ESA Science & Technology - Publication Archive
SPICAV VIS-IR spectrometer on-board the Venus Express mission measured the H2O abundance above Venus' clouds in the 1.38 µm band, and provided an estimation of the cloud top altitude based on CO2 bands in the range of 1.4–1.6 µm. The H2O content and the cloud top altitude have been retrieved for the complete Venus Express dataset from 2006 to 2014 taking into account multiple scattering in the cloudy atmosphere. The cloud top altitude, corresponding to unit nadir aerosol optical depth at 1.48 µm, varies from 68 to 73 km at latitudes from 40°S to 40°N with an average of 70.2 ± 0.8 km assuming the aerosol scale height of 4 km. In high northern latitudes, the cloud top decreases to 62–68 km. The altitude of formation of water lines ranges from 59 to 66 km. The H2O mixing ratio at low latitudes (20°S-20°N) is equal to 6.1 ± 1.2 ppm with variations from 4 to 11 ppm and the effective altitude of 61.9 ± 0.5 km. Between 30° and 50° of latitude in both hemispheres, a local minimum was observed with a value of 5.4 ± 1 ppm corresponding to the effective altitude of 62.1 ± 0.6 km and variations from 3 to 8 ppm. At high latitudes in both hemispheres, the water content varies from 4 to 12 ppm with an average of 7.2 ± 1.4 ppm which corresponds to 60.6 ± 0.5 km. Observed variations of water vapor within a factor of 2-3 on the short timescale appreciably exceed individual measurement errors and could be explained as a real variation of the mixing ratio or/and possible variations of the cloud opacity within the clouds. The maximum of water at lower latitudes supports a possible convection and injection of water from lower atmospheric layers.
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Understanding what processes govern atmospheric escape and the loss of planetary water is of paramount importance for understanding how life in the universe can exist. One mechanism thought to be important at all planets is an "ambipolar" electric field that helps ions overcome gravity. We report the discovery and first quantitative extraterrestrial measurements of such a field at the planet Venus. Unexpectedly, despite comparable gravity, we show the field to be five times stronger than in Earth's similar ionosphere. Contrary to our understanding, Venus would still lose heavy ions (including oxygen and all water-group species) to space, even if there were no stripping by the solar wind. We therefore find that it is possible for planets to lose heavy ions to space entirely through electric forces in their ionospheres and such an "electric wind" must be considered when studying the evolution and potential habitability of any planet in any star system.
Waves are ubiquitous phenomena found in oceans and atmospheres alike. From the earliest formal studies of waves in the Earth's atmosphere to more recent studies on other planets, waves have been shown to play a key role in shaping atmospheric bulk structure, dynamics and variability. Yet, waves are difficult to characterize as they ideally require in situ measurements of atmospheric properties that are difficult to obtain away from Earth. Thus, we have incomplete knowledge of atmospheric waves on planets other than our own, and we are thereby limited in our ability to understand and predict planetary atmospheres. Here we report the first ever in situ observations of atmospheric waves in Venus's thermosphere (130–140 km) at high latitudes (71.5°–79.0°). These measurements were made by the Venus Express Atmospheric Drag Experiment (VExADE) during aerobraking from 24 June to 11 July 2014. As the spacecraft flew through Venus's atmosphere, deceleration by atmospheric drag was sufficient to obtain from accelerometer readings a total of 18 vertical density profiles. We infer an average temperature of T = 114 ± 23 K and find horizontal wave-like density perturbations and mean temperatures being modulated at a quasi-5-day period.
