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Why are there no missions planned to Enceladus?
by
Star One
on 22 Jun, 2016 19:27
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An Ocean lies a few kilometers beneath Saturn's moon Enceladus's icy surface
Summary:
With eruptions of ice and water vapor, and an ocean covered by an ice shell, Saturn's moon Enceladus is one of the most fascinating in the Solar System, especially as interpretations of data provided by the Cassini spacecraft have been contradictory until now. Astronomers recently proposed a new model that reconciles different data sets and shows that the ice shell at Enceladus's south pole may be only a few kilometers thick. This suggests that there is a strong heat source in the interior of Enceladus, an additional factor supporting the possible emergence of life in its ocean.
https://www.sciencedaily.com/releases/2016/06/160621115743.htmWith news like this tell me again why we haven't got a mission planned already for Enceladus, as in many ways it looks an easier target than Europa other than being further out.
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#1
by
whitelancer64
on 22 Jun, 2016 19:46
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A flyby probe to capture some of the material from the jets at the tiger stripes would be great, and would be a relatively easy sample return mission, but it is complicated by the challenges associated with getting a probe out to Saturn within a reasonable budget. RTGs would be much too expensive, so we're talking solar power. It would have to be a very simple probe and it would have to operate on a very small energy budget. There have been several proposals for a flyby sample mission like this or other exploration of Enceladus,
https://en.wikipedia.org/wiki/Enceladus#Proposed_mission_conceptsbut none have been funded yet.
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#2
by
MattMason
on 22 Jun, 2016 19:59
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The moon's geology is pretty clear and Cassini has gathered a lot of data.
As much as this and many other moons have things that would be awesome to study, I agree that funding is unlikely unless the powers that want sacrifice something else they want to visit, if that.
That said, if we really get serious about interplanetary flight, Enceladus as a fuel depot is too good an opportunity to study and utilize. Is there any other moon with as much water ice other than Europa?
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#3
by
as58
on 22 Jun, 2016 20:15
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Enceladus (and/or Titan) was added recently to the list of candidate missions for the fourth New Frontiers slot.
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#4
by
Star One
on 22 Jun, 2016 20:27
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The moon's geology is pretty clear and Cassini has gathered a lot of data.
As much as this and many other moons have things that would be awesome to study, I agree that funding is unlikely unless the powers that want sacrifice something else they want to visit, if that.
That said, if we really get serious about interplanetary flight, Enceladus as a fuel depot is too good an opportunity to study and utilize. Is there any other moon with as much water ice other than Europa?
I'd rather we didn't use it as a fuel depot if it does contain life. We've done enough of that nonsense here on Earth without starting in the rest of the Solar System.
Enceladus (and/or Titan) was added recently to the list of candidate missions for the fourth New Frontiers slot.
That's good to hear.
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#5
by
Blackstar
on 23 Jun, 2016 03:16
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A flyby probe to capture some of the material from the jets at the tiger stripes would be great, and would be a relatively easy sample return mission
Can you explain what you mean by "easy"?
For starters, there's the issue of approach velocity--how do you capture the sample without destroying it with the high velocity impact with the sample collector?
Then there's the overall time required for such a mission--approximately 8+ years there and an equal or greater time back, for a total roundtrip of over 16 years.
Then there's the fact that if your Level 1 science goals define "success" as "return sample safely to Earth," and your spacecraft unsurprisingly dies in year 17 of its 18 year mission, it fails.
Then there's the lifetime cost of a mission that lasts 16+ years, which is not exactly cheap.
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#6
by
Dalhousie
on 23 Jun, 2016 03:26
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There are at least two studies going on that I am aware of.
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#7
by
Eric Hedman
on 23 Jun, 2016 04:08
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I'd rather we didn't use it as a fuel depot if it does contain life. We've done enough of that nonsense here on Earth without starting in the rest of the Solar System.
I doubt that anyone will be in a position to decide on using the ice on the surface of Enceladus as a fuel source for many decades to come if not more than a century. Even so why is using the ice nonsense if life is present? It won't likely be more than a miniscule fraction of a percent of the ice for millennia to come.
