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No shortage of mysteries on Venus
by the European Space Agency
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View of the volcano Sif Mons on
Venus
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What kind of mysteries and scientific intrigue await
the European Space Agency's Venus Express once it has left Earth for its
nearest planetary neighbour in 2005? A closer inspection promises to
reveal a planet that is hugely different from our own despite a few
similarities.
Astronomers often call Venus the Earth's twin
because both are about the same size and have the same mass.
In other ways, however, Venus seems to be an altogether different class of
planet. Scientists are keen to take a closer look at this cloudy,
mysterious planet. After a 150-day cruise from Earth, Venus Express will
manoeuvre into an orbit that loops over the poles of the planet once every
10 -16 hours. What will we see?
The first of many curiosities is the nature of the Venusian magnetic
field. It is so weak that particles ejected from the Sun, known as the
solar wind, do not go around the planet, as they do at Earth. Instead they
continuously strike Venus's upper atmosphere. Scientists want to know more
about how this process takes place.
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What is absorbing ultraviolet light in the Venusian
atmosphere?
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| The atmosphere itself
contains plenty of puzzles. Hakan Svedhem, project scientist for Venus
Express, says, "The atmosphere of Venus is unique in the Solar System,
so understanding it is very important." What we know about our own
atmosphere does not much help us understand Venus. How can 'Earth's twin'
possess such a different atmosphere? The thick atmosphere creates a
greenhouse effect, making Venus hotter than a kitchen oven. This
greenhouse effect is definitely worth studying. Another mystery concerns
the movement of the atmosphere. About 60 kilometres above the surface,
winds race through the cloud cover at almost 400 kilometres per hour. They
make the atmosphere rotate, but we do not know how this so-called
super-rotation occurs.
The planet's peculiar backward rotation is also a riddle. Venus rotates
in the opposite direction to Earth and most of the other planets in the
Solar System. It also spins incredibly slowly, taking around 250 Earth
days to spin once, as compared to 1 day for Earth. Recent computer models
suggest that Venus used to rotate on its axis the same way as Earth did
but its heavy atmosphere dragged it to a standstill before causing the
present, slow backward rotation.
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View of the Golubkina crater on
Venus
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| When we think of the
planet's surface, there are many more mysteries. Are there still active
volcanoes? Is the entire planet's surface a single solid crust or does it
consist of continental plates that float on a partially molten interior,
similar to Earth? We know the planet itself is 4 thousand million years
old but the entire surface of Venus appears to be 500 million years old!
Was the planet resurfaced? If so, how did that happen?
Perhaps the most exciting phenomenon of all is in the atmosphere, just
above the super-rotation layer. Here, at about 80 kilometres altitude,
something is absorbing ultraviolet wavelengths of light. There is no
obvious explanation of these mysterious absorption patches. However, some
scientists believe that they could be acid-eating microbes using
ultraviolet light in some alien photosynthesis process.
There is a large range of mysteries for Venus Express to investigate.
As Svedham says, "This mission will enhance our entire picture of
Venus. We will understand it as a planet much more."
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