When a young PhD student and his professor were studying more than 100 stars at an observatory in south-east France in 1994, they made a discovery that revolutionised the world's understanding of the cosmos.
Student Didier Queloz and his adviser, astrophysicist Michel Mayor, noticed that one of the stars was wobbling, a sign that a planet's gravity might be pulling on it.
A year later, a momentous announcement shocked the astronomy scene: The two Swiss scientists had discovered the first planet outside the solar system that spins around a sun-like star. Such planets are known as exoplanets.
Finding new worlds beyond the Milky Way became a reality, and the field of exoplanet research was born.
Since then, more than 4,000 exoplanets have been discovered, many of them by Prof Queloz, who is currently a Professor of Astronomy at the University of Geneva, and Professor of Physics at the University of Cambridge, where he leads a research programme to understand the formation, structures and habitability of exoplanets.
In 2019, Prof Mayor and Prof Queloz received the Nobel Prize in Physics for their discovery of the first exoplanet, 51 Pegasi b, orbiting a sun-like star.
Prof Queloz, 54, is one of 21 globally recognised scientists who will be speaking at this year's Global Young Scientists Summit, where more than 500 young researchers from dozens of countries will gather virtually.
The Swiss astronomer will deliver a plenary lecture on the exoplanet revolution and participate in a panel discussion on renewable energy during the virtual summit that will run from Tuesday to Friday.
The gas giant 51 Pegasi b challenged many theories of planet formation that were based on the solar system.
The exoplanet is 50 per cent larger than Jupiter - the biggest planet in our solar system - and it is located much closer to its star than Mercury is to the sun. Back then, a gas planet located so close to its star went against scientists' existing knowledge of planets.
"We really had a hard time convincing our colleagues that we had a true planet... But many exoplanets are awkward compared to the planets of the solar system, in the sense that they are way closer to the sun," Prof Queloz told The Straits Times.
The challenge in the next 20 years is to find a solar system twin, added the astronomer, since scientists have already found exoplanets with the same mass and size as earth, and others that are similar to Jupiter and Saturn, for instance.
Prof Queloz strongly believes that there is life beyond earth, and has said before that humans may discover extraterrestrial life in the next 30 years.
But life on other planets may not be what we think of as life.
At his Nobel Lecture in 2019, Prof Queloz said: "We are very practical and focused on life as we know it. For me, life is like a chemistry experiment that turned bad because it took control of itself."
The question is whether the chemical reaction in one planet triggers the creation of microscopic life forms or large animals, or something else, he told ST.
To further expand scientists' knowledge of exoplanets, Prof Queloz chaired the European Space Agency's CHaracterising ExOPlanet Satellite mission that aims to unearth the features and traits of many of these vast new worlds.
The team published its first paper in September last year, with a detailed study of one of the most extreme planets known - WASP-189b - which is located 322 light years away from earth and is a scorching 3,200 deg C.
"How useful is the study of exoplanets and the cosmos? Well, you never know. When Einstein developed the equations about relativity, he would have never guessed that this equation would be used for GPS satellites a hundred years later," said Prof Queloz.
"The beauty of natural science is that you don't do it for a purpose, because the purpose will come from the society at some point."