There appear to be more planets in space than stars. And new figures released this week from the Kepler Space Telescope suggest that there could be 10 billion of them in our galaxy that are suitable for life.

But proving that life is out there will be difficult; connecting with it, nearly impossible.

Life is likely incredibly common in space. After all, look at how many life forms live in extreme environments on Earth, from the depths of the sea floor, to acidic hot springs, to glacial ice and deep underground. So, there is no reason to doubt that life could adapt to different conditions on alien planets.

There is only one problem; we are all separated by vast distances and time. So, the chances of us contacting each other are very small, at least according to our present technology.

The planets that have been confirmed to exist by Kepler are roughly 500 light years away, which is relatively close by cosmic standards. Our Milky Way Galaxy is 100,000 light years from one side to the other. But even studying just the planets in our galactic backyard for signs of life is a huge challenge, because the planets themselves are difficult to see at great distances.

Proving that some kind of life form is crawling around on the surface or swimming in seas is harder still.

Telescopes, especially the new James Webb Space Telescope, due to be launched in 2018, should be able to detect the chemistry in the atmospheres of these planets to see if there is any water vapour, methane, or oxygen, which are involved in life processes here on Earth. But that doesn't prove there's life on alien planets, because those chemicals can also be produced by other methods besides life.   

Kepler space satellite

This artist's impression shows the Kepler Space Telescope, which has gathered data suggesting there could be 10 billion planets in our galaxy that are suitable for life. (NASA)

Perhaps we will see seasonal colour changes on the planets, suggesting green forests in summer and leafless winters. Or it could be just clouds moving around in the atmosphere.

In fact, if you were to look at the Earth from a great distance, it would be hard to prove that there is life on it. Even our great cities do not show up from deep space, despite the myth that the Great Wall of China is visible from the moon. You have to get very close to, or land on, a planet to really find life, and until we develop faster-than-light travel our spaceships are woefully slow.

We could listen for radio signals from alien technological civilizations, but our radio telescopes have been scanning the skies for decades, through the SETI program, and haven't heard anything artificial ... yet.

And even if we did hear a clear broadcast and wanted to send a "Hello" signal to them, it would take hundreds of years for our message, travelling at the speed of light, to get to other planets beyond our solar system. So, half a millennium later if aliens catch our signal, if they understand it, figure out where it came from and send us a reply, it will be another 500 years before we hear, "Yeah, what do you want?"

That is, of course, if anyone on Earth 1,000 years from now remembers that we sent a message in the first place and is listening for a reply.

National Radio Astronomy Observatory (NRAO)

This radio telescope, which stands near Green Bank, West Virginia, has been used to search for signals from extraterrestrial life. (NASA)

In addition to this distance-time problem of communicating in space, there is another time-related problem, which is the age of our galaxy, estimated to be more than 13 billion years.

That's almost the age of the universe itself. Our sun has only been around for 4.6 billion of those years, which means there are stars much older and much younger than our sun. Some of them have completely lived out their lives and either exploded or puffed away their outer shells and turned into burned-out cinders, taking their planets with them.

This means that alien life forms could have evolved, developed into advanced civilizations, looked around to see if there is anyone else in the galaxy, saw no one, then disappeared — all before our own solar system was even born.

This could have happened many times in the past and be a continuing process today. In that way, no matter how good technologies for searching for life become, we can keep missing each other in time. It's like flash bulbs going off at a concert. There are many flashes, but they are not all happening at the same time.

So, instead of life in the universe forming a galactic club or federation of planets, it's more like a bunch of individuals stranded on widely spaced desert islands, who cast messages in bottles into the ocean and die before the message is received.

Of course, this is no reason to stop looking for other life in the universe. There is likely plenty of it out there. It is just very dilute, spread over vast distance and deep time.

It would be nice to find out that we are not alone in this vast universe. Because if we are all there is, then in the words of the famous astronomer Carl Sagan, "We are a way for the cosmos to know itself."

That comes with a responsibility to know as much about it as we possibly can.

(Tune into Quirks & Quarks this week to hear our interview with one of the NASA scientists who confirmed this latest batch of new planets).