The number of confirmed exoplanets has recently exceeded the 5,000 mark, marking a 30-year journey of discovery led by NASA space telescopes.
What do planets outside our solar system, or exoplanets, look like? A variety of possibilities are shown in this illustration. Scientists discovered the first exoplanets in the 1990s. As of 2022, the tally standsat just over 5,000 confirmed exoplanets [Credit: NASA/JPL-Caltech]
Not too long ago, we only knew of a few planets in the universe that orbited our sun. However, a recent surge in discoveries marks a pinnacle of scientific achievement: more than 5,000 planets have now been confirmed to exist outside our solar system.
On March 21st, the tally of confirmed exoplanets surpassed 5,000 with the addition of 65 new exoplanets to the NASA Exoplanet Archive. The archive logs exoplanet discoveries that appear in peer-reviewed scientific papers and have been confirmed using multiple detection methods or analytical techniques.
The 5,000+ planets discovered so far include small, rocky worlds similar to Earth, gas giants many times larger than Jupiter, and “hot Jupiters” in extremely close orbits around their stars. There are also “super-Earths,” which are rocky worlds that could be larger than our own planet, and “mini-Neptunes,” smaller versions of our own solar system’s Neptune. Additionally, there are planets that orbit two stars simultaneously and planets stubbornly orbiting the collapsed remains of dead stars.
What we do know is that our galaxy likely holds hundreds of billions of such planets. The consistent pace of discovery began in 1992 with the detection of new worlds orbiting a peculiar star. This star was a type of neutron star known as a pulsar, a rapidly spinning remnant of a star that pulses with bursts of searing radiation every millisecond. Scientists were able to reveal planets in orbit around the pulsar by measuring slight changes in the timing of the pulses.
How to find other worlds
According to Wolszczan, “it is inevitable that we will find some form of life somewhere – most likely in a primitive form.” The close relationship between the chemistry of life on Earth and the chemistry found throughout the universe, coupled with the detection of widespread organic molecules, suggests that the discovery of life itself is only a matter of time.
The outlook wasn’t always so promising. The first planet discovered orbiting a sun-like star in 1995 turned out to be a hot Jupiter, a gas giant about half the mass of our own Jupiter in an extremely close orbit around its star, lasting only four days.
More of these planets were discovered in data from ground-based telescopes as astronomers learned to identify them, initially dozens and then hundreds. They were detected using the “wobble” method, which tracks slight back-and-forth movements of a star caused by gravitational pulls from orbiting planets. However, none of these planets seemed habitable.
The more than 5,000 exoplanets confirmed in our galaxy so far include a variety of types—some that are similar to planets in our solar system, others vastly different. Among these are a mysteriousvariety known as “super-Earths” because they are larger than our world and possibly rocky[Credit: NASA/JPL-Caltech]
The next major breakthrough in exoplanet discovery came with the development of the “transit” method, which enabled astronomers to find small, rocky planets more similar to Earth. Astronomer William Borucki proposed the idea of attaching highly sensitive light detectors to a telescope and launching it into space. The telescope would then observe a field of over 170,000 stars for years, searching for tiny dips in starlight when a planet passes in front of a star.
This idea became a reality with the launch of the Kepler Space Telescope in 2009.
Borucki, the principal investigator of the now-retired Kepler mission, says its launch opened up a new window on the universe.
“I feel a sense of satisfaction and awe at what’s out there,” he says. “None of us expected this enormous variety of planetary systems and stars. It’s truly amazing.”
