They're some of the biggest and long-living questions in astronomy and science fiction: are we alone?
Do aliens exist on some far away planet?
Is our precious blue planet special in being able to develop life, or are there numerous others?
Answering these questions have proven to be very difficult for a variety of reasons.
The search for extra-terrestrial intelligence (SETI) has constantly been monitoring the skies for signs of intelligent life for over a century, with no result.
However, it turns out that even finding potentially habitable planets is a very difficult task.
That's not to say that astronomers haven't tried.
Using all the tricks and techniques in the astronomical book, we have been particularly looking for planets that exist in the so called "habitable-zone" around their host stars.
This is a region around a star where the temperature and radiation from the star is just right to allow for liquid water on the planet.
Whether this is the right definition of "habitable" is still up for debate, and many scientists and philosophers love asking the question on whether we should even be searching for carbon-based life that depends on liquid water.
Maybe silicon-based, robot-like lifeforms are the norm in our galaxy?
Regardless, with our current telescopes and equipment, determining whether these habitable-zone exoplanets host life (or just simple habitable) is right at the limit of our ability.
This is because, in order to identify whether a planet has an atmosphere and what gases may be in that atmosphere, we need to take a spectrum of that planet.
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This involves taking the planet light and dispersing it into a rainbow of colours.
Interestingly, this rainbow will have certain colours being fainter than others, which is due to certain atoms and molecules preventing certain wavelengths (or colours) of light escaping the atmosphere.
This is exactly what happens in reverse with the ozone layer - it absorbs most of the UV light from the Sun, preventing us from getting sunburnt every time we walk outside.
By identifying what colours are faint or missing, we can identify what elements are in the atmosphere and how much of them are there.
The problem though lies in the fact that we need to get light reflected from the planet, and compared to the star this is incredibly faint.
Imagine a firefly next to a car's high beam, the difference between a planet and its star is so much more stark than this.
If we take the Earth and the Sun as an example, the Earth is ten BILLION times fainter!
Somehow, we need to block out the starlight, and just look at the planet's light despite such a contrast.
But the problems don't stop there, because stars are so far away, the apparent distance between a star and a planet is absolutely tiny.
If we take our closest star, Proxima Centauri, which is four light years away and hosts a planet inside its habitable zone; to see this planet we need the equivalent of seeing a 50c coin in the middle of Sydney from Canberra.
And this is one of the best-case scenarios!
So, what can we do about this?
Stay tuned for the next article!
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