All indications are that three and a half billion years ago, Mars looked like Earth. It had lakes. It had rivers. It had river deltas. It had snow-capped peaks and puffy clouds and blue sky. Three and a half billion years ago, it was a happening place. The same time on Earth, that's when life started. So did life start on Mars?

I was not really scared on my spacewalks. We practice so much and need to stay so focused that it has a calming effect on me. I do a kind of visualization and meditation in the airlock prior to going outside, to guide my first activities once I get out in space.

Here on Earth, we're exposed to asteroids hitting the Earth, eventual changes in the Sun, changes in the Earth's climate, things we're doing to the Earth's climate. If we want to survive, we need to become a multi-planet species. That's further down the road, but the first wave is going to be the explorers.

The truth is, every single rocket launch off of planet Earth is risky.

Are we alone? Many, many people on planet Earth want to know. We are on the cusp of being able to answer that question... because of the investments we're making in space technology.

The biggest honor is to be an astronaut. It's such a tremendous privilege to be able to represent humankind in our quest to explore space.

When I grew up as a kid, we didn't know there were any other planets outside of our own solar system. It was widely speculated that planet formation was an incredibly rare event and that it's possible that other planets just don't exist in our galaxy, and it's just this special situation where we happen to have planets around our sun.

I kind of feel like I found my cause in life servicing the Hubble Space Telescope.

When I grew up on the south side of Chicago, it was kind of a rough neighborhood, and when my parents saw the prospect of my older sister going to middle school, high school, they decided that we would move to the north side of Chicago, Highland Park, and for me, that was a whole new ballgame.

The only reason Hubble works is because we have a space shuttle.

I can't imagine anywhere I'd rather be than outside the space shuttle in my space suit next to the Hubble Space Telescope.

Only by studying large numbers of people can we figure out, are astronauts dying at a higher rate of cancer, and what types of cancers, than other people?

A deep ocean under the icy crust of Ganymede opens up further exciting possibilities for life beyond Earth.

After my spacewalks, I am quite exhilarated but also tired, similar to a workout on Planet Earth.

Growing up in Highland Park, in high school, I had some very influential teachers: I had a math teacher who taught calculus that helped me learn to be in love with mathematics; I had a chemistry teacher who inspired us to work what was in the class and to go beyond.

Science fiction has been an inspiration to generations of scientists and engineers, and the film series 'Star Wars' is no exception.

Going to Mars would make NASA great again.

I see no difference between scientific exploration and human exploration.

Hubble showed us the marvel and majesty of stars being born.

Regardless of what dreams you have, work very hard, play very hard, and have fun.

InSight will get to the 'core' of the nature of the interior and structure of Mars, well below the observations we've been able to make from orbit or the surface.

The moon's a nice place to visit, but you wouldn't want to live there.

It's pretty amazing to me that we have had a space shuttle program that's lasted for 30 years - for one space shuttle. That's quite an achievement.

Sciences are being unified by the search for life in the universe.

Once we get beyond Mars, which formed from the same stuff as Earth, the likelihood that life is similar to what we find on this planet is very low.

As a young boy growing up on the South Side of Chicago, I was inspired by the nascent space age.

We don't know how many planets we're going to have to examine before we find life, and not finding it on 10 or 100 doesn't mean it's not there. This may be very tricky.

The most striking thing to me about human space flight and my own personal experience is that I've seen dramatic changes on Earth. We humans are rapidly changing the planet. I've watched Amazonia as the rainforest has been cut down. That's something I've seen out the window. I'm very worried about that.

Our country... invests a tiny fraction of 1 percent in NASA, and this is what's so amazing to me, is with that small investment, we do so much for the country.

I look forward to working with the NASA team to help enable new discoveries in our quest to understand our home planet and unravel the mysteries of the universe.

To help enable the kind of science Hubble is performing makes my life worthwhile.

Absolutely the most fun thing to do in space and rewarding thing, in many ways, is to look back at planet Earth.

Once in a while, the universe lets you be free alone and in peace.

I have had the privilege to be a member of many high-performance teams at NASA, both on and off the planet.

Small bodies in our solar system, like comets and asteroids, help us understand how the solar system formed and provide opportunities to advance exploration.

The strangest thing I've found is that when I got to space, I felt more comfortable in space that I've ever been on Earth before. I just felt this is my home.

I got lucky and got assigned to Hubble.

The best would be to fly in space with family and friends.

There are some things worthy of risking your life for.

The surface of Mars is bathed in ultraviolet light, bathed in radiation. Mars's magnetic field is essentially gone, so the surface of Mars is essentially sterilized.

Hubble uniquely has been able to look in the atmosphere of a planet orbiting a nearby star and figure out what's in that atmosphere.

Getting a team of scientists on Mars could be transformative.

I think it's really a sign of great American strength that we do invest the money we do in technology, in these hard projects, in NASA.

Life outside of Earth is probably going to be really hard to find.

One of the things that happens in space is that there is a fluid shift. You get a lot of extra pressure, and it fills your sinuses, and the horseradish is a miracle worker for cleaning that out.

What we do at NASA is inspiring. It's reaching, it's visionary, and it inspires people on Earth to try hard things.

I don't particularly want to jump out of an airplane with a parachute if I don't have to. I don't want to go bungee jumping. I like adventure with a real purpose that I can buy into.

The first thing to know about space food - it is the ambiance; it is the environment. It is not the food.

Being an astronaut, there are not a lot of things that have really shocked me in my life.

We're being very careful that we don't send a spacecraft to Mars with the intention of detecting Martian life - and find out that we detected the Earth life that we took with us.