The Morning Star
Among the tiny points of light that bejewel the firmament, the most
resplendent of all shines brightly at the dawning of a new day or at twilight as
the Sun goes down. It is the planet Venus named after the Goddess of
Love. It is often wrongly referred to as 'the morning star' or 'the evening star'.
Apart from the Moon, it is the nearest planetary body to us, in yet
before the coming of the space age we knew almost nothing about it.
It was constantly enshrouded in clouds and remained an enigma clothed
with romantic imaginations.
During the early years of the twentieth century, since it was
known to be only very slightly smaller that our own world, it was thought of as Earth's
twin. It became a favourite
fantasy to think that the conditions on Venus may be very like those on the
Earth. Many people including some scientists envisaged a place full of warm oceans
and tropical rainforests, garlanded by brilliant flowers and inhabited by a
fascinating fauna of strange animals that would keep biologists busy for
centuries when we began to colonise our neighbour world.
With the coming of the space probes, the romantic dream of a
lush tropical planet teeming with life was destroyed
Unlike the beautiful woman, after
which our neighbour world is named, Venus was found to be ugly and horrible beyond
our most hideous nightmares. The space probes sent to the planet by Russia and the United
States with their sophisticated instrumentation, between 1961 and 1989 unmasked the mystery of what really lies beneath the canopy of
clouds. Apart from size, Venus and Earth are as different as any two worlds could be.
Apart from the conditions on the planet there is the great mystery as to why
Venus rotates in the opposite way to the other planets and why it rotates so
slowly that its day is even longer than its year. Venus orbits the Sun in
approximately 225 Earth days and rotates on its axis once in 243 Earth days.
Perhaps shortly after its formation or perhaps during the period of the late
bombardments (see web page on this subject) it underwent a catastrophic
Earth's twin planet', which shines like a beautiful jewel in the early
morning sky, is the nearest thing to hell in the Solar System. The clouds that
concealed the true nature of the planet for so long, are composed of
sulphuric acid. Beneath the upper cloud level there is a haze
layer. Among other substances it are droplets of liquid or solid sulphur, sulphur dioxide and fluoro-sulphuric acid one of the most corrosive
substances known to science.
About 30 kilometres above the surface, the atmosphere becomes surprisingly
clear and, during the venusian 'day-time', the sinister orange light that penetrates through the clouds is
remarkably brilliant. At the surface a suffocating atmosphere, which is composed
mostly of carbon dioxide with relatively minor amounts of nitrogen and a
cocktail of toxic trace compounds, bears down upon the barren rocks at a mean pressure
of ninety-two atmospheres. The temperature on the surface varies with altitude
but its mean value is 470 degrees Celsius, which is more than enough to melt lead.
The two illustrations below based on NASA Radar results convey some idea of the
terrible nature of the surface of Venus. Welcome to Dante's Inferno!
On the left is the volcano called Maat Mons and on the right are three
volcanic calderas. Courtesy NASA Magellan Mission
The Message of the Space Probes
Since the early years of the 1960s, extensive missions to Venus have been undertaken by Russian and American space scientists and engineers.
The Russians achieved spectacular success in landing spacecraft on one of the most inhospitable
environments in the Solar System. They managed to obtain analytical data on the rocks and the atmospheric conditions at the
surface and even obtained photographs taken from the cameras of the landers before the high
temperatures and pressures destroyed the space probes.
The Flight of the Magellan
To the scientists and engineers of NASA we owe the incredibly thorough radar
survey by the Magellan spacecraft which has enabled a map of almost the whole
surface to be produced.
The globe shown below is the result of radar mapping by the Magellan Mission
to Venus Credit for illustration NASA/JPL
In May 1989, a spacecraft was launched from the space shuttle Atlantis. The
mission was named after the famous Portuguese explorer Ferdinand Magellan who sailed
round the world from 1505 to 1521 and whose name was given to the Magellanic Clouds,
the two small satellite galaxies that orbit the Milky Way. The task of the Magellan was to map the planet by radar from above the clouds. On 15 September 1990, the spacecraft began
scanning the surface of Venus. For two years, it systematically surveyed 99% of the
It emitted thousands of radio pulses per second, which penetrated the clouds, and from
the radar reflections, a picture of the Venusian surface was built up.