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#8
by
JH
on 23 Jun, 2016 04:19
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The simplest answer to your original question, Star One, is that no one expected Enceladus to be interesting until Cassini got there in 2005 and it takes a while to build a constituency around sending a mission to an object, particularly one in the outer solar system.
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#9
by
plutogno
on 23 Jun, 2016 05:25
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no one expected Enceladus to be interesting until Cassini got there
actually, Enceladus was an intriguing little object already after Voyager 2 flew by and revealed its young surface. it was already suspected that something must be going on
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#10
by
Comga
on 23 Jun, 2016 05:34
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no one expected Enceladus to be interesting until Cassini got there
actually, Enceladus was an intriguing little object already after Voyager 2 flew by and revealed its young surface. it was already suspected that something must be going on
In fact, in a
book on Project Orion, the atomic explosion powered spaceship project by his son George, Freeman Dyson picked Enceledus as the place he would most like to take the 7000 ton spaceship. That was long before the Voyagers, but I don't recall his motivation.
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#11
by
JH
on 23 Jun, 2016 05:36
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These things are relative, of course. However, an object with areas that looked young based on ~1 km/px imagery is in an entirely different category than one which has observed, active plumes of water ice.
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#12
by
robertinventor
on 23 Jun, 2016 09:12
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A flyby probe to capture some of the material from the jets at the tiger stripes would be great, and would be a relatively easy sample return mission, but it is complicated by the challenges associated with getting a probe out to Saturn within a reasonable budget. RTGs would be much too expensive, so we're talking solar power. It would have to be a very simple probe and it would have to operate on a very small energy budget. There have been several proposals for a flyby sample mission like this or other exploration of Enceladus,
https://en.wikipedia.org/wiki/Enceladus#Proposed_mission_concepts
but none have been funded yet.
Actually with modern "labs on a chip" you can do a powerful in situ life finder mission for Enceladus. That would also let you study the plumes at different heights to sample different sizes of particles, and also watch for changes, e.g. if there are algae blooms or similar, or if you get better results at particular times in its orbit. All the mass that would be needed for the sample return could be used instead for extra instruments. With many instrument just a chip and perhaps half an amp of power, that's a lot of in situ study for the mass of a return capsule + fuel to get it back to Earth, and you get the results right away.
Also if there is life in the sample, then you don't know how to best preserve it for the journey back, until you know what it's like.
And then there's the issue of how you handle the sample return. I think it's best done above GEO in a telerobotic facility, given the rather high chance that there might be exobiology there not based on DNA, with almost no communication with Earth - if life is common in our galaxy, then there may well be exobiology on Enceladus. Impossible to assign a probability of that, but surely it's a few percent at least if life is common? Though almost zero if life is very rare in our galaxy. If returned to Earth's surface, then it's an immensely complex thing to sort out legally, Margaret Race looked into it, you wouldn't believe how many new laws would need to be passed and even quite simple international laws can take many years to pass - it might easily take over a decade to pass all the laws needed for a surface to Earth sample return while a return to a telerobotic facility above GEO can be done within our current legislation. Then return sterilized samples to Earth surface until you know a bit more about it.
I see that as possible, but in situ is just far easier to do first, and safest of all the life missions we can do both for Enceladus and for Earth. Almost no possibility of forward contamination and none at all of backward contamination.
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#13
by
robertinventor
on 23 Jun, 2016 09:28
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Then there's the overall time required for such a mission--approximately 8+ years there and an equal or greater time back, for a total roundtrip of over 16 years.
Then there's the fact that if your Level 1 science goals define "success" as "return sample safely to Earth," and your spacecraft unsurprisingly dies in year 17 of its 18 year mission, it fails.
For the sample return idea - I agree that it's better to study in situ but we have very capable "instruments on a chip", many different concepts indeed, for in situ life detection. Things have moved on a lot since just a decade ago, instruments that would fill a laboratory can now be tiny things you can put on a spacecraft.
To minimize impact velocity, best is to have an Enceladus orbiter. It can only orbit the equatorial regions and even that orbit is unstable long term. But it can do many excursions to the poles and then sample at relative velocities of 100 meters per second, which is only ten times faster than Usain Bolt runs, at that velocity and into material designed to soften the impact, you could get reasonably intact particles.
