In 2015 the physicist Stephen Hawking said:
In an infinite Universe, there must be other life. There is no bigger question. It is time to commit to finding the answer.
The idea that there is not just life, but intelligent life, on other planets is one that has fascinated me since reading Whitley Strieber’s Communion when I was a teenager.
Whether you are a believer like I am or not, the enormity of the universe should be enough to make you doubt that we humans are not a singular anomaly. To get a a sense of this scale, let’s begin with a short astronomy lesson:
Our galaxy is big
Planet Earth is the third amongst eight planets in our solar system (sorry Pluto, you are just a dwarf planet now), all orbiting a star we call the Sun, which scientists estimate was formed some 4.6 billion years ago. Our Sun is in turn one of an estimated 250 billion (+-150 billion) in an island of stars known as the Milky Way galaxy.
The Milky Way is known as a barred spiral galaxy, and it’s an enormous structure, approximately 100 million light years wide, with the Sun located around 25,000 light years from the centre. The image below shows where our sun is located.
Now that we know there are around 250 billion stars in our ‘local’ galaxy, the next question is how many of those stars are part of solar systems much like ours, with planets orbiting just the right distance from the sun such that life is possible? Scientists refer to this as the Goldilocks zone, which is a range of orbits around a star where a planetary surface is capable of supporting liquid water.
In 2013, astronomers used data collected from the Kepler space mission to estimate that there are around 11 billion Earth-sized planets orbiting in the Goldilocks (habitable) zone of Sun-like stars in the Milky Way galaxy, as well as another 30 billion more orbiting red-dwarf stars (which also have habitable zones like Sun-like stars do).
So that’s around 40 billion planets possibly capable of supporting life in our ‘home’ galaxy, but how about further beyond in other galaxies?
The Universe is even bigger
Astronomers estimate there is an astonishing 10 trillion galaxies in the observable universe. This number was formulated by counting the number of galaxies in a particular region, and then multiplying this up to provide an estimate for the whole universe. Another way to look at it is to hold up a grain of sand to the night sky. The small patch of the sky that it covers contains 10,000 galaxies.
We are getting into really big numbers now, but in short, there are an estimated 1 septillion, that’s 1,000,000,000,000,000,000,000,000 stars in the universe, and around 7.6% of those are class G stars, all of which are thought to have at least one planet. Astronomers estimate that around one quarter of those planets is thought to be in the habitable zone of the local star. Which leaves us with 19,000,000,000,000,000,000,000, or 19 sextillion stars similar to ours with at least one planet similar to Earth. Amazing!
How can we meet?
Hopefully at this point we can agree that it’s likely that intelligent life exists in other solar systems, in our galaxy or in others. The next question I’ve been thinking about is how likely are we to make contact?
The biggest roadblock to finding evidence of extraterrestrial life, let alone making first contact, is the enormous distances involved. Astronomers estimate that the closest sun-like star to us with a high probability of having an earth-like planet in it’s habitable zone is Alpha Centauri, which is 4.37 light years away. That’s 40 trillion kilometres.
Let’s say that we did find an earth-like planet orbiting Alpha Centauri and wanted to send a mission to have a closer look. How long would it take the spacecraft to get there?
The short answer is, a really long time, at least with current technology.
At present the fastest spacecraft so far launched into space are the NASA-Germany Helios probes, which traveled at 250,000 kilometers per hour. At that speed, it would take 18,000 years to reach Alpha Centauri.
The challenge for scientists is to develop the technology so that a spacecraft can travel at a substantial fraction of light speed – at least 10%. At that rate, it would take around 44 years to reach Alpha Centauri, and any data or signals we send back would take an additional 4.37 years.
NASA have plans to launch a mission to Alpha Centauri in 2069, and more recently a project called Breakthrough Starshot announced plans to develop a proof-of-concept fleet of thousands of tiny 1cm sized spacecraft, each with four high-quality cameras and laser communications systems on-board. Using ground-based lasers combined with ‘sails’ on the craft to accelerate them to 15-20% of light speed, they would reach Alpha Centauri in approximately 20 years and beam back high-quality images to Earth. With 100M USD in initial funding already allocated, I think this is the project to watch as they plan to get the first craft launched as soon as 2036.
Hopefully one of these missions will be able to gather conclusive evidence of the existence of extra-terrestrial life in my lifetime, so they’ve got 50 years or so, give or take. Will technology leap forward to allow not just tiny spacecraft to travel at near-light speeds, but actual manned missions? I certainly hope so.
So far I’ve only looked at this from the point of view of us going out there. There is also the subject of them coming here, and maybe that’s something that will happen a lot sooner, or has it already? For more on that, check out part 2.