So... some questions to kick off the discussion:
1. If the 2020 Mars rover mission is responsive to the Planetary Decadal Survey, it will collect and cache a suite of samples for eventual return to Earth. With the focus on sample selection and documentation, rather than in situ science, what would be an appropriate scientific payload for such a rover?
2. Knowing what we currently do about Mars, what would be the best place on the planet to collect the first suite of samples to be returned to Earth? What would be appropriate analog sites on Earth?
3. What is the best approach for use of instrumentation in analog research? Is it better to take field-capable but non flight-like instruments out to the analog site? Or is it better to collect samples and bring them back to lab-based prototypes of flight-like instruments?
4. Putting it all together, what kind of analog experiment (site(s) and instruments) would provide the best preparation for a sample selection and caching rover mission?
In response to Steve's questions:
1) It depends. If the rover goes to a site that was already visited, then it should bring a camera and nothing else in order to maximize lofted mass and minimize cost. If you go somewhere new, you'll need a suite of analytical tools along the lines of MER. ...which leads directly to question 2...
2) Re-visit MSL's landing site. We probably cannot afford, both in terms of mass and cost, a dual-mission rover that will both explore AND cache. Pick one. The best analog sites will amount to desert locales featuring short-lived, previous aqueous activity and plenty of aeolian action. MSL's drill sample shows a relatively reduced sedimentary material with a thin, oxidized surface rind. This reminds me an awful lot of the Devonian redbed deposits in Svalbard (read: AMASE expedition), where the cold environment has preserved a reduced deposit with a red, oxidized surface. The redbed deposits are a very similar shade of blue, not far beneath the oxidized surface. A thorough description of the mineralogy of that site may be useful.
3) Yes. One of the most important roles of analogue studies is as a test-bed for landed missions. Try it all, and see what works best.
4) The best preparation would be to build a dedicated Mars sample recieving laboratory. Instrumentation on the actual 2020 rover should be minimal, and we should re-visit the MSL site to obtain samples. For analogue sites, a visit to Svalbard to focus on the redbeds would be useful for studying ancient Mars at the time the MSL drill sample was laid down. The Atacama may also be a good site to study desert alteration since the MSL site dried out. Other sites have merits as well, but these two stand out to me.
I should clarify... In my opinion, the 2020 rover should collect and loft samples. I see no need for further exploration solely to select samples (given that MSL has returned evidence of native, N-bearing carbonaceous species and aqueous activity), and long-term caching will only degrade the samples. We have a great site - let's go get pieces of it ASAP.
Okay, let me poke at the first one a little... a camera and nothing else. That makes sense if you go >exactly< where a previous rover went. But suppose you go to the same general site but want poke around a little more? Or what about carrying some other instrument or two that MER didn't carry? Just a camera seems like a pretty lean science payload for a $2 billion mission.
And let me poke at the last one a little too. :) Svalbard and the Atacama are very interesting sites, but is it really necessary to range that far afield? If you're after an analog of the MSL site, could you do the same kind of work at a more logistically convenient site in the American Southwest somewhere?
Low-hanging fruit first - I agree that there are great sites in the US southwest. That was actually running around in the back of my mind when I added the last part of my comment. Mind-reader.
And yes, it is a very sparse science mission IF you look at it only within the context of the mission. If you look at it as a vital part of a larger mission that plants carefully-collected martian material in terrestrial laboratories, however, the science return is orders of magnitudes more than that collected on previous landed missions. Such a mission would plant this material under the beams of many more techniques than have been used previously, with a greater degree of sensitivity and resolution. And many instruments, such as FIB-TEM, simply can't fly on a rover.
And if 2020 misses the MSL site, then it should rove its furry little robotic butt over there. :-) How long has Opportunity been traveling now?
...but as I sit here thinking about it, I still like the Devonian redbeds in Svalbard. Those were laid down in ancient times under aqueous conditions, and have been preserved in a cold, dry environment much like the MSL site. The analogy there is pretty strong. It might be that I just don't have the entire US southwest memorized, but I can't think of any sites where ancient, reduced sediment is preserved under a thin oxidized rind quite like that.
So what would you do at those Devonian redbeds on Svalbard? The AMASE group has been working those over for years. Is there something new you would do there to simulate a sample selection and cacheing mission?
