Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

A "Dragon" on the Surface of Titan

15.04.2004


Titan surface map at wavelength 1.575 micron (ESO VLT + NACO/SDI)


Four SDI-NACO Images


VLT looks through narrow atmospheric window and produces most detailed images yet New images of unsurpassed clarity have been obtained with the ESO Very Large Telescope (VLT) of formations on the surface of Titan, the largest moon in the Saturnian system. They were made by an international research team [1] during recent commissioning observations with the "Simultaneous Differential Imager (SDI)", a novel optical device, just installed at the NACO Adaptive Optics instrument [2].

With the high-contrast SDI camera, it is possible to obtain extremely sharp images in three colours simultaneously. Although mainly conceived for exoplanet imaging, this device is also very useful for observations of objects with thick atmospheres in the solar system like Titan. Peering at the same time through a narrow, unobscured near-infrared spectral window in the dense methane atmosphere and an adjacent non-transparent waveband, images were obtained that are virtually uncontaminated by atmospheric components. They map the reflectivity of a large number of surface features in unprecedented detail.

The images show a number of surface regions with very different reflectivity. Of particular interest are several large "dark" areas of uniformly low reflectivity. One possible interpretation is that they represent huge surface reservoirs of liquid hydrocarbonates.



Whatever the case, these new observations will be most useful for the planning of the delivery of the Huygens probe - now approaching the Saturn system on the NASA/ESA Cassini spacecraft and scheduled for descent to Titan’s surface in early 2005.

Views of Titan - the quest for the surface

Titan, the largest Saturnian moon and the second largest moon of the solar system (only Jupiter’s Ganymede is slightly larger), is the only satellite known with a substantial atmosphere. It is composed mainly of nitrogen (like that of the Earth) and also contains significant amounts of methane. Opaque orange hazes and clouds of complex organic molecules effectively shield the solid surface from view, cf. e.g. the Voyager images.

Recent spectroscopic and radar observations suggest that there are huge surface reservoirs of liquid hydrocarbonates and a methane-based meteorological cycle similar to Earth’s hydrological cycle. This makes Titan the only known object with rainfall and potential surface oceans other than the Earth and thus a tantalizing research object for the
study of pre-biotic chemistry and the origin of life on Earth.

The Huygens probe from the NASA/ESA Cassini-Huygens mission will enter Titan’s atmosphere in early 2005 to make measurements of the physical and chemical conditions, hopefully surviving the descent to document the surface as well.

Coordinated ground-based observations will provide essential support for the scientific return of the Cassini-Huygens encounter. However, only 8-10 m class telescopes with adaptive optics imaging systems or space-borne instruments can achieve sufficient image sharpness to attain a useful level of detail.

The new map of a large part of Titan’s surface, shown in PR Photo 11a/04, represents an important contribution in this direction.

A question of atmospheric windows

The first intriguing views of Titan’s surface were obtained by the Hubble Space Telescope (HST) in the 1990’s. From the ground, images were obtained in 2001-2 with the Keck II and Gemini North telescopes and more recently with the ESO Very Large Telescope (VLT), cf. ESO PR Photos 08a-c/04. All of these observations were made through a single narrow-band filter at a time.

The wavelengths used for such observations are critical for the amount of surface detail captured on the images. Optimally, one would look for a spectral band in which the atmosphere is completely transparent; a number of such "windows" are known to exist. But although the above observations were made in wavebands roughly matching atmospheric windows and do show surface features, they also include the light from different atmospheric layers. In a sense, they therefore correspond to viewing Titan’s surface through a somewhat opaque screen or, more poetically, the sight by an ancient sailor, catching for the first time a glimpse of an unknown continent through the coastal haze.

One narrow "window" is available in the near-infrared spectral region near wavelength 1.575 micron. In February 2004, an international research team [1] working at the ESO VLT at the Paranal Observatory (Chile) obtained images of Titan’s surface through this spectral window with unprecedented spatial resolution and with the lowest contamination of atmospheric condensates to date.

They accomplished this during six nights (February 2, 3, 5, 6, 7 and 8, 2004) at the time of the commissioning phase of a novel high-contrast imaging mode for the NACO adaptive optics instrument on the 8.2-m VLT YEPUN telescope, using the Simultaneous Differential Imager (SDI) [2]. This novel optical device provides four simultaneous high-resolution images (PR Photo 11b/04) at three wavelengths around a near-infrared atmospheric methane absorption feature.

