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Van Kane

Mars and Europa: Contrasts in Mission Planning

Posted by Van Kane

19-07-2014 14:08 CDT

Topics: Europa, Future Mission Concepts, Mars

The big news for future planetary exploration this month is likely to be the announcement of the instrument selection for NASA’s 2020 Mars rover that will define how it will fulfill its scientific goals. In the meantime, there have been several announcements for proposed missions to Mars and on the planning for a NASA return to Europa that highlight the contrasts in planning missions for these two high priority destinations. 

China’s chief scientist for its lunar program has stated that China is planning a rover mission to Mars for 2020 and a sample return from that planet by 2030. The Chinese space program tends to be tight lipped about its plans (especially those still several years out), and I’ve been unable to find any more information. Is this mission a placeholder on the space agency’s roadmap – much like an eventual Martian sample return for NASA – or an approved and funded program? Would the rover be delivered by a small lander and therefore be small itself, perhaps like NASA’s 1996 Sojourner rover? Or perhaps it would be a medium sized rover like China’s Yutu lunar rover and NASA’s Opportunity rover? Given China’s string of successes and careful build up to more complex missions, if a Martian rover is firmly in their plans, they seem likely to succeed. 

A Chinese rover would find itself part of a crowd on the Martian surface in 2020. As mentioned above, NASA plans its own Curiosity-class rover for that year. Europe’s ExoMars rover is likely to still be operating along with its Russian stationary lander. I’m willing to bet that NASA’s 2016 InSight lander and Curiosity rover will still be functioning, and I have some hope that the Energizer bunny-Opportunity rover will still be alive (although perhaps as a stationary platform by then).

If two private organizations have their way, the party at Mars will be more raucous still. The BoldlyGo Institute would like to raise funds for its SCIM spacecraft that would dip briefly into the upper atmosphere during a high speed flyby to snag dust and atmosphere samples to return to Earth. While we have some 130 rocks delivered as meteorites that are believed to be from Mars, this mission would return samples of the dust that ubiquitously blankets the planet. If this idea seems familiar, it was proposed twice before in NASA’s Mars Scout and Discovery mission competitions. Now its backers hope that this mission will have better success at securing private funders.

Private Mars missions

BodlyGo Institute and Mars One

Private Mars missions
Mars exploration has reached the point where private organizations can promote credible plans for complex Mars missions on the web.

Another organization, Mars One, has been planning to land humans on Mars in about a decade’s time. Recently, it announced plans for a Martian lander for 2018 built on the same platform as NASA’s Phoenix and InSight landers. Mars One is seeking proposals for instruments that would be useful to eventually colonization of Mars. For example, the organization is requesting proposals to demonstrate water extraction from the soil. It would also deliver one instrument developed by a university to the surface of Mars.

Both of these missions depend on finding funding from some combination of rich donors, corporate sponsors, and crowd sourcing from small donors. I’m never quite certain how much hope to hold out for missions that depend on private donations. Given their scope, these two missions would likely costs of several hundred million dollars; each mission would either need a fantastic number of small contributors or one or more wealthy contributors. While rich space enthusiasts exist (I’m thinking of Elon Musk of SpaceX as an example), if you are very, very rich and have the slightest inkling towards philanthropy, then fund raisers from many worthy causes from universities to global health to saving species are already in touch with you. 

Rather than dividing potential support, having multiple organizations trying to raise funds may benefit private planetary exploration. We can’t know beforehand which, if any, approaches will open check books and competition may help us learn what will work. (The B612 Foundation is another player looking to finance a challenging mission, in their case a space telescope to search for near Earth asteroids.)

Jeff Foust at The Space Review had a story recently on the potential for private funding of space missions. While raising hundreds of millions of dollars may prove too daunting, technology is on the cusp of enabling small planetary spacecraft based on CubeSat and SmallSat technologies that would cost just a few tens of millions of dollars. The Planetary Society’s LightSail project is an example of such a mission (although it will test critical hardware in Earth orbit rather than fly to another world).

Europa's red bands

NASA / JPL-Caltech / SETI Institute

Europa's red bands
Reddish features in this colorized image of Europa's surface likely contain water ice mixed with hydrated salts, potentially magnesium sulfate or sulfuric acid that may represent material from the interior ocean. Full caption available here.

If planning for Mars missions is becoming commonplace, NASA is still trying to find a plan to for a dedicated mission to Europa. In a step forward, the agency has released a request for proposals to the scientific community for instruments for a Europa mission. It did so, however, in a rather odd fashion.

Usually when NASA requests instrument proposals, it has a solid mission concept in mind. For this call, NASA said that the Europa mission might be an orbiter or might be a multi-flyby spacecraft. The request document was vague as to the budget for instruments and just said that past studies assumed it would likely be around 15% of the total mission cost. While many instruments by their nature have modest costs, some could be quite costly and it might help proposers to know whether the total instrument budget is closer to $150M (for the $1B total mission cost NASA would like) or to $300M (for the ~$2B that past studies have said is needed to achieve all the high priority scientific goals).

