Life outside our solar system is certainly possible, but we do not know for sure yet.

Scientists have been looking for outer space lives for decades. Recently scientists just found an earth-like planet not too far from us (4.2 light-years, around 25 trillion miles), which may have a life-friendly condition. Stephen Hawking has proposed to send tiny probes to other stars, and if this project becomes successful, it takes about 20 years for these probes to travel to that planet. So the optimistic estimate is that, in 20 years we will know for sure if there is indeed life on that planet.

But of course, it is also possible for aliens to contact us, assuming they have equipped with advanced technology.

It is currently not known if there is life outside of our planet, but there are pretty good chances that there is. You've probably heard the estimate that there are more stars in the universe than there are grains of sand on Earth. This is an enormous number of stars, and on average, each star has at least one planet. Our sun is a called a "main sequence star," which means that its development follows a very typical path that many other stars take. To me, that suggests that there should be many other stars that may have planets and moons that are similar to ours in terms of their chemical composition and possibly even having an atmosphere that can sustain life!

So why is chemical composition of a planet's atmosphere and surface important for the existence of carbon-based life (life as we know it)? Life as we know it requires water, carbon, oxygen, hydrogen, and nitrogen. So planets that have these compounds and elements and an atmosphere that contains the right balance of them are more likely to be able to sustain life.

The first life on Earth was thought to begin in a "primordial soup," in the oceans. There are experiments that have shown that with help from light or electricity (i.e. things that the sun or lightning could provide), carbon, hydrogen, oxygen, and nitrogen can react to form amino acids and nucleic acids. These are chemical compounds that can go on to form the basis of proteins, RNA, and DNA -- and if you have DNA, then you can have life, since part of the definition of life includes the ability to reproduce!

So what does this all mean in terms of discovering life outside of our solar system? And what would that life even look like? Scientists who are looking for life in outer space are first looking for planets whose atmospheres look amenable to the sustenance of life. That means they're looking for planets that look like they have water and the other appropriate chemicals that seem necessary to the life we are currently aware of. More likely than not, any life that might be found in outer space would probably be something that looked like bacteria, but there's no way to know for sure.

As to when such information could be discovered, the earliest time would be when probes returned information from planets and/or moons they have gone by/sampled. I believe there are currently plans for probes to be sent toward Jupiter's moon Europa, which is icy and may have once had life. Even traveling within our solar system requires years of preparation and years of travel. To get to Europa alone it will take six years, then the information gathered will need to be processed and studied. Pursuing travel outside of our solar system to other stars and planets would require even more time, and a lot of other logistical matters, including funding and planning, would need to take place to do so. I realize this part of the answer is vague, but so much of which endeavors are pursued or not, do end up coming down to science policy and funding!

These are all really good questions and we don't know the answers. Here is what we do know, however:

-We can see out into the universe a distance of about 14 billion light years. This is because the universe is only 14 billion years old, and so light has had only 14 billion years to travel. The real universe is probably much bigger than this, and may indeed be infinite. Within the 14-billion-light-year radius that we can see, there are about 50 billion galaxies, and the average galaxy contains about 100 billion stars.

-We don't know how common life in the universe is, but considering how big the universe is, it seems quite likely that there is other life out there. We haven't found any of it yet, but except for intelligent life that might be trying to communicate with us, it would be very difficult for us to detect life outside of the solar system at this time. For this reason, life could be quite common and we still wouldn't know.

-Right now, we know of only one type of life: carbon-based life using DNA for information storage, proteins to actually do stuff, and water as the solvent in which all of this chemistry takes place. If we encountered something else in the universe that used these or other, very similar, chemicals, we would probably be able to identify it as life. However, there might be other ways to make life that we don't yet know about, and some of them might be difficult for us to recognize.