(WHTM) — At some point in your education, you probably had that “just think” learning moment-“Just think, some of the molecules in the water you just drank may have been drunk by–
-George Washington”
–Julius Ceasar”
—a Wooly Mammoth”
—-a Tyrannosaurus Rex.”
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The point of this exercise is to impress upon us that the water on our planet has been here a long, long time. But how long? And how did it get here in the first place? Well, recently some new observations made by the European Southern Observatory (ESO), and published on March 8 in Nature, brought us closer to answers to both questions. “We can now trace the origins of water in our Solar System to before the formation of the Sun,” says John J. Tobin, an astronomer at the National Radio Astronomy Observatory, USA, and lead author of the study.
This image shows an aerial view of the Chajnantor Plateau, located at an altitude of 5000 meters in the Chilean Andes, where the array of ALMA antennas is located. The large antennas have a diameter of 12 metres, while 12 smaller antennas with a diameter of 7 metres make up the ALMA Compact Array (ACA). On the horizon, the main peaks from right to left are Cerro Chajnantor, Cerro Toco, and Juriques. This photo was taken in December 2012, four months prior to the ALMA inauguration. (European Southern Observatory) 
Antennas of the Atacama Large Millimeter/submillimeter Array (ALMA), on the Chajnantor Plateau in the Chilean Andes. The Large and Small Magellanic Clouds, two companion galaxies to our own Milky Way galaxy, can be seen as bright smudges in the night sky, in the centre of the photograph. (European Southern Observatory) 
This chart shows the location of the young star V883 Orionis in the famous constellation of Orion. Most of the stars visible to the naked eye on a clear dark night are plotted. The location of V833 Orionis is marked with a red circle. This star is very faint and needs a large amateur telescope to be seen visually. It is very close in the sky, and physically associated with, the huge and brilliant Orion Nebula just to the north-west. (European Southern Observatory) 
This artist’s impression shows the planet-forming disc around the star V883 Orionis. In the outermost part of the disc water is frozen out as ice and therefore can’t be easily detected. An outburst of energy from the star heats the inner disc to a temperature where water is gaseous, enabling astronomers to detect it. (European Southern Observatory) 
ALMA images of the disc around the star V883 Orionis, showing the spatial distribution of water (left, orange), dust (middle, green) and carbon monoxide (blue, right). 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. (European Southern Observatory) 
This artist’s impression shows the planet-forming disc around the star V883 Orionis. In the outermost part of the disc water is frozen out as ice and therefore can’t be easily detected. An outburst of energy from the star heats the inner disc to a temperature where water is gaseous, enabling astronomers to detect it. The inset image shows the two kinds of water molecules studied in this disc: normal water, with one oxygen atom and two hydrogen atoms, and a heavier version where one hydrogen atom is replaced with deuterium, a heavy isotope of hydrogen. (European Southern Observatory) 
This diagram illustrates how a cloud of gas collapses to form a star with a disc around it, out of which a planetary system will eventually form. (European Southern Observatory) 
Antennas of the Atacama Large Millimeter/submillimeter Array (ALMA), on the Chajnantor Plateau in the Chilean Andes. The Large and Small Magellanic Clouds, two companion galaxies to our own Milky Way galaxy, can be seen as bright smudges in the night sky, in the centre of the photograph. (European Southern Observatory)
The ESO operates multiple telescope arrays in the Atacama Desert in Chile. One of these is ALMA, the Atacama Large Millimeter/submillimeter Array, a group of radio telescopes. Recently astronomers focused this array on V883 Orionis, a star in the constellation Orion about 1300 light-years away. The star is in the process of forming a solar system; it’s surrounded by a disk of gas and dust which is slowly clumping into solar system-type stuff-comets, asteroids, and ultimately planets. A large part of this disk is water.
The ALMA observations revealed the water circling V883 Orionis comes in two varieties-standard, ordinary “simple” water made of two atoms of Hydrogen and one atom of oxygen, and “heavy” water, where one of the hydrogen atoms is replaced with deuterium — a heavy isotope of hydrogen. The two varieties form under different conditions, so measuring the ratio between the two can help trace when and where the water was formed. In the case of our own Solar System, this ratio in some comets is similar to that in water on Earth, suggesting that comets might have delivered water to our planet.
Astronomers have observed the journey of water from clouds to young stars, and from comets to planets, but until now they didn’t really know how water moved from young stars to comets. “V883 Orionis is the missing link in this case,” says Tobin. “The composition of the water in the disc is very similar to that of comets in our own Solar System. This is confirmation of the idea that 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.”
Observing the water wasn’t easy. Water in a gaseous form is detected by ALMA from radiation emitted by molecules as they spin and vibrate, But if the water is actually frozen, the molecules vibrate less and are harder to detect. Gaseous water is mostly near the center of the disc, warmed by the star-but it’s hidden by the dust disc itself.
But the V883 Orionis disc, as it turns out, is unusually hot. Energy from the star heats the disc, “up to a temperature where water is no longer in the form of ice, but gas, enabling us to detect it,” says Tobin. Thanks to this warmth, and the sensitivity of ALMA, the scientists could detect the water, determine its composition, and map its distribution in the disc, which as it turns out has at least 1200 times the amount of water in all Earth’s oceans.
For future studies, astronomers are planning observations with another ESO telescope that’s still under construction, the ELT (Extremely Large Telescope), described by ESO as “the world’s biggest eye on the sky”, and its Mid-Infrared ELT Imager and Spectrograph (METIS). According to ESO, “This instrument will be able to resolve the gas-phase of water in these types of discs, strengthening the link of water’s path all the way from star-forming clouds to solar systems.”
