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Juno Extended Mission, Perijove 34-76
volcanopele
post Sep 2 2020, 08:05 PM
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At today's Outer Planet Assessment Group (OPAG) meeting, Scott Bolton gave a presentation on Juno, providing an update on the mission and providing more information on its extended mission proposal. The proposal has been sent to NASA and they expect a final decision later this year.

The proposed extended mission starts where the current one ends at perijove 34 in June 2021 and continues through orbit 76 in September 2025. The continued northward progression of the perijove latitude, and continued lower altitude of the ascending node, is going to enable a lot of great science both at Jupiter (higher resolution views of Jupiter's poles) and of its satellites. Most excitingly for me, Juno will perform several flybys of the Galilean satellites. This includes a 1000-km encounter with Ganymede next June during PJ34, a 320-km encounter with Europa in late 2022, and TWO Io flybys in early 2024 at an altitude of 1500 km. There are also a number of "Voyager-class" encounters with Ganymede, Europa, and Io between mid-2021 and mid-2025.

The PDF for Scott Bolton's presentation can be found on the page for the OPAG meeting: https://www.lpi.usra.edu/opag/meetings/opag2020fall/


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JRehling
post Sep 2 2020, 09:18 PM
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That is exciting.

I know that the eye candy is fun for all of us, and this forum is a particularly good medium (and talent base) for image processing but I am getting increasingly interested in the less-flashy and slower-to-evolve science on the interior of Jupiter and the synergistic study of the interior of Saturn that capitalized heavily on the last phase of the Cassini mission.

The status, on a meta-level is that Juno has placed some important constraints on the interior structure of Jupiter but there's still a lot of uncertainty regarding the details and no consensus regarding Jupiter's origin. I don't know with what certainty more perijoves will answer those questions, but the questions are important and more perijoves sure can't hurt.

It's also very interesting that Jupiter and Saturn are significantly different internally.

All of that said, I'm also looking forward to the Galilean eye candy. There could be some important science there, in advance of Europa Clipper getting to the vicinity.
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volcanopele
post Sep 2 2020, 09:37 PM
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And it won't just be eye candy with the Galileans. For example, the Europa encounter will allow for mapping of one hemisphere with the MWR at 100-200 km resolution. That instrument can probe to a depth of 10 km allow for the direct detection of lakes within the Europan ice sheet. The Io encounters will include JunoCAM imaging sure, but also JIRAM mapping of Io's hotspots with resolutions down to 355 m/pixel as well as gravity science and magnetometer measurements, which when combined with future IVO passes, will provide some strong constraints on the state of Io's lower lithosphere and upper asthenosphere.

For Jupiter, with closer passes over the poles, they will be able to do better 3D mapping of the atmosphere below the north polar cyclones as they will be able to do repeated passes over the same part of Jupiter.


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rlorenz
post Sep 3 2020, 02:19 AM
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QUOTE (volcanopele @ Sep 2 2020, 05:37 PM) *
And it won't just be eye candy with the Galileans. For example, the Europa encounter will allow for mapping of one hemisphere with the MWR at 100-200 km resolution. That instrument can probe to a depth of 10 km allow for the direct detection of lakes within the Europan ice sheet.


I would like to see the assumptions that went into that, it seems very doubtful to me. Scattering by fractures, and absorption by contaminants (salts, sulfuric acid..) in Europan ice is such that even the sort of 10 MHz ice penetrating radar on Clipper has a good chance of not penetrating that deep, and the ~1 GHz MWR wavelength being 100 times shorter will sound commensurately less deep.

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JRehling
post Sep 3 2020, 05:52 AM
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I'm curious if the Europa imagery could be sufficient to determine the rate of rotation of the shell/surface, which is not synchronous with the core. It's known that the rotation rate of the shell relative to the core is very slow, and the baseline between Voyager 2 and Galileo was not sufficient to measure visibly any rotation. The time from Galileo to Juno imaging would be, once again, about 20 years, but the resolution of Juno imaging would be higher than that of Voyager 2. Getting any measurement of that rotation, even to first order, could tell us a lot about the dynamics of the shell, in which the major linea represent cracking along stress lines that must have taken place when the shell was oriented very differently with respect to Jupiter. But since then, has it undergone ~0.25, ~1.25, ~2.25, etc. full rotations?
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vjkane
post Sep 3 2020, 02:50 PM
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Ralph, thanks for the dash of reality. Hope that the microwave instrument provides some new insights. (BTW, Ralph, your new Titan book is excellent. Been enjoying it.)

One thing not mentioned so far in this thread is that Juno will conduct a "sensitive" search for Europan plumes. Will use the camera and the much more sensitive star sensors.


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rlorenz
post Sep 4 2020, 03:37 AM
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QUOTE (vjkane @ Sep 3 2020, 09:50 AM) *
Ralph, thanks for the dash of reality. Hope that the microwave instrument provides some new insights.


