Friday, April 15, 2005

Planetary Society: T5 Plans; Tethy Tweak

The Planetary Society has an article on its website on tomorrow's Titan flyby. This article also has information on the recently approved Tethys targeted flyby in September. Not much new WRT tomorrow's flyby. They are still repeating the idea that VIMS can get better resolution than ISS at their highest resolution. Mark my words, we will get better than VIMS resolution on the T5 flyby.
The second part describes the Tethys tweak. This is the adjustment of the tour whereby a non-targeted Tethys encounter in September at 33,000 km has now become a targeted flyby at 1500 km. However, the article quotes the flyby distance as 1000 km. Not sure which is correct...

Cassini Significant Events for 04/07/05 - 04/13/05

JPL has published online their status report for the last week. Among the highlights include:
  • the start of mission sequence S10 that includes Revs 06 and 07 last Friday
  • INMS "unexpected boot" anomaly declared solved last Saturday

Mimas Raw Images for Rev06

Raw Images from today's Mimas non-targeted encounter are starting to appear on the JPL Raw images. I'll post more here as they show up.

UPDATE 04/16/2005 10:22am: Added a couple of new images.

Rev06 Icy Satellite Targets

In addition to the flyby of Titan on Saturday, today's periapsis offers a few non-targeted icy satellite opportunities as well. First up is Rhea. Images of Rhea on this pass are already on the JPL Raw images page.

This 1.5 km/pixel image shows the ray crater, first hinted at by Voyager, but now best seen by Cassini. This image shows the ray's of the ray crater in much more detail than in images take last month, that although they were higher resolution than this image, showed the crater much closer to the terminator where topographic shading trumps albedo markings. Now the crater is a bit farther than the terminator, giving scientists a better look at the rays, perhaps allowing for the idenitification of secondaries from this crater (though this maybe limited given the available resolution). This image is also farther south than last month's observations, providing a closer look at Rhea's southern hemisphere. More Rhea images should be forthcoming.

The next target for Cassini on this orbit is Mimas. The closest approach to Mimas was last night, providing Cassini's best look at this satellite to date. The previous opportunity in January gave us a great look at Herschel on the terminator, a possible ray crater on Mimas, and a more head-on view of Herschel and a canyon system to its east. The highest resolution of these images from Rev 0C had a pixel scale of 970 meter/pixel while at closest approach, the best Mimas images from this encounter could have resolutions in the 500 meter/pixel range given a range of 84,000 km.

New Enceladus Image: Sideways Shadow

CICLOPS has released this processed view of Enceladus "hanging over the rings of Saturn. Some slight albedo variations are visible across the visible disk of Enceladus but at this resolution it is difficult to make out much structure (though this could be because we are looking at a fairly bland area). This image was taken in early March. The distance to Enceladus is 1.1 million km yielding a resolution of 6 km/pixel.

Wednesday, April 13, 2005

T5 Coverage Plot

CICLOPS has released a coverage plot showing the regions that will be imaged by ISS during tomorrow's flyby of Titan. This is the same region that was covered during the last Titan flyby only 16 days earlier. The main attraction of this flyby is that we will get higher resolution images over many of the areas imaged during the last encounter. These images will include a number of the bright-dark boundaries bordering the "H" feature. This should help to further constrain the nature of the albedo boundaries and will give VIMS great coverage over this region.

See the T5 post below for more information on this encounter.

Raw Images of the Day

New Dione Image: Saturn-lit Surface

CICLOPS has released this processed view of Dione taken in February. This shows on a crescent view of Dione's wispy terrain. However, on the night side, light reflected from Saturn's atmosphere is enough to illuminate the terrain, revealing the western portion of the wispy terrain (like Carthage Linea and Palatine Linea). This image has a resolution 8 km/pixel and was taken from a distance of 1.3 million kilometers.

Tuesday, April 12, 2005

Titan-5 Flyby Info

View of Titan from Cassini 30 minutes into ISS' high resolution observation (sub-spacecraft point=7.16N, 26.75W). The plot was generated in GISS' Titan 24 software. The map is derived from ISS map released last month (ask for full version used here, just adds blank space north of 34N). The full version of above plot is available. The data for plot was obtained from Mission description document.

JPL has released the mission description for this week's 1025-km altitude, Titan flyby over the sub-Saturnian hemisphere. The usual goodies are include like instrument goals for the flyby, timeline of events, and the playback table to you (and I) can have a reasonable idea of when the data will be played back. Like T4, most of the data is played back at a reasonable hour, the early to mid morning period on Sunday. Some earlier encounters had data coming back in the late evening.

T5 is largely a magnetospheric flyby with "MAPS" instruments like MAG, MIMI, RPWS, and CAPS taken up much of the observing time after closest approach.