Good question, and I'll try not to answer it in a manner that does not deflect from the "what instruments would you bring" theme. :-) I find the redbeds interesting for the same reason that I find the MSL drill sample interesting. (And this is with the big caveat - at LPSC, I believe the data on the drill sample was still embargoed and so my knowledge base is sparse) But apparently, in the martian site we're looking at a sediment that was laid down under standing water, in relatively reduced conditions. First, the straightforward questions: why is it blue? I assume that there are fine sulfides in there giving it its color, and those sulfides "rust" to produce the red surface rind. Has it seen water since the site dried out? And (bigger question), if there were organisms there at the time of deposition, how can we expect to identify their signatures? The redbeds allow direct interrogation of the first (sulfides) and last (biota) questions. Some fairly fine-scale mineralogy should help with the first - I'd bring ChemMin and try out Raman, although the commercially available, hand-held Raman instruments tend to use too much laser power. The second is assisted by the fact that the redbeds contain fish scale fossils in them, so they were laid down with a biological component. I would want to identify the light carbonaceous components in the rock, so a GC-based instrument would be a good idea. One that can identify nitrogen-bearing compounds would be especially useful. And a means of ID'ing hopanes. That would do for a field assessment, I think, and then I'd want a closer look at the mineralogy in the lab. As well as isotopic and chirality analyses. Perhaps the chirality could be a field measurement; I'd have to leave that question to the GC experts. Finally, I'd want to do all this with fresh samples and not those collected on AMASE, because these are clearly samples that are sensitive to oxidation and all the AMASE samples have been warm and open to atmosphere for years.
So let's follow up on that very thoughtful answer with reference to my original question 3. You've listed a lot of very cool and sophisticated instrumentation. Do you need to take all that stuff back to the AMASE site and make the measurements in situ? That's a lot of work. Or can you just fly to Longyearbyen, rent a helicopter for a day, fly to the redbeds, grab some samples, freeze them very cold, and take them back to your comfortable laboratory and do the exact same science at your leisure?
"Or can you just fly to Longyearbyen, rent a helicopter for a day, fly to the redbeds, grab some samples, freeze them very cold, and take them back to your comfortable laboratory and do the exact same science at your leisure?"
Yes! ....by that I mean, just get the samples and bring them back to the lab under dry argon. Nitrogen might be okay, but if your measurement includes a search for N-bearing organics then using argon eliminates the worry that you've introduced nitrogen (negligible cause for any worry at all, but if you can eliminate it...)
Let me add some background from my own recollection... I visited the redbeds for a day, when we did the astronaut/rover interaction exercise on AMASE. I collected some samples from the float and noted that some were red and some were blue, but just assumed that they were coming from different layers. We returned to the ship and I placed the samples in the on-board lab. The next morning, all the samples were red! A single night's exposure to relatively warm, humid air produced the red surface rind. We didn't go back so I couldn't pry into that further. It was the first thing I thought of when I saw pictures of the MSL drill sample.
So that raises an interesting possibility: Analog sites focused on variable redox conditions. You've mentioned the Devonian redbeds of Svalbard as one such interesting site. What would be some others? Could there be a valuable project that focuses on sample collection at multiple such sites around the globe, and then brings them all (under dry argon or something similar) back to the laboratory and analyzes them all with a common suite of instruments?
That's an interesting approach, and it plays to an interesting question - is it possible to definitively pick out redox signatures arising from biology? Biology on Earth has altered the global redox state from the top of the atmosphere well into the mantle, which can make it tricky to study here. As for other sites... I'll have to think about this, but it is intriguing.
That's a thing about biology, though - in the limited, single-planet experience we have, it has made enormous, obvious changes; chemically, isotopically, morphologically, mineralogically, even geologically... The challenge of a good analogue site is finding a place where it isn't so obvious, and then finding the subtle signatures of a process that is titanically disruptive. I suspect that if we ever do find evidence of life, it will be a, "Well, now that's pretty blatant" sort of experience.
Re analogue sites for MSL. It all depends on what aspect you are interested in. If you are after geology and geomorphology, then sure the US southwest might be a good analogue. However if you are after organic biomarkers, or the preservation of OC, then you better go to environments on Earth with the lowest possible biological activity (Antarctica, Atacama, Svalbard), where chemical diagenesis of OC is important, and therefore can be extrapolated to Mars
Agree with Marc's MSL landing site idea. However, some in situ sample screening capability would still be important.
