Tag Archives: 67p

67P/Churyumov-Gerasimenko.

Comet 67P harbors oxygen molecules as old as the Solar System

Molecular oxygen found on the comet 67P/Churyumov-Gerasimenko isn’t produced on the surface — it comes from the early days of the Solar System.

67P/Churyumov-Gerasimenko.

Mosaic of four images taken by Rosetta’s navigation camera (NAVCAM) on 19 September 2014 at 28.6 km (17.8 mi) from the centre of comet 67P/Churyumov–Gerasimenko.
Image credits ESA / Rosetta / NAVCAM.

Between August 2014 and September 2016, the European Space (ESA) Agency’s Rosetta craft tagged along with the comet  67P/Churyumov-Gerasimenko as it was trekking around the Sun. The mission also saw a probe delivered to the comet’s surface.

Among other things, the ESA wanted to use Rosetta to study the comet’s coma — the nebulous envelope around the nucleus of a comet. This structure is created by ice subliming — turning from a solid directly into a gas — on the comet’s surface under the sun’s rays. Rosetta’s analysis of the coma revealed that it contains water, carbon monoxide and dioxide (all compounds we were expecting to find), but also molecular oxygen.

Retro oxygen

Molecular oxygen is composed of two oxygen atoms tied together by a covalent bond. Here on Earth, it’s produced by plants via photosynthesis, but researchers are well aware that oxygen is abundant in many places of the universe — we’ve detected molecular oxygen around some of Jupiter’s moons, for example. By mass, oxygen is the third-most abundant element in the universe, after hydrogen and helium — but finding it around a comet was surprising, to say the least.

With the finding also came questions regarding the origin of this molecular oxygen. Some researchers suggested that it might be produced on the comet’s surface under the action of charged ions in the solar wind.

A new paper published by members of the Rosetta team has analyzed data beamed back by the craft to get to the bottom of the issue. The research, led by researchers from the Imperial College London, found that the proposed ionic mechanism for molecular oxygen generation couldn’t account for levels of this molecule observed in the coma. This would mean that the oxygen molecules Rosetta stumbled upon are primordial — meaning they were already fully formed as the comet itself quickened during the early days of the Solar System 4.6 billion years ago.

“We tested the new theory of surface molecular oxygen production using observations of energetic ions, particles which trigger the surface processes which could lead to the production of molecular oxygen,” said lead author Mr Kevin Heritier. “We found that the amount of energetic ions present could not produce enough molecular oxygen to account for the amount of molecular oxygen observed in the coma.”

The findings don’t rule out oxygen generation at the surface level of 67P — but that the majority of the oxygen in the comet’s coma is simply not produced through such a process.

While there are other theories regarding the origin of 67P’s oxygen, the team didn’t address them in any way, either to confirm or infirm them. So far, however, they say that the primordial oxygen theory is the one which fits available data best. This is further supported by other theoretical work that treats the formation of molecular oxygen in dark clouds and the presence of molecular oxygen in the early Solar System, they add. In the team’s model, preexisting molecular oxygen froze into tiny grains that later clumped together, attracted more material, and eventually got bound up in the comet’s nucleus.

The paper “On the origin of molecular oxygen in cometary comae” has been published in the journal Nature Communications.

We have new data from the Philae lander – it identifies several new organic molecules on Comet 67P, charts internal structure

NASA’s Rosetta mission began with what some would call a streak of bad luck.

After the successful separation procedure, Philae’s anchoring harpoons failed to fire and the 220-lb. (100 kilograms) lander bounced off 67P’s surface, clipped a crater rim and then bounced a second time before finally coming to rest nearly two hours after first making contact with the comet’s surface.

Philae’s landing points on Comet 67P/Churyumov-Gerasimenko on Nov. 12, 2014.

The plan was for it to recharge its power supply using photo-voltaic panels, but the place it eventually landed on was quite shady. The stranded probe transmited preliminary data until its primary battery was depleted (about 60 hours), and then went into hibernation.

The initial observations, published on July 30 in the journal Science, show that the comet is a porous body with a fairly homogeneous interior. It also has a diverse surface that harbors many different carbon-containing organic molecules, the scientists said.

