Летим на Венеру в 2016

Рельеф тессер на Венере мог сформироваться под действием водных потоков • Новости науки

Традиционно считается, что тессеры на Венере — возвышенности, сильно изрезанные трещинами, — образовались в ходе тектонических процессов. Недавнее исследование предлагает новый взгляд на их формирование. Ее авторы считают, что тессеры можно считать следами водных потоков, текших по поверхности Венеры в те древние времена, когда климат на ней был более мягким. В то же время авторы признают, что пока не появились более подробные данные, к их идеям лучше относиться как к экзотической гипотезе. //  elementy.ru

 

Данных о скорости приповерхностных ветров и их влиянии на породы на данный момент, к сожалению, слишком мало, но некоторые оценки существуют. В статье 2016 года Surface winds on Venus: Probability distribution from in-situ measurements приводятся цифры 1,7–2,2 м/с, что вполне достаточно для того, чтобы переносить мелкий песок и пыль.

 

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A surface wind specification is needed for future landed missions to Venus. While sparse, there exist enough data from the limited surface and near-surface measurements to date to define a probability density function that guides expectations of winds for rational design of landing systems. Following a review of all available data (mostly from the Venera missions), a Weibull function, used previously for Mars and Titan, and widely used in terrestrial engineering applications, is proposed. Best-estimate wind measurements are reasonably described by P(>V) = exp[−(V/c)k], with c = 0.8 m/s, k = 1.9: this function yields a 95% chance of winds <1.4 m/s and 99% <1.8 m/s.

 

Wind measurements on Venus

There are sadly very few direct surface windspeed measurements on Venus, only those by Venera 9 and 10 in 1976. These landers carried cup anemometers able to operate at 500 °C. The Venera 9 wind record spans 49 min (Avduevskii et al., 1977) and that of Venera 10 only 90 s, sampled at a 0.4 Hz frequency with a resolution of the order of ∼0.2 m/s. The Venera 9 and 10 records have been characterized (noting that the wind speed reported by the instruments mounted on the drag disk on the lander may differ from the freestream winds by an aximuth-dependent factor) as having a means of 0.4 and 0.9 m/s respectively, with standard deviations of 0.1 and 0.15 m/s (Golitsyn, 1978; see also Keldysh, 1977).

 

Surface winds were also estimated from the intensity of sounds recorded by the Groza microphone on Venera 13 and 14 to be of the order of 0.55 and 0.35 m/s, but there exists substantial uncertainty in this measurement (Ksanfomality et al., 1983).

Counselman et al. (1980) report radio tracking of the four Pioneer Venus probes, using a combination of Doppler and DLBI (Differential Long Baseline Interferometry) methods see also Lorenz (2015). These provide indications of the probe speed along the line of sight, and the position in the plane of the sky respectively. The Venera landers were tracked by Doppler-only methods, in some cases measured on Earth, and in others by a relay spacecraft (e.g. Marov et al., 1973, Kerzhanovich et al., 1980, Kerzhanovich et al., 1982, Kerzhanovich and Marov, 1980). A list of surface wind speed measurements on Mars and Titan is presented in Table 3.2 of Lorenz and Zimbelman (2014).

 

Evidence of sediment transport by surface winds on Venus exists in the form of dunes, wind streaks and microdunes. There exist a couple of dunefields with dunes large enough to be resolved in Magellan data (e.g. Greeley et al., 1992, Weitz et al., 1994, Lorenz and Zimbelman, 2014) as well as microdunes implied by the unresolved anisotropy of radar scattering properties (Kreslavsky and Vdovichenko, 1998). Wind tunnel tests show that just above the saltation threshold, at 0.63 m/s, ∼18 cm long dunes with slip faces developed and higher speeds caused progressive lengthening, until at ∼1.5 m/s, bedforms were destroyed (Greeley et al., 1984).