Where Does Earth’s Water Come From? Rosetta Solves One Part Of The Puzzle

Credit: awesomeocean.com

During the formation of the solar system temperatures were too hot to maintain any initial water supplies that may have existed on Earth. Confronted with this fact leads to the question: where does the vast quantity that constitutes our oceans, seas, lakes, rivers, etc come from—the water we see all around us, so intrinsic to life, should have evaporated billions of years ago?

This is a long standing mystery within planetary science. However, there are various theories concerning the necessary mechanisms; solving them could put the mystery to bed: comets and/or asteroids are the obvious candidates, although which one is the primary source is still to be ascertained.

To help solve this problem, new data received from ESA’s Rosetta satellite has revealed the water composition found on comet 67P/Churyumov-Gerasimenko is deuterium rich and does not match Earth bound deposits—by a considerable margin (yellow plot on diagram). 

By measuring the deuterium/hydrogen ratio (D/H) in the comet’s water ice, scientists have been able to confirm such vast quantities probably did not originate from ‘Jupiter family’ or Oort cloud comets as originally thought.

Solar system objects highlighting Deuterium/Hydrogen ratios. Asteroids, although having less water than comets, could prove to be the solution

Solar system objects highlighting Deuterium/Hydrogen ratios. Asteroids, although having less water than comets, could prove to be the solution.

Utilising previous D/H ratio studies, asteroids could prove to be the primary source (see diagram): ‘Our finding also rules out the idea that Jupiter-family comets contain solely Earth ocean-like water, and adds weight to models that place more emphasis on asteroids as the main delivery mechanism for Earth’s oceans’, said Kathrin Altwegg, principal investigator for ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis).

This throws the origins-of-water debate wide open as Matt Taylor, ESA’s project scientist, highlights: ‘We knew that Rosetta’s in situ analysis of this comet was always going to throw up surprises for the bigger picture of Solar System science, and this outstanding observation certainly adds fuel to the debate about the origin of Earth’s water’.

New data is being received continuously from Rosetta, therefore further insights regarding the nature of the solar system should be forthcoming as the mission proceeds.

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Paul Hattle

As a strong advocate for science and learning, I am a passionate supporter of the 'Campaign for Science and Engineering' (CaSE) Fellow of the 'Royal Astronomical Society' (RAS) Associate Member of the 'Institute of Physics' (IOP) & 'The Institute of Scientific and Technical Communicators' (ISTC)

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