It took altimetric measurements and measured the heights of the landforms.
It collected radiometric data and provided geochemists with a global survey of the surface chemistry. In addition, it carried out
measurements of the surface gravities across the globe.
From the data obtained from the radar mapping and gravity mapping a detailed picture of the landscape of
Venus was obtained. The data showed that we were looking at a young planetary surface and that
there seemed to be very few rocks that were earlier than 500 million years old.
Many geologists think that there was a period of enormous volcanic activity, which occurred
between 300-500 million years ago. It is uncertain whether or not there
are any volcanoes actually active at the present time. This is one of the
things that the European Space Agency's Mission called Venus Express is looking
for at the present time (January 2007)
The globe on the right shows the topography of Venus as
measured by the instruments on board the Magellan Space Craft . Courtesy
NASA/JPL and the US Geological Survey
Some of the volcanoes resemble those in Hawaii but others show formations very different to Earth and are, among the planets in the Solar
System, unique to Venus. Unlike the Earth plate tectonics does not seem to operate on the planet, and
the Venusian Crust seems to consist of one single plate.
It appears that for plate tectonics to operate water or water containing minerals need to be present in the rocks.
If in the dim and distant past Venus did have surface water and hydrated minerals, it may also
have operated a plate tectonic system. However, since the surface of the planet is only
300-500 million years old, all signs of its earlier history have been lost. It is as if the geological clock had been reset half a billion years ago and little is known of the planet's history
before that time. Very little is really known about the surface chemistry and mineralogy and
the collection of rock samples to bring back to Earth is
many orders of difficulty greater than the collection of such samples from the Moon or even Mars. It appears that the
surface mainly consists of volcanic basalts. Because of the vastly different conditions between the Earth and Venus, the planet may well be the home of an unusual mineralogy
The surface area of Venus is 460,300,000 square kilometres which is
slightly less than that of the Earth. The total surface area including the hydrosphere of
the Earth is 511,200,00 square kilometre with a land area of 149,800,000 square
Topography of Venus
The map shown below shows that there are two large areas of highland
'continents' on the planet
named Ishtar Terra fairly close to the North Pole and Aphrodite Terra in
the southern Hemisphere. On Ishtar terra is the highest mountain range.
The tallest peak is Maxwell Montes. It is the only place on Venus with a
masculine name and is named after James Clerk Maxwell the famous physicist.
All other places on Venus have been given feminine names
Credit Davison E. Soper, Institute of Theoretical Science, University of
Oregon, Eugene OR 97403 USA
firstname.lastname@example.org based on the results from the Magellan Mission.
This map shows the surface of Venus as captured in altimeter topography data
from the Magellan spacecraft during its first three 8-month cycles in orbit
around the planet. The map is displayed in Mercator projection. Areas not mapped
by Magellan are shown in grey, filled with data from the altimeter on the
earlier Pioneer Venus spacecraft. Areas mapped by Magellan are color-coded, with
red marking the highest areas such as Maxwell Mons and Maat Mons, and blue
marking the lowest areas. Synthetic "shadowing" has also been added to enhance
the visibility of features. The Jet Propulsion Laboratory manages the Magellan
mission for NASA's Office of Space Science and Applications
Chasma is the lowest point on the planet. It is a zone of narrow mountain
and canyon pairs in the western part of the continent of Aphrodite Terra.
It extends over 1000 kilometers in length. The northern arm of Diana
Chasma has a mountain range that rises 3.25 kilometers above the plateau whilst
the canyon drops down to 3.5 kilometers below the level of the plateau to the
lowest point on the planet. There is a sharp drop of 7 kilometers across
the northern part of the canyon. This kind of steep height change is not
possible on Earth . The strength of the rocks on Venus is much higher
than those on Earth allowing geological features like Diana Chasma to exist for
longer periods of time
The Atmospheres of Earth and Venus Compared.
