Pioneer 11 Jupiter, Cylindrical Maps Options

[scalbers]

True, though at least it is a somewhat reasonable phase angle to start to get a brighter plume. Do I see a hint of a bluish color as well?

[ugordan]

A quick'n'dodgy enhance of the image, I hope Ted doesn't mind:

It indeed does appear to have a plume-like characteristic. If it really is Pele's plume, I'm officially in awe of the sensitivity pulled out of the data. Either that or the eruption was absolutely massive.

[nprev]

..stunning! Same for Ted's montage, esp. the Ganymede image. Amazing that such detail can be extracted from this heritage data; you guys are something else.

[tedstryk]

Would a plume even be detectable with exposures optimized for Io's dayside and with probably not-so-sensitive equipment? We're talking about the fuzz at the limb, right?

We will never know. It is so dependent on so few pixels that while it is tempting, there is no way to be sure whether or not it is a plume or noise, unless there is some other corroborating data, such as infrared photometry, which might indicate the plume was active at the time, which might solidify it. When I first processed the Io image, I sent it to John Spencer, who had the same conclusion - it is intriguing, but can't be proven in and of itself.

[Bjorn Jonsson]

Extremely interesting even though I doubt the Pioneer IPP instrument was sensitive enough to detect a plume - maybe it could detect a huge Tvashtar-like plume though.

As a check I enhanced all of the Galileans in Ted's image to check if the other Galileans exhibited similar behavior. They didn't.

I was unable to determine the exact viewing geometry using SPICE kernels but know that the subspacecraft latitude is +60° and the subsolar longitude 184°. So this is the approximate viewing geometry:



And without the grid:



From these renderings I doubt this could be Pele's plume - it would be closer to the terminator. But needless to say this might be a different plume...

BTW if anyone knows the exact subspacecraft longitude I'd like to know - the source of my geometric information (Pioneer: First to Jupiter, Saturn and Beyond - NASA SP-446) only mentions the subspacecraft latitude.

EDIT: The pixel size in the Io image is ~375 km so apparently the plume's 'source data' only consists of about three pixels.

[tedstryk]

The problem is that there aren't more images of Io. Since the Callisto and Europa images are based on scans, comparison isn't really useful. Only two things would really convince me. One, some sort of light curve infrared data that might indicate that there was a major eruption consistent with Pele or Pillan. Also, if I were able to dig up digital data for other images, even those of Jupiter from a distance, and found no similar effects.

[scalbers]

Elaborating just a bit, is there a way to estimate/calibrate from the digital data the relative brightness of Io and the plume (as well as any bluish colors)? In theory this could be compared with data from other spacecraft. I was encouraged by seeing a moderately high phase angle where the plumes start to get brighter (due to scattering) relative to Io. Had this been a really low phase angle image I'd be more apt to discount it.

[tedstryk]

Elaborating just a bit, is there a way to estimate/calibrate from the digital data the relative brightness of Io and the plume (as well as any bluish colors)? In theory this could be compared with data from other spacecraft. I was encouraged by seeing a moderately high phase angle where the plumes start to get brighter (due to scattering) relative to Io. Had this been a really low phase angle image I'd be more apt to discount it.

It would still be hard. Most images are CCD or Vidicon. The Imaging Photopolarimeter is different. What would help is digital images of similar size disks. I still say the best bet is if some infrared photometry exists from around that period to indicate an eruption at Prometheus or Pillan at the time.