Comet 67P (The Guardian)

Catching up on some old stuff which I had saved to post on the blog.


Loved this picture, from an aesthetic and scientific point of view.  In addition, text described well the picture to a non-science audience.

Exposed Water Ice on Comet Reveals Clues About Its Evolution - See more at: http://www.space.com/31607-water-ice-comet-rosetta-mission.html?cmpid=NL_SP_weekly_2016-1-13#sthash.wi0CUq4Z.dpuf

The European Space Agency's Rosetta spacecraft detected relatively large grains of water ice in two different places on the surface of Comet 67P/Churyumov-Gerasimenko, which the probe has been orbiting since August 2014.

These big grains may have formed after heat from the sun sublimated (or vaporized) buried water ice, which then recondensed and was redeposited in subsurface layers, without ever leaving Comet 67P, researchers said.
"If the thin ice-rich layers that we see exposed close to the surface are the result of the comet's activity, then they represent its evolution, and it does not necessarily require global layering to have occurred early in the comet's formation history," study lead author Gianrico Filacchione, of the Institute for Space Astrophysics and Planetology at the National Institute for Astrophysics in Rome, told Space.com via email.
Comets are made primarily of water ice, but the stuff is rarely observed on their frigid surfaces. Indeed, the 2.5-mile-wide (4 kilometers) Comet 67P appears to be covered by a nearly uniform layer of dark dust, Filacchione said.
"We have measured that the surface reflects only a few percent of solar light," he said. "Ices are not stable for a long time on the surface of the nucleus because, during the perihelion passage [closest approach to the sun], they sublimate, originating the gaseous coma."
Filacchione and his colleagues studied observations of Comet 67P made by Rosetta's Visual and Infrared Thermal Imaging Spectrometer (VIRTIS) instrument. VIRTIS detected surface water ice in two separate, 3.3-foot-wide (1 meter) areas within a region of the comet dubbed Imhotep, the researchers report in a study published online today (Jan. 13) in the journal Nature.

Rosetta detects oxygen on comet 67P (Chemistry World)

Molecular oxygen has been detected in the cloud of gas surrounding comet 67P/Churyumov-Gerasimenko by the Rosetta space probe, which has been orbiting the comet for over a year. It is the first time molecular oxygen has ever been detected on a comet.

The measurements were taken by the ROSINA-DFMS mass spectrometer on board Rosetta between September 2014 and March 2015. In the areas sampled, the abundance of oxygen relative to water ranged from one to 10%.
Molecular oxygen has never been detected on a comet before, although it has been observed in the atmospheres of icy moons orbiting Saturn and Jupiter. Measurements taken by other spacecraft show the coma of a comet – the cloud of gas surrounding the nucleus – is usually made up of water vapour, carbon dioxide and carbon monoxide.
The observations may help shape new models of how the comet formed. Measurements of the ratios of different gases indicate that the oxygen in 67P’s coma comes from its icy nucleus, which in turn suggests that ‘primordial’ oxygen, present in the giant molecular cloud that gave rise to the solar system, was incorporated into the comet as it formed.

Rosetta's First Peek at the Comet's Dark Side (NASA/ESA)

