An artist’s depiction of the transiting exoplanet TI-DYE 1b. The planet is estimated to be three million years old, one of the youngest ever recorded.NASA/JPL-Caltech/R. Hurt, K. Miller (Caltech/IPAC)/Supplied
Since astronomers first began detecting exoplanets – planets beyond our solar system – in the 1990s, they have come across thousands of worlds, large and small. But few have ever been found as young as TI-DYE 1b.
The fledgling orb (pronounced “TIE-DYE 1b”) is estimated to be three million years old, or about 0.07 per cent the age of Earth. That alone makes it a potential Rosetta Stone for understanding the process by which planets are made.
As an added bonus, the planet is orbiting a star located some 520 light years away, in the direction of the constellation Taurus, near enough to make it a good candidate for a more detailed study.
“We originally believed that planets this young couldn’t be found,” said Madyson Barber, a graduate student at the University of North Carolina at Chapel Hill, who made the discovery, reported Wednesday in the journal Nature.
There was good reason to doubt. Planets are formed inside disks of gas and dust that swirl around newborn stars and obscure whatever is happening within. In the past, when such young planets have turned up, it has been in solar systems that are oriented face-on, so that the inner portion of the disk can be seen more easily.
But TI-DYE 1b is orbiting in a plane that is edge-on from Earth’s perspective. That makes it a transiting exoplanet – one that repeatedly crosses in front of the star it orbits. Its detection was possible only because the outer portion of the disk surrounding the star is tilted at an odd angle, like a bent hat brim. This permits a clear line of sight into the inner regions.
Even so, the planet is too small and dim to be seen directly. Its presence was unearthed in data from NASA’s Transiting Exoplanet Survey Satellite (TESS). Since it was launched in 2018, the orbiting telescope has been methodically scanning the heavens for exoplanets by looking for stars that dip in brightness in a predictable way as planets pass in front and temporarily block some of the starlight. The size of the dip reveals the size of the planet while the length of time between transits yield the planet’s orbital period and distance from its star.
Last year, Ms. Barber began working her way through the publicly available TESS data, concentrating only on stars that are less than 500 million years old. The goal of the project is to spot transiting planets of different ages, which can be used as “snapshots in time to better understand their evolutionary paths,” she said.
Transiting planets are important to astronomers because they can be explored in ways that other planets cannot.
For example, each time TI-DYE 1b crosses in front of its star, some of the star’s light is absorbed by the planet’s atmosphere. The way this light is absorbed provides information about the composition and structure of the planet’s atmosphere.
So far, the data suggest the planet is puffed up like a cotton ball. It is nearly as large as Jupiter, but it is not greater than one-third of Jupiter’s mass. Newly forming planets are expected to be somewhat puffy as they aggregate material from the surrounding disk. Ms. Barber said that over millions of years the planet would likely settle into a gaseous planet that is smaller than Saturn, or a “super-Earth” – a planet that is made of rocky material like Earth but somewhat larger and heavier than our own world. So far it is not yet clear which.
The planet is also extremely close to its star – circling around it once every 8.8 days.
David Lafrenière, an astronomer at the University of Montreal who was not involved in the new find, said planets are unlikely to form at such close quarters so it’s more probable that TI-DYE 1b migrated inward toward the star after it formed. But because of the planet’s young age, all of this had to have happened within three million years.
That age is ”a critical time,” Dr. Lafrenière said, because it is when disks that give rise to planets begin dissipating, a process that could be illuminated by further observations of the system.