There are now more than 5,000 confirmed planets beyond our solar system, according to NASA.
The latest addition of 65 exoplanets to the NASA Exoplanet Archive contributed to the scientific milestone marked on Monday. This archive is the home to exoplanet discoveries from peer-reviewed scientific papers that have been confirmed using multiple methods of detecting the planets.
"It’s not just a number," said Jessie Christiansen, science lead for the archive and a research scientist with the NASA Exoplanet Science Institute at the California Institute of Technology in Pasadena, in a statement. "Each one of them is a new world, a brand-new planet. I get excited about every one because we don’t know anything about them."
We’re currently living in a golden age of exoplanet discovery. Although the existence of planets outside of our solar system had been previously proposed and certainly depicted in science fiction, these worlds were only first discovered in the 1990s.
The diversity of exoplanets represent populations of planets unlike anything found in our solar system. They include rocky worlds larger than Earth called super-Earths, mini-Neptunes bigger than Earth but smaller than Neptune, and scorching hot Jupiters that dwarf our solar system’s largest planet and closely orbit their host stars.
Scientists have also found planets that orbit more than one star and even some around the remnants of dead stars called white dwarfs.
So far, of the confirmed exoplanets, 30% are gas giants, 31% are super-Earths, and 35% are Neptune-like. Just 4% are terrestrial, or rocky planets like Earth or Mars.
Previous exoplanet discoveries have been made thanks to planet-hunting telescopes and satellites like the Spitzer Space Telescope, the Kepler Space Telescope and the Transiting Exoxjmtzywplanet Survey Satellite.
When Christiansen was a graduate student in the early 2000s, there were only about 100 known exoplanets.
"That’s partly why I wanted to go into the field — because it was brand new and so exciting that people were finding planets around other stars," Christiansen said in a question and answer session shared by Caltech. "Now, exoplanets are almost ordinary. My colleague David Ciardi (chief scientist for the NASA Exoplanet Archive) pointed out the other day that half of the people alive have never lived in a world where we didn’t know about exoplanets."
Kepler helped scientists discover about two-thirds of the 5,000 confirmed planets, Christiansen said.
In the new batch of 65 planets, many are super-Earth and sub-Neptune planets, along with some hot Jupiter-size planets. There are also two Earth-size planets, but they’re about 620 degrees Fahrenheit (327 degrees Celsius), so more like "hot rocks" than habitable planets, Christiansen said.
She also noted that one is a system with five planets orbiting a small, cool red dwarf star — not unlike the TRAPPIST-1 system, where a similar star hosts seven rocky planets.
New telescopes will only increase the potential for exoplanet discovery. The James Webb Space Telescope, launched in December, will be able to peer through the atmospheres of exoplanets.
The Webb telescope is poised to study the TRAPPIST system in detail.
The Nancy Grace Roman Space Telescope will launch in 2027 and aid in the search for exoplanets with a variety of techniques. The European Space Agency’s ARIEL mission, launching in 2029, will study exoplanet atmospheres.
Although scientists have confirmed more than 5,000 exoplanets, there are likely hundreds of billions of them across the Milky Way galaxy.
"Of the 5,000 exoplanets known, 4,900 are located within a few thousand light-years of us, Christiansen said. "And think about the fact that we’re 30,000 light-years from the center of the galaxy; if you extrapolate from the little bubble around us, that means there are many more planets in our galaxy we haven’t found yet, as many as 100 to 200 billion. It’s mind-blowing."
