen ratio in the melt inclusions was relatively low and matched the ratio found in carbonaceous chondrites. These meteorites originated in the asteroid belt near Jupiter and are thought to be among the oldest objects in the solar system. That means the source of the water on the moon is primitive meteorites.

Comets, like meteorites, are known to carry water and other volatiles. But most comets were formed in the icy Oort Cloud, more than 1,000 times more distant than Neptune. Because comets formed so far from the sun, they tend to have high deuterium/hydrogen ratios—much higher ratios than in the moon's interior, where the samples in this study originated.

"The measurements themselves were very difficult," Hauri said, "but the new data provide the best evidence yet that the carbon-bearing chondrites were a common source for the volatiles in the Earth and moon, and perhaps the entire inner solar system."

To determine the ratios that would currently be found deep in the moon's interior, Van Orman and Saal modeled the loss of gasses from inside melt inclusions and the influence of degassing on the deuterium. The researchers also had to take into account the impact of cosmic rays—high-energy rays that carry charged particles—on the water trapped inside the inclusions. The interaction produces more deuterium than hydrogen. In total, the effects proved to be small for the melt inclusions, and the ratios remained consistent with the those of the .

Recent research, Saal said, has found that as much as 98 percent of the water on Earth also comes from primitive meteorites, suggesting a common source for water on Earth and the moon. The easiest way to explain that, Saal said, is that the water was already present on the early Earth and was transferred to the moon.

The finding is not necessarily inconsistent with the idea that the moon was formed by a giant impact with the early Earth, but presents a problem. If the moon is made from material that came from the Earth, it makes sense that the water in both would share a common source, Saal said. However, there's still the question of how that was able to survive such a violent collision.

"Our work suggests that even highly volatile elements may not be lost completely during a giant impact," said Van Orman. "We need to go back to the drawing board and discover more about what giant impacts do, and we also need a better handle on volatile inventories in the ."

Explore further: Computer model shows moon's core surrounded by liquid and it's caused by Earth's gravity

More information: "Hydrogen Isotopes in Lunar Volcanic Glasses and Melt Inclusions Reveal a Carbonaceous Chondrite Heritage," by A.E. Saal et al. Science Express, 2013.

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User comments : 11

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Yellowdart
1.4 / 5 (11) May 09, 2013
It's always amazing to me that modern science insists on bringing water to the earth via some mass of meteorites from space... Why invent some unknown source when we are standing on the largest known source of water in the whole solar system, if not galaxy. The moon has an earth-like water because it's from the earth, would the be the simplest, most rational, and logical explanation. We are on the water planet.
Howhot
3 / 5 (4) May 09, 2013
Yellow say
The moon has an earth-like water because it's from the earth, would the be the simplest, most rational, and logical explanation

I think you missed the point my friend. There was "comet water" on Earth before the Moon was created. This just shows more proof that the Moon was created from Earth due to a planetary size collision and the moon was just spun off from that collision. That has become widely believed to be the predominate theory of how the Moon was created and is trapped orbiting Earth. This article just adds more experimental support to that theory.
yep
1.9 / 5 (9) May 10, 2013
I always thought the solar wind with its hydrogen ionizing with oxygen in our upper atmosphere was a more likely cause of water.
Howhot
2.8 / 5 (4) May 10, 2013
Nope, @yep, It's much more fascinating than that. We are talking about 4.5 Billion years ago when the sun was just a wirrlng pile of gas and a dense object got trapped in orbit around the sun. From there it collected mass from the gas and other iron/rock materials ejected from early supernovas. The ejects from supernovas included everything needed for comets; water, silicon, iron, nickel, and water. Comets are what formed proto-earth. So, yea, proto-earth had lots of water. It's thought that proto-earth was a small planet, mostly ice, but it could have been ocean covered and that is suspect, but no one knows.

So from proto-earth a planet object about the size of Mars collided with Earth at just the right angle, speed and gravity that it stuck! It stuck and spit off a chunk that is now the Moon. 4 billion years later, we Humans are just recognizing how unique the Moon is. What a wonder!

As my good friend Carl used to say before he passed; "We are all just star stuff".
verkle
1.3 / 5 (7) May 10, 2013
Analysis does not show that water on Moon and Earth came from same primitive meteorites. It just shows that the amount of deuterium to standard hydrogen is similar. Anything beyond that is just a hypothesis, of which there are many.

MarkmBha
1 / 5 (3) May 10, 2013
Very interesting article!
Torbjorn_Larsson_OM
3 / 5 (2) May 10, 2013
This combines with the recent observation of volatile poor terrestrial material like our own habitable planets (Earth, early Mars) outside our system, by seeing terrestrial bodies hit and pollute white dwarfs.

