Okay kiddo, let me explain to you about the Viking Lander Biological Experiments.
So, a long time ago, some smart humans built a spacecraft called Viking Lander which travelled all the way to a planet named Mars. Now, this planet is very different from our planet Earth. It has a very thin atmosphere and is very cold. So, to make sure that there is no harmful life on Mars, the Viking Lander was equipped with some science experiments.
One of these experiments was called the Viking Lander Biological Experiments or VBEX. Now, the aim of this experiment was to look for any signs of life on Mars. Scientists put soil samples from Mars into the experiment to see if any microbes (tiny living things) would grow.
At the VBEX, they added some special chemicals to the soil to see if the chemicals would react with the microbes and produce some gases. If they saw some gas being produced, it would mean that there were living things in the soil. It was like a science experiment that you do in your school lab, but on a much bigger scale!
So, the VBEX ran some experiments for a few weeks and they found some gas being produced. Scientists thought that they had found evidence of life on Mars! But, they weren't 100% sure if it was actual living things or if it was just some chemicals reacting to the soil.
Some scientists say that there was no life on Mars at all and that the Viking Lander Biological Experiments were not able to detect any life forms. But, it's still a very important experiment, because it helped us learn more about Mars and how we can find life on other planets in the future.
I hope that explains it to you, kiddo!