Now that we know how to recognize living from non-living things, we want to actually understand where it makes the most sense to search for life. Since life on Earth is the only example we know, most of our search for life in the Universe is focused on life-as-we-know-it.

Can you think of any requirement of life? What is the bare minimum needed for living? For example, in our previous experiment with yeast (see 2. Alive or not Alive, that is the question), what allowed the yeast to create this bubbling reaction?

⇒ Scientists have agreed that life on Earth requires water, organic molecules (like carbon) and a source of energy.

Can you cite different energy sources for life on Earth? For example:

 

 

What is the energy source for animals?  ⇒ food!

 

 

 

 

 

For plants?  ⇒ sunlight and nutrients in the soil!

 

 

 

 

 

 

For deep-sea organisms?  ⇒ heat from volcanoes and nutrients in the water!

 

 

 

 

Keeping this in mind, it’s time to start thinking about which environments meet these conditions beyond Earth. That’s it! We begin our search for life in the Universe!

Let’s start small (not that small actually…): the Solar System. Where could there be life in the Solar System? Look at these beautiful pictures from NASA and pick the places where you think life is the most likely to survive:

 

 

A mild 5 000°C environment…

 

 

 

 

 

Once covered in land and oceans, it’s now a cold, dry and very dusty place…

It might be interesting here to introduce the idea of present VS past life and how Astrobiology can also look for fossilized forms of life.

 

 

 

 

 

 

Our twin planet with sulfuric acid clouds and a concentrated CO2-atmosphere…

 

 

 

 

 

 

Under its thick ice crust lies an immense ocean…

 

 

 

 

 

 

 

These wonderful asteroid rings dance around a high gravity, high pressure and extremely windy place with no “hard surface” to step on…

 

 

 

 

 

A small object that travels enormous distances only to vaporize instantly when it enters our atmosphere…

 

 

 

 

⇒ For now, scientists have determined that the most astrobiologically interesting objects in our Solar System were:

• Mars, especially for past life as it was once very similar to Earth
• Europa and Enceladus as huge water-oceans lie under their thick ice shells
• Controversially, Venus and its thick clouds (Indeed, did you know that clouds on Earth are teeming with microscopic life?)

 

The playground where we get to search for life gets even bigger… Beyond the Solar System are thousands of other planets – called exoplanets – that orbit other stars and form other stellar systems. More than 4 000 exoplanets have been discovered so far! The Galaxy counts more than 100 billion stars and astronomers think that each one of them hosts at least one planet! Yes, all the little shiny dots that you observe at night are the home to a planet where some form of life might be present!

 

 

 

 

 

 

 

 

 

However, most of these exoplanets look like nothing we’ve seen before and determining which one is habitable is extremely complicated. It’s already hard to figure out what our own Solar System hosts, so you can imagine for planets many MANY billions of kilometres away from us…

How do we do that and where are we in our endeavours? How close are we to a first bit of answer?

Go to the next step to find out!