So what would be good instrumentation for screening? Think of it as a triage problem: you have a very large number of samples to choose among... how do you make the choice?
Also, most sample collection scenarios I've see include the ability to "highgrade" the sample set... to remove an already-collected sample from the set and replace it with one that's better.
So: What kinds of instruments would you want to make these sorts of decisions? And what kind of analog site is a good place to try it?
If we assume we are drilling as Carol suggests below, looking for modern style life in a habitable zone, then you would want to be able to prep and detect modern life molecules. Automation-wise, you might be able to do this with some of the developing microfluidics coupled with a detection capability for DNA. It would be a next step past SAM, but at the MSL site you've already used SAM anyway... (just read Marc's post below, and he's already stolen my thunder by pointing this out...)
Okay, microfluidics and DNA detection... that would challenging to get ready for flight by 2020, but not impossible. So, if that's what you want to fly, two questions:
1) What are the implications for an analog site. Where should you go?
2) Do you need to build a field-capable microfludics/DNA instrument? Or can you go to an analog site, collect samples, and then just bring them back to your instrument?
In my opinion, I'd steer clear of DNA-based analyses because they're too Earth-life-centric. A positive signal could be terrestrial contamination, and a negative signal would be ambiguous because martian microbes may not use terrestrial-like DNA. So you're left with an ambiguous measurement either way.
So what about something a little more general? Amino acids, for example (including chirality)? Or are biologically-oriented analyses best left for the returned samples?
This isn't just a long-term question, either. These are important questions for near-term analog studies... they fundamentally drive the choice of analog site and the work that you'll do there.
Amino acids are a wonderful target, with the same caveat that we face all the time - you have to pick out your biological AAs from abiological amino acids such as those in carbonaceous chondrites. For specifics, I'd defer to Danny Glavin and co-workers and the wonderful work they do at Goddard. I may be wrong on this, but my understanding is that the only currently bulletproof means of this analysis is with GC-based methods. And that means an MSL-sized mission, or some fairly bulky equipment at your field site of choice. If someone can point out something I'm missing, I'd be glad to hear it.
To answer #1: Probably something like the Atacama, with trace endolithic life that you would need to test out extreme mechanisms to separate DNA from rock or spore, followed by insertion into the sample prep/detection instrument. #2. I think you could get to something that would be field-capable. There are combination sample-prep / microfluidics / detection instruments coming online (around TRL-3/4) that are small and portable.
To answer Steve, I don't think the American Southwest can do it.
If you are looking at traces of life, which is very much what we have in some sites of the Atacama with barely colonization of a few rocks as environmental refuge for microorganisms, it will be very difficult to see that when you have abundant colonization on/in every rock, plants, and animals around. I suspect Svalbard is the same, and so are the upper Dry Valleys in Antartica.
Okay, so that raises a really interesting and different question! Saying that you need to go to a place like the Atacama to test out your instrument suite -- because there is so little life there -- implies to me that the instruments that would be carried on the sample collection rover actually have the ability to look for traces of life. That's a completely different scenario from what Marc suggested.
So: If you wanted to take an instrument suite for sample selection and collection to the Atacama, what instruments would you take?
This is indeed a different direction than where I was going. I have been sitting here cogitating a brilliant answer, and found myself in a sort of logic loop. If I were to select a Dream-Team instrument suite, I'd wind up with a package very similar to that on MSL. And I'd want to go to a landing site ....very similar to MSL's. So - and I'm honestly not trying to be a smartass here - I'd want to fly MSL ahead of sample collection, and that brings us to where we are now. I don't know if that answer is helpful or not.
Well, the MSL project would be the first to tell you that they're not searching for "traces of life"... they're searching for evidence of past habitability. So Jocelyne has raised a really interesting question... and Carol touched on it too. Should the 2020 rover actually carry some kind of true life-detection instrument? If so, what should it be and where would be a good place to go to test it?
And if not, do we really reach the conclusion that the 2020 rover should go to Gale Crater with just a camera and a sampling system, and grab pieces of the best stuff that MSL finds?
