NASA Europa Missions, projects and proposals for the 2020s Options

[Mariner9]

I just read the blog posting on the instrumenta over on the Planetary Society website. Nine instruments on this mission. Wow. I know it is considered a Flagship mission, but with all the talk of trying to keep mission costs down I expected a bit smaller payload.

Not that I am complaining.

The item that really caught my eye was the EIS (Europa Imaging System).
- Near global coverage at 50 meters per pixel, and selected areas up to 100 times higher. -

My back of the envelope math comes out to highest resolution images being a half meter per pixel. Very nice.

[dvandorn]

Well, think about it. If you're prospecting for the best places to melt through the ice down into the Great Ocean, you need to characterize the surface on a global scale. You can't run your ice-penetrating radar and sounding radar globally, so you have to have good enough photo coverage to match visual characterizations to the deep-structure information you get slices of from those lower-resolution, more limited coverage instruments. Then you can apply those matches to figure out all of the good potential ocean entry points, where the ice crust is the thinnest.

I would be really surprised if there aren't good visual cues in the high-resolution images of the surface that correlate to the thickness of the crust beneath. It might take some analysis, and the cues might be subtle. Bit I bet we'll find them.

Now, this all makes sense if you're using the next mission to plan your assault on the Great Ocean with a melting probe. If you're planning on bringing your melting probe with you on this next flight, well -- good luck finding a good, thin-crust spot to land it on within your mission timing constraints.

-the other Doug

[monitorlizard]

I'm surprised that there is no laser altimeter in the Europa spacecraft payload. There's no indication of an altimetry mode in the radar instrument, so the mystery deepens. I was under the impression that determining the exact shape of Europa was important for modeling the tidal heating from Jupiter. It's possible to get some topographic information from stereo imaging, but it's hard to imagine getting the large area coverage with high resolution I think is necessary for detailed shape modeling.

[nprev]

I would think that altimetry information would be at least indirectly acquired by the radar instrument in any case, though. Perhaps it's just a matter of mining the data properly.

[djellison]

I was under the impression that determining the exact shape of Europa was important for modeling the tidal heating from Jupiter. It's possible to get some topographic information from stereo imaging, but it's hard to imagine getting the large area coverage with high resolution I think is necessary for detailed shape modeling.

You can do a lot lot better with stereo imaging that you could ever do with 40 flybys with a laser altimeter.

[JRehling]

Keep in mind that there are at least two different kinds of sub-surface water hypothesized:

1) The global ocean.
2) Lakes which are melt-lenses and may never have had direct contact with the global ocean.

The ferocious debate over the thickness of the crust may be due to the apparent contradictions created by these two distinct phenomena. Just as, once upon a time, people about the nature of nebulae, before finding out that there are several very different kinds of nebulae, the surface phenomena indicating subsurface liquid may have gotten scientists arguing because some phenomena were produced by (1) and some were produced by (2).

If so, we can virtually forget about direct probing of (1) anytime soon, but the depth down to (2) may be arbitrarily small at any given time. And then the possible pathways for future surface exploration become quite complex, presenting, for example, trade-offs between the surface units that were most recently in contact with liquid water, the surface units closest to subsurface water at present, and/or the surface units that most assuredly had contact with "dirty" ocean water at some point (however ancient) in the past.

As painful as it is to say, we're still at a quite primitive phase in understanding Europa. Mars missions are still surprising us after ≥ half dozen landers and orbiters each. Europa is at the Mariner 9 stage in its exploration, and we're only now planning the second mission after Voyager 2, which can't arrive for another 15 years or so!

The next mission there will be, roughly speaking, the Viking Orbiter of Europa (pending any pleasant surprises regarding a lander). This is a deep chess game we're playing with Europa and it's going very slowly.

[vjkane]

I'm surprised that there is no laser altimeter in the Europa spacecraft payload. There's no indication of an altimetry mode in the radar instrument, so the mystery deepens. I was under the impression that determining the exact shape of Europa was important for modeling the tidal heating from Jupiter. It's possible to get some topographic information from stereo imaging, but it's hard to imagine getting the large area coverage with high resolution I think is necessary for detailed shape modeling.