Since its arrival at comet 67P/Churyumov-Gerasimenko, the European Space Agency's Rosetta spacecraft has been surveying the surface and the environment of this curiously shaped body. But for a long time, a portion of the nucleus -- the dark, cold regions around the comet's south pole -- remained inaccessible to almost all instruments on the spacecraft.
Due to a combination of its double-lobed shape and the inclination of its rotation axis, Rosetta's comet has a very peculiar seasonal pattern over its 6.5-year-long orbit. Seasons are distributed very unevenly between the two hemispheres. Each hemisphere comprise parts of both comet lobes and the "neck."
For most of the comet's orbit, the northern hemisphere experiences a very long summer, lasting over 5.5 years, while the southern hemisphere undergoes a long, dark and cold winter. However, a few months before the comet reaches perihelion -- the closest point to the sun along its orbit -- the situation changes, and the southern hemisphere transitions to a brief and very hot summer.
When Rosetta arrived at 67P/C-G in August 2014, the comet was still experiencing its long summer in the northern hemisphere, and regions on the southern hemisphere received very little sunlight. Moreover, a large part of this hemisphere, close to the comet's south pole, was in polar night and had been in total darkness for almost five years.
With no direct illumination from the sun, these regions could not be imaged with Rosetta's OSIRIS (the Optical, Spectroscopic, and Infrared Remote Imaging System) science camera, or its Visible, InfraRed and Thermal Imaging Spectrometer (VIRTIS). For the first several months after Rosetta's arrival at the comet, only one instrument on the spacecraft could observe and characterize the cold southern pole of 67P/C-G: the Microwave Instrument for Rosetta Orbiter (MIRO).
In a paper accepted for publication in the journal Astronomy and Astrophysics, scientists report on the data collected by MIRO over these regions between August and October 2014.
"We observed the 'dark side' of the comet with MIRO on many occasions after Rosetta's arrival at 67P/C-G, and these unique data are telling us something very intriguing about the material just below its surface," said Mathieu Choukroun from NASA's Jet Propulsion Laboratory (JPL), Pasadena, California, lead author of the study.
Observing the comet's southern polar regions, Choukroun and colleagues found significant differences between the data collected with MIRO's millimeter and sub-millimeter wavelength channels. These differences might point to the presence of large amounts of ice within the first few tens of centimeters below the surface of these regions.
"Surprisingly, the thermal and electrical properties around the comet's south pole are quite different than what is found elsewhere on the nucleus," said Choukroun. "It appears that either the surface material or the material that's a few tens of centimeters below it is extremely transparent, and could consist mostly of water ice or carbon-dioxide ice."
The difference between the surface and subsurface composition of this part of the nucleus and that found elsewhere might originate in the comet's peculiar cycle of seasons. One of the possible explanations is that water and other gases that were released during the comet's previous perihelion, when the southern hemisphere was the most illuminated portion of the nucleus. The water condensed again and precipitated on the surface after the season changed and the southern hemisphere plunged again into its long and cold winter.
These are, however, preliminary results, because the analysis depends on the detailed shape of the nucleus. At the time the measurements were made, the shape of the dark, polar region was not known with great accuracy.
"We plan to revisit the MIRO data using an updated version of the shape model, to verify these early results and refine the interpretation of the measurements," added Choukroun.
Rosetta scientists will be testing these and other possible scenarios using data that were collected in the subsequent months, leading to the comet's perihelion, which took place on Aug. 13, 2015 and beyond.
In May 2015, the seasons changed on 67P/C-G and the brief, hot southern summer, which will last until early 2016, began. As the formerly dark southern polar regions started to receive more sunlight, it has been possible to observe them with other instruments on Rosetta, and the combination of all data might eventually disclose the origin of their curious composition.
"In the past few months, Rosetta has flown over the southern polar regions on several occasions, starting to collect data from this part of the comet after summer began there," said Matt Taylor, ESA Rosetta project scientist. "At the beginning of the southern summer, we had a paucity of observations in these regions as Rosetta's trajectory focused on the northern hemisphere due to ongoing communication with the lander, Philae. However, closer to perihelion we were able to begin observing the south."
Rosetta is currently on an excursion out to about 930 miles (1,500 kilometers) from the nucleus to study the comet's environment at large. But the spacecraft will soon come closer to the comet, focusing on full orbits to compare the northern and southern hemispheres, as well as some slower passes in the south to maximize observations there. In addition, as activity will start to wane later this year, the team hopes to get closer to the nucleus and gain higher-resolution observations of the surface.
"First, we observed these dark regions with MIRO, the only instrument able to do so at the time, and we tried to interpret these unique data. Now, as these regions became warmer and brighter around perihelion, we can observe them with other instruments, too."
Mark Hofstadter, MIRO principal investigator at JPL, adds, "We hope that, by combining data from all these instruments, we will be able to confirm whether or not the south pole had a different composition and whether or not it is changing seasonally."
The MIRO instrument is a small, lightweight spectrometer that can map the abundance, temperature and velocity of cometary water vapor and other molecules that the nucleus releases. It can also measure the temperature up to about one inch (three centimeters) below the surface of the comet's nucleus. One reason the subsurface temperature is important is that the observed gases likely come from sublimating ices beneath the surface. By combining information on the gas and the subsurface, MIRO is able to study this process in detail.
Comets are time capsules containing primitive material left over from the epoch when the sun and its planets formed. Rosetta is 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 the formation of planets.