“What really blows my mind is to have this combination of complementary results, allowing us at the same time to ‘feel’ the surface of the comet, very locally, as if we were there, while also getting the bigger picture through the sounding of the cometary interior structure,” Nicolas Altobelli, acting Rosetta project scientist, told Space.com via email.

“The implications of these measurements, and in particular the fairly homogeneous, very porous structure of the interior, will help constrain the formation models of planetesimals in the solar nebula, by a better understanding of the accretion processes,” Altobelli added, referring to the process by which planetary bodies, stars, comets and so on are formed from spacedust.

Not elegant but effective

While the landing definitely had scientists on the edge, in the end it seems to have been a boon in disguise, as it allowed observations of different locations on 67P’s body, in its initial and final landing spots (which have been dubbed Agilkia and Abydos, respectively).

And those two sites are quite different, it turns out. Agilkia’s surface is relatively soft, covered with a layer of granular material about 0.82 feet (0.25 meters) deep, while Abydos is much harder.

 

Two trajectory reconstructions of the lander’s touchdown.

“Before the landing of Philae, we believed cometary surfaces might be very soft (loose regolith under low gravity). Some colleagues even feared the lander may sink deeply into the surface at touchdown,” Philae project manager Stephan Ulamec, of the German Aerospace Center (DLR), told Space.com via email. “Although we were aware of our limited knowledge, the fact that some of the material is so hard, and that the surface is so heterogen[eous], was indeed a bit surprising.”

Images captured by Philae’s Comet Infrared and Visible Analyser camera, or CIVA, highlight the diversity and complexity of 67P’s surface, showing fractured, boulder-studded terrain with a variety of grain sizes and reflectivity.

The soft layer of “dirt” goes up to 6.5 feet (2 meters) deep in some places on the surface of the comet, and nonexistent in others, suggest images taken from the ROLIS (Rosetta Lander Imaging System) during the probe’s descent.

The images also show a boulder about 16.5 feet (5 m) wide, which is partly surrounded by a depression resembling a “wind tail,” an erosional feature also seen on our planet, and Mars. Another 17 such structures have since been identified by mission scientists, with lengths ranging from 16.5 feet to 100 feet (5 to 30 m). They are caused by particles abrading the surface of the comet during its travels, like an interstellar sandblasting.

Temperatures also vary on the surface from very uncomfortable to extremely uncomfortable, without the thermal balance offered by a thick atmosphere – daytime temperatures on the comet’s surface in November 2014 ranged from minus 226 degrees Fahrenheit to minus 298 degrees Fahrenheit (minus 143 to minus 183 degrees Celsius). However, as the comet is closer to the sun, those temperatures have probably risen by now but the difference between the dark and lighted side is presumed to be higher.

An organic cocktail

Two different Philae instruments, known as Ptolemy and COSAC (Cometary Sampling and Composition), hunted for organic compounds— the building blocks of life as we know it — on and around Comet 67P.

While the initial data burst received from the lander did hint at the existence of organics on its surface, the data was limited and its meaning not very clear.

The new data is much more interesting. Both instruments detected lots of molecules. COSAC, for example, found 16 different organics, including four (methyl isocyanate, acetone, propionaldehyde, and acetamide) that had never been spotted on or around a comet before.

“If such cometary material falls onto a planet in the right environment, emerging life could make use of it,” COSAC principal investigator Fred Goesmann, of the Max Planck Institute for Solar System Research in Germany, told Space.com via email.

Ptolemy’s observations also revealed a rich mix of organics, along with lots of water and carbon dioxide.

“I think an understanding of the organic compounds that are present in this particular comet will have tremendous ramifications for origin-of-life studies,” Ptolemy principal investigator Ian Wright, of the Open University in the United Kingdom, told Space.com.

The newly reported Ptolemy data were gathered during a calibration run, Wright said, adding that more results from the instrument will be published soon.

Internal structure also charted.

Using its CONSERT (Comet Nucleus Sounding Experiment by Radiowave Transmission) instrument, the Rosetta lander also studied the interior structure of the comet. This instrument picks up long-wavelength signals beamed through 67P by the orbiting Rosetta mothership.