Europa strawman instrument list

NASA

Europa strawman instrument list
Examples of instruments that the scientific community may propose to study Europa. From the Europa instrument Announcement of Opportunity.

For some instruments, proposers will have to bet that NASA either selects a multi-flyby spacecraft or an orbiter. For example, measuring Europan tides would help pin down the depth of the ice covering the ocean. A laser altimeter could accurately measure the tides, but it requires an orbiting platform to pin down the size of the tides. If NASA goes with a flyby spacecraft, any group that proposed an altimeter is likely to be out of luck.

The request for proposals gives two roadmaps for how NASA will select the winning proposals. Its managers expect that they will select up to 20 proposals in April 2015 for which they will fund further development towards a final selection of approximately eight instruments a year later. NASA also reserves the right to simply select the final instrument suite in April 2015. The document implies that the longer timeline assumes a launch no earlier than 2021, while the shorter timeline could either reflect a possible earlier launch date or the possibility that the proposals seem ready for selection without an additional year of maturation. 

With this request, NASA appears to be showing its commitment to an eventual Europa mission, but it still hopes to find a cheaper alternative that will win the allegiance of the scientific community. The large cost overruns on the Curiosity Mars rover and James Webb Space Telescope have made the White House’s budget managers and NASA’s senior managers wary of multi-billion dollar missions. 

SpacePolitics.com reports that NASA has received a number of concepts for Europa missions that might cost no more than $1B. The agency is currently assessing these ideas for their cost, technical, and scientific feasibility. Comments by NASA’s chief scientist suggest that these missions likely would perform only a fraction of the science considered high priority by the scientific community (and that would be accomplished by the current ~$2B mission concept).

In the request for instrument proposals, NASA specifically asked for instruments that could study possible plumes of water erupting from Europa. The recent possible discovery of plumes at Europa has raised the question of whether and how planning to explore this world should be changed. If the plumes are verified, then they represent a chance to directly study material being ejected into space from beneath Europa’s surface as Cassini has been able to do for Saturn’s moon Enceladus. 

The request comes despite the recommendations a few weeks earlier of NASA’s Europa Science Definition Team. They reviewed both the evidence for Europan plumes and the experience studying plumes erupting from Saturn’s moon Enceladus with the Cassini spacecraft. Their recommendation was that a mission to Europa should be capable of exploring plumes if they exist, but that a dedicated focus on the plumes would not be appropriate. 

First of all, the team noted, only one observation made by the Hubble Space Telescope saw possible plumes. Other searches for plumes by telescopes and by the Galileo spacecraft when it orbited Jupiter have not found unambiguous evidence for plumes (some Galileo data is consistent with plumes but also have other possible explanations). Even if the Hubble did observe one or more plumes, they may occur at sporadic intervals separated by years or decades. If so, they would be more like the sporadic eruptions of each volcano on Io than the so-far continuous eruptions seen at Saturn’s Enceladus. A mission to Europa lasting a few years might entirely miss plumes if they sporadically erupt.

Second, Cassini’s observations of Enceladus’ plumes have shown the power of a diverse instrument set to characterize plumes. Instruments already recommended for the ~$2B Europa mission concept could be used to search for and study any plumes. A mass spectrometer, for example, could determine the composition of the gases expelled from the surface, while the thermal imager could look for warm spots that would be the source of the plumes. A couple of instruments such as a UV spectrometer and a dust spectrometer that haven’t made the straw man list of instruments used for mission studies to date would enhance plume studies, but these instruments also would be useful for studying the rest of Europa.

The instrument request document acknowledges the science team’s assessment, but states that, “the scientific potential presented by the plumes is sufficiently high that NASA will continue to emphasize the importance of plume investigations and encourages instrument investigations focused on this area.”

Europa plume findings

Europa Science Definition Team

Europa plume findings
Draft summary of findings by the Europa Science Definition Team regarding possible Europa plumes and planning for a mission to that moon.

While NASA’s management decides the scope of a Europa mission, engineers at JPL continue to refine the design of the current leading concept, the Europa Clipper that comes with an estimated cost of $2.1B. The current concept would have the Clipper spacecraft make 45 dashes through the radiation fields surrounding Europa for close up looks at the surface and interior. Building a spacecraft and instruments that can survive that radiation exposure is one of the factors that has driven the cost well above the $1B NASA’s senior managers would like to see.

A presentation made to the science team also provides more insight as to why a large number of encounters are required to study Europa. The science team has carefully justified what measurements are needed at Europa to understand this world and to enable planning for a lander that would follow the Europa Clipper. 

As an example, the science team has stated a requirement that the composition of 70% of the surface be mapped at resolutions of less than 10 kilometers by an instrument known as a short-wave infrared spectrometer. With 45 encounters, this goal would be just missed with 68% of the surface mapped. (Thirty flybys would map 50% at this resolution or better.) Similarly, mapping 70% of the surface with an imaging camera at resolutions of 1 kilometer or better would require 38 flybys. A global distribution of flybys to study the structure of the ice and ocean beneath the surface with an ice penetrating radar would not be met until 43 flybys. 