Having the first observations being volatile poor should mean that dry habitables are common, despite the Kepler observations of mostly water worlds. There is a selection bias in Kepler observations since water worlds have larger radius (lower density). Maybe that is what we are seeing akin to the early hot Jupiters of Kepler.

[ http://www.univer...-hyades/ ]

Together this hints that once dry planets can stay dry, despite being bombarded by clearing debris disks and developing Oort clouds (giant migration, late bombardment et cetera).
Torbjorn_Larsson_OM
3 / 5 (2) May 10, 2013
Re volatile escape during the collision, I am starting to wonder if the recent collision scenario where Tellus [suggested protoplanetary name by geologists clearing up the terminology of the early planetary system] and Theia are similar size bodies is promoted by the problem. Like the Vesta first collision in the Rheasilvia area, the Veneneia crater, they would make a low-velocity essentially non-rotational collision, presumably going relatively easy on the volatiles in respect to the gravity well involved.

If protoplanet Vesta was accreted to be non-rotational on average, why not protoplanets Tellus & Theia? And we might say the same about virtually non-rotating Venus. I hope collision modelers can hash these questions out relatively soon, now that they have promising leads on the possible dynamics.
Torbjorn_Larsson_OM
3 / 5 (2) May 10, 2013
@Yellowdart: I'm not sure I understand your question.

The science question here is where the volatiles comes from as the Earth, or similar terrestrials, accreted.

The hot protoplanetary disk has a so called ice line, outside of which water is plenty such as on ice moons. Chondrites have some ~ 10 % water by mass, while Earth/Moon/Mars has some ~ 0.05 %. Our terrestrials are also carbon poor, there is a similar tar line and again chondrites are filled with it.

Luckily, or our planets would drown in water (water worlds) and/or have metals locked beneath a 30 % carbon/diamond crust (putative carbon worlds). In an earlier comment I noted that this seems to be a general regime, despite Kepler's early finds of many water worlds (by composition).

Another source would be water locked within protoplanetary minerals. This paper may kill that theory, making our water balance hinge not on late bombardment luckily but on late accretion. The debris clearing rate were larger then, makes sense.
Torbjorn_Larsson_OM
3 / 5 (2) May 10, 2013
@yep: Actually the Sun removes water by UV dissociation and then solar wind sputtering of hydrogen (most likely), cf Venus. Our magnetic field protects us from that, but the geodynamo didn't arise until the planet was well differentiated (had an established hot core and a mantle with thermal convection movements).

@Howhot: I wish people stopped thinking of our terrestrials as "lots of water". They are, luckily, water poor in comparison with almost all other solid bodies.

As for our Moon being unique, it isn't. It is believed the martian Moons, and some deorbited equatorial elliptic craters, are the remains of a similar late collision which didn't make one large accretionary body.

But the best analogs are all the many debris disk binaries, which often are results of similar collisions. In fact, the even more striking Pluto/Charon system with all its moons are a good duplicate.

@verkle: Not many hypotheses tests out good and remains as observations. This likely did, bar errors.
Fedot5
1 / 5 (4) May 10, 2013
Имеет право на существование и такая версия формирования Земли. Около 4,5 миллиарда лет назад сформировавшиеся Марс, Земля и Венера были одинаковы по составу и приблизительно по размерам. Но ввиду того что в то время орбиты всех планет солнечной системы были эллиптическими с планетой Земля столкнулась планета (либо спутник) группы Юпитера (Сатурна) типа современной Европы в 2-3 раза меньше Земли. В результате лобового столкновения ядро меньшего объекта врезалось в ядро Земли вытолкнув в результате инерции силы удара часть ядра Земли и сернокислую атмосферу на орбиту и образовав выступ магмы с противоположной стороны удара который в последствии стал так называемой Пангеей.. Ледяная азотная и водная оболочки планеты которая столкнулась с Землей окутала поверхность Земли и в результате разницы температур сформировался океан воды и атмосфера а выступ (Пангея) постепенно под действием протяжения и тектонических процессов стал раскалываться… Часть ядра выбитая в результате удара не смогла упасть обратно на Землю, осталась на орбите и сформировалась в спутник Земли Луну и ввиду того что самая тяжелая часть Луны оказалась повернутой к Земле то и вращение вокруг оси синхронизировалось с вращением Земли а также повернутая к Земле часть Луны более гладкая чем обратная сторона и более тяжелая что обуславливает ее ударное происхождение и нынешнее положение на орбите Земли. Эта версия также обьясняет то что более тяжелые элементы в результате такого сильного столкновения оказались частично вытолкнутыми и распыленными в более верхних слоях планеты Земля и ее спутника Луны и человек имеет возможность доступа к ним. Также наличие драгоценных камней в относительно верхних слоях поверхностного слоя твердого базальта свидетельствуют о ударном их происхождении.