Philae poses comet chemistry conundrum (Chemistry World)

The estimated landing points of Philae as it bounced its way across comet 67P © ESA/ROSETTA/NAVCAM/SONC/DLR

As the Philae lander bounced across comet 67P/Churyumov–Gerasimenko’s surface in November last year, two chemical instruments were able to take tentative – but intriguingly contradictory – sniffs of its environment. Those mass spectrometry measurements provide compositional details important for deciphering the origins of life on Earth, a key aim of the Rosetta mission that carried Philae. But while the cometary sampling and composition (COSAC) instrument detected 16 organic molecules1, half of which contain nitrogen atoms, Ptolemy reports very low concentrations of nitrogen-containing compounds2.

Nevertheless, Jen Blank, a senior scientist at the Nasa Ames Research Center in California, US, highlights the historic achievement of syncing orbit with a comet and sending a lander down to the surface. ‘The Philae data are amazing,’ enthuses Blank, who’s studied how comets may have supplied Earth with molecules needed for life, but wasn’t involved in Rosetta or Philae. ‘These are the first measurements of organic compounds collected directly on a comet or asteroid.’

Philae was programmed to take sniffs shortly after touching down on 67P as an ‘insurance policy’, explains Ian Wright from the Open University in Milton Keynes, UK, and principal investigator for Ptolemy. That was well planned, because the touchdown became a rebound that sent Philae out of communication range, preventing further measurements to date.

The lander was also therefore in motion in the minutes between the instruments doing their respective basic analyses, or sniffs, of whatever material happened to have entered them. One potential explanation for the distinct results is therefore that they reflect differences between locations on the comet, Wright suggests. The fact that COSAC’s sample port is on Philae’s underside, and Ptolemy’s is on its top is another. ‘Have we analysed separate grains?’ Wright asks. ‘We’ve no reason to expect that the surface would be homogenous.’

Exhausting serendipity

COSAC’s best sniff happened automatically 25 minutes after Philae’s first contact, while the lander was around 150 metres above the surface. The instrument consists of a gas chromatograph and a time-of-flight mass spectrometer intended to analyse organic compounds in samples drilled from the comet’s surface. Though Philae couldn’t drill, the impact threw up some solid material, part of which apparently entered COSAC’s two exhaust pipes. The COSAC team, headed by Fred Goesmann from the Max Planck Institute for Solar System Research in Göttingen, Germany, thinks the exhaust’s warmth evaporated volatile compounds, allowing their detection. 

The compounds COSAC identified included methyl isocyanate, acetone, propionaldehyde and acetamide, which have not previously been reported in comets. Acetamide is also one of four compounds detected that can produce important biological molecules like amino acids, sugars and DNA bases. Blank is especially excited by acetamide’s presence. ‘It's easy to imagine a pathway to an amino acid,’ she says.  However, Goesmann is cautious not to read too much into their presence. ‘Comets with such a composition do not work against life,’ he tells Chemistry World. ‘In the right environment, emerging life could make use of it.’

However, the small amount of material COSAC was looking at meant it couldn’t detect anything but the smallest compounds. That means it wouldn’t have seen any ‘molecules of life’, such as amino acids, even if they were present. And although it could have, it didn’t see much ammonia, formaldehyde or carbon dioxide, which are common components of cometary ice, or any sulfur compounds. The COSAC scientists link the lack of ice to measurements previously made by Rosetta showing 67P’s surface is covered in a carbon-based coat rather than frozen.  