If the radiation belt did not exist, the next stage to exploring Europa would be to orbit it instead of frantically gathering data during numerous brief flybys. (Europe, for example, will send the JUICE spacecraft to orbit Europa’s sister moon Ganymede, but that moon lies outside the harshest portions of the radiation belt.) JPL’s studies suggest that a Europa orbiter would cost about the same as the Europa Clipper, but its lifetime would be so short that the Clipper with its many flybys would better study this moon.

We are left with contrasting opportunities for studying these two worlds. Mars is close enough and benign enough that both China and private organizations can seriously consider challenging missions. Europa’s location within harsh radiation belts leaves it as both a technical and a budget challenge.

 
See other posts from July 2014

 

Or read more blog entries about: Europa, Future Mission Concepts, Mars

Comments:

Arbitrary: 07/20/2014 11:34 CDT

In 2030, 35 years after Galileo, JUICE will arrive at Jupiter, if nothing goes wrong politically or technically during the next 16 years... It might fly by Europa, but it will orbit Ganymede. I hope its UV spectrograph can detect temporary plumes on Europa from there, more than 300 000 km away. I doubt it will map Europa enough to identify a future landing site. It might not help us much with designing a plume capture follow on mission. And now NASA wants to do a tiny copy of JUICE at half the cost. $1 billion during a 20+ years long mission is 1/(17*20) = 0.3% of NASA's budget during those two decades ($50 million/yr). Why do icy moons have such an extremely low priority for NASA during the rest of our lifetime? A lander gets 50% radiation shielding from the ground and it could drill/melt its sensitive electronics into the ice to get 100% protection. I wonder if its not worthwhile to invest in landing instead of mass for shielding and orbit correction fuel, especially given the much better science a lander can give about Europas interior. Luckily Russia is considering to put a lander on JUICE! But a Ganymede lander.

Enzo: 07/20/2014 05:27 CDT

The elephant in the room when we talk about funding for a mission to Europa is that there would be plenty of money for a Clipper type of mission NOW hadn't NASA already allocated $1.5 B for MSL-2. There would be no need to wait another decade, write to congress members, talk to the White House etc. etc. It should be the Mars people that have already two rovers on the ground and numerous orbiter there and on the way that should be doing this. Budgets can always be bigger, but the real reason we are not going to Europa in the foreseeable future is that NASA overspent his on Mars. As simple as that.

Enzo: 07/20/2014 08:59 CDT

India has sent a probe to Mars. China wants to send a lander and maybe sample return. To celebrate 50 years of independence the United Arab Emirates wants to send a probe to.....Mars. Do these guys have any imagination ? I can understand that, besides the moon, it's probably just about the only other place they can hope to get to in one piece. Can I suggest another worthy target, especially to the Chinese ? Ceres. I don't know enough of space navigation to know if it is much harder to get to then Mars but surely it should be a LOT easier to land and to take off from. By the time a lander/rover is organized, Dawn will have mapped it in hi-res for you, so you'll even know where to land. Even if you can only afford an orbiter, there are instruments like a magnetometer, that Dawn could not afford. It might even have its own plumes a bit like Europa and Enceladus : http://news.discovery.com/space/asteroids-meteors-meteorites/water-plume-unequivocally-detected-at-dwarf-planet-ceres-140122.htm

Stephen: 07/21/2014 07:15 CDT

"JPL’s studies suggest that a Europa orbiter would cost about the same as the Europa Clipper, but its lifetime would be so short that the Clipper with its many flybys would better study this moon." I disagree. 1) An orbiter can produce global maps (altimetry, gravity, thermal, & visual) of the entire surface of a given world at fairly high resolution over a comparatively short period of time. In contrast, a flyby mission is likely to produce only limited high-res coverage. 2) Since most of a flyby mission's time will be spent nowhere near Europa, to get the same degree coverage as an orbiter would probably require dozens if not hundreds of flybys, which in turn would require penetrating the Jovian radiation belts dozens (or hundreds) of times. True, each time it will only be in those belts briefly. But then it will only be studying Europa from close-up for a brief period each time.. 3) You have to work out your flyby orbits carefully to minimise going over old ground. The more flybys keep going over the same ground the less comprehensive the coverage of the surface will be and therefore the more likely the mission will miss potential sites for a lander. Especially a lander you want to be able to land at a place where the crust is thin enough to drill through to the ocean below. If such sites (especially suitably safe ones) turn out to be few and far between. a flyby mission could well miss most of them.

Arbitrary: 07/21/2014 08:18 CDT

@Enzo, Yes, I almost wish that damned planet didn't exist. It is an obsticle to space exploration and settlement. The biggest sand box in the solar system. Dead as a rock, but crowded with human machines. And Mars is still difficult. Most Mars missions fail. Like all 20 or so Soviet/Russian attempts, the Chinese attempt to hitch a ride on Russian Phobos Grunt, the only Japanese attempt, and one out of ESA's two attempts. India next? Even Dawn went into safe mode when it flew by Mars! As a contrast, all 7 missions beyond Mars have been successful. Venus needs some attention too. Isn't the morning star especially important in arabic culture? Should be a better target for UAE to sample its upper atmosphere or something. The private SCIM mission proposal people should lobby the sheik to finance a Venus version.

