Discovery of Ancient Water in Planet-Forming Disks

Scientists have provided new evidence that the water found in planet-forming disks around young stars may be older than the stars themselves, possibly originating in the cold, dark molecular clouds from which these stars were born. The discovery of heavy water in the planet-forming disk around the star V883 Orionis is a significant scientific achievement in understanding the origins of water in the universe.

What is Heavy Water?

Ordinary water consists of two hydrogen atoms and one oxygen atom. However, some hydrogen atoms have an additional neutron in their nucleus, making them an isotope known as deuterium. As a result, heavy water contains two deuterium atoms instead of two regular hydrogen atoms.

Heavy water exists in our solar system, for example in comets, and the ratio of heavy water to ordinary water in a cometary body can reveal its formation history. Scientists believe that the discovery of heavy water in the disk surrounding V883 Orionis provides evidence that the water in this region may be older than the star itself.

The Role of ALMA in the Discovery

Scientists were able to detect heavy water in the disk of the star V883 Orionis using the ALMA radio telescope array located in Chile. The star is 1,350 light-years away and is part of a group of stars that originated from the famous Orion Nebula.

Observations showed that the ratio between heavy water and ordinary water in the V883 Orionis disk matches the ratios found in molecular gas clouds before the formation of stars or planets. This ratio is much higher than expected if the water had been broken down and reformed in the disk.

Significance of the Discovery

This discovery is an important step in understanding the journey water takes during the planet formation process. It demonstrates that the water we see in planet-forming disks may be older than the central stars, having formed in the early stages of star and planet formation.

The water discovered could be billions of years older than the star V883 Orionis, having existed in the molecular cloud that later became the Orion Nebula. No planets have been discovered in the disk yet, but the high ratio of heavy water suggests that any comets formed may reflect this ratio, indicating that the water has not been thermally processed in the disk.

Conclusion

The discovery of heavy water in the planet-forming disk around V883 Orionis provides strong evidence that water in our solar system may be older than we think, originating in ancient molecular clouds before the formation of stars and planets. This discovery represents a missing link between molecular clouds and planet-forming disks, offering a deeper understanding of how water transitions through the stages of star and planet formation and eventually reaches Earth.