Gravity Assist Podcast: Venus, with David Grinspoon (Part 2)
The Gravity Assist Podcast is hosted by NASA’s Director of Planetary Science, Jim Green, who each week talks to some of the greatest planetary scientists on the planet, giving a guided tour through the Solar System and beyond in the process.
This time around he spoke to astrobiologist and planetary scientist David Grinspoon, of the Planetary Science Institute, about the second planet from the Sun: Venus, a world with surface temperatures hot enough to melt lead. In the first part of their discussion, they spoke about Venus’ volcanoes, its clouds of sulfuric acid and its backwards rotation. Now, in part 2, they discuss how Venus has influenced cultures all over the world, landing on Venus and the heroic ‘Apollo 11’-like story of the Akatsuki spacecraft.
Jim Green: Venus is an easy planet to see. It’s close to the Sun most of the time. During its orbit around the Sun, it can be very bright because it can be close to the Earth. I know many cultures have been thinking about Venus and placing them in their own histories, and so it has a fascinating role from that perspective. Do you have any favorite stories about that?
David Grinspoon: Yeah. I’m fascinated by the fact that, as you say, nearly every culture, probably every culture, has stories about Venus, because it is so bright and also has such a different kind of behavior in the sky [compared to] a lot of other planets, because it’s what we call an inferior planet, meaning that it orbits closer to the Sun than Earth. It just appears, for a few months, at sunset and then disappears, and then reappears for a few months at sunrise and then disappears. You’ll never see it in the middle of the night in the midnight sky, like you might see Jupiter or Mars or Saturn. So, it sort of has this almost playful kind of behavior, where it kind of flirts with us and then disappears and then reappears on the other side [of the Sun]. A lot of cultures had stories that reflected that.
One area that I love about this sort of archaeoastronomy is the Mesoamerican stories about Venus. The Aztecs and the Toltecs and the Mayans were really astute and impassioned Venus observers. They were very good at predicting the motions of Venus and it was tied into their culture and their origin stories, their beliefs. The Mayans had these really neat stories about what they called Venus, Kukulkan. To the Aztecs, it was Quetzalcoatl, but it’s basically the same character. Venus was the brother of the Sun. Together, Venus and the Sun would go into the underworld and do battle with the enemies of mankind. That kind of makes sense because you see Venus, you know, at sunset, sort of trailing the Sun and disappearing. So, they’re going down to do battle. [There are] all these stories about Venus and the Sun together, beating back pestilence and disease and war and all these enemies of mankind, and basically making the world safe for humanity.
Jim Green: Well, in modern culture over the last 100 years or so there have been stories, like those by Edgar Rice Burroughs, inn which life on Venus could have arisen. Part of that comes from the increased scientific knowledge about Venus, like what happened in 1761 with the Venus transit. What happened during that transit?
David Grinspoon: I love that story. It’s basically the discovery that Venus had an atmosphere, by a very astute observer in Saint Petersburg, Russia, an astronomer named Lomonosov. Venus does these transits in front of the Sun, as you mentioned, in this sort of weird pattern [where there are] pairs of transits eight years apart, separated by about a century. We’ve just had a two Venus transits in 2004 and 2012, and we won’t [see one] again for almost another century. When it does [transit], you can learn a lot because you see the little disk of Venus, of course a little dot, passing across the Sun. Historically, we’ve learned a lot. It helped us figure out the size of the Solar System through geometry.
[In] this particular discovery that you mentioned, Lomonosov noticed that it wasn’t just a circle moving across the Sun, [but] that there was this weird effect when Venus was just touching the Sun on one side and then the other. [It was] what he called ‘the black drop’: this weird sort of extension of the circle [of Venus’ disk] into this strange sort of stretched-out shape, which we now associate with the refraction of [light] in the atmosphere of Venus that you can see in those moments when it’s just touching the Sun. He was the first one to deduce that and he said Venus must have an atmosphere, and he was right.
Jim Green: And of course, that feeds into all kinds of stories. This is the first planet beyond Earth that was known to have an atmosphere, and so what would life be like, etc. So, indeed, Venus has been very important in our literature and culture.
David Grinspoon: Yeah, and it’s not that long ago that we figured out, in some sense, the way Venus really is. A lot of the science fiction that I grew up reading was written when we still thought that Venus might be an oceanic planet. So, a lot of the science fiction stories that were written in the 1940s and 1950s, classic ones by Isaac Asimov and people like that, they still have this oceanic Venus and, you know, the Earth explorers are in submarines, exploring exotic creatures under the water there.
Jim Green: Today, there’s one spacecraft that’s orbiting Venus, but it seems like it’s been a planet that’s been observed by many different space agencies. Do you remember the one that’s there now?