Data suggest that the “head” of the comet is homogeneous -on the scale of a few tens of meters- and really porous, with open space making up 75 to 85 percent of its volume, researchers said.

Observations done with this instrument have also narrowed down the area where the lander might be found -we lost it a little– to a ribbon about 69 feet wide by 112 feet long (21 by 34 m).

“Philae provided us unique information on a comet’s surface properties (and interior) that could not be obtained from orbiter measurements alone,” Ulamec said. “We learned so much about comets that now future missions can be adapted in a much better way to this challenging environment.”

And Philae’s not out yet!

The newly released studies are not necessarily the last word from Philae, as the lander woke from hibernation in mid-June.

Communication between Philae and its handlers here on Earth remains extremely spotty — the last contact occurred on July 9 — but the mission team holds out hope that it can get the lander up and running again soon.

“We keep listening and sending commands to Philae, every time we have an opportunity for communication,” Altobelli said.

 

Philae could be sitting on a comet filled with alien life and not even know it

Comet lander Philae may be sitting on top of microbial life and not even know it – even worse, it has no way of figuring out if it actually is. According to two researchers, the comet’s characteristics (as well as computer simulations) might indicate that the surface may be teeming with microbes.

The black layer on the comet’s surface may be a result of microbial activity, scientists claim.

The Rosetta spacecraft was launched in March 2004 by the European Space Agency (ESA). Along with Philae, its lander module, its main goal was to perform a detailed study of comet 67P/Churyumov–Gerasimenko (67P); this was actually the first mission to orbit and study a comet up close. In late 2014, Philae successfully landed on a comet and obtained detailed images of the comet’s surface. On 15 November 2014, Philae entered its hibernation mode after its batteries ran down due to reduced sunlight, but in June 2015, Philae woke up and started communicating again, sending some important clues regarding potential alien life on the comet.

The comet has a black, organic-rich crust, which could with organisms making their way beneath its icy surface. Of course, there are other (more reasonable) explanations, but researchers seem adamant in their claims. If there is in fact life on comet 67P, then it would be nothing more than microbes, but these microbes would be huge (figuratively, not literally) – it would be mind boggling, which is why so many are skeptical about these claims.

Director of the Buckingham Centre for Astrobiology professor Chandra Wickramasinghe and his colleague Dr Max Wallis from the University of Cardiff have said that comet 67P and others like it may have significant populations of extremophiles on it – organisms that can survive in extreme conditions, like the ones on 67P.

“These are not easily explained in terms of prebiotic chemistry. The dark material is being constantly replenished as it is boiled off by heat from the sun. Something must be doing that at a fairly prolific rate,” Wickramasinghe said.

The comet has a black hydrocarbon crust overlaying ice, smooth icy ‘seas’, and flat-bottomed craters containing ‘lakes’ of re-frozen water overlain with organic debris.

To make things even more tantalizing, Wickramasinghe and Wallis conducted computer simulations which showed that it would be (theoretically) possible for microbes to survive on the comet. The astronomers present their case for life on 67P at the Royal Astronomical Society’s National Astronomy Meeting in Llandudno, Wales. Now, scientists are kicking themselves for not adding life-detection technology to Philae.

“I wanted to include a very inexpensive life-detection experiment. At the time it was thought this was a bizarre proposition,” Wickramasinghe added.

Furthermore, several cracks in the ice had been shown to be ‘spewing out material’ that is falling on to the surface, which also points to microbial activity.

“I think the microbiotic activity just under the surface results in gas which builds up to the point where the overlaying layers of ice can’t withstand the stresses,” said the professor.

If this were actually the case, if life actually exists on comet, it would be huge – potentially force us to rethink what we know about the very emergence of life. It also has vast implications for life on Earth; would life on Earth evolved by itself, or would have it been “seeded” by comets? But as strange and difficult to accept this may be, we have to keep an open mind.

“Five hundred years ago it was a struggle to have people accept that the Earth was not the center of the universe. After that revolution our thinking has remained Earth-centered in relation to life and biology. It’s deeply ingrained in our scientific culture and it will take a lot of evidence to kick it over,” Wickramasinghe said.

