25 August 2009

Flyover on Triton - Voyager +20 Years

Twenty years is a long time, but that is how long its been since Voyager 2 completed its primary mission during a close pass of the planet Neptune. The planet's largest Moon would steal much of the thunder. I myself was a relatively new post-doctoral researcher working at Jet Propulsion Lab, where I had been an intern 10 years earlier during the Voyager 2 Jupiter encounter. I was not part of the Project at that time, but a friend escorted me and another friend into the imaging control center to watch as the Triton images came in. We weren't really supposed to be there I guess and no doubt we ruffled a few feathers but I doubt many would truly begrudge us the experience.

In those days lab workers could watch the mission unfold as each new image of Neptune and its storm clouds flashed on our monitors. Each day it grew larger and more detailed. Triton was the real mystery as even a week before the big August 25th encounter, the actual size of this cold moon was still unknown! The first high resolution images of Triton flashed on the screens and everyone could see that the surface was geologically complex and very young. There were very few craters on the surface (its age is still uncertain but is likely even younger than that of ocean-covered Europa and most of Enceladus). Long ridges, volcanic craters and an odd terrain that looked remarkably like the skin of a cantaloupe marked the surface.

To this day, Triton's surface looks alien and unlike any we have seen elsewhere. Much of this is related to the ice-rich composition, with water, methane, nitrogen, CO, CO2, and other ices in abundance. Triton is likely a captured Kuiper Belt object and residual heat from that event has keep it very warm inside. There may evn be an ocean beneath its surface. Triton bears some remarkable similarities to Pluto but we will have to wait until summer 2015 to find out iif the two bodies look even remotely similar. Nonetheless, there are still things to be learned about Triton from 20 year old data. One of those is the topography of the surface. I have put together a new topographic map of the surface and used it to make a flyover movie simulating the navigations of a vehicle a few thousand kilometers above the surface. A word of warning, the surface of Triton does not have mountains higher than a mile so you will not see towering volcanoes like on Mars or deep basins like on the Moon. What you can see is a complex landscape scarred by small ridges, mounds and pits, many of which are volcanic in origin. There are even a few small impact craters, as well as walled volcanic plains. [By the way, Wikipedia is not entirely correct. The diapir hypothesis for cantaloupe terrain originated with Schenk and Jackson, in Geology, 21, 299, 1993!]

The video begins near the western edge of Neptune-facing hemisphere with an approach over cantaloupe terrain and two large smooth walled plains. The video tracks due east for roughly 1500 kilometers over a large province of volcanic pits, calderas and smooth plains. The video was produced from using a new topographic map of Triton, combined with a 1.65-kilometer resolution image mosaic. Topographic mapping was based on shape-from-shading analysis of the original Voyager images. Data such as these are being used to help plan New Horizons encounter with Triton's estranged twin Pluto in 2015.

Vertical relief has been exaggerated by a factor of ~25 to aid interpretation. It has been formatted to be iPod and iPhone compatible, and can also be downloaded at www.unmannedspaceflight.com and the NASA Photojournal. Additional still images from the movie can be found in the second post to this blog and on the NASA Photojournal.


All Images Credit: NASA/JPL and Paul Schenk, Lunar and Planetary Institute.
Use is not restricted, but a request for use (or for a quality digital copy) should be forwarded to the author. Proper credit is always appreciated!

23 August 2009

More Ariel

While I prepare the new Triton Movie for release on August 25 (the 20th anniversary of the Voyager flyby of Triton and Neptune), I will show some more of the images and data from Ariel (original data acquired January 1986). Included are a movie and the digital topography. Perspective views can be found in the original post a few days ago.

Ariel: The Movie

The Image data have a resolution of 1 kilometer. The topographic base map has a variable resolution but can resolve features taller than about 250 meters (I think). The topography is based on both stereo image analysis (stereogrammetry) and shape-from-shading (photoclinometry, PC). Stereo data were produced across most of the mapping area while PC is only available for the portion near the terminator (shadow) line. The two maps have been merged here to produce the topographic map we now see (the original data have been JPEG compressed for display.)

Image mosaic of southern hemisphere of Ariel (top). Topographic map of same region (bottom).

There are a variety of interesting features to see on Ariel. Most obvious are the 50 to 140 kilometer wide troughs along the terminator. The floors of these downdropped blocks are 3 to 5 kilometers deep and have been resurfaced by water or ammonia lavas long since frozen over. Note also the narrow ridges and troughs to the top, and the two large craters near center, which are 65 to 85 kilometers across. One of these craters is deep, the other shallow (due to relaxation or volcanic filling).

Ariel is interesting because it is even more geologically deformed and resurfaced than Miranda, which gets all the good press. Almost no ancient surface remains on Ariel, although Voyager only saw ~40% of the surface in 1986. The heat source responsible for making Ariel so volcanically active (it is likely quiet today) is unknown but is probably related to gravitational tides.

A New Global map of Ariel

This is my best current map of Ariel showing the global mapping coverage acquired by Voyager. Note that all the good stuff is south of the equator (the horizontal line in this cylindrical projection). The fuzzy area north of the equator was actually captured in Uranus-shine, and although poor in quality allows us to see another bright craters and the continuation of severa troughs. (I thank Ted Stryk for discovering that these dark-Ariel data exist.)

All Images Credit: Paul Schenk, Lunar and Planetary Institute.
Use is not restricted, but a request for use (or for a quality digital copy) should be forwarded to the author. Proper credit is always appreciated!

21 August 2009

Surface of Triton

Perspective Views of Triton

The views shown here are derived from topographic mapping of Voyager images obtained August 1989, 20 years ago this week! Triton was the last solid object visited by the Voyager spacecraft on their epic 10 year tour of the Outer Solar System. The surface of Triton is very rugged, scarred by diapirs, faults and volcanic eruptions and flows composed of melted ices. The surface is also extremely young and sparsely cratered. It may even be younger than the surface of Europa, one of the first objects visited by Voyager 30 years ago this summer. These views show volcanic pit chains and terrains. The middle view shows two large walled plains 150 to 200 kilometers across. Each view is on the order of 500 km across. A new version of the flyover movie posted on my Facebook site will be released later this week to commemorate the Voyager anniversary.

All Images Credit: Paul Schenk, Lunar and Planetary Institute.

Use is not restricted, but a request for use (or for a quality digital copy) should be forwarded to the author. Proper credit is always appreciated!

Stereo Moons

Stereo images, and especially those of planetary surfaces, are a big part of what I do. I've been searching for a suitable place to host these images and some of the products I've been making from them. So if you like, please leave some feedback so that I post more! I will explain more about these in the coming days and weeks, right now I just want to begin uploading some of the dozens of images and Videos I have been generating the past 20 years or so . . .


Perspective Views of Ariel
Data derived from stereo topographic mapping of Voyager images. (Thanks to Ted Stryk for 2 desmeared images)
Credit: Paul Schenk, Lunar and Planetary Institute

All images credit: NASA/JPL and Paul Schenk/Lunar and Planetary Institute, Houston
All data files credit:  Paul Schenk/Lunar and Planetary Institute, Houston