A star 1,300 light-years from Earth could have revealed one of the best-kept secrets in the Solar System.
It’s called V883 Orionis, a young star surrounded by a huge disk of material that will one day coalesce into orbiting planets. It is in that disk that scientists have made an unequivocal detection of water vapor, swirling with all the rest of the dust and gas destined to become part of an alien world.
This suggests that water in the Solar System, including that now found on Earth, was present in the gaseous cradle from which the Sun was born; that it was here, not just before Earth, but before the Sun, and helped our planet grow.
“We can now trace the origins of water in our Solar System before the formation of the Sun,” says astronomer John Tobin of the US National Radio Astronomy Observatory.
Water is fairly common throughout the Universe, though Earth in particular wouldn’t be the same “pale blue dot” without it. It coils around the planet’s surface, permeates the atmosphere as vapor, falls from the sky. It seems mundane enough to us, but we couldn’t live without it; almost all the chemical processes of life require 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, spinning, begins to accumulate more material from the surrounding cloud that forms a disk that feeds the baby star.
Once the star is done growing, all other features of the planetary system form from what is left of the disk. Dust grains stick together electrostatically, forming larger and larger clumps until the object is massive enough for gravity to take over.
We can measure where and how water forms based on isotopes of hydrogen. Normal hydrogen does not have neutrons in its nucleus. Heavy hydrogen, also known as deuterium, has a neutron in its nucleus. Water molecules that include heavy hydrogen are known as heavy water, and they form under conditions that differ from those that produce normal water.
Here on Earth, we can trace some water back to comets because the isotope ratios of water to heavy water are similar. This suggests that water may be trapped in comets and asteroids and delivered to planetary bodies. But how the water got to the comets had not yet been fully explained. Now, by studying the 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 endpoints look like, which is water on planets and comets, but we wanted to trace that path back to the origins of water.” Tobin says .
“Before now, we could link Earth to comets and protostars to the interstellar medium, but we couldn’t link protostars to comets. V883 Ori has changed that and has shown that water molecules in that system and in our Solar System have a similar ratio of deuterium to hydrogen.”
The star is so young that it is still growing, surrounded by a huge disk. By studying the light emitted by that disk, the researchers have been able to identify the spectral signature of the water vapor; even better, they have identified the hydrogen isotope ratios.
“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 is confirmation of the idea that water in planetary systems formed billions of years ago, before the Sun, in interstellar space, and has been inherited by both comets and Earth relatively unchanged. ”.
What makes the V883 Orionis so special is that it has undergone a growth spurt, which means it is temporarily hotter than usual. Most of the water in the accretion disks around protostars is frozen, existing as a vapor only near the star, where it is difficult to distinguish. However, V883 Orionis’s burst of activity has pushed its snow line out to a point much farther from the star than usual; any water closer to that 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 the water in V883 Orionis’ disk, as well as quantify it. There are more than 1,200 times the volume of Earth’s oceans, drifting as steam around V883 Orionis.
The findings suggest that all the water in a planetary system comes almost directly from the clouds from which its star is born.