Has Orbited "Earth's Twin" For Over 500 Days
The European Space Agency noted last
week its Venus Express has now orbited Earth's twin for over 500
Earth days, completing as many orbits. While the satellite
maintains steady and excellent performance, the planet continues to
surprise and amaze the agency.
"In spite of experiencing a challenging environment, Venus
Express is in an excellent condition," ESA tells ANN. "It receives
four times the amount of solar radiation as compared to its sister
spacecraft, Mars Express, but modifications to the spacecraft
design have worked just as intended and operation has been very
stable.
"Many different activities transpire on board with each orbit:
instruments are switched on and off, they change modes and targets
and the spacecraft checks out and monitors its subsystems more or
less continuously. The few anomalies that occurred were quickly
resolved by vigilant spacecraft controllers.
"On 18 August, Venus was at the shortest distance from Earth,"
the agency notes. "The planet was also aligned with Earth and the
Sun. Given the short distance, all instruments worked at full speed
and the communication system at its maximum. Back on Earth, data
was downloaded without difficulty."
The situation is very different from when Venus is on the far
side of the Sun. Due to the large distance, the rate at which data
can be downloaded plummets to 22 kbps, a tenth of the maximum. At
such times, competition between the instruments can be quite tough.
Despite this, an impressive amount of data - about 1 Terabits, or
one million million bits - has been transmitted to Earth over the
first 500 days.
"The scientists analysing the data have a challenging but
exciting task ahead," said Hakan Svedhem, Venus Express Project
Scientist.
Right on both counts. Scientists will have to archive the data
and extract the most important detail from an immense collection of
images, spectra and profiles of temperature, pressure and chemical
composition.
Some of the first detailed analyses are now being completed, ESA
notes, and will soon be published in acclaimed scientific
journals.
Among many other findings that have surprised scientists, Venus'
atmosphere seems extremely fickle. Recent observations with the
Visible and Near-Infrared Mapping Spectrometer (VIRTIS), have shown
that Venus' atmospheric structure changes quite rapidly, from day
to day.
Giuseppe Piccioni, co-Principal Investigator for VIRTIS on board
Venus Express says, "It seems that the mid latitudes form a sort of
transition region with mostly laminar flow. Moving equatorward,
there is more convective flow in the atmosphere, whereas the polar
region is dominated by huge vortices."
The meteorology of the planet, including its deep atmosphere is
highly variable. "Although the configuration of the flow is
similar, the intensity of turbulence changes significantly from one
orbit to the next," adds Pierre Drossart, co-Principal Investigator
for VIRTIS.
The polar region or the 'black hole' seen in the images is where
the polar dipole dominates. The polar dipole is the name given to a
giant double-vortex, each of which is about 2000 km across, similar
to the eye of a hurricane. The double-vortex has been seen at both,
the north and south poles, rotating in opposite directions
(clockwise at the north pole and counter-clockwise at the south
pole). Observations with Venus Express show that the vortex at the
south pole also changes its shape rapidly, from one orbit to the
next.