It is one of the great questions of astronomy and evolution: How did water come to earth – the element that makes life as we know it possible?
There are many theories about this: water could have rained down on the still young planet along with many meteorites. Another explanation is that it comes from comets, structures made of ice, dust and rock that race through space and occasionally cross the orbits of planets. According to a third theory, our Earth and probably many other planets have contained water since the beginning of their formation.
Now scientists have made a surprising discovery that gives new support to this theory: astronomers discovered that a huge disk of water vapor is moving around the sun-like star HL Tauri, 450 light-years from Earth. It contains three times as much water as all of Earth’s oceans combined. And: It is located in a region of HL Tauri where planets are probably formed.
Researchers are certain that the birth of planets takes place in so-called proplanetary disks. Such a disk consists of dust, gas and rock and always shows ring-shaped gaps where a forming planet attracts matter like a magnet and thereby grows.
Astronomers have long known that water also plays a role in planet formation. But never before had they been able to determine the distribution of water in a proplanetary disk.
“I never thought we could capture an image of oceans of water vapor in the same region where a planet is likely to form,” says Stefano Facchini. He is an astronomer at the University of Milan, Italy, and led the study published Thursday in Nature Astronomy. This suggests that this water vapor could influence the chemical composition of planets forming in these regions.
“It’s really exciting to directly observe how water molecules are released from icy dust particles in an image,” says Elizabeth Humphreys, an astronomer at the European Southern Observatory (ESO), who was also involved in the study.
These dust grains that make up a disk are the nucleus for the formation of planets. As they orbit the star, they collide and clump together to form ever larger bodies. Scientists say it is cold enough there for water to freeze on the dust particles, making the particles stick together better – an ideal place for planet formation. “Our results show how the presence of water can influence the evolution of a planetary system, just as it did in our own solar system about 4.5 billion years ago,” adds Facchini.
Observing water at such huge distances with a ground-based telescope is no easy task. The Earth’s atmosphere itself contains a lot of water vapor, which weakens astronomical signals.
The new findings were made possible by a very special telescope: the Atacama Large Millimeter/submillimeter Array, known as ALMA for short. It is located in the Chilean Atacama Desert at an altitude of around 5,000 meters. In the high and dry environment, there is hardly any water vapor in the atmosphere. A look into space allows us to look far back into the history of the earth.
