David Grinspoon

What we should really be thinking about is what it would look like for a truly intelligent technological species to be interacting with their planet's atmosphere.

Mars does not have an atmosphere and does not have a magnetic field today, so the planet doesn't have the protection from radiation that our atmosphere and magnetic fields provide us on Earth.

Radiation is one of the important factors in evolution. It causes mutation, and some level of mutation is actually good for evolution.

I'm an astrobiologist, and I come from a planetary science background, so in a very broad sense, I study the evolution of planetary environments.

Earth is going to lose its oceans in the future, just as Venus did in the past. How long planets retain their oceans is a function of distance from the sun, all other things being equal.

As a young planet, Venus was losing hydrogen rapidly to space. The oceans boiled off, and after some period of time, perhaps 600 million years, there was no surface water.

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

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

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?

We have all this very clever technology and all these abilities to manipulate the world in all these ways, yet we are faced with the very real question of whether we can be sustainable on this planet - whether or not, in fact, we can endure.

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.

It's one of the big mysteries about Venus: How did it get so different from Earth when it seems likely to have started so similarly? The question becomes richer when you consider astrobiology, the possibility that Venus and Earth were very similar during the time of the origin of life on Earth.

We're pretty sure there's plenty of organic material on Pluto. The atmosphere is largely methane, and in sunlight, methane builds organic molecules. We see reddish stuff on the surface that we think is organic material.

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.

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

Time and time again, our species has escaped existential threats by reinventing ourselves, finding new skills not coded in our genes to survive new challenges not previously encountered.

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.

I think Pluto has to be considered among the places in the solar system that are possible homes for life.

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.

I think the best SF writers are very aware of what we, in the scientific community, are doing, thinking, and discovering.