Icy isolation

To determine isotope ratios of chemicals on 67P and establish their origins, Ptolemy’s gas chromatograph and ion trap mass spectrometer were also supposed to be fed drilled samples. However, it was reduced to making six sniffs at 14 second intervals about 20 minutes after Philae hit 67P. Like COSAC, it failed to find any signs of sulfur. Ptolemy saw mostly water and carbon dioxide, ice components expected on comets, but no significant indication of ammonia, and very low levels of nitrogen compounds overall. The COSAC scientists suggest that the absence of this key source of nitrogen could be because it has evaporated or been used up in reactions.

Ptolemy also found hints of polyoxymethylene, a polymer thought to be produced from formaldehyde by cosmic radiation, previously detected on Halley’s Comet. This source of formaldehyde is another important potential resource for origin-of-life chemistry, Wright underlines. ‘It can produce simple sugars like ribose,’ he says. ‘These are things that we hope will be picked up by astrobiologists in refining their ideas.’

Rosetta Comet Outburst Captured (NASA)

The European Space Agency's Rosetta spacecraft has been witnessing growing activity from comet 67P/Churyumov-Gerasimenko as the comet approaches perihelion (its closest point to the sun during its orbit). On July 29, while the spacecraft orbited at a distance of 116 miles (186 kilometers) from the comet, it observed the most dramatic outburst to date. Early science results collected during the outburst came from several instruments aboard Rosetta, including the Double Focusing Mass Spectrometer (DFMS), which uses NASA-built electronics. The DFMS is part of the spacecraft's Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument.
When the outburst occurred, the spectrometer recorded dramatic changes in the composition of outpouring gases from the comet when compared to measurements made two days earlier. As a result of the outburst, the amount of carbon dioxide increased by a factor of two, methane by four, and hydrogen sulfide by seven, while the amount of water stayed almost constant.
"This first quick look at our measurements after the outburst is fascinating," said Kathrin Altwegg, principal investigator for the ROSINA instrument from the University of Bern, Switzerland. "We also see hints of heavy organic material after the outburst that might be related to the ejected dust.
"But while it is tempting to think that we are detecting material that may have been freed from beneath the comet's surface, it is too early to say for certain that this is the case."
A sequence of images taken by Rosetta's scientific camera OSIRIS shows the sudden onset of a well-defined, jet-like feature emerging from the side of the comet's neck. The jet, the brightest seen to date, was first recorded in an image taken at 6:24 a.m. PDT (9:24 a.m. EDT, 13:24 GMT) on July 29, but not in an image taken 18 minutes earlier. The jet then faded significantly in an image captured 18 minutes later. The OSIRIS camera team estimates the material in the jet was traveling at 33 feet per second (10 meters per second), at least.
A composite of the three images taken by Rosetta's OSIRIS is online at:
http://rosetta.jpl.nasa.gov
On Thursday, Aug. 13, the comet and Rosetta will be 116 million miles (186 million kilometers) from the sun -- the closest to the sun they will be in their 6.5-year orbit. In recent months, the increasing solar energy has been warming the comet's frozen ices -- turning them to gas -- which pours out into space, dragging dust along with it. The period around perihelion is scientifically very important, as the intensity of the sunlight increases and parts of the comet previously cast in years of darkness are flooded with sunlight. The comet's general activity is expected to peak in the weeks following perihelion.
Comets are time capsules containing primitive material left over from the epoch when the sun and its planets formed. Rosetta's lander, Philae, obtained the first images taken from a comet's surface and will provide analysis of the comet's possible primordial composition. Rosetta is 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 are helping 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

Philae poses comet chemistry conundrum (Chemistry World 30th July)

As the Philae lander bounced across comet 67P/Churyumov–Gerasimenko’s surface in November last year, two chemical instruments were able to take tentative – but intriguingly contradictory – sniffs of its environment. Those mass spectrometry measurements provide compositional details important for deciphering the origins of life on Earth, a key aim of the Rosetta mission that carried Philae. But while the cometary sampling and composition (COSAC) instrument detected 16 organic molecules¹, half of which contain nitrogen atoms, Ptolemy reports very low concentrations of nitrogen-containing compounds².

