'Extremely Large Telescope' being built in Chile could detect signs of alien life in a single night

The Extremely Large Telescope (ELT), currently under construction in northern Chile, will give us a better view of the Milky Way than any ground-based telescope before it.

It's difficult to overstate how transformative it will be. The ELT's primary mirror array will have an effective diameter of 39 meters. It will gather more light than previous telescopes by an order of magnitude, and it will give us images 16 times sharper than the Hubble Space Telescope. It's scheduled to come online in 2028, and the results could start flooding in literally overnight, as a recent study shows.

One of the most powerful features of the ELT will be to capture faint atmospheric spectra from the atmospheres of exoplanets. This is usually done as a planet passes in front of its star from our vantage point. A small bit of starlight passes through a planet's atmosphere to reach us, and by analyzing the absorption spectra we can determine the molecules contained in the planet's atmosphere, such as water, carbon dioxide, and oxygen. The James Webb Space Telescope (JWST) has gathered data on several exoplanet atmospheres, for example.

But sometimes the transit data we can gather is inconclusive. For example, when JWST looked for atmospheres on the planets of the TRAPPIST-1 system, it seemed that the planets b and c were airless, but the data isn't strong enough to rule out the presence of atmospheres. There might be thin atmospheres with spectral lines too faint for JWST to observe. The ELT's greater sensitivity should be able to settle the question.

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What's even more exciting is that the ELT should be able to gather spectra not just on exoplanets that transit their star, but also from non-transiting exoplanets via reflected starlight.

To determine just how powerful the ELT will be, this new study simulated results for several scenarios. They focused on planets orbiting nearby red dwarf stars, since those are the most common types of exoplanets, and looked at four test cases: a non-industrial Earth rich in water and photosynthesizing plants, an early Archean Earth where life is just starting to thrive, an Earth-like world where oceans have evaporated, similar to Mars or Venus, and a pre-biotic Earth capable of life but where there is none. For comparison, the team also considered Neptune-sized worlds, which should have significantly thicker atmospheres.

The idea was to see if the ELT could distinguish between the different Earth-like worlds, and more importantly, whether the data could trick us into a false positive or negative. That is, whether a lifeless world would appear to have life or a living world would appear barren.

Based on their simulations, the authors found that we should be able to make clear and accurate distinctions for nearby star systems. For the closest star, Proxima Centauri, we could detect life on an Earth-like world with only ten hours of observation. For a Neptune-sized world, the ELT could capture planetary spectra in about an hour.

So it seems that if life exists in a nearby star system, the ELT should be able to detect it. The answer to perhaps the greatest question in human history could be found in just a few years.

The original version of this article was published on Universe Today.