Scientists have found that cometary dust affects the interpretation of spacecraft measurements, reopening the case for comets like 67P as possible sources of water for the early Earth.
Researchers have found that water on comet 67P/Churyumov–Gerasimenko has a similar molecular signature to water in Earth’s oceans. Contrary to some recent findings, this finding reopens the case that Jupiter-family comets such as 67P could have helped deliver water to Earth.
Water was essential for life to form and flourish on Earth, and it is still central to life on Earth today. Although there was some water in the gas and dust that formed our planet about 4.6 billion years ago, most of the water must have evaporated as Earth formed near the intense heat of the Sun. How Earth eventually became rich in liquid water remains a matter of debate for scientists.
Research shows that some of the Earth’s water came from volcanic vapors. that the vapors condense and fall on the oceans. But scientists have found evidence that much of our oceans came from ice and minerals on asteroids, and possibly from comets, that crashed into Earth. A wave of comets and asteroids colliding with the inner planets of the solar system would have made this possible 4 billion years ago.
While the case for asteroids connecting water to Earth is strong, the role of comets has puzzled scientists. Multiple measurements of Jupiter-family comets — which contain ancient material from the early Solar System and are thought to have formed outside Saturn’s orbit — revealed a strong connection between their water and Earth. . The link was based on a key molecular signature that scientists use to trace the origin of water throughout the solar system.
This signature is the ratio of deuterium (D) to regular hydrogen (H) in an object’s water, and it gives scientists a clue as to where the object formed. Deuterium is a rare, heavy type — or isotope — of hydrogen. When compared to Earth’s water, this ratio of hydrogen in comets and asteroids can reveal whether there is a connection.
Because water with deuterium is more likely to form in cooler environments, objects formed farther from the Sun, such as comets, have higher concentrations of the isotope than objects formed closer to the Sun, such as asteroids.
Measurements within the past two decades of deuterium in the water vapor of several other Jupiter-family comets have shown levels similar to those of Earth’s water.
“It really looked like these comets played an important role in bringing water to Earth,” said Kathleen MendtPlanetary scientists at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Mandt led the research, Published in Science Advances. On November 13, Joe revises the deuterium abundance in 67P.
But in 2014, the ESA (European Space Agency) Rosetta mission 67P challenged the idea that Jupiter-family comets helped replenish Earth’s water reservoirs. Scientists who analyzed Rosetta’s water measurements. The highest concentration of deuterium was found of any comet, and about three times more deuterium than Earth’s oceans, containing about 1 deuterium atom for every 6,420 hydrogen atoms.
“It was a huge surprise and it made us rethink everything,” Mendt said.
Mandt’s team decided to use an advanced statistical technique to automate the laborious process of deuterium-rich isolation. Water in more than 16,000 Rosetta measurements. Rosetta made these measurements in a “coma” of gas and dust around 67P. Mandt’s team, which included Rosetta scientists, was the first to analyze all of the European mission’s water measurements spanning the entire mission.
The researchers wanted to understand what physical processes caused the variation in hydrogen isotope ratios measured on comets. Lab studies and observations of comets show that comet dust can affect the hydrogen ratio readings that scientists detect in comet vapor, which could change our understanding of where comet water comes from. And how does it compare to Earth’s water?
“So I was just curious if we could find evidence of that happening at 67P,” Mendt said. “And this is one of those very rare cases where you propose a hypothesis and actually find it happening.”
In fact, Mendt’s team found a clear correlation between measurements of deuterium in the coma of 67P and the amount of dust around the Rosetta spacecraft, indicating that measurements taken nearer to the spacecraft in parts of the coma could be a comet. May not be representative of structure. The body
As a comet approaches the Sun in its orbit, its surface heats up, causing gas to escape from the surface, including dust with patches of water ice on it. Research shows that water with deuterium sticks to dust grains more easily than plain water. When the ice on these dust grains is released into the coma, the impact can expose the comet to excess deuterium.
When the dust reaches the outer part of the coma, at least 75 miles from the comet’s body, it dries up, Mendt and his team said. After the deuterium-rich water is depleted, the spacecraft can accurately measure the amount of deuterium coming from the comet’s body.
The paper’s authors say the discovery has major implications not only for understanding the role of comets in Earth’s water supply, but also for understanding observations of comets that provide insight into the formation of the early solar system.
“This means we have a great opportunity to revisit our past observations and prepare for the future so that we can better account for the effects of dust,” Mendt said.
by the Lonnie Shechtman
NASA’s Goddard Space Flight Center, Greenbelt, Md.
