Download Venus is the brightest object in the sky except for the Sun and Moon

Venus passing in
front of the Sun
Venus is sometimes called the Earth’s twin planet. It is closest
to the Earth in size and mass, and is our nearest neighbour.
However, the resemblance ends there. Venus is the hottest
planet in the Solar System and its surface is an extremely
hostile environment. Its dense atmosphere is mainly
carbon dioxide and there are several thick layers of cloud
made of sulphuric acid. The atmosphere acts as a blanket,
trapping incoming solar radiation and generating an average
temperature of 464° Celsius – hot enough to melt lead!
Missions to study the Venusian atmosphere show that this
extreme greenhouse effect means there is little temperature
variation between night and day.
Venus
Venus is the brightest object in the sky except for the Sun
and Moon. The planet is often called the “morning star” or
“evening star” because it is visible at dawn and dusk.
Venus is named after the Roman goddess of beauty and
love. To the ancient Romans, Venus was the patron
goddess of vineyards and gardens – rather ironic,
given the planet’s scorched surface! As Greek
influence spread, Venus was attributed with the
characteristics of the goddess Aphrodite, whose
legendary beauty made her irresistible to gods
and mortals alike.
If you would like to know more about
the Venus Express mission, try the
following resources:
WORLD WIDE WEB SITES
www.esa.int/venus
www.uk2planets.org.uk
www.mssl.ucl.ac.uk/www_plasma/
missions/vex.html
www.nineplanets.org
www.esa.int/marsexpress
www.esa.int/rosetta
www.atm.ox.ac.uk/project/virtis
www.venus.wisc.edu
BOOKS
Venus Sir Patrick Moore
Cassell Illustrated, 2002
The Cambridge Photographic
Guide to the Planets
Frederic W Taylor
Cambridge University Press, 2001
Venus Revealed
David Grinspoon
Perseus Books, 1998
Empire of the Sun
John Gribbin and Simon Goodwin
Constable, 1998
IMAGES
Astrium (Mars Express)
NASA/JPL/MSSS (Mars)
NASA/JPL/Arizona State University
(Evidence of Flow)
ESA
NASA/JPL/AOPP (Venus)
Venus is the second planet from the Sun and, when it is
precisely aligned with the Earth, we can see it pass in front
of the Sun’s disk. These alignments are rare because the
orbital plane of Venus is slightly tilted relative to that of
the Earth. The Transit of Venus in 2004 was the first time in
121 years that the phenomenon had been visible. The next
transits are in 2012 and 2117. Historically, Transits
of Venus are important because they were used to calculate
the distance between the Earth and the Sun. The transit
of 1769 was the reason for Captain James Cook’s epic
voyage around the world which also led to a wide range of
discoveries about Australia, New Zealand and the islands
of the Pacific.
The Science and Technology Facilities
Council operates world-class, large-scale
research facilities; supports scientists and
engineers world-wide; funds researchers in
universities and provides strategic scientific
advice to government.
Venus Express is also closely related to the
comet chaser, Rosetta, and uses copies of its
detectors to study the Venusian magnetic field and
the chemical composition of the planet’s atmosphere.
The Council’s Science in Society unit offers a
wide range of support for teachers, scientists
and communicators to facilitate greater
engagement with STFC science which includes
astronomy, space science, particle physics and
nuclear physics:
For schools
• Free Publications and resource guides
suitable for teaching ages 10-18. Go to www.
scitech.ac.uk - Public and Schools - Schools
and Education - Resources
• Funding schemes for projects and school
visits. Go to www.scitech.ac.uk - Public and
Schools - Funding
• A Moon rock and meteorite loan
scheme. Go to www.scitech.ac.uk - Public and
Schools - Schools and Education - Loan Scheme
• Visits to STFC’s UK laboratories in
Cheshire, Oxfordshire and Edinburgh plus
CERN in Geneva. Go to www.scitech.ac.uk
- Public and Schools - Visits and Events
• Researchers in Residence. Teachers are
placed in partnership with young scientists who
have been trained to support the teacher, act as
role models and introduce their research.
Go to www.researchersinresidence.ac.uk
For scientists
• Communication and media training
courses; funding schemes and Fellowships
for public engagement. Go to www.scitech.
ac.uk - Public and Schools - Fellowships and
Communications Training
For further information telephone 01793
442175 or email [email protected]
Venus Express is the European Space Agency’s first
mission to Venus. The spacecraft shares more than a
speedy-sounding name with Red Planet explorer, Mars
Express. The basic structure of both spacecraft is
identical, as is much of the scientific instrumentation.
Venus Express uses copies of Mars Express sensors to
study the Venusian atmosphere at different altitudes,
monitor the plasma environment and to take images
of cloud patterns.
Air-pressures on Venus are also extreme, averaging 92
atmospheres. This is approximately the same pressure as
you would experience 1 kilometre beneath the sea surface
on Earth.
The Venusian atmosphere once contained large quantities
of water but it is now completely dry, unlike its twin planet.
