By Parshati Patel, PhD
Humans are naturally curious, and one of the most profound questions we have ever asked is: could there be life elsewhere in the universe?
What is life?
Before we can explore whether life exists elsewhere in the universe, we must first consider: what is life? Surprisingly, there isn’t a single definition everyone agrees on! NASA’s definition of life is “a self-sustaining chemical system capable of Darwinian evolution”. This definition encompasses a wide variety of life we see here on Earth, where liquid water is essential for sustaining life.
Since Earth is the only known planet where life exists, it serves as our only reference. Astrobiologists often study a special group of organisms, called extremophiles, that thrive in extreme environments. These organisms live in places that would be hostile or even deadly for most of the other lifeforms on Earth, like boiling hot springs in Yellowstone National Park or the depths of the ocean. By understanding how these organisms survive in such harsh places, we can imagine the types of environments and conditions that may support life elsewhere. From what we know, life requires temperatures that allow liquid water to exist, a source of energy, and the presence of chemical elements linked to life. These are the key elements scientists look for when they search for life in the universe.
Life in our Solar System
Within our Solar System, scientists are looking for life, or signs that life existed in the past, in places like the surface of Mars, and the subsurface oceans beneath the icy crusts of Jupiter’s moon Europa and Saturn’s moon Enceladus. Using spacecraft, rovers, and landers, we continue to explore these environments for clues of signs of life, either now or in the distant past.
How do scientists search for life outside of our Solar System?
Since we can only physically explore the objects in our Solar System due to the limitations of our current technologies, we use telescopes on Earth and in space to search for signs of life on exoplanets – planets that orbit stars outside our Solar System. Astronomers study the light from these exoplanets to understand what their atmospheres are made of, particularly, focusing on those in the habitable zone – the region around a star where conditions might allow for liquid water to exist. At the same time, scientists at the Search for Extraterrestrial Intelligence (SETI) Institute scan the skies for signals from distant civilizations that might be advanced enough to send messages into space.
Interestingly, scientists have found the building blocks of life – such as chemical elements and conditions needed for life – almost everywhere they have looked in space. With over 100 billion stars in our home galaxy and more than 100 billion galaxies in the universe, plus the discovery of more than 5,600 exoplanets so far and billions more that are believed to exist, many scientists believe that the Earth cannot be the only place with life. Whether that life is as simple as microorganisms or as complex and intelligent as humans remains to be discovered!
So, is there life beyond Earth? Most scientists believe there is, but we are still searching for the evidence!
Did you know there is an entire field of science dedicated to studying the potential for life beyond Earth? It is called astrobiology. The scientists in this field focus on understanding the origin, evolution, and distribution of life in the universe, searching for clues beyond and even right here at home.
Dr. Parshati Patel is an astrophysicist turned freelance science communicator and educator based in London, Ontario.
