Revealed: hundreds of billions of stars. Now let’s search them for life.

 Extract from The Guardian

Opinion

James Webb space telescope

Louisa Preston

For astrobiologists like me, the first image from Nasa’s James Webb Space Telescope reveals infinite possibilities of life beyond Earth.

Two observations of the Southern Ring nebula – in near-infrared light (left) and mid-infrared light (right).

Thu 14 Jul 2022 17.00 AEST

Last modified on Fri 15 Jul 2022 02.16 AEST

This week the James Webb Space Telescope made history, proving itself to be the most powerful space-based observatory humanity has ever built and revealing a tiny sliver of the vast universe around us in breathtaking detail. Astronomers the world over have been shown cheering, in floods of tears and lost for words. Astrobiologists like myself, who study the origins, evolution, distribution and future of life in the universe, are getting pretty excited too. By revealing images of galaxies from the dawn of time and chemical data of planetary atmospheres, the JWST has the power to help us answer one of humanity’s oldest questions: are we alone in the universe?

The first spectacular image released was of the galaxy cluster SMACS 0723, known as Webb’s First Deep Field. This image covers just a patch of sky approximately the size of a grain of sand held at arm’s length by someone on the ground – and yet it is crowded with galaxies, literally thousands of them. Within each galaxy, there could be on average 100 billion stars, each with its own family of planets and moons orbiting them.

Given the fact that in our solar system alone we have multiple habitable (Earth) or potentially habitable (Mars, Europa, Enceladus, Titan) worlds, then the odds of finding other planets or moons out there with the potential for hosting life as we know it have increased exponentially. The universe is probably littered with them.

Using a different instrument called MIRI (Mid-Infrared Instrument) on the same view reveals even more about the character of these stars and galaxies . Some appear blue because of not having much dust and older stars, while other objects, probably galaxies, appear red because they are shrouded in dust. For me, the most exciting are the galaxies now coloured green. The green indicates that the dust in these galaxies includes a mix of hydrocarbons and other chemical compounds – the chemical building blocks of life. ]

Galaxy cluster SMACS 0723 taken from Webb’s First Deep Field, the first infrared image from NASA’s James Webb Space Telescope, shows dust levels in galaxies indicated by the colours blue, red and green. Photograph: NASA/Reuters

The team has also released an infrared spectrum taken with the Fine Guidance Sensor and Near Infrared Imager and Slitless Spectrograph (FGS-NIRISS) instrument, which analysed starlight as it passed through the atmosphere of Wasp-96b, a hot, Jupiter-like planet 1,150 light years away, orbiting closer to its star than Mercury does to our Sun. This bunch of wavy lines revealed to us the presence of water vapour in its atmosphere (the planet is way too hot for liquid water). This is a sensational result, and now the detective work really begins as we search the smaller, rocky planets in the hope of finding worlds where conditions are suitable for life.

So how will we do this? We look for Earth-like atmospheres, ones dominated by nitrogen, carbon dioxide and water, as an Earth-like atmosphere is, by definition, our gold standard of habitability. But Earth’s atmosphere over the history of life hasn’t always been composed this way, and we are sure other atmospheric mixtures can create habitable worlds. We call these “habitability markers”, and they also include the glint of light reflecting off of oceans and the effects of vegetation.

Astrobiologists are also looking to find biosignature gases in these distant exoplanetary atmospheres – that is, gases indicative of biological activity. For example, oxygen is a dominant gas in Earth’s modern atmosphere, and most of it is produced from photosynthesis. Also, the dominant source of methane in our atmosphere is produced via methanogenesis, an ancient form of metabolism for some micro-organisms. I should say here that identifying unambiguous signatures of life isn’t going to be easy. Many have abiotic (non-life) sources as well as biological ones; they can be produced by volcanoes, water-rock interactions or even human activity.

At least for now, only those biosignatures with a global, planetary impact will probably be detectable. However, the detection of these habitability markers or biosignature gases using the JWST will be enough of an enticement to make us pause and more deeply explore the worlds in question. And that is more than exciting enough for now.

The JWST has already, in just a few days, transformed the way we look at the universe and will in the future open our eyes to the chemical and, if we are lucky, biological makeup of other worlds in it. Perhaps, we will finally get the proof that life in one form or another is universal, and, as I have always believed, that we have never actually been alone.

• Louisa Preston teaches planetary science and astrobiology at the UCL Mullard Space Science Laboratory.