David Grinspoon: Yes. We are fortunate that our colleagues in the Japanese space agency (JAXA) have a spacecraft called Akatsuki. It’s a word that means dawn in Japanese, which makes sense, given we are talking about Venus being the Morning Star. Akatsuki is actually a spacecraft that has a sort of heroic story, because it was launched in 2010 and made it to Venus just fine, in less than a year. But then it was supposed to burn its main engine for 12 minutes and go into orbit, and sadly, something went wrong with the main engine and it spun off helplessly around the Sun. Amazingly, it span off on a trajectory that was going to bring it back to Venus five years later. So, they had a chance to get it into orbit, but they didn’t have a main engine. Then some very clever Japanese engineers figured out if they’d take these little maneuvering thrusters and fire them all in the same direction for 20 minutes, which they were not designed to do, that they might be able to get it into orbit. Of course, they couldn’t practice it because they only had enough fuel to do it once. But it worked, and now Akatsuki is in orbit and making all kinds of neat observations of the atmosphere and the clouds and some observations of the surface at these wavelengths where you can peer a little bit through the clouds. It’s a wonderful sort of a resurrected mission.
Jim Green: You know, NASA’s currently got some proposals for Venus in a set we call the New Frontiers call for missions. We’re analyzing those and perhaps we’ll be selecting a Venus mission, which would be pretty spectacular if we were able to do that.
David Grinspoon: That would be terrific. I’m hopeful that one of these years NASA will return to Venus. There’s certainly a lot more left to explore there.
Jim Green: What would you do, from an exploration point of view? What would be the top science activities that we ought to be going after?
David Grinspoon: Venus is a challenging place to explore. Part of the reason we haven’t been there more is that the surface environment is so severe, you can’t see the surface from orbit, like you can from Mars, at least not in visible [light]. There are a few things that would really help us with our understanding of its history. One, is that we’ve never really gotten good measurements of the rare gases, what we call the noble gases, and their isotopes. Other things we would love to do are orbit again with a really much more sophisticated radar.
Now, we have these radar interferometers, which for instance, on Earth, can do these amazing measurements where you can actually see the motion of the San Andreas Fault, because they’re so sensitive. If we had something like that on Venus, we could actually see if it’s tectonically active, let alone map the surface in much more detail.
Of course, we would love to really land on Venus. The Soviets did it a long time ago. But, now, again with modern instrumentation and armed with the more sophisticated questions we have now based on what we’ve learned, we’d love to dig into the dirt and measure the minerals and really look for clues to the history of that surface and the history of climate and some of those big mysteries, [such as] what happened to the water on Venus? How long ago did Venus lose its water, and what has the climate done since then?
Jim Green: Unlike the Earth, Venus doesn’t have a moon. Why do you think that is?
David Grinspoon: Our current understanding of why the Earth has its Moon, again, has to do with that early impact history, the sort of last stages of formation of the Earth [where] we think that a Mars-sized object hit Earth and in just the right way that it span a glowing ring of material into orbit around the Earth, which then coalesced to form the Moon. That was actually, if you think about it, a somewhat random and very specific event. If that impact hadn’t happened, or it had a slightly different geometry, Earth might not have a Moon, or it might have several moons, like Mars.
So, the fact that Earth has its Moon, we think, comes down to this slightly chaotic and random event. It may just be as simple as Venus’ final stages of formation happened a little bit differently from Earth’s, in terms of the sizes and geometries of those last few big crashes that formed Venus.
Jim Green: We all get into this business some way or another, and I refer to that as that gravity assisted pulls you in. What’s your story on that?
David Grinspoon: Well, I’m not one of these people that had to figure out what I was going to do and had many false starts. I feel like I was always on the sort of path, so I didn’t need too many gravity assists. Partly, I was born at the right time. Literally, my earliest memory, my earliest vivid memory, is the Apollo 11 landing on the Moon. Yeah, I was in fourth grade and I was just so captivated. I think you’ll find a lot of space scientists of my generation will say the same thing. Apollo was a big event for them.
Also, when I was young, I had some influential people and mentors in my life. Actually, it turns out one of my dad’s best friends when I was little was Carl Sagan. They were both Harvard professors. This was before he [Sagan] was famous. He was just this cool guy we knew, who would lead these public observing nights at the Harvard Observatory and let us go run the controls at the planetarium. So, that was certainly an influence.
Then, when I went to college, I had some great mentors. In fact, [during] my first semester at Brown University, I took a class called ‘Mars, the Moon and the Earth’, with Jim Head, who is a little bit of a pied piper of planetary geology. He gets a lot of young students excited, and I was one of those.
And, then while I was in college I got a summer job, working for Professor Head, analyzing some of the new Viking images of Mars, which were just a few years old [at the time]. One thing led to another and I was just pulled in and captivated [by it] and [I] never lost that excitement.