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10.12.2014
RosettaWatch: Comet water is not like Earth's
IF EARTH got its water from space, it probably wasn't delivered by comet. That's according to the latest data from the European Space Agency's Rosetta spacecraft, which has been analysing the water content of comet 67P/Churyumov-Gerasimenko and found it doesn't match the water on Earth.
The question of where Earth got its water – whether from asteroids, comets or in some other way – is a subject of ongoing debate. So analysing comet 67P's water was one of Rosetta's main goals. The spacecraft's ROSINA instrument has been sniffing the vapour around the comet ever since reaching it in August.
Kathrin Altwegg of the University of Bern in Switzerland and her colleagues have now analysed 67P's water, by looking at the amount of deuterium, a heavy isotope of hydrogen, and comparing it with the amount of regular hydrogen (Science, DOI: 10.1126/science.1261952).
"As soon as we got water from the comet, the pattern changed immediately," says Altwegg. The comet's water has around three times as much deuterium as water on Earth, the researchers found. The ratio found on some other comets is much closer to that on Earth, suggesting a link between the icy space rocks and terrestrial water. The different composition of 67P's water suggests a more complex picture.
"We know there is material out there that has the signature of Earth's water in it, but is it the material that supplied it?" says Edwin Bergin of the University of Michigan, Ann Arbor, who previously found that comet Hartley 2 has similar water to that of Earth. Models of asteroid and comet motion within the solar system suggest asteroids were more likely to cross paths with Earth, but we don't yet know if they had the right mix of water to create the oceans. "We need many more measurements of this type to get an understanding of the diversity within the population," Bergin says
"In the end, Earth's oceans are probably a mix of many things," says Altwegg.
The data collected so far may not be the last word on 67P's water. It is possible that there are pockets of water with a different deuterium-to-hydrogen ratio that could be released as the comet nears the sun and heats up. The two halves of the duck-shaped 67P might even have different hydrogen signatures, which would suggest they were once distinct bodies that formed in different parts of the solar system before colliding. "That would be a very interesting result," says Altwegg.
ROSINA's job has been made harder by the loss of Philae, the probe that landed on 67P in November but was unable to survive due to a lack of solar power. That could make signals of heavier molecules, particularly the amino acids necessary for life, more ambiguous.
"The identification of molecules is certainly more difficult," says Altwegg, who had hoped to compare ROSINA's data with Philae's Ptolemy instrument, which was designed to measure molecules in a different way. "If you have two different instruments you can resolve it, and this we cannot do, so it's all on ROSINA more or less."
Quelle: NewScientist
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ROSETTA FUELS DEBATE ON ORIGIN OF EARTH’S OCEANS
Rosetta has found that the composition of the water vapour at Comet 67P/C-G is significantly different to that found on Earth.
The measurements were made in the month following the spacecraft’s arrival at Comet 67P/Churyumov–Gerasimenko’s on 6 August. It is one of the most anticipated early results of the mission, because the origin of Earth’s water is still an open question. A leading hypothesis is that comets and asteroids played a role in delivering it to Earth, but the relative contribution of each class of object to our planet’s water supply is widely debated.
The key to determining where the water originated is in its ‘flavour’, in this case the proportion of deuterium – a form of hydrogen with an additional neutron – to normal hydrogen.
Previous measurements of the deuterium/hydrogen (D/H) ratio in other comets have shown a wide range of values. Of the 11 comets for which measurements have been made, it is only the Jupiter-family Comet 103P/Hartley 2 that was found to match the composition of Earth’s water, in observations made by ESA’s Herschel mission in 2011.
By contrast, meteorites originally hailing from asteroids in the Asteroid Belt also match the composition of Earth’s water. Thus, despite the fact that asteroids have a much lower overall water content, impacts by a large number of them could still have resulted in Earth’s oceans.
It is against this backdrop that Rosetta’s investigations are important. Interestingly, the D/H ratio measured by the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis, or ROSINA, is more than three times greater than for Earth’s oceans and for its Jupiter-family companion, Comet Hartley 2. Indeed, it is even higher than measured for any Oort cloud comet as well.
