- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
-
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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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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