Friday, April 29, 2005

Celestia Titan Map

The Planetary Society website has a map of Titan produced by Celestia software developer Fridger Schrempp that combines the global view from T4 with the map released last month. The resolution of map has been degraded from the original to compensate for margins between individual images.

Cassini Significant Events for 04/21/05 - 04/27/05

The Significant Events report for the last week is now up on the JPL website. Nothing major. The Enceladus-2 flyby in July was shifted down to an altitude of 175 kilometers, as reported here earlier. In addition, the report mentions a Mimas non-targeted encounter at 62,700 kilometers. If this is on the same orbit, this would be a reduction in encounter distance (not sure where it stood before the tweak). If they are refering to the encounter on August 2, then this is an increase in altitude, from the 48,968 kilometers reported earlier.

New Dione Image: Daybreak on Dione

CICLOPS has released this view of Dione, taken on March 12. This view shows the wispy terrain of Dione near the terminator. Several crater are also evident along the terminator, the boundary between day and night. This image has a resolution on Dione of 10 km/pixel though the image has been magnified by 2x to aid the visibility of features.

New Rhea Image: Rhea’s Relief

CICLOPS has released this view of Saturn's moon Rhea, taken last month. This half-phase view of this satellite emphasizes the relief of the many large impact craters that litter the moon's surface. This image has a resolution of 9 km/pixel and shows primarily the leading hemisphere of this satellite.

Wednesday, April 27, 2005

My New Blog

I now have a new blog cover my life and news other than space science. It is called The Ionian Journal. I will not hold back when discussing politics, though right now I don't have anything to really say politically right now. So if you want to hear more from me, or you are my parents and would like to have more evidence of my continuing existence. So if you are interested, feel free to check it out. Same basic format as this blog, so if you wish to comment, feel free. This also means that I will not post any off-topic posts here simply because I have another forum to express my other thoughts on. So if you don't feel like hearing me rant, you won't have to :-D

New VIMS Titan Image: Titan Crater in Three Views

I am in complete shock. The VIMS team ACTUALLY released a Titan image. This must mean the end of the world is nigh. Given this news, I shall build a bomb shelter and pray... And they included so far unreleased RADAR data. How'd they spring that? I wish we could do that with our images....

Seriously, this is a pretty interesting release. This release shows the VIMS view of an 80-km wide crater first seen by RADAR and then by ISS during the T4 flyby on March 31. This view, taken by VIMS during the T5 flyby on April 16, confirms the ISS result that the crater is indeed filled with dark material, perhaps material thin enough for the RADAR beam to pass through. In addition, VIMS sees the bright spot at the center of the crater, again seen by ISS (though not this prominently).

One of the main puzzles the ISS team has encountered when comparing this feature in our images with how it is seen by RADAR (center panel in VIMS release, see RADAR release from February or the Stanford RADAR site for a full resolution, though poorer stretch view). The ejecta blanket surrounding the crater has a different shape in RADAR (which shows how smooth or how rough a terrain area is) and in ISS (which sees only brightness variations). In ISS, this blanket is much smaller and has a more rounded shape, while the RADAR bright island surrounding the crater has a more parabolic shape, consistent with the parabolic blankets surrounding some Venusian craters. The false color VIMS image resolves this. Like ISS, VIMS see only albedo (though they maybe able to see topographic 5 microns). But VIMS has multiple methane windows to work with, and might be able to detect compositional and/or grain size variations. In the color image, a brighter blue halo, curiously in the shape of the RADAR-bright (and thus rough) island. What this tells us is that the RADAR parabola is made of materials with different albedos. This outer portion, consisting of material nearer the surface at the time of the crater's formation, is likely made of organics with little water ice, while the inner region consists of material derived from deeper within Titan. This picture that this view creates is one where the impactor crashed in the "H" region, first digging up the organic layer and spewing that farther from the crater, then punching through to the water ice beneath, depositing it closer to the impact site. So to VIMS and ISS, we see two different zones of material thanks to the two different compositions, while RADAR sees only one, very rough unit. I'm not much of a crater, but maybe the depth of the dark material can be estimated by finding out how much of the material ejected was water ice and how much was dark organics.

Sounds of Enceladus

The Cassini Magnetometer team has released this plot showing ion cyclotron waves during the February 17 Cassini flyby of Enceladus. Actually, the caption for this release has very little to do with the plot and much more to do with the Quicktime audio file released with this image. The audio file, which I have yet to listen to, "shows the power of these waves near Enceladus". The caption says that these ion cyclotron waves in Saturn's magnetosphere provide information on the types of ions present in Cassini's environment. Based on other release, like the CDA release mentioned below, it appears these come from water ions.

New Epimetheus Image: Epimetheus: Up-Close and Colorful

CICLOPS has released this color view of Saturn's small inner moon Epimetheus, taken shortly before the T4 Titan flyby. This view was discussed here when it was posted on the JPL Raw images page. Thanks to Phil for the crater identifications.

