Οι
εντυπωσιακοί ανεμοστρόβιλοι της Αφροδίτης. Έχουν διάμετρο χιλιάδων χλμ και
ταχύτητες 400 χλμ/ώρα. On 9 November 2005, 10 years ago today, ESA’s Venus Express spacecraft left Earth and
began its 153-day journey to Venus. The craft then spent eight years studying the planet in detail before
the mission came to an end in
December 2014. One of the mission aims was to observe the planet’s atmosphere
continuously over long periods in a bid to understand its dynamic behaviour. The
atmosphere is the densest of all the terrestrial planets, and is composed
almost entirely of carbon dioxide. The planet is also wrapped in a thick layer
of cloud made mostly of sulphuric acid. This combination of greenhouse gas and
perennial cloud layer led to an enormous greenhouse warming, leaving Venus’
surface extremely hot – just over 450ºC – and hidden from our eyes. Although
winds on the planet’s surface move very slowly, at a few kilometres per hour,
the atmospheric density at this altitude is so great that they exert greater
force than much faster winds would on Earth. Winds at the 65 km-high
cloud-tops, however, are a different story altogether. The higher-altitude
winds whizz around at up to 400 km/h, some 60 times faster than the rotation of
the planet itself. This causes some especially dynamic and fast-moving effects
in the planet’s upper atmosphere, one of the most prominent being its ‘polar
vortices’. The polar vortices arise because there is more sunlight at lower
latitudes. As gas at low latitudes heats it rises, and moves towards the poles,
where cooler air sinks. The air converging on the pole accelerates sideways and
spirals downwards, like water swirling around a plug hole. In the centre of the
polar vortex, sinking air pushes the clouds lower down by several kilometres,
to altitudes where the atmospheric temperature is higher. The central ‘eye of
the vortex’ can therefore be clearly seen by mapping thermal-infrared light,
which shows the cloud-top temperature: the clouds at the core of the vortex are
at a higher temperature, indicated by yellow tones, than the surrounding
region, and therefore stand out clearly in these images. Venus Express has
shown that the polar vortices of Venus are among the most variable in the Solar
System. This series of images of Venus’ south pole was taken with the VIRTIS
instrument from February 2007 (top left) to April 2008 (bottom right). The
shape of this vortex core, which typically measures 2000–3000 km across,
changes dramatically as it is buffeted by turbulent winds. It can resemble an
‘S’, a figure-of-eight, a spiral, an eye, and more, quickly morphing from one
day to the next. Each of the images in this frame is roughly 4000 km across. Credit:
ESA/VIRTIS-Venus Express/INAF-IAPS/LESIA-Obs. Paris/G. Piccioni
Ο
Ευρωπαϊκός Οργανισμός Διαστήματος (ESA) έδωσε στη δημοσιότητα εντυπωσιακές
εικόνες που έστειλε από την Αφροδίτη το σκάφος Venus Express που έφτασε στον
πλανήτη το 2006 και τον εξερεύνησε για οκτώ έτη. Οι εικόνες απεικονίζουν
ανεμοστρόβιλους με διάμετρο τεσσάρων χιλιάδων χλμ και ταχύτητα 400 χλμ/ώρα!
This movie, built
with infrared images taken by the Ultraviolet/Visible/Near-Infrared
spectrometer (VIRTIS) on board ESA’s Venus Express, provides a close-up view of
the double-eyed vortex at Venus south pole. The images (ranging from 4.5 to 5.1
microns) were taken on 29 May 2006, from a distance of about 64 000 kilometres
from the planet. Thanks to the use of different wavelengths, VIRTIS probed the
atmosphere at different depths, ranging from 70 kilometres to about 60
kilometres altitude. It is interesting to see how the images contrast and the
details increase while approaching the 60 kilometres altitude. Credit: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA
H
Αφροδίτη θεωρείται ξαδέρφη της Γης, αφού διαθέτει ανάλογο μέγεθος και μάζα με
τον πλανήτη μας και επιπλέον οι επιστήμονες πιστεύουν ότι πριν από
δισεκατομμύρια χρόνια είχε περιβάλλον ανάλογο με αυτό της Γης. Οι ειδικοί
πιστεύουν ότι υπήρχαν ωκεανοί και άρα συνθήκες ικανές για την ανάπτυξη ζωής.
Στη συνέχεια όμως η Αφροδίτη για κάποιον λόγο πλησίασε περισσότερο προς τον Ήλιο
και η ραγδαία αύξηση της θερμοκρασίας αποξήρανε τον πλανήτη.