Carbon dioxide content. On Venus most of the atmosphere consists of 'gaseous'carbon
dioxide. The pressures and temperatures of the 'gas' are so high that it is really in the form of a
supercritical fluid. Thus the atmosphere is more like a vast ocean of CO2
On Earth most of the carbon dioxide is either dissolved in water, or
incorporated into carbonate rocks. In addition, considerable amounts of
carbon are bound in living organisms, both in the shells of sea creatures and in
other ways. The actual mass of carbon on Venus is probably fairly comparable to
the mass of carbon on Earth.
Because the carbon dioxide molecule absorbs strongly in the infrared it
prevents much of the heat received from the Sun leaving the planet and is the main
cause of the maintenance of the intensely high temperatures on the planet.
Nitrogen Content. There is a common misconception that the Earth's atmosphere is far richer in
nitrogen than that of Venus. In actual fact, as a table of partial pressures
will show the pressure due to
nitrogen in the atmosphere of Venus is over three times as great as its
pressure on Earth. Even allowing for the very high temperatures it would be higher even at the
atmospheric temperatures on Earth.
The actual mass of nitrogen on the two planets is probably comparable since
on Earth since a great deal of nitrogen is dissolved in the oceans and is present in the
form of biological compounds.
Water The investigations made by the space missions to Venus have revealed a great
deal of information about its present state and posed many questions about its past
Some of the questions as to why the twin planets evolved so differently have been
tentatively answered from the interpretation of the data received from the space
missions-the most important factor of all is the question of water.
One of the In the early days of the Solar System in all the inner planets there was a
period of violent volcanic activity in which large quantities of steam, carbon dioxide,
nitrogen and other gases were given off. It is believed that on Venus, Earth and
Mars carbon dioxide, nitrogen and water vapour predominated in the early atmospheres.
The early Solar System was a very violent place and the planets were very hot so that much of the
volatile matter was lost after the first stages of degassing.
Apart from heat produced as a result of catastrophic collisions there was about ten times as much radioactivity in those days as
there is at the present time.
All the inner planets were constantly being bombarded by asteroids and comets.
The comets brought with them a large quantity of volatiles including water as a major constituent.
Together with the original water from the planet itself this cometary water certainly resulted on oceans being produced on Earth and almost certainly on Mars. It is moreover
possible that seas and oceans were also formed on Venus. The Sun's radiation was
about thirty percent lower in the early times of the Solar System's history so
Venus could well have been in the habitable zone for a short time. However
the general opinion among Venus scientists is that it probably lost its water by
a runaway greenhouse effect fairly early on before life could start to develop.
Current evidence suggests, although it is not yet completely certain, that
Venus was at one time an Earth-like planet. It is surmised that as the Sun grew hotter the temperature rose and the seas grew
warmer. The air grew more humid and the atmospheric water vapour pressure rose. Water vapour is a
powerful greenhouse gas and more and more of the Sun's heat was trapped.
Positive feedback caused the temperature to rocket. Dissolved carbon dioxide was released and contributed further to the heating effect. The runaway greenhouse was in 'full flight' and had taken over the planet. The oceans boiled, any
carbonate rocks decomposed leaving a suffocating atmosphere of steam and carbon dioxide.
Because of the large amount of H2O in the form of gas well above the boiling point, the
pressure and temperature would have even been higher than they are at the present time.
Under the ultra-violet radiation of the Sun, the water molecules would have
split into hydrogen atoms and hydroxyl radicals in the upper atmosphere of the planet by
a process called photo-dissociation or PHOTOLYSIS
H2O + ultraviolet radiation = H atoms
+ OH (hydroxyl radicals) The hydrogen atoms escape into
interplanetary space and the hydroxyl radicals react to give water and oxygen
The gravitational pull of Venus can prevent most gases from being lost to
space. However, hydrogen is the lightest gas of all and, because of the high speed at which
atoms and molecules of hydrogen travel, there would have always been a small fraction
of them that would have reached escape velocity.
