Most Jupiter-sized planets orbit the mother star in a highly elliptical orbit. This means they will often cross the orbit of any Earth-like planet and fling it into outer space, making life impossible. But our Jupiter travels in a near-perfect circular orbit, preventing a collision with any Earth-like planet, making life possible.

Manned spaceflight has lost its glamour - understandably so, because it hardly seems inspiring, 40 years after Apollo, for astronauts merely to circle the Earth in the space shuttle and the International Space Station.

The boundary between space and the earth is purely arbitrary. And I'll probably always be interested in this planet - it's my favorite.

We're not up there in space just to joyride around. We're up there to do things that are of value to everybody right here on Earth.

Each black hole spins on its axis like the Earth spins. That spin creates two vortexes of twisting space, somewhat like vortexes in a bathtub or a whirlpool.

From space, the earth appears predominantly blue; the clouds are brilliant white. Surprisingly, you don't see much green, although Ireland looks green, and so do Scandinavia and New Zealand. The deserts are brick red and really stand out.

My job in space will be to observe and write a journal. I am also going to be teaching a class for students on earth about life in space and on the space shuttle and conducting experiments.

You don't see any borders between countries from space. That's man-made, and one experiences it only when you return to Earth.

On Earth, men are seen as superior because of their physical strength, but it means nothing in space, where there is no gravity.

Watching sunrise and sunset from space, which is a beautiful sight, has been a personal privilege I have attained while being there. Another reflection from within I felt was that there was nothing which was neither visible and nor with a supportive environment as to how Planet Earth is.

For me, the Earth had always been a kind of a safe haven, you know, where I could go to work or be in my home or take my kids to school. But I realized it really wasn't that. It really is its own spaceship. And I had always been a space traveler.

The International Space Station is a phenomenal laboratory, an unparalleled test bed for new invention and discovery. Yet I often thought, while silently gazing out the window at Earth, that the actual legacy of humanity's attempts to step into space will be a better understanding of our current planet and how to take care of it.

The main goal of the International Space Station is to work on peaceful projects. In space, we're all people from Earth.

We have one planet in our solar system that's habitable, and that's the Earth, and space travel can transform things back here for the better. First of all, by just having people go to space and look back on this fragile planet we live on. People have come back transformed and have done fantastic things.

Trees bear fruits only to be eaten by others; the fields grown grains, but they are consumed by the world. Cows give milk, but she doesn't drink it herself - that is left to others. Clouds send rain only to quench the parched earth. In such giving, there is little space for selfishness.

You get this overview effect where you realize how small we are and how fragile our planet is and how we're really all in it together. You don't see borders from space, you don't see diversity and differences in people on Earth.

Astronauts have been stuck in low-Earth orbit, boldly going nowhere. American attempts to kick-start a new phase of lunar exploration have stalled amid the realisation that NASA's budget is too small for the job.

There are thousands of asteroids whose orbit in the Solar System crosses that of Earth. And we have a little acronym for them - NEOs: near Earth objects. And our biggest goal is to try to catalogue them, so we know in advance if one is going to put us at risk.

Our astronauts, when they go orbiting around the earth, they actually come back slightly younger than a twin that they would have on the planet Earth who was stationary. This is called the twin paradox.

Man must at all costs overcome the Earth's gravity and have, in reserve, the space at least of the Solar System.

We have the capability - physically, technically - to protect the Earth from asteroid impacts. We are now able to very slightly and subtly reshape the solar system in order to enhance human survival.

It's very dangerous to put astronauts on a moon base where there's radiation, solar flares and micro meteorites. It'd be much better to put robots on the moon and have them mentally connected to astronauts on the Earth.

The images of Earth's delicate biosphere, contrasting with the sterile moonscape where the astronauts left their footsteps, have become iconic for environmentalists: these may indeed be the Apollo programme's most enduring legacy.

It would take an extremely large spacecraft to deflect a large asteroid that would be headed directly for the Earth.