Skip to comments.Rosetta Instrument Reignites Debate on Earth's Oceans
Posted on 12/11/2014 2:15:28 AM PST by iowamark
The question about the origin of oceans on Earth is one of the most important questions with respect to the formation of our planet and the origin of life. The most popular theory is that water was brought by impacts of comets and asteroids. Data from the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument aboard the European Space Agencys Rosetta spacecraft indicate that terrestrial water did not come from comets like 67P/Churyumov-Gerasimenko. The findings were published today in the journal Science.
Researchers agree that water must have been delivered to Earth by small bodies at a later stage of the planets evolution. It is, however, not clear which family of small bodies is responsible. There are three possibilities: asteroid-like small bodies from the region of Jupiter; Oort cloud comets formed inside of Neptune's orbit; and Kuiper Belt comets formed outside of Neptune's orbit.
The key to determining where the water originated is in its isotopic flavor. That is, by measuring the level of deuterium a heavier form of hydrogen. By comparing the ratio of deuterium to hydrogen in different objects, scientists can identify where in the solar system that object originated. And by comparing the D/H ratio, in Earths oceans with that in other bodies, scientists can aim to identify the origin of our water.
The ROSINA instrument on the Rosetta spacecraft has found that the composition of comet 67P/Churyumov-Gerasimenkos water vapor is significantly different from that found on Earth.
The value for the D/H ratio on the comet is more than three times the terrestrial value. This is among the highest-ever-measured values in the solar system. That means it is very unlikely that comets like 67P/Churyumov-Gerasimenko are responsible for the terrestrial water.
The D/H ratio is the ratio of a heavier hydrogen isotope, called deuterium, to the most common hydrogen isotope. It can provide a signature for comparison across different stages of a planet's history.
We knew that Rosettas in situ analysis of this comet was always going to throw us surprises," said Matt Taylor, Rosettas project scientist from the European Space Research and Technology Center, Noordwijk, the Netherlands. The bigger picture of solar-system science, and this outstanding observation, certainly fuel the debate as to where Earth got its water.
Almost 30 years ago (1986) the mass spectrometers on board the European Giotto mission to comet Halley could, for the first time, determine D/H ratio in a comet. It turned out to be twice the terrestrial ratio. The conclusion at that time was that Oort cloud comets, of which Halley is a member, cannot be the responsible reservoir for our water. Several other Oort cloud comets were measured in the next 20 years, all displaying very similar D/H values compared to Halley. Subsequently, models that had comets as the origin of the terrestrial water became less popular.
This changed when, thanks to the European Space Agency's Herschel spacecraft, the D/H ratio was determined in comet Hartley 2, which is believed to be a Kuiper Belt comet. The D/H ratio found was very close to our terrestrial value -- which was not really expected. Most models on the early solar system claim that Kuiper Belt comets should have an even higher D/H ratio than Oort cloud comets because Kuiper Belt objects formed in a colder region than Oort cloud comets.
The new findings of the Rosetta mission make it more likely that Earth got its water from asteroid-like bodies closer to our orbit and/or that Earth could actually preserve at least some of its original water in minerals and at the poles.
Our finding also disqualifies the idea that Jupiter family comets contain solely Earth ocean-like water, said Kathrin Altwegg, principal investigator for the ROSINA instrument from the University of Bern, Switzerland, and lead author of the Science paper. It supports models that include asteroids as the main delivery mechanism for Earths oceans.
Comets are time capsules containing primitive material left over from the epoch when the sun and its planets formed. Rosetta's lander obtained the first images taken from a comet's surface and will provide analysis of the comet's possible primordial composition. Rosetta will be the first spacecraft to witness at close proximity how a comet changes as it is subjected to the increasing intensity of the sun's radiation. Observations will help scientists learn more about the origin and evolution of our solar system and the role comets may have played in seeding Earth with water, and perhaps even life.
Rosetta is an ESA mission with contributions from its member states and NASA. The Jet Propulsion Laboratory, Pasadena, California, a division of the California Institute of Technology in Pasadena, manages the U.S. contribution of the Rosetta mission for NASA's Science Mission Directorate in Washington. JPL also built the MIRO instrument and hosts its principal investigator, Samuel Gulkis. The Southwest Research Institute (San Antonio and Boulder) developed the Rosetta orbiter's IES and Alice instruments, and hosts their principal investigators, James Burch (IES) and Alan Stern (Alice).
For more information on the U.S. instruments aboard Rosetta, visit:
More information about Rosetta is available at:
There are two types of comet tails: dust and gas ion. A dust tail contains small, solid particles that are about the same size found in cigarette smoke. This tail forms because sunlight pushes on these small particles, gently shoving them away from the comet’s nucleus. Because the pressure from sunlight is relatively weak, the dust particles end up forming a diffuse, curved tail. A gas ion tail forms when ultraviolet sunlight rips one or more electrons from gas atoms in the coma, making them into ions (a process called ionization). The solar wind then carries these ions straight outward away from the Sun. The resulting tail is straighter and narrower. Both types of tails may extend millions of kilometers into space. As a comet heads away from the Sun, its tail dissipates, its coma disappears, and the matter contained in its nucleus freezes into a rock-like material.
I was commenting on what the article above postulates, that this particular comet differs in ratio.
My musings are the sun could possibly change these ratios over a few billion years' time, due to it's influence when comets pass by, thus making the ratios valuable for comparison, but not for absolute statements.
That is both true, and not particularly helpful. The question natural sciences ask is not "Who did it?" but "How was it done?"
Question, what type of gas would that be that gets stripped of it's electron (s), thus becoming ionized?
Do ionized particles in space behave similar to ionized particles on earth?
Do they seek a more stable relationship with other ions?
While comets *may* be billions of years old, they only spend a few days or weeks in proximity to the Sun during each of their orbits.
Still others would sport an ion trail while still quite a bit out there , more than a few weeks, on approach.
Going to have to go back to my learnin' and retune my memories.
Thank you for the information.
Amazingly, the earths water is really a miniscule amount | 5/15/2012 | thanks central_va.The Louis Frank keyword:
Comet’s water ‘like that of Earth’s oceans’
Solar System Ice: Source of Earth’s Water
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