Well, Where BY AUSTIN GLOCK Over the summer, I was working in the university’s observatory to detect exoplanets, which are essentially any planet outside of our solar system. This concept usually inspires the same kind of questions in people, some variation of “Do you believe in aliens?” I always gave a generic response. Something like “I don’t believe aliens have been to Earth if that’s what you mean.” We would continue talking about aliens and, probably, science fiction media, and eventually move on. Once, after I gave my usual answer, I was asked, “Well, where are they?” Honestly, it’s a good question. Scientists have discovered over 5200 exoplanets as of the end of 2022 (1). You would think that, on one of those planets, there would be signs of life. In the grand scheme of the universe, it’s not as easy as it may sound. There are four main classifications of exoplanets that range in size and in type. The first two are the gas giant and the Neptune-like. These are both planet types with gaseous compositions that make up over half of all discovered exoplanets (1). But life as we know it wouldn’t be able to exist on these planets. Even though there’s a solid core, the gaseous planets don’t have a surface like other planets. Instead, we’ll need to look instead, to the other two classifications. First is the super-Earth. Don’t let the name fool you, all this means is that these planets are smaller than Neptune but larger than Earth. They can have a gaseous atmosphere like Neptune or a rocky surface like Mars. Finally, and arguably most importantly,
Are
They?
is the terrestrial planet. As the name implies, these are planets that would have a solid surface similar to Earth, Venus, or Mercury. They make up only about four percent of all confirmed exoplanets, but these are the planets that would be able to host life somewhat recognizable to us (1). We know what planets to look at. Now we need to figure out what to look for. Astronomers will look for planetary signatures that would only appear if life was present. Biosignatures are a great example. The idea is that life changes the composition of the planets, whether intelligent or not. If the Earth were being observed from a different galaxy, those scientists would see how society has changed the composition of our atmosphere. There are three types of biosignature detection methods. Gaseous detection, where things such as photosynthesis would lead to the production of oxygen from carbon dioxide. Then there is surface detection, where the formation of forests, cities, and other physical structures can affect the reflection and absorption of light. Finally, temporal detection, where time-dependent factors are used. Let’s say aliens several galaxies away were observing Earth, the changing of seasons could be detected using the temporal method (2). If astronomers wanted to look for advanced civilizations, it becomes even harder. A planet with flora and fauna would be detectable with biosignatures, but what if scientists are looking for a response? Well luckily, there are technosignatures.
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