Laser altimetry would be useful only if the measurements are made over the same location at different points in Europa's orbit.

[TheAnt]

@monitorlizard: A laser altimeter would be great on one spacecraft that orbit Europe. Yet this spacecraft will orbit Jupiter and only do flyby's of Europa.

@JRehling: Yes that Europa might have water closer to the surface would fit some observations of surface features such as the chaos terrain, at the same time having a thick ice over the ocean closer to the core.
Dual layers of ice have been noted in the arctic ocean as well as in sweet water lakes in the arctic and sub-arctic region. On lakes here on Earth the energy source generally comes from above, the sun that melts snow on the surface to freeze to create the second ice sheet. On Europa the energy would come from below.
On a few rare cases I seen double ice formed from a spring of water at the bottom of the lake in lime rich areas, the icesheet formed at the inversion layer in deeper water of the lake. At least to me that provided a model of how a double ice layer might form. Blankenship Schmidt and Schenk provided a very nice model for those melt lenses, but the intermediate layer of water might be more widespread.

[Habukaz]

The Europa mission has entered a new phase (and has gotten itself a Twitter account as well):

NASA’s mission concept -- to conduct a detailed survey of Europa and investigate its habitability -- has successfully completed its first major review by the agency and now is entering the development phase known as formulation.

[pioneer]

I'm not complaining, but I'm wondering what this mission will accomplish that the Galileo mission didn't. Both spacecraft have a magnetometer, dust detector, cameras and UV instruments. The Europa mission will also conduct flybys rather than orbit Europa just like Galileo. With the exception of the radar and more advanced versions of the instruments Galileo had, what do scientists hope to get that they couldn't get from Galileo?

[MahFL]

I'm not complaining, but I'm wondering what this mission will accomplish that the Galileo mission didn't. Both spacecraft have a magnetometer, dust detector, cameras and UV instruments. The Europa mission will also conduct flybys rather than orbit Europa just like Galileo. With the exception of the radar and more advanced versions of the instruments Galileo had, what do scientists hope to get that they couldn't get from Galileo?

More detail. The camera for instance will have up to 100 times more resolution. Also GALILEO only flew by Europa two times, I believe, 45 flyby's are planned for the new mission.

[Phil Stooke]

Pioneer - Galileo was useful for what it gave us, but it was absolutely - uh - challenged by its high gain antenna failure. Sometimes we only got a few dozen images (or the equivalent in highly compressed or windowed images) from an entire orbit. Cassini routinely takes thousands of images per orbit, and this new mission will do the same or better. Look at maps of Europa - only a few limited areas are high resolution. Now we will get the whole moon in superb resolution. Plus, don't forget that Galileo was roughly 1980 vintage despite its launch being delayed until 1989. Instruments designed in 2015/6/7 will be orders of magnitude better than early 1980s instruments - especially in terms of composition data.

MahFL - Galileo made a lot more than 2 close flybys of Europa, at least 11 by my count, not including more distant flybys. The first (arrival) orbit (not counted in the 11) produced about as much data on Europa as both Voyagers combined.

Phil

[Y Bar Ranch]

I'm not complaining, but I'm wondering what this mission will accomplish that the Galileo mission didn't.

Here's my thinking.

If you consider Europa as a constantly evolving system, then this is like the extension of Galileo. We can see what possibly changed in the years between the two, which is possible because they have the same instruments. Can you imagine the excitement when they go back to the same site and see significant changes in the surface coupled with changed measurements? Fingers = crossed.

But ultimately it is all about the bandwidth. Mooorrrrreee data. Fire hose instead of a dripping faucet.

[djellison]

what do scientists hope to get that they couldn't get from Galileo?

Data..


Galileo - 120bps.

Europa Mission - probably three orders of magnitude more.

Globe maps of Europa at significantly higher resolution that currently available

Instruments 30 years more modern than those on Galileo.

And - there may be a lander along for the ride.

What will we get from this mission that we didn't get from Galileo?

EVERYTHING.

[tedstryk]

What will we get from this mission that we didn't get from Galileo?

EVERYTHING.

Everything except on-chip mosaics