This view shows the craters Hilairea and Pollux. Pollux in this view appears to be slightly reddish, while the rest of the moon appears slightly bluish. Normally, such color variations are the result of compositional and/or grain size variations. However, given the fact that a polarized filter was used for green,the phase angle (sun-Epimetheus-Cassini angle) at the time of the observation, and the location of the redder and bluer units, these color variations are likely the result of photmetric effects, where the color of an object can depend on the angle it is observed at. Io, which I worked quite a bit on with Galileo data, was notorious for having such color changes depending on phase angle (compare this low phase angle view from July 1999 to this view from March 1998 and then to this high phase angle view from June 1997).

This view was taken from a distance of 74,000 km and has a resolution of 450 meters/pixel, though the image has been magnified by two to aid visibility.

Tuesday, April 26, 2005

Press Release: Cassini Finds Particles Near Saturn's Moon Enceladus

According to a press release put out today, the High Rate Detector on the Cosmic Dust Analyzer detected a high rate of hits from particles, about the width of a human hair, during Cassini's two recent close passes of Enceladus, first on February 17 at an altitude of 1,167 km and again on March 9 at 500 km. Presently, the CDA team can't distinguish in their data the source of these particles, whether they come from the E-Ring, which is densest near Enceladus, or from Enceladus itself, which would be further evidence for an active Enceladus. During the same encounter, the MAG instrument found evidence for water ions near Enceladus, perhaps part of an atmosphere. Such an atmosphere would require constant refreshment to persist, due to Enceladus' low gravity.

One bit of news that I think is being publically released for the first time, though I could always be wrong, I am a bit tired... The Enceladus flyby on July 14 has been lowered to 175 kilometers, which should allow for further understanding of Enceladus' active nature.

Monday, April 25, 2005

Press Release: Organic Materials Spotted High Above Titan's Surface

JPL has a press release up on their site from the INMS team regarding the data returned from the instrument for April 16's T5 flyby. This data was covered on Friday.

From the Press Release:
Scientists believe that Titan's atmosphere may be a laboratory for studying the organic chemistry that preceded life and provided the building blocks for life on Earth. The role of the upper atmosphere in this organic "factory" of hydrocarbons is very intriguing to scientists, especially given the large number of different hydrocarbons detected by Cassini during the flyby.

Cassini's ion and neutral mass spectrometer detects charged and neutral particles in the atmosphere. It provides scientists with valuable information from which to infer the structure, dynamics and history of Titan's atmosphere. Complex mixtures of hydrocarbons and carbon- nitrogen compounds were seen throughout the range of masses measured by the Cassini ion and neutral mass spectrometer instrument. "We are beginning to appreciate the role of the upper atmosphere in the complex carbon cycle that occurs on Titan," said Dr. Hunter Waite, principal investigator of the Cassini ion and neutral mass spectrometer and professor at the University of Michigan, Ann Arbor. "Ultimately, this information from the Saturn system will help us determine the origins of organic matter within the entire solar system."

Hydrocarbons containing as many as seven carbon atoms were observed, as well as nitrogen- containing hydrocarbons (nitriles). Titan's atmosphere is composed primarily of nitrogen, followed by methane, the simplest hydrocarbon. The nitrogen and methane are expected to form complex hydrocarbons in a process induced by sunlight or energetic particles from Saturn's magnetosphere. However, it is surprising to find the plethora of complex hydrocarbon molecules in the upper reaches of the atmosphere. Titan is very cold, and complex hydrocarbons would be expected to condense and rain down to the surface.

"Biology on Earth is the primary source of organic production we are familiar with, but the key question is: what is the ultimate source of the organics in the solar system?" added Waite.

Interstellar clouds produce abundant quantities of organics, which are best viewed as the dust and grains incorporated in comets. This material may have been the source of early organic compounds on Earth from which life formed. Atmospheres of planets and their satellites in the outer solar system, while containing methane and molecular nitrogen, are largely devoid of oxygen. In this non-oxidizing environment under the action of ultraviolet light from the Sun or energetic particle radiation (from Saturn's magnetosphere in this case), these atmospheres can also produce large quantities of organics, and Titan is the prime example in our solar system. This same process is a possible pathway for formation of complex hydrocarbons on early Earth.
While, the discovery of complex hydrocarbons on Titan is no surprise, finding them so high up in Titan's ionosphere is puzzling. How such massive molecules reach such altitudes will surely be an important topic for this INMS team for some time to come.

New Dione Image: Far off Cracks

CICLOPS has released this processed view of Saturn's moon Dione. This image is a great view of the so-called "wispy" terrain, found in December to be the bright faces of fractures (though the floors of these graben/horst systems are still bright).
This view was taken last month using an ultraviolet filter centered at 338 nanometers. Surface contrast on many of Saturn's satellites is maximized at this wavelength and albedo features are clearly seen.