追尋地球的宇宙分身：終極行星狩獵冒險

The hunt for a planet just like Earth has fascinated scientists for decades. Before the 1990s, people believed our Solar System was the only place with planets. All our ideas about how planets formed came from studying just the nine planets around our Sun. But everything changed in 1995 when Swiss astronomers Michel Mayor and Didier Queloz announced they had discovered a planet orbiting a star outside our Solar System. This planet, called 51 Pegasi b, was a gas giant much larger than Earth and orbited its star very closely, making it extremely hot. The discovery was made using a spectrograph, a tool that splits starlight into a spectrum of colors and reveals details about the star’s chemistry. Mayor and Queloz noticed that the star’s light shifted back and forth every few days, a sign that something was tugging on the star. After careful study, they confirmed it was a planet. This was the first time anyone had found a planet around a Sun-like star outside our Solar System, and it opened the door to finding thousands more.

Since then, scientists have discovered over 6,000 exoplanets, which are planets outside our Solar System. These exoplanets are incredibly diverse. Some are hot Jupiters, massive gas planets that orbit very close to their stars. Others are rocky and small, more like Earth. There are even planets that orbit two stars, similar to the fictional planet Tatooine from Star Wars. To find these planets, scientists use different techniques. One method is the transit technique, where they watch for a planet passing in front of its star, causing the star’s light to dim slightly. Another method is radial velocity, which measures how a planet’s gravity makes its star wobble. These techniques allow scientists to learn about the planet’s size, mass, and sometimes even its composition.

The ultimate goal for many astronomers is to find an Earth twin—a planet that matches Earth in size, mass, and temperature, and orbits a star similar to our Sun at a similar distance. This is important because such a planet could potentially support life. Scientists use advanced telescopes and instruments, often working together in international teams, to search for these Earth-like worlds. They have found some planets that are similar to Earth in size and mass, but most are either too hot or too close to their stars. The search is challenging because Earth-like planets are hard to detect with current technology. However, new instruments are being developed, and scientists are optimistic that they will eventually find a true Earth twin. Discovering such a planet would be a major breakthrough in understanding our place in the Universe and the possibility of life elsewhere. The search continues, and each new discovery brings us closer to answering the age-old question: Are we alone in the Universe?