Nevertheless, Jen Blank, a senior scientist at the Nasa Ames Research Center in California, US, highlights the historic achievement of syncing orbit with a comet and sending a lander down to the surface. ‘The Philae data are amazing,’ enthuses Blank, who’s studied how comets may have supplied Earth with molecules needed for life, but wasn’t involved in Rosetta or Philae. ‘These are the first measurements of organic compounds collected directly on a comet or asteroid.’
Philae was programmed to take sniffs shortly after touching down on 67P as an ‘insurance policy’, explains Ian Wright from the Open University in Milton Keynes, UK, and principal investigator for Ptolemy. That was well planned, because the touchdown became a rebound that sent Philae out of communication range, preventing further measurements to date.
The lander was also therefore in motion in the minutes between the instruments doing their respective basic analyses, or sniffs, of whatever material happened to have entered them. One potential explanation for the distinct results is therefore that they reflect differences between locations on the comet, Wright suggests. The fact that COSAC’s sample port is on Philae’s underside, and Ptolemy’s is on its top is another. ‘Have we analysed separate grains?’ Wright asks. ‘We’ve no reason to expect that the surface would be homogenous.’

Exhausting serendipity

COSAC’s best sniff happened automatically 25 minutes after Philae’s first contact, while the lander was around 150 metres above the surface. The instrument consists of a gas chromatograph and a time-of-flight mass spectrometer intended to analyse organic compounds in samples drilled from the comet’s surface. Though Philae couldn’t drill, the impact threw up some solid material, part of which apparently entered COSAC’s two exhaust pipes. The COSAC team, headed by Fred Goesmann from the Max Planck Institute for Solar System Research in Göttingen, Germany, thinks the exhaust’s warmth evaporated volatile compounds, allowing their detection.

The compounds COSAC identified included methyl isocyanate, acetone, propionaldehyde and acetamide, which have not previously been reported in comets. Acetamide is also one of four compounds detected that can produce important biological molecules like amino acids, sugars and DNA bases. Blank is especially excited by acetamide’s presence. ‘It's easy to imagine a pathway to an amino acid,’ she says. However, Goesmann is cautious not to read too much into their presence. ‘Comets with such a composition do not work against life,’ he tells Chemistry World. ‘In the right environment, emerging life could make use of it.’

However, the small amount of material COSAC was looking at meant it couldn’t detect anything but the smallest compounds. That means it wouldn’t have seen any ‘molecules of life’, such as amino acids, even if they were present. And although it could have, it didn’t see much ammonia, formaldehyde or carbon dioxide, which are common components of cometary ice, or any sulfur compounds. The COSAC scientists link the lack of ice to measurements previously made by Rosetta showing 67P’s surface is covered in a carbon-based coat rather than frozen.

Icy isolation

To determine isotope ratios of chemicals on 67P and establish their origins, Ptolemy’s gas chromatograph and ion trap mass spectrometer were also supposed to be fed drilled samples. However, it was reduced to making six sniffs at 14 second intervals about 20 minutes after Philae hit 67P. Like COSAC, it failed to find any signs of sulfur. Ptolemy saw mostly water and carbon dioxide, ice components expected on comets, but no significant indication of ammonia, and very low levels of nitrogen compounds overall. The COSAC scientists suggest that the absence of this key source of nitrogen could be because it has evaporated or been used up in reactions.

Ptolemy also found hints of polyoxymethylene, a polymer thought to be produced from formaldehyde by cosmic radiation, previously detected on Halley’s Comet. This source of formaldehyde is another important potential resource for origin-of-life chemistry, Wright underlines. ‘It can produce simple sugars like ribose,’ he says. ‘These are things that we hope will be picked up by astrobiologists in refining their ideas.’

John Plane from the atmospheric and planetary chemistry group at the University of Leeds calls these measurements ‘technically incredible’. ‘It’s a wonderful achievement to get any data,’ he says. Plane is especially pleased because COSAC’s findings support lab experiments showing cometary ice can produce small organic molecules. ‘It’s nice to have them confirmed, and get a first idea of relative abundance,’ he says. ‘That’s useful if you want to simulate the next step, how these molecules could react together to make peptides and DNA.’
Meanwhile, Rosetta has recently regained tenuous contact with Philae, enough for scientific commands to be sent to Ptolemy last week, Wright reveals. ‘We haven’t got any data back,’ he admits. ‘When we get a communication window it might come back, but it’s a fingers crossed job. As time goes on we’re becoming less convinced that’s going to happen.’

