Webb Space Telescope Might Be Able To Detect Other Civilizations by Their Air Pollution

The James Webb Space TelescopeThe James Webb Space Telescope (JWST or Webb) is an orbiting infrared observatory that will complement and extend the discoveries of the Hubble Space Telescope. It covers longer wavelengths of light, with greatly improved sensitivity, allowing it to see inside dust clouds where stars and planetary systems are forming today as well as looking further back in time to observe the first galaxies that formed in the early universe.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>James Webb Space Telescope (JWST), launched last December, has been slowly powering up its instruments and unfurling its sunshield, and is now in the process of aligning its mirrors in preparation for operation. Within a few months, the most powerful space telescope ever built is going to set its sights on the stars. Astronomers are hoping that what JWST sees will change the way we understand our universe, just as the Hubble Space TelescopeThe Hubble Space Telescope (often referred to as Hubble or HST) is one of NASA's Great Observatories and was launched into low Earth orbit in 1990. It is one of the largest and most versatile space telescopes in use and features a 2.4-meter mirror and four main instruments that observe in the ultraviolet, visible, and near-infrared regions of the electromagnetic spectrum. It was named after astronomer Edwin Hubble.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>Hubble Space Telescope did decades before.

One tantalizing capability that JWST offers that Hubble could not is the opportunity to directly image planets orbiting distant stars, and maybe, just maybe, detect signs of life.

The possibility of remotely detecting biosignatures has been a hot topic in recent years. In our own solar system, the recent discovery of phosphine in VenusVenus, the second planet from the sun, is named after the Roman goddess of love and beauty. After the moon, it is the second-brightest natural object in the night sky. Its rotation (243 Earth days) takes longer than its orbit of the Sun (224.7 Earth days). It is sometimes called Earth's "sister planet" because of their similar composition, size, mass, and proximity to the Sun. It has no natural satellites.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>Venus’ atmosphere sparked speculation that the chemical might be created by a microbial lifeform. Similarly, remote sensing experts have proposed that plant life – which uses photosynthesis for energy – could be detected in infrared wavelengths, as chlorophyll absorbs visible light, but shows up brightly in infrared, and would give planets covered in foliage a distinct ‘red edge‘. A single-pixel photo of a distant planet just might contain enough information to tell us if biological life is there, based on the information stored in the wavelengths of light that reach the telescope lens.

An artist’s impression of the James Webb Space Telescope, fully deployed. The James Webb Space Telescope is expected to be fully operational this summer. Credit: NASA

But what about intelligent life? Could JWST detect civilizations similar to ours? How would we look for them? The best answers come from understanding what humanity’s presence on Earth looks like from outer space. We give off waste heat (from industry and homes and so on) and artificial light at night, but perhaps most significantly, we produce chemicals that fill our atmosphere with compounds that wouldn’t otherwise be present. These artificial atmospheric constituents just might be the thing that gives us away to a distant alien species scanning the galaxy with their own powerful telescope.

A recent paper – available in preprint on ArXiv – examined the possibility of using JWST to search for industrial pollutants in the atmospheres of exoplanets. The paper focused specifically on chlorofluorocarbons (CFCs), which, on Earth, are produced industrially as refrigerants and cleaning agents. CFC’s infamously created a massive hole in Earth’s ozone layer in the 1980s, before an international ban on their use in 1987 helped reduce the level of CFCs back to less harmful levels. These “potent greenhouse agents with long atmospheric residence times,” if found elsewhere in the galaxy, are almost certain to be the result of a civilization capable of rampant industrialization.

In other words, some of humanity’s worst byproducts – our pollution – may be the very things that make us detectable. And it means that we may be able to find other species capable of treating their own planet’s atmosphere with the same disregard.

An artist’s rendition of TRAPPIST-1e, a potentially habitable, Earth-sized planet circling a red dwarf 40 light-years away. Credit: NASA/JPL-Caltech

There are some limitations to JWST’s CFC finding capabilities. If a planet’s star is too bright, it will drown out the signal. The telescope will therefore have the most success by looking at M-class stars, which are dim, long-lived red dwarfs. A nearby example is TRAPPIST-1, a red dwarf 40 light-years away, with several Earth-sized planets orbiting within its habitable zone. JWST would be able to see CFCs on TRAPPIST-1’s planets, because the dim star won’t drown out the CFC signature in the same way that a bright star, like our Sun (a G-type star), would.

Conversely, a JWST-like telescope at TRAPPIST-1 wouldn’t be able to see Earth’s CFCs: our Sun is just too bright.

Unfortunately, M-class stars are not usually conducive to life, because when they are young, they are unstable, sending out powerful solar flares that might just exterminate any nascent life on nearby planets. They do, however, tend to calm down as they age, so it isn’t an impossibility. It just means that we should temper our expectations a bit.

Whatever we find, or don’t find, out there, the fact that we are about to have the capability to look at all is a game-changer. As the paper concludes, “with the launch of JWST, humanity may be very close to an important milestone in SETI [the Search for Extra-Terrestrial Intelligence]: one where we are capable of detecting from nearby stars not just powerful, deliberate, transient, and highly directional transmissions like our own (such as the Arecibo Message), but consistent, passive technosignatures of the same strength as our own.”

Reference: “Detectability of Chlorofluorocarbons in the Atmospheres of Habitable M-dwarf Planets” by Jacob Haqq-Misra, Ravi Kopparapu, Thomas J. Fauchez, Adam Frank, Jason T. Wright and Manasvi Lingam, 11 February 2022, Astrophysics > Earth and Planetary Astrophysics.
arXiv:2202.05858

Originally published on Universe Today.