This is the second of our articles about the recent achievements of the European Space Agency. Since 2003, the ESA has launched three similar missions: the Mars Express probe in June 2003, the Rosetta comet mission in March 2004 and the Venus Express mission in November 2005. Last week, we took a look at Mars Express, which has provided us with stunning pictures and science from the red planet. In this article, we will look at Venus Express, which has been equally successful in sending back data on that planet. Next week, we will discuss the Rosetta comet mission.
These three missions are really just variations on the same theme. The probes themselves are very similar to each other, using many of the same kinds of equipment and ground facilities and even some of the same personnel, which made the design and preparatory phases much quicker and easier than if each mission had started from scratch. The word “Express” in the names of the Mars and Venus probes refers to the fact that they were constructed and launched in record time, and with relatively low cost. Besides being stellar achievements in space science (pun intended!) they are also models of the kind of faster and more efficient missions that have become the norm in recent years. These missions prove the point that while space exploration will always be an expensive and lengthy undertaking, there are ways to greatly limit the cost and the amount of time needed for preparation.
Venus Express was launched from Baikonur, Kazakhstan on November 9, 2005 aboard a Soyuz-Fregat launcher. It traveled through space for 155 days, arriving at Venus in April 2006. Its mission was primarily to study the atmosphere and weather patterns on Venus, which are quite different from the kinds of patterns that we see here on Earth, despite the basic physical similarity of the two planets. The mission’s assignments included several firsts on Venus:
1. First global monitoring of the composition of the lower atmosphere in near-infrared transparency “windows.”
2. First coherent study of atmospheric temperature and dynamics at different levels of atmosphere, from the surface up to 200 km.
3. First measurements from orbit of global surface temperature distribution.
4. First study of middle and upper atmosphere dynamics from oxygen and nitrogen oxide emissions.
5. First measurements of non-thermal atmospheric escape.
6. First coherent observations of Venus in the spectral range from ultraviolet to thermal infrared.
7. First application of solar/stellar occultation technique at Venus to analyse how light is absorbed by the atmosphere, revealing atmospheric characteristics.
8. First use of 3D ion mass analyser, high-energy resolution electron spectrometer and energetic neutral atom imager.
9. First sounding of top-side ionospheric structure.
Venus Express was designed to address several open questions suggested by previous research. One of the most baffling mysteries is the cause of the super-fast atmospheric rotation and hurricane-force winds that have been observed on Venus. The Venusian atmosphere is whipping around the planet in a vast, global motion that is more than 60 times the speed of the planet’s rotation. This is a mystery, since such rapid motion cannot be explained by any conventional theory of atmospheric dynamics. Venus Express was designed to study the atmosphere in an effort to discover where all that energy is coming from. Another mystery is the double atmospheric vortex that has been observed at both Venusian poles, and has persisted for the entire observation period. The fact that similar features exist at both of the Venusian poles indicates a global symmetry that has so far eluded explanation. Scientists do not know how these features maintain their shape, and will be observing them closely in an attempt to figure out their dynamics.
Another part of Venus Express’ mission was the study of certain mysterious ultraviolet markings that have been seen at the tops of Venusian clouds. The upper clouds have areas visible in the ultraviolet that mysteriously absorb half of the solar energy received by the planet. The origin of these markings, and their remarkable absorption power, were among the questions being asked by Venus Express.
While the probe was designed to study the composition and dynamics of the Venusian atmosphere, it is also able to gain some information about the surface underneath that atmosphere. For instance, one of the questions regarding Venus is the nature and extent of volcanic activity on the planet, and how recently that activity occurred. Because it is capable of compiling detailed data on the temperature distribution and chemical composition of the atmosphere, Venus Express is capable of sensing both the heat of a volcanic eruption, and the chemicals that such an eruption would release into the air. By doing this, the probe should be able to spot places where eruptions have happened recently and determine how frequently they have occurred. In addition, Venus Express should be able to obtain valuable data on surface temperature, mineralogy, chemical weathering and the occurrence of earthquakes.
Since Venus Express has been in orbit around Venus for some time now, it has been able to obtain preliminary data on some of these questions. The picture that is emerging is of a planet that has changed radically from its earlier days. While Venus is hot and dry today, there is growing evidence that it may have been much more earthlike in its infancy.
For instance, Venus Express has observed that there is a color difference between the highland regions of Venus and the lowlands. On Earth, such a color difference would indicate that the highlands are composed primarily of granite. Granite is a relatively light rock formed by the action of water on basalt. In order for large amounts of granite to be present on the planet today, there must have been a lot of water sometime in the past.
In fact, theories of planetary formation would lead us to think that Venus and Earth started out with similar amounts of water. The two planets were formed from the same protoplanetary material, and were subjected to the same cometary bombardment in the early history of the solar system. Because of this, there is every reason to think that the two planets were once much more similar than they are today.
On Earth, granite literally floats on the heavier molten rock underneath, and forms the basis of the continents. So, when we look at Venus today and see highland regions that resemble the continental masses of Earth, the obvious conclusion is that these are the ancient continents of Venus, and that they were once surrounded by oceans as extensive as those on Earth. We are looking back billions of years, to a time when Venus, once called “Earth’s twin,” may have really deserved that title.
The question is unavoidable: was there life? Given the data that we have at the moment, we can’t answer that question- but it certainly is an intriguing possibility.
There is also some new data on the UV markings at the polar regions. It has been determined that these are caused by plumes of UV-absorbing material that has been brought up from deep in the atmosphere by convection currents. In other words, these UV-absorbing regions are really just the tops of tall columns of material. Where they well up, areas of high absorption are created, and the areas where they do not appear remain UV bright. That’s the phenomenon that is taking place, but the reason for it, and the exact nature of the absorbing material, are still unknown.
In regard to the vortexes at the north and south poles, we now know that they are much more variable than was originally thought. Observations on successive orbits have shown that the formations change their shape quickly and extensively, sometimes forming two separate “eyes” and sometimes a single oval or circular formation. A classic “eye of the hurricane” shape has been observed at the center of the south polar vortex. The dynamics of these features seem to be very complex, and will warrant much observation in the future.
Venus Express has also seen an eerie infrared glow in the night-time atmosphere of Venus, caused by nitric oxide which is produced when the sun’s radiation bombards the atmosphere and breaks up molecules, which recombine and release energy in the form of infrared light. This night glow can tell us much about the composition and movement of the atmosphere.
These are only a few of the things being learned from Venus Express. A full discussion of the data is far beyond the scope of this humble article. (For those who want more detail, the ESA website provides fascinating reading.) The probe continues to function well, and its mission has now been extended through December of 2012. Considering the huge success of the mission so far, we can only expect more great things in the future.
As new data comes in, it will be covered here. Watch this site for updates.
Sources:
Space Topics: Venus Express at website of the Planetary Society: planetary.org/explore/topics/venus_express/
Venus Express mission page at ESA website: esa.int/esaMI/Venus_Express/index.html
Venus Express Education and Outreach website maintained by the University of Wisconsin-Madison: venus.wisc.edu/
Malik, Tariq: A Cloudy Target: Europe’s Venus Probe to Explore Shrouded Planet at SPACE.com: space.com/businesstechnology/051026_techwed_venusexp.html