Rosetta's lander Philae wakes up from hibernation (14 June)

Rosetta's lander Philae has woken up after seven months in hibernation on the surface of Comet 67P/Churyumov-Gerasimenko.
The signals were received at ESA's European Space Operations Centre in Darmstadt at 22:28 CEST on 13 June. More than 300 data packets have been analysed by the teams at the Lander Control Center at the German Aerospace Center (DLR).
"Philae is doing very well: It has an operating temperature of -35ºC and has 24 Watts available," explains DLR Philae Project Manager Dr. Stephan Ulamec. "The lander is ready for operations."
For 85 seconds Philae "spoke" with its team on ground, via Rosetta, in the first contact since going into hibernation in November.
When analysing the status data it became clear that Philae also must have been awake earlier: "We have also received historical data – so far, however, the lander had not been able to contact us earlier."
Now the scientists are waiting for the next contact. There are still more than 8000 data packets in Philae’s mass memory which will give the DLR team information on what happened to the lander in the past few days on Comet 67P/Churyumov-Gerasimenko.
Philae shut down on 15 November 2014 at 1:15 CET after being in operation on the comet for about 60 hours. Since 12 March 2015 the communication unit on orbiter Rosetta was turned on to listen out for the lander.

Rosetta Comet 'Pouring' More Water into Space

There has been a significant increase in the amount of water "pouring" out of comet 67P/Churyumov-Gerasimenko, the comet on which the Rosetta mission's Philae lander touched down in November 2014.

The 2.5-mile-wide (4-kilometer) comet was releasing the earthly equivalent of 40 ounces (1.2 liters) of water into space every second at the end of August 2014. The observations were made by NASA's Microwave Instrument for Rosetta Orbiter (MIRO), aboard the European Space Agency's Rosetta spacecraft. Science results from the MIRO team were released today as part of a special Rosetta-related issue of the journal Science.

"In observations over a period of three months [June through August, 2014], the amount of water in vapor form that the comet was dumping into space grew about tenfold," said Sam Gulkis, principal investigator of the MIRO instrument at NASA's Jet Propulsion Laboratory in Pasadena, California, and lead author of a paper appearing in the special issue. "To be up close and personal with a comet for an extended period of time has provided us with an unprecedented opportunity to see how comets transform from cold, icy bodies to active objects spewing out gas and dust as they get closer to the sun."

The MIRO instrument is a small and lightweight spectrometer that can map the abundance, temperature and velocity of cometary water vapor and other molecules that the nucleus releases. It can also measure the temperature up to about one inch (two centimeters) below the surface of the comet's nucleus. One reason the subsurface temperature is important is that the observed gases likely come from sublimating ices beneath the surface. By combining information on both the gas and the subsurface, MIRO will be able to study this process in detail.

Also in the paper released today, the MIRO team reports that 67P spews out more gas from certain locations and at certain times during its "day." The nucleus of 67P consists of two lobes of different sizes (often referred to as the "body" and "head" because of its duck-like shape), connected by a neck region. A substantial portion of the measured outgassing from June through September 2014 occurred from the neck region during the afternoon.

"That situation may be changing now that the comet is getting warmer," said Gulkis. "MIRO observations would need to be carefully analyzed to deter
mine which factors in addition to the sun's warmth are responsible for the cometary outgassing."
Observations are continuing to search for variability in the production rate and changes in the parts of the nucleus that release gas as the comet's distance from the sun changes. This information will help scientists understand how comets evolve as they orbit and move toward and then away from the sun. The gas production rate is also important to the Rosetta navigation team controlling the spacecraft, as this flowing gas can alter the trajectory of the spacecraft.

