How much water around DG Tau!

Thanks to the observations of the space telescope Herschel ESA a large amount of water vapor had been discovered in the disc around a young star from which it formed a planetary system similar to ours; a result of fundamental importance because it could explain the origin of life and water on Earth. The discovery was led by a young Italian researcher associated INAF. Imagine how much water can be contained in all the seas and oceans of the Earth. Yet, although it may seem a huge value, in the cosmos, water is in vastly greater quantities. The last one, gigantic ‘reservoir’ of this chemical compound that is essential for life , at least the one that has developed on our planet , was discovered in the form of vapor and ice around DG Tau , a young star located in the direction of constellation Taurus and is about 450 light years from us. And even there, there would be quantities of water something like a thousand times that of our oceans.

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The discovery was made by an international team of researchers, led by Linda Podium of the University of Grenoble and associated INAF, attended by Claudio Codella INAF- Arcetri Astrophysical Observatory and Brunella Nisini INAF- Astronomical Observatory from Rome, exploiting the observations made by ESA’s Herschel space telescope.

DG Tau has a few million years, but in a few billion years could become like the Sun and its circumstellar disk may form planets, asteroids and comets, similar to our Solar System. The ‘water- hunting’ in this and other similar systems becomes very important because the presence of this compound may be a clue to conditions favorable to the onset of life. Scientists believe that most of the water in these structures has in the outer regions of the disc, where the temperatures are very low, well below -100 degrees centigrade. ” Under these conditions, the water freezes on the surface of dust grains in the disc, covering them with thick ice mantles and making it ‘invisible’ to the observations,” says Linda Podium. “However, the high energy radiation emitted by the star brightens and warms the outer layers of the disc, so that the ice mantles on dust grains can dissolve releasing the water in the gas phase.” Once in the form of steam, the main emission lines of this molecule are visible to far-infrared wavelengths, cannot be observed from Earth because of atmospheric absorption but accessible to the instruments on board the Herschel satellite.

Thus, even the protoplanetary disk of DG Tau has been scrutinized by the spectrometer HIFI (Heterodyne Instrument for the Far-Infrared) of Herschel and the analysis of the results was unmistakable. “Now we can say with certainty that our suspicions were correct. In fact, we were able to observe the water vapor in the disk of DG Tau continues” says Linda Podium. The data analysis has allowed us to earn from which region of the disk water is emitted, and derive the abundance: the amount of water vapor observed is equivalent to hundreds or thousands of Earth’s oceans. “The researchers were also able to locate the position of this enormous reservoir, which is in a range between 10 and 100 astronomical units from the star (an astronomical unit is equivalent to the Earth-Sun distance). Furthermore, since the water in the form of steam is only a small part of the total, it is deduced that the amount of water trapped in the mantles of the grains of powder in the form of ice is much greater.

” This discovery has fundamental implications for astronomers and geologists who study the origin of our solar system , and in particular the origin of water on Earth ,” said Linda Podium . ” In fact, the most likely hypothesis is that our planet was completely ‘ dry ‘ at the time of its formation and that water has reached about 4 billion years ago , thanks to asteroids and comets that would have formed in the outer regions of the our disk and crash on Earth during that takes the name of ‘ intense bombardment late ‘ . The amount of water that we have observed in the disk of DG Tau , a star similar to our Sun, definitely supports this scenario . “

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