Available online 24 September 2013
High resolution images of Venus Northern hemisphere obtained with the Venus Monitoring Camera (VMC/VEx) allow studying small-scale dynamical phenomena at the cloud tops (~62-70 km altitude) including features like wave trains. A systematic visual search of these waves was performed; more than 1500 orbits were analyzed and wave patterns were observed in more than 300 images. Four types of waves were identified in VMC images on the base of their morphology: long, medium, short and irregular type waves. With the aim to characterize the wave types and their possible excitation source, we retrieved wave properties such as location (latitude and longitude), local time, solar zenith angle, packet length and width, orientation, and wavelength of each wave. The long type waves appear as long and narrow straight features extending more than a few hundreds kilometers and with wavelengths between 7 and 17 km. Medium type waves exhibit irregular wavefronts extending more than 100 km and with wavelengths in the range 8-21 km. Short wave packets have a width of several tens of kilometers and extend to few hundreds kilometers and are characterized by smaller wavelengths (3-16 km). Irregular wave fields appear to be the result of wave interference. The waves are often identified in all VMC filters and are mostly found in the cold collar region at high latitudes (60-80°N) and are concentrated above Ishtar Terra, a continental size highland that includes the highest mountain belts of the planet. The high speed of the Venus Express spacecraft close to the pericentre does not allow to measure phase speed of waves due to the short temporal interval between image pairs. [Remainder of abstract truncated due to character limitation]
Published online 5 April 2012, in Science Express
Observations with the Venus Express magnetometer and low-energy particle detector revealed magnetic field and plasma behaviour in the near-Venus wake symptomatic of magnetic reconnection, a process that occurs in the Earth's magnetotail but is not expected in the magnetotail of a non-magnetized planet like Venus. On 15 May 2006, the plasma flow in this region was toward the planet and the magnetic field component transverse to the flow was reversed. Magnetic reconnection is a plasma process that changes the topology of the magnetic field and results in energy exchange between the magnetic field and the plasma. Thus, the energetics of the Venus magnetotail resembles that of the terrestrial tail where energy is stored and later released from the magnetic field to the plasma.
This issue of Icarus presents papers on the planet Venus based principally on presentations at two international conferences during the summer of 2010. Under the sponsorship of the European Space Agency, the International Venus Conference (Aussois, France, 20-26 June 2010) focused on the results from the Venus Express Mission. Venus Express is expected to continue operations through December 2014 and beyond. The second conference, "Venus Our Closest Earth-like Planet: From Surface to Thermosphere - How does it work?", was sponsored by the Venus Exploration Analysis Group (VEXAG) chartered by NASA in Madison, Wisconsin (29 August-1 September, 2010). The work presented at these conferences illustrates the resurgence in Venus research since the arrival at Venus of the European Space Agency's Venus Express orbiter in April 2006. The issue also includes papers that were inspired by JAXA's launch of Venus Climate Orbiter (also known as Akatsuki) in May 2010.
The papers reflect the international interest in Venus and cover many different aspects of the planet, ranging from interior and surface to the upper atmosphere, with many results focusing on the coupling between different layers.
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Made available online 25 August 2011
To date, ozone has only been identified in the atmospheres of Earth and Mars. This study reports the first detection of ozone in the atmosphere of Venus by the SPICAV ultraviolet instrument onboard the Venus Express spacecraft. Venusian ozone is characterized by a vertically confined and horizontally variable layer residing in the thermosphere at a mean altitude of 100 km, with local concentrations of the order of 107-108 molecules cm-3. The observed ozone concentrations are consistent with values expected for a chlorine-catalyzed destruction scheme, indicating that the key chemical reactions operating in Earth's upper stratosphere may also operate on Venus.
Comparative planetology has long been a field of general interest but with a fairly small number of scientists actively involved. During the last decade, until recently, there has been no significant growth, possibly much due to lack of new data from Venus; perhaps the most obvious planet to compare with the Earth. Availability of ample data of high quality is of paramount importance for proper comparisons. With the arrival of Venus Express at Venus in March 2006 a new impulse to the field has been injected. Venus Express addresses a large number of topics relevant to comparative planetology; in particular in the field of atmospheric dynamics and chemistry, clouds and atmospheresolar wind interaction.
Mars has been the subject of significant interest and many space missions in the recent years. Being smaller and cooler and in several aspects more evolved, Mars is still a planet of great interest for comparison with the Earth on the other end of the parameter space.
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