The main application of the SDI is high-contrast imaging for the search for substellar companions with methane in their atmosphere, e.g. brown dwarfs and giant exoplanets, near other stars. However, as the present photos demonstrate, it is also superbly suited for Titan imaging.

Mapping Titan’s surface in unprecedented detail

Titan is tidally-locked to Saturn, and hence always presents the same face towards the planet. To image all sides of Titan (from the Earth) therefore requires observations during almost one entire orbital period, 16 days. Still, the present week-long observing campaign
enabled the team to map approximately three-quarters of the surface of Titan.

A new map of the surface of Titan (in cylindrical projection and covering most, but not all of the area imaged during these observations) is shown in PR Photo 11a/04. For this, the simultaneous "atmospheric" images (at waveband 1.625 micron) were "subtracted" from the "surface" images (1.575 and 1.600 micron) in order to remove any residual atmospheric features present in the latter. The ability to subtract simultaneous images is unique to the SDI camera [2].

This truly unique map shows the fraction of sunlight reflected from the surface - bright areas reflect more light than the darker ones. The amount of reflection (in astronomical terms: the "albedo") depends on the composition and structure of the surface layer and it
is not possible with this single-wavelength ("monochromatic") map alone to elucidate the true nature of those features.

Nevertheless, recent radar observations with the Arecibo antenna have provided evidence for liquid surfaces on Titan, and the low-reflection areas (dark on PR Photos 11a/04 and 11f/04) could indicate the locations of those suspected reservoirs of liquid hydrocarbonates. They also provide a possible source for the replenishment of methane that is continuously lost in the atmosphere because of decomposition by the sunlight.

Presumably, the bright, highly reflective regions are ice-covered highlands.

Provisional names of the new features

A comparison (PR Photo 11e/04) with an earlier NACO image (available as PR Photo 08c/04) obtained through another filter is useful. It demonstrates the importance of employing a filter that precisely fits the atmospheric window and hence the gain of clarity with the present observations. It also provides independent confirmation of the reality
of the gross features, since the observations are separated by 15 months in time.

Over the range of longitudes which have been mapped during the present observations (PR Photo 11a/04), it is obvious that the southern hemisphere of Titan is dominated by a single bright region centered at approximately 15 deg longitude. (Note that this is not the so-called "bright feature" seen in the HST images at longitude 80 - 130 deg, an area that was not covered during the present observations).

The equatorial area displays the above mentioned, well-defined dark (low-reflection) structures, cf. PR Photo 11g/04. In order to facilitate their identification, the team decided to give these dark features provisional names - official names will be assigned at a later moment by the Working Group on Planetary System Nomenclature of the International Astronomical Union (IAU WGPSN). From left to right, the SDI team [1] has referred to these features informally as: the "lying H", the "dog" chasing a "ball", and the "dragon’s head".

More observations to come

The team expects to continue imaging and monitoring of Titan in the coming months, with the goal of assisting the Cassini-Huygens team in the interpretation and understanding of what will certainly be a rich and complex flow of information about this enigmatic moon.

Contacts:

Markus Hartung
ESO Santiago, Chile
Tel: +56 2 463 3071
mhartung@eso.org

Laird Close
University of Arizona, USA
Tel: +1 520 626 5992
lclose@as.arizona.edu

Rainer Lenzen
Max-Planck Institut fuer Astronomie
Heidelberg Germany
Tel: +49 6221 528 228
lenzen@mpia.de

Richard West | alfa
Further information:
http://www.eso.org/outreach/press-rel/pr-2004/pr-09-04.html

More articles from Physics and Astronomy:

nachricht Breakthrough with a chain of gold atoms
17.02.2017 | Universität Konstanz

nachricht New functional principle to generate the „third harmonic“
16.02.2017 | Laser Zentrum Hannover e.V.

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Biocompatible 3-D tracking system has potential to improve robot-assisted surgery

17.02.2017 | Medical Engineering

Real-time MRI analysis powered by supercomputers

17.02.2017 | Medical Engineering

Antibiotic effective against drug-resistant bacteria in pediatric skin infections

17.02.2017 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>