Future Venus Missions |
Future Venus Missions |
Jul 1 2005, 01:30 AM
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#201
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Solar System Cartographer Group: Members Posts: 10186 Joined: 5-April 05 From: Canada Member No.: 227 |
Oh well, might as well start that new topic since it's already well advanced in the Juno area...
My perspective on landers is as follows. All the landers we've had so far were dropped blind onto an essentially unknown surface. Any future landers can be targeted for specific terrains. It really is not true that we have had representative landings. Even a descent image or two, a panoramic photo plus a bit of surface composition, from a simple Venera-class lander just updated a bit, would be useful if we could put several down at well chosen targets. My choices would be: Examples of the main plains units (smooth, fractured, ridged) tesserae high elevation radar-bright tesserae large fresh lava flow unit ('fluctus') crater dark parabola crater ejecta outflow unit dunes area. And I have always assumed, rightly or wrongly, that it would be relatively easy to put these down, so they ought to be fairly inexpensive as planetary landers go. Phil -------------------- ... because the Solar System ain't gonna map itself.
Also to be found posting similar content on https://mastodon.social/@PhilStooke Maps for download (free PD: https://upload.wikimedia.org/wikipedia/comm...Cartography.pdf NOTE: everything created by me which I post on UMSF is considered to be in the public domain (NOT CC, public domain) |
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Oct 16 2020, 08:55 AM
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#202
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Member Group: Members Posts: 706 Joined: 22-April 05 Member No.: 351 |
Another team observing Venus in the thermal infrared has failed to detect phosphine, suggesting an upper limit on concentrations several times lower than that suggested by observations at millimeter wavelengths. Press release link on SpaceRef Following the announcement of the detection of phosphine (PH3) in the cloud deck of Venus at millimeter wavelengths, we have searched for other possible signatures of this molecule in the infrared range. Since 2012, we have been observing Venus in the thermal infrared at various wavelengths to monitor the behavior of SO2 and H2O at the cloud top. We have identified a spectral interval recorded in March 2015 around 950 cm−1 where a PH3 transition is present. From the absence of any feature at this frequency, we derive, on the disk-integrated spectrum, a 3-σ upper limit of 5 ppbv for the PH3 mixing ratio, assumed to be constant throughout the atmosphere. This limit is 4 times lower than the disk-integrated mixing ratio derived at millimeter wavelengths. Our result brings a strong constraint on the maximum PH3 abundance at the cloud top and in the lower mesosphere of Venus. T. Encrenaz (1), T. K. Greathouse (2), E. Marcq (3), T. Widemann (1), B. Bézard (1), T. Fouchet (1), R. Giles (2), H. Sagawa (4), J. Greaves (5), C. Sousa-Silva (6) ((1) LESIA, Observatoire de Paris, PSL Université, CNRS, Sorbonne Université, Université de Paris, (2) SwRI, (3) LATMOS/IPSL, UVSQ Université Paris-Saclay, Sorbonne Université, CNRS, (4) Kyoto Sanyo University, (5) School of Physics and Astronomy, Cardiff University, (6) Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology) Comments: Astronomy & Astrophysics, in press Subjects: Earth and Planetary Astrophysics (astro-ph.EP) Cite as: arXiv:2010.07817 [astro-ph.EP] (or arXiv:2010.07817v1 [astro-ph.EP] for this version) Submission history From: Bruno Bézard [v1] Thu, 15 Oct 2020 15:11:37 UTC (805 KB) https://arxiv.org/abs/2010.07817 Astrobiology, Astrochemistry, Modify message -------------------- |
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Oct 16 2020, 05:34 PM
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#203
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Junior Member Group: Members Posts: 28 Joined: 17-April 08 From: Okemos, MI, USA Member No.: 4097 |
The original paper attempted to pre-rebut this argument:
QUOTE We caution that mid-infrared and far-infrared observations might not detect any phosphine in absorption, depending on the height where the quasi-continuum signal is generated in these wavebands; e.g. at high altitudes, the molecules are expected to be photo-destroyed. This paper makes some arguments as to why the original signal would actually have to be at high altitude: QUOTE the core of millimeter line is very narrow (less than about 20 MHz). If the PH3 millimeter line was formed within the clouds, at a pressure level of 100 mbars or more, its HWHM would be at least 0.01 cm−1, i.e. 300 MHz. Such a broad line would not be observable by heterodyne spectroscopy. This implies that the millimeter line observed by Greaves et. al. (2020) must be formed relatively high in the mesosphere I suppose one would need a great deal more expertise to know whose argument is stronger. |
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Oct 17 2020, 03:10 AM
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#204
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Member Group: Members Posts: 611 Joined: 23-February 07 From: Occasionally in Columbia, MD Member No.: 1764 |
I suppose one would need a great deal more expertise to know whose argument is stronger. Expertise, maybe. But as humans, we can also employ our heuristic tools of caricature, profiling and prejudice. Therese Encrenaz has been in *planetary* spectroscopy a long time. I think (and my Planetary Climate book gives many examples) in planetary science there are many instances of spectroscopic detections being disproved by in-situ or other data, which make some people (like her) cautious. In stellar astronomy (which seems to be where the Cardiff group has more pedigree), I could imagine there are fewer disproved 'discoveries' just because there are fewer ways to confirm or refute initial announcements. So, IMHO, if Therese says it isnt in her data, then it isnt in her data... (and knowing her, she wouldnt say it wasnt there on Venus, only that there wasnt evidence for it in her data). It may be non-PC to consider such meta-factors, but at the hairy edge of detectability, one is obliged - Bayeswise - to weigh all the information. There are sadly a lot of incentives in the journals and the media to talking up anything that could bear on life in the universe - indeed Nature Astronomy even had an editorial congratulating itself on how much press the paper had generated and how this was only possible because of their media embargo policy. Cui bono.... All this said, Venus deserved the attention. |
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