 

Rosetta spacecraft finds huge sinkholes on comet’s surface

Rosetta is a robotic space probe built and launched by the European Space Agency. Along with Philae, its lander module, the craft is performing a detailed study of comet 67P/Churyumov–Gerasimenko.

The probe usually orbits 67P at a distance of a few hundred kilometers. Footage received from Rosetta over the last year showed a number of dust jets coming from the comet, which we expected to see. But, after analyzing high-fidelity images from the lander’s OSIRIS instruments, taken just ten to 30 km from the comet’s center, scientists saw that at least some of the dust jets come from specific locations on the comet’s surface, being projected from huge sinkholes.

The scientists have picked out 18 quasi-circular pits in the northern hemisphere of the comet, some of which are still active now. Each sinkhole is anywhere from a few tens of metres to hundreds of metres in diameter and go below the surface by up to 210m to a smooth dust-covered floor.

A catalogue of sinkholes spotted by Rosetta on comet 67P/Churyumov-Gerasimenko.
Image via: forbes.com

“We see jets arising from the fractured areas of the walls inside the pits. These fractures mean that volatiles trapped under the surface can be warmed more easily and subsequently escape into space,” says Jean-Baptiste Vincent from the Max Planck Institute for Solar System Research, lead author of the study.

Similar to the ones on Earth, these sinkholes form when a cavity opens up under the surface. As it widens and deepens, the loss of material makes the ceiling too thin to support its own weight, and collapses. After the collapse, the volatile materials can evaporate or be eroded more easily, and the sinkhole enlarges over time.

“Although we think the collapse that produces a pit is sudden, the cavity in the porous subsurface could have growing over much longer timescales,” says co-author Sebastien Besse, of ESA’s ESTEC technical centre in the Netherlands.

So, what caused these cavities to form in the first place? The team has three theories that they are pursuing.

The first one is that they are artifacts of the comet’s weak gravitational field. When it formed, material accreted by means of low-velocity impacts, leaving behind void areas due to the imperfect fit between primordial building blocks. Over time, seismic events or space impacts cause the surface to weaken enough to cause it to collapse.

Another possibility is that the pits are full of volatile ices like carbon dioxide and carbon monoxide, sitting just beneath a layer of dust. These ices could be melted by the warmth of the Sun as the comet draws closer in its orbit every year.

Or it could be that the ice manages to melt itself away by transforming from amorphous ice made up of irregularly packed molecules to crystallised ice, a process that would release heat which could be sufficient to cause evaporation.

Close-up photo of sinkholes on 67P.
Image via: esa.int

“Regardless of the processes creating the cavities, these features show us that there are large structural and/or compositional differences within the first few hundred metres of the comet’s surface and the cavities are revealing relatively unprocessed materials that might not otherwise be visible,” says Besse.

Researchers analyzing the interior structure of the sinkholes found that their interiors differ quite significantly, with some showing fractured material and terraces, others showing horizontal layers and vertical striations and others also showing globular structures nicknamed “goosebumps”.

“We think that we might be able to use the pits to characterise the relative ages of the comet’s surface: the more pits there are in a region, the younger and less processed the surface there is,” explains Vincent. “This is confirmed by recent observations of the southern hemisphere: this is more highly processed because it receives significantly more energy than the northern hemisphere, and does not seem to display similar pit structures.”

Active pits on Churyumov-Gerasimenko.

Rosetta scientists are hopeful that the spacecraft might yet get to see the formation of a sinkhole in action. The probe did see one outburst during its approach to the comet back in April 2014, which generated between 1,000kg and 100,000kg of material. But although a pit collapse could have been responsible for this, it was much smaller than the researchers expect.

With the collapse of a typical large pit of 140m wide and 140m deep, the team would expect to see the release of around a billion kilograms of material.

“Being able to observe changes in the comet, in particular linking activity to features on the surface, is a key capability of Rosetta and will help us to understand how the comet’s interior and surface have evolved since its formation. And with the extension of the mission until September 2016, we can do the best job possible at unravelling how comets work” says Matt Taylor.