guys angry.

Hello, I'm Ian O'Neill, space producer for Discovery News. As we discover more and more

alien worlds orbiting distant stars, the question "Are we alone?" becomes more and more pressing.

Surely there are other life forms out there -- perhaps even alien civilizations.

Unfortunately, space is big. Really, REALLY big. In the future we might be able to send

a probe to another solar system to find intelligent extraterrestrial life, but that's a tough

prospect. The nearest star is around 4 light-years away and using current propulsion technology

it would take us tens of thousands of years to get there.

So until we develop new ways of speeding around the galaxy to find intelligent life, astronomers

are thinking up some ingenious methods of detecting their presence without even leaving

Earth.

Here are some of my favorites:

The first is an obvious one and is currently the main method behind the Search for Extraterrestrial

Intelligence, or "SETI". This is to look for radio signals (or even laser pulses) that

may be transmitted by ET.

Humanity has been leaking artificial signals into space for over 100 years and we've been

blasting radar into the solar system for many decades. This "accidental" leakage could be

picked up by a nearby alien civilization.

We are also beaming radio signals at stars known to have planets in orbit in the hope

our electromagnetic "message in a bottle" gets picked up.

What if aliens are leaking radio signals into space as well? That's why we are trying to

"look out" for their signal using radio antennae. So far, there have been a few isolated cases

of bizarre signals, but nothing definitive.

A second cool way we may detect an alien civilization is if we observe dust and small chunks of

depleted asteroids in a distant star system. Astronomers may be confused by the anomalous

quantities of dust and may hint at a spacefaring alien race mining asteroids for resources.

Now that we're getting rather good at detecting exoplanets, eventually we'll be able to develop

telescopes that will be able to analyze the chemical makeup of atmospheres of small planets

orbiting very close to their stars. Astronomers can use spectroscopy to identify the fingerprint

of certain atmospheric chemicals.

Say if they detected chemicals like chlorofluorocarbons, or CFCs? Humanity has been struggling with

CFCs for some time and they were commonly used in pressurized containers like hairspray

and refrigerators -- but when released into the atmosphere the chemical breaks down our

protective ozone layer. But CFCs are ONLY created through industrial processes.

So imagine if we saw CFCs in the atmosphere of an exoplanet! It could mean only one thing:

industrialized aliens! Many other chemical groups that have no known natural production

mechanism would also make for a fascinating discovery.

Astronomers could also search for astronomical signatures of alien mega-engineering projects

like Dyson spheres, huge artificial planets or even extreme stellar power stations that

use black holes as fuel! This search is called, perhaps unsurprisingly, the Search for Extraterrestrial

Technology, or simply "SETT."

But ultimately, the only sure-fire way we'll find any form of alien life -- intelligent

or otherwise -- is to actually get out there. In the short term, we need to send robots

and eventually humans to planetary bodies in the Solar System to seek out basic lifeforms

-- perhaps even complex lifeforms in the oceans of Europa... who knows!

But if we do happen to stumble across an intelligent alien civilization, or if they happen to stumble

across us, let's just hope they're friendly.

Do you think we should seek out intelligent aliens? Or should we just keep quiet to avoid

being attacked? Tell us in the comments below, and don't forget to subscribe for more DNews.