Even now, theories and hypotheses on the origins of water in our solar system are being revised and debated. However, a fundamental understanding of the dynamic history of water in the Solar System is helpful. The following is a brief review of some of the most recent hypotheses that have acquired some traction among researchers in the field.

Water molecules such as H2O have likely been present in the universe since the earliest stars burned out and discharged oxygen into the interstellar medium, if not earlier.

Indeed, H2O is widely believed to be one of the most common interstellar molecules. Hydrogen and helium would make up the great majority (>99 percent) of the material in the early solar nebula. Because the water was mostly frozen at this time, it would have experienced the same inward migration, increase in pressures and temperatures, as all other nebula components at this stage of its development.

During the process of star creation, water and ice would have been vaporized and propelled outwards, perpendicular to the sun’s rotation, to higher heliocentric distances as temperatures increased. Eventually, it would have gotten close enough to Jupiter’s current distance of 5.2 AU that it might start condensing again. It is possible that the so-called “snow line,” which was occupied by a huge number of icy planets, was responsible for Jupiter’s speedy early development.

These comets, which had managed to escape Jupiter’s expanding gravitational pull, could therefore have played an important part in the distribution of water in the nascent Solar System, which at this point was virtually dry. There is a possibility that Jupiter’s gravitational pull may have dispersed some, while others have returned to the inner Solar System.

Water may have been redistributed to the inner regions of the Solar System where terrestrial planets were developing due to a drag effect operating on larger frozen bodies that caused them to halt and fall inwards towards the sun and migration of the snow line inwards to at least 3 AU. Many of the bodies in the inner Solar System, from asteroids to planets, now contain water that was once part of a far more active water cycle.

The distribution of deuterium in the solar system is greatly influenced by the water circulation record. Ion-molecular chemistry in the cold of interstellar space enriches water from the interstellar medium (ISM) in deuterium [5]. Deuterium, on the other hand, is depleted in stars, resulting in a pool of hydrogen around the sun that can be exchanged for water vapor.

[6] The deuterium content of water migrating from the central portions of the forming Solar System may consequently be reduced, resulting in a separate population of comet-like entities [6]. Using D/H measurements to determine the source of water on either Earth or Mars can be difficult because of the wide range of deuterium enrichment observed in other Solar System worlds. Water’s oxygen isotopic composition is a three-isotope system, rather than a two-isotope system, which makes it a more strong geological indicator. This allows us to distinguish between typical fractionation/homogenization processes and the preservation of original isotopic heterogeneity by the presence of three isotopes.