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Greenhouse gases can help detect alien life on distant planets

The search for extraterrestrial life has captivated our imaginations for centuries. Now, a study from the University of California, Riverside (UCR) suggests a tantalizing possibility: we may be able to detect alien activity and civilizations by identifying artificial greenhouse gases they use to terraform planets.

What is terraforming?

Terraforming, a concept popular in science fiction, involves transforming a planet’s environment to make it hospitable for life as we know it. This process aims to alter various aspects of a planet to create conditions that are suitable for human habitation or for Earth-like organisms to thrive.

Altering the atmosphere

One of the primary goals of terraforming is to modify the planet’s atmosphere. This could mean increasing or decreasing the levels of certain gases to create a breathable environment.

For instance, adding oxygen and reducing harmful gases like carbon dioxide or methane could make the air safe for humans. Another aspect could involve creating a stable climate by controlling greenhouse gases to regulate the planet’s temperature.

Temperature modification

Adjusting the planet’s temperature is crucial for making it habitable. This could involve warming a planet that is too cold or cooling one that is too hot.

Techniques might include introducing greenhouse gases to trap heat and raise temperatures or installing reflective materials to reduce heat from the sun. The goal is to reach a temperature range where liquid water can exist, as water is essential for life.

Surface topography changes

Terraforming may also involve altering the planet’s surface topography. This could include creating bodies of water, such as lakes or oceans, and modifying landforms to support vegetation and human infrastructure.

The addition of soil and nutrients to barren landscapes could enable the growth of plants, which in turn could help produce oxygen and stabilize the environment.

Creating suitable conditions for life

The overarching aim of terraforming is to create conditions similar to those on Earth. This involves ensuring the right balance of atmospheric pressure, gravity, and radiation levels.

By mimicking Earth’s environment, terraformers hope to establish a stable ecosystem where humans and other Earth-like organisms can live and thrive.

Gases signal alien activity

UCR astrobiologist Edward Schwieterman and his team have identified five specific greenhouse gases that could serve as technosignatures, or indicators of technological activity, on distant exoplanets (planets outside our solar system). 

These gases are fluorinated versions of methane, ethane, and propane, along with gases made of nitrogen and fluorine or sulfur and fluorine. They are primarily used in industrial processes on Earth, such as manufacturing computer chips.

“For us, these gases are bad because we don’t want to increase warming. But they’d be good for a civilization that perhaps wanted to forestall an impending ice age or terraform an otherwise-uninhabitable planet in their system, as humans have proposed for Mars,” explained Schwieterman.

Why do planet gases indicate alien life?

These fluorinated gases offer several advantages as potential terraforming agents:

Potent greenhouse effect: They are incredibly effective at trapping heat, with some having thousands of times the warming power of carbon dioxide. This means a relatively small amount could significantly raise the temperature of a cold planet.

Longevity: The gases are remarkably long-lived, persisting in Earth-like atmospheres for tens of thousands of years. This reduces the need for frequent replenishment to maintain a habitable climate.

Ozone-friendly: Unlike some other proposed technosignature gases, like CFCs, these fluorinated gases are chemically inert and wouldn’t harm the ozone layer, which is essential for protecting life from harmful ultraviolet radiation.

Detectable infrared signatures: The gases absorb infrared radiation, creating unique signatures that could be detected by space telescopes like the James Webb Space Telescope or future observatories.

Linking alien activity and planet gases

The researchers simulated a scenario in which these gases were present on a planet in the TRAPPIST-1 system, located about 40 light-years away. TRAPPIST-1 is home to seven known rocky planets and is a prime target for studying exoplanetary atmospheres. 

The simulations showed that even tiny concentrations of the gases – as little as one part per million – could be detectable with current or planned technology.

Schwieterman noted that searching for these technosignatures wouldn’t require any additional effort if telescopes are already examining a planet’s atmosphere for other reasons. 

“You wouldn’t need extra effort to look for these technosignatures, if your telescope is already characterizing the planet for other reasons,” he said. “And it would be jaw-droppingly amazing to find them.”

New era in the search for alien life

This research not only opens up a novel avenue for detecting extraterrestrial intelligence but also highlights the remarkable capabilities of our current and future telescopes. 

“Our thought experiment shows how powerful our next-generation telescopes will be. We are the first generation in history that has the technology to systematically look for life and intelligence in our galactic neighborhood,” said Daniel Angerhausen, a collaborator from the Swiss Federal Institute of Technology.

While the odds of finding these technosignatures in the near future remain uncertain, the possibility of detecting alien civilizations through their planetary engineering efforts is both exciting and thought-provoking. 

As our technology advances, we may be on the cusp of answering one of humanity’s most profound questions: Are we alone in the universe?

The study is published in The Astrophysical Journal.


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