I'm certain it will. Any time you use a new instrument on a target, you make discoveries. And the MWR is an exquisite instrument.

But one must always (both post-hoc for 'discoveries', and pre-hoc for 'opportunities') consider the motivations behind any claim. Fame, tenure etc. can be the prize of high-profile publications, so there is often a 'race to the bottom' for the lowest standard of evidence that will satisfy peer review for 'discovery' of something exciting - claims of discovery of cryovvolcanism on Titan are a case in point. And some of the higher-profile scientific journals are complicit in this process, they like the headlines. Similarly, claiming that a mission/instrument/observation may discover X is not a disprovable statement, and is a rational thing for someone advocating for said mission/instrument/observation to claim as a possibility. But that isnt the same thing as saying dispassionately that it is an expected result.

QUOTE
(BTW, Ralph, your new Titan book is excellent. Been enjoying it.)

Cheers! Tell your friends ! oh, I guess you just did ;-)

QUOTE
One thing not mentioned so far in this thread is that Juno will conduct a "sensitive" search for Europan plumes. Will use the camera and the much more sensitive star sensors.


That is potentially a very interesting observation. (And not unrelated to my earlier point : the discovery of plumes on Enceladus is, reasonably, attributed to the Cassini magnetometer team. But in fact the Cassini imaging team saw evidence of the plumes before that, but wanted to be sure that what might have been a plume wasn't some scattered light artifact in the images, and so waited to get more data. Because they (laudably) imposed on themselves a high standard of proof, other evidence emerged first and they got perhaps less credit than they might have deserved).

So, the fact that the Juno Mag/SRU - in effect a low-light camera - is so sensitive is great, and it has had some nice results detecting lighting, but this alone does not necessarily make it a good plume detector. Careful characterization of the scattered light response of the camera will be essential for robust plume detection.

Again, there are temptations in plume detection to give oneself the benefit of the doubt in marginal situations, both for individual scientists, and for 'selling' a mission (the timing of the first reported HST plume discovery, at very low signal to noise, I might add, was let's say fortuitous with respect to the timing of Congressional support for what became Europa Clipper). So it is rational in the run-up to a senior review for a mission extension to note the instrumental sensitivity and the observation opportunity, but some careful scrutiny may be in order before one raises expectations too high. (the OPAG presentation did not permit the PI to present much detail - it may well be that a strong case for the MWR detection of Europa's ice thickness, and the SRU detection of possible plumes exists, I just note that I haven't seen it yet.)

All this is only natural, science is a human process. You only find the evidence if you think it is there in the first place. But as Robert Louis Stevenson said, 'The cruelest lies are told in silence'......


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vjkane
post Sep 4 2020, 01:32 PM
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QUOTE (rlorenz @ Sep 2 2020, 06:19 PM) *
I would like to see the assumptions that went into that, it seems very doubtful to me. Scattering by fractures, and absorption by contaminants (salts, sulfuric acid..) in Europan ice is such that even the sort of 10 MHz ice penetrating radar on Clipper has a good chance of not penetrating that deep, and the ~1 GHz MWR wavelength being 100 times shorter will sound commensurately less deep.


It may be that the contribution of Juno's microwave observations may be to characterize how noisy observations of the the ice shell's structure will be. Bolton had less than a minute to describe the microwave observations, and as I recall, I believe that he said that the instrument had the capability to observe as deep as 10 km, not that it would observe that deep.

QUOTE (rlorenz @ Sep 3 2020, 07:37 PM) *
And the MWR is an exquisite instrument.


Off topic, I would like to see an MWR like instrument flown on an ice giant mission (and some proposed missions would include it), but its mass is a significant issue. I saw that Bolton has a grant to do technology development for a lighter weight and more capable version with an eye toward an ice giant orbiter.

QUOTE (rlorenz @ Sep 3 2020, 07:37 PM) *
Again, there are temptations in plume detection to give oneself the benefit of the doubt in marginal situations, both for individual scientists, and for 'selling' a mission (the timing of the first reported HST plume discovery, at very low signal to noise, I might add, was let's say fortuitous with respect to the timing of Congressional support for what became Europa Clipper). So it is rational in the run-up to a senior review for a mission extension to note the instrumental sensitivity and the observation opportunity, but some careful scrutiny may be in order before one raises expectations too high. (the OPAG presentation did not permit the PI to present much detail - it may well be that a strong case for the MWR detection of Europa's ice thickness, and the SRU detection of possible plumes exists, I just note that I haven't seen it yet.)

All this is only natural, science is a human process. You only find the evidence if you think it is there in the first place. But as Robert Louis Stevenson said, 'The cruelest lies are told in silence'......


