NASA scientists discover water resembling the Earth as a comet passes by

Our search for E.T. in the great dark forest of the universe is looking for signs of water. We know how important it is for life to prosper. But closer to home, there is a more pressing question: where does the water from the Earth come from?

A team of international astronomers took some steps to answer this question by studying the water found in a near-Earth comet, 46P / Wirtanen.

"We have identified a vast, earth-like water reservoir in the far reaches of the solar system," said Darek Lis, lead author of the study, in a statement.

The study, published in Astronomy and Astrophysics Letters on May 20, used NASA's Stratospheric Observatory for Infrared Astronomy (SOFIA) to study the so-called Christmas comet, makes a closer approach to the Earth in December 2018. The instrument runs from a specially designed Boeing 747 above the clouds, which allows it to see cosmic phenomena with a pair of eyes brighter than some of our Earthly methods.

A long-standing theory postulates that the Earth's water has been supplied by icy comets from the confines of the solar system. Comets traverse a space filled with dust, ice and other chemicals and occasionally collide with planets. The formation of the Earth probably occurred during the collision of small rock bodies – but these were very poor in water. So, the theory suggests that comets may have delivered some of the water that makes up 70% of the planet when they collided with Earth at first.

However, the evidence that comets contained the same type of water as the Earth, good old H2O, was limited. To determine if the comet was carrying "earth-like" water, SOFIA examined 46P / Wirtanen and examined the relationship between two types of water.

The water we know and love, H2O, is composed of two atoms of hydrogen and an atom of oxygen. These hydrogen atoms contain a proton and zero neutrons. This form of water constitutes most of the water found on Earth. A less common form of water, "heavy water", is composed of the same atomic structure, but the hydrogen atom contains a proton and a neutron. This form of water is known as deuterium. The study of the deuterium hydrogen ratio (D / H ratio) can tell us a little more about its origin.

The ratio D / H in comets generally varies 1 to 3 times more than the ratio of the Earth's oceans, but astronomers have found that the ratio between 46P / Wirtanen is basically the same as the one we see here on Earth.

Two previous comets presented similar ratios: 103P / Hartley 2 and 45P / H-M-P. Notably, all three are classified as "hyperactive comets", which release ice water to their surface and into their atmosphere when they warm up as the sun approaches. The team found that the D / H ratios in all three cases were related to the presence of water in their atmosphere. As a result, they think that all comets could contain water resembling the Earth trapped in their rocky bodies.

Such a discovery opens up again the debate on the origins of the water of the Earth. Other comets, originating from the Oort cloud around the solar system, do not exhibit similar D / H ratios.

Asteroids, which differ from comets in that they are more metallic and rocky, have also been suggested as a source. It should be noted the number of asteroids found with water similar to the Earth in the asteroid belt between Mars and Jupiter.