Dmitrij V. Titov教授是一位出生于前苏联的杰出科学家。他获得莫斯科物理技术学院博士学位后，被聘为莫斯科空间研究所高级研究员。他从上世纪90年代起，积极参与了欧洲航天局各类大型深空探测项目。Titov教授是金星快车计划发起人，主持了任务的科学战略制定和科学运作协调，被誉为“金星快车之父”。此外了，Titov教授还是火星快车计划的科学负责人，Venus Monitoring Camera载荷科学技术负责人，前苏联Venera系列卫星合作负责人，Mars Pathfinder数据分析科学家，并负责了JUICE、EnVision等卫星的科学运作协调。 Titov教授累计获得各类项目经费资助超过1亿欧元，迄今为止在Science、Nature等多个国际主流学术期刊发表论文140余篇，曾荣获欧洲地球科学学会极富盛名的大卫贝茨爵士奖，以及空间科学界最大机构--国际空间研究委员会授予的泽尔多维奇青年科学家奖等众多奖项。
The main scientific interests and achievements of the applicant comprise remote sensing of planetary atmospheres, in particular cloud morphology, dynamics and radiative energy balance of the Venus atmosphere, water vapour and dust cycles on Mars. These investigations contribute to comparative planetology and are crucial for understanding habitability and evolution of the planets, as well as the climate change on Earth. The applicant’s expertise also includes development of scientific concepts of planetary missions and payloads as well as top level planning of science operations. Until now the applicant has more than 130 publications in international journals, about 120 of them are peer-reviewed including 7 Nature papers (1 first-authored, 2 second-authored). The applicant’s research achievements could be summarized as follows.
A. Systematic and comprehensive characterization of the cloud morphology, dynamics, and radiative energy balance of the Venus atmosphere
1. Properties of the Venus cloud layer
(1) Using Venus Express images, the applicant investigated the Venus cloud morphology at global to sub-kilometer scale. This study provided complete morphological characterization of the Venus clouds and revealed complex structure with features ranging from global spiral/circular streaks/ grooves and dense “polar cap” to “lace” clouds, convective cells, and waves. A global depression of the cloud top with its altitude decreasing by ~8 km and much higher cloud opacity were discovered in the Southern polar regions.
(2) The nature of the UV absorption in the Venus cloud layer has been a long-standing puzzle for many decades. Using Venus Express data, the applicant showed that dark low latitudes of Venus are dominated by convective mixing which brings the ultraviolet absorbers up from depth. This original finding suggests that atmospheric structure and dynamics are likely the cause of ultraviolet cloud markings. The applicant retrieved the abundance and variability of SO2 and H2O, the cloud-forming species, at the Venus cloud top (60-65 km) from the IFSE/Venera-15 infrared spectrometer data. He proposed a new mechanism of formation of the unknown UV absorber based on chemicalreaction between SO2 and NH3 that led to formation of fine aerosols with optical and thermodynamic properties matching observations.
(3) The aerosol size distribution is an outstanding issue of the Venus cloud structure. The applicant derived such a distribution from the IOAV spectrophotometer measurements onboard Venera-11 descending probe. Fine aerosols with radius of <1 mm and number density of » 103 cm-3 were found to be dominant above 60 km. Below this level the cloud is composed of particles with r » 1.4 mm and N » 50 cm-3.Joint interpretation of the spectrophotometer and nephelometer data on the same probe led to an estimate of the particle refractive index. The role of microphysical processes in the cloud formation was numerically assessed.
2. Dynamics and temperature structure of the Venus atmosphere
(1) The mechanism maintaining superrotation of the Venus atmosphere still remains one of the main fundamental problems. The applicant and his team used Venus Express multi-wavelength imaging and cloud features tracking to derive wind field at 50-70 km. In equatorial and middle latitudes, the zonal winds were found to be almost constant with latitude with speed reaching more than 100 m/s at the cloud top and wind shear of 2-3 km/s/km within the cloud deck. The zonal wind decreased with latitude in the polar regions. The cloud top zonal wind accelerated from 80 m/s to ~110 m/s over the course of the Venus Express mission (~ 10 Earth years) likely due to influence of the surface topography. The meridional wind speed is 10-15 m/s with poleward motions dominating at the cloud tops and equatorward circulation in the deep cloud likely indicating existence of a Hadley cell in the Venus upper cloud associated with the presence of the unknown UV absorber there that causes significant heating.
