Astrobiology is the science of life in the universe. It's an attempt to scientifically deal with the question of whether or not we're alone in the universe, looking at the past of life, the present of life, and the future of life. It's an interdisciplinary study incorporating astronomy, biology, and the Earth sciences.

Our most valuable resources - creativity, communication, invention, and reinvention - are, in fact, unlimited.

Astrobiology is a great point of contact for science outreach. The public is naturally interested in extra-terrestrial life. Astrobiology provides an accessible point of access that leads to deeper questions.

The hallmark of the human species is great adaptability.

There's eco-pragmatism, where you recognize, 'Yeah, we live on a planet that's permanently altered by humanity, and rather than seek to return to or preserve pure wilderness, we recognize that's an illusion, and we proceed under the new knowledge that we live, in fact, in a human-dominated planet.'

Even cynical, selfish people will realize, one way or the other, that it's not in their self-interest to act in self-destructive ways.

The reason you see so many volcanoes on Venus is partly due to the fact that there's virtually no erosion there. So on Venus, you're seeing features, some of which are hundreds of millions of years old on the surface. On Earth, we do not see any surface features nearly that old - you only see much more recent features.

I intend to apply the perspective of astrobiology, which is a deep-time way of looking at life on Earth, towards the question of the Anthropocene. What does the human phenomenon on Earth look like viewed from an interplanetary perspective?

There's no question to my mind that saving our civilization and many other species is more important than our ability to do ground-based astronomy for a few decades.

Humans are possessed, to some degree, with the power of foresight. Yet we so often learn things the hard way, through disaster.

I was a science fiction geek from an early age, enthralled by the questions of life in the universe. As I got older, I learned that space exploration was real. I wanted to get involved in that. I knew I wanted to be a scientist.

It's OK to pursue speculative ideas because we don't want to be too cozy and safe and assume that we know everything about life in the universe. However, we have to be rigorous and careful and honest and logical and scientifically meticulous when we speculate.

If we gutted NASA Earth Science, it wouldn't be NOAA or some other agency that would take the lead. It would be the Chinese and the Europeans and the Japanese.

Why should we consider defining intelligence as something global and as something that hasn't actually yet appeared on Earth? It may be useful for envisioning the future of our own civilization and any others that may be out there among the stars. It might give us something to strive for.

Part of the point of SETI has always been a search for answers about our own cosmic potential and destiny. If 'they' are out there, it means that there may be hope for us.

When you think about alien intelligences making art, you then have to think about what art is and how bound up it is in the nature of consciousness. Why do we make art? And what can we expect to have in common with other creatures in universe?

I'm a strong advocate of new missions to Venus.

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. And 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.

NASA, and all the other spacefaring nations of the world, have agreed to a set of 'planetary-protection' principles, aimed at preventing the accidental contamination of another habitable world with organisms from Earth.

Seriously, we should start taxing churches and have tax-exempt places for worship and study of nature and art. Charge ten bucks for Sunday services and make the Botanic Gardens free.

The basic ability to not wipe oneself out, to endure, to use your technological interaction with the world in such a way that has the possibility of the likelihood of lasting and not being temporary - that seems like a pretty good definition of intelligence.

As long as we can imagine a better path, of course we are obligated to seek it. This is why unwarranted pessimism about our future is actually irresponsible.

Earth's biosphere gave birth to humans and our thoughts, which are now reshaping its planetary cycles. A planet with brains? Fancy that.

It's quite possible that the end of us will not be the end of the Earth. Even if we really screw things up and things go badly for us and our civilization, the Earth is pretty resilient.

Certainly for me, as an astrobiologist, science fiction has played an important role. One of the quandaries of our field is that we are trying to study and search for something - life - that we can't define in a rigorous way. We only have one example of a biosphere, so we can't really give a good definition.

We're going to stop looking at Earth from orbit because we don't like what we are seeing and the conclusions that leads us to? That's nonsense.

Even as a kid enthralled with science fiction, I wondered about the role of people in the long-term evolution of the Earth, the far future and the fate of humanity.

Even as our unwitting alterations to Earth's carbon and hydrological cycles slowly make storms more damaging, our ability to monitor our planet from space and make reliable short-term forecasts have equipped us enormously to withstand them.

A lot of the science fiction that I grew up reading was written when we still thought that Venus might be an oceanic planet.

I think a lot of people interested in space exploration tend to hear stories about the great missions, how they work technically, what we learned. But they don't really hear the story of what it takes to get a mission from scratch to the launch pad and into space.

The story of our species is one of overcoming existential risk through new forms of cooperation and innovation.

Venus and Mars are our next of kin: they are the two most Earth-like planets that we know about. They're the only two other very Earth-like planets in our solar system, meaning they orbit close to the sun; they have rocky surfaces and thin atmospheres.

We don't know that Venus had oceans, but there's every reason to believe it did.

It's quite possible there's as much lightning on Venus as on Earth.

I do comparative studies of climate evolution, and the interactions between planetary atmosphere and surfaces and their radiation environment, and try to understand the environmental factors that can affect a planet's habitability and how they change over time.

I'd been politically active ever since my parents wheeled me in a stroller in a 'ban the bomb' march in Boston in 1963.

There is a history of thinking about space science from an environmental ethics perspective. And part of what I want to do is turn that back and use that experience to see if it reflects how we think about the Earth.

What if life is not carbon-based? Can life exist as a gas or a plasma? Could planets or stars in some sense be alive? What about an interstellar cloud? Could life exist on such a small or large scale, or move so fast or so slowly that we wouldn't recognize it? Could you have an intelligent virus?

There is a real danger of unintended consequences, of encouraging people to give up. Pessimism, if it becomes a habit, can reinforce a narrative of unstoppable decline. If there is nothing we can do, that releases us from our obligations.

One of the weird things about modern physics is that we do find there are apparently these other dimensions that we don't directly experience that explain some aspects of the overall geometry and reality of our universe.

The planet Mars - crimson and bright, filling our telescopes with vague intimations of almost-familiar landforms - has long formed a celestial tabula rasa on which we have inscribed our planetological theories, utopian fantasies, and fears of alien invasion or ecological ruin.

It will be a long time, if ever, before we get to study Earth-like planets orbiting around other stars, so really, the study of Venus and Mars is the best opportunity that we have, and can imagine having anytime in the future, to understand the evolution of Earth-like planets.

I think that an advanced planetary civilization will modify their own planets to be more stable, to prevent asteroid impacts and dangerous climate fluctuations.

We need to have a vision of the world we want to create so that we can see ourselves as collaborators with future generations in the project of shaping it.

When I first went to college, I went into physics, and my goal was to help perfect nuclear fusion so I could solve the energy crisis and global warming. I probably would have done it, too, if I'd stuck to it.

Fixing global warming is more important than astronomy.

There are other planets besides the Earth and Mars. I'd like to remind you that studying Venus is vital to understanding life elsewhere.

In order to have a decent chance to be a communicating species, you would have to learn to think and plan and act over time scales of a century or a millennium.

We have to learn to become a new kind of entity on this world that has the maturity and the awareness to handle being a global species with the power to change our planet and use that power in a way that is conducive to the kind of global society we want to have.

Now, humans have become a dominant force of planetary change and, thus, we may have entered an eon of post-biological evolution in which cognitive systems have gained a powerful influence on the planet.