Thus, over the very long periods of geological time Venus would have lost most of its water by the evaporation of hydrogen into
interplanetary space. At first sight it may seem that oxygen would not
evaporate. However another factor comes into play. Unlike the Earth,
Venus does not have a magnetic field and current evidence suggests that
considerable oxygen as well as hydrogen is lost as O+ ions due to the action of the
fierce solar wind since unlike Earth the atmosphere of Venus is not protected by
The other possible scenario is that the water produced by outgasing from the
hydrated minerals of the early rocks of Venus and cometary water
that landed on Venus never property condensed. In such an event the greenhouse
effect due to the steam would have been so high as to prevent the condensation of H2O
into the liquid phase and no oceans would have formed even in the very early
Whichever theory is true, it is a sobering thought that had Venus been just a
little further out from the Sun or had the Sun been just a little less hot it may
well have been a second Earth. Even more sobering is the fact that had Earth been just a
little nearer the Sun or had the Sun been just a little hotter it would have been a second Venus and
we would not be here. The balance may be very fine and it may only take very small changes to
trigger off the development of Venusian conditions on Earth.
The present amounts of water are low in the Venusian atmosphere although
water is still present. Its actual value may vary at different altitudes
and different localities.
Even at the low values of between 2 X 10-5 to 5 X 10-4 mole fractions, the
amounts are still considerable.
One of the strongest supports for the theory that Venus once had considerable
quantities of water rests on isotopic evidence.
Deuterium is a rare but stable isotope of hydrogen. It combines with oxygen
to give D2O or heavy water. (Because of its rarity most naturally occurring water molecules containing deuterium will in fact be DHO).
Since the deuterium atom is about twice as massive as hydrogen it would be far less easily lost to space and would thus
evaporate more slowly.
the relative amounts of deuterium were found to be appreciably
higher than hydrogen this would be clear evidence that there was much more water on Venus
in past epochs.
During the Pioneer space missions, orbiting spacecraft measured the amounts
of deuterium and hydrogen in the upper atmosphere of Venus. Water on Earth has
about 10,000 atoms of hydrogen to one atom of its heavy isotope, deuterium. The ratio
of deuterium to the tiny amounts of normal hydrogen revealed that Venus is in fact enriched in
the heavier isotope by more than 150 times compared to the Earth. Its presence in such
relatively much larger amounts suggests that there were in fact considerable quantities
of water on Venus at one time.
Surface Landings by Soviet Landers
From the mid-1970s into
the early 1980s, the former Soviet Union succeeded in landing automated craft on
the hellish surface of cloud-veiled Venus. The Soviet
exploration of Venus, from 1961 to 1984, was an
impressive effort that put to the test the
fundamentals of interplanetary spacecraft design
and remote sensing. Successful Soviet missions
to Venus included 3 atmospheric probes, 10
landings, 4 orbiters, 11 flybys or impacts, and
2 balloon probes of the clouds.
Decades later, imagery produced by several of
the Soviet Venera series of craft have undergone
reprocessing by an imaging specialist, yielding
a clearer, crisper look at the eerie-looking
landscape. Donald Mitchell, a former image
specialist for AT&T Bell Labs, has utilized new
techniques on original telemetry broadcast from
Soviet Venus lander craft. Hyperlinks are
given at the end of this chapter to web-sites
detailing the work of Donald Mitchell.
In one excellent
web-site Mitchell includes the biographical
details of many of the top scientist and
engineers involved in the work carried out on
Details are given below of the last two
landers the last two lander/orbiters Venera 13 and Venera 14 sent to Venus in
The two pictures above show the lander on the left and the orbiter on the
left. Credit NASA NSSDC. For questions about this
mission, please contact: Dr. David R. Williams NASA Goddard Space Flight
Center, Greenbelt, MD 20771
Venera 13 and 14 were identical spacecraft built to take advantage of the
1981 Venus launch opportunity and launched 5 days apart. The missions consisted
of a bus and an attached lander . In each case the lander was a hermetically
sealed pressure vessel, which contained most of the instrumentation and
electronics, mounted on a ring-shaped landing platform and topped by an antenna.
The lander carried instruments to take chemical and isotopic measurements,
monitor the spectrum of scattered sunlight, and record electric discharges
during its descent phase through the Venusian atmosphere. The spacecraft
utilized a camera system, an X-ray fluorescence spectrometer, a screw drill and
surface sampler, a dynamic penetrometer, and a seismometer to conduct
investigations on the surface.
After launch and a four month cruise to Venus, the Venera 13 descent vehicle
separated from the bus and plunged into the Venus atmosphere on 1 March 1982.
