Juno Extended Mission, Perijove 34-76 |
Juno Extended Mission, Perijove 34-76 |
Sep 2 2020, 08:05 PM
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Senior Member Group: Moderator Posts: 3234 Joined: 11-February 04 From: Tucson, AZ Member No.: 23 |
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/ -------------------- &@^^!% Jim! I'm a geologist, not a physicist!
The Gish Bar Times - A Blog all about Jupiter's Moon Io |
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Sep 3 2020, 02:50 PM
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Member Group: Members Posts: 706 Joined: 22-April 05 Member No.: 351 |
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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Sep 4 2020, 03:37 AM
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Member Group: Members Posts: 611 Joined: 23-February 07 From: Occasionally in Columbia, MD Member No.: 1764 |
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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Sep 4 2020, 01:32 PM
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Member Group: Members Posts: 706 Joined: 22-April 05 Member No.: 351 |
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. 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. 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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