Arbitrary: 07/21/2014 08:31 CDT

@Stephen I think your right. All 7 missions beyond Jupiter have flewn by Jupiter for gravity assist anyway. Europa fly-by's are spinoffs from all missions to the outer solar system. A mission to Europa needs to orbit or land on Europa or sample-return its plumes. The long term activity of Europa plumes, its potential correleation with its orbit, can be studied from LEO space telescopes. However, I don't know if any capable UV space telescope is planned. Its so easy to be an armchair NASA administrator :-D

Stephen: 07/21/2014 05:01 CDT

@Arbitrary: "All 7 missions beyond Jupiter have flewn by Jupiter for gravity assist anyway." Actually, I was thinking more in terms of Galileo & Cassini. Both were/are orbiters (of Jupiter & Saturn, respectively) but are only doing flybys of their planets' moons. Cassini has performed wonders with Titan and Galileo's coverage was heroic, but they pale in comparison to the sort of coverage a Titan or Europa orbiter would be able to give, notwithstanding the problems such orbiters would both have (one with radiation, the other with Titan's distended atmosphere making it difficult to get in close). @Arbitrary: "A mission to Europa needs to orbit or land on Europa or sample-return its plumes." You can't send a lander until you know whereabouts on Europa you are going (or are able to) land it. You could send it with the next Europa mission, but that would vastly increase the cost CUTTING seems to be an important. (If it wasn't, then we wouldn't be talking about sending a Europa Clipper but a Europa Orbiter.) A lander would therefore be a followup mission to the next Europan mission (be it a clipper or an orbiter). However, that is not likely fly before the 2060s given current funding levels for US unmanned space exploration of the outer solar system.

Stephen: 07/21/2014 05:05 CDT

@Arbitrary That last post got partially garbled in the editing. "You could send it with the next Europa mission, but that would vastly increase the cost CUTTING seems to be an important. " ==> "You could send it with the next Europa mission, but that would vastly increase the cost of a mission where cost CUTTING seems to be an important factor. "

Arbitrary: 07/21/2014 06:19 CDT

Roskosmos seems to plan putting a lander on Ganymede together with the ESA JUICE mission. The requirement of detailed maps is not available. We can land anyway! We landed on Venus and Titan without any kind of knowledge of their topography. Spending billions of dollars and waiting several extra decades only to diminish the "landing on a rock with an AI-incompetent lander" is insane. Of course we can land on Europa! Much cheaper to do it now than having our grandchildren do it for us. A tiny Jupiter orbiter spending all of the 2030's to avoid risks, would be a nightmare. All space flight is exposed to risk. As long as the risk is not the result of sloppy engineering, but a result of our limited scientific knowledge, that risk is acceptable.

Stephen : 07/21/2014 07:44 CDT

@Arbitrary: "The requirement of detailed maps is not available. We can land anyway! We landed on Venus and Titan without any kind of knowledge of their topography." 1) Venus and Titan have dense atmospheres, which allow the use of heat shields and parachutes to slow the craft down sufficiently that they land intact--as distinct from a splatter. It also allows designers to keep such a lander comparatively small and light. Europa has no atmosphere and so unless you want a splatter any lander will need a rocket engine and therefore fuel, all of which increase the size, weight, and complexity of the lander. 2) Venus is a fiery hellhole with a punishingly high atmospheric pressure. Europa has no atmosphere or heat to worry about, but it is bathed in deadly ionising radiation which will fry any electronics which are not suitably protected. The protection required may well see a lander which needs to survive for a reasonable period to be as heavily armoured as the Russian Veneras were. Which in turn will increase the weight further, and thereby the amount of fuel and the size of the retrorocket needed to bring it safely down. 3) Much depends on what want those missions to do. The ones to Venus and Titan did not much care where they landed since their mission was mainly to see what the conditions on the surface were like. In contrast, a Europan lander would most likely be focused BELOW the surface, and in particular on the ocean believed to exist somewhere beneath the ice. To drill down to that a lander will probably not be able to land just anywhere. It will need to land where the ice is thinnest. Which means we first need to find where those thin spots are.

Arbitrary: 07/22/2014 06:47 CDT

@Stephen Soft landing on airless bodies isn't too difficult nowadays. I used Venus and Titan as examples of landings in unseen topography. Even the Chang'e 3 hoovered over the Lunar surface before it decided where to land. We don't need precursors to precursors. We need to get into the ice of Europa. Even just a few meters to get 100% radiation protection and seismic contact. That's how we can find out about its ice layers. A Europa orbiter is twice as exposed to radiation as a surface lander and will either be much heavier or live only half as loong. It is easier and better to land on Europa, than to orbit it. And as I said, fly-by is done by everything going past Jupiter, don't need a dedicated Galileo-light mission for that.

