Hubble observations of Ganymede, Teleconference on March 12, 2015 Options

[JRehling]

http://www.nasa.gov/press/2015/march/nasa-...n/#.VP6JwEJBDjI

This seems to hint at something momentous. Ganymede hasn't been breaking news very often since the Galileo mission ended, so what's the announcement?

I would think that HST observations of Ganymede could only be worthy of a teleconference if it's one of these:

1) The existence of plumes/geysers as were observed at Europa.
2) Something interesting detected in Ganymede's very-thin atmosphere.
3) Something interesting deposited in the ices on the surface.

One of the speakers, Joachim Saur, has had publications regarding Ganymede's surface, aurorae at Io, Enceladus, and was on the paper announcing plumes at Europa.

Maybe we've got another Galilean with a buried ocean that sprays its contents skyward?

[TheAnt]

The presence of the magnetic field in itself had been seen as one indication of a subsurface layer of salty water. And that's what it is required for it to be electrically conductive to create the field in the first place.

So the detection of aurora is more an indication of how the magnetic field interacts with the environment there.
What bugs me is that illustrations show the aurora as blue. No nitrogen have been detected in the very thin atmosphere of Ganymede.

[katodomo]

At the teleconference Saur corrected this by saying the aurora as seen from the surface would be red.

Should probably be more like orange-red/light red, possibly shifted towards yellow or green too.

[TheAnt]

At the teleconference Saur corrected this by saying the aurora as seen from the surface would be red.

Should probably be more like orange-red/light red, possibly shifted towards yellow or green too.

Aha Saur did note that detail also, good of him.

And yes you're right, red is to far to the right in the spectrum. If it strong enough to see with the naked eye, such aurora would be orange-yellow or pink.

[DFortes]

And yes you're right, red is to far to the right in the spectrum.

Right, left??? Which way around depends on whether you plot wavelength or frequency on the horizontal axis, and even then if you choose to plot values in ascending or descending order. Maybe we should stick to SI units rather than an entirely anthropocentric reference frame.

Would a subsurface ocean of liquid water give rise to some form of plate tectonics as on Earth?

The low-pressure form of water ice is always less dense than liquid water, regardless of temperature, so cannot founder into the subsurface as cold oceanic slabs do into the Earth's mantle.