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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.
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.
In environments that are energy-rich but liquid-poor, like near the surface of Titan, natural selection may favor organisms that use their metabolic heat to melt their own watering holes.
Among the radio astronomers of SETI - the Search for Extraterrestrial Intelligence - it's only sort-of a joke that the true hallmark of intelligent life is the creation of radio astronomy.
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.
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'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.
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.
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.
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.
In my Ph.D. thesis, written in 1989, I discussed the fact that when a civilization develops the technology to prevent catastrophic asteroid impacts, it marks a significant moment in the evolution of the planet.
Ever since the environmental movement was sparked by photos of the whole Earth taken by astronauts onboard Apollo Lunar Modules, I've seen planetary exploration as an extension of a reverence and care for Earth.
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.
We've almost been wiped out as a species many times, going back millions of years, and we've survived by reinventing ourselves and enlarging our circles of awareness, inventing new technologies and social structures.
The more we look at the kinds of soils and the nature of the atmosphere and the polar caps, it all adds up to tell us that some liquid, which we very much believe was water, did flow in abundance on Mars in the past.
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.
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.
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.
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.
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.
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.
As long as we are a single-planet species, we are vulnerable to extinction by a planetwide catastrophe, natural or self-induced. Once we become a multiplanet species, our chances to live long and prosper will take a huge leap skyward.
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.
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.
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.
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?
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.
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.
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?
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.
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.
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.
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.
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.
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.
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?
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.
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.
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.
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.
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 planeto-logical theories, utopian fantasies, and fears of alien invasion or ecological ruin.
It is said that Mahatma Gandhi, when asked about Western civilization, remarked, 'I think it would be a good idea.' That's how I feel about intelligent life on Earth, especially when I think about the question of what truly intelligent life might look like elsewhere in the universe.
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.
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.
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'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.'
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.
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.
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.