Venus Express Frequently Asked Questions (FAQs)

• How do the complex global dynamics of the planet work?
  - What causes the super-fast atmospheric rotation and the hurricane-force winds?
  - 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 atmosphere?

• 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 on Venus?

• 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 planet?

• Why Venus rotates backwards and so slowly, just one revolution every 243 Earth days?

• Why is the planet’s magnetic field so weak?

If their atmospheres were very similar in the beginning, then obviously something changed on Earth or on Venus, but we do not know what or when. Moreover, the 'greenhouse effect' alone cannot account for today's extreme conditions on Venus.

Most importantly, the combined knowledge of structures, chemistry and dynamics of planetary atmospheres, such as Venus, Mars and Titan, will help in better understanding Earth's atmosphere and improving our climate models.

It is hoped it will also achieve several other 'firsts', such as:

• First global monitoring of composition of lower atmosphere in near-infrared transparency ‘windows’;

• First coherent study of atmospheric temperature and dynamics at different levels of atmosphere, from surface up to ~200 km;

• First measurements from orbit of global surface temperature distribution;

• First study of middle and upper atmosphere dynamics from oxygen (atomic and molecular), and nitrogen oxide emissions;

• First measurements of non-thermal atmospheric escape;

• First coherent observations of Venus in spectral range from ultraviolet to thermal infrared;

• First application of solar/stellar occultation* technique at Venus;

• First use of 3D ion mass analyser, high-energy resolution electron spectrometer and energetic neutral atom imager;

• First sounding of Venusian top-side ionospheric structure.

Also the experience of ongoing operations on Mars Express are passed on to the Venus Express teams to determine their applicability to the Venus Express design and the future operations. In some cases, software modifications added to Mars Express after launch to improve the spacecraft functioning have already been applied to Venus Express.

Where Mars Express had about 10 thermal control zones, Venus Express has four times more to ensure the best working environment for the instruments. While Mars Express was wrapped into a black thermal insulation to retain some heat in the coldness of the outer Solar System, Venus Express bears 27 layers of kapton insulation with a shiny golden upper cover to evacuate as much thermal radiation as possible.

The solar arrays had to be redesigned too. They extend only half of the span of those on Mars Express despite the fact that their size was actually not dictated by the conditions upon arrival at Venus but at departure from Earth, where the solar flux is halved compared to Venus but nearly the double of its level at Mars.

To withstand the high thermal stress of continual pointing toward the Sun while around Venus, which could lead to thermal peaks at 250°C, the solar cells are arranged alternately with lines of tiny radiating mirrors to evacuate the excess heat. The backside of the arrays has also been protected against the reflection of the solar flux by the Venusian atmosphere.

The antenna system also had to be redesigned as the behaviour of Earth in the Venusian sky is very different from what it is as seen from Mars. For a probe orbiting the Red Planet, Earth is an inner planet and it appears always within 40° of the Sun.

This enables a rather simple pointing of both the solar arrays and the antenna in nearly the same direction. As seen from Venus, Earth is an outer planet, which can be in any direction relative to the Sun. To enable communications in any configuration, a second antenna (directly taken from the Rosetta project) was added on top of Venus Express, pointed in opposite direction to the high-gain antenna.

The payload has also been changed, as it includes only three instruments derived from those flown on Mars Express. The other four are either derived from instruments flown on Rosetta or new developments.