Water under the bridge

By | Science & Technology
Space. Credit@Sweetie187

Question now surrounds whether comets delivered Earth’s enormous supply of water, according to Rosetta’s latest results. The results published in the journal Science, show that the water belonging to the 67P/C-G comet is unlike the water found on Earth and that it is more likely derived from denser, rock-based asteroids than comets. These findings provide important insights into the origins of Earth as well as life that sprung from it.

For the first time in human history, the European Space Agency (ESA) used a spacecraft, named Rosetta, to catch the comet 67P/Churyumov-Gerasimenko (67P/C-G) and land a robotic probe (an entire science laboratory essentially) on the surface, called Philae.  After ten years of travel it finally made contact on Wednesday 12th November 2014. To put that into perspective, this comet has been hurtling through space at more than 30,000 mph and is over 373,000,000 miles from Earth according to the ESA.

Though Rosetta’s probe, Philae’s, battery life ran dry soon after touchdown, the mission has already been marked a success having completed 80% of its planned observations and collected a vast amount of data on the comet’s composition as well as incredible photographs. Furthermore, the Rosetta spacecraft continues to orbit and analyse the comet through probes and analytical equipment.

Comets have been in the deep freeze of space since the formation of our Solar System, which is why scientists think they may provide a wealth of information on its early composition. It has been a commonly postulated theory that comets may have delivered huge volumes of water to Earth during its formative years, more than 4 billion years ago. However the latest data from Rosetta’s ROSINA tool indicates otherwise. The probe gathered information about the ratio of hydrogen (H) to its heavier isotope, deuterium (D) from the gas streaming off the surface of 67P/C-G. Typically, Earth’s water is made of hydrogen and oxygen, with very small amounts of hydrogen substituted for deuterium. If this ratio is similar in the cometary ice then it might indicate that some of Earth’s water supply originates from comets. However, the water on 67P/C-G was found to be more than three times heavier than the terrestrial value because it is much richer in deuterium. This ratio is very characteristic and remains constant for a very long time and means it’s unlikely that similar comets dispatched water to Earth.

ESA Rosetta ROSINA Infographic. Credit@KathrinAltwegg

ESA Rosetta ROSINA Infographic. Credit@KathrinAltwegg

Previous measurements and the team’s latest finding suggest a wide range of D/H ratios in the water of Jupiter family objects in the Kuiper Belt where 67P/C-G resides. These comets show a mixture of light and heavy water compared to Earth. The average D/H ratio of these suggests their origin is somewhere with much heavier water than Earth. Nevertheless, the comet theory may still have some traction. Prof Alan Fitzsimmons, from the Astrophysics Research Centre at Queen’s University Belfast advised that averaging the few Kuiper Belt comets now measured might inaccurately reflect Earth’s water composition. Therefore, the possibility endures that comets might have delivered some water to Earth.

Scientists aim to gather more information from the surface by Philae’s landing instruments COSAC and Ptolemy, which may provide more detailed data of the ice on the comet’s surface as well as a deeper insight to their role in the Solar System.

As it stands, asteroids seem like the most likely candidate for delivery of water to Earth. While appearing dry and rocky, it is thought that many carried water during the early days of the Solar System and bombarded the Earth with water once it cooled; about 800 million years ago. Scientists aim to navigate the Rosetta spacecraft through a jet in the comet as it travels around the sun, to learn about 67P/C-G’s composition more deeply. The ESA informs that Rosetta’s 12-year mission aims to end around December next year after reaching its closest point to the sun.

What other discoveries through space exploration might change theories about Earth’s history?

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