No aliens yet, but signs from distant planet are interesting

Imagine observing our Sun from 120 light-years away, using an observatory as powerful as our James Webb Space Telescope (JWST), trying to figure out whether there are planets around our Sun, and whether there are signs of life on any of them.

- Somak Raychaudhury

Even with the most powerful of telescopes, the planets are so close to the bright star that they cannot be individually seen, but the presence of the largest ones like Jupiter can be felt as a tiny dimming in brightness as it passes in front of the star. During this transit, some of the starlight passes through the atmosphere of the planet on the way to the telescope. Different gases in the atmosphere absorb light at specific wavelengths, leaving a unique "fingerprint" in the transmitted light spectrum. JWST's infrared range allows it to probe wavelengths where many important molecules, including water, methane, carbon dioxide, and various potential biosignatures, exist.

The oxygen and methane in the Earth's atmosphere, which are indicators of biological activity, albeit inconclusive, would be too faint to be detected by an alien JWST from 120 light-years ago. However, from an orbit near the Earth, the JWST has indeed detected possible biosignatures such as methane and carbon dioxide between wavelengths of 2-6 micrometers in several exoplanets hundreds of light-years away.