“This surprising finding could indicate a diverse origin for the Jupiter-family comets – perhaps they formed over a wider range of distances in the young Solar System than we previously thought,” says Kathrin Altwegg, principal investigator for ROSINA and lead author of the paper reporting the results.
“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.”
This is just an excerpt from our story published on the ESA web portal today; read our full report – including more background information and graphics – here: Rosetta fuels debate on origin of Earth’s oceans
Quelle: ESA
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Update: 11.12.2014
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COMETWATCH 9 DECEMBER
This four-image mosaic comprises images taken from a distance of 20.4 km from the centre of Comet 67P/Churyumov-Gerasimenko on 9 December. The image resolution is 1.74m/pixel and the individual 1024 x 1024 frames measure 1.8 km across. The mosaic is slightly cropped and measures 2.9 x 2.7 km.
As usual, rotation and translation of the comet during the image sequencing makes it difficult to create an accurate mosaic. In this particular instance, some distortion terms were introduced to make the mosaic, but careful inspection will show slight remaining mismatch errors at one of the peaks on the top edge of the mosaic and at the limb of the comet on the right-hand edge.
Some cleaning has been applied to lower the impact of NAVCAM scattering and make the boundaries between images continuous. So, be cautious in pushing the intensities too far to look at very faint features: there will be some artefacts.
In this orientation, the smaller lobe of the comet is to the right, and the larger lobe to the left.
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Four-image NAVCAM mosaic comprising images taken on 9 December. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
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The lower left part of the mosaic has some particularly interesting features. Towards the left of the smooth neck region, there are a series of curved trough-like features. The longest of these features, at the bottom of this set in this orientation, is reminiscent of the feature close to the Cheops boulder.The same features are also just visible in the image published earlier this week, towards the centre of the frame, but the image presented here provides a much clearer view.
However, it is difficult to spot these particular features in earlier images (e.g those taken on 2 Oct and 20 Oct), suggesting that changes may be occurring on the surface. That said, changes in viewing angle, illumination conditions, and image resolution could also be responsible, and a more detailed analysis at high resolution and over a wider range of viewing conditions will be needed to see if these features are changing in appearance over time.
Towards the right of the neck region, you may also spot what appears to be a chain of small pits – these were also identified in earlier images, and almost give the impression that perhaps a boulder has bounced and rolled along a linear track.
Finally in the same region, towards the bottom left of the mosaic, brighter cliffs also stand out against the darker background, seemingly devoid of the dust that covers the majority of the comet’s surface.
Of course, the rest of the mosaic offers incredible views of the comet’s surface details too, and the region at far right gives another look across the large depression that the 7 December image set focused on.
As mentioned previously in the blog, a full geologic interpretation of the comet’s features and evolutionary processes will be made available by the Rosetta science teams via peer-reviewed papers in due course.
The individual image frames are provided below.
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Quelle: ESA
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Update: 12.12.2014
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WHAT’S UP WITH ROSETTA
First off: watch this!
It's a visualisation of Rosetta’s trajectory from the delivery of Philae to the surface of Comet 67P/C-G through to the end of 2014.
Following the lander delivery on 12 November, a series of thruster burns on 19, 22 and 29 November brought the spacecraft to a 30 x 30 km orbit (see 'Rosetta continues into its full science phase' in the main ESA website).
On 3 and 6 December, a pair of burns brought it back down into a 20 km x 20 km circular orbit, following the terminator, i.e. orbiting above the day-night line on the comet's ragged surface. This is where Rosetta will stay until 20 December, when the first of a new pair of burns will kick it back up to 30 km x 30 km circular orbit. The second burn will take place on 24 December.
Rosetta will stay from then on in a 30 km orbit until 3 February 2015.
"After that, Rosetta will begin flying a series of flybys,” says Spacecraft Operations Manager Sylvain Lodiot. "And that will be the pattern for the rest of the nominal mission."
