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.
There are millions of stars out there. It is difficult to think that life does not exist in any one of them.
To me, it's the kind of interesting question the human race should be investing in. Is there intelligent life out there? Are there other beings out there?
One of the jovian moons, Europa, is coated with twice as much liquid water as is sloshing around our planet.
We think that life develops spontaneously on Earth, so it must be possible for life to develop on suitable planets elsewhere in the universe. But we don't know the probability that a planet develops life.
Stars, of course, are too hot to support life, so wherever life might exist in the universe, it has to be on planets or moons that are warmed, but not incinerated, by the stars they travel around.
By monitoring auroral activity on exoplanets, we may be able to infer the presence of water on or within an exoplanet.
We know too little about how life began on Earth to lay confident odds. It may have involved a fluke so rare that it happened only once in the entire galaxy. On the other hand, it may have been almost inevitable, given the right environment.
A 'serious' scientist in 1992 or 1993 had to admit the possibility that planets were really rare, that most stars might not have planets. We've gone from there to here - where most stars have planets.
I believe in aliens. I think it would be way too selfish of us as mankind to believe we are the only lifeforms in the universe.
The first exoplanet to be found around a sun-like star was discovered in 1995, just two years before I began studying exoplanet detection.
I am confident that life once thrived on Mars and may well still exist there today.
I think obviously there is some kind of life form somewhere else. Whether it looks like the creature in 'Alien Autopsy,' I'm not sure.
I think anybody would have to be with out common sense to think there weren't aliens. There are billions of planets, and I am convinced Earth is not the only one that's inhabited. It would be quite an ego trip to think that. I think about it all the time.
We know that within the solar system is very unlikely there will be anything more advanced than microbial life, but if we think outside the solar system and then, the distances are, of course, immense, then there could be Earth-like planets with more advanced form of life.
Maybe the search for life shouldn't restrict attention to planets like Earth. Science fiction writers have other ideas: balloon-like creatures floating in the dense atmospheres of planets such as Jupiter, swarms of intelligent insects, nano-scale robots and more.
When I was a little kid, we only knew about our nine planets. Since then, we've downgraded Pluto but have discovered that other solar systems and stars are common. So life is probably quite prevalent.
Many different planets are many different distances from their host star; we find ourselves at this distance because if we were closer or farther away, the temperature would be hotter or colder, eliminating liquid water, an essential ingredient for our survival.
The earth appears fragile and defenceless in the harsh environment of space and when one sees the amount of technology required to keep a human alive in that environment, one begins to feel blessed that one is an inhabitant of planet earth that supports human life.
Mars is the only place in the solar system where it's possible for life to become multi-planetarian.
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.
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.
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.
The usual metric for whether a planet is habitable or not is to ascertain whether liquid water could exist on its surface. Most worlds will either be too cold, too hot or of a type (like Jupiter) that may have no solid surface and be swaddled in noxious gases.
The Moon and Mars were the two most likely candidates for life in the solar system; what exists beyond our solar system is mere guesswork.