I agree. Ignore the press release, read the paper. (Even better, wait for the synthesis review of papers that weighs evidence from a number of studies.) I did look up the original Europa plume paper, and the authors, as I recall, did state that the observations were right at the edge of detector capability. Then NASA made the most of it, as they did for the claim that the Martian meteorite had fossilized micro organisms. Will say, that NASA is good a parlaying press releases into missions (or in the case of Mars, a whole program of missions).


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mcaplinger
post Sep 4 2020, 03:42 PM
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QUOTE (rlorenz @ Sep 3 2020, 07:37 PM) *
the fact that the Juno Mag/SRU - in effect a low-light camera - is so sensitive is great...

The SRU is unrelated to the magnetometer. Maybe you're confusing it with the magnetometer's ASCs (Advanced Stellar Compasses)?

On this thread in general: The mission extension proposal will be quite detailed, and evaluated carefully. I think criticizing it on the basis of an OPAG overview presentation is a little inappropriate.


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volcanopele
post Sep 4 2020, 04:04 PM
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I agree with Mike. Putting moderator hat on...

Some these questions would've been great to bring up during the Q&A part of the OPAG session on Wednesday, but without Scott Bolton here to better explain the factors that went into their claims or the hedging that might have gone into their actual senior review proposal (which for the vast majority of missions are much more detailed than a PDF presentation), it might be best to drop the discussion of MWR performance at Europa for now. And without details on how exactly they will be looking for plumes, again, we need to be careful about speculating then criticizing what we speculate.

Taking moderator hat off...

That being said, with the SRU being used for science as well as navigation, I do hope that the Juno team considers posting that data to the PDS.


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rlorenz
post Sep 5 2020, 02:53 AM
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QUOTE (mcaplinger @ Sep 4 2020, 11:42 AM) *
The SRU is unrelated to the magnetometer. Maybe you're confusing it with the magnetometer's ASCs (Advanced Stellar Compasses)?

On this thread in general: The mission extension proposal will be quite detailed, and evaluated carefully. I think criticizing it on the basis of an OPAG overview presentation is a little inappropriate.


Sorry, I'm not a mission insider, yes I meant the magnetometer's star camera (which I guess happens in this instance to be called an ASC - a strange name : a magnetometer has a compass that isnt a magnetometer ;-)

And I didnt criticize anything or anyone. I merely said I'd like to see more analysis backing the claims that were made, and I made general observations about the scientific process.
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Decepticon
post Sep 7 2020, 02:43 AM
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Will images be taken during Europa and Io Encounters?

Will they be comparable to Voyager 2 Best images?
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mcaplinger
post Sep 7 2020, 06:37 PM
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QUOTE (rlorenz @ Sep 4 2020, 06:53 PM) *
yes I meant the magnetometer's star camera...

Once more for clarity: there are multiple star cameras on the spacecraft. The SRU (two for redundancy, one active) is an engineering subsystem and the ASCs (four total) are part of the magnetometer, used for getting high-resolution orientation data for the magnetometer to remove the effects of boom motion. They can all be used for imaging, but it's the SRU that has been most used for low-light imaging and radiation monitoring at Jupiter.


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JRehling
post Sep 8 2020, 06:44 PM
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I don't have any information on planned instrument usage, but the closest satellite flybys would certainly allow imaging at much higher resolution than Voyager 2 at Europa. Note that the satellite flybys in the presentation span a huge range of distances and the farthest ones are similar to the opportunistic imagery already acquired during the main mission.

My sense from the distances is that the main scientific playoffs will be:

1) The spectral range of Juno instruments in making hemispheral maps of Ganymede and Europa hinting at composition. It will be the spectral capabilities here that add to the knowledge more than the spatial resolution.
2) A search for Europa's plumes.
3) Monitoring the current activity of Io volcanoes.
4) Perhaps contributing original detailed mapping of Europa on the one really close encounter.
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mcaplinger
post Sep 8 2020, 07:55 PM
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QUOTE (JRehling @ Sep 8 2020, 10:44 AM) *
the closest satellite flybys would certainly allow imaging at much higher resolution than Voyager 2 at Europa.

Considering that the resolution of the Voyager ISS NAC was 72x higher than the resolution of Junocam at the same distance, I'm not sure I'd say "certainly". If the closest approach was 320 km and if illumination conditions and spacecraft orientation were compatible with imaging there, then the maximum resolution Junocam could get is about 0.2 km/pixel at nadir. JIRAM could do about 3x better.

The Bolton presentation says 1-2 km resolution.

I'm not sure what the best resolution image of Europa from Voyager was, but there is global coverage at about 0.5 km/pixel from a mixture of Voyager and Galileo https://astrogeology.usgs.gov/search/map/Eu...bal_mosaic_500m although there are some gaps where the coverage is much worse or (near the south pole) even missing entirely.


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