Astronomers uncover largest group of rogue planets yet

I’m imagining at least one rogue planet out there (they said they could be billions) was happily orbiting a star for billions of years, life formed, even relatively intelligent life, and then another rogue planet fell in to the solar system and passed right by the first planet in such a way as to eject it from the solar system without hitting it, and all this life on the planet suddenly loses daylight as their planet flies off in to deep space. And now their ancient civilization is frozen in time, adrift in deep space.

I'm kind of burned out on exoplanet discoveries since they're a dime a dozen nowadays but this title caught my eye because I've been rewatching Star Trek DS9 recently. The antagonist in the latter half of the series is the Dominion empire which is unilaterally controlled by a race of hivemind-y shapeshifters called the Changelings. The only time we get to see most of their species is on their home world, a rogue planet somewhere in the gamma quadrant.

I've been fascinated by the idea of detecting rogue planets ever since and it's incredible they found so many. Unfortunately, it looks like their detection method might not be useful for older (billion+) or rocky planets (from the footnote):

> The exact number of rogue planets found by the team is hard to pin down because the observations don't allow the researchers to measure the masses of the probed objects. Objects with masses higher than about 13 times the mass of Jupiter are most likely not planets, so they cannot be included in the count. However, since the team didn't have values for the mass, they had to rely on studying the planets' brightness to provide an upper limit to the number of rogue planets observed. The brightness is, in turn, related to the age of the planets themselves, as the older the planet, the longer it has been cooling down and reducing in brightness. If the studied region is old, then the brightest objects in the sample are likely above 13 Jupiter masses, and below if the region is on the younger side. Given the uncertainty in the age of the study region, this method gives a rogue planet count of between 70 and 170.

That said, this is exciting news!

> The study suggests there could be many more of these elusive, starless planets that we have yet to discover. "There could be several billions of these free-floating giant planets roaming freely in the Milky Way without a host star," Bouy explains.

Only tangentially related, but Melancholia is a beautiful (and uh melancholic) movie about a rogue planet that perfectly captures a prevailing mood about our present moment: https://en.wikipedia.org/wiki/Melancholia_(2011_film)

Not that we ever actually have to worry about a collision with a rogue planet.

Do these form like stars (as the primary mass in a cloud collapse?), or do they form like solar planets (secondary masses around a star) and get ejected? If the former, is there any mechanism for ejecting light elements to produce something like a terrestrial planet or are these inherently gas planets?

Would not a "group of rogue planets" more properly be called a "gang"?

I imagine most planets might be rogue. Stellar formation is incredibly energetic and violent. That any planets remain in stable arrangements is amazing.

I wasn't aware that planets could have traditional RPG roles. Whatever class Earth chose, it really needs to roll a 20 right now.

More in topic, I really like the idea of random planets floating the void on their own. I'd be really curious about they have a unique composition. Although the lack of an external energy source probably means there wouldn't be much potential for activity.

Does that mean the universe is still considered "new"?