Water molecules on Earth are older than the Sun

(ORDO NEWS) — Astronomers have determined that water molecules travel from the interstellar medium directly into protoplanetary disks around young stars, and then into icy bodies such as comets, which can carry them to planets.

Thus, water molecules in the solar system, including on Earth, arose in the interstellar medium even before the formation of the sun.

Water is important not only for the emergence and existence of life forms known to us, but also for the processes of formation of stars and planets.

Scientists have long been interested in the entire journey of water molecules, which begins in interstellar clouds of gas and dust, and ends on the surfaces and atmospheres of planets.

It can help to understand it by measuring the ratio of heavy water molecules (HDO) to ordinary water (H2O) in nebulae, young stars and small bodies of the solar system, which will provide information about where certain water molecules were formed.

However, for a long time, the problem was the observation of water molecules in protoplanetary disks around young stars, since water vapor, which is quite easy to detect, is observed only within a narrow snow line (less than 10 astronomical units from the star), and behind it turns into ice on the surface of dusty stars. particles, which are already much more difficult to detect.

A team of astronomers led by John J. Tobin of the US National Radio Astronomy Observatory has published measurements of the HDO/H2O content in the protoplanetary disk around the sun-like protostar V883 Orionis using the ALMA radio telescope system.

V883 Orionis has a mass of 1.3 solar masses, is about half a million years old, and lies 1,300 light-years from the Sun. The disk around the star has a mass of 0.02-0.09 solar masses, dust and gas radiation is recorded up to 125 and 320 astronomical units from the star, respectively.


The researchers directly registered the emission of HDO and H218O molecules in the gas phase in the disk.

This became possible due to the fact that about 130 years ago the system experienced an outburst of accretion of matter onto a protostar, due to which its luminosity increased to 200 solar luminosities, and most of the disk heated up above the sublimation temperature of water.

Thanks to this, the snow line for water was at a distance of 40-120 astronomical units from the star.

Water molecules on Earth are older than the Sun 3
Diagram of the structure of a typical protoplanetary disk around a star of solar luminosity (a) and a disk around the star V883 Orion (b)

The radius of the snow line for water measured in the current work was about 80 astronomical units from the star.

The total mass of water vapor in the protoplanetary disk is equivalent to about 1200 masses of all the Earth’s oceans, and this is the lower limit, since water molecules at a distance of less than 40 astronomical units from the star and in the form of ice in the outer part of the disk are not taken into account.

The HDO/H2O ratio in the disk around V883 Orionis was (2.26±0.63)×10–3.

This value is comparable with the values ​​obtained for the shells of protostars and comets of the Solar System, and exceeds the value obtained for the Earth’s oceans.

This means that both water, methanol, and deuterated particles are formed in the icy mantle of dust particles in the interstellar medium even before the formation of a star, and during the formation of a protoplanetary disk or comets, there is no significant chemical change of these molecules, enclosed in ice, which then falls into composition of comets, planetesimals or asteroids.

In the case of the solar system, this means that water molecules originated in the cold interstellar medium before the formation of the sun, and then entered the disk around it, from which comets and planets formed.


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