After entering the atmosphere a parachute was deployed. At an altitude of 47 km
the parachute was released and simple airbraking was used the rest of the way to
the surface. Venera 13 landed about 950 km northeast of Venera 14 at 7 deg 30
min S, 303 E, just east of the eastern extension of an elevated region known as
After landing an imaging panorama was started and a mechanical drilling
arm reached to the surface and obtained a sample, which was deposited in a
hermetically sealed chamber, maintained at 30 degrees C and a pressure of about
.05 atmospheres. The composition of the sample was determined by the X-ray
The lander survived for 127 minutes (the planned design life was 32
minutes) in an environment with a temperature of 457 degrees C and a pressure of
84 Earth atmospheres. The descent vehicle transmitted data to the orbiter which
acted as a data relay as it flew by Venus. This basic operation was
carried out years later when the Huygens probe transmitted its data to the main
Cassini spacecraft (see web-site section on Titan).
The Venera 14 lander plunged into the Venus atmosphere on 5 March 1982. After
entering the atmosphere a parachute was deployed. At an altitude of
about 50 kilometers the parachute was released and simple airbraking was
used for the rest of the way to the surface. Venera 14 landed about 950 km
southwest of Venera 13 near the eastern flank of Phoebe Regio at 13 deg 15 min S
by 310 E on a basaltic plain. The lander survived for 57 minutes (the
planned design life was 32 minutes) in an environment with a temperature of 465
degrees C and a pressure of 94 Earth atmospheres. As with Venera 13, the descent
vehicle transmitted data to the orbiter, which acted as a data relay as it flew
Venera 13 Lander image of the surface of Venus at 7.5 S, 303.
E, east of Phoebe Regio. Venera 13 survived on the surface for 2 hours, 7
minutes, long enough to obtain 14 images on 1 March, 1982. This color 170 degree
panorama was produced using dark blue, green and red filters and has a
resolution of 4 to 5 min. Part of the spacecraft is at the bottom of the image.
Flat rock slabs and soil are visible. The true color is difficult to judge
because the Venusian atmosphere filters out blue light. The surface composition
is similar to terrestrial basalt. On the ground in foreground is a camera lens
cover. (Venera 13 Lander, VG00261,262) . Credit NASA
Venera 14 Black and White images Courtesy
The Vega Balloon Missions
first, and so far only, planetary balloon missions were
performed by the Space Research Institute of the Soviet Academy
of Sciences in cooperation with the French Space Agency CNES in
1985. A small balloon, similar in appearance to Earthly weather
balloons, was carried on each of the two Soviet Vega Venus
Missions and were launched in 1984.
Credit NASA NSSDC
first balloon was inserted into the atmosphere of Venus on 11
June 1985 followed by the second balloon on 15 June 1985
The first balloon failed after only 56 minutes, but the second
operated for a little under two Earth days until its batteries
included both a balloon and a lander The UV spectrometer, the mass
spectrograph, and the pressure- and temperature-measuring instruments were
developed in cooperation between French and Soviet investigators. Data collected
by the instruments were transmitted to the Vega 2 spacecraft and relayed to
The primary scientific objective of the Vega balloon probes
was to obtain information about the large- and small-scale motions, structure,
and cloud properties of the Venus atmosphere at the float altitude. The probes
floated at an altitude of about 54 km in the middle, most active layer of the
Venus three-tiered cloud system and measured the local atmospheric dynamics,
pressure, temperature, lightning, illumination levels, and cloud properties over
a period of about 46 hours in both the night- and day-side.
Twenty ground stations were used for Very Long Baseline
Interferometry (VLBI) tracking of the balloons. Six of these stations were on
Soviet territory and were coordinated by IKI, the Soviet space agency. The other
fourteen antennas were coordinated by CNES (France) and included three NASA Deep
Space Network antennas and eleven radio astronomy observatories.
The Vega 2 Lander/Balloon capsule entered the Venus
atmosphere (125 km altitude) at 2:06:04 UT (Earth received time; Moscow time
5:06:04 a.m.) on 15 June 1985 at roughly 11 km/sec.
