Water plumes over Europa Options

[JRehling]

As mentioned earlier, opportunities when Europa occults a background object and its light passes through the plumes (or fails to do so) could give us information about the presence and composition.

Pluto has occulted stars every few years, and Europa moves against the background of stars much faster (about 20x) than Pluto does, which should provide a lot more opportunities. The downside is: Europa provides a lot more background light than Pluto does, and Jupiter is likely a factor for some observations, so a favorable signal-to-noise ratio might requires a brighter star being occulted.

As I also mentioned, Io could possibly serve as the occulted body, although that doubles the background noise of the observation.

Clearly, we will need to characterize the frequency and perhaps periodicity of the plumes before committing to any exploration. They may be very cooperative, like the Old Faithful geyser, or extremely unpredictable, like most terrestrial volcanoes.

[Paolo]

I am too lazy to go through the references, so I ask: would the plumes be detectable by the Japanese SPRINT-A UV space telescope?

[MarcF]

I am probably very naive, but I thought, if we cannot detect the plume itself, may be it could be possible to detect the hotspot where it originates from (like for Enceladus).
Do we have instruments able to detect this ?
(Again I'm thinking about GPI, since I'm so amazed by the resolution of its pictures).
Regards,
Marc.

[Greenish]

According to this document among others, Gaia will drastically increase the number of stars available for predictable occultations of solar system objects, as well as the precision resulting from those measurements. Perhaps in addition to small bodies (where if I'm reading it right, at 20-50km size the number of opportunities could go from 0.1 to 20+ events/object/year and the orbit precision could improve 100x), this will help for things like this plume study... but of course the useful occultation frequency will very much depend on how bright the star needs to be, and I suppose its spectral type, too, for this work.

[ugordan]

I am probably very naive, but I thought, if we cannot detect the plume itself, may be it could be possible to detect the hotspot where it originates from (like for Enceladus).

For Enceladus, Cassini CIRS had the advantage of being fairly close to the moon and the detector footprint was relatively small compared to the tiger stripes. For ground-based observations, any localized hotspots would be averaged over hundreds of kilometers of "regular" cold terrain.

[MarcF]

Thanks for the answer Ugordan. So we will have to wait 2 decades to know for sure.
Marc.

[vjkane]

We will know long before two decades whether or not the Hubble observations can be repeated. I suspect that we'll also get more sensitive stellar occulations as outlined above.

Then in the late 2020s...

Before the plume announcement, one of the goals for the JUICE mission was to use the UVS and cameras to look for plumes using long distance remote observations. (I.e, watch Europa throughout its orbit.) If plume sources have been discovered through any means, then the spacecraft instruments will be nearly ideal. The mass spectrometer is sensitive to AMUs near a thousand (recalling from memory). The radar unit could measure the subsurface structure around the vents. The only key instrument missing would be a thermal imager to image whatever the equivalent of Enceladus' tiger stripes turn out to be at Europa.

One other limitation of the JUICE mission is that its Europa flybys are planned for a single position in Europa's orbit. The plumes may not be active or have reduced activity at this location and the sources might be in darkness.

[JRehling]

One note on the geometry of the plumes: They, like Enceladus's plumes, seem to be associated with the south pole. Unlike the saturnian system, the jovian system has essentially no seasons, so it's conceivable that the plume source, if its sunken into the terrain, might never (or rarely) have a line of sight to Earth and/or the Sun.

On the other hand, most of the plumes themselves would never (or rarely) be in Europa's shadow.

If the sources have hotspots, it is not inconceivable that they could be observed and pinpointed from Earth, but the devil's in the details: While any IR thermal analysis would of course lack the spatial resolution to pinpoint the plumes, a temperature sufficiently higher than the background could radiate IR at wavelengths that should be at nearly zero emission from Europa's baseline. This works just fine with Io's hotspots. Moreover, occultation of Europa by Io or Ganymede could allow some extremely precise pinpointing of the source, when the hotspot passes behind the other moon.

However, it seems unlikely to me that Europa's hotspots, if any, would be nearly hot enough to allow this observation to work. The temperature difference between Europa's ambient surface and any hotspots is probably less than 300K°, probably far less than that, as well as being very limited in scale.

