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Comets may have been potential sources of water for early Earth, researchers said this week.
When Earth formed around 4.6 billion years ago, some water likely existed in that gas and dust — though much of it would have been vaporized by the sun’s intense heat. How Earth got so much liquid water remains a source of debate, but research has shown some came through volcanic vapor that became rain.
There is also new evidence that a substantial portion of Earth’s oceans came from ice and minerals on asteroids — and maybe comets — that crashed into Earth. Measurements of Jupiter-family comets, controlled by the planet’s gravitational effects, have shown a strong link between their water and Earth’s based on a key molecular signature.
NASA says its scientists found that water on Jupiter-family Comet 67P/Churyumov–Gerasimenko, the first comet to be orbited and landed upon by robotic spacecraft from Earth, had a similar molecular signature to the water in Earth’s oceans and that cometary dust infects the interpretation of spacecraft measurements.
These results, the agency said, contradict some recent research. In 2014, the European Space Agency’s Rosetta mission to the comet analyzed water measurements, finding the highest concentration of deuterium on it compared to of any other comet – and about three times more deuterium than there is in Earth’s oceans.
Deuterium is a rare type of the element hydrogen, and the molecular signature is its ratio to regular hydrogen in the water of any object. The ratio helps researchers figure out where the object was formed, and water with deuterium is more likely to form in cold environments. There are 33 grams of deuterium in every cubic meter of seawater.
“It was a big surprise and it made us rethink everything,” Kathleen Mandt, planetary scientist at NASA’s Goddard Space Flight Center, said in a statement.
That research might now be incorrect based on the new findings after the robot spacecraft landed on the comet and scientists analyzed the findings. Mandt led the new research that was published last month in the journal Science Advances.
Measurements of deuterium in the last couple of decades in the water vapor of other Jupiter-family comets had shown similar levels to Earth’s water.
“It was really starting to look like these comets played a major role in delivering water to Earth,” said Mandt.
By using a method combining computer science and statistics, her team was able to automate the process of isolating water rich in deuterium in more than 16,000 of the Rosetta spacecraft measurements made in the gas and dust surrounding the comet.
In doing so, they found a link between deuterium measurements around the comet and the dust around the spacecraft, showing that 2014 measurements taken from one part of the comet may not represent its whole composition.
NASA said that when a comet warms as it moves closer to the sun, gas and dust with bits of water and ice are released from its surface. Water that contains deuterium is believed to stick to dust more easily than regular water. When ice is released into the part of the atmosphere surrounding the nucleus, known as the coma, it could make it seem like the comet has more deuterium than it actually does.
By the time the dust is released to the outer part of its coma, at least 75 miles from the body itself, it is dried out. A spacecraft can measure the amount of deuterium coming from its body.
The study’s authors say this finding will help to better understand comets’ role in bringing water to Earth.
“This means there is a great opportunity to revisit our past observations and prepare for future ones so we can better account for the dust effects,” Mandt said.
Source: independent.co.uk
