Search for Life

An artistic representation of the surface of the exoplanet TRAPPIST-1 f. (Credit: NASA/JPL-Caltech)
An artistic representation of the surface of the exoplanet TRAPPIST-1 f. (Credit: NASA/JPL-Caltech)

Humans have wondered “Are we alone in the Universe?” since before recorded history. Now, for the first time, our scientific and technological progress has reached a point where we can seriously imagine answering that question in the near future.

So far, we have only one example of life in the Universe, and that’s right here on Earth. As wildly different as life can be here at home (from bacteria to blue whales), one thing they all share is a fundamental need for liquid water. Water plays a crucial role as a universal solvent that allows molecular processes to happen inside cells. Without liquid water, nothing on Earth would be alive. This is a good place to start our search for extraterrestrial life and provides a solid criterion for planet hunting.


Potentially Habitable Exoplanets


An artist’s rendering of the habitable zones in the TRAPPIST-1 system (top) and our Solar System (bottom). Habitable zones are shown in green (Credit: NASA/JPL-Caltech)

Astronomers use the term habitable zone when they discuss how far away a planet is from its host star. A planet too close or too far from its star will have its water boiled away or frozen solid. The habitable zone is the region of space around every star where the temperature is just right for water to exist on its surface in liquid form. Just being in the habitable zone doesn’t guarantee a planet is habitable, however. For example, the habitable zone around our Sun may stretch from somewhere near Venus to somewhere near Mars, but Earth-like life is unlikely to survive on their hot and cold surfaces.

A large effort has been made to discover small rocky, or “terrestrial,” exoplanets. Among other projects, iREx has played a key role in developing SPIRou and NIRPS, two instruments designed to identify Earth-like exoplanets around small stars. A few dozen such “Earth 2.0” planets in the habitable zone have been discovered, but each planet needs to be studied individually to determine its habitability. We only have to look within our own Solar System at Venus, Earth, and Mars to see that having similar composition and size doesn’t mean the planets are habitable in the same way.

Mars is a dry, frozen tundra with very little atmosphere while Venus’ atmosphere is crushingly heavy, scorching hot, and full of acid. New generations of observatories like the James Webb Space Telescope are being designed with such powerful capabilities that they can study the individual atmospheres of small rocky exoplanets. The Canadian NIRISS instrument on the Webb Telescope, which was designed and built by many iREx researchers and their collaborators, is a perfect instrument to inspect these exoplanet atmospheres.


What might alien life look like?

Some examples of molecules detected in the atmosphere of an exoplanet that could be biosignatures. (Credit: Meixner, et al. 2021, JATIS)

Judging by Earth’s example, many researchers think that the most common type of life out there are simple life forms. If we look at Earth’s 4.5 billion year history, single-cell life appeared very quickly after its formation. Despite its early rise, all life on Earth remained microscopic for billions of years.

However, microbes being small doesn’t mean they’re undetectable!  Non-biological processes such as volcanoes and erosion produce chemicals like oxygen, carbon dioxide, and water vapour, but they do so with a specific balance. Biological processes can produce chemicals that change these balances in a way that only life can do. Such imbalances are called biosignatures and may be hints that life could be present on a planet. For example, if an alien observer were to measure Earth’s atmosphere, their detection of the extra oxygen might lead them to believe that Earth hosts lifeforms capable of photosynthesis (e.g. trees, algae, plankton, etc.).

What about intelligent life? The most straightforward way to search for sapient life is to look for civilizations that communicate using radio waves (like we do) using sensitive radio telescopes. The Search for ExtraTerrestrial Intelligence (SETI) Institute has been “listening” to the sky for years. So far, there have been no conclusive detection of life yet, but the search continues, and we are always learning things in the process.


The search for alien life at iREx

Many iREx researchers are making important contributions to the search for habitable planets and extraterrestrial life. To learn more, we invite you to read their profiles: