Alan Stern Quotes

It shouldn't be so difficult to determine what a planet is. When you're watching a science fiction show like 'Star Trek' and they show up at some object in space and turn on the viewfinder, the audience and the people in the show know immediately whether it's a planet or a star or a comet or an asteroid.

There was a time when Pluto - which NASA's New Horizons spacecraft at last explored in 2015, a mission I led - was considered the last planet. We now know there are thousands of other - possibly inhabited - planets.

I agree that we should go back to the moon and on to Mars. We should treat all objects in the solar system, including comets and asteroids, as exploration targets.

We should be ready to reach out beyond our planet and beyond our solar system to find out what is really going on out there.

No matter how you measure it, whether you measure the amount of mass or you measure the number of bodies, most of our solar system exists out beyond the orbits of the asteroids. So we could not have claimed to know our own solar system until Voyager had toured the giant planets.

Titan is the one place in our solar system whose geographical and atmospheric diversity and complexity are rivaled only by the Earth's. It's very Earth-like, but it's also very different, which means we have a lot to learn as well as a prayer of understanding what we find.

My field is called planetary science.

There are other planets besides the Earth and Mars. I'd like to remind you that studying Venus is vital to understanding life elsewhere.

There's a lot to do in space. I want to learn more about the greenhouse effect on Venus, about whether there was life on Mars, about the environment in which Earth and the Sun is immersed, the behavior of the Sun.

The cosmic game changed forever in 1992. Before then, logic told us that there had to be other planets besides the nine (if you still count poor Pluto) in our solar system, but until that year, when two astronomers detected faint, telltale radio signals in the constellation Virgo, we had no hard evidence of their existence.

In future, children won't perceive the stars as mere twinkling points of light: they'll learn that each is a 'Sun', orbited by planets fully as interesting as those in our Solar system.

A time will come when men will stretch out their eyes. They should see planets like our Earth.

There's so much interest and curiosity about alien life, interstellar travel. It's always in the news.

You see billions and billions of stars and recognize that you know some of those have planets, too, and maybe there's life out there, and this is just one of billions of galaxies... and so it gives you this huge perspective of how far we potentially have to go for real exploration.

Just speaking for myself, I think the return of people to the Moon has a lot to offer for understanding the formation and evolution of terrestrial worlds; so would the exploration of near-Earth asteroids by people.

As a planetary system, Saturn holds the greatest promise for answering questions that have a far broader scientific reach than Saturn itself.

As far as I'm concerned, Enceladus has become the go-to place in our solar system for issues bearing on extraterrestrial life. It's a great place to examine extraterrestrial organic chemistry that is water-based and, therefore, like biotic chemistry on Earth.

Because Alpha Centauri is so close, it is our first stop outside our solar system. There's almost certain to be small, rocky planets around Alpha Centauri A and B.

Among the plausible niches for extraterrestrial life in our solar system, the clouds of Venus are among the most accessible and the least well explained.

We've explored every type of environment in the solar system at least once.

Most of the solar system resides beyond the orbits of the asteroids. There is more to learn there about general planetary processes than on Mars.

The universe is very big - there's about 100,000 million galaxies in the universe, so that means an awful lot of stars. And some of them, I'm pretty certain, will have planets where there was life, is life, or maybe will be life. I don't believe we're alone.

No one planet can tell us everything about the universe, but Neptune seems to hold more than its share of information about the formation of our own solar system - as well as the solar systems beyond.

Our field is very focused on finding Earth 2.0, and anything we can do to narrow the search is helpful.

The story seems to be that almost every star has a planetary system... and, also, the definition of 'habitable zone' has expanded. In our system, it used to be that only Mars and Earth were potentially habitable. Now we've got an ocean on Europa... Titan.