Wednesday, February 24, 2021

The multidisciplinary approach of astronomy

One of my favourite aspects about the subject of astronomy is that it inevitably leads one to examine other areas of science. In order to understand the other planets that inhabit our solar system, we must formulate an understanding in astronomy, physics, geology, chemistry, and meteorology. Without this multidisciplinary approach, most of the universe would be a mystery to us. I recall first learning about the planet Venus, which was one of the earliest examples I can recall of coming to this multidisciplinary realization. 

I found it interesting that although Venus is further from the sun than Mercury, it still has a surface temperature that was higher. With temperatures reaching over 450°C on the surface, Venus is home to the highest surface temperatures in the solar system. However, stranger still is the fact that the surface of Venus is completely hidden by a complete cover of clouds that encompasses the planet. In fact, Venus reflects more sunlight into space than the Earth does. About 70% of the sunlight that reaches Venus is reflected back into space, while the Earth reflects about 30%. When this is taken into account to calculate the surface temperature of Venus, it should have a surface temperature lower than the Earth. Although its atmosphere is about 90 times heavier than Earths, even this can’t account for the drastic difference in surface temperature. However, as it turns out, it’s the composition of the Venusian atmosphere that causes surface temperatures to be so high. Unlike the Earth, where our atmosphere is composed mostly of nitrogen and oxygen, the atmosphere of Venus is almost entirely composed of carbon dioxide. As a greenhouse gas, carbon dioxide is transparent to incoming solar radiation but opaque to outgoing heat. Greenhouse gases have a unique configuration, with their shape allowing heat to pass through but trapping it near the surface of a planet. On Earth, we’ve been fortunate enough to live under a relatively moderate greenhouse effect. Without greenhouse gases in our atmosphere, the Earth would freeze over.

Although a bit of a greenhouse effect is a good thing, too much greenhouse gases in a planetary atmosphere can cause a runaway greenhouse effect, as is the case with Venus. Although Venus reflects most of the sunlight reaching it, the sunlight that does manage to penetrate the cloud layer is unable to escape into space. Rather, the heat gets stuck near the surface, raising the temperature to truly hellish conditions. Venus is a sobering reminder of just how important it is for a planet to maintain a stable greenhouse effect if it is to remain habitable. Over the last century, scientists have observed a disturbing rise in the concentration of greenhouse gases in our atmosphere, a rise that is unprecedented in the last few million years. Although the Earth won’t likely end up in a situation like Venus, even slight changes to our greenhouse effect can have drastic consequences for the average surface temperature of our planet. As the primary cause of these changes, we humans have a lesson to learn from our nearest planetary neighbour. Image credit: NASA 

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