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The best books on Life Beyond Earth

recommended by James Kasting

How to Find a Habitable Planet by James Kasting

How to Find a Habitable Planet
by James Kasting


Geoscience professor and NASA adviser James Kasting talks us through the scientific possibilities for life beyond earth. He recommends books by both 'optimists. and 'pessimists.'

How to Find a Habitable Planet by James Kasting

How to Find a Habitable Planet
by James Kasting

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Tell me about your first choice, Rare Earth by Peter Ward and Don Brownlee.

Rare Earth was one of the prime motivations for me to write my book. I know both the authors and they are fine scientists, but they are very pessimistic about the chances of complex life outside Earth, by which they mean animal life, and, of course, that includes intelligent life.

They think we are very lucky to be here at all?

They do. They have a whole list of arguments about things that they think the Earth was lucky about, which makes Earth so rare. And some of those things, I think, are not so rare. For example, plate tectonics – the crust and the lithospheric plates lying around on top of the asthenosphere. It actually is very important not just for geology but for climate legislation because it helps to modulate the carbon cycle that controls CO2 levels over long time scales. I agree with them that plate tectonics is important for a planet. But what Ward and Brownlee say is that in our solar system there are 20 large solid bodies – planets and moons – and of those Earth is the only one that has plate tectonics, so that makes it rare.

But you have to then ask why the other ones don’t have plate tectonics. For Mars the answer is simple: it is much smaller than the Earth. It is only about a tenth of the Earth’s mass so it cooled off too quickly. Small objects cool off faster than larger ones. And for Venus, the problem is probably lack of water. Water lubricates plate movement just like oil lubricates an engine. So Venus’s lack of plate tectonics is most likely caused by the fact that it lost its water. After reading Rare Earth I decided to write a book showing that some of their arguments are not so strong.

Let’s move on to Distant Wanderers by Bruce Dorminey.

Bruce Dorminey is a science writer and he wrote this book several years ago. He is looking into the early days of exploration for extrasolar planets. Bruce is interested in the same thing that many of us are interested in these days, looking to see first of all if there are planets around the stars, and eventually to determine if they are inhabitable planets.

I feel like I am picking up where Bruce left off and talking more about what it takes to have a habitable planet.

It’s a competitive business isn’t it?

Yes, most of the 400 or so planets that have been found were found using ground-based telescopes, using a particular technique called the radial velocity technique. What you are doing with this method is looking for the back and forth wobbles of the star in your line of sight. There are several different groups doing it now. There is a group in the United States that used to be Geoff Marcy and Paul Butler working together. There is another group over in Switzerland – Michel Mayor and Didier Queloz were the initial leaders of that group. Those two groups were and still are competing to find the most planets from these observations.

There are two schools of thoughts among those looking for life on other planets: the optimists like you and Carl Sagan, who we will discuss later, and the pessimists like the authors of Rare Earth. What arguments have you and the optimists come up with to show that there is life on other planets?

What I am most optimistic about is that the chances of finding other Earth-like planets are good. That means planets that are small and rocky with atmospheres and with liquid water on their surfaces. There are many conditions under which planets like that can form. Now, whether any of those have life is still a matter for speculation. We only have one origin of life and we don’t know whether that happens on every planet when the conditions are right or whether that only happens once in a blue moon.

And do you think that if such planets do exist, given what is going on here on Earth, we can conceivably go and live on them?

It’s not impossible. If you found a habitable planet around a relatively nearby star like Alpha Tauri, you might not send people themselves but we could code up genetic sequences and human genomes and put it on computer chips to send there. Then you would have to figure out how you raise a civilisation from scratch with no parents ­– but if we get good at making robots maybe you could do that.

Tell me about James Lovelock’s Ages of Gaia.

Lovelock has written five or six books. I chose his second book, Ages of Gaia. Gaia is the Greek goddess of Mother Earth and Lovelock’s Gaia hypothesis is the idea that life itself stabilises a planet’s environment. He would say that the reason the Earth is habitable is precisely because it is inhabited. It’s an interesting theory but I don’t think you have to have an inhabited planet in order to have a habitable planet.