An important consideration for the payload and site selection for a sample caching rover is having a sample collection system designed to address the question of life, either past or present. Exploring ancient habitable environments has been the focus of the missions MER and MSL, but the recent MSL results suggest that an organic record of life will not be found near the surface. According to Dartnell et al. (Biogeosciences Discussions 4, 455-492, 2007) the ionizing radiation penetrates to at least 50 cm. Relevant materials must be accessed by drilling beneath the radiation exposed surface or possibly obtained from inside a recent impact crater.
It is important for a sample return mission to also address the question of modern life, and that requires obtaining materials that are habitable in modern times. The near subsurface ice deposits sampled by Phoenix are habitable and therefore are important targets to sample. Since the 2020 rover can’t be placed in a high latitude location like Phoenix, near subsurface deposits of ice at lower latitudes are possible targets. Accessing these deposits will still require drilling to reach subsurface ice or going to a recent crater exposing ice as HIRISE data has revealed.
Both good points. So let's say you had a sample collection drill that could get beneath the zone that you think has been affected by ionizing radiation, or that you can get to a site with accessible ice. What instrumentation would you need to take with you to look at the samples before you cache them?
Is it enough just to drill to a depth you think is deep enough? Do you need some kind of simple assay instrument that will give you real data to tell you it's deep enough? Do you need to take a full-up SAM-like capability with you?
I'm focused on the phrase "recent impact crater". Interesting. Outside of NASA, the term for "Entry, Descent and Landing" is "Targeting". I wonder if it would be possible to follow a specifically-targeted impactor with a caching rover, if subsurface samples are an absolute necessity. Insta-crater.
That would be very tough to do with just kinetic energy... you need a lot of mass. You could do it with explosives, though. Now that would be a fun analog experiment! :)
Yes!!! Count me in.
Hi Carol: Dartnell et al.'s [2007 http://dx.doi.org/10.1029/2006GL027494] discussion suggests that even the net radiation flux, not limited to ionizing particles, of ~0.85 Gy/a at Mars may not destroy radiosensitive terrestrial microbes directly. Instead, Martian microbes would face a formidable challenge of repairing DNA damage at temperatures < 240 K [e.g., Achberger et al., 2011 10.3389/fmicb.2011.00255] and water activity below ~0.5 [e.g., Kminek et al., 2010 10.1016/j.asr.2010.04.039]. If conditions allow microbes to remain metabolically active, they may survive GCR/solar radiation damage indefinitely at the Martian surface [Amato et al., 2010 10.1089/ast.2010.0477].
Burial may not ensure bio-viability. Mars contains radiactive elements even in the shallow surface, which may well intensify radiation damage beyond some depth in the regolith. For example, Dartnell et al. [2007] quote models indicating the dominance of Martian background radiation over GCR beginning at ~4.5 m depth.
Synthesizing the terrrestrial cryospheric observations and experiments with extremophile microbes, I would suggest an optimization of sampling depth instead of focusing solely on ionizing radiation.
In addition to imaging, other "point and shoot" instruments would be useful for high grading and sample selection. My feeling is that the most useful such instrument is a reflectance spectrometer operating in the near IR range, analogous to the OMEGA instrument on Mars Express. Another very useful instrument would capable of detecting organics without sample processing. UV fluorescense spectrascopy is a promising technology for this purpose.
Again, both good suggestions. Here's another possibility... what do people think about Raman for sample selection?
I'm almost too positive-biased to register an opinion on that one. I think not only "yes", but that a Raman instrument is long overdue. You get very good mineralogy information, good (but not trace-level) organics detection, detection of hydrated minerals, sensitivity to every known carbon phase in the universe, and the literature includes a track record of carbonaceous detection/characterization in martian meteorites. And it is small, low power, and long-lived. If 2020 visits a site that has not been visited previously, I think it would be a good candidate instrument. ...
After you nuke the site from orbit to get at sub-surface samples. Its the only way to be sure. ;-)
I should amend the "not trace level" part. Some biomolecules show up brilliantly even in small concentrations - beta-carotene is one of them, and it serves to ID fungi in your sample. And its a fairly solid biosignature.