Torbj??rn Larsson: 07/22/2014 03:03 CDT

The Decadal Survey should have made a good analysis of Mars vs Europa priorities, and the confluence between manned and unmanned exploration on Mars. But my snapshot analysis would be: - Everything else alike, Mars is closer so net a higher turnaround on science. - Each has its own astrobiological (and of course geophysical et cetera) value. Mars benchmarks definitions of habitability, within the radiative habitability zone and outside. There are pathways for emergence of life where investigating Mars would be essential to understand life on Earth. (E.g. Benner's mixed Mars emergence, Earth survival scenario. Not likely IMO, but it is out there.) And of course sample return is the next necessary step. Europa benchmarks the tidal habitability zone (THZ). The only way to investigate its habitability would be to survey our own tidal icemoons. That is a long term project of centuries perhaps. But already Europa would give the benefit of allowing rough estimates, including of likelihood of life in the universe as we have to include the THZ bodies. The balanced approach mirrored in Van's article seems like a good compromise. @Enzo: "the real reason we are not going to Europa in the foreseeable future is that NASA overspent his on Mars". We can't know that. These pathways are complex and as one off's hard to test. The major constraint is that Mars is prioritized in the Decadal Survey, . @Stephen: "I disagree [with JPL's study]." Pitting unsubstantiated opinion against substantiated studies is a losing strategy. @Arbitratry: "[Mars is] Dead as a rock". We don't know that. Geophysically, Insight promises to tell one way or another. Astrobiologically, sample return may start to constrain the question. Those areas are wide open, which is a substantial part of the reason people explore Mars.

Stephen: 07/23/2014 06:49 CDT

@Torbj??rn Larsson:"'… [with JPL's study].' Pitting unsubstantiated opinion against substantiated studies is a losing strategy.'" Since the article merely alludes to "JPL studies" without providing a link which allows the rest of us to read them, or even such basic information as titles, dates, and authors' names, then what we have is the equivalent of an article which uses the phrase "experts say" without telling you who those experts were. Are anonymous experts and anonymous "JPL studies" more substantial than "unsubstantiated opinion"? One possible way of cross-checking the "substantialness" of those "JPL studies" is from this line in the article. "JPL’s studies suggest that a Europa orbiter would cost about the same as the Europa Clipper," Then go back and read the most recent Decadal survey, which got an independent study done of the costs of the missions it looked at and priced the Europa orbiter mission at $4.7 billion. So are these JPL studies REALLY claiming that a Europa Clipper would "cost the same",as a $4.7 billion Europa orbiter? After all, is not a Clipper's cost supposed to be more like $2 billion? There are several possibilities but the kindest one is that these "JPL studies" were pre-Decadal survey ones, ones in which JPL used its OWN cost analysis to come up with a value, a value more palatable to those who fund such things. Like Congress and the Administration. Such undercostings are one of the reasons everyone acts surprised when mission costs blow out. It is also the reason the Decadal Survey did their own cost study this time around. Which begs a question. If JPL undercosted the Europa orbiter, what do you imagine that says about those JPL studies' estimation of a Clipper's cost? Bearing that in mind, I would be careful before I used that word "substantiated" of those JPL studies. After all, if hype can make one aspect (cost) look good, it is equally capable of doing the same to others.

Enzo: 07/23/2014 06:50 CDT

@Torbj, "@Enzo: "the real reason we are not going to Europa in the foreseeable future is that NASA overspent his on Mars". We can't know that. These pathways are complex and as one off's hard to test. " Look, it's so bleeding obvious that I shouldn't even need to point it out. At the moment I keep reading how fantastic an Europa mission would be, how it really should happen, if only we had the money to do it......what a hide! Of course there's no money to do it when we just spent or allocated $5B to Mars (Curiosity+Insight+MAVEN+ MSL-2). I see the byzantine NASA decision process as a black box : I'm not interested in how it works, just its output. And at its output I see a countless list of Mars missions. There are currently 2 working rovers and (I think) 3 orbiters. Another orbiter, a lander and a rover are on their way (let's exclude additional ESA, Chinese, etc stuff to come whose decision do not depend on NASA). On the other hand, for Europa I see only a string of cancellations and no starters : Europa Orbiter, JIMO, now Clipper and whatever else. And cancellation of other Outer Planets programs like ASRG for good measure. Given that Europa is a worthwhile target at least as Mars,I don't need glass ball to tell that whatever process within NASA determined this outcome, it is so deliberately biased an inequitable in its funds distribution that it cannot be called scientific by any stretch of imagination. It can only be defined as politics. The fact that it comes from a large committee with a sanctimonious name does not change this fact. So, the space exploration program, with its relatively small budget, in the place with the highest technological capability (NASA) is hijacked by politics so profound to render it dysfunctional. This would not matter if there were heaps of places where space exploration goes on, but, sadly, that is not the case.

