New Delhi: NASA has confirmed the existence of more than 5,000 planets beyond our solar system. These planets are known as exoplanets. This cosmic milestone represents a 30-year journey of discovery led by NASA space telescopes. 


NASA has also shared a time-lapse video on Twitter which depicts the number of exoplanets discovered each year, from 1991 to 2022.  






However, these exoplanets confirmed by astronomers are only a fraction of the likely hundreds of billions in the Milky Way galaxy. 


On March 21, the planetary odometer turned on. As many as 65 exoplanets were added to the NASA Exoplanet Archive, the US space agency said on its website. All exoplanet discoveries recorded in the archive have appeared in peer-reviewed, scientific papers, and have been confirmed using detection techniques or by analytical techniques. 


According to NASA, a total of 5,005 exoplanets have been confirmed. As many as 8,709 NASA mission discoveries are NASA candidates, which means they could be planets, but are unconfirmed. 


Also, the US space agency has confirmed 3,759 planetary systems. In other words, there are 3,759 stars with confirmed planets. 


What Are The Different Types Of Exoplanets?


The 5000-plus exoplanets include small, rocky worlds like Earth, gas giants many times larger than "hot Jupiters" in scorchingly close orbits around their stars. A hot Jupiter is a gas giant about half the mass of our own Jupiter in an extremely close, four-day orbit around its star. Astronomers have also discovered "super-Earths", which are possible rocky worlds bigger than the Earth, and "mini-Neptunes", which are smaller versions of Neptune. There are also planets which orbit two stars at once, and those which stubbornly orbit the collapsed remnants of dead stars. 


Quoting Jessie Christiansen, a research scientist with the NASA Exoplanet Science Institute at California Institute of Technology, a statement issued by NASA said that each exoplanet is a new world, a brand-new planet. She said she gets excited about every exoplanet because nothing is known about them.


Our Galaxy Likely Holds Hundreds Of Billions Of Exoplanets


She said one thing which is known, is that the Milky way galaxy likely holds hundreds of billions of such planets. She explained that the steady drumbeat of discovery began in 1992 with strange new worlds orbiting an even stranger star. 


Christiansen said that the star was a type of neutron star known as a pulsar, a rapidly spinning stellar corpse that pulses with millisecond bursts of searing radiation. She added that measuring slight changes in the timing of the pulses allowed scientists to reveal planets in orbit around the pulsar. 


Alexander Wolszczan, the lead author of the paper which unveiled the first planets to be confirmed outside our solar system, 30 years ago, said that finding just three planets around the spinning star essentially opened the floodgates. 


He said that one can find planets around a neutron star, planets have to be basically everywhere. He noted that the planet production process has to be very robust.


One of the most important satellites which makes new exoplanet discoveries is the Transiting Exoplanet Survey Satellite (TESS), which was launched in 2018. 


Powerful Telescopes Which Will Search For Exoplanets


Soon, powerful next-generation telescopes and their highly sensitive instruments, beginning with the recently launched James Webb Space Telescope, will capture light from the atmospheres of exoplanets, according to NASA. These powerful telescopes will read which gases are present potentially to identify biosignatures. 


Other powerful telescopes include the Nancy Grace Roman Space Telescope, which is expected to launch in 2027. It will make new exoplanet discoveries using a variety of methods. The European Space Agency (ESA) mission ARIEL, launching in 2029, will observe exoplanet atmospheres. The mission will carry a piece of NASA technology aboard, called CASE, which will help astronomers understand exoplanet clouds and hazes.


"To my thinking it is inevitable that we'll find some kind of life somewhere – most likely of some primitive kind," NASA quoted Wolszczan as saying.


Methods To Find Other Worlds


In 1995, the first planet around a Sun-like star was detected. It turned out to be a hot Jupiter. 


Once astronomers learnt to recognise such planets, several other candidates appeared in the data from ground based-telescopes. Initially, astronomers used the "wobble" method. This is the method of tracking slight back-and-forth motions of a star, caused by gravitational tugs from orbiting planets.