In another 67P paper released today, it was revealed that the comet's atmosphere, or coma, is much less homogenous than expected and that comet outgassing varies significantly over time.
"If we would have just seen a steady increase of gases as we closed in on the comet, there would be no question about the heterogeneity of the nucleus," said Myrtha Hässig, a NASA-sponsored scientist from the Southwest Research Institute in San Antonio. "Instead we saw spikes in water readings, and a few hours later, a spike in carbon dioxide readings. This variation could be a temperature effect or a seasonal effect, or it could point to the possibility of comet migrations in the early solar system."
The measurements on the coma were made by the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis Double Focusing Mass Spectrometer (ROSINA DFMS) instrument. Measuring the in situ coma composition at the position of the spacecraft, ROSINA data indicate that the water vapor signal is strongest overall. However, there are periods when the carbon monoxide and carbon dioxide abundances rival that of water.

"Taken together, the MIRO outgassing results and results about heterogeneous fountains from ROSINA suggest fascinating new details to be learned about how comets work,"said Claudia Alexander, NASA project scientist for the U.S. Rosetta team, from JPL. "These results are helping us move the field forward on how comets operate on a fundamental level."

Rosetta is currently about 107 million miles (171 million kilometers) from Earth and about 92 million miles (148 million kilometers) from the sun. Comets are time capsules containing primitive material left over from the epoch when the sun and its planets formed. By studying the gas, dust and structure of the nucleus and organic materials associated with the comet, via both remote and in situ observations, the Rosetta mission should become a key to unlocking the history and evolution of our solar system, as well as answering questions regarding the origin of Earth's water and perhaps even life. Rosetta is the first mission in history to rendezvous with a comet, escort it as it orbits the sun, and deploy a lander to its surface.

Rosetta Instrument Reignites Debate on Earth's Oceans

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 Agency's 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 planet's 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 Earth's 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-Gerasimenko's 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 Rosetta's in situ analysis of this comet was always going to throw us surprises," said Matt Taylor, Rosetta's 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 Earth's 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.

Most of Earth's Water Came from Asteroids, Not Comets

Asteroids, not comets, may have delivered most of Earth's water to the planet when the solar system was young, new data from a probe orbiting a comet suggests.
Comets are some of the solar system's most primitive building blocks, with many dating to soon after its formation. Scientists think that these dirty snowballs probably helped seed Earth with key ingredients for life, such as organic compounds.
The European Space Agency's (ESA) Rosetta spacecraft is helping scientists learn more about the role these icy nomads have played in the evolution of the solar system and life on Earth by analyzing the composition of Comet 67P/Churyumov–Gerasimenko. In August, Rosetta became the first spacecraft to orbit a comet, and in November, its Philae lander became the first probe to make a soft touchdown on a comet's surface. Rosetta is also the first mission to escort a comet as it travels around the sun. [See images from ESA's Rosetta mission]

Now, Rosetta has helped solve a mystery about how Earth became the watery world it is today. Before Rosetta began orbiting Comet 67P/C-G in August, it was using an instrument known as ROSINA (short for Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) to analyze the chemical fingerprint of gases in the comet's fuzzy envelope. Scientists focused on data from the instrument regarding water to help uncover whether asteroids or comets delivered the water in Earth's oceans.

Heavy water on Earth and in comets

Models of Earth's birth suggestthat the planet was quite hot after its formation about 4.6 billion years ago, so scientists think it's unlikely that any water currently on Earth's surface dates back to the time of the planet's creation. However, prior studies have hinted that cosmic impacts could have easily brought water later, during a violent era known as the Late Heavy Bombardment, about 800 million years after Earth's formation.

To uncover the source of Earth's water, scientists look for bodies elsewhere in the solar system with similar water. Out of every 10,000 water molecules on Earth, three are not normal water molecules, but instead are so-called heavy water molecules.

