A free-floating or “rogue” exoplanet has been found adrift within our solar neighborhood. Just 10 million years in age, this giant loner is essentially a baby on galactic time scales. Without a star to call its own, this makes it an orphan, too – but don’t fret, it’s only 95 light-years from Earth, so it’s not too far away from some celestial company.
As a new paper uploaded to the arXiv server reveals, this planet is between four to eight times the mass of Jupiter, but not quite large enough to be a brown dwarf, sometimes referred to as a “failed star.” The object, with its decidedly cacophonous name 2MASS J1119-1137, was first spotted when its powerful infrared emissions were picked up by a team of astronomers led by Kendra Kellogg, a graduate student from the University of Western Ontario.
Initially, the astronomers had to first rule out that the infrared emission was not actually a distant, old star. Distant stars’ light, as it crosses the cosmos towards us, is stretched by the constantly expanding universe and gets stretched into a longer wavelength as a result. This means that by the time it arrives, it’s often “red-shifted” into infrared.
In addition, expanses of dust also redden the light from distant stars, giving them the appearance of young planet-like objects that would naturally emit red light at much closer distances. Using the gloriously named FLAMINGOS-2 spectrograph instrument, which picks apart the very specific types of wavelengths of light emitted by bright objects, the team confirmed that the object was nowhere near as dense as a star, and could instead be an exoplanet.
The position of the new rogue exoplanet in the night sky. Western University
Planets that have just formed are incredibly hot, thanks to their fiery, impact-prone construction process. Unlike many younger planets, this newly identified objected was still surprisingly hot. “It emits much more light in the infrared part of the spectrum than it would be expected to if it had already aged and cooled,” Kellogg said in a statement. This implied that the exoplanet was probably quite young.
Using careful measurements of how the object moved through the sky, and how much its emitted light was redshifted, the team identified it as being around 95 light-years away near the star TW Hydrae, in the constellation of Hydra.
Emissions from this region of space are of particular interest to astronomers: The 30-plus stars here nearby or “associated” with TW Hydrae are all around 5 to 10 million years of age, making them very young, so this area provides insights into the very early stages of stellar systems, which sometimes include very young planets or protoplanets.
Based on both the planet’s powerful infrared emissions, and its association with incredibly young stars, this new member of the TW Hydrae association is just 10 million years old, one of the youngest ever discovered. Incredibly, the team couldn’t find any star it is orbiting around, meaning that it’s known as a free-floating exoplanet – the second brightest ever discovered.
So why has this exoplanet been orphaned? No-one knows for sure, but one possibility is that a nearby massive planet, with its vast gravitational pull, threw it out of its own star system in a dangerous orbital dance.