IPB

Welcome Guest ( Log In | Register )

 
Reply to this topicStart new topic
The Surface Age of Triton
volcanopele
post Aug 21 2007, 07:24 PM
Post #1


Senior Member
****

Group: Moderator
Posts: 2864
Joined: 11-February 04
From: Tucson, AZ
Member No.: 23



There is a new paper in press in Icarus on Triton:

On the Negligible Surface Age of Triton
Paul M. Schenk and Kevin Zahnle

The article was published online on Sunday. I just got my hands on it. I haven't ready through all of it yet, but it is very intriguing. The authors preformed a new crater counting analysis of Voyager 2 images of Triton. The counted only 100 craters larger than 5 km across, and 21 craters larger than 10 km across. Their analysis allowed them to differentiate between craters and circular diapir features in the cantaloupe terrain.

What is particularly striking isn't so much the low number of observed impact craters. Smith et al. (1990) suggested a surface of less than 500 My based on the low number of crater they counted. What makes Schenk and Zahnle's analysis striking is the complete and utter lack of impact craters on the trailing hemisphere. Every single one of the measured impact craters are on the leading hemisphere. There are a couple of possible impact features on the trailing hemisphere, but all the definitive impact craters are on the leading hemisphere. The authors suggest that this indicates that all the craters likely formed from planetocentric sources (e.g. impact spalls from one of the other Neptunian satellites or disrupted satellites). Calculations of the impactor flux at Triton from planetocentric and heliocentric sources suggest a surface age of 50 My for the "heavily" cratered terrain and 6 My for the cantaloupe terrain. This suggest that Triton has a younger surface than everyone's darling, Europa.

Once you start looking at surface ages like this, the authors suggest that Triton (EDIT: not Neptune, silly) is likely still experiencing cryovolcanism, in the form of diapirs and cryoflows. They further suggest, as Stern and McKinnon did back in 2000, that this level of activity could be evidence that the south polar plumes are driven by internal heat rather than solar heating.


--------------------
&@^^!% Jim! I'm a geologist, not a physicist!
The Gish Bar Times - A Blog all about Jupiter's Moon Io
Go to the top of the page
 
+Quote Post
Rob Pinnegar
post Aug 21 2007, 10:35 PM
Post #2


Member
***

Group: Members
Posts: 501
Joined: 2-July 05
From: Calgary, Alberta
Member No.: 426



This is *very* interesting, but...

QUOTE (volcanopele @ Aug 21 2007, 01:24 PM) *
The authors suggest that this indicates that all the craters likely formed from planetocentric sources (e.g. impact spalls from one of the other Neptunian satellites or disrupted satellites).


...I don't buy this.

Impacts from Neptunian satellite fragments could only concentrate on one hemisphere of Triton if (1) Triton's rotational and orbital periods were synchronized right from the get-go after capture, or (2) the impacts occurred a long time after Triton's capture.

It's hard to imagine either of these being very likely.
Go to the top of the page
 
+Quote Post
volcanopele
post Aug 21 2007, 10:57 PM
Post #3


Senior Member
****

Group: Moderator
Posts: 2864
Joined: 11-February 04
From: Tucson, AZ
Member No.: 23



(2) seems to be the best bet. These craters formed very recently.


--------------------
&@^^!% Jim! I'm a geologist, not a physicist!
The Gish Bar Times - A Blog all about Jupiter's Moon Io
Go to the top of the page
 
+Quote Post
nprev
post Aug 22 2007, 12:07 AM
Post #4


Senior Member
****

Group: Moderator
Posts: 7097
Joined: 8-December 05
From: Los Angeles
Member No.: 602



Hmm. How much tidal heating does Triton get, VP? Wondering if it got an early boost (if not a pretty thorough melting) from the capture...maybe it's only been with Neptune for 50 My? huh.gif


--------------------
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
JRehling
post Aug 22 2007, 12:52 AM
Post #5


Senior Member
****

Group: Members
Posts: 1572
Joined: 20-April 05
Member No.: 321



QUOTE (volcanopele @ Aug 21 2007, 03:57 PM) *
(2) seems to be the best bet. These craters formed very recently.


As an added consideration, Triton revolves in retrograde. Its leading face is doing the equivalent of driving north in the southbound lanes of traffic. Material spalling off of another Neptunian satellite would have to REALLY be moving fast to lose all of its orbital velocity, and also catch up to Triton's trailing face. In fact, those speeds are certainly impossible for material with that sort of origin. An event like that would essentially only crater the leading face.
Go to the top of the page
 
+Quote Post
tasp
post Aug 22 2007, 02:06 AM
Post #6


Member
***

Group: Members
Posts: 885
Joined: 30-January 05
Member No.: 162



Would that curious 'finger' imaged projecting poleward into the cantelope terrain possibly be a nascent 'tiger stripe' ??

Is it greatly difficult to do a Monte Carlo type simulation of a large number of objects randomly encountering the Neptune vicinity and doing stats on the resulting crater distribution on Triton ??


