Sunday, March 12, 2023

3913 - WATER - how did it arrive on Earth?

 

-   3913  -    WATER  -   how did it arrive on Earth?  In the early Earth formation with the planets it was too close and hot for water to exists on the surface.  We believe that water came later arriving from asteroids and space itself.


------------  3913  -     WATER  -   how did it arrive on Earth?

-    Astronomers have detected an abundance of water in the form of gas in a disk of planet-forming material that surrounds a distant star. The disk appears to contain hundreds of times more water than in all of Earth's oceans.

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-   The discovery could give clues as to how water moves from star-forming clouds of gas and dust to planets, and could also indicate that Earth's water may be older than the sun.

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-   The is a result of observations of “V883 Orionis”, an infant star or "protostar" located around 1,300 light-years from Earth in the Orion constellation using the Atacama Large Millimeter/submillimeter Array (ALMA) in Northern Chile.

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-    We can now trace the origins of water in our solar system to before the formation of the sun.   Astronomers studied a heavier version of water in the disk of gas and dust around the young star which will one day collapse to create planets, comets, and asteroids.

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-    Instead of the usual composition of one oxygen atom and two hydrogen atoms in heavy water, the hydrogen atoms are replaced with deuterium, a hydrogen isotope that contains a proton and neutron in its nucleus rather than just a proton.

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-    Because heavy water forms differently than traditional water, it can be used to trace when and where water is formed. A similar technique has previously been used to determine that the water / heavy water ratio on Earth is the same as that of the wider solar system, implying water may have been delivered to our planet via comets.

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-   A "path" for water is from massive clouds of gas and dust that collapse to form stars, to the planetary disks that grow around these infant stars and eventually birth planets, asteroids and comets, and finally presumably to those objects themselves.

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-    Water's journey from star-forming clouds to the clouds themselves has been observed in the past, as has the transfer of water from comets to planets, but the link that sees waters move from around stars to comets has been missing until now.

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-    The composition of the water in the disk is very similar to that of comets in our own solar system.  The water in planetary systems formed billions of years ago, before the sun, in interstellar space, and has been inherited by both comets and Earth, relatively unchanged.

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-    One of the reasons that this connection in the journey of water may have been unobserved is that water exists in the form of ice while found in planet-forming disks of gas around young stars, and is thus hidden from view. This is because water in the form of gas can be spotted via the radiation it emits as its molecules vibrate, but the motion of these molecules is far more subdued when water is frozen solid.

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-    The problem is complicated further by the fact that water in its gas form is more common at the heart of these disks closer to the warmth of the central star, but here its emissions are obscured by the dust in the disk. These regions are also too small to be spotted with current telescopes.

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-    Astronomers were able to side-step these difficulties in this case because the disk of V883 Orionis is usually hot as a result of dramatic outbursts from the central protostar heating it. This brings the temperature up to the point at which water is no longer in the form of ice but is gaseous even in more distant regions and is therefore detectable.

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-     Because water freezes out at higher temperatures than carbon monoxide, it can only be detected in gaseous form closer to the star. The apparent gap in the the water and carbon monoxide images is actually due to the bright emission of the dust, which attenuates the emission of the gas.

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-    The sensitivity of ALMA, which is comprised of 66 radio telescope antennas spread across the Atacama Desert, not only allowed the team to spot gaseous water around V883 Orionis but also let them determine the composition of the water and its distribution. This showed that the disk contains no less than 1,200 times the water found in all of Earth's oceans combined.

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-    Following anothr theory involved samples from asteroid Itokawa collected by a Japanese space probe suggest that Earth's water may have been created by the sun. This water may have rained on the fledgling Earth in the form of dust grains produced by the interaction of the solar wind, the stream of charged particles emanating from the sun, with various bodies in the solar system.

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-    The solar winds are streams of mostly hydrogen and helium ions which flow constantly from the sun out into space.  When those hydrogen ions hit an airless surface like an asteroid or a spaceborne dust particle, they penetrate a few tens of nanometers [one inch has 24.5 million nanometers] below the surface, where they can affect the chemical composition of the rock.

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-    Over time, this space weathering effect of the hydrogen ions can eject enough oxygen atoms from materials in the rock to create water, which remains locked within the asteroid.

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-    This mechanism may be the missing link explaining the abundance and chemical composition of water on Earth that has long baffled scientists. Earth's surface is 70% covered with water.

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-  That's much more than any other planet in the solar system. But none of the existing theories can fully explain all of it. A dominant view suggests that asteroids rich in carbon, which pummeled the young Earth some 4.6 billion years ago, delivered this water to the planet.

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-  But detailed chemical analysis of meteorites known as carbonaceous chondrites, which are chunks of these carbon-rich asteroids, revealed that the water locked inside them doesn't quite match the chemical fingerprint of Earth's water.

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-   This discrepancy in what scientists call “isotopic composition” led researchers to believe that there must be at least one additional source of our planet's life-giving liquid.

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-     Isotopes are forms of chemical elements that differ just by the number of uncharged neutrons they contain. The carbonaceous chondrites tend to have water that contains more deuterium, a form of hydrogen with one neutron, while Earth's hydrogen is mostly a lighter form called protium that has no neutrons.

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-     Researchers analyzed the composition of a rocky type of asteroid rich in silicon oxide using a technique called the “atom probe tomography”.   The researchers measured the atomic structure of these grains one atom at a time to detect individual water molecules.

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-    The samples analyzed in this study came from the asteroid Itokawa, famously visited by the Japanese probe Hayabusa, which delivered tiny pieces of this space rock to Earth in 2010.

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-  Their technique lets scientists take an incredibly detailed look inside the first 50 nanometers [one inch has 24.5 million nanometers] or so of the surface of dust grains on Itokawa, which orbits the sun in 18-month cycles. This allowed them to see that this fragment of space-weathered rim contained enough water that, if we scaled it up, would amount to about 4.4 gallons for every cubic meter [35 cubic feet] of rock.

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-   This strongly suggests that fine-grained dust, buffeted by the solar wind and drawn into the forming Earth billions of years ago, could be the source of the missing reservoir of the planet's water.

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-   The findings also suggest that water might be locked in the surface rocks of many space bodies, including the moon and asteroids. If so, this could be good news for future human exploration in deep space, as necessary supplies might be easier to find than scientists fear.

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-   One of the problems of future human space exploration is how astronauts will find enough water to keep them alive and accomplish their tasks without carrying it with them on their journey.

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-    We think it's reasonable to assume that the same space weathering process which created the water on Itokawa will have occurred to one degree or another on many airless worlds.  That could mean that space explorers may well be able to process fresh supplies of water straight from the dust on the planet's surface.

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-  I guess I can dispense with my boy scout canteen.  I did not carry much water anyway. 

                   March 11, 2023         WATER  -   how did it arrive on Earth?            3913                                                                                                                          

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