Exoplanet biosignations in the atmosphere

Exoplanet biosignations in the atmosphere

The chemical composition of the exoplanet atmosphere can be studied with spectroscopy. The elements and molecules needed for life, called bio-signs, make the planet potentially lifeable. However, they will require suitable telescopes, one of which is James Webb.

Astrobiologists and those who search for life in the universe study how star light interacts with the planet's surface or atmosphere, because if the surface or atmosphere has been changed by life, light can contain some clues called biosignations.

Spectroscopy as a Biosynchronous Detection Method

There are three main methods for studying the exoplanet atmosphere:

  • When the planet passes before its star, we can observe the change in the light flux of the star. First, it will be reduced because part of the star will be hidden by the planet during its passage. Also, by watching the light of the star filter through the planet ' s atmosphere, we will notice that some wave lengths have been absorbed. This is because some molecules and atoms in the atmosphere absorb certain wave lengths. This method can be used to recognize the presence of certain atmospheric gases associated with life, such as oxygen or methane, because these gases leave very specific traces on the light. Reflective spectroscopy. At any time in orbit, but especially during the coating period, the light of the star may reflect from the atmosphere and return to Earth. Emission spectroscopy. When the planet and/or its atmosphere are hot enough to produce enough radiation to detect them. Of course, they are only visible when the planet is not in front of the star, but is in a state of "out of transit".

Earth as a test site

Before trying to discover alien life on another planet, it would be good to understand what the atmosphere and the surface of the planet on which we believe life has evolved, so let's start with our own Earth.

Of course, the habitat profile of our planet has changed over several billion years, and during the first half of its existence, there was a simple, one-cellular life on it, and at that time its atmosphere was devoid of oxygen, and if we had seen it in a telescope from a distant planet, we would have seen light biological traces in it.

The situation changed dramatically, 2.4 billion years ago, when a new algae family came into being, and there was a photosynthesis process that produced free oxygen. . Since then, the oxygen-rich atmosphere of the Earth has left strong and easily detectable biosyngatures in its passing light.

Can James Webb detect bio-symbols?

To detect these subtle changes in the light of a potentially life-friendly exoplanet, you need an incredibly powerful telescope. So far, the only telescope capable of doing this is James Webb's space telescope. One of the first images of Webb released last week is the exoplanet spectrum itself. It's a gas giant, WASP-96b.

However, the fact that the spectrum showed the presence of water and clouds should not impress us. It is unlikely that life may exist on a planet as large and hot as WASP-96b. However, these first data show that Webb can detect weak chemical traces in the light of an exoplanet. Webb will turn its mirrors in the coming months towards TRACPIST-1e, potentially suitable for a planet the size of Earth, just 39 light years from us.

Webb will be searching for biological signatures on TRACPIST-1e and other exoplanets using spectroscopy. But since it is not designed to look for life, it can only detect changes in atmospheric levels of carbon dioxide, methane and water vapour. Although some combinations of these gases may indicate the existence of life, unconnected oxygen remains the strongest signal. And Webb cannot detect its presence.

Most suitable telescopes for biosynchronization

There are several plans for future space telescopes that favour the spectroscopy of reflection and include plans to block the bright light of the planet's host star to detect the star light reflected from the planet itself.

This idea is like using a hand to cover up sunlight to see something far away. Future space telescopes can use small inner masks or large outer spaceships like umbrellas to do so. When the light of the stars is blocked, it becomes much easier to study the light reflected from the planet.

There are also three huge ground telescopes currently under construction that can search for biosymbols: the Giant Magellen Telescope, the 30-metre telescope, and the European Very Large Telescope, each of which is much more powerful than the telescopes that currently exist on Earth, and although the Earth's atmosphere distorts the light of the stars, these telescopes may be able to explore the atmosphere of the nearest worlds in search of free oxygen.