A star 1,300 light-years from Earth may have just revealed one of the solar system’s best-kept secrets.
It’s called V883 Orionis, a young star surrounded by a huge disk of material that will one day merge into orbiting planets. It was in this disk that scientists made an unambiguous detection of water vapor, swirling along with all the other dust and gases destined to become part of an extraterrestrial world.
This suggests that water in the solar system – including that currently on Earth – was present in the gaseous cradle from which the Sun was born; that it was here, not only before the earthbut before the Sun, and helped our planet to develop.
“We can now trace the origins of water in our solar system to before the formation of the Sun,” says astronomer John Tobin from the US National Radio Astronomy Observatory.
Water is fairly common throughout the Universe, although Earth in particular would not be the same”pale blue dot” without it. It wraps around the surface of the planet, permeates the atmosphere as vapour, falls from the sky. It seems quite commonplace to us, but we could not live without it; almost all the chemical processes of life demands it.
It is also an important ingredient in the formation of planets. Stars are born from clouds of dust and gas in space; a dense clump collapses under gravity and, as it spins, begins to roll up more material from the cloud around it which forms into a disk that powers the small star.
After the star has finished growing, all other features of the planetary system form from what remains of the disk. The dust grains stick together electrostatically, forming larger and larger clumps until the object is massive enough for gravity to take over.
Water is thought to play a important role in this process; beyond the point at which the water vapor freezes – called the snow line – it coats the dust grains as ice, giving them a extra grip which helps particles cling together in the very early stages of planetary growth.
We can measure where and how water forms from hydrogen isotopes. Normal hydrogen has no neutrons in its nucleus. Heavy hydrogen, also known as deuterium, has a neutron in its nucleus. Water molecules containing heavy hydrogen are called heavy water and form under different conditions than normal water.
Here on Earth, we can trace water to comets because the water/heavy water isotope ratios are similar. This suggests that water can be bound in comets and asteroids and delivered to planetary bodies. But how water got into comets had not yet been fully explained. Now, by studying V883 Orionis, Tobin and his team have filled that gap.
“We can think of the path of water through the Universe as a trail. We know what the ends look like, which is the water on planets and in comets, but we wanted to trace that trail back to the origins. some water”, Tobin says.
“We used to be able to relate Earth to comets and protostars to the interstellar medium, but we couldn’t relate protostars to comets. V883 Ori changed that and proved that water molecules in this system and our solar system have a similar ratio of deuterium and hydrogen.”
The star is so young that it is still growing, surrounded by a huge disc. By studying the light emitted by this disc, the researchers were able to identify the spectral signature of water vapour; even better, they identified the isotopic ratios of hydrogen.
“V883 Orionis is the missing link in this case,” Tobin says.
“The composition of the water in the disk is very similar to that of comets in our own solar system. This confirms the idea that water in planetary systems formed billions of years ago. years, before the Sun, in interstellar space, and was inherited by both comets and Earth, relatively unchanged.”
What makes the V883 Orionis so special is that it has undergone an accelerated growth spurt, which means it is temporarily warmer than usual. Most of the water in accretion disks around protostars is frozen, existing as vapor only near the star, where it is difficult to distinguish. The burst of activity from V883 Orionis, however, pushed his snow line at a point much farther from the star than usual; any water closer than this snow line is steam.
Steam is much easier to detect and analyze than ice, so the researchers were able to make a reliable measurement of the isotopic composition of water in the disk of Orionis V883, as well as quantify it. There are over 1,200 times the volume of Earth’s oceans, drifting as vapor around V883 Orionis.
The results suggest that all the water in a planetary system comes almost directly from the clouds from which its star originated.
“We conclude that the disks directly inherit water from the star-forming cloud and that this water becomes incorporated into large icy bodies, such as comets, without substantial chemical alteration,” the researchers write in their article.
“Although the specific mechanism for bringing water to Earth remains debated (comets and/or asteroids), the [hydrogen isotope ratio] found in V883 Ori is proof that water molecules in our solar system originated in the cold interstellar medium before the Sun was formed. Therefore, space-resolved observations of water to young planet-forming disks are crucial for linking the water reservoir and the formation of terrestrial planets.”
The research has been published in Nature.