Theodor Kostiuk

Overview of the coordinated ground-based observations of Titan during the Huygens mission

Coordinated ground-based observations of Titan were performed around or during the Huygens atmospheric probe mission at Titan on 14 January 2005, connecting the momentary in situ observations by the probe with the synoptic coverage provided by continuing ground-based programs. These observations consisted of three different categories: (1) radio telescope tracking of the Huygens signal at 2040 MHz, (2) observations of the atmosphere and surface of Titan, and (3) attempts to observe radiation emitted during the Huygens Probe entry into Titans atmosphere. The Probe radio signal was successfully acquired by a network of terrestrial telescopes, recovering a vertical profile of wind speed in Titans atmosphere from 140 km altitude down to the surface. Ground-based observations brought new information on atmosphere and surface properties of the largest Saturnian moon. No positive detection of phenomena associated with the Probe entry was reported. This paper reviews all these measurements and highlights the achieved results. The ground-based observations, both radio and optical, are of fundamental importance for the interpretation of results from the Huygens mission.

Direct measurement of winds on Titan

We report the first direct measurement of wind velocity in the atmosphere of Titan, one of only two examples in our solar system of a slowly-rotating body with a dense atmosphere and a prime target of the Cassini mission. Zonal wind velocity was determined from Doppler shift of ethane lines emitted from Titans stratosphere (∼0.1–7 mbar) measured by infrared heterodyne spectroscopy near 12 µm (λ/Δ λ ≥ 106). Prograde zonal circulation, in the direction of global rotation, is established with 94% statistical confidence. Results provide information regarding Titan meteorology constraining dynamical theories for slowly-rotating bodies, provide otherwise unobtainable data to optimize the Cassini Huygens Probe investigations, and demonstrate the capability for remotely measuring winds on a small, distant object.

Remote sensing by IR heterodyne spectroscopy

The use of IR heterodyne spectroscopy for the study of planetary atmospheres is discussed. Infrared heterodyne spectroscopy provides a convenient and sensitive method for measuring the true intensity profiles of atmospheric spectral lines. Application of radiative transfer theory to measured line shapes can then permit the study of molecular abundances, temperatures, total pressures, excitation conditions, and dynamics of the regions of line formation. The theory of formation of atmospheric spectral lines and the retrieval of the information contained in these molecular lines are illustrated. Notable successes of such retrievals from IR heterodyne measurements on Venus, Mars, Jupiter, and earth are given. A discussion of new developments in IR heterodyne technology is also presented.

Absolute wind velocities in the lower thermosphere of Venus using infrared heterodyne spectroscopy

Abstract Absolute wind velocities in the thermosphere of Venus were retrieved using NASA/Goddard Space Flight Center infrared heterodyne spectrometers at the NASA Infrared Telescope Facility (IRTF) and the McMath Solar Telescope, December 1985 to March 1987. Measurement of beam-integrated Doppler shifts in the nonthermal emission core of the 12C16O2 10.33-μm R(8) line provided sampling of the lower thermospheric wind field (100–120 km) projected along the line of sight. The spectrometers 1–2 arc-sec diffraction-limited beam yielded the spatial resolution necessary for circulation model discrimination. Saturated resonance (Lamb dip) stabilization of the reference CO2 laser local oscillator provided continuous absolute frequency calibration of the spectrometer to

Collision of comet Shoemaker-Levy 9 with Jupiter observed by the NASA infrared telescope facility

The National Aeronautics and Space Administration (NASA) Infrared Telescope Facility was used to investigate the collision of comet Shoemaker-Levy 9 with Jupiter from 12 July to 7 August 1994. Strong thermal infrared emission lasting several minutes was observed after the impacts of fragments C, G, and R. All impacts warmed the stratosphere and some the troposphere up to several degrees. The abundance of stratospheric ammonia increased by more than 50 times. Impact-related particles extended up to a level where the atmospheric pressure measured several millibars. The north polar near-infrared aurora brightened by nearly a factor of 5 a week after the impacts.

Sensitivity limits of an infrared heterodyne spectrometer for astrophysical applications.