Enzo: 07/23/2014 07:18 CDT

@Torbj, The irony of all this is that, with each mission or study, Mars looks less and less habitable. In the 70s even some form of multicellular life seemed possible, now : 1) the place is bone dry 2) RADAR experiments like SHARAD and MARSIS have failed to find any amount of water. Even under the polar caps where a combination of geothermal heat and insulation should have favoured the formation of Vostok-like lakes, nothing. 3) Two separate missions failed to find any organics. Curiosity doesn't seem to have found any either. 4) Mars Odissey scanned the whole surface at nighttime in the infrared to find thermal vents or signs of activity : nothing 5) Results from Phoenix indicate that the soil is less habitable than thought : 6) The famous Mars gullies that seem to indicate a much needed aquifer now seem formed by CO2: In contrast Europa : 1) Has an ocean of water similar in size to Earth's 2) This ocean has an energy source (otherwise it would not be liquid), probably geothermal springs from tidal heating 3) Much has been written about the thickness of the ice but the young surface and the possible presence of plumes strongly indicate an interaction with the ocean. This means a second energy source from the oxidizing compounds on the surface. This makes Europa so much more habitable compared to Mars. If NASA is really looking for life, then its unscientific bias in its distributions of funds is even more clear.

Enzo: 07/23/2014 07:20 CDT

Sorry, the Phoenix link : http://spaceref.com/news/viewpr.html?pid=35954 and the CO2 gullies study : http://www.space.com/13855-martian-polar-gullies-mystery-carbon-dioxide.html

Stephen: 07/23/2014 07:32 CDT

@Arbitrary: "Soft landing on airless bodies isn't too difficult nowadays." Did I use the word "difficult"? @Arbitrary: "We don't need precursors to precursors." Where did you get that idea? The 'precursor" for a lander mission would be a single Europa orbiter or clipper. You would only need "precursors of precursors" if the single orbiter or clipper failed or or did not provide sufficient information to send the lander mission. @Arbitrary: "We need to get into the ice of Europa. Even just a few meters to get 100% radiation protection and seismic contact. That's how we can find out about its ice layers." Boring into Europa's ice is one thing, but that statement appears to want: * the lander itself to descend into the ice; and * the lander to be COVERED by ice. Both are probably technically possible, but they would (probably) substantially complicate the mission, which in turn would boost the cost of that mission, which in turn would increase the chance that it would never be funded. (Which is the same reason many are now talking about Europa clippers instead of Europa orbiters.) BTW, part of the lander would (probably) still need to remain above the ice. Namely, the radio antennae and the solar power arrays (assuming solar is used). @Arbitrary: "A Europa orbiter is twice as exposed to radiation as a surface lander and will either be much heavier or live only half as loong." Which studies are those claims based upon? @Arbitrary:"It is easier and better to land on Europa, than to orbit it." You seem awfully certain. Just how many landers have their been to Europa? @Arbitrary:"fly-by is done by everything going past Jupiter," Methinks thou art confusing Jupiter flyby missions (eg Voyager & Cassini) with Jovian moon flyby missions (eg Galileo & Europa Clipper) which orbited (or would orbit) Jupiter but do flybys of Jupiter's moons.

Stephen : 07/23/2014 03:07 CDT

@Enzo: [said of Mars] "the place is bone dry" Correction. The Moon is "bone dry" (except maybe for the polar regions) but Mars does have water.In contrast, Mars does seem to have some water, even if only at the poles in the form of ice or deep under ground or bound up in rock minerals. That said, you make a fair point point that Mars is looking "less and less habitable".. The high point was with Percivial Lowell, who envisaged intelligent life and a canal-building civilisation there. It's been downhill ever since. @Enzo: "Europa…Has an ocean of water similar in size to Earth's" Careful, Enzo! As I understand it, this has yet to be finally proven. The evidence for an ocean is certainly extremely compelling (esp. the magnetometer evidence), but proving the existence of an ocean was one of the task a Europan orbiter was supposed to do. Whether a flybying Europa Clipper can do the same thing remains to be seen. Don't commit Lowell's mistake by making the existence of Europan life seem a foregone conclusion when that existence has yet to be demonstrated. Being habitable is NOT the same as being inhabited.

Enzo: 07/23/2014 05:43 CDT

@Stephen To me something not dry is associated with liquid water and/or atmospheric humidity, both severely lacking on Mars. Ice is not "wet". There's a lot of ice on Mars but it's still dry. Regarding the ocean on Europa, the evidence is very compelling. Look at this recent talk that explains why ~ 26:00 : https://www.youtube.com/watch?v=2k-N3CD31H8#t=1908 Basically, from Galileo gravitational data we know of a layer of density = 1 (water or ice). From magnetometer's data we know that layer can induce a magnetic field => the water is liquid and probably salty. The most important question at the moment is the thickness of the ice. From that depends a lot of other things like explorability and another energy source for possible biological activity. "Don't commit Lowell's mistake by making the existence of Europan life seem a foregone conclusion" Excuse me, why are you putting words into my mouth ? Where did I say that life is a forgone conclusion ? I said that : 1) Europa is much more habitable than Mars (because liquid water + energy source that keeps it liquid) 2) If you are looking for life, it makes sense to go for the most habitable place. At the very least, send at least one mission, since there have been scores to Mars.

topnob: 07/23/2014 06:45 CDT

Mars is much closer to earth and the Sun and private companies are planning to send people there. Not sure how well people would a get to Europa and b live there, therefor lower priority. If you don't think mars one can make it, spacex's CEO Evon Musk said by 2020 he would have a ship that can take 100 people to mars per trip, given his track record, I'd say the possibility of people on mars by 2025 likely and 2030 even more likely.