You can get to that orbit with almost no delta v using multiple flybys of Titan, Rhea, Dione and Tethys which also gives us a chance to look at them close up.
The most worked out mission study for this I know of is the study for the Decadal review of an impact velocity of 100 meters per second
Enceladus Orbiter - the wikipedia article didn't have a link to it and I've just added it now.
You might also be interested in my article:
"Super Positive" Outcomes For Search For Life In Hidden Extra Terrestrial Oceans Of Europa And EnceladusI think that Enceladus is by far our surest bet for an early mission to find out about subsurface oceans. Europa may have geysers too, and so you could have a copy of the same mission, though needing to be radiation hardened, to send as a Europa geyser in situ sampler / studier as well. I don't think we should send a Europa lander yet myself, I think we need to study it first, and design what we send based on what we see there, especially as by the time we get results back from Europa, we'd already surely have much faster ways to send follow up missions to Europa. The power requirements can be dealt with using RtGs, and I've seen suggestions that you could also use solar power even for Saturn though it needs very large solar panels out there.
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#14
by
Blackstar
on 23 Jun, 2016 11:13
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And then there's the issue of how you handle the sample return. I think it's best done above GEO in a telerobotic facility,
No. All laboratory analysis equipment has been designed for use on Earth. There are lots of pieces of equipment--like a cyclotron--that you could not make small and light enough for space use. Doing lab analysis in space would require all new equipment and techniques and would never be as good.
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#15
by
robertinventor
on 23 Jun, 2016 12:25
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No. All laboratory analysis equipment has been designed for use on Earth. There are lots of pieces of equipment--like a cyclotron--that you could not make small and light enough for space use. Doing lab analysis in space would require all new equipment and techniques and would never be as good.
The cyclotron is the main thing you can't take into space. But it's the same for a sample receiving laboratory on the ground. The laboratory would need to contain the sample and probably it would handle it telerobotically and there'd certainly be no space to put a cyclotron inside, not a large one. So the plan is to remove smaller samples from it, pre-sterilized, for use in larger facilities. My suggestion just moves that into above GEO, and you remove the samples from the telerobotic facility and return to Earth.
As for experiments that are designed around presence of gravity - no need for the facility to be in zero g, unless that is required for some reason. Use a counterweight (e.g. spent third stage, or another hab) to spin it to generate artificial gravity (AG). Technically easy to do. Main thing would be how to dock - need a module at the hub of the spin for docking, docking port counterspun.
I would envision it as starting quite small, just a Bigelow habitat, say, but with no humans on board. Starts off as just a zero g hab. Do preliminary investigations first. Maybe they find there is no possibility of any life in it, then they just sterilize it to be sure with ionizing radiation and then return it to Earth. But if they do find life, any possibility of present day life, then they would send up more elaborate equipment to study it, and this could be the hub of a telerobotic exobiology station above GEO. At that point you could convert to an AG facility if that was found useful.
Or, they then build the ground station based on containing what is now a known thing. In some cases it might be no risk to Earth at all. For instance if it is RNA only life, or early autopoetic cells not yet quite alive, you might perhaps find out early on that it is rapidly destroyed if exposed to any Earth life, and it might then be clear that it is safe to return. Or if you are confident there is no life only prebiotic organic chemistry.
So I see it as evolving in various possible directions depending what you find. Hope the idea is a bit clearer now, whatever others here think about it.
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#16
by
the_other_Doug
on 23 Jun, 2016 13:02
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...Is there any other moon with as much water ice other than Europa?
As much water ice? Yes, of course. According to current theories, most of the moons of the outer planets are made primarily of water ice, surrounding small, rocky cores. They
all have a huge amount of water ice available for utilization. Enceladus and Europa are currently unique in that they seem to have subsurface
liquid water oceans. And I grant you, liquid water may be a more usable resource than hard-frozen ice, but still, there's gigatons of ice out there.
