We measured the ratio of semi-heavy to normal water and found that the ratio was very similar to ratios found in comets as well as the ratios found in younger protostar systems. The data revealed a strong signature of semi-heavy and normal water coming from V883 Ori’s proto-planetary disk. In 2021, the Atacama Large Millimeter/submillimeter Array took measurements of V883 Ori for six hours. Saxton (NRAO/AUI/NSF), CC BY Completing the water trail The proto-planetary disk around V883 Ori contains gaseous water, shown in the orange layer, allowing astronomers to measure the ratio of semi-heavy to normal water. V883 Ori emits 200 times more energy than the Sun, and my colleagues and I recognized that it was an ideal candidate to observe the semi-heavy to normal water ratio. Using the Atacama Large Millimeter/submillimeter Array, a powerful radio telescope in northern Chile, we discovered a large, warm proto-planetary disk around the Sunlike young star V883 Ori, about 1,300 light years from Earth in the constellation Orion. Due to this higher energy output, the proto-planetary disks around FU Orionis stars are heated to much higher temperatures, turning ice into water vapor out to large distances from the star. FU Orionis stars are unique because they consume matter about 100 times faster than typical young stars and, as a result, emit hundreds of times more energy. Most young stars consume matter from the proto-planetary disks around them.
It is possible to detect semi-heavy and normal water when water is a gas unfortunately for astronomers, the vast majority of proto-plantary disks are very cold and contain mostly ice, and it is nearly impossible to measure water ratios from ice at interstellar distances.Ī breakthrough came in 2016, when my colleagues and I were studying proto-planetary disks around a rare type of young star called FU Orionis stars. Doing so has proved to be incredibly difficult. To truly determine where the water on planets comes from, astronomers needed to find a goldilocks proto-planetary disk – one that is just the right temperature and size to allow observations of water. Earth’s ratio sits somewhere in between the inheritance and reset ratio, making it unclear where the water came from.
Saxton (NRAO/AUI/NSF), CC BY Measuring water during the formation of a planetĬomets have a ratio of semi-heavy to normal water almost perfectly in line with chemical inheritance, meaning the water hasn’t undergone a major chemical change since it was first created in space. V883 Orionis is a young star system with a rare star at its center that makes measuring water in the proto-planetary cloud, shown in the cutaway, possible. This difference means that by measuring the ratio of semi-heavy to normal water in a place, astronomers can tell whether that water went through the chemical inheritance or chemical reset pathway. Chemical models and experiments have shown that about 1,000 times more semi-heavy water will be produced in the cold interstellar medium than in the conditions of a protoplanetary disk. The ratio of semi-heavy to normal water is a guiding light on the water trail – measuring the ratio can tell astronomers a lot about the source of water. Semi-heavy water is made of one oxygen atom, one hydrogen atom and one atom of deuterium – a heavier isotope of hydrogen with an extra neutron in its nucleus. Water is normally made of two hydrogen atoms and one oxygen atom. To test these theories, astronomers like me look at the ratio between normal water and a special kind of water called semi-heavy water. Dirk Hünniger/Wikimedia Commons, CC BY-SA
Normal hydrogen, or protium, does not contain a neutron in its nucleus, while deuterium contains one neutron, making it heavier.
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