On 9 November 2005 the European Space Agency's
first probe to Venus was launched from the Baikonur Cosmodrome in Kazakhstan.
On 11 April 2006 the probe was inserted into an orbit round the planet.
This phase of the operation is very challenging. The spacecraft's main engine
burns for about 50 minutes, to reduce its speed with respect to Venus to allow
the spacecraft to be captured by the planet's gravitation. Illustration of
lift-off shows the Soyuz-Frigate carrying Venus. Credit ESA/STARSEM-S.CORVAJA.
The illustration of the orbital insertion is an artist's impression Credit ESA -
The Venus Express
spacecraft, on mission around Venus, is a virtual twin of Mars Express, but
adapted to survive the harsh environment around this planet.
Venus Express Probe in Intespace
facility Credits ESA - J.L.Atteleyn
ESA's Venus Express probe during
testing in February 2005.
Venus Express, ESA's first mission
to Earth's nearest planetary neighbour, Venus. It was launched from Baikonur
a top a Soyuz-Fregat vehicle on 9 November 2005 and arrive around the planet
on 11 April 2006. The mission is due to last for two Venusian days, i.e.
about 500 Earth days.
The probe's payload comprises a
combination of spectrometers, spectro-imagers and imagers covering a
wavelength range from ultraviolet to thermal infrared, a plasma analyser and
a magnetometer to study the atmosphere, plasma environment and surface of
Venus in great detail.
With its set of
state-of-the art instruments for planetary investigations, mostly inherited
by the Mars Express and Rosetta mission, Venus Express is designed to make
unprecedented studies of the largely unknown phenomena taking place in the
Venusian atmosphere. It will also investigate the interaction between the
solar wind and the planetary environment and will gather glimpses about the
planet's surface, and its relationship to the dense atmosphere.
Volcanic activity on
Venus? Credits ESA - AOES Medialab
This image is an artistic interpretation of a
possible volcano on Venus. In fact, from previous missions to the planet, Venus
appears to be among the most geologically active planets in the solar system.
Venus Express is able to detect gaseous markers in the lower layers of the
atmosphere and variations in its temperature, possible signs of volcanic
activity. Local variations in atmospheric temperature and pressure may also
indicate the presence of seismic activity.
Quoting the ESA web-site
"In the most comprehensive study of the
Venusian atmosphere ever, Venus Express will address many open questions
- How do the complex global dynamics of the planet work?
- What causes the super-fast atmospheric rotation and the hurricane-force
- What maintains the double atmospheric vortex at the poles?
- How does the cloud system work?
- How do clouds and haze form and evolve at different altitudes?
- What is at the origin of mysterious ultraviolet marks at the clouds tops?
- What processes govern the chemical state of the
- What role does the ‘green-house effect’ play in the
global evolution of the Venusian climate?
- What governs the escape processes of the atmosphere?
- Are there water, carbon dioxide or sulphuric acid cycles
- What caused the global volcanic resurfacing of Venus 500
million years ago?
- Why are some areas on the surface so reflective to radar?
- Is there present volcanic or seismic activity on the
Analyser of Space Plasma and Energetic Atoms
Led by Institute of Space Physics, Kiruna, Sweden
= Venus Express magnetometer
Led by IWF, Graz, Austria
= Planetary Fourier Spectrometer
Led by IFSI-INAF, Rome, Italy
SPICAV/SOIR = Ultraviolet and Infrared Spectrometer
Led by CNRS,France Inst for Space Aeronomy, Belgium; IKI, Russia
= Venus Radio Science Experiment
Led by Univ. der Bunderswehr, Munich, Germany
Ultraviolet/Visible/Near Infrared Mapping Spectrometer Led
by CNR-IASF, Rome, Italy, and Observatoire de Paris, France
= Venus Monitoring Camera
Led by MPS, Katlenburg-Lindau, Germany
Loss of atmosphere
Artist's view of
Venus a planet with no magnetic field. Credits ESA - C.Carreau
As shown in this artist's impression, Venus is
a planet with no intrinsic magnetic field and so, differently from Earth, it has
no shield to protect it from the continuous attack of the capricious and violent
solar wind. ESA's Venus Express will study how much of the atmosphere of the
planet escaped under the bombardment of the solar wind and how much it combined
with the surface material.
