The Planet Factory

"Yes, she has what I would call a jaunty style. I like it. Her writing has a very approachable flavor. She uses analogies well, she nicknames things. She’s British and works at the Japan Aerospace Exploration Agency now. It was a fun book. I enjoyed it. No, it’s not general in the way that Winn’s book lays it out and is almost pedagogically encompassing. She’s more interested in the quirks of the planets. I wouldn’t call it The Guinness Book of Records approach, but there’s a bit of that. She says, ‘Wow, there are oddball planets!’ Then she takes it beyond that, and asks, ‘How do they happen? How does nature make these strange planets? Why are they strange compared to the planets in our solar system? Is our solar system dull? Is it typical?’ These are important scientific questions, but she does have a lot of fun with the oddballs—the planet where it’s raining molten lava or diamonds or the planets that have been stretched into a pear shape because they’re so close to their star. She writes about all sorts of extreme planets that we’ve found. It’s not clear that we’re typical. The Copernican principle would say we should be average, but the single most common exoplanet type is a super-Earth that’s a few times larger, and five or eight times heavier than the Earth. Our solar system doesn’t have any of those, so we don’t have the most common type of exoplanet among the eight in our system. We’ve got Venus as a twin of the Earth and then you jump up by almost a factor of ten to Uranus and Neptune. There are other things about our solar system that may not be typical. But the diversity is so large now that you stop knowing what’s normal. She’s not as interested in the biology per se. She’s spending a lot of time talking about the planets that are so weird they probably won’t be habitable. I think she has more of a geological planetary science perspective, where she just is amazed at how these things form and that their properties are so bizarre. She’s laying that all out. I do. It’s a probability argument, which is dangerous, but if you take some notion of habitability—where the planet’s temperature is okay for liquid water, it probably has an atmosphere and geological activity, which we think facilitates the evolution of life—then your round number is 10 billion habitable worlds in the galaxy. Then multiply that by 100 billion galaxies. On statistical grounds, I think it’s very, very likely there’s life and even quite likely there’s intelligent life. But that’s no guarantee. When you have the example of one, you don’t know if there were fluky things that happened in the history of life on Earth. Also, for 90% of the history of life on Earth, you couldn’t see it without a microscope. Getting advanced life—plants and animals—took billions and billions of years. Maybe that’s hard, maybe sometimes it takes 10 or 20 billion years or never happens. Maybe it’s easy to get microbes and hard to get complex life. Or maybe just getting the first cell is harder than we think. You can’t draw any conclusion from the fact that it happened here. That’s the trouble. That’s why the motivation for finding those first examples elsewhere is so strong, because once we find another version of biology the game will be on. Then we can ask, ‘Is it the same biology as us or is it different?’ If it’s the same, then that’s very interesting. If it’s different, the box will be open, and biologists are going to have to develop a general theory of biology they don’t have yet. To a planetary scientist, Mars is probably on the edge of habitability. It doesn’t have a lot of geological activity, it’s dead now. It doesn’t hold much of an atmosphere, so it’s torched by cosmic rays and UV radiation. If there is life there now it would have to be quite far underground and farther than any of these rovers, which just scratch around on the surface, can find. There are almost certainly subsurface water aquifers, so there could be microbial life there now. Then there’s quite strong indirect evidence that 3 billion years ago, there was a thicker atmosphere and standing bodies of water. There definitely could have been life in the past. But we’re going to have rocks back from Mars in about eight years. There are rovers collecting samples as we speak, in a place called the Gale Crater which was almost certainly under shallow water a few billion years ago. There could be fossilized life forms in those rocks that are going to come back to Earth in the early 2030s. That will be very exciting. That’s probably the first way we’ll be able to answer the question. We do have 130 Mars rocks that came to us through meteorites. It’s just bad luck that almost none of them are sedimentary rocks. And then the problem with meteorites is you don’t know where they came from. They just got blasted off Mars somewhere and then came to Earth many years later. They landed in our laps. You can’t draw the conclusions that you could when you go to a place that you think was habitable, drill, make a sample and bring it back and study it in the lab. Then there’s Titan, where we’re sending a quadcopter, which is this drone technology. That’ll arrive in the mid-2030s. Titan could have Life 2.0, as we don’t know it, because it has ethane and methane lakes rather than water lakes. There could be hydrocarbons, and a weird form of biochemistry there. That will be amazing. There’s also the Europa Clipper, the ice mission due to be launched in 2024. It’s heading towards the watery moons of Jupiter. We’re not going to get down onto the surface and go under the ice pack—that’s a harder thing and that will take a while—but we may also get hints of life on Europa also in the next decade. So yes, our solar system has possibilities. Right. There’s the failure of SETI, the Search for Extraterrestrial Intelligence . It’s been 70 years now and nothing has been received. Then there is the issue of whether there is microbial life. Advanced technological life could be very, very rare compared to microbial life . I think if you have the ingredients for biology, you probably get biology in a large fraction of cases or at least some fraction of cases. There are billions of habitable worlds around the galaxy and they probably have pond scum and various forms of microbial life. And maybe Earth—where it took a very long time to get advanced, complex life—doesn’t happen very often. If intelligent life is thinly scattered through the galaxy, then operationally we’re alone. The signals take too long to reach us or they become too weak with distance. It could exist and if it’s rare, it might be hard to know."