Mars does not belong to 'America,' nor to Earth, nor to human beings.

The future peopling of Mars is much more than a scientific endeavor. It is a step of historic and spiritual importance for the human race.

Once we become a multiplanet species, our chances to live long and prosper will take a huge leap skyward.

The mature Anthropocene begins when we acquire the ability to live sustainably and become a lasting presence on this world.

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.

Thinking about the new epoch - often called the Anthropocene, or the age of humanity - challenges us to look at ourselves in the mirror of deep time, measured not in centuries or even in millennia, but over millions and billions of years.

Through space-based climate studies, my colleagues and I have learned that a stable and comfortable climate is not something to take for granted.

As Earth's climate changes, we can expect more destructive hurricanes. As sea level and surface temperatures rise, more solar energy is trapped in the atmosphere, revving up the hydrological cycle of evaporation and precipitation and sometimes manifesting in terrifying storms.

We're going to get off fossil fuels, no question. We may not do it quickly enough to avoid some pain, and I'm quite worried about that. But by the 22nd century, there's no way we'll be on fossil fuels.

I do a lot of work with NASA and am involved in research projects studying planetary evolution, Earth-like planets, and potential conditions for life elsewhere.

It turns out one of my dad's best friends was Carl Sagan when I was little. They were both Harvard professors.

If you were on the surface of Venus, assuming you could see the Sun, which, you know, would be hard because it's so cloudy there, but the Sun would actually rise in the west and set in the east. And, it would do so very, very slowly, because the planet rotates incredibly slowly.

Titan has rivers and lakes of liquid methane and ethane, methane weather systems of clouds and storms that mirror Earth's hydrologic cycle, and seasonal cycles that rival Earth's in complexity.

We definitely don't want to go through another Ice Age or another natural cycle of global warming. Both happen over a long period of time. It would be disastrous for our civilization, and not just for us but many other species.

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.

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

I will defend the NASA Earth Science Division with everything I've got.

You cannot study other planets without referring to Earth and without applying the techniques and the insights of Earth science. And you cannot really do a good job understanding the Earth without the insights from planetary exploration.

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.

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?