Are we alone? The search in exoplanets for life beyond earth

Over the past few decades, astronomers have identified thousands of exoplanets — worlds orbiting stars beyond our own Sun — including some located within the so-called “habitable zone.” But does this imply the presence of life? The quest to find alien biology is only just beginning.

Until the latter half of the 20th century, the idea of planets existing outside our solar system remained largely in the realm of science fiction. That changed in 1995 when Swiss researchers Michel Mayor and Didier Queloz made a groundbreaking discovery: 51 Pegasi b, a gas giant orbiting a star roughly 50 light-years away. Though vastly different from Earth, its detection marked the dawn of a new astronomical era.

Today, thanks to advanced space observatories like NASA’s Kepler and TESS missions, the catalog of confirmed exoplanets exceeds 5,000. Many of these are situated in regions where surface temperatures could, in theory, allow liquid water — a key ingredient for life as we know it. This ongoing exploration has transformed the age-old question “Are we alone in the universe?” from a matter of philosophy into a subject of scientific inquiry.

Among the stars scattered across the cosmos, could some of these distant planets host life?

Detecting Other Worlds

Because exoplanets are incredibly faint and often lost in the glare of their host stars, astronomers typically rely on indirect detection techniques. The most widely used is the transit method, which involves monitoring a star’s brightness for periodic dips caused by a planet passing in front of it. Another approach, known as the radial velocity method, measures subtle changes in a star’s motion—caused by the gravitational tug of an orbiting planet—through shifts in its light spectrum.

These techniques have unveiled a remarkable diversity of planetary systems, from gas giants orbiting perilously close to their stars, to rocky Earth-sized planets in compact orbits. Some systems share structural similarities with our own, while others seem unlike anything previously imagined.

The “Goldilocks” Zone and Its Promise

Among the multitude of discovered planets, a select group lies in the so-called habitable zone — the orbital sweet spot where conditions might allow for liquid water. Earth sits comfortably within this range. By contrast, Venus is too hot and Mars too cold. Other potentially habitable exoplanets, such as Kepler-186f and TRAPPIST-1e, raise intriguing possibilities.

However, being in this zone doesn’t guarantee a planet is hospitable. Several other factors — including planetary mass, atmospheric composition, magnetic fields, and tectonic activity — play critical roles in sustaining life. A planet could theoretically be in the perfect orbit yet remain entirely barren or hostile to life.

Life on Earth has proven to be astonishingly adaptable, flourishing in environments as extreme as hydrothermal vents and radioactive zones. This resilience suggests that, once life begins, it may find a way to persist under a broad range of conditions. But what would life look like on a completely different world?

The Unknown Shapes of Alien Life

The truth is, we don’t yet know. Most scientific conjecture revolves around microbial organisms, as simple life evolved quickly and robustly on Earth. If more complex organisms exist elsewhere, they would likely require a long period of planetary stability to evolve. On planets with thick atmospheres, flying organisms might develop vast wingspans; on those orbiting dim stars, creatures with infrared vision might dominate.

Some worlds may be covered entirely by oceans, while others might be tidally locked, with one hemisphere in perpetual daylight and the other in eternal darkness. Any life that arises in such places would be shaped by these unique environmental constraints. It may not rely on photosynthesis, may not use oxygen, and may not resemble any plant or animal we’ve ever known. Such lifeforms might challenge even our definitions of biology.

Scientists also warn against assuming that life elsewhere must be carbon-based simply because it is so on Earth — a tendency sometimes called “carbon chauvinism.” Silicon, with its ability to form complex molecular chains, is a frequently proposed alternative. In theory, life could also arise using entirely different chemistries — perhaps based on metal-oxides or using methane or ammonia as a solvent instead of water.

While these ideas remain hypothetical, they remind us to keep an open mind and expand our criteria when searching for alien life.

New Tools for a New Frontier

Although we haven’t yet found concrete evidence of extraterrestrial life, cutting-edge telescopes are designed to change that. The James Webb Space Telescope (JWST) is already observing the atmospheres of exoplanets, looking for gases such as methane, oxygen, and water vapor that might suggest biological processes. Upcoming missions, including the European Space Agency’s ARIEL and NASA’s proposed Habitable Worlds Observatory, aim to refine this work even further.

These observatories analyze the starlight that filters through a planet’s atmosphere during transit, searching for subtle chemical signatures — indirect but potentially compelling indicators of life.

Earth took nearly four billion years to evolve intelligent beings. If such a timeline is typical, then life — particularly intelligent life — may be exceedingly rare. And yet, considering the vast number of stars and planets in the universe, even rare events may occur often.

The journey to find life beyond Earth is still in its infancy. But with each discovery, we come closer to resolving one of humanity’s most enduring questions: Are we truly alone?

Credits: Article is originally written by Shravan Hanasoge, Astrophysicist at the Tata Institute of Fundamental Research, published at Indian Express, on July 09, 2025.

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