A few facts about this encounter:
  • Occurs on April 16 at 1:28 pm PDT
  • Closest Approach Distance = 1025 km (bumped up from 950 km)
  • Relative speed WRT Titan = 6.1 km/sec
  • Closest Approach Lat and lon = 74N, 272.5W
  • First near-polar pass (74N at C/A)
  • Outbound flyby (sunlit inbound)
  • Phase angle at -3hours = 57 deg.
Here are some highlights in the flyby goals:
  • ISS will once again look at the sub-Saturnian hemisphere. Unlike the last flyby where ISS imaged much of the visible hemisphere at global-scale (~1.5 km/pixel) resolution, on this encounter, ISS will get 12, higher resolution (725-250 m/pixel) snap-shots across the disk, including some along the T03 SAR swath). This is to designed to understand features seen upclose on the last encounter as well as to give VIMS optimum spatial coverage.
  • This is the most important Titan flyby for MAG and is also very important for CAPS. The flyby geometry (both in terms of its low altitude and approach geometry) is close to optimum for electromagnetic studies of Titan's interior via induction effects. Both CAPS and MAG will examine Titan's Alfven currents that couple Titan to Saturn's magnetosphere. This will allow better understanding of the origin of Alfven wings and slow mode wings. MAG will use the low altitude to search for an internal magnetic field with a dipole near the rotation axis. CAPS will be prime for 16 hours after closest approach to observe signatures of Titan's interaction with Saturn's magnetosphere.
  • INMS (Ion and Neutral Mass Spectrometer) will use its open source channel at closest approach to measure minor ion and neutral densities and to help calibrate data taken during the Titan flyby last October.
  • CIRS (Composite Infrared Spectrometer) will search for new species at high northern latitudes (~55 deg) and will map CH4, CO, and HCN, etc. distribution by examining lon-wavelength rotational lines.
  • VIMS will map parts of the northern sub-Saturnian hemisphere as well as map the sub-Saturnian hemisphere during the ride-along with ISS mentioned earlier.
  • UVIS will map Titan's atomic emissions, acetylene distribution (a chemical that has taken on new prominence), and haze properties.
  • RPWS (Radio and Plasma Wave Science instrument) will measure large-scale and distant aspects of Titan s interaction with Saturn s magnetosphere by observing during entire period around closest approach and from 10 to 25 Saturn radii.
Images start being played back at 6:56 am on Sunday morning. Playback continues (for imaging) until 11:30 am. How does this translate into being placed on the JPL Raw images page? On T4, images didn't show up until almost a day after images had been returned to earth, to the disappointment of the public and to the consternation of the imaging team who couldn't even release slightly processed images until after JPL had the images up on their raw images page. Hopefully, there won't be the same delay on this flyby but I can't make any guarantees. Depending on how JPL has the system setup, given that it is a Sunday when these images come down, it could be Monday before the images start showing up.

Huygens Flat-fielded MRI images

Rene Pascal has posted online a zip file contain all non-duplicated medium resolution imager frames from DISR taken during Huygens descent in January. Each image has been flat-field, a image-processing procedure where camera and/or CCD defects are removed from an image by ratioing the image with an image that contains just the defects. Rene created that file by summing several bland MRI images together to produce an average bland file. This bland file thus contains only the defects and no contrast due to surface features. This procedure produces far cleaner and scientifically useful images than the raw images that were released.

New Tethys Image: Eye of Tethys

CICLOPS has released this low resolution view of Tethys showing the large impact basin Odysseus along the terminator. A things to note include the ridge circling the crater some 30 degrees away as well as a dark band that can be seen crossing the moon from southwest to northeast. The original image had a resolution of 10 km/pixel (now magnified 2x) and was taken in early March.

Monday, April 11, 2005

VIMS images of Titan

Finally found some online images taken by VIMS of Titan. This comes from the public relations page for the Lunar and Planetary Laboratory (where I work). On their "What's New" page, they have a graphic showing various images taken by VIMS. Most of these have been released, like the global view, the Huygens landing site image (on the lower left, not lower right as the caption claims), haze view from T0 at lower middle, and the VIMS snail (the lower right framelet of the four Ta HIRES images in the upper right). Those not released so far elsewhere include the views of the snail in different filters and the "rabbit" feature, imaged during the Tb encounter and shown in the lower right (the left image is the raw view at 2 microns, the right view has been geometrically corrected).

Raw Images of the Day

BBC News: Titan probe's pebble 'bash-down'

The BBC News website has an article up regarding a conference talk given by the Huygens SSP Principal Investigator John Zarnecki at the UK National Astronomy Meeting. He reported that based on test drops run at Open University in Milton Keynes, the probe likely landed on one of the fist-sized pebbles strewn across the Titanian landscape before slipping into the icy sand. Shortly after the probe landing, the SSP investigators reported that the penetrometers results were consistent with a surface that consisted mostly of sand-sized particles covered by a thin crust. This led to the early analogy developed by Ralph Lorenz of the SSP team (and the principal developer of the penetrometer component) of creme brule. While the hard crust-sandy middle model has not been ruled out, from the article:
"A crust is still a possibility, but we now think it's most likely we hit one of those water-ice pebbles you see in the ground image; the biggest you see is about 15cm," Professor Zarnecki told the BBC News website.

"We probably pushed the pebble to one side and then ploughed into the stuff underneath which we are pretty convinced is a 'sand' made of ice," the principal investigator on the Huygens surface science package explained.

The article also reported that the penetrometer results were consistent with a matrix of sand- to gravel-sized particles up to 8 mm in size.

Thanks to paxdan over at the Unmanned Spaceflight forum for the link.