Enzo: 07/23/2014 07:18 CDT

@topnob The space exploration program is (comparatively) a very low budget program whose goal should be scientific exploration. If Mars is really that important for human space flight and/or settlement, let the much more generously founded manned space program pay for the extra Mars exploration required. If the Mars bias is really due to the human space flight, then it means that small funds for solar system exploration are being used to subsidize the much much richer human exploartion program.

@enzo: 07/24/2014 03:11 CDT

Have you been in Pasaden last week? This statement reads much like what a few people said at the Mars 8 conference. But more like the point that if human space flight wants Mars they need more precursor and tech-demonstration missions. Which should come from the budget of human exploartion program.

Enzo: 07/24/2014 06:36 CDT

No, I haven't been in Pasadena. A while ago there was a similar discussion on this forum and someone posted something similar to topnob. By the time I got around to reply, the thread was a bit stale. This time I was ready :-) I take the opportunity (no pun intended :-) ) to stress that I'm not against Mars exploration at all. Quite the contrary : I follow it with interest. I am for a more equitable distribution of scarce funds amongst various interesting targets. And I am surprised at the passive acceptance of the current unbalance : if people here are really passionate about space exploration, then more should be worried about a monochromatic (red :-) ) program and speak out. My next worry is Mars Sample Return. I heard of costs of $ 6B or more : that is about the cost of a mission to Europa plus one to Titan plus one to Uranus/Neptune. The most worrying thing is the process : a sample return is planned even before something worth returning for $6B is found. To me, unless traces of life or, at the very least, some strong organic indicator is found, then I feel that this enormous sum could be better spent for places we know so little that the delta of knowledge acquired per dollar should be greater. Still, the black box has already indicated that Sample Return will be one of its next outputs regardless of Curiosity/MSL-2 findings. NASA apologists will try to explain that the expense of Sample Return will not affect any other mission. That is logic defying : if you spend money on Mars there is obviously something else you are not spending it on.

Paul McCarthy: 07/25/2014 09:37 CDT

Although there may be uncertain aspects, Enzo's basic theme that life on Mars seems to retreat and retreat (not saying abandon the search), while the potential of Europa seems to grow and grow, seems very strong. The situation reminds somewhat of the attempt to sequence the human genome : the in situ establishment hammering away in the relentless sequence of steps which they "know" will eventually yield results, but Venter seeing a faster, better, radical way to do it. Except no private entrepreneur is going to come to "Europa's" rescue! The discovery of the Europa plumes only HUGELY intensifies the mismatch. If they can be confirmed, here we have samples of a long-lived ocean venting to within our reach! All efforts should be dedicated to finding a paradigm-smashing route, a la Venter, to directly return plume samples. If that can be facilitated in any way by using the SLS, and/or surmounting contamination concerns by sample assessment on the ISS, then that's the sort of thinking that's needed. Costs should be minimised by only loading such instrumentation on the mission as could easily and cheaply be accommodated, as "second order priorities" -- that would still turn out to be plenty of stuff. To get a fix on where sample return from these (putative) plumes should lie in our priorities, imagine that such plumes had been known on Mars or Venus from before the birth of the space age! How many decades ago would they have been sampled???

Stephen: 07/26/2014 02:08 CDT

@topnob: "spacex's CEO Evon Musk said by 2020 he would have a ship that can take 100 people to mars per trip" When did Musk claim this? 2020 is only six years away and a 100-person spacecraft would be impressively large. I'm still waiting for him to put one person into LEO. Even 2030 seems overly optimistic. Are you use he didn't mean 2120?

Stephen: 07/26/2014 02:25 CDT

@Enzo: "why are you putting words into my mouth ?" To judge from your post, the habitability of Europa seemed to be a foregone conclusion. Just as the habitability of Mars once seemed to be a foregone conclusion (and in some respects may still be in some quarters). Hence the sending of Viking landers 1 and 2, whose primary goal was the confirmation of life on Mars. Nearly 40 years on the issue has become far less clear-cut. So too with Europa. AFAIK, even the very existence of an ocean under Europa's ice remains a HYPOTHESIS, not a FACT. Turning that hypothesis into a fact by confirming its existence was supposed to be one of the tasks of a Europa orbiter through multiple lines of evidence. Whether a flybying Clipper can accomplish the same end remains to be seen. "I said that...Europa is much more habitable than Mars (because liquid water + energy source that keeps it liquid)." You're jumping to conclusions, Enzo. AFAIK, LIQUID water has yet to be discovered on Europa--as distinct from presumed (eg the plumes), and the energy sources remain hypothetical. As distinct from confirmed fact. Mars has an energy source too (the Sun) plus it has some evidence (albeit controversial and contested) for liquid water. I know we're all impatient, but let's not overhype reality (eg Europa "Has an ocean of water similar in size to Earth's"); and the reality is that we still don't enough about Europa to judge FOR CERTAIN whether a Europan ocean actually exists, much less what its potential habitability is.

