(Paris) The ALMA radio astronomy telescope has provided the first detailed images of water molecules in the disk where planets can form from the very young star HL Tauri, according to a study Thursday.
Posted at 7:17 am
Pierre CELERIER Agence France-Presse
“I never thought that we could get an image of an ocean of water vapor in the exact region where a planet could probably form,” commented Stefano Facchini, an astronomer at the University of Milan and lead author of the study published in Nature Astronomy.
Located in the constellation Taurus and very close to Earth at “only” 450 light-years, HL Tauri, twice as massive as the Sun, has long been in the crosshairs of terrestrial and space telescopes.
Because its proximity and its youth – a million years at most – offer a breathtaking view of its protoplanetary disk, the mass of gas and dust that surrounds a star and allows planets to form.
According to theoretical models, this formation process would be particularly fruitful at a very specific point on the disk: the ice line. Where water, which is in the form of vapor near the star, turns into a solid state when cooled. The layer of ice that covers them would make the dust grains coagulate all the more easily.
Already in 2014, ALMA had created unprecedented images of the protoplanetary disk, which showed an alternation of bright rings and dark furrows. The latter would reveal the presence of embryos of planets formed by dust accumulation.
Ice line
Other instruments had detected water around HL Tauri, the study recalls, but with too low a resolution to accurately delineate the ice line. The European Southern Observatory (ESO) radio telescope is the first to identify this boundary from its high-altitude location at over 5,000 meters in Chile's Atacama Desert.
“So far, ALMA is the only facility capable of spatially resolving the presence of water in a cold planet-forming disk,” claimed Professor Wouter Vlemmings of Sweden's Chalmers University, co-author of the study, quoting him along with Professor Facchini in an ESO press release.
The radio telescope discovered the equivalent of at least three times the amount of water in all of Earth's oceans. All in an area very close to the star, with a radius equal to 17 times the distance between the Earth and the Sun.
Perhaps more significantly, the ALMA images “show a significant amount of water vapor at various distances from the star, including a space where a planet could potentially form at present,” says Professor Facchini.
There seems to be no shortage of raw materials for the creation of such a planet: calculations from another observatory estimate the mass of available dust to be thirteen times the mass of the Earth.
The study would show “how the presence of water can influence the evolution of a planetary system, as was the case in our own solar system 4.5 billion years ago,” says Stefano Facchini.
However, the understanding of the formation mechanism of the solar system's planets is still incomplete.