Venus Express: unexpected detail in first-ever Venus south pole images

Missioni robotiche concluse Venus Express
1

ESA News

13 April 2006

Unexpected detail in first-ever Venus south pole images

ESA’s Venus Express has returned the first-ever images of the hothouse
planet’s south pole from a distance of 206 452 kilometres, showing
surprisingly clear structures and unexpected detail. The images were taken
12 April during the spacecraft’s initial capture orbit after successful
arrival on 11 April 2006.

Engineers have lost no time in switching on several of the instruments and
yesterday the VMC (Venus Monitoring Camera) and VIRTIS (Visible and
Infrared Thermal Imaging Spectrometer) imaged, for the first time in space
history, the southern hemisphere of Venus as the spacecraft passed below
the planet in an elliptical arc.

Scientists are especially intrigued by the dark vortex shown almost
directly over the south pole, a previously suspected but until now
unconfirmed structure that corresponds to a similar cloud structure over
the north pole. “Just one day after arrival, we are already experiencing
the hot, dynamic environment of Venus,” said Dr Hakan Svedhem, Venus
Express project scientist. “We will see much more detail at an
unprecedented level as we get over 100 times better resolution as we get
closer to Venus, and we expect to see these spiral structures evolve very
quickly.”

The initial, low-quality images were taken from an extreme distance of 206
452 kms from the planet, yet caught scientists’ attention, particularly
with the surprisingly clear structures and unexpected details shown in the
VIRTIS spectrometer images.

The false-colour VIRTIS composite image shows Venus’s day side at left and
night side at right, and corresponds to a scale of 50 kms per pixel.

The day half is itself a composite of images taken via wavelength filters
and chiefly shows sunlight reflected from the tops of clouds, down to a
height of about 65 km above the planet’s surface.

The more spectacular night half, shown in reddish false colour, was taken
via an IR filter at a wavelength of 1.7 microns, and chiefly shows dynamic
spiral cloud structures in the lower atmosphere, around 55 km altitude.
The darker regions correspond to thicker cloud cover, while the brighter
regions correspond to thinner cloud cover, allowing hot thermal radiation
from lower down to be imaged.

The smaller VMC image shows Venus at a scale of 150 kms per pixel and is
also shown in false colour. It was recorded in ultraviolet.

Venus Express fired its main engine to enter Venus orbit on 11 April 2006
and is now in the first 9-day capture orbit taking it to apocentre
(maximum height) at 350 000 kilometres below the south pole. It will swing
back up to pass pericentre (minimum height) at an altitude of 250
kilometres over the planet’s north pole.

Towards the 24-hour final orbit

In the first capture orbit, Venus Express will have 5 additional
opportunities for gathering data until reaching pericentre. These
observations represent a great opportunity because, at apocentre, the full
disc of Venus is fully visible for the spacecraft’s imagers. Such
opportunities will not occur again during the nominal mission, starting on
4 June 2006, when the range of distances from the planet will be much
smaller.

In addition to VMC and VIRTIS, the spacecraft’s MAG (Venus Express
Magnetometer) has been switched on for initial verification and is
operating nominally. Together with the ASPERA (Analyser of Space Plasma
and Energetic Atoms), the two instruments are expected to gather
information about the unperturbed solar wind and the atmospheric escape
processes on Venus, a planet with no magnetic protection.

A series of further engine and thruster burns are planned to gradually
reduce the apocentre during the following 16 orbital loops around the
planet and the spacecraft is due to attain its final 24-hour polar orbit
on 7 May, ranging from 66 000 to 250 kilometres above Venus.

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IMAGE CAPTIONS:

[Image 1:
http://www.esa.int/esaCP/SEM9FZNFGLE_index_1.html]
Composite, false-colour view of Venus south pole captured by VIRTIS 12
April 2006 onboard Venus Express.

Credits: ESA/INAF-IASF, Rome, Italy, and Observatoire de Paris, France

[Image 2:
http://www.esa.int/esaCP/SEM9FZNFGLE_index_1.html#subhead3]
False-colour view imaged in ultraviolet of Venus south pole captured by
VMC 12 April 2006 onboard Venus Express.

Credits: ESA/MPS, Katlenburg-Lindau, Germany

[Image 3:
http://www.esa.int/esaCP/SEM9FZNFGLE_index_1.html#subhead5]
View imaged in ultraviolet of Venus south pole captured by VMC 12 April
2006 onboard Venus Express.

Credits: ESA/MPS, Katlenburg-Lindau, Germany