I am not a Raman spectroscopy expert, but I have worked with it a bit. I have only found interpretable spectral signatures of minerals with pure mineral samples. In mixtures, like most rocks are, the fluorescenses from silicates create noise that swamp the spectral signatures. This limits its utility. For identification of phyllosilicates, a much better choice is Near IR spectrascopy. Raman is also not going to see a low abundance (ppm) of organics, whereas UV fluorescesce has been demonstrated to detect selected organics at ppb or lower concentrations. Furthermore, it can operate in a standoff mode with good results at distances up to 1m. Maybe that is not important if the only organics you will find will have to be drilled out, but it could be a good quick look way to know whether the sample contains organics or not. Granted it will not allow the detailed analysis of organics like SAM, but there is not point to doing a SAM analysis if there are no organics present.
I do not anticipate fluorescence being a great threat for in situ Raman measurements on Mars based on three observations. (1) A detailed data analysis [Goetz et al., 2012] of Optical Microscope results for the Phoenix Mars Lander reported no detection of UV (360-390 nm)-simulated luminescence from the soil grains at the Phoenix landing site. (2) 158 samples were examined during a set of UV-Stimulated Fluoorecence experiments [Wang et al., 2003] that included martian meteorites, lunar rocks, terrestrial rocks and minerals, coral and shells, fungi and spores, plants, and bones. We have not observed natural fluorescence from any of the tested martian meteorites, and only very weak reddish fluorescence from some lunar Apollo samples known to be enriched in REE (Rare Earth Elements). (3) A fluorescence microscopic observation on a set of common terrestrial clay samples (from the Clay Minerals Society) shows that the fluorescing "spots" in these clays are mostly well separated from each other, suggesting that they are not intrinsic constituents of clay minerals but probably contamination from coexisting biogenic species in the geologic (sedimentary) setting on Earth.
I agree that during a planetary surface exploration, natural fluorescent emissions can shed light on the potential existence of biogenic species. There are 370 nm LEDs on OM of Phoenix and MAHLI of MSL for that purpose. I havd not seen a possitive ID up to now.
The LCROSS experiment shows that if your carrier spacecraft can impact something into the surface, either spacecraft structure or a copper ball, you can make a crater. It does not need to be a very deep crater and with a rover it should be possible to drive to it. However, I think it is better to carry a drill. That way, you have a choice of the most interesting surface to sample. If the impactor approach had been used with MSL, I don't think the most interesting materials would have been impacted. You really want to use the ground truth to pick the drill site.
Doing it kinetically is possible on Mars, but the atmosphere does complicate things... you're going to lose kinetic energy on the way down in a way that LCROSS didn't on the Moon. Also, Mars landed missions aren't well known for having lots of mass margin, to put it delicately. :)
Despite my enthusiasm (and Marc's) for an explosive approach, I agree with Carol that a drill is probably best. It's far more controlled, both in terms of where you can place it and what result you'll get.
In this context, it's worth taking a look at the comments made in Kris Zacny's forum yesterday. There was some interesting discussion there about why it was good to test a Mars sampling drill at an analog site (Antarctica), rather than just in an environmental chamber. Check it out when you have a moment.
Just coming back to the discussion.
As much as I would like to find extant life on Mars the chances are pretty slim, but traces of past life is a possibility. Any DNA-based detection methods would be nearly impossible in sediments since we can barely extract DNA from Atacama soils. Microbial communities inside transluscent rocks is a much better options and macromolecules such as scytonemin could be detected with Raman (see Vitek et al. 2012. Astrobiology DOI: 10.1089/ast.2012.0879).
This is of course if we are still looking at surface samples, or possibly buried rocks. Evaporitic rocks is also an interesting sites because of the hygroscopic properties of salts (Wierzchos et al. 2012. Biogeosciences doi:10.5194/bg-9-2275-2012)
The idea of a focus on evaporitic rocks is an interesting one, since a variety of likely evaporitic rocks have been identified on Mars (e.g., sulfates, chlorides). What would be some good analog sites on Earth for Mars-relevant evaporite analog studies?
I see the best analog sites on earth for evaporitic enviroments are those saline playas at Tibet and at Atacama, especially those that reach the formation of Mg-sulfates, very last period of brine evoaporation.
Do you have an opinion about Searles Lake, in the Mojave? You do get some fairly unusual evaporites there, like hanksite - a carbonate/sulfate mineral.
I learned that there are three ways to assiss the biomass in a geo-sample: (1) living oragnism, like those halophiles found in the rocksalts of Antactica, Atacama, and Tibet; (2) bio-markers, the chemical compunds as residual of organism survived from long period of geo-processing, some lipids, fatty acids, etc; (3) reduced carbon.