“Contrary to the pre-landing phase, where the trajectories flown were designed with the lander delivery always in mind, science now drives trajectory design,” says Michael Küppers, Science Operations Coordinator for the Rosetta mission.
Rosetta’s trajectories are designed by the Science Operations team in ESAC, Madrid, on behalf of the instrument teams, and are delivered to ESOC for implementation. Science planning is performed against two different trajectories: a ‘preferred’ and a ‘high activity’ trajectory. While the intention is to always fly the preferred, in the event that comet activity increases beyond that expected for the preferred case, the spacecraft will move to the high-activity trajectory. This will allow the science operations to continue, besides the initial impact on science planning that such a move would entail.
“The desire is to continue to keep the spacecraft as close as feasible to the comet before its activity becomes too high to maintain closed orbits,” says Laurence O’Rourke, also a Rosetta Science Operations Coordinator at ESAC. “Once we leave the closed orbits, we will then carry out science linked to close & far flybys of the comet.”
High-resolution mapping of the comet will therefore continue, along with the collection of gas, dust and plasma as the comet’s activity continues to increase. The science teams also hope to sample rare molecules in the gas that may include complex organics that could have played a role in the origins of life on Earth.
An exciting manoeuvre is planned for Valentine’s Day 2015, when Rosetta will make the closest-ever flyby of Comet 67P/C-G at just 6 km from the surface. To achieve this, the spacecraft will leave its 30-km orbit on 4 February 2015, flying out to a distance of over 140 km from the comet before beginning to swoop down once more.
This close flyby will allow instruments to take images and spectra of the surface with unprecedented resolution and to directly sample the very inner cometary coma where the nucleus material is processed into the coma and tail as we know it from remote observations.
“Landing week marked an epoch where we began the one-hundred-percent science phase,” says Matt Taylor, Rosetta Project Scientist.
“From now on, that’s all we focus on with the mission. The measurements we make now set the tone for the entire mission. The comet’s activity will continue to increase and we’ll be watching.
Science has started with gusto, thanks to the work of the instrument teams and the Rosetta science operations team.”
The spacecraft is in excellent shape; all systems on board are performing as expected and the mission systems on ground are nominal.
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COMET 67P/C-G IN LIVING COLOUR
Rosetta’s OSIRIS team have produced a colour image of Comet 67P/Churyumov-Gerasimenko as it would be seen by the human eye. As anticipated, the comet turns out to be very grey indeed, with only slight, subtle colour variations seen across its surface.
To create an image revealing 67P’s “true” colours, the scientists superposed images taken sequentially through filters centred on red, green, and blue wavelengths.
However, as the comet rotated and Rosetta moved during this sequence, the three images are slightly shifted with respect to each other, and are taken from slightly different observing perspectives. Painstaking work is needed to superimpose the images accurately, which is one reason it has taken so long to come up with the first meaningful colour image of 67P/C-G.
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A colour image of Comet 67P/Churyumov-Gerasimenko composed of three images taken with the Narrow Angle Camera (NAC) of the scientific imaging system OSIRIS in red (centred at 744 nm wavelength), green (536 nm), and blue (481 nm) filters on 6 August 2014 from a distance of 120 kilometres. The image covers roughly 4 x 4 km at a resolution of about 3.9 metres per pixel. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
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“As it turns out, 67P/C-G looks dark grey, in reality almost as black as coal,” says the instrument’s Principal Investigator Holger Sierks from the Max Planck Institute for Solar System Research (MPS).
As explained in earlier blog posts for the NAVCAM images, the intensity of the images has been enhanced to span the full range from black to white, in order to make surface details visible. But the colours have not been enhanced: the comet really is very grey.
A more detailed first analysis nevertheless reveals that the comet reflects red light slightly more efficiently than other wavelengths. This is a well-known phenomenon observed at many other small bodies in the Solar System and is due to the small size of the surface grains. That does not, however, mean that the comet would look red to the human eye. Natural sunlight peaks in the green part of the spectrum and the response of the human eye is similarly matched. Thus, overall, the comet would look rather grey to the human eye, as seen here.