Enzo: 07/26/2014 04:29 CDT

@stephen Even if I jumped to conclusions about habitability, I still didn't say that life is a forgone conclusion. Did you see the talk I sent on Youtube ? There is an external layer of density 1. We know this from the gravitational data from Galileo. This is assumed to be water or ice (the measurement is not fine enough to tell the difference in density). Then there is the induced magnetic field that, apparently can't be coming from the nucleus of Europa and it is attributed to this layer of density 1. Ice would not induce the magnetic field, hence the layer is liquid water. I don't know if there is an exotic material besides water that : 1) Has density = 1 2) Can induce a magnetic field 3) Is also abundant in the outer solar system. An exotic material that it is covered by surface ice (we know that the surface is ice from spectroscopic data since the' 50-60s). By Occam's razor, the indication is, overwhelmingly, that it is liquid water. Add the fact that the surface that has essentially no craters, the cracks that go with Jupiter's tides and now, the plumes. Gravitational data alone is enough for JPL to announce that Titan also has a liquid water ocean : http://science.nasa.gov/science-news/science-at-nasa/2014/02jul_saltyocean/ Besides, what do you think a probe will do at Europa to PROVE that the layer is water ? There are no plans to drill anytime soon. RADAR ? You might get an echo at the interface between the surface ice and the mysterious material with density 1. Will it prove to you it's water ?

Stephen: 07/27/2014 11:26 CDT

@Enzo: "Then there is the induced magnetic field that, apparently can't be coming from the nucleus of Europa" *etc etc) I guess you didn't read my earlier post where I mentioned the magnetometer evidence ("The evidence for an ocean is certainly extremely compelling (esp. the magnetometer evidence)") @Enzo: "and it is attributed to this layer of density 1" As I understand it, a Europan ocean would need to be salty in a order to carry an induced magnetic field. A pure water ocean (ie one with a density==1) does not have that capability. Ergo the density of that liquid water layer would likely be some value >1 (though probably not that much greater). @Enzo: "Is also abundant in the outer solar system" Lots of things are potentially abundant in the outer solar system. Like methane. (Titan, for example, appears to have seas of methane and ethane.) @Enzo: "By Occam's razor, the indication is, overwhelmingly, that it is liquid water." You're confusing EVIDENCE with PROOF. For example, there ia a certain amount of evidence pointing to the existence of a thing called "dark matter", but thus far scientists have yet to prove its existence. So too with an ocean on Europa. The line of argument you gave is merely evidence, NOT proof. And that is quite apart from other issues yet to be resolved. Like is the ocean truly global? How thick is the ice layer over it: only one mile thick or a 100 miles? Are there thinner spots (and where are they)? @Enzo: "Gravitational data alone is enough for JPL to announce that Titan also has a liquid water ocean" Once again you're confusing an hypothesis with demonstrated fact. Once upon a time there was believed to be a GLOBAL methane/ethane ocean on Titan. Evidence from Cassini knocked that hypothesis on the head. @Enzo: "what do you think a probe will do at Europa to PROVE that the layer is water ?" You can't prove an ocean consists of water until you first prove it even exists!

Anonymous: 07/27/2014 08:14 CDT

There was a question earlier in the comments on whether a Europa orbiter or multiple flyby mission would return more data. The limiting factor on how much data can be returned is not time in proximity to Europa but rather time available to transmit data back. An ~$2B Europa orbier would not have a long life, perhaps a month or two. During that time for most orbits, the spacecraft is behind Europa. As a result, the total volume of data measured as megabytes is limited. A multi-flyby spacecraft stores the data it gathers during the flyby and then has weeks between encounters to return the data to Earth. As a result, the total data volume is more. When JPL looked at both an orbiter and multi-flyby mission option, the high data volume instruments were on the multi-flyby spacecraft and the orbiter had lower data volume instruments. The scientific community looked at the two options and concluded that the multi-flyby spacecraft would better address the science goals than a short-lived orbiter.

Paul McCarthy: 07/28/2014 01:03 CDT

@Stephen: it reads pretty clearly to me that you're over-egging the rebuttals to Enzo. He makes it pretty clear, over and over, that he's not claiming a water ocean on Europa is "proven", but that all the evidence makes it extremely likely. (It's notable that neither you nor anyone else has proposed an alternative that fits the data). Certainly likely enough to justify higher priority for Europa missions.

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