Artist impression of the geysers and subsurface ocean, credit NASA / JPL / CalTech

In case of Enceladus, with our mole next to a geyser, a new geyser might erupt or the vent shift or widen, and our mole ends up in the ocean. And it could plunge tens of kilometers and rupture.

So I suggest just as a concept for discussion, that we could have a mission end sterilization gamma ray source or similar. Shielded from the mole - and the orbiter of course. But the shielding need not be that heavy because it just needs to prevent radiation in the direction of the mole itself, not in all directions. Just a plate in between of sufficient thickness, maybe on a boom if necessary to reduce the cross section and give some extra attenuation.

Then at end of mission, to remove the shielding, and the mole then remains there, but irradiated by several thousand Grays a week or whatever is feasible. 

The most radioresistant life can withstand around 50,000 Grays. So to be safe, ensure that that amount of radiation is received in a short enough time so that there is no risk that it lands in the ocean with viable life. But it might need to be more than that if you also have to make sure that it doesn't include even dead fragments of life. Eventually ionizing radiation would break most of the bonds of any complex molecule until all you have left are gases. So just leave it to sterilize itself for all future time.

Sample return with sterilized sample

Then that's the same, after you receive the sample, use an ionizing radiation source, to sterilize it. So we will get material back that is split up into many pieces by the radiation. But still, we can detect biosignatures even after a lot of radiation damage. And as well, we have in situ measurement to inform our analysis.

Potentially, if totally sure it is adequately sterilized, can return to the Earth.

Sample return with unsterilized sample

You'd think this was easy, but it turns out to be surprisingly complex and difficult. I'm going to suggest it is best to find a way to just bypass all these issues. But first let's see what the issues are.

Back in the 1990s then the general idea was, common sense idea that we can just return samples to a glove box facility in a biohazard 4 laboratory.

But as studies were undertaken, the precautions needed got more and more complex. Ending with ideas that need hundreds of millions of dollars facilities with capabilities never tested before.

The problem is that it is easy to contain a known pathogen, say smallpox, or anthrax, or the Ebola virus etc. And that's the general situation for a biohazard laboratory.

But what can you do when you don't know what is in the sample, what its capabilities are, what size it is, or even what biochemistry it has? Quite possibly doesn't use DNA?

XNA based life in the sample return may be sub optical resolution as well.

Smallest size for cells not containing all the machinery of modern DNA generally estimated as about 40 nm. (But depends on advances of science, like all of this, and see the 3 nm theoretical example above).

So successive studies by the National Research Council (NRC), USA (two studies) then the European Science Foundation (ESF) (one study) gradually lead to more and more stringent requirements. 

First, reduction to 200 nm by the NRC after discovery of the ultramicrobacteria

Then reduced to 50 nm by the ESF. as a result of discovery of the profligate way that archaea can share their DNA through the tiny Gene Transfer Agents (GTAs) through a mechanism that is so pervasive and ancient that even archaea in totally different phyla can exhange their DNA, and very quickly also. 47% of the microbes in a sample of sea water left overnight with a GTA conferring antibiotic resistance had taken it up by the next day.

Some ancestor of today's pea aphid incorporated a gene for createing carotenoids from a fungus. It's the only organism known at the time of the research to have capability of synthesizing its own caretonoids, which it uses for body colouration. This shows that gene transfer is possible between a fungus and an aphid. Archaea can also transfer genes between phyla that are as different from each other as fungi are different from aphids.

Credit: Zina Deretsky, National Science Foundation

So if the life is at all related to Earth life, you have the possibility of this exchange of DNA bringing new capabilities to Earth microbes from space. Even if the microbes themselves don't survive.

"Unsterilised particles smaller than 0.01 µm would be unlikely to contain any organisms, whether free-living self-replicating (the smallest free-living self-replicating microorganisms observed are in the range of 0.12–0,2 µm, i.e. more than one order of magnitude larger), GTA-type (the smallest GTA observed is 0,03 µm, i.e. three times larger) or virus-type (the smallest GTA observed is 0,017 µm, i.e. almost twice as large). This level should be considered as the bottom line basic requirement when designing the mission systems and operation.

...

"Any release of a single unsterilised particle larger than 0.05 µm is not acceptable. The ESF-ESSC Study group considers that a particle smaller than 0.05 µm would be unlikely to contain a free-living microorganism, but that larger particles may bear such an organism. As self-replicating free-living organisms are likely to be the main concern following a release event, the study group considers that the release of a particle larger than 0.05 µm is not acceptable under any circumstance.

