The Japan Aerospace Exploration Agency (JAXA) has recently announced what is hopefully the final launch date for its Venus Climate Orbiter. After several delays and changes of schedule, the date has now been set for Tuesday, May 18, 2010. In addition to the Venus Climate Orbiter, there will also be five secondary missions which will be included in the payload of this same launch, taking advantage of the large payload capacity of the H-IIA Launch Vehicle that will be used. It’s an ambitious project that will test new technology and help scientists unravel the baffling secrets of Venus’ unusual weather patterns, and if it all comes off as planned, it will be a stunning achievement for JAXA. The organization has a very active schedule planned for the next few years, including the HAYABUSA asteroid probe and the BepiColombo Mercury mission, which we have talked about here.
In one of our earlier articles, still posted here, we took a look at the European Space Agency’s Venus Express probe, which is already in orbit around Venus. These two projects are not redundant, nor are they in competition with each other. The projects have been in close communication with each other since their beginning phases, and have been planned to complement each other in the construction of the most complete picture possible of the Venusian environment. In some cases, the two Venus probes will work together on composite science projects, while in other cases, they will be doing separate work of a complementary nature.
The Venus Climate Orbiter, also called Akatsuki, will weigh 480 kg. with fuel, and will carry a science payload of 34 kg. Basically, it will be a rectangular box with “paddle wheel” solar panels extending on either side. There will be small thrusters at all eight of the corners for minor attitude adjustments, and a larger engine for orbital maneuvering in the rear of the unit. There will be five instruments onboard, taking observations at different wavelengths to obtain various types of information.
Departing from Earth in May of this year, Akatsuki will first deploy all of its secondary payloads. These include some experiments proposed by prominent Japanese universities relating to information encoding and transmission, observation of the Earth’s atmosphere for meteorological purposes, and the testing of computer technology for space use. The last of the secondary payloads to be deployed will be the IKAROS lightsail, an exciting experiment to test the use of the pressure of sunlight to propel a spacecraft. (See our article on lightsails at this site.) On the journey to Venus, Akatsuki use the travel time to perform various astronomical observations and to study the interplanetary dust cloud.
Akatsuki will arrive at Venus in December 2010 and settle into a long, elliptical orbit near the planet’s equatorial plane. This will be a 30-hour orbit in a westward direction. The apoapsis (farthest point from the primary) will be 79,000 km., and the periapsis (nearest point to the primary) will be 300 km. Global images of the atmosphere and the ground surface will be taken every two hours continuously. Because of its stretched-out orbit, the probe will be making close-up observations of mid-scale features at periapsis, and more long-range observations at apoapsis. It will take advantage of periods when it is in the planet’s shadow to make low-light studies of phenomena such as lightning and air-glow. (Lightning has never been observed on Venus, and there is some question as to whether it even exists there at all. Scientists will be eagerly waiting to see if Akatsuki spots any.)
Akatsuki is being called an “interplanetary meteorology” mission, because its main function is to peer deep into Venus’ murky cloud cover and obtain 3-D images of the phenomena happening there. It is hoped that the probe will be able to see the different layers of the atmosphere, how they are moving, and how they interact with each other and with the planet’s surface.
The whole purpose is to try and understand the amazing movement of the Venusian atmosphere. As we saw in our article on the European Space Agency’s Venus Express probe, the big mystery about this planet that has emerged in recent years is that the entire atmosphere is racing around the globe in a planet-wide gale that moves at 60 times the rate of the planet’s rotation. If you were unlucky enough to be standing on the surface of Venus, you would literally be knocked flat by a non-stop wind of 100 meters per second. This is called “super-rotation,” and it is a complete mystery. There is nothing in our Terrestrial meteorology to explain such rapid motion of an entire planet’s atmosphere. Where is all that energy coming from? Granted, Venus is close to the sun and has an average temperature of 460 degrees C both day and night, but even that isn’t enough to explain this amazing movement of air.
In some ways, Venus and Earth are very similar. They are small, rocky planets with roughly the same mass, and it makes sense to think that they should be fairly similar. The weird thing is, they’re not. These two planets have taken very different paths in their evolution, and ended up in very different states. In contrast to our own pleasant world, Venus is a pressure-cooker with a carbon dioxide atmosphere of enormous density. And now we learn about this super-rotation, and the mystery deepens. We certainly don’t have anything like that here at home. How did these two planets, which probably started out as very similar little pebbles in the beginning, end up so completely different?
And as we saw in our Venus Express article, there is another factor that makes the whole thing even more intriguing. There now seems to be convincing evidence that there are continent-size masses of granite on Venus. Granite only forms in the presence of water, but due to the heat and pressure, liquid water can’t even exist on Venus today. If there’s so much granite on Venus, there must have been an awful lot of water there at one time, and that implies a different environment from what we see now. It must have been an environment with much lower air pressure and much lower temperatures- a planet more like Earth, in fact.
Just how much like Earth? We don’t know yet, but it is that central question, and other questions connected to it, that will dominate Venusian research in the coming years. And this thing with the super-rotation has to do with that, because it is very unlikely that this movement of the air was happening with such energy in the earlier, more Earth-like world we’re thinking of. When did it start, and why? Why does it continue, with no obvious source of energy? For that matter, why did the whole environment change from a world with water and granite continents into the oven-like place we see today?
Venus is turning out to be a big box of questions, and so far, we don’t have many answers. However, there is an ominous note in all this: while there are many things we don’t know about Venus, we do know why it is so hot. The cause of its 460-degree heat is runaway global warming caused by carbon dioxide buildup in the air. This probably doesn’t result from the same source as our global warming here on Earth. Since we have absolutely no evidence that Venus ever supported an industrial society, it is far more likely that its carbon dioxide buildup is the result of some natural process. What process, we don’t know. Could it happen here? Of course it could- but will it? We don’t know, but perhaps it would be prudent to find out. When you think of it that way, this line of research suddenly becomes more than just an academic question.
If we imagine this ancient Venus, so different from the one we see today, we are tempted to think of a place very much like Earth: balmy islands with palm trees swaying in the breeze. In all likelihood, this view only shows our provinciality, the fact that we only know one planet. If there is anything that our study of Venus has already taught us, it is just how different two similar planets can be. Whatever Venus was like in that long-ago age, it probably wasn’t just like Earth.
As for what it really was like, we will have to guess for the moment. However, someday in the not-too-distant future, landers will descend to the surface of Venus and start taking samples of the soil and rocks. At that point, we will finally begin to unravel the evolution of this planet. If it turns out that those ancient oceans really did exist, perhaps we will find the fossilized remains of things that swam in them.
Between now and then, smaller revelations will be coming out, some of them perhaps in the near future. When that happens, you can read about it here.
Sources:
Akatsuki Special Site at the website of the Japan Aerospace Exploration Agency: jaxa.jp/countdown/f17/index_e.html
“JAXA Explores the Planets of the Solar System- Anticipating Amazing Discoveries” at the website of Japan Aerospace Exploration Agency: jaxa.jp/article/special/explore/imamura02_e.html
“Satellites and Spacecraft- Venus Climate Orbiter ‘Akatsuki’” at website of the Japan Aerospace Exploration Agency: jaxa.jp/projects/sat/planet_c/index_e.html
“Akatsuki- Planet C” at website of the Institute of Space and Astronautical Science: isas.jaxa.jp/e/enterp/missions/planet-c/index.shtml