Home / Science / It has been 25 years since we found the first exoplanet. We now know thousands of them and some may harbor life

It has been 25 years since we found the first exoplanet. We now know thousands of them and some may harbor life


An artistic rendering of 51 Pegasi b. Credit – NASA

Nobody gives awards for the worst planet in the galaxy, and at best it would be a dubious honor. Somewhere out there may be other garden planets like Earth. Even somewhere there may be nearly missed worlds like Mars. And somewhere out there are planets like 51 Pegasi b that, if it hadn’t won the worst planet nod, it would have definitely made it to the medal.

Located about 50 light-years from Earth, 51 Pegasi b is a gas giant like Jupiter, with a mass about 150 times that of Earth, surrounding its host star at a distance of only 7 million km (4.3 million). me.). Orbiting so close, 51 Pegasi b has an estimated surface temperature of 1,000 ° C (1,800 ° F). It is also tidally locked, which means that one side is always facing the solar oven.

But 51 Pegasi b is more than just a ball of superheated gas. In fact, it is one of the most significant planets ever discovered, so important that, in 2019, the astronomers who found it were awarded the Nobel Prize in Physics. Because? Because whatever its flaws, it was the first planet ever discovered outside our solar system orbiting a main sequence star like the sun. With this was born the field of exoplanets.

51 Pegasi b was discovered on October 6, 1995, and 25 years later, the number of exoplanets has grown enormously. According to the most recent count, there are 4,354 known exoplanets, including 712 multi-planet systems, for a total of 3,218 solar systems beyond our own. It is currently believed that virtually every one of the hundreds of trillions of stars in the universe hosts at least one world and many host entire litters. The Earth, which once stood at the center of humanity’s cosmos map, is now known to be an incredibly tiny part of an incredibly vast planetary census.

Astronomers have not directly identified 55 Pegasi b: it is no longer possible to visualize a planet in the glow of its parent star from a distance of 50 light years than it is to see a moth flitting near a lamppost from half a dozen blocks away . Instead, the investigators used the radial velocity method, which consists of observing the slight gravitational wobble that a planet causes in its star as it orbits its orbit. It’s an ingenious method of discovering planets, but it’s slow, as only one star can be observed at a time.

With the 2009 launch of the Kepler Space Telescope, astronomers switched to a technique that could collect entire networks of worlds at once. Known as the transit method, the technique involves looking for the slight dimming of light that occurs when a planet passes through the Earth-facing side of its parent star. The greater the obscuration, the larger the planet’s diameter. The more frequently the darkening occurs, the faster the planet orbits. Both Kepler and its next observatory, the Transiting Exoplanet Survey Satellite (TESS), stare without blinking at entire patches of sky at once, observing thousands of potential transits that astronomers can study.

The transit method had uncovered far more promising worlds than 55 Pegasi b. There is Proxima Centauri b, an Earth-like planet only 4.2 light-years away, which orbits its star in the “Goldilocks zone”, where temperatures are right for water to exist. liquid. There’s Ross 128 b, another Earth-sized world just 11 light-years away, where surface temperatures are estimated to be 23 ° C (73 ° F). There is the Trappist-1 solar system, only 39 light-years away and home to no less than seven Earth-like worlds, at least six of which could orbit in the Goldilocks area.

The 25 years we’ve gone from not knowing other exoplanets to identifying thousands of them (and being certain of trillions more) is long when measured against the length of human life. On the cosmological time scale, it is certainly not a flicker. But in that glimpse, our understanding of our place in the universe was forever transformed. Earth may seem far less special than when it was one of only eight known planets. But it is home to a wiser and humbler species for the knowledge it has acquired.

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