Is there life on other planets? To find out, scientists have developed novel ways to search for life on other planets. Searching within our own Solar System and beyond. Two of the techniques they use are:
Let's compare the atmospheres of Earth, Venus, and Mars. We can do this by looking at the spectrum of the light which is reflected from their atmospheres. The spectrum tells us which gases make up each atmosphere. We can then tell that the atmospheres of Venus and Mars are distinct from Earth. Both Venus and Mars show evidence of carbon dioxide in their atmospheres. Earth's atmosphere also has some carbon dioxide. But, it also contains ozone and water.
Ozone is a by-product of oxygen (O2). Finding large amounts of ozone means that there are large amounts of O2. Some scientists believe that large amounts of O2 can only be produced by the process of photosynthesis. This process is driven by plants and trees on land, and tiny plants called phytoplankton in the oceans. This means that if we discover a planet with ozone in the spectrum of its atmosphere, we might find life on it. Space telescopes are being designed to look for ozone in the atmospheres of distant planets.
Gasses like ozone tell us if there is likely to be life on a planet. We call indicators like these biomarkers. They mark the likely presence of biology or life. Of course, biomarker gases such as ozone only relate to life as we know it. We have to remember that extra-terrestrial life may not be what we expect. Alien life may not require O2. In fact, there is life in the deep ocean which survives without O2.
The SETI programme is a global project. It employs more than 100 scientists, educators and support staff. They are dedicated to searching for signals. Signals from advanced alien species from distant planets.
In truth, we don't know what an alien signal will be like. It is likely that they will have more advanced technology than us. It is hard for us to imagine their thought processes. Or their reasons and methods for interacting with us. All we can do is make some educated guesses. Guesses based on our own knowledge and technology.
SETI's first assumption is about the frequency of a first signal. We think it will be at or around the frequency of 1420 MHz. This is the spectral frequency of Hydrogen. It is the most common element in the universe. This means it may be a universal reference point for other intelligent species.
To detect strong signals at this wavelength, SETI uses radio telescopes around the world. One of those is the Allan Telescope Array (pictured). This is used to scan the night sky. Some telescopes have targeted nearby stars to try and detect signals beamed in our direction.
To learn more about the SETI programme, click here.