MEXICO: How do you go about hunting for life on another planet elsewhere in our galaxy? A useful starting point is to imagine looking from afar for signs of life on Earth.
In a telescope like those we have on Earth, those aliens would likely just see the Earth and sun merged together into a single pale yellow dot.
If they were able to separate the Earth from the sun, they’d still only see a pale blue dot.
There would be no way for them to image our planet’s surface and see life roving upon it.
However, those aliens could use spectroscopy, taking Earth’s light and breaking it into its component colours, to figure out what gases make up our atmosphere. Among these gases, they might hope to find a “biomarker”, something unusual and unexpected that could only be explained by the presence of life.
On Earth, the most obvious clue to the presence of life is the abundance of free oxygen in our atmosphere. Why oxygen? Because it is highly reactive and readily combines with other molecules on Earth’s surface and in our oceans. Without the constant resupply coming from life, the free oxygen in the atmosphere would largely disappear.
