Venus Unveiled

Something over a week ago I had the pleasure of making my way up to the little ski resort of La Thuile in the Val D’Aosta to learn about the latest results from the Venus Express mission. (You can imagine it was a tough decision to go to La Thuile and hear real scientists talking about Venus when I could have instead been listening to luminaries such as Mark Morano drone on at the Heartland Institute pseudoscience bash. ) My own connection with the Venus Express meeting came about through some work I’ve been doing on habitability of the newly discovered "Super Earth" extrasolar planets like Gliese 581c. Many of us think these may be "super-Venuses" rather than "Super-Earths," so it seemed like time to touch base with the people working on our own Venus. The fact that we can put together the same bits of physics we use to understand global warming on Earth in order to understand the interplay of the carbon dioxide greenhouse with sulfuric acid clouds on Venus is a testament to the fundamental power of climate science, and gives the lie to Claude Allègre’s oft stated claim that there is no such thing as a science of climate. Altogether, it was a thrilling meeting.

The Venus Express mission was described in this earlier RealClimate article, and you can read more about the mission at the VEX home page. Venus Express was done on the cheap, mostly using instruments cobbled together from leftover hardware from Mars Express and the Rosetta comet mission. The results have been nonetheless spectacular, and La Thuile provided a suitably spectacular venue in which to discuss them. This meeting was one in the series of Rencontres de Moriond in which scientists get together for a week of intensive discussion of leading-edge topics in physics — plus equally intensive skiing, climbing, hiking and enjoyment of good Northern Italian cooking. If you’ve ever read any of Jeremy Bernstein’s accounts of how he got involved in mountaineering through his attendence at particle physics meetings conducted in similar circumstances, you’ll know the general idea about how such things work. It’s a great way to shake loose creative thinking. And it’s one of those things that makes real science so much fun. Perfectly aside from the setting, it was a thrill to see the vigor of this field, and the influx of talented new young postdocs and graduates students, with all their fresh ideas and enthusiasm. I hope to give just a bit of the flavor of what went on during that eventful week.

A Field Guide to Venus

Venus has an Earthlike mass and surface gravity, the latter being 8.9 meters per second per second, only slightly less than Earth’s. Venus is in a very nearly circular orbit about the Sun with orbital period (year) equal to 224.65 Earth days. Venus rotates much more slowly than Earth, however, and this has many consequences for the atmospheric dynamics, since it greatly reduces the Coriolis accelerations that do so much to organize Earth’s large scale atmospheric circulations. In fact, the rotation of the planet is retrograde — i.e. opposite in direction to the rotation of the orbit. The siderial day on Venus — the period with which the star patterns would repeat, if you could see the stars from the surface — is 243 Earth days, but since this is in the retrograde direction, it adds to the angular velocity of the planet relative to the Sun. Thus, the rate of rotation relative to the Sun is 1/224.65 + 1/243 rotations per Earth day, leading to a solar day of 1/(1/224.65 + 1/243), or 116.7 Earth days. This is the time between sunrises, as would be seen from the planet’s surface. Thus, Venus’ solar day is roughly half of its year, as illustrated in the sketch below (credit K. Fuller).

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