Long before Rosetta’s arrival at the comet, ground-based telescope observations had shown 67P/C-G to be grey on average, but it was not possible to resolve the comet and see any surface details. However, now that OSIRIS is able to take images from close-up, scientists are surprised to see an extremely homogeneously coloured body even on a detailed scale, pointing at little or no compositional variation on the comet’s surface.
For example, any ice on the surface should appear brighter in the blue filter, leading to the appearance of blue-ish patches. This image contains no indication of any such icy patches, consistent with observations made by some of Rosetta’s instruments.
The overall grey colour of the surface shows that it is covered some kind of dark dust. Further studies using other combinations of the 25 filters in OSIRIS’ arsenal will focus on trying to understand the composition of this dust, by looking for different minerals such as pyroxenes, common in the Earth’s crust, or minerals containing water. OSIRIS will also be trying to detect various gas species in the coma surrounding the nucleus.
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ROSETTA SCIENCE TO BE PRESENTED AT AGU
Some of the first scientific results from the Rosetta mission after its arrival at Comet 67P/Churyumov-Gerasimenko on 6 August and since the landing of Philae on 12 November will be presented to the scientific community next week, during the 2014 autumn meeting of the American Geophysical Union (AGU). The meeting, the largest annual Earth and space science conference in the world, is being held in San Francisco from 15–19 December.
We won’t be reporting live from the conference, but some of the presentations in a number of sessions will be streamed live for you to follow. Visit AGU’s website and follow the links from “Virtual Options” to see when virtual sessions are available. Given the location of the conference, all times are given in Pacific Standard Time (PST).
In addition, at 08:00 PST on 17 December there will be a press conference highlighting the latest Rosetta and Philae science: this press conference will also be live streamed. Speakers will include Matt Taylor (ESA Rosetta Project Scientist), Claudia Alexander (NASA Rosetta Project Scientist), Kathrin Altwegg (ROSINA Principal Investigator), and Jean-Pierre Bibring (Philae lander Lead Scientist).
We will put together a summary of the key new findings discussed at the AGU, and will continue to make results available as scientific papers resulting from Rosetta data are published.
Quelle: ESA
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Update: 15.12.2014
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COMETWATCH – 10 DECEMBER
This four-image mosaic comprises images taken from a distance of 20.1 km from the centre of Comet 67P/Churyumov-Gerasimenko on 10 December. The image resolution is 1.71 m/pixel and the individual 1024 x 1024 frames measure 1.75 km across. The mosaic is slightly cropped and measures 2.9 x 2.6 km.
As usual, rotation and translation of the comet during the image sequencing make it difficult to create an accurate mosaic. In this particular instance, some distortion terms were introduced to make the mosaic, and careful inspection may reveal some slight mismatches in features at the seams.
In addition, some cleaning has been applied to lower the impact of NAVCAM scattering and make the boundaries between images continuous. So, be cautious in pushing the intensities too far to look at very faint features: in particular, an apparent discontinuity in the main outflow from the neck of the comet is an artefact.
In this orientation, the smaller lobe of the comet is to the right, and the larger lobe to the left.
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Four-image NAVCAM mosaic comprising images taken on 10 December. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
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The lower right part of the image provides a stunning view on the comet's 'neck' and its constellation of boulders, which were also visible in an image published last week. A hint of activity stemming from the neck is also visible.
The four-frame montage and the individual image frames are provided below.
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Quelle: ESA
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Update: 17.12.2014
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Rosetta Orbiter to Swoop Down On Comet in February
zu sehen hier: https://www.youtube.com/watch?v=BOSyNtuWhGk
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The European Space Agency’s orbiting Rosetta spacecraft is expected to come within four miles (six kilometers) of the surface of comet 67P/Churyumov–Gerasimenko in February of next year. The flyby will be the closest the comet explorer will come during its prime mission.
