Not long ago, we lived in a universe with just a small number of planets known to humans and all of them were orbiting a star, our Sun. But now a whole new bunch of discoveries marks a scientific climax, which confirms that more than 5,000 planets exist beyond our solar system.
The planetary odometer turned on March 21, with the recent batch of 65 exoplanets added to the NASA Exoplanet Archive. Exoplanets are the planets outside our immediate solar family. The archive records exoplanet discoveries that appear in peer-reviewed, scientific papers, and that have been confirmed using multiple detection methods or by analytical techniques.
The over 5,000 planets found till now include small, rocky worlds like Earth, gas giants which are multiple times larger than Jupiter, and “hot Jupiters” in blistering close orbits around their stars. There are “super-Earths,” which are possible rocky worlds bigger than our own, and “mini-Neptunes,” smaller versions of our system’s Neptune.
“It’s not just a number,” said the science lead for the archive, Jessie Christiansen. He is also a research scientist with NASA’s Exoplanet Science Institute at Caltech in Pasadena. With excitement he added, “Each one of the planets is a new world, a brand-new planet. I get excited about each one of them because we don’t know anything about them.”
What we know for sure is that our galaxy most likely has hundreds of billions of such planets. The discovery of the planets began in 1992 with unfamiliar new worlds orbiting an even stranger star. It was a type of neutron star known as a pulsar, a rapidly spinning galactic corpse that pulses with millisecond bursts of blistering radiation. Measuring small changes in the timing of the pulses allowed researchers to reveal planets in orbit around the pulsar.
Discovering mere three planets around this spinning star fundamentally opened the floodgates, said Alexander Wolszczan, the lead author on the paper that unveiled the first planets to be confirmed outside our solar system, 30 years ago.
Wolszczan said that if one can find planets around a neutron star, it means that the planets are present basically everywhere. The planet production process has to be very strong, he added.
Wolszczan even today searches for the exoplanets as a professor at Penn State. He said that we are opening a new era of discovery that will move beyond the boundaries of just adding new planets to the long list. The Transiting Exoplanet Survey Satellite (TESS) that was launched in 2018 is carrying on to make new discoveries of the exoplanets.
But very soon, the powerful and enhanced next-generation of telescopes and their extremely sensitive instruments, such as the recently launched James Webb Space Telescope, will capture light emitted from the atmospheres of exoplanets and thus will help in reading and analyzing the gases that are present to potentially identify significant clues of the habitable conditions.
The Nancy Grace Roman Space Telescope, which is expected to be launched in 2027, will make new exoplanet discoveries with the help of a number of methods. The ESA (European Space Agency) mission ARIEL, scheduled to be launched in 2029, likewise, will observe the atmospheres of the exoplanets; additionally, a technological instrument by NASA on its board, called CASE, will help it zero in on the clouds and hazes of the exoplanets.
“To my thinking, it is inevitable that we’ll find some kind of life somewhere – most likely of some primitive kind,” Wolszczan said. The close correlation between the chemistry of life on Earth and the chemistry found throughout the universe, as well as the spotting of omnipresent organic molecules throughout the universe greatly suggests the detection of life itself is only a matter of time, he added.
How NASA Finds Exoplanets
The first planet that was found around a Sun-like star, in 1995, turned out to be a hot Jupiter, i.e., a gas giant around half the mass of the Jupiter in our solar system; only in an extremely close, four-day orbit around its star. In simpler words, a year on this planet is just four days long.
More such planets came up in the data accessed from ground-based telescopes once astronomers learned the ways to recognize them, first in dozens and then in hundreds. These planets were discovered utilizing the “wobble” technique, i.e., by tracking the small back-and-forth motions of a star, which is brought about by the gravitational pulls from the orbiting planets. Even then, nothing came up that could be termed habitable.
Finding small, rocky worlds which may represent our own earth needed a huge breakthrough in the exoplanet hunting technology: the “transit” technique. Astrophysicist William Borucki came up with the revolutionizing idea of connecting extremely sensitive light detectors to a telescope, then launching it into space.
The idea was that the telescope would look for years at a score of more than 170,000 stars, all the while searching for tiny dips in starlight when a planet crossed a star’s face. The idea got realized with the launch of the Kepler Space Telescope.
Borucki, who was the lead researcher of the now-retired Kepler mission, says that its launch in 2009 opened up a new window to the universe. “I get a real feeling of satisfaction, and really of awe at what’s out there,” he said. “None of us expected this enormous variety of planetary systems and stars. It’s just amazing.”
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