For in situ detection, to play optimism, we may detect (2), because green Raman can stimulate strong reasonance effects from some carotinoids; to play pessimism, we may detect (3), because the high covelance of C-C bonding. When getting the sample back, we may try to culture (1) .... ;-).
I think the most important thing to test is the newest element, and that will be the sample caching system. I think the process of sample selection, putting it into a cache, sealing the cache, high grading (if that is provided) all should be tested in a real field site where subsequent ground truth can be used to see how the actual results matched with expectations.
I think it is important to test things as a system as much as possible. So, if the mission carries a drill and a particular suite of sample selection instruments, that suite should be tested together. This is like the operational readiness test needed for team training, but for field tests not everything needs to have the level of automation and software validation that is needed for an actual mission. The field needs to provide relevant type of materials. If the mission is to drill in ice, then testing the system drilling in icy materials is really important. The sample handing requirements should drive where relevant test environments are located. It may be fun to go to Svaalbard, but there is near surface ground ice in Alaska and North Dakota and in ND the weather is colder than Antarctica much of the time.
Alian raises an interesting point: There was indeed a model payload specified for the sample caching rover in the Decadal Survey report. It was this:
Panoramic high resolution stereo imager
Near-infrared point spectrometer
Microscopic imager
Alpha particle x-ray spectrometer
Dual wavelength Raman/fluorescence instrument
And then, of course, there was all the sample collection and handling stuff. Now a model payload is just a model payload -- its primary value is that it helps the cost estimators come up with a cost. But here's a question... would this actually be a good payload for this mission? It omits some of the more complex organic and life detection instruments that have been mentioned here, but it's also a lot more than just a camera.
Thoughts?
I've answered this earlier so I'm not going to harp on instrumentation needs. There's a mission-philosophy question buried in there that is worth discussing, though. If you land another exploration mission (as opposed to something that re-visits MSL's site), you run the risk of finding less-interesting samples than what MSL has found. How big of a consideration is that? Are there other martian sites that may be more astrobiologically interesting than the Gale Crater site?
We are right now using molecular tool to investigate microbial communities insite halites and gypsum rocks in the Atacama. These are photosynthetic-based communities associated with bacteria and archaea first discovered in by Wierzchos, McKay, Davila et al. These habitats are considered "Islands of Life" in the desert. Other interesting substrate are ignimbrite, calcite, all colonized when nothing else is.
I am not taking about finding these microorganisms on Mars, but certainly biosignatures (organic or not) at the result of microbial activities in the rock substrate. These communities are concentrated in a few mn under the rock surface, providing much more material, or remant of material, than in sediment where the loose structure result in disperse microorganisms.
Sandstone in Antarctica are also a good place. Same idea.
An instrument for capturing and preserving ice?
Getting back to Steve's first question, I was a participant on the SAG for what became MAX-C mission concept (Astrobiology 10, 127-163, 2010) and we had a LOT of discussion on this topic. My recollection is that we basically came to the conclusion that, in order to make the best decisions about what samples to throw in your collection bag for return to Earth, any rover would need to take a full suite of intruments, comparable to what you would send on a standalone mission. Otherwise, you would be selecting samples on very limited information, and it could be hit-or-miss whether you would bring back what you were looking for. Another element in this discussion is the possbility that you could come across something very novel that you'd like to investigate and possibly return, but there would be no way to investigate it further without onboard intstrumentation.
With regard to the second question, I would argue that don't yet know enough to make an informed selection of the next landing site, and that this should be a focus of the Mars community over the next couple of years. We now have enormous amounts of data from past and ongoing missions, and analysis of this data needs to be given priority. As part of this process, I think that rather than narrowing our focus to a few analog sites, we should think about expanding the scope of analogs to make certain we include a spectrum of possible analog environments that might be reprentative of those on Mars that would allow us to make better informed interpretations about what we are seeing. For example, sulfate-bearing deposits are one possible target for future missions, but the sulfate minerals that have been observed on Mars can form a variety of different environments (e.g., evaporative basins, sulfide alteration, volcanic). By looking at a spectrum of analogs for these envrionments on Earth, we may find ways to differentiate among the minerals that are formed in ways that will allow us to make better informed and more confident interpretations of what we see on Mars.
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