 This is one of the designs they came up with in 2008, the one with the telerobotics.

 

 

The LAS sample receiving facility uses a fully robotic workforce, including robotic arms that manipulate samples within interconnected biosafety cabinets. Carrier robots would transport the samples around the facility. Credit: NASA/LAS

http://www.astrobio.net/news-exclusive/keeping-mars-contained/#sthash.60GemsqD.dpuf

where the whole thing is enclosed and only robots handle the samples. This is for just a less than 1 kg of samples returned most likely, yet you have to build something like this, and still reason to doubt that it is effective enough to completely guarantee safety of the Earth.

 

It's easy to dismiss and think it is impossible to be an issue. So just to quickly go over some of the arguments

Meteorite extinctions

First, most meteorites are long sterilized, have spent millions of years in transit before they hit Earth. And return in a sample is much gentler than return in a container.

And how do we know that meteorites don't cause extinctions over timescale of many millions, even hundreds of millions of years.

The NRC looked into it in assessment of a Mars sample return, and they concluded:

Certainly in the modern era, there is no evidence for large-scale or other negative effects that are attributable to the frequent deliveries to Earth of essentially unaltered martian rocks. However, the possibility that such effects occurred in the distant past cannot be discounted. .

We are not worried here about viruses or most other popular science fiction hazard, because they have to be adapted to their host.

But we should be concerned about the possibility of

• XNA based life that DNA can't recognize as a hazard, that is able to take up residence in our ecosystems, our animals, soil, the sea, even ourselves(like legionnaires disease).

• XNA life could create molecules that closely resemble life molecules but are not identical and taken by mistake. Like BMAA. Implicated in Alzheimers.

• XNA life that takes over from other organisms in the ecosystem. is better than it, more efficient metabolism say.

• GTAs that tranfer capabilities to Earth life.

On the first possibility, Joshua Lederberg who first characterized the Archaea said:

On the one hand, how could microbes from Mars be pathogenic for hosts on Earth when so many subtle adaptations are needed for any new organisms to come into a host and cause disease? On the other hand, microorganisms make little besides proteins and carbohydrates, and the human or other mammalian immune systems typically respond to peptides or carbohydrates produced by invading pathogens. Thus, although the hypothetical parasite from Mars is not adapted to live in a host from Earth, our immune systems are not equipped to cope with totally alien parasites: a conceptual impasse

Not saying it is going to happen, but you have to prepare for the possibility if the sample is unknown.

Legal complexities

Margaret Race covered these in an excellent paper, there's far more to it than you'd think. Back in days of Apollo, then the quarantine rules for the Apollo 11 return were only published on the day that they launched to the Moon. That would simply not be permitted today. And the Apollo regulations have lapsed BTW.

And there are many domestic and international regulations to be negotiated and new laws to be passed. She considered the whole process likely to take ten years or more, and it can also potentially involve the domestic laws of nations that are not receiving the sample, because of the potential effect of the worst case scenario could impact on all nations.

First idea to bypass all this - characterize before return

So this whole baroque complexity can be bypassed completely if we simply don't return it to Earth quite yet. 

So the simplest solution is to characterize the sample before you return it. If we start with in situ missions first, then by the time we do a sample return, we may know what is in it so well that we don't need to do anything much. Either we know it is harmless, or we know it is hazardous but know what needs to be done to prevent harm.

Second idea, to return to HEO

If we do return and are unsure, then I think safest return is to High Earth Orbit. Above geostationary, or geostationary.

With L1 or L2 it could potentially spiral out and then after flybys of Earth and Moon leave the Earth and enter independent orbit around the sun and eventually return and impact Earth.

In HEO then it's orbit is stable for the indefinite future. So we have plenty of time to decide what to do.

Then to study it telerobotically. This is for the 2030s. So by then we will already be using telerobotics routinely for repairing satellites I think. And able to send hundreds of tons into HEO. We could already do this, do missions to HEO like a rover mission to Mars, but much shorter duration just to study the sample with new instruments.

We already have telerobotic surgery

FIGURE 1: The Da Vinci Telerobotic Surgical System permits the surgeon to perform an operation on a patient from a remote site. Currently, the FDA requires the surgeon to sit physically in the same room as the patient on whom he is operating. 

The first ever trans-continental telerobotic surgery was done in 2001, when a patient in France was operated on by a surgeon in the US in order to test the feasibility of intercontinental operation- an operation to remove a gall bladder. Which was a success.

