Biomedical subjects

C de Bergh

Publications and source records attributed to C de Bergh.

7 recordsLinked to original sources

PubMed2005

Rain, winds and haze during the Huygens probe's descent to Titan's surface.

The irreversible conversion of methane into higher hydrocarbons in Titan's stratosphere implies a surface or subsurface methane reservoir. Recent measurements from the cameras aboard the Cassini orbiter fail to see a global reservoir, but the methane and smog in Titan's atmosphere impedes the search for hydrocarbons on the surface. Here we report spectra and high-resolution images obtained by the Huygens Probe Descent Imager/Spectral Radiometer instrument in Titan's atmosphere. Although these images do not show liquid hydrocarbon pools on the surface, they do reveal the traces of once flowing liquid. Surprisingly like Earth, the brighter highland regions show complex systems draining into flat, dark lowlands. Images taken after landing are of a dry riverbed. The infrared reflectance spectrum measured for the surface is unlike any other in the Solar System; there is a red slope in the optical range that is consistent with an organic material such as tholins, and absorption from water ice is seen. However, a blue slope in the near-infrared suggests another, unknown constituent. The number density of haze particles increases by a factor of just a few from an altitude of 150 km to the surface, with no clear space below the tropopause. The methane relative humidity near the surface is 50 per cent.

Atmosphere↗

PubMed1995

Dark matter in the outer solar system.

There are now a large number of small bodies in the outer solar system that are known to be covered with dark material. Attempts to identify that material have been thwarted by the absence of discrete absorption features in the reflection spectra of these planetesimals. An absorption at 2.2 micrometers that appeared to be present in several objects has not been confirmed by new observations. Three absorptions in the spectrum of the unusually red planetesimal 5145 Pholus are well-established, but their identity remains a mystery.

Astronomy↗

PubMed1995

Isotopic ratios in planetary atmospheres.

Recent progress on measurements of isotopic ratios in planetary or satellite atmospheres include measurements of the D/H ratio in the methane of Uranus, Neptune and Titan and in the water of Mars and Venus. Implications of these measurements on our understanding of the formation and evolution of the planets and satellite are discussed. Our current knowledge of the carbon, nitrogen and oxygen isotopic ratios in the atmospheres of these planets, as well as on Jupiter and Saturn, is also reviewed. We finally show what progress can be expected in the very near future due to some new ground-based instrumentation particularly well suited to such studies, and to forthcoming space missions.

Atmosphere↗

PubMed1993

The D/H ratio and the evolution of water in the terrestrial planets.

The presence of liquid water at the surface of the Earth has played a major role in the biological evolution of the Earth. None of the other terrestrial planets--Mercury, Venus and Mars--has liquid water at its surface. However, it has been suggested, since the early seventies, from both geological and atmospheric arguments that, although Venus and Mars are presently devoid of liquid water, their surfaces could have been partially or completely covered by water at some time of their evolution. There are many possible diagnostics of the long-term evolution of the planets, either from the present characteristics of their surfaces or from their present atmospheric compositions. Among them, the present value of the D/H ratio is of particular interest, although its significance in terms of long term evolution has been challenged by some authors. Recent progress has been made in this field. We now have evidence for higher D/H ratios on Mars and Venus than on Earth, with an enrichment factor of the order of 5 on Mars, and about 100 on Venus. Any scenario for the evolution of these planets must take this into The most recent models on the evolution of Mars and Venus are reviewed in light of these new measurements.

Atmosphere↗

PubMed1991

Deuterium on Venus: observations from Earth.

Absorption lines of HDO and H2O have been detected in a 0.23-wave number resolution spectrum of the dark side of Venus in the interval 2.34 to 2.43 micrometers, where the atmosphere is sounded in the altitude range from 32 to 42 kilometers (8 to 3 bars). The resulting value of the deuterium-to-hydrogen ratio (D/H) is 120 +/- 40 times the telluric ratio, providing unequivocal confirmation of in situ Pioneer Venus mass spectrometer measurements that were in apparent conflict with an upper limit set from International Ultraviolet Explorer spectra. The 100-fold enrichment of the D/H ratio on Venus compared to Earth is thus a fundamental constraint on models for its atmospheric evolution.

Atmosphere↗

PubMed1990

Monodeuterated methane in the outer solar system. IV. Its detection and abundance on Neptune.

We have detected the 3 nu 2 band of CH3D in the spectrum of Neptune near 1.6 micrometers recorded at a spectral resolution of 4 cm-1 with the Cassegrain Fourier Transform Spectrometer at the 3.6 m Canada-France-Hawaii Telescope (CFHT) on Mauna Kea. Our analysis of this spectrum, using spectral synthesis techniques, yielded a CH3D/CH4 ratio of 6(+6)(-4) x 10(-4), which corresponds to a global D/H ratio for Neptune of 1.2(+1.2)(-0.8) x 10(-4), if CH3D is in isotopic fractionation equilibrium with HD. This value is about an order of magnitude larger than an earlier estimate by Orton et al. based on deconvolution measurements of unresolved molecular emission in the 8-10 micrometers region. Comparison of this new determination with previous studies of CH3D in the outer solar system shows that, as in the case of Uranus, the D/H on Neptune is strongly enhanced over that found on Jupiter and Saturn and is comparable to the D/H in methane on Titan and in terrestrial methane and water.

Astronomical Phenomena↗

PubMed1986

Deuterium in the outer Solar System: evidence for two distinct reservoirs.

We have just completed a series of determinations of the CH3D/CH4 ratio in the atmospheres of Saturn, Titan and Uranus. These results, coupled with the work of other investigators, suggest that the Solar System contains at least two distinctly different primordial reservoirs of deuterium: that contained in gaseous hydrogen and that contained in the volatiles which have been maintained at low temperatures or isolated from hydrogen; for example, trapped in cold, solid material. Both of these reservoirs were established before the formation of the Solar System.

Atmosphere↗