How are planets born, and how do they grow? This is an essential question in astronomy, one that researchers try to answer by observing “young planets.” That’s easier said than done. All the planets in our solar system are the same age, 4.6 billion years old. Astronomers therefore need to look elsewhere to find planets that have formed more recently—making exoplanets enticing research grounds.
Still, the vast majority of the approximately 6,000 exoplanets confirmed to date are also billions of years old. That’s not because there aren’t youthful planets out there, but old planets are easier to discover using common techniques such as the transit method, in which astronomers detect the slight dimming of a star’s light as a planet passes in front of it.
Newly formed exoplanets are often buried within disks of gas and dust, the leftover building blocks from a planet’s formation, also known as a protoplanetary disk. The difficulty of just locating such a new celestial body is part of what makes the discovery of the exoplanet Elias 2-24b—now the youngest ever confirmed—so exciting.
The research team, led by Andrea Bernardi at Diego Portales University in Chile, identified the exoplanet by focusing on seven protoplanetary disks where there were notable gaps in the dense matter, since it is believed that growing planets carve out such voids. They reanalyzed “coronagraph” data, in which the central star is blocked out, making the dim reflected light from surrounding celestial bodies stand out.
Scientists had known about a gap in the disk surrounding the star Elias 2-24 for nearly a decade. The European Southern Observatory’s Very Large Telescope (yes, that’s its official name) had detected a point of light within this gap, sparking an ongoing debate over whether it was truly a planet. The researchers used data collected in 2018 and 2020 at the W.M. Keck Observatory in Hawaii to compare the dot’s positions over the years. They concluded that this bright spot was not an unrelated background star or noise from the equipment, but rather a celestial object gravitationally bound to Elias 2-24—in other words, a planet.
Elias 2-24b is located approximately 450 light-years from Earth. It orbits its star at a distance of approximately 55 astronomical units (one astronomical unit being the average distance between Earth and the sun). Its mass is estimated to be at most 1.9 to 4.0 times that of Jupiter, though researchers believe its volume is likely to be much smaller than our local gas giant. Since its host star is less than 1 million years old, Elias 2-24b is estimated to be similarly young.
Until now, the youngest exoplanets confirmed through direct observation were those orbiting the stars PDS 70 and WISPIT 2, both of which are over 5 million years old. This new discovery breaks those records by a significant margin.
