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.

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.

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.”

USEFUL LINKS FOR THIS STORY

* More about Venus Express
http://sci.esa.int/home/venusexpress/index.cfm

IMAGE CAPTIONS:

[Image 1:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=1&cid=1&oid=31063&ooid=31064]
View of the volcano Sif Mons on Venus.

The volcano, Sif Mons, on Venus shows evidence for past
activity in the form of a solidified lava flow that shows
up in this image as a brighter streak down the sides of
its cone. Planetary scientists would like to know if such
eruptions are taking place today. This 3-D view of the
surface of Venus was produced in a computer using radar
data collected by NASA’s Magellan spaceprobe from orbit,
in the early 1990s.

[Image 2:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=1&cid=1&oid=31063&ooid=31065]
What is absorbing ultraviolet light in the Venusian
atmosphere?

This is a Hubble Space Telescope ultraviolet-light image
of the planet Venus, taken on January 24 1995, when Venus
was at a distance of 70.6 million miles (113.6 million
kilometers) from Earth. There are mysterious dark
atmospheric features, which some scientists have speculated
could be produced by microbes in the Venusian atmosphere.
Such microbes would have to be at home in the sulphuric
acid of Venus’s atmosphere.

[Image 3:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=1&cid=1&oid=31063&ooid=31066]
View of the Golubkina crater on Venus

Golubkina crater on Venus is 34 kilometres in diameter.
Studying the number and size of craters on Venus proves
that the surface of the planet is only 500 million years
old. Scientists believe that some kind of volcanic
catastrophe, 500 million years ago, spilled molten lava
across the entire surface of the planet destroying all
the older craters.