“It is the earliest we could carry it out without impacting the vitally important bound orbits that are currently being flown,” said Matt Taylor, the Rosetta project scientist from the European Space Research and Technology Center, Noordwijk, the Netherlands. “As the comet becomes more and more active, it will not be possible to get so close to the comet. So this opportunity is very unique.”
The low flyby will be an opportunity for Rosetta to obtain imagery with a resolution of a few inches (tens of centimeters) per pixel. The imagery is expected to provide information on the comet’s porosity and albedo (its reflectance). The flyby will also allow the study of the processes by which cometary dust is accelerated by the cometary gas emission.
“Rosetta is providing us with a grandstand seat of the comet throughout the next year. This flyby will put us track side -- it’s going to be that close,” said Taylor.
The Rosetta orbiter deployed its Philae lander to one spot on the comet's surface in November. Philae obtained the first images taken from a comet's surface and will provide analysis of the comet's possible primordial composition.
Comets are time capsules containing primitive material left over from the epoch when our sun and its planets formed. 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 a European Space Agency 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).
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From the location where it came to rest after bounces, the Philae lander of the European Space Agency's Rosetta mission captured this view of a cliff on the nucleus of comet 67P/Churyumov-Gerasimenko. The feature is called "Perihelion Cliff." The image is from the lander's CIVA camera.
Image Credit: ESA/Rosetta/Philae/CIVA
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This mosaic of images from the navigation camera on the European Space Agency's Rosetta spacecraft shows the nucleus of comet 67P/Churyumov-Gerasimenko as it appeared at 5 a.m. UTC on Dec. 17, 2014 (9 p.m. PST on Dec. 16).
Image Credit: ESA/Rosetta/NAVCAM
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This graphic depicts the position of the Philae lander of the European Space Agency's Rosetta mission, and a nearby cliff photographed by the lander, in the context of topographic modeling of the surface of comet 67P/Churyumov-Gerasimenko's nucleus.
Image Credit: ESA/Rosetta/Philae/CNES/FD/CIVA
Quelle: NASA
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COMETWATCH 14 DECEMBER
This four-image mosaic comprises images taken from a distance of 19.4 km from the centre of Comet 67P/Churyumov-Gerasimenko on 14 December. The image resolution at that distance is 1.66 m/pixel and the individual 1024 x 1024 frames measure 1.7 km across. The mosaic is slightly cropped and measures 3.0 x 3.1 km.
As usual, rotation and translation of the comet during the image sequencing make it difficult to create an accurate mosaic. As always, refer to the individual images below before drawing conclusions about strange structures seen on the comet or low intensity extended emission.
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Four-image NAVCAM mosaic comprising images taken on 14 December. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
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Today’s mosaic shows the underside of the larger lobe of Comet 67P/C-G, providing yet another view of the region that is home to Cheops and its neighbouring boulders.
In line with the Ancient Egyptian naming scheme agreed by Rosetta scientists for features on the comet, this smooth region and the rougher terrain towards the upper right from there has been named Imhotep, after the famous architect of Egyptian pyramids from the 27th century BC. The name of this region was revealed during a talk at AGU today.
The image also highlights the difference between the smooth region where Cheops is located and the areas around it, rich in craters, pits and cliffs.
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In addition, it is interesting to note that the Cheops boulder (upper and lower left frames in the montage above; see here, here and here for previous views) has now become an essential element in the proposal for establishing a scientific coordinate reference frame on the comet. In fact, one of the axes of this reference frame runs from the centre of mass of Comet 67P/C-G through the Cheops boulder.
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MIDAS AND ITS FIRST DUST GRAIN
This blog post is contributed by Mark Bentley, MIDAS Principal Investigator at the Space Research Institute (IWF) in Graz, Austria.
One of the big challenges in planning MIDAS operations is predicting the amount of dust that we collect during an exposure. Measuring the rate of dust grains flying past Rosetta and their size distribution is, of course, part of our science, but to plan our operations, we need to have some idea of what to expect beforehand! This is particularly complicated because with MIDAS, we are interested in measuring the smallest cometary dust particles, less than 1 µm (micrometre or millionth of a metre) in size, and ground-based telescope observations that are used to study dust remotely are almost blind to these sizes.