{Triton's orbital velocity around Neptune is rather large, is it really that surprising the surface evidences a 'wake shielding' effect ??}

{if someone would like to post a link to a nice Voyager II Triton image, feel free . . . }
Go to the top of the page
 
+Quote Post
ElkGroveDan
post Aug 22 2007, 04:38 AM
Post #7


Senior Member
****

Group: Admin
Posts: 4660
Joined: 15-March 05
From: Sloughhouse, CA
Member No.: 197



----
Attached thumbnail(s)
Attached Image
 


--------------------
If Occam had heard my theory, things would be very different now.
Go to the top of the page
 
+Quote Post
nprev
post Aug 24 2007, 12:40 PM
Post #8


Senior Member
****

Group: Moderator
Posts: 7097
Joined: 8-December 05
From: Los Angeles
Member No.: 602



QUOTE (tasp @ Aug 21 2007, 07:06 PM) *
Is it greatly difficult to do a Monte Carlo type simulation of a large number of objects randomly encountering the Neptune vicinity and doing stats on the resulting crater distribution on Triton ??


I wondered that too...but then again, I also wonder if we have a good understanding of meteoroid density in the outer Solar System. Accurately determining the age of Triton's surface plus considering both the 'driving north in the southbound lane' and gravitational focusing effects of Neptune on the impact rate might yield some very valuable insight with respect to the distribution of debris out there.


--------------------
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
Juramike
post Aug 27 2007, 09:20 PM
Post #9


Senior Member
****

Group: Moderator
Posts: 2716
Joined: 10-November 06
From: Pasadena, CA
Member No.: 1345



QUOTE (tasp @ Aug 21 2007, 10:06 PM) *
Would that curious 'finger' imaged projecting poleward into the cantelope terrain possibly be a nascent 'tiger stripe' ??



The finger might be a cycloid (which could also be the origin of the "tiger stripes" on Enceladus).

Check out the most poleward ridge in ElkGroveDan's posted image. It definitely has the "cycloid look". The finger may actually be a tailcrack off the cycloid.

Here is an article on proposed ridge formation on Triton:
Procktor, L.M; Nimmo, F., Pappalardo, R.T. LPS 36 (2005) Abstract 1722. "A Shear Heating Theory for Ridges on Triton."
(free abstract. but this link is for the whole shebang of abstracts, it may take a while to download: ftp://www.lpi.usra.edu/pub/outgoing/lpsc2005/full96.pdf

In the abstract the authors state:

"Since diurnal stressing was important when Triton began to circularize its orbit (not too long after capture) and the surface is young, capture must be relatively recent IF diurnal stresses are an important mechanism for ridge formation."

Recent stress cracking, recent resurfacing, and recent cratering all seem to add up to a recent capture.

-Mike


--------------------
Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
Go to the top of the page
 
+Quote Post
TritonAntares
post Aug 30 2007, 10:03 AM
Post #10


Member
***

Group: Members
Posts: 267
Joined: 28-September 05
From: Orion arm
Member No.: 516



QUOTE (Juramike @ Aug 27 2007, 11:20 PM) *
...
Here is an article on proposed ridge formation on Triton:
Procktor, L.M; Nimmo, F., Pappalardo, R.T. LPS 36 (2005) Abstract 1722. "A Shear Heating Theory for Ridges on Triton."
(free abstract. but this link is for the whole shebang of abstracts, it may take a while to download: ftp://www.lpi.usra.edu/pub/outgoing/lpsc2005/full96.pdf)
...

Mike, your link doesn't work unfortunately...
Attached Image


As far as I know there was some speculation of sublimated N2 migrating from the sunlighted into the dark hemisphere and freezing there again.
Hence Triton's surface should be refreshed in a short time.
As Triton has a 158 retrograde orbit and Neptune's axis tilt is about 23, the illumation conditions there are quite chaotic.
I remember this french article dealing with the question of latitude changes of Triton's subsolar point over historical time showing some tables:
http://bugle.imcce.fr/fr/observateur/support/Triton/
There seems to be some disagreement on the calculation of those variations... huh.gif ?
Anyhow, Triton's seasons don't look that simply predictable as Earth's... blink.gif

Combinating both aspects should cause a very differentiated and complex terrain structure.
Sadly we know only 30-40% of Triton in detail... sad.gif

Hopefully Neptune and Triton will be the next target for a major orbiter project in not so far away future...

Bye.
Go to the top of the page
 
+Quote Post
ugordan
post Aug 30 2007, 10:06 AM
Post #11


Senior Member
****

Group: Members
Posts: 3570
Joined: 1-October 05
From: Croatia
Member No.: 523



QUOTE (TritonAntares @ Aug 30 2007, 11:03 AM) *
Mike, your link doesn't work unfortunately...
Remove the closing bracket ")" from the URL and it should work.


--------------------
Go to the top of the page
 
+Quote Post
DrShank
post Sep 13 2007, 04:43 AM
Post #12


Member
***

Group: Members
Posts: 161
Joined: 6-March 07
From: texas
Member No.: 1828



pele is correct, these craters are relatively recent, and so is the event that produced the impacting bodies.
the surface is extremely young, given that there are essentially no impacts on the trailing side. hence we see no record at all of Tritons earlier geologic epochs.
paul


--------------------
Go to the top of the page
 
+Quote Post

Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 31st October 2014 - 05:11 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 a project of the Planetary Society and is funded by donations from visitors and members. Help keep this forum up and running by contributing here.