Archive for the ‘Venus’ category

Solar System Tour: Venus

June 4, 2010

Venus is the second planet out from the sun, and is just slightly smaller than Earth. It is 12,102 km across, which is about 95% the size of earth. You can see Venus in the sky in the morning or evening as a very bright “star”. In fact, for a long time it was called the “morning star” or “evenstar”. It is always pretty close to the sun in the sky because it is close to the sun in the solar system. You might think, since it’s about the same size as earth, but is closer to the sun, Venus would be a nice place to live. It would be nice and warm, maybe the whole planet’s a tropical paradise! Let’s go!

You might want to reconsider. Here’s why. About the only thing Venus and the earth have in common is their size. Venus is a really awful place. Try to think of the most unpleasant place imaginable, and I bet Venus is still worse. There’s no water on Venus, but it has a very thick atmosphere. At the surface, the pressure is 92 times the pressure here on earth. The whole planet is covered in clouds (that’s why is shines so brightly in the sky, clouds are pretty reflective). Not just any clouds though. The clouds on venus are made mostly of sulfuric acid. As if that wasn’t bad enough, Venus is the hottest planet in the solar system. That’s right, even hotter than Mercury! The reason for this is the greenhouse effect. The atmosphere on venus is almost all carbon dioxide, the same gas that is causing climate change on earth. What happens in the greenhouse effect is, energy from the sun comes in and then gets trapped by the atmosphere and can’t leave. On venus, the surface temperature is 482 degrees C (900 degrees F!). Unlike mercury, it doesn’t cool down much at night thanks to the blanket of clouds.

For a long time, nobody knew what the surface of venus looked like because all those clouds were in the way. Luckily, radar came to the rescue. Radio waves can go through the clouds easily. Radar works by sending out a bunch of radio waves, and then measuring how much gets reflected back. Several probes have been to Venus, and almost the whole surface has been mapped using radar. Here’s what it looks like underneath the clouds.

Venus has a structure similar to earth. It has an atmosphere, and a thin crust. Unlike earth, venus’ crust is probably all in one piece rather than broken into separate plates. Below the crust is a rocky mantle, and a metallic core. Scientists aren’t sure whether the core on venus is solid or not, but it is probably about the same size as earth’s core, about 6000 km across.

You might notice that, compared to mercury, venus has hardly any craters. Part of this is because of the very thick atmosphere. Stuff just burns up before it hits the ground. That’s not enough though. The lack of craters means that venus is geologically active, so its surface is pretty young. Venus has a lot of volcanic activity, 85% of its surface is covered with volcanic rock. There are huge lava flows hundreds of miles long and large plains created when lava filled low-lying areas. There are more than 100,000 small volcanoes and hundreds of large ones. The radar image below is of Sapas Mons, which is a very big volcano (250 miles across and a mile high). You can see lots of lava flows coming out from the center. They look bright because rough surfaces scatter radar waves better than smooth surfaces.

Here’s an example of some of the thousands of smaller volcanoes. Each little bump in the picture is a volcano.

Here are four “pancake” volcanoes. They form when thick lava oozes up from below onto level ground, and just expands in all directions.

You might think that, being such a nasty place, there’s no way we could ever land anything on venus. Believe it or not, the Russian space program put 10 landers on the planet between 1975 and 1982. They were called the Venera landers. Venera 13 lasted the longest: 2 hours, 7 minutes. It managed to take 14 pictures. Here’s what the surface of Venus looks like:

The pictures look distorted because of the type of lens used by the lander’s camera. The upper left and right corners show little patches of the sky. You can see part of the lander at the bottom, and the thing on the ground in the left picture is the camera’s lens cap. The rocks look like basalt, a volcanic rock found on earth.

All in all, venus is not a nice place to be. It looks nice enough shining in the morning sky, but it just stands as another reminder that looks can be deceiving. In the future we will send more probes, but the chances are very slim that people will ever walk on its deadly surface.

Check out the previous posts in the Solar System Tour:

Solar System Overview

The Sun

Mercury

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AGU 2009 – Day 3: Venus and the Moon

December 20, 2009

I’m splitting day 3 into two posts because there were so many interesting sessions. Stay tuned for the second post about astrobiology and society. But for now, Venus and the moon!

Image credit: Nick Anthony Fiorenza/NASA

I started the day off at the Venus session. One of the first talks I heard was by Cedric Gillman about the history of water on Venus. He suggested a very thick primordial H2O atmosphere with a surface pressure of 300 bars, eventually escaping until just 15 bars of O2 were left. That oxygen then was absorbed as it reacted with the rocks. Gillman cautioned that Venus’ evolution shows that you can have a very hostile environments but still have water and oxygen in the atmosphere; something that we should keep in mind when looking for “habitable” exoplanets.

The next two Venus talks described using two complementary laser-based techniques on a lander mission. Shiv Sharma showed that Raman spectroscopy, which uses laser pulses to characterize the molecules in a target, would work under Venus-like conditions for a variety of rock types. In the following talk, Sam Clegg showed that Laser-Induced Breakdown Spectroscopy (LIBS), which analyzes the elements in a sample by zapping it with a laser and collecting the spectrum emitted by the resulting plasma, would also work under Venus conditions. Sam is my main contact on the ChemCam team and allows me to use his laser lab for some of my work, so it was cool to see some of the other LIBS work that he does.

A sample being zapped by a LIBS laser.

Both Raman and LIBS are great for Venus because they are fast, capable of remotely analyzing a sample in seconds. When your probe is only going to live for an hour in the crushing pressure and deadly heat of Venus, every second counts, and these techniques could be extremely useful.

