The 5 Youngest Planets Ever Discovered

On November 20, 2024, researchers at the University of North Carolina at Chapel Hill published a paper in Nature detailing the discovery of one of the youngest known transiting exoplanets in existence. IRAS 04125+2902, referred to as the slightly more succinct TIDYE-1b, is only 3 million years old, putting it somewhere on the timeline of planetary lifespans as little more than an astronomical baby.

Exoplanets are any planets that exist outside of our solar system (transit simply refers to a planet passing between the star it orbits and an observer). Depending on a number of different characteristics, including age, they can provide key insights into the life cycle of planetary bodies that orbit stars in the universe, including our own. Earth, for example, took somewhere between 10 to 20 million years to form, making TIDYE-1b's 3-million-year emergence a scientific rarity that could completely change what we know about the speed and stages of planetary formation.

As Madyson Barber, the lead author of the research study and member of UNC-Chapel Hill's Department of Physics and Astronomy, explained in a statement to the university, "Astronomy helps us explore our place in the Universe — where we came from and where we might be going. Discovering planets like this one allows us to look back in time, catching a glimpse of planetary formation as it happens." To carry out their work, the study's authors utilized data and other resources provided by the NASA High-End Computing Program via the Ames Research Center in California's Silicon Valley. Given NASA's and other organizations' ongoing quest to discover new exoplanets, let's take a closer look at some of the youngest planets we've ever discovered and what they mean for our understanding of the universe.

Discovered in 2016 using data from NASA's Kepler Space Telescope and the W.M. Keck Observatory in Hawaii, K2-33b is a Neptune-like planet that orbits a star roughly 450 light-years away from Earth (here's our guide to the characteristics of actual Neptune). At only 5 to 10 million years old, it's one of the youngest exoplanets ever discovered. Despite having the mass of almost four Jupiters (though we've never found a planet more than 14 times the mass of Jupiter), K2-33b cruises around its M-type star, K2-33, at a brisk pace, orbiting the stellar body once every 5.4 days.

K2-33b was first detected by K2, the name scientists gave to the Kepler Space Telescope after technical failures resulted in it losing its ability to point in the direction researchers wanted. Picking up on the periodic dimming of K2-33's light, scientists understood that there could be an orbiting planet regularly moving in front of the star and obscuring its light. Observations from the Keck Observatory aided in confirming the planet's surprisingly young age.

One of K2-33b's peculiarities is how close it is to its star — roughly 10 times closer to K2-33 than Mercury is to the sun. The result is that the planet is astronomically hot. Previously studied planets with such tight orbits have been theorized to take hundreds of millions of years to make it that close to their system's star, making K2-33b's youthfulness even more bizarre. As a result, scientists have begun to give more credence to the idea that, rather than forming at a farther distance and moving into a close orbit, K2-33b's emergence occurred right where it is today. If true, it could mean altering how we search for exoplanets planets in the galaxy.

PDS 70b, discovered in 2018, is a compelling find that has advanced our understanding of planetary formation. Orbiting the young, orange dwarf star PDS 70, this gas giant is roughly 370 light-years away from Earth in the constellation Centaurus and contains the mass of several Jupiters. The fun thing about this exoplanet is that scientists discovered it while it was still forming. Given that its star is only about 5.4 million years old, PDS 70b is likely around the same age, thought to be in the tail-end of a formation process that has lasted some 5 million years.

The exoplanet's star is ringed by a disk of gas and dust roughly 130 astronomical units (AU) wide. An AU is a standard unit of astronomical measurement of 93 million miles — the average distance of Earth to the sun. Scientists were clued into PDS 70b's existence by the fact that this disk features a large gap in it, the sign of a planet pulling in material to its own formative disk via gravity. Fascinatingly, researchers believe that magnetic forces from the disk around the planet are helping to guide material to its surface as it slowly accretes mass.

In a rare photographic win, a following investigation of the planet resulted in astronomers being able to nab an image of the PDS 70 system. In it, the planet is visible in the inner rim of the stellar gas and dust ring. The discovery presents researchers with a singular opportunity to test models of how planets form.

Discovered in 2016, V830 Tauri b was initially hailed as one of the youngest exoplanets ever identified, with an estimated age of around 2 million years. This "hot Jupiter" was reported to orbit its host star, V830 Tauri, at a distance of 0.057 AU and complete an orbit in under 5 days. Like other young exoplanets, its discovery meant a chance for scientists to study planets in their infancy, and the planet's proximity to its equally young and magnetically active host star allowed astronomers to challenge traditional theories about how such planets form.

But the existence of V830 Tauri b is now mired in controversy. Follow-up observations using the HARPS-N spectrograph, an advanced radial velocity instrument used by the European Southern Observatory and similar to an instrument on a telescope in Chile, were unable to confirm the planet's presence. Radial velocity is a method that assesses minute changes in the velocity of a star and its planet as they move around a common center of mass. Researchers suggest that the intense magnetic activity of the proposed planet's star could produce signals that mimic those expected from V830 Tauri b. This stellar "noise" may be the source of a false positive, which has resulted in doubt being cast on the original detection.

The case of V830 Tauri b highlights the challenges in detecting exoplanets around young stars. To the general public, it's a healthy reminder to appreciate the fact that our civilization has advanced to a point where we can detect cosmological bodies at mind-breaking distances at all.

In 2011, astronomers Adam Kraus and Michael Ireland announced the discovery of LkCa 15b, a protoplanet forming around the young star LkCa 15. Located 450 light-years away in the constellation Taurus, its discovery was made with the help of the Keck Observatory in Hawaii. Using the observatory's Adaptive Optics methodology — a process in which astronomers are able to correct for distortions in the Earth's atmosphere due to particles and gases — scientists observed what appeared to be a planet coalescing within a gap in LkCa's protoplanetary disk (much like that of PDS 70b and other planets detected using the same method).

LkCa 15b is estimated to be around 2 million years old, making it one of the youngest planetary objects ever identified. Thought to be a young gas giant, the planet appears to orbit a K-type star (those just a tad cooler than our own sun that glow orange in color).

Sadly, just like V830 Tauri b, follow-up studies have brought LkCa 15b's existence into question. In 2019, researchers published a study in The Astrophysical Journal Letters stating that there is "no clear, direct evidence" for exoplanets orbiting LkCa 15. Its authors claim that the detection of the planet is likely due to interactions with the disk of material surrounding the system's star rather than a distinct protoplanetary body. For now, LkCa 15b's status remains a mystery. If you're interested in checking out the planets in your own stellar backyard, though, you can always learn how to make a powerful telescope at home.