This artist’s impression shows the planet-forming disc around the star V883 Orionis. In the outermost part of the disc water is frozen out as ice and therefore can’t be easily detected. An outburst of energy from the star heats the inner disc to a temperature where water is gaseous, enabling astronomers to detect it. Credit: ESO/L. Calçada

How did water move from young stars to comets in our Solar System? A new paper looking at a planet-forming disc more than 1000 light years away, has found the ‘missing link’ in our understanding of the Solar System.

“We can now trace the origins of water in our Solar System to before the formation of the Sun,” says John Tobin, National Radio Astronomy Observatory astronomer.

“V883 Orionis is the missing link.”

V883 Orionis is a ‘protostar’ in the earliest stages of star creation, and is still hoovering up dust from its outer disc.

This disc, which will eventually form planets, comets and other celestial objects, has some striking similarities to the Solar System – if the Solar System hadn’t yet formed planets.

“The composition of the water in the disc is very similar to that of comets in our own Solar System,” says Tobin. 

“This is confirmation of the idea that the 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.”

The ‘normal’ water that you or I would drink has one oxygen and two hydrogen atoms. But there’s another, heavier form of water where one of the hydrogens is replaced with a heavier isotope of hydrogen called deuterium.

ALMA images of the disc around the star V883 Orionis, showing the spatial distribution of water (left, orange), dust (middle, green) and carbon monoxide (blue, right). Credit:
ALMA (ESO/NAOJ/NRAO), J. Tobin, B. Saxton (NRAO/AUI/NSF)

The mixture of heavy and normal water can give us clues about when the water was formed.

With discs normally being so cold though, the water is usually frozen, and less easily analysed.  

But V883 Orionis is much hotter than most discs due to a dramatic outburst of energy from the protostar.

The disc was heated “up to a temperature where water is no longer in the form of ice, but gas, enabling us to detect it,” says Tobin.

The researchers used the ALMA, an array of radio telescopes in northern Chile, to detect the water, and were able to show that the journey of water between young protostars and comets.

Quelle:COSMOS