Researchers have found that water on Comet 67P\/Churyumov\u2013Gerasimenko has a similar molecular signature to the water in Earth\u2019s oceans. Contradicting some recent results, this finding reopens the case that Jupiter-family comets like 67P could have helped deliver water to Earth.\u00a0\u00a0<\/p>\n
Water was essential for life to form and flourish on Earth and it remains central for Earth life today. While some water likely existed in the gas and dust from which our planet materialized around 4.6 billion years ago, much of the water would have vaporized because Earth formed close to the Sun\u2019s intense heat. How Earth ultimately became rich in liquid water has remained a source of debate for scientists.<\/p>\n
Research has shown that some of Earth\u2019s water originated through vapor vented from volcanoes; that vapor condensed and rained down on the oceans. But scientists have found evidence that a substantial portion of our oceans came from the ice and minerals on asteroids, and possibly comets, that crashed into Earth. A wave of comet and asteroid collisions with the solar system\u2019s inner planets 4 billion years ago would have made this possible.\u00a0\u00a0\u00a0<\/p>\n
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<\/a><\/figure>While the case connecting asteroid water to Earth\u2019s is strong, the role of comets has puzzled scientists. Several measurements of\u00a0Jupiter-family comets \u2014 which contain primitive material from the early solar system and are thought to have formed beyond the orbit of Saturn\u00a0\u2014 showed a strong link between their water and Earth\u2019s. This link was based on a key molecular signature scientists use to trace the origin of water across the solar system.<\/p>\n
This signature is the ratio of deuterium (D) to regular hydrogen (H) in the water of any object, and it gives scientists clues about where that object formed. Deuterium is a rare, heavier type \u2014\u00a0or isotope \u2014 of hydrogen. When compared to Earth\u2019s water, this hydrogen ratio in comets and asteroids can reveal whether there\u2019s a connection.\u00a0\u00a0<\/p>\n
Because water with deuterium is more likely to form in cold environments, there\u2019s a higher concentration of the isotope on objects that formed far from the Sun, such as comets, than in objects that formed closer to the Sun, like asteroids.\u00a0<\/p>\n
Measurements within the last couple of decades of deuterium in the water vapor of several other Jupiter-family comets showed similar levels to Earth\u2019s water.\u00a0<\/p>\n
\u201cIt was really starting to look like these comets played a major role in delivering water to Earth,\u201d said Kathleen Mandt<\/a>, planetary scientist at NASA\u2019s Goddard Space Flight Center in Greenbelt, Maryland. Mandt led the research, published in Science Advances<\/a> on Nov. 13, that revises the abundance of deuterium in 67P.\u00a0<\/p>\n