David Grinspoon

What I wonder most about the Anthropocene is not when did it start - but when, and how, will it end? Will it end? Or is it possible that our own growing awareness of our role on Earth can itself play a pivotal role in shaping the outcome toward one that we would desire?

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

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.

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.

Humanity has at least a dim, and growing, cognisance of the effects of its presence on this planet. The possibility that we might integrate that awareness into how we interface with the Earth system is one that should give us hope.

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.

There's something cool about being involved in new missions to other planets.

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

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.

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.

There was a long history of people believing there was life on Venus. It was about the same size as Earth. It had clouds. It was commonly believed it was tropical - wet, hot and steamy.

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?