Water is older than the Sun, finds new study

NEW DELHI: Over half of the water in our Solar System, found on Earth, and in various planets, their moons, comets and asteroids, existed from before our Sun was born 4.5 billion years ago, finds a new study published in the journal Science.This has huge implications for the search for extraterrestrial life because ancient frozen water would have originated in inter stellar space and could have carried molecules of precursors to life. It would have seeded several cosmic bodies with these precursors.

"Our findings show that a significant fraction of our Solar System's water, the most-fundamental ingredient to fostering life, is older than the Sun, which indicates that abundant, organic-rich
interstellar ices should probably be found in all young planetary systems," said Conel Alexander of the Carnegie Institute for Science who was part of the team.

How did the scientists find out where water originated and whether it predated Sun or not? The team led by L. Ilsedore Cleeves from the University of Michigan studied hydrogen and its heavier isotope deuterium. Isotopes are atoms of the same element that have the same number of protons but a different number of neutrons. The difference in masses between isotopes results in subtle differences in their behavior during chemical reactions. As a result, the ratio of hydrogen to deuterium in water molecules can tell scientists about the conditions under which the molecules formed.

There are about 26 deuterium atoms for every million hydrogen atoms across the universe, but it is six times as prevalent in the water on Earth and in other solar system bodies. The scientists found that this could happen only under very special conditions - very low temperatures (just a few degrees above absolute zero, that is, -273 degrees C), oxygen and ionizing radiation. These conditions are available only in the interstellar medium that pervades space.

To find out whether the same process of deuterium enrichment could happen in the rubble surrounding the new born Sun, the team created models that simulated a protoplanetary disk in which all the deuterium from space ice has already been eliminated by chemical processing, and the system has to start over "from scratch" at producing ice with deuterium in it during a million-year period. They did this in order to see if the system can reach the ratios of deuterium to hydrogen that are found in meteorite samples, Earth's ocean water, and "time capsule" comets. They found that it could not do so, which told them that at least some of the water in our own Solar System has an origin in interstellar space and pre-dates the birth of the Sun.