Components of the Atmosphere In particular
ASPERA will inestigate the interaction between the Solar Wind and the Atmosphere
and the escape of molecules and ions such as O+ H+ and He+
and He++ The Mullard Laboratory in Holmbury St Mary
near Dorking in Surrey England is particularly involved in these investigations.
Venus has no magnetic field of its own
and any field is due to the interaction of the Solar Wind on the atmosphere The
Magnetometer will thus also be involved in the escape of components of the
atmosphere and the effect of the solar wind.
The Planetary Fourier Spectrometer
will be able to measure the temperature of
the atmosphere between altitudes of 55–100 kilometres at a very high resolution.
It will also be able to measure the surface temperature and therefore be able to
search for volcanic activity. In addition to its temperature measurements, PFS
will be able to make composition measurements of the atmosphere.
VIRTIS will be able to study the
composition of the lower atmosphere between 40 kilometres altitude and the
surface. It will track the clouds in both ultraviolet and infrared wavelengths
and allow scientists to study atmospheric dynamics at different altitudes.
The temperature maps of the Venusian surface
shown in this image were built thanks to direct measurements obtained by Venus
Express’ VIRTIS instruments (left), compared with surface temperature
predictions based on the Magellan topographic data obtained in the early 1990s
(right). VIRTIS gathered the data combined into this
mosaic on 10 August 2006, during a single orbit (orbit 112). The spacecraft was
flying over the Themis and Phoebe Regiones in the southern hemisphere of Venus.
Themis Regio is a highland plateau located on the 270º East meridian and at
about 37º South latitude.
This is a region that has experienced strong
volcanic activity in the past, and possibly still does today. The Phoebe
Regio is a highland region of Venus (such regions are called 'tesserae'), where
most of the Soviet Venera probes landed.
Large highland regions are clearly visible, as
well as single volcanic structures such the Mielikki Mons, in the centre of the
mosaic. On the south-eastern part of the mosaic VIRTIS covered a region for
which Magellan maps are not available.
SPICAV assists in the
analysis of Venus’s atmosphere. In particular, it will search for the small
quantities of water expected to exist in the Venusian atmosphere. It will also
look for sulphur compounds and molecular oxygen in the atmosphere. It will
determine the density and temperature of the atmosphere at 80–180 kilometres
VeRa uses the powerful
radio link between the spacecraft and Earth to investigate the conditions
prevalent in the ionosphere of Venus. Scientists will also use it to study the
density, temperature, and pressure of the atmosphere from 35–40 km up to 100 km
from the surface, and to determine roughness and electrical properties of the
surface. It will also allow investigations of the conditions of the solar wind
in the inner part of the Solar System.
Mineralogy of Venus
The types of minerals on the surface of Venus
differ in different localities. In particular the stable minerals
vary according to the altitude.
An example of this is the work carried out
by three scientists at the Harvard for Astrophysics at Cambridge Massachusetts.
Klose, Wood and Hashimoto published a paper in the Journal of Geophysical
Research in 1992 (JOURNAL OF GEOPHYSICAL RESEARCH,
VOL. 97, NO. E10, PAGES 16,353–16,369, 1992) in which they outlined the
relationship between altitude and microwave emissivity as deduced from
measurements made by the Magellan spacecraft. A study of ten highland
regions found that above a critical altitude which ranges from 4.75
km on Maxwell Montes to 2.49 km on Sapas Mons, the emissivity undergoes an
abrupt decrease. They explain this by the theory that the electrical
semiconductor iron pyrites FeS2 is the stable form of iron mineral whereas below
this altitude iron occurs as the oxide magnetite. Work has even been
carried out on a mineral called tremolite to see if hydrated minerals can still
exist on the planet pointing to a time where liquid water was present on the
planet. These sort of observations illustrate how it is possible using modern
instrumentation aboard space probes to learn about the minerals on a planetary
surface without even going down to that surface. Venus Express is also
carrying out research into the nature of the Venusian Surface. It may well
be that evidence about the past as well as the present of Venus may be unearthed
by the clever use of space probes.