Article

Searching for Evidence of Past Oceans on Venus

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Abstract

The lower bound for the longevity of an early ocean on Venus has been calculated to be about 600 My (Kasting, Icarus 1988). However, the inclusion of water clouds in recent models of an early wet Venusian atmosphere shows reduced solar forcing, resulting in oceans that could have lasted billions of years (Grinspoon and Bullock, BAAS 2003). If Venus did indeed have warm oceans for this long, it may well have been a crucible for the origin of life. Evidence for past oceans may be difficult to obtain, but there are a few promising avenues that, taken together, could provide substantial clues. One is the nature of the highlands crust. If rocks from these regions were produced from melts that had substantial interaction with an ocean, it is possible that they are andesitic or granitic. Mineralogical and petrographic information on the highlands crust will be crucial for making this determination. A second line of evidence involves the likely existence of hydrated minerals. Laboratory experiments have shown that the tremolite is metastable on Venus, decomposing on timescales of billions of years (Johnson and Fegley in Lunar and Planetary Science XXXI 2000) . Because of the large range of temperatures from lowlands to highlands on Venus ( 100 K), measurements of differential tremolite abundance can constrain the time a particular lithologic unit formed, the average surface temperature since its emplacement, or both. In situ X-ray diffraction analysis coupled with X-ray fluorescence spectroscopy on the surface of Venus can quantify the abundances of hydrated and other minerals with sufficient accuracy for these determinations. Finally, measurements of the isotopic ratios of hydrogen, carbon and oxygen in surface minerals and the atmosphere will help constrain how reservoirs of these elements have interacted over time, including the involvement of possible aqueous processes.

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... Now Venus is not very similar to a suitable place for living. Its surface temperature exceeds 730 K, the pressure is 90 atmospheres, the cloud layer consists of sulfur dioxide, and the fog cloud above is a solution of sulfuric acid [1][2][3]11]. Venus is quite close in size and mass to our planet. This fact gives gravity 0.9 of terrestrial value. ...
... This simulation gives an idea that under this scenario on the planet there could then was some form of life. That is, under the above conditions with moderate temperature, sufficient heat and liquid water, Venus would be quite suitable for the emergence of certain microorganisms and for the existence of primitive life there, especially in the oceans [2]. It is noted that the birth of life on Venus could have occurred earlier than even life appeared on Earth. ...
... It is noted that the birth of life on Venus could have occurred earlier than even life appeared on Earth. And then the Earth could become a new abode for living microorganisms that arrived from Venus [2,3]. One way to check whether the ancient Venus was once covered by the oceans is the study of the tremolite found on Earth. ...
Conference Paper
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Now Venus is not very similar to a suitable place for living. It surface temperature exceeds 730 K, the pressure is 90 atmospheres, the cloud layer consists of sulfur dioxide, and the fog above cloud is a solution of sulfuric acid. But about 3 billion years ago, this planet among the Earth-type planets within the Solar System was perhaps the most suitable place for the existence of some form of life there. Measurements of the ratio of hydrogen isotopes in the atmosphere also showed that the planet once had much more water, and perhaps it was enough even for the oceans. In early years on Venus was similar to the earth's climate, have a satisfactory temperature and oceans of liquid water. That is, under the above conditions with moderate temperature, sufficient heat and liquid water, Venus would be quite suitable for the emergence of certain microorganisms and for the existence of primitive life there, especially in the oceans. One way to check whether the ancient Venus was once covered by the oceans is the study of the tremolite found on Earth. It is necessary to hope to find the tremolite at some depth below the surface of Venus. Also necessary to search for some biosignals in the form of petrified remains, of possibly simple thermophilic microorganisms. We believe that such an experiment can be prepared and technically carried out during the next decades.
... Si aujourd'hui, les océans sont le principal réservoir de H 2 O sur Terre, sur Vénus c'est la couche nuageuse d'H 2 SO 4 qui en est le principal réservoir, entre 48 et 70 km d'altitude. Les nuages H 2 SO 4 contiennent 10 fois plus d'atomes H que la vapeur d'eau atmosphérique [Grinspoon and Bullock (2007)]. Une abondance colonne de 1 micromètre de vapeur d'eau précipitable correspondà un rapport de mélange de ≥2 ppm [von Zahn et al. (1983)]. ...
... Cette libération arrache les atomes d'oxygène ainsi que plus rarement les molécules de dioxygène O 2 [Gillmann et al. (2009)] ce qui amène a une augmentation du deutérium par appauvrissement en hydrogène. Grinspoon and Bullock (2007) ont modélisé un modèle radiatif d'effet de serre couplé a un modèle de microphysique d'un nuage H 2 O, en reprenant les conclusions de Kasting (1988) sur la possibilité un océan primitif sur Vénus. Leur modèle a pris en compte l'accroissement supposé de la luminosité du soleil avec le temps, et a mis enévidence la difficulté d'un tel travail en l'absence de contraintes sur la circulation atmosphérique primitive, la convection ou la distribution des masses continentales pré-existantes. ...