(2) The Venus mesosphere is considered to be roughly in the cyclostrophic state when the centrifugal force of superrotating air parcels is provided by the atmospheric pressure gradient. This hypothesis was confirmed by the applicant who compared cyclostrophic winds derived from the temperature structure retrieved from Venera-15 and Venus Express temperature soundings to the cloud tracked winds.
3. Radiative energy balance in the Venus middle atmosphere
In the dense Venus atmosphere balance of radiative energy defines the atmospheric structure and drives the circulation. The applicant calculated the outgoing thermal fluxes and cooling rates based on joint retrievals of temperature and cloud structure from the Venera-15 infrared spectrometer data and assessed variability of the radiative energy budget due to changes in the cloud structure observed by Venus Express. The applicant also assessed sources and sinks of the radiative entropy that revealed remarkable differences between Venus and Earth. These assessments paved a way to more detailed study of Venus atmosphere as a non-linear dissipative system that can be pushed by radiative energy forcing into a non-equilibrium state with maximum entropy (e.g. superrotation).
4. Venus surface composition and active volcanism discovery
Venus surface composition is virtually unexplored. The applicant and his team performed the study of Venus surface using Venus imaging in the spectral transparency “window” at 1µm by the Venus Monitoring Camera (VMC) onboard Venus Express. The analysis indicated that tesserae, the oldest regions on Venus, are not basaltic, but are likely to be felsic. This result might have important implications on geochemical environments in the early history of Venus. The VMC observations discovered transient hot spots consistent with fresh lava flows in Ganiki Chasma, young region similar to rift zones on Earth. This provides strong evidence for current volcanic activity on Venus.
B. Investigation of water vapour and dust cycles on Mars
Water vapour and dust cycles on Mars provide remarkable examples of dynamic systems. Their understanding requires long observation time series, careful data analysis and extensive modelling.
1. Distribution of the Martian atmospheric water vapor and coupling with the surface
Water vapour is the most variable trace gas in the atmosphere of Mars suggesting a complex chain of processes in action. The applicant used spectroscopic observations of the atmospheric water vapour by ISM/Phobos-2, Planetary Fourier Spectrometer (PFS) and OMEGA experiments onboard ESA’s Mars Express. This analysis revealed strongly variable annual cycle of water column abundance varying from about 100 precipitable microns (pr. µm) at the Northern polar cap in spring to ~6 pr. µm in dry places and seasons. The observed spatial variations of atmospheric water column were found to be correlated with topography, surface properties and local time suggesting significant contribution of the surface in the atmospheric water cycle and indicating that at least in some places atmospheric water can be confined to 1-3 km layer close to the surface. The applicant confirmed these conclusions by analysis of the measurements by NASA’s Imager for Mars Pathfinder lander. He also developed a model based on the analytical solution of one-dimensional diffusion equation describing adsorption-desorption processes in the regolith and vertical mixing in the planetary boundary layer.
2. Aerosol structure in the Martian atmosphere
The applicant derived aerosol vertical structure from the measurements of thermal radiation at limb by Termoscan thermal imager onboard Soviet Phobos-2. Two components were found: exponential aerosol with a scale height of ~10 km, and a variable layer at 25-35 km.Microphysical properties of the Martian dust were also studied from the data collected by the NASA’s Imager for Mars Pathfinder.
C. Concepts of planetary missions, instruments, and operations
The applicant’s expertise also includes development of scientific concepts of planetary missions and payloads as well as top level planning of science operations. The applicant was the lead proposer of the ESA Venus Express mission and was responsible for development and implementation of the mission science activity plan. He was the technical and science manager of the Venus Monitoring Camera instrument onboard Venus Express. While working at the European Space Agency (ESA) the applicant coordinated development of science case and requirements for ESA’s L (Large)-class mission JUICE (Jupiter Icy Moons Explorer) and M (Medium)-class mission EnVision (an orbiter at Venus). The applicant was also involved in the development of science cases for European Venus Explorer (EVE), science definition of the NASA Venus Flagship Mission.