He came to that view thinking about the faint young sun problem. This is a problem which is near and dear to my heart, because I have worked on it for a long time. We know that the solar system – the Earth and the sun – are about four and a half billion years old, and the sun, we think, was about 30 per cent less bright early in solar system history. This means that if the Earth was no different from how it is today and we have the same atmosphere and the same greenhouse effect, then the Earth would have been frozen over during the first half of its history.

Lovelock was aware of this. CO2, along with water vapour, is our main greenhouse gas so Lovelock suggested that there was more CO2 in the early atmosphere, and then organisms took CO2 out of the atmosphere by using photosynthesis. And that counteracted the increase in solar luminosity. That is really how he came up with the Gaia hypothesis.

Your next book, The Crowded Universe: The Search for Living Planets by Alan Boss, is described as being rather like a diary.

This is a more up-to-date story from an astronomer’s standpoint, of the search for extrasolar planets. Alan works at the Carnegie Institute in Washington. He is a real political insider, so there are lots of stories in there of the politics of this whole enterprise. For example, he writes about how NASA is continually starting up programmes and then cancelling them, and Alan is privy to much of this information.

He is also a very good scientist: he does computer modelling of the formation of planets. He’s got his own perspective. He is much more astronomical than I am – I am more of a planetary scientist. And this book tells the story over the last decades of the development and research in this field, showing all the successes and frustrations along the way.

How did you become interested in looking for life on other planets?

I read a lot of science fiction growing up and the last book that I have chosen, Intelligent Life in the Universe by the Russian I S Shklovskii and Carl Sagan, is old. It came out in 1968 and that was right before I went to college. I read that book as an undergraduate and I was fascinated, so I would say that Carl Sagan is a big influence on my work and on my thinking.

So tell me about Intelligent Life in the Universe.

This book was written first in Russian by Shklovskii, who was an astrophysicist in what was then the Soviet Union. Carl Sagan had it translated, and he thought it was a great book but he had lots of additional thoughts that he put in. So he annotated the whole thing. They use different fonts for Shklovskii’s writing and for what Carl added to it, and it ended up being a wonderful book that talked about the possibility not just of life but intelligent aliens, with whom we might one day communicate.

Your authors include the optimists and the pessimists in this debate – who is winning?

I run into a lot of pessimists these days, but it is because they have read Rare Earth, which came out about ten years ago. But it hasn’t been addressed by a comparable book in literature, and I am hoping some people will read my book and become more optimistic!

How can you make them change their minds?

For the last 40 years or more, people like Carl Sagan and Jill Tarter, who is now head of the SETI Institute [the search for extraterrestrial intelligence], have been out there looking for intelligent life in the universe. In fact, Frank Drake, who was one of the early radio astronomers in this business and founded SETI, wrote out an equation which is often referred to as the Drake equation. It is a way of estimating the number of intelligent communicating civilisations in the galaxy. They have been looking for extraterrestrial life mostly using radio telescopes. When you do that you are looking for civilisations like ours that broadcast radio signals. That is great, but it turns out we can only eavesdrop for radio signals around a handful of nearby stars, so we really need to extend our search and do it in a different way.

From my way of thinking it is getting the cart ahead of the horse. Because before you start looking for intelligent life you should try to figure out if life itself is common. I think that is the most interesting question in the coming decade or two. We need to address the life signal. If you do that we don’t need radio signals. We just need to be able to observe either visible light or infrared radiation from extrasolar planets and look for signatures of atmosphere gases to establish if there is life – and then the next step is to see if it is intelligent.

July 15, 2010

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James Kasting

James Kasting

James Kasting is Distinguished Professor of Geosciences at Pennsylvania State University. He is an expert in planetary atmospheric evolution and is actively involved in the search by NASA for habitable planets outside our solar system.

James Kasting

James Kasting

James Kasting is Distinguished Professor of Geosciences at Pennsylvania State University. He is an expert in planetary atmospheric evolution and is actively involved in the search by NASA for habitable planets outside our solar system.