So that should completely safe for planetary protection so long as material is only transferred one way. And no chance of impact with Earth.

So that then would simplify everything. No need to convince general public and ourselves that we have everything covered and that nothing can possibly escape containment. Because it is in GSO, or just above, obviously can't impact on the Earth.

So we have:

Simplification suggestion for sample return

• return it to HEO,

• make it clear it is only to be studied telerobotically until we know clearly what is in the sample and are certain it is safe. And materials go only one way.

If so that could be a low cost sample return from Enceladus.

We don't need to build the receiving facility in orbit. The capsule needs to be returned with trajectory biasing, obviously not aerobraking in LEO, and need a way for it to get into HEO without close approaches to the Earth that endanger collision with the Earth.

Once there in a stable orbit, then anyone who wants to can send their own robotic missions up there to study it. Don't even need anything to receive it there in advance, though obviously nearer the date you'd expect to send some spacecraft with equipment on board to rendezvous with it remotely and house the sample ready for remote telerobotic examination.

Which can also be done in a vacuum with none of the complications of examining it back on Earth, trying to keep Earth life out of it. 

In Situ Exploration

However it might be that we can do a much better job of the sample return, including better design, if we know more about the sample.

For instance if we find a protocell or newly evolved early form of life, we need to deal with a sample that is fragile and may be hugely demanding to return to Earth sufficiently intact to find out much more about it than we can learn in situ. And many need to be kept under conditions of liquid water and pressure, correct pH and correct salinity to return it relatively intact.

While if we find a microbe with a UV and ionizing radiation resistant dormant state, then we may not need to do too much to return it intact, but may be best then to keep it dry because then it is in a resistant dormant state and can be revived in HEO.

Just to give a couple of examples.

In Situ capabilities

There are many instruments developed for Mars. Whether they can be used as is for Enceladus, or need more modification, this shows the range of instruments we can send. And I've no idea about the engineering challenge, to examine materials captured in an aerogel "in situ".

Anyway here are some of the instruments we can send:

• Urey for ExoMars, or astrobionibbler, with liquid extraction using supercritical water. 

• Solid3, using monoclonal antibodies to detect organics. These detect a wide range of organics not specific to DNA based life.

• Microbial fuel cells, where you check for redox reactions directly by measuring the electrons and protons they liberate. This is sensitive to small numbers of microbes and has the advantage it could detect life even if not based on carbon or any form of conventional chemistry we know of. 

• Levin's idea of labelled release, where he has refined it so you feed the medium with a chiral solution with only one isomer of each amino acid, and if the CO2 is given off only with one isomer and not the other, that would be a reasonably strong indication of life there. 

  This has the advantage that the life just needs to be organics metabolizing and to produce a waste gas that contains carbon.

•  Miniaturized scanning electron microscope. Can't detect whether it is life or not, but useful along with the others.

• Miniaturized DNA sequencer could work if we had a common ancestor that was introduced to both Enceladus and Earth in the very early solar system, is in a reasonably advanced state they say could be made space ready by 2018. 

• Raman spectroscopy and gas chromatography of course and using chiral media for those.

 There are many instruments like this we could send, and several of them already space qualified but never flown. 

I also wonder about an optical microscope. Why not send, not just a "geologist's hand lens" but a diffraction limited optical microscope? With resolution of 200 nm. It could tell us things about the behaviour and structure of micro-organisms or protocells we might not be able to find out by other methods. 

Ideally you want to see the structure of protocells if they exist, and other sub-optical limit structures, so I do wonder also about the microscopes that go beyond the diffraction limit, but I'd have thought they are probably too complex to send into space? Probably won't verify life or protolife unless it is actually still viable and active. But could give interesting data in combination with the other instruments.

I suggest we send as many different ways of examining the potential life as is practical and feasible. So then they can cross-check with each other and produce a complete picture. In the case of the Viking labelled release, there were only two other instruments to compare it with. If we had several instruments, that would surely increase the chance of getting collaborated observations with two or more instruments observing the same thing in different ways. And if we have a duplicate orbiter for Europa, can examine both the same way.

 Whole generations of astrobiologists have had a multitude of ingenious and carefully designed and thought out ideas for instruments to send to space, but never seen any of these instruments fly. So far, nobody, world wide, has had a life detection instrument fly to another place outside the Earth since the 1970s. ExoMars will be the first true opportunity, and its capabilities are, though interesting, by no means exploring the full range of what can now be done by in situ exploration.

Just to have their instruments fly on an interesting mission like this would surely invigorate the field.