A young and nascent world lies close to its parent star, passing from our point of view into this artist’s concept. Credit: NASA/JPL-Caltech/R. Wounded, K. Miller (Caltech/IPAC)
Not far from Earth, a newborn planet is just starting life. And by peering beneath the thick cocoon of material that surrounds it, astronomers may have a rare opportunity to watch a world for which our solar system has no equivalent settle into its early years.
The planet orbits the star IRAS 04125+2902, which is about 520 light-years away. The star is very young, about 3 million years old, and represents only about 70% of the mass of the Sun. Its young age means that its protoplanetary disk – the thick veil of dust and debris that makes up the building blocks of planets – it has not been completely eliminated.
In this disk, astronomers witnessed something never seen before: a transiting exoplanet. (Transit planets are those that appear to pass in front of their parent stars from our perspective.) Astronomers have dubbed it TIDYE-1 b, derived from “TESS Investigation – Demographics of Young Exoplanets.” Madyson Barber, a graduate researcher at the University of North Carolina at Chapel Hill, says the strange nickname is “an alternative to IRAS 04125+2902 b (which is a mouthful).”
Barber and colleagues published their discovery of the planet today Nature.
Wrapped
Not only is TIDYE-1 a baby planet, but it could transform into a type of planet we don’t have in our solar system, called sub-Neptune. Sub-Neptunes (and their related brethren, super-Earths) are objects with masses between that of Earth and Neptune, and astronomers are still trying to reconstruct what they look like. Depending on their mass, they can look like a mini ice giant (sub-Neptune) or a huge terrestrial planet (super-Earth).
Related: Where is the super-Earth in our solar system?
TIDYE-1 b will not reveal its true nature in our lifetime. It is still wrapped in the hydrogen envelope that often surrounds embryonic planets, which gives it a current mass of about 0.3 Jupiter masses: something closer to a mini-Saturn, in terms of weight. But because a planet of that mass still wrapped in a hydrogen envelope is bound to shed those outer layers over time, the actual planet will be much smaller in its teens.
“This mass is not consistent with the mature population of hot Jupiter [massive gas giants circling close to their stars]and young planets are thought to get smaller with age, so we think the planet will probably end up within 2 to 4 times the radius of Earth once it finishes evolving,” Barber says.
Fast development
The fact that the planet could be seen was a rather impressive discovery. It would be a difficult feat in most scenarios to peer into a protoplanetary disk, as it’s like trying to spot stars in the sky on a very cloudy day. But the disk around the planet’s parent star is only slightly misaligned, allowing the team to glimpse TIDYE-1 b.
Barber says the planet shows that some exoplanets can form quite quickly, as TIDYE-1 b is in a “cohesive form” in just under a third of the time it took our Earth to form. This may partly be due to its proximity to its star: the planet completes an orbit of IRAS 04125+2902 in 8.83 days.
It probably didn’t form there, Barber says, but rather migrated there, since “It’s difficult to form large planets near the star because the disk first dissipates away from the nearest star, so there isn’t enough material there to form large planets “. so quickly.”
There is no evidence (yet) of multiple planets in the system, but there may be more. Meanwhile, Barber says TIDYE-1 b’s large radius and low mass could make it an ideal candidate for follow-up observations with the James Webb Space Telescope (JWST). JWST can see in the infrared, which is where young, hot worlds shine brightest, so it can examine the exoplanet and find out more about its composition and how it formed.
Barber’s thesis research focuses on learning more about young exoplanets transiting their stars, so TIDYE-1 b is perfect for his work. The second-youngest planet in his data set, Barber says, is about 10 million years old. “I hope our investigation increases this number to allow statistical comparisons between planets of all ages,” he says.
