IPB

Welcome Guest ( Log In | Register )

 
Reply to this topicStart new topic
Hyperion strikes back
TheAnt
post Oct 17 2014, 10:55 PM
Post #1


Member
***

Group: Members
Posts: 495
Joined: 12-February 12
Member No.: 6336



An analysis of Cassini data from 2005 have shown that static electricity from Hyperion briefly did strike the space probe with static electricity when it passed the moon at a distance of 2000 km.
Go to the top of the page
 
+Quote Post
nprev
post Oct 18 2014, 12:41 AM
Post #2


Merciless Robot
****

Group: Admin
Posts: 8783
Joined: 8-December 05
From: Los Angeles
Member No.: 602



So, I guess it's safe to nickname Hyperion "The Death Sponge"... laugh.gif

Seriously, that's rather odd. Wonder if Hyperion's somewhat irregular orbit & passage in & out of Titan's H2 torus is causing it to become charged. Could its chaotic rotation state have something to do with this as well?


--------------------
A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
Go to the top of the page
 
+Quote Post
brellis
post Oct 18 2014, 05:31 PM
Post #3


Member
***

Group: Members
Posts: 754
Joined: 9-February 07
Member No.: 1700



Was this event entirely random, or was Cassini flying over a magnetic pole?
Go to the top of the page
 
+Quote Post
nprev
post Oct 18 2014, 05:47 PM
Post #4


Merciless Robot
****

Group: Admin
Posts: 8783
Joined: 8-December 05
From: Los Angeles
Member No.: 602



Hyperion doesn't have an intrinsically generated magnetic field (at least I've seen no claims that it does) so not in the sense I think you mean, Brad. The article says that the most likely cause of the moon's charge is interaction with the solar wind despite my previous speculation.

So, I dunno. Most likely interpretation is that, yeah, this was a random event, but at a range of 2000 km that almost sounds like the spacecraft encountered something like a flux tube connecting it to Saturn's magnetosphere--which seems unexpected. Hopefully there will be more to follow about this interesting observation.


--------------------
A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
Go to the top of the page
 
+Quote Post
dvandorn
post Oct 18 2014, 09:30 PM
Post #5


Senior Member
****

Group: Members
Posts: 3419
Joined: 9-February 04
From: Minneapolis, MN, USA
Member No.: 15



A flux tube was my first thought, too. But the only flux tube I've heard of around an outer planet's moon (or at least through which the moon travels) is Io's, and that one is generated (AIUI) more than anything else by the sulfur ring caused by Io's volcanoes. I would think Hyperion would have to be venting something with a high dialectric constant for it to have generated a flux tube...

-the other Doug (With my shield, not yet upon it)


--------------------
“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
Go to the top of the page
 
+Quote Post
nprev
post Oct 18 2014, 10:36 PM
Post #6


Merciless Robot
****

Group: Admin
Posts: 8783
Joined: 8-December 05
From: Los Angeles
Member No.: 602



You're probably right (and welcome back, BTW, oDoug! smile.gif ) I keep wondering about the fact that Hyperion passes in & out of Titan's hydrogen torus, which is extremely voluminous; could that impart enough of a charge over time to explain the apparently VERY high potential of the moon?

Seems like that thing's gotta have quite a charge no matter how you slice it. Either there's a flux tube-like mechanism going on or it spontaneously reached out & and touched Cassini from a considerable distance indeed. Have there been any comparable events observed during flybys of small objects by Cassini or other spacecraft?


--------------------
A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
Go to the top of the page
 
+Quote Post
ynyralmaen
post Oct 19 2014, 08:17 PM
Post #7


Member
***

Group: Members
Posts: 125
Joined: 18-July 05
Member No.: 438



All the inactive/airless bodies build up charge. Sunlight tends to charge things positive, through the photoelectric effect releasing electrons, whilst the flow of plasma in the magnetosphere onto bodies tends to charge them negative. The dust detected by Cassini has been found to be charged. Close to Saturn, it's negatively charged, where the plasma in the magnetosphere is denser, whilst roughly beyond the orbit of Rhea, it tends to charge positive, where the effect of sunlight dominates.

Cassini itself has a potential, which varies depending on where it is and whether it's in shadow, and the potential follows the same general pattern as observed on the dust. That can be a problem for certain observations, when for example very low energy electrons can't reach the spacecraft when it's got a negative potential, so they can't be detected by the plasma instruments.

For the moons, it's a little more complex as you'll have one half continuously exposed to plasma, because they're sitting inside Saturn's magnetosphere, and another, usually overlapping hemisphere exposed to the Sun. You can also get local effects such as shadowed regions, etc. that complicate things quite a bit, and the effects of the plasma depend on its temperature too.

When a moon's surface has a negative potential, it can reflect low energy electrons, and can also accelerate electrons away from its own surface. Hyperion didn't really zap Cassini has it went past - this process of electron reflection and acceleration is going on all the time, and the electrons stream away along Saturn's magnetic field lines that pass through Hyperion. During the encounter in 2005, Cassini happened to be on magnetic field lines connecting the moon to the spacecraft, and the CAPS instrument happened to be looking in the right direction to detect the electrons arriving from the direction of Hyperion. The feature was spotted in the data at the time, but it took a few years to fully understand what was being observed, and it's a neat result!

