Honestly, I wish I could tell you: “Yeah, we know of aliens that are actually very similar to Yoda in Star Wars, and they thrive on a planet very similar to ours on the other side of our galaxy.”

But the truth is: WE HAVE NO IDEA what aliens look like or where they could exist!

That being said, there are steps we can take that bring us closer to answering the big question: Are We Alone?

The first one is to settle on what we are looking for, that is:

What do we mean by Life? Or put in a more comprehensible way: What do we consider alive or living, and how do recognize it?

Have a chat with your friends, compare living and non-living objects and go outdoors to find living things! What are the characteristics that distinguish them?

Easy quiz about living and non-living things and their characteristics: https://www.turtlediary.com/quiz/living-and-nonliving-things.html

Scientists define life in very different ways: chemists, biologists, physicists, philosophers, etc all use different descriptions.

However, they tend to agree on common characteristics which are the ability to use energy, grow and reproduce.

Now, plants and animals are easy: you can see them move, eat, and you can tell they are alive from the naked eye! But there is also a great deal of life forms we can’t see! For example, did you know that human cells only represent 43% of your total body-cell count? The rest is made up of bacteria and all sorts of micro-organisms that thrive on us!

How do we account for that in Astrobiology?

Well, the good news is, even though we can’t see them, usually when we look hard enough, we can spot their impact on their surroundings. You can do the following ACTIVITY to see that for yourself:

• In two different containers, pour a bit of sand.
• Add a tablespoon of dry yeast into one of the containers only = adding life
• Add one spoon of sugar in each container = adding food
• Add a small amount of hot water to each container

QUESTIONS: Do you observe any reaction? In which container? What do you think it means?

⇒ We observe a bubbling reaction in the yeast container, which we interpret as a sign that the yeast is eating the sugar. Although we can’t see the yeast itself, we can prove it is there!

If you’re curious, here’s what yeast feasting on sugar looks like under the microscope: https://www.youtube.com/results?search_query=yeast+eating+sugar.

Therefore, when we can’t see living things, what we look for is evidence of their presence. In short, astrobiologists embark in a constant treasure hunt for hints of life – whether it is actually defining these hints or looking for them using powerful instruments! Go to the next step to learn more about this!