Venus lies 41 million kilometres closer to the Sun than Earth
and is in a zone that’s too hot for water to last long. Mars is
78 million kilometres further away from the Sun than us and
has an average surface temperature of –50 degrees, so cold
that any water is locked away as ice. However the Earth is
positioned in what’s known, after the well-known fairytale,
as the “Goldilocks Zone”. Its distance from the Sun is just
right for water to exist in liquid form – probably a necessary
condition for life to evolve.
This sharing of
technology meant that
Venus Express could
be developed on a
rapid timescale that’s
unprecedented. Most
planetary missions are
developed over several
years but plans for Venus
Express were approved
at the end of 2002, just
three years before its
launch in late 2005.
Venus Express has been so successful that its original
mission, which was due to last 500 days, has been
doubled in length to 1000 days. It is due to finish in
May 2009. Venus spins very slowly – once every 243
days – this means that even with its extended mission,
Venus Express will have only orbited the planet for 4
Venusian days.
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Venus has a similar interior to Earth, with a partially molten
core, mantle and crust, so why does it not have a similar
magnetic field? It had one for a billion years, generated by
convection currents in the core, driven by left over heat after
Venus’s formation. When that energy ran out 3.5 billion years
ago, the field disappeared. This didn’t happen on Earth.
The reason for this is a mystery, but the lack of a magnetic
field means that Venus is unprotected from the Solar Wind.
This stream of electrically charged particles hits the upper
layers of Venus’s atmosphere, colliding with atoms and
molecules and carrying them into space.
UCL’s Mullard Space Science Laboratory and STFC’s Rutherford
Appleton Laboratory have helped develop the ASPERA-4
instrument which is investigating these interactions and
the rate at which atmospheric gases are stripped away.
Scientists from Imperial College London have helped build
the magnetometer that is studying the weak magnetic
effects produced where the Solar Wind meets the planet’s
atmosphere. Recent results from Venus Express show that
Earth and Venus started off with very similar atmospheres
suggesting that Venus was once a very wet planet; however,
water no longer exists on the surface and Venus continues to
get dryer as the Solar Wind and cosmic radiation strip away
hydrogen, oxygen and helium from the atmosphere much
faster than happens on Earth.
3D Perspective View of Maat Mons by Magellan Imaging Radar © JPL
d
Venus’s thick cloudy atmosphere means it is difficult to see
the surface using normal cameras. Between 1990 and 1994,
the Magellan spacecraft orbited Venus and used radar to
map the planet’s surface.
This showed two large continents and other highland
plateaux, separated by lowland areas where liquid may
once have flowed. There are four mountain ranges and
numerous volcanoes, plus areas of broken terrain called
“tessera” that suggest Venus’s surface is moving.
Venus has a complex atmosphere with distinct layers and
turbulent weather systems. There is a thick cloud layer
of sulphuric acid droplets concealing lower patchy cloud
cover, similar to cumulus clouds on Earth. Venus Express
is using infrared wavelengths to penetrate the outer layers
and map the whole atmosphere.
Clouds on Venus move at about 350 km/h and the whole
atmosphere rotates 60 times faster than the planet itself!
Venus Express is measuring atmospheric temperature
differences as air moves round the planet and through
different altitudes. It is also measuring concentrations of
sulphuric acid, sulphur dioxide and other chemicals.
VENUS’S ATMOSPHERE
Venus has a thick crust, which prevents continental drift,
so the cracking and buckling found must be caused by
different processes to the Earth’s plate tectonics.
96% CARBON DIOXIDE
Venus like Earth, shows relatively few impact craters,
which suggests its surface is “young” in geological terms
(around 500 million years old).
1% TRACE OTHER GASES
(Including sulphur dioxide and water vapour)
The VIRTIS instrument carried by Venus Express is
looking for evidence of volcanic activity by measuring
the concentrations of gases in the atmosphere and and is
trying to identify any volcanic hotspots.
Scientists from Oxford University have collaborated in
building an infra-red sensor, VIRTIS, to study the bottom
100km of the atmosphere – looking at the evolution and
movement of weather features.
3% NITROGEN
(a) A false colour mosaic of the Venusian
surface, composed from about 1000
individual Venus Monitoring Camera (VMC)
images taken in April and August 2007.
(b) This composite image of Venus is a combination
of ultraviolet images obtained by the Venus
Monitoring Camera (VMC) and infrared images obtained
by the Visual and Infrared Thermal Mapping Spectrometer (VIRTIS)
on board ESA’s Venus Express.
(c) Infrared views of south polar double-vortex
(d) While Earth has a planetary magnetic field, which can deviate the flow of solar
wind, Venus (and Mars) don’t. Gases in the upper atmospheres of these planets
are ionised, and can thus interact with the solar wind.
Previous missions have found giant vortices, like
hurricanes, funnelling air downwards at the poles.
The northern vortex appears to have a double ‘eye’
surrounded by much colder air. Scientists do not
understand why this occurs.