... De plus, les effets des nuages sur le bilan radiatif et donc l'évolution climatiqueà long terme sont fortement dépendants de leur altitude, le modèle reste donc fortement sous-contraint. En l'absence totale de nuages, Grinspoon and Bullock (2007) ont calculé l'équilibre en température d'une atmosphère dense de H 2 O/N 2 pour une couverture nuageuse allant de 0à 100%. Ces résultats montrent que si la Vénus primitiveétait dépourvue de nuages, elle débuterait la phase d'effet de serre catastrophique (runaway greenhouse) environ 500 millions d'années après sa formation, en accord avec le modèle de Kasting (1988). ...
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Le transit de Vénus devant le Soleil est un événement rare et l’occasion unique pourétudier la réfraction de la lumière du Soleil à travers l’atmosphère, afin de déterminer les propriétésatmosphériques de la planète et en particulier la structure thermique de la haute atmosphère.L'objectif de cette thèse a été la modélisation de cette réfraction lors du passage devant le Soleilqui a eu lieu les 5-6 juin 2012, modèle dont les résultats ont pu être comparés aux données de lamission Venus Express.La première partie est consacrée à l’analyse des images des satellites qui a permis lacréation de courbes de lumière en fonction de la latitude de l’auréole qui serviront de référencepour les modèles. L’étude de l’atmosphère a d’abord été réalisée par une approche isotherme(théorie de Baum et Code,1953). Le modèle a ensuite été affiné en simulant trois couchesisothermes concentriques établies grâce à l’analyse préalable des données SPICAV/SOIR deVenus Express. Pour finir, le dernier modèle développé pour l’étude de l’auréole est un modèlemulticouche concentrique à très haute résolution verticale. Ce modèle a permis d’obtenir un profilvertical de densité en fonction de la latitude, ainsi que l’altitude du tau = 1 (le long de la ligne devisée) induite par les aérosols. Ces données ont ensuite été ensuite utilisées pour générer descartes 2D de température en fonction de la latitude et de l’altitude, que nous comparons auxdonnées d’occultation solaire de la mission Venus Express. Cette étude a également permis dedéterminer de façon indépendante l’échelle de hauteur des aérosols et leur chromaticité dansl’atmosphère de Vénus.Dans un second temps, l’étude de la courbe du transit de 2004 a été menée conjointementavec le Dr. Andréa Chiavassa afin de mettre en évidence l’impact de la granulation stellaire sur lescourbes de transit exoplanétaires.
... However, due to the greenhouse effect, Venus' atmosphere is hotter and denser than that of Earth [2]. It is primarily made up of CO2 [3], has clouds of sulfuric acid, and contains 4% nitrogen [4]. Some studies predict that the surface temperature of ancient Venus was around +11 °C. ...
Article
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The similarity of Venus and Earth in bulk properties make Venus an appealing target for future colonization. Several proposals have been put forward for colonizing and even terraforming Venus despite the extreme conditions on the planet's surface. Such a terraforming project would face large challenges centred around removing Venus's massive carbon dioxide atmosphere and replacing it with a habitable environment. Although the atmosphere of Venus is the most Earth like environment in the solar system (apart from Earth itself) at a height of around 50 kilometres above the surface, Venus' surface is a highly hostile environment. Here it is suggested that in the near future aerostat vehicles in Venus' atmosphere could be used for human exploration, and that in the long run cities built to float at an altitude of around 50 kilometres could be used for permanent settlements. Venus' atmosphere is a fascinating area to research scientifically and to explore with humans in the future. Because of its hostile environment, which is the result of a huge and dense super-greenhouse atmosphere, Venus is frequently passed over as a candidate for habitation or terraforming. In the scenario presented in this research, Venus might be made habitable and ready for colonization in a matter of centuries. In addition, the materials used to build the orbital infrastructure required to start and sustain the terraforming process are also utilised to build orbital homes.
... Согласно некоторым моделям, средняя температура на поверхности древней Венеры была около +11С. Такое умеренное ее значение, достаточное количество тепла и жидкая вода -могли быть там в необходимом сочетании для зарождения определенной формы жизни [2,[14][15][16]. До настоящего времени все зонды, опускавшиеся на поверхность Венеры, из-за экстремальных условий передавали оттуда данные всего лишь по несколько часов. ...
