What do you do when you smell petrichor?

What do you do when you smell petrichor-that pleasant fragrance that accompanies the first rain after a long period of dry, warm weather-in the air? Do you step out to enjoy the rain? Do you wish for your favourite snack while you have a look at the rains from the balcony? For some researchers from Harvard, however, raindrops are the answer to identifying potentially habitable planets outside our solar system.

Size matters

In a recent study, these researchers have identified that raindrops are very similar across different planetary environments, even if these planets are as different as Earth and Jupiter. Furthermore, they have realised that understanding the behaviour of raindrops on other planets would not only be key to finding out the ancient climate on planets such as Mars, but also in identifying potentially habitable planets outside the solar system.

Water in the atmosphere plays, a big role in planetary climate. Therefore, whether or not a raindrop makes it to the surface of a planet is an important aspect and this is determined by its size. If the drop is too big, it will break apart due to insufficient surface tension irrespective of the material it is made of. If it is too small, it will evaporate before striking the surface.

Three vital properties

Using three properties, researchers were able to identify a zone for the raindrop size that would be just right. One of these is the drop shape, which depends on the heaviness of the drop and is the same across different rain materials. The falling speeds of the raindrops, which is a function of this shape, gravity and thickness of air, and evaporation speed, which is more complicated, are the two other properties. Based on these three properties, the conclusion that only a small fraction of possible drop sizes can reach the surface of any planet was reached.

If human beings eventually step foot on another habitable planet, a lot of things might be very different from how it is on Earth. One thing that might feel familiar could be the raindrops!

 

Picture Credit : Google

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