One definition of a flux tube is the collection of magnetic field lines that thread a moon, so, yes, Cassini did cross Hyperion's flux tube. smile.gif
Go to the top of the page
 
+Quote Post
ngunn
post Oct 19 2014, 09:24 PM
Post #8


Senior Member
****

Group: Members
Posts: 3516
Joined: 4-November 05
From: North Wales
Member No.: 542



Hey - really good explanation of the situation. smile.gif Thanks for taking the trouble to post that.

I echo nprev's question Could its chaotic rotation state have something to do with this as well? Any thoughts?
Go to the top of the page
 
+Quote Post
dvandorn
post Oct 20 2014, 01:04 AM
Post #9


Senior Member
****

Group: Members
Posts: 3419
Joined: 9-February 04
From: Minneapolis, MN, USA
Member No.: 15



QUOTE (nprev @ Oct 18 2014, 04:36 PM) *
...and welcome back, BTW, oDoug! smile.gif


Thanks, Nick! It's awful darned good to be back. Though, with all that I've gone through in the past year and a half (I'm not going to go into the gory details, it just suffices to say that there was a fair amount of luck involved in me being here today to once again share this marvelous forum with y'all), I think that the "With my shield, not yet upon it" phrase is going to become a permanent part of my sig. I've been through the battles, and I'm back home to tell about it, by the gods! wink.gif

As for the electrical field structures around Saturn, I will note that the magnetic field obviously develops a strong "static electricity" component as it travels along in its rotation around the planet. Look at what happens in the rings as the magnetic field passes through them -- the electrical effects cause enough particle separation from the ring plane to produce the spokes phenomenon. A larger mass, like an electrically conductive spacecraft, would definitely notice that kind of effect if it passed through that area. So I guess it's not surprising that most of the bodies in the Saturn system are sufficiently charged electrically to cause arcing on Cassini as it passes through.

All of that said, we've passed closer to Enceladus than we passed Hyperion. Heck, I think we'e had closer passes of Titan (albeit above the deep atmosphere) and Rhea, among other moons. Any signs of arcing at those points, I wonder? It might also be good to run through Galileo close approaches, especially with Io, to look for such phenomena.

-the other Doug (With my shield, not yet upon it)


--------------------
“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
Go to the top of the page
 
+Quote Post
ynyralmaen
post Oct 20 2014, 07:11 AM
Post #10


Member
***

Group: Members
Posts: 125
Joined: 18-July 05
Member No.: 438



QUOTE (ngunn @ Oct 19 2014, 09:24 PM) *
I echo nprev's question Could its chaotic rotation state have something to do with this as well? Any thoughts?


Given that the charging times are much, much shorter than the rotation/tumbling period, I doubt that the rotation state is likely to have a signficant effect, apart from making it difficult to predict what the potential is going to be across the surface at any one time. The irregular shape and rugged surface make it difficult to simulate too.

oDoug - welcome back! Regarding other bodies... something is in the works; watch this space!
Go to the top of the page
 
+Quote Post
TheAnt
post Oct 20 2014, 08:30 PM
Post #11


Member
***

Group: Members
Posts: 495
Joined: 12-February 12
Member No.: 6336



Thank you for the explanation ynyralmaen.

Spacecom did a page with this story also, and they did indeed mention charged dust.
It's nice to get that detail confirmed. =)

Now with ynyralmaen's hint of some other interesting news arriving soon I wonder if that other body might be the "Death star" Mimas since said space orientated website got this piece about the libration and what that might mean for the contents of the core of that moon.
Go to the top of the page
 
+Quote Post
ngunn
post Oct 20 2014, 08:44 PM
Post #12


Senior Member
****

Group: Members
Posts: 3516
Joined: 4-November 05
From: North Wales
Member No.: 542



QUOTE (ynyralmaen @ Oct 20 2014, 08:11 AM) *
Given that the charging times are much, much shorter than the rotation/tumbling period, I doubt that the rotation state is likely to have a signficant effect


I meant the other way around. Uneven charging of the surface could give Hyperion a net electric dipole moment at any given time. This in turn could produce variable torques on the moon, contributing to its chaotic rotation.
Go to the top of the page
 
+Quote Post
Bjorn Jonsson
post Oct 20 2014, 10:27 PM
Post #13


IMG to PNG GOD
****

Group: Moderator
Posts: 2250
Joined: 19-February 04
From: Near fire and ice
Member No.: 38



QUOTE (TheAnt @ Oct 20 2014, 08:30 PM) *
Spacecom did a page with this story also, and they did indeed mention charged dust.


There is certainly a lot of dust in the Saturnian system - the first thing that comes to my mind is the rings (and the spokes). But the satellites are dusty as well and as Cassini's images have shown, some of the small ones look really weird.

Go to the top of the page
 
+Quote Post
ynyralmaen
post Oct 21 2014, 05:21 PM
Post #14


Member
***

Group: Members
Posts: 125
Joined: 18-July 05
Member No.: 438



QUOTE (ngunn @ Oct 20 2014, 08:44 PM) *
I meant the other way around. Uneven charging of the surface could give Hyperion a net electric dipole moment at any given time. This in turn could produce variable torques on the moon, contributing to its chaotic rotation.


Ah, I see. I haven't looked at the numbers, and I appreciate it's been orbiting Saturn for a very very long time, so small effects could build up (as the YORP effect can be significant on asteroids), but still I'd be extremely surprised if this would make an observable contribution. Would be very happy to be proven wrong though!

By the way, the Hyperion paper is open access, so anyone can read it here.
Go to the top of the page
 
+Quote Post

Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 28th March 2024 - 09:06 PM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is funded by the Planetary Society. Please consider supporting our work and many other projects by donating to the Society or becoming a member.