University of Helsinki
Do you feel lonely in this vast universe? Hoping that the twinkling star you’re gazing upon is someone else’s sun? Astronomers are working hard to uncover the mysteries of our universe and maybe, one day, find us an exoplanetary pen pal.
Firstly, where would we find these far-away friends? Most likely not on a sun, or an asteroid, and especially not in a black hole (although who knows?). A planet maybe much like our own – but many, many lightyears away, an exoplanet. An exoplanet is what you call a planet outside of our solar system, the nearest one being “only” 4.7 lightyears away, great. Now, let’s get embark on our search!
One way to do it is the radial velocity method. No matter how big the stars get, they are still influenced by their planet’s gravity. And through observing the wavelengths that radiate off of the star, scientists can tell if a planet is dancing around it, as the slight movement of the star makes the lightwaves shift between blue and red periodically. They can even determine the size of the planet and how fast it orbits the star just by looking at the waves!
But the most successful way of finding these far-away planets so far has been the transit method. A whopping 77% of all exoplanets have been found using this method! As a planet passes in front of the star, the star dims a tiny amount, just like a fly speeding around a light bulb. Through monitoring the star’s reoccurring decrease in brightness, which is called a “transit,” scientists can identify an exoplanet.
So we have found planets, great! Specifically, over 5000 exoplanets have been found, and now we just need to rule out the ones that are non-habitable. We can start with what we know: our life. By examining Earth’s circumstances, scientists have acquired many guidelines for what to look for: the planet’s distance from the sun, the atmosphere, and the presence of liquid water, among others. So how do we do it?
It’s easier said than done, but we can start by looking for planets that lie within the so-called habitable zone, also known as the Goldilocks zone. These planets are just in the sweet spot where it’s not too cold and not too hot, but just right. Here, carbon-based life can survive; the sun’s radiation is not too high, and water can exist in its liquid form. But the location is not all that’s needed for life to thrive. Life, as we know it, needs a sufficient atmosphere of oxygen, ozone, and methane, and of course, water.
But unfortunately finding exoplanets is far from easy. It requires intricate calculations, a mix of methods and fair amount of waiting, and in the end it is costly, and our technology is quite limited. Space is way vaster than we could ever fathom, and even examining the closest exoplanets is a colossal challenge. But almost daily new exoplanets are being found, but the crucial question of whether they are habitable or not remains mostly unanswered. Most of the planets found are not rocky like earth, they are gassy, like Jupiter, – which we, or anybody else, would find inhospitable.
When searching for habitable planets, we look for Earth-like circumstances. As the only life we know is on our green and blue planet. Searching and determining the properties of these thousands of exoplanets is time-consuming and, simply put, super hard. So while you may not have an alien pen pal, we can hope that someday our descendants have, so for now you’ll have to find yourself a new friend here on earth – maybe even in this comment section!
Name: Fiia Virtanen
Source: Ghezzi, L. (2023) “The search for habitable planets”, “Revista Mexicana de Astronomía y Astrofísica Serie de Conferencias (RmxAC)”, 55, 10-14
https://www.astroscu.unam.mx/rmaa/RMxAC..55/PDF/RMxAC..55_LGhezzi-II.pdf