[vexgizmo]

Back in December, there was discussion of the available imaging data for the reported plumes region. A blog entry has just been published by Lorenz Roth describing the discovery, along with a nice orthographic view of the identified source region. http://solarsystem.nasa.gov/europa/blogs_l...roth_plumes.cfm

[Phil Stooke]

I had a vague recollection that Voyager images of possible Europa plumes were published long ago, but most people didn't really accept them.

I managed to find the references, and now they make very interesting reading.

Sky & Telescope, Jan. 1983, p. 15: Allan Cook (Harvard-Smithsonian) - in a post-flyby Voyager 1 image looking back at a crescent Europa, a bright patch at the southern cusp and a faint plume 100-150 km high. Not seen in other images.

JGR Oct. 1982, Intriligator and Miller: Pioneer 10 may have encountered a plasma cloud emanating from Europa in 1973.

IAU Colloquium 77 (Natural Satellites), Brown U. Preprint #A546 (July 1983, p. 22): A. F. Cook (Hertzberg Inst. and Harvard-Smithsonian) plus Paul Helfenstein (then at Brown): six Voyager 2 images taken during approach show a diffuse plume, not seen in similar Ganymede images. Best view is image 0391J2-002.


Phil

[Ian R]

IAU Colloquium 77 (Natural Satellites), Brown U. Preprint #A546 (July 1983, p. 22): A. F. Cook (Hertzberg Inst. and Harvard-Smithsonian) plus Paul Helfenstein (then at Brown): six Voyager 2 images taken during approach show a diffuse plume, not seen in similar Ganymede images. Best view is image 0391J2-002.

Image 0391J2-002, aka c2060558, does show a 'plume', but it's likely a residual artifact of the reseaux dot removal process; none of the raw images in this sequence appear to show any plumes, tenuous or otherwise:

c2060558 raw:

[Ian R]

Sky & Telescope, Jan. 1983, p. 15: Allan Cook (Harvard-Smithsonian) - in a post-flyby Voyager 1 image looking back at a crescent Europa, a bright patch at the southern cusp and a faint plume 100-150 km high. Not seen in other images.

This post-flyby Voyager image of Europa got me excited:

http://pds-rings.seti.org/browse/VGISS_5xx...649524_full.jpg

Until I realized it was just an unfortunately situated speck of dust on the camera lens:

http://pds-rings.seti.org/browse/VGISS_5xx...649518_full.jpg

[Phil Stooke]

Not so fast! I was summarizing. The version of that image printed in the reference shows the plume area, much bigger than a reseau removal artifact (and we can see where the reseaux are, it's not there) - I'm not saying the Voyager observations are correct, but they are not disproven by this quick look.


Phil

[Ian R]

I'm glad to hear that Phil. Makes me wonder how they managed to tease out a putative plume out of this dataset.

[JohnVV]

Makes me wonder how they managed to tease out a putative plume out of this dataset.

the plume
isis is lousy at Reseaus removal so i left them in

c2060558.imq > voy2isis > voycal > isis2raw ( omin set to 0.0000 )
convert the 32 bit raw to a 32 bit tiff
normalize ( in 32 bit float to 0 to 255 )

screen shot of the normal image

then rescaled

false color


there is something at the top of the image , but it looks like "camera shake" from the spacecraft movement
unfortunately "spiceinit" is not working well on this small of a image
--- edit ---
the area at the top IS from the spacecraft movement

there is a "bright spot" in between two reseaus BUT that is the DUST mentioned a few posts up

------------- edit --------------
from a few more images the "plume " center is at -65 x 183
so the above 3 images that is in the lower left

a few more images
( same processing as above)

so for image "c2062524.imq" the "plume" would be in the lower left


that ? might ? be something or it might be image shake from the spacecraft movement


For those that can not see the thumbnails
well no thumbnails but a link to a folder on my picasa albums
full size only
https://picasaweb.google.com/10269590129139...941/EuropaPlume
g+ ( b**s** that is even more useless than FB )
https://plus.google.com/photos/102695901291...4849?banner=pwa