So with that in mind, we started our first exposure in mid-September, opening the shutter for about 4 days. MIDAS works by collecting dust grains on sticky targets that are then scanned at very high resolution using an atomic force microscope.
Initial calculations suggested that we might find one particle of around 1 µm in an 80x80 µm scan. The “before” and “after” images are shown in the panel below - as you can see, nothing jumps out, as most of the features seen in the after image were also there before we opened the shutter, meaning that they are background contamination (this is why we need to take a scan before!). If you look closely, you might even convince yourself that one or more particles have disappeared, but this is just a result of small offsets in the position of each pixel.
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Images of the MIDAS target before (left) and after (right) exposure in September 2014. The image shows an 80x80 µm portion of the target (the full target measures 1.4 x 2.4 mm). An indication of size is provided, and the colour scale provides a measure of the third spatial dimension (height). Image courtesy of Mark Bentley.
During the following weeks, the same target was exposed and scanned several more times to search for particles. Again, we didn’t see anything obvious. Then, as you may recall, something special happened in mid-November: the Philae lander was deployed to the surface of comet 67P/C-G. Instruments on-board the orbiter had to be in a state where they would be safe regardless of what happened during the lander delivery and, for MIDAS, this meant opening the shutter and exposing the target once more from 9–14 November.
Immediately afterwards, we began yet another scan of the centre of the exposed target. Unfortunately, this scan aborted after several lines – this can happen for several reasons, for example if a temperature change on-board causes the microscope to lose contact with the surface. As a result, it took us a week or so to look back at this small section of a scan. When we did, however, we had a surprise:
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Scan of the MIDAS target exposed in November 2014. The image shows an 80x80 µm portion of the target (the full target measures 1.4 x 2.4 mm). Image courtesy of Mark Bentley.
Although it doesn't look like much, this is in fact our first cometary dust particle!
A few things to note. The bottom black part of the image is not real data – this was after the scan aborted. Similarly, the white horizontal stripes in the upper part of the image, mostly towards the right side, are not real. MIDAS works by rastering over the sample - in this case from left to right in lines, starting from the top. If the sharp tip of the atomic force microscope moves to the next position and immediately thinks that it has detects the surface ... oops, we've hit a dust particle!
In this case, MIDAS plays it safe and moves the tip up and away from the particle. However, there’s a limit to this movement and if it can’t move up far enough to get above the particle, the current line is aborted and the tip is moved down to the start of the next one – this is what produced the white horizontal stripes. If the topography is too high even at the start of the new line making it impossible for MIDAS to retract any further, the whole scan aborts.
Both of these things happened here, because the particle was much larger than expected!
If we zoom in on the “feature” in the first few lines, we can begin to get some idea about what was collected: the complex pattern visible in the upper right part of the image is, in fact, our first dust particle.
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Above and below, two zooms of the MIDAS target exposed in November 2014. An indication of size is provided, and the colour scale provides a measure of the third spatial dimension (height). Images courtesy of Mark Bentley.
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The first thing we see is that the particle is roughly 10 µm in size in the plane of the target, and slightly less in height. Interestingly, we expected to find many smaller particles before catching such a large one.
The next thing to note is that this dust particle appears to be complex in shape and not compact, suggestive of a “fluffy” aggregated grain.
To measure the full size of the grain and to answer more detailed questions, we will need to re-image it – knowing now that it is so large, we can optimise the scanning parameters to avoid hitting the particle from the sides and instead just tap it gently, something that MIDAS is designed to do.
This may not look like much, but it already tells us a lot about the dust environment of comet 67P/C-G and allows us to optimise our collection and scanning strategies. And don’t forget, it’s MIDAS's first confirmed cometary dust particle – 20 years after the instrument was proposed, and after 10 years in flight! Watch this space for more details in the coming weeks.
Quelle: ESA
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