The final Venus talk that I heard was a status report on the Japanese Venus climate orbiter. They unveiled its new name: Akatsuki, which means “dawn” in Japanese, specifically the time of the morning when Venus is just visible as the morning star. Akatsuki is going through final thermal vacuum tests in January and will launch some time in 2010.

Artist's rendition of Akatsuki at Venus. Image credit: JAXA/Akihiro Ikeshita

Later that day, I stopped by the lunar dust session to hear a talk by Bonnie Cooper about the toxicity of lunar dust and implications for astronauts. Chronic exposure to dust on earth can cause serious problems, especially to the lungs, but I was surprised to hears some of the other effects. My lack of biology knowledge is probably getting this partly wrong, but Cooper said that very small dust particles can actually enter the tissue around small blood vessels and prevent them from expanding when the body needs them to do so! Not good!

Crushed quartz is quite nasty stuff on earth and Cooper said that there was reason to believe that moon dust might be even more reactive because of its jagged surface, the many fresh fractures in the grains caused by micro-meteorites, and because of solar wind protons. All of these things result in unbonded ions known as free-radicals, which are very reactive and cause damage to the body. Dust loses its danger somewhat when it is exposed to air and all the free radicals are neutralized, but Cooper said that their experiments show this takes several hours. They are working on doing experiments with actual lunar samples and lunar soil simulant to find the exact effects of dust inhalation, but it sounds like this is a significant problem that human explorers will have to face.

A particle of moon dust. Image credit: David S. McKay, NASA/JSC

Finally, at the end of the day there were a couple of talks about the detection of water on the moon with the Moon Mineralogy Mapper on Chandrayaan. The most interesting one, given by Roger Clark, showed that the initial water detection actually underestimated the depth of the water absorption feature because it didn’t correct for an overall slope in the background of the spectrum. With that correction, the mapped water extends to all latitudes. There is still a stronger signature near the poles, but that is superimposed on much more complex variation with geology. There are craters that appear to be digging up material with a stronger water band, but other fresh craters dig up less water-rich debris. He also said that he was cautiously optimistic that they had detected some hematite, an iron oxide responsible for Mars’ rusty color, but said that scattered light in the instrument made it difficult to tell for sure. Clark concluded, saying that he didn’t think that the variation of the band strength observed during the lunar day represented a change in the actual amount of water, but rather was due to the viewing geometry.

The press-released M3 map of water on the moon (blue). With recent corrections (not shown here), the mapped water extends all the way down to the equator.

AGU Day 2: Venus

December 17, 2008

Poor Venus. Even though it is right next door to Earth, it tends not to get much attention. This is because it’s so hot that we can’t last long if we land there, and it’s so cloudy that we can’t study its surface very easily from orbit. It’s a really interesting place though: it is the closest planet in size to the Earth, but it’s climate is drastically different. NASA has quietly begun looking at what it would take to send a flagship mission to Venus, and so the first couple of talks this morning considered what we know about Venus and what the remaining big questions are.

venus_magellan

Jim Head gave a whirlwind tour of what we know about Venus. He especially emphasized that the best way to study Venus is in terms of comparative planetology. In other words, how and why is Venus similar to the other planets and how/why is it different? One of the very strange things about Venus is that, unlike Mars and Mercury and the Moon, its surface is not very old. There are some craters, but most of the planet is volcanic plains and tectonic ridges. On the other hand, it doesn’t seem to have active plate tectonics like the earth. Venus seems to be a third, unique case. Its craters are completely randomly distributed. There is no place on Venus that clearly has a higher or lower concentration of impact. This means that the whole surface is about the same age and may imply that it underwent “catastrophic resurfacing”. Obviously, it would be nice to know how such a process works and whether it could happen to earth…

Ellen Stofan gave a good introduction to the Venus Exploration Advisory Group’s (VEXAG’s) list of outstanding questions for Venus exploration. The questions are:

  • Did Venus ever have an ocean?
  • Was its atmosphere ever earthlike?
  • Why does it rotate so slow? (Venus rotates once every 243 days)
  • Why does its atmosphere rotate so fast? (The winds on Venus circulate around the planet about 60 times as fast as the solid planet spins)
  • What caused Venus’s resurfacing, and what was its relation to climate change?
  • Was Venus ever habitable?

photo

This morning I also heard about Japan’s upcoming “Planet-C” Venus Climate Orbiter, which is set to launch in 2010 and will have a nominal mission of 2 years in orbit around Venus. The orbiter will carry 5 cameras to look at Venus in UV, visible, near-infrared and long-wave-infrared. Its main focus is atmospheric dynamics, but will also provide information about lightning, cloud physics, and potential active volcanoes. It will be in an elliptical orbit so that at the farthest point from the planet its orbit will be synchronous with the rotation of the atmosphere.

The final Venus talk of the morning was by Dave Senske about NASA’s study of doing a flagship mission to Venus in the 2020-2025 timeframe. The mission that he described was very ambitious: it would involve two launches! The first would deliver an orbiter and the second would follow with 2 balloons and 2 landers. The balloons would float between 50 and 70 km high in the atmosphere and would last at least a few weeks. The landers would go all the way to the hot, high-pressure surface and would be designed to last at least 5 hours, although Senske mentioned that obviously it would be nice if they lasted for days or months.

A Venus balloon prototype.

A Venus balloon prototype.

The biggest obstacle to landing things on Venus is that we just don’t have technology that can handle the extreme temperatures and pressures. Senske said that their mission concept is pretty conservative in terms of new technology needed, but I still suspect that there will be a lot of difficult problems to overcome to succeed. Of course, this is the sort of thing that NASA engineers love to do, and I bet a lot of the technology needed for a Venus mission would have applications here on Earth.