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If humanity really wants to become a multi-planetary species, then it is necessary to colonize other space objects, such as Moon, Mercury, Mars and Venus. The development of Venus is complicated by a hot atmosphere. But in such a dense environment one can fly. At altitudes of 50-65 km, the main cloud layer of acid aerosols has a temperature of +80 to -30 °C, and pressure of 2 to 0.2 atmospheres. It is this atmospheric layer of Venus in its parameters that is closest to earthly conditions. This means that it is there that the most suitable conditions exist for the possible human habitation. The air pressure is about one bar, the thickness of the atmospheric layer above this level is quite enough to protect against solar radiation, and the temperature is approaching a comfortable value of about + 30 °C. In such conditions, colonists can live there for many years without harm to the bones and muscles. A balloon, which is filled with a mixture of nitrogen and oxygen in “terrestrial” ratio, in the atmosphere of Venus will be more than 50% easier, than the air of Venus. For this reason, the balloon will “float” at a given level. Such balloon will have lifting force, which is necessary to keep inside inhabitants, and the items they need. For example, a sphere with a diameter of 1 km can lift 350,000 tons; a sphere with a diameter of 2 km – can lift about 3 million tons. To protect the inhabited spherical city from the influence of sulfuric acid, the outer part of the balls must be covered with teflon, which for a long time provid protection from sulfuric acid, remaining flexible and elastic at temperatures from -250 to +250 °C.
... Similarly, hotter, inner-habitable zone Venus-like planets would end their habitable lifetimes in a hotter and potentially geologically active state (the Venus Express spacecraft found evidence of recent volcanism on Venus - Smrekar et al. 2010). The habitable lifetimes of such planets would likely be much shorter than Earth-like planets (if warm oceans were present on early Venus, its habitable lifetime would correspond to the lifetime of liquid surface water on the planet -estimates for this range from 600 Myr (Kasting 1988) to a few Gyr (Grinspoon & Bullock 2003)). The upper atmosphere would likely be the best final refuge for any life that developed on such planets. ...
Article
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The biosignatures of life on Earth do not remain static, but change considerably over the planet's habitable lifetime. Earth's future biosphere, much like that of the early Earth, will consist of predominantly unicellular microorganisms due to the increased hostility of environmental conditions caused by the Sun as it enters the late stage of its main sequence evolution. Building on previous work, the productivity of the biosphere is evaluated during different stages of biosphere decline between 1 Gyr and 2.8 Gyr from present. A simple atmosphere-biosphere interaction model is used to estimate the atmospheric biomarker gas abundances at each stage and to assess the likelihood of remotely detecting the presence of life in low-productivity, microbial biospheres, putting an upper limit on the lifetime of Earth's remotely detectable biosignatures. Other potential biosignatures such as leaf reflectance and cloud cover are discussed.
Article
The solar wind interaction contributes to the loss of Venus atmospheric constituents, especially oxygen, by direct antisunward acceleration of planetary ions and possibly by related sputtering of neutrals. Both comet-like “ion pickup” and related sputtering processes may have played a key role in Venus' atmosphere evolution, but the significance of their effects, as well as other proposed escape mechanisms, is still uncertain. In particular, recent reports of only modest ion escape rates measured on Venus Express (VEX) during the current low-activity phase of the solar cycle make it important to reconsider the evidence seen in both Pioneer Venus Orbiter and VEX observations suggesting significantly enhanced escaping O+ ion fluxes during periods of disturbed interplanetary conditions. At present, the most extreme interplanetary conditions result from the effects of coronal mass ejections (CME), which may have been more prevalent in the first 1–2 billion years of the Sun's history. The Analyser of Space Plasmas and Energetic Atoms 4 (ASPERA-4) Ion Mass Analyzer and Magnetometer on Venus Express have now made detailed measurements during several periods when CME disturbances encountered Venus. The observations and models described in this report provide further insights into the possible response of oxygen ion escape to solar activity. In particular, they illustrate nuances of in situ sampling of large-gyroradius pickup ions, related to the atmospheric source properties, spacecraft orbit geometry, and the prevailing interplanetary conditions, that make the estimation of the variable global escape fluxes due to that process particularly challenging. In three of the four cases examined in some detail, ionospheric oxygen ions were either unobservable or below the limit of detectability for passes well within interplanetary coronal mass ejection (ICME) intervals. In the fourth example, where ionospheric ions were observed as expected from the model, O+ pickup ions were observed in greater abundance than is typical in undisturbed solar wind. Other escape processes are not considered here, although it is assumed the source population for the modeled pickup ions is a preaccelerated upper atmosphere component. Analysis of many more ICME events, expected to be obtained as the Sun becomes more active in future years, are necessary to resolve the question of the importance of ICME to Venus oxygen escape.
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