A normal water molecule is made of two hydrogen atoms and one oxygen atom. In heavy water, a normal hydrogen atom is replaced with deuterium, which is like hydrogen except that it has an extra neutron in its nucleus. (A regular hydrogen atom has only one proton in its nucleus.)
To see if comets might be the source of Earth's water, in 1986, the ESA probe Giotto flew by Halley's Comet, becoming the first spacecraft to make close observations of a comet. It discovered that Halley's Comet had twice the amount of heavy water compared to normal water as Earth does.
Halley's Comet comes from the Oort Cloud, a giant spherical cloud of trillions of icy bodies that extends from 5,000 to 100,000 times the distance of Earth to the sun. The data from Halley's Comet and from other Oort Cloud comets "ruled out Oort Cloud comets as being the source of terrestrial water," said lead study author Kathrin Altwegg,of the University of Bern in Switzerland, principal investigator for the ROSINA mass spectrometer on Rosetta. [

But the Oort Cloud is not the only source of comets in the solar system. Another home to the dirty snowballs is the disc-shaped Kuiper Belt, which extends from about 30 to 55 times the distance of Earth to the sun. In 2011, data from ESA's Herschel Space Observatory revealed that Kuiper Belt comet 103P/Hartley 2 had a deuterium-to-hydrogen ratio "that matched terrestrial water's perfectly," Altwegg said during a news conference Tuesday (Dec. 9). "The Hartley 2 measurement — that was a real big surprise."

Not all comets are alike

Now, Rosetta has provided data from Comet 67P/C-G, another Kuiper Belt comet. However, Rosetta has discovered that this comet possesses an even higher deuterium-to-hydrogen ratio than seen in Oort Cloud comets — three times the amount of heavy water compared to normal water as Earth has.

This probably rules out Kuiper Belt comets from bringing water to Earth," Altwegg said. Instead, most of Earth's water was probably delivered by asteroids, Altwegg said.

"Today's asteroids have very little water — that's clear," Altwegg added. "But that was probably not always the case. During the Late Heavy Bombardment 3.8 billion years ago, at that time, asteroids could have had much more water than they could now."

The asteroids seen now "have stayed in the vicinity of the sun for 4.6 billion years," Altwegg said. "They've lost water due to the sun, due to heat. But to start with, they might have had much more water than they have now." Future analysis of ice-rich bodies in the asteroid belt could shed light on whether Earth's water really did come from there, Altwegg said.

The differences seen between Comet 103P/Hartley 2 and Comet 67P/C-G suggest that Kuiper Belt comets are much more diverse than previously thought. This could mean that "they were probably not all assembled in the same location in the solar system," Altwegg said. Kuiper Belt comets with relatively low deuterium-to-hydrogen ratios might have formed close to the sun, where solar warmth may have helped them lose deuterium, while those with relatively high deuterium-to-hydrogen ratios might have originated farther away.

In the future, when Comet 67P/C-G flies closer to the sun, the scientists hope to fly Rosetta through a jet of gas that the comet will give off as it gets warmer and more active. This will help reveal if the deuterium-to-hydrogen ratio seen from the water near the comet's surface is the same as that from near its core.

"Hopefully, we'll get to fly directly through a jet [in the] summertime [of] next year," said Matt Taylor, ESA Rosetta project scientist.

Where could Philae be?

Scientists are also still on the lookout for Philae, which made a bouncy landing on Comet 67P/C-G's surface in mid-November. The refrigerator-size probe's anchoring harpoons did not fire as planned during touchdown, and it bounced off the comet twice before settling down on its surface.
It broadcasted scientific data for about 57 hours on the comet's surface before its primary batteries ran out.
ESA officials aren't sure where Philae is now. Panoramic images from the probe reveal "one side of the lander appears to be in a hole," Taylor said during the news conference. "I see an overhanging clifflike structure."
A radio instrument known as CONSERT, short for Comet Nucleus Sounding Experiment by Radiowave Transmission, on both Rosetta and Philae has narrowed the lander's position to a strip a few hundred feet long by a few dozen feet wide.
"We're using that to kind of nail down where we think we should be looking harder," Taylor said. "Once we get identification of where the lander is, that will give us a better fix on what we believe the illumination conditions are and a better idea of when we should expect the lander to have sufficient illumination to start charging its batteries and come back online."
A "back-of-a-beer-mat calculation" suggests Philae might come back online around May, Taylor added.
The new comet findings are detailed in this week's issue of the journal Science