The sensitivity of an ideal heterodyne spectrometer approaches the quantum detection limit provided the local oscillator power is sufficiently large and the shot noise dominates all other sources of noise. The postintegration minimum-detectable-number of photons/sec for an ideal heterodyne system is (B/tau)((1/2)), where B is the IF bandwidth, and tau is the integration time. For astronomical observations, however, a number of factors (Delta(i)) tend to degrade the sensitivity, a fact that becomes significant particularly when the laser power is insufficient. A discussion and an evaluation of the degradation in sensitivity are given for a heterodyne spectrometer employing a HgCdTe photodiode mixer and tunable diode lasers. The minimum detectable source brightness is considered as a function of the mixer parameters, transmission coefficient of the beam splitter, and local oscillator emission powers. The degradation in the minimum detectable line source brightness that results from the bandwidth being a fraction of the line width is evaluated and plotted as a function of the wavelength and bandwidth for various temperature to mass ratios. It is shown that the minimum achievable degradation [pi(i)(Delta(i))] in the sensitivity of a practical astronomical heterodyne spectrometer is ~30. Estimates of SNRs with which ir line emission from astronomical sources of interest may be detected are given.

Variability of ethane on Jupiter

Abstract Abundances and spatial distributions of ethane in Jupiters stratosphere were obtained from ultrahigh-resolution ( Λ ΔΛ ∼ 10 6 ) spectra of individual C2H6 emission lines in the ν9 band near 12 μm. The accuracy of the retrieved C2H6 mole fractions was evaluated in the context of varying stratospheric temperature profiles and C2H6 altitude distributions. A twofold uncertainty in the accuracy of the obtained abundances is possible. A mean equatorial value for the C2H6 mole fraction of 2.8 ± 0.6 × 10t-6 was retrieved. Significant variability in the ethane line emission and retrieved mole fractions was found near the footprint of Ios flux tube and within the auroral regions. An increase in the ethane emission and abundance is obtained near the south polar region, relative to equatorial and northern latitudes. A significant decrease in ethane emission and abundance was observed in April 1983 near the known “hot spot” at 180° long (System III, 1965) and 60°N lat, where enhanced CH4 and C2H2 emission was previously observed. We suggest that these observed phenomena are caused by a modification of local stratospheric chemistry, possibly by higher order effects of charged particles precipitating along magnetic field lines.

NH3 spectral line measurements on Earth and Jupiter using a 10 μm superheterodyne receiver

Measurements of absolute line positions and shapes of eleven absorption lines of NH3 were made using an infrared heterodyne spectrometer. Line profiles were obtained with 5 MHz resolution. NH3 line positions relative to 12C16O2 and 13C16O2 local oscillator laser line emission frequencies were determined to ±3 MHz. Using the obtained data a search list for NH3 spectral lines on Jupiter was generated. Observations of Jovian polar regions in search of NH3 aR(1,1) and sQ(2,1) auroral emission revealed possible strong nonthermal features. The line widths were consistent with low local kinetic temperatures. The relatively high line intensities, determined by local pumping mechanisms, corresponded to temperatures of several hundred Kelvins. Experimental details and implications of these measurements are discussed.

Precision measurements of NH 3 spectral lines near 11 μm using the infrared heterodyne technique

Absolute line-center frequencies for eleven lines of ammonia in near coincidence with CO(2)-laser transitions have been determined to accuracies of +/-3 MHz by infrared heterodyne detection. These results were obtained by heterodyning a blackbody with a stable, grating-tuned CO(2) gas laser. A discussion of the apparatus and method of calculation, including error analysis, is presented. With these accurately determined line-center positions, the ammonia molecule will be a useful secondary-frequency standard for diode-laser spectroscopy in the 11-microm wavelength region.

Ground-based infrared measurements of the global distribution of ozone in the atmosphere of Mars

We report measurements of the global distribution of ozone in the atmosphere of Mars, based on Doppler-limited infrared spectroscopy during the period 3–7 June 1988. The Martian spectrum was measured in the region of the P36 transition of 12C16O2 (1031.4774 cm−1) in a search for two O3 lines arising in the ν3 band at 1031.4515 and 1031.4559 cm−1. Surface pressures and temperature profiles were retrieved by inversion of the fully resolved 12C16O2 line. Ozone measurements were obtained at eight beam positions over a range of Martian latitudes (80° S to 20° N) and local solar hour angles (−0.5h to +5.5h). The total O3 column abundance at each position was retrieved by fitting the lines with synthetic spectra generated by a radiative transfer program. The only previous ozone measurement at this season (Ls ∼ 204°) was made above the south polar cap by Mariner 7 and revealed an abundance of 10 μm-atm. However, the retrieved O3 column burdens of this investigation are less than 2.2 μm-atm for all latitudes sampled, consistent with seasonal abundances predicted by the models of Liu and Donahue, and Shimazaki and Shimizu.