But before we go overboard about Enceladus and Europa and the prospects they may offer for both resource utilization and for exobiology, I'd like to point out that we're beginning to see a shift in paradigm, and it's beginning to look like a
lot of these small water-ice worlds have bodies of liquid water underneath their hard-frozen icy crusts. Enceladus seems to be the only untidy body that's currently leaking water vapor in observable quantities, but I've seen speculations on liquid water oceans still extant everywhere from Ganymede to Pluto. It may be that there are both resource options and exobiology possibilities on (or, more appropriately, within) dozens of small, frozen worlds out where the shrunken sun shines dim and cool...
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#17
by
robertinventor
on 23 Jun, 2016 13:12
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That said, if we really get serious about interplanetary flight, Enceladus as a fuel depot is too good an opportunity to study and utilize. Is there any other moon with as much water ice other than Europa?
Yes, from Jupiter outwards, most of the smaller bodies are consisted almost entirely of ice. The ring system of Saturn is as well.
Ideally you would want a fuel depot where you aren't going to contaminate any subsurface ocean with Earth life. So you'd choose the ones without oceans, or ones with very thick crusts.
An ideal target there would be Callisto in the Jupiter system. It's got a
subsurface salty ocean, but thought to be so deep below the surface that there is no chance of contaminating it with surface activities. Also it orbits outside the hazardous radiation of Jupiter. So it would be an ideal place to send humans.
In the Saturn system, Titan has an Earth pressure atmosphere permitting aerobraking, but low gravity for take off. It has a subsurface ocean of water also, so it depends on whether there is communication between its subsurface and the surface, which nobody knows. If there isn't any, well modern Earth life couldn't contaminate the Titan seas, far too cold for Earth life. There might be exobiology there, if so it's the one place where humans could actually land and study it in situ without risking contaminating what they study with Earth life
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So a base on Titan in the Saturn system would be pretty cool I think. Very exotic location. Would need to look into it carefully but I don't see any major issues with that apart from the issue of possibly contaminating the subsurface ocean.
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#18
by
the_other_Doug
on 23 Jun, 2016 13:46
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That said, if we really get serious about interplanetary flight, Enceladus as a fuel depot is too good an opportunity to study and utilize. Is there any other moon with as much water ice other than Europa?
Yes, from Jupiter outwards, most of the smaller bodies are consisted almost entirely of ice. The ring system of Saturn is as well.
Ideally you would want a fuel depot where you aren't going to contaminate any subsurface ocean with Earth life. So you'd choose the ones without oceans, or ones with very thick crusts.
An ideal target there would be Callisto in the Jupiter system. It's got a subsurface salty ocean, but thought to be so deep below the surface that there is no chance of contaminating it with surface activities. Also it orbits outside the hazardous radiation of Jupiter. So it would be an ideal place to send humans.
In the Saturn system, Titan has an Earth pressure atmosphere permitting aerobraking, but low gravity for take off. It has a subsurface ocean of water also, so it depends on whether there is communication between its subsurface and the surface, which nobody knows. If there isn't any, well modern Earth life couldn't contaminate the Titan seas, far too cold for Earth life. There might be exobiology there, if so it's the one place where humans could actually land and study it in situ without risking contaminating what they study with Earth life .
So a base on Titan in the Saturn system would be pretty cool I think. Very exotic location. Would need to look into it carefully but I don't see any major issues with that apart from the issue of possibly contaminating the subsurface ocean.
Yep, great comments. And while there is all sorts of speculation about exotic surface biology on Titan, I think it's safe to say that such biology would be so alien to terrestrial biology that cross-contamination would be nearly impossible. And anything we could contaminate lies well below easy contact with a tiny human presence there.
It's amazing to see how many of these little ice worlds seem to have remnant liquid water bodies buried deep under their crusts, isn't it? All sorts of potential abodes for non-terrestrial life...
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#19
by
jgoldader
on 23 Jun, 2016 14:00
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Because of the much more benign radiation environment, Enceladus is a lot easier place to work than Europa. In my mind, that would be the big "plus" of going there.
The big "minuses" are the much greater travel time, and the need for RTGs at Saturn's heliocentric distance.
A Cassini-like mission that was designed as an Enceladus orbiter with an advanced chemistry and mass spectroscopy suite for investigating the plumes, plus radar, would be pretty nice. And cost billions of dollars, not including a sure-to-be-SLS launch.
.