In 1992, when the first discovery of exoplanets was announced by astronomers Aleksander Wolszczan and Dale Frail, no one could have imagined that just 30 years later thousands of exoplanets would be known to mankind.
However, on Monday, NASA announced that to date, 5,000 exoplanets have been detected.
“This is definitely a milestone to celebrate,” said Sara Seager, an astrophysicist and planetary scientist at MIT. “When exoplanets began  years ago people laughed and thought the estate was going nowhere. Today, not only do we have 5,000 planets, but the potential for discovery is unprecedented.”
Exoplanets, worlds orbiting distant stars, were once only theorized. And even then, astronomers believed that only certain stars contained planets. Today, astronomers believe that, on average, a star is home to at least one planet.
And the different types of these distant worlds are not lacking. There are “super-Earths” – rocky planets larger than our own planet – “gas giants” larger than Jupiter, “hot Jupiters” which are massive worlds orbiting close to their host stars, and even mini Neptunes.
There is also a weird and wonderful assortment of these different planets. There was a planet with the cotton candy density; a planet with iron rain; and a planet with “snow sunscreen.”
One of the most intriguing planetary systems is TRAPPIST 1.
This system of seven planets – including three that could be potentially habitable – were discovered in 2017. They lie relatively close to the earth at just 40 light-years away.
Looking for signs of life
The first exoplanet was discovered orbiting a pulsar, a dense star called a neutron star, which spins rapidly and produces millisecond bursts of radiation. It was unlikely that any life could survive these intense explosions, but it was a promising finding.
“If you can find planets around a neutron star, the planets must be pretty much everywhere,” Wolszczan said in a NASA statement. “The planet’s production process must be very robust.”
In 1995, the first exoplanet orbiting a sun-like star was discovered, although it ended up being a gas giant orbiting close to its host star.
But the desire to search for more Earth-like planets eventually led to the 2009 launch of the Kepler Space Telescope. The workhorse would continue to discover most of the 5,000 planets we know today, even after suffering a blackout in 2013. It was declared dead in 2018even if the analysis of its data continues.
Since then the Transiting exoplanet study satellite (TESS), has been launched and is searching the stars for new worlds. And the James Webb Space Telescopeonce online, will seek to lift the veil on the atmospheres of these planets, looking for signs of potential habitability.
“In my view, it’s inevitable that we’ll find some kind of life somewhere – most likely of a primitive type,” Wolszczan said.
And there are even more of these planet-hunting telescopes to come.
the Nancy Grace Roman Space Telescope should be launched in 2027, and the European space agency Atmospheric Infrared Remote Sensing Exoplanet Major Survey (ARIEL) is expected to launch in 2029.
“It’s not just a number,” Jessie Christiansen, archival scientist and NASA Exoplanet Science Institute researcher at Caltech, said of the 5,000 exoplanets in a NASA statement.
“Each of them is a new world, a whole new planet. I’m excited about each one because we don’t know anything about them.”
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