A flock of free-floaters

Planets and stars: they’re always together
The star is a bird. Each planet’s a feather
What happens, you ask, when a feather falls out,
Gets caught in the wind, drifts up and about?

We’ve found countless planets that orbit their stars –
Some planets are gaseous, some rocky (like Mars).
They’re called exoplanets: they’re really quite awesome
Abundant, diverse; like flowers in blossom.

A handful of planets have likewise been found
Without any star.  Completely un-bound!
Mysterious objects, these rogues out in space
So faint it’s a challenge to see just a trace.

Here’s something brand new – we made a big splash!
A pile of free-floaters just dropped with a crash!
A hundred new rogue planets! Yup, we just found ‘em
They orbit among stars instead of around ‘em.

How did we find all these rogues? You might ask.
It really was hard – a gargantuan task.
Nuria did the real work (no, not me!)
The project a key piece of her PhD.

We first had to find out where rogues would be bright
The youngest of planets can shine in the night
Each planet starts hot, then cools as it ages
It’s brightest, by far, in the earliest stages

The best place to look is a star-forming cloud
Where stars (and their planets) are shining out loud
A cloud – Upper Scorpius – close to the Sun
A few thousand stars.  It’s young. It’s the one.

The problem – it’s huge!  It’s stretched far and wide.
A patch on the sky 30 full Moons a side!
The plan: gather pictures wherever we can
Combine them together to build up a scan.

The project we built is called Cosmic-DANCE
It’s based at the Uni of Bordeaux in France.
A database – hundreds of tera-ma-bytes
Upper Sco imaged on dozens of nights

Locations of 115 potential free-floating planets in Upper Scorpius (red circles). Credit: ESO/N. Risinger (skysurvey.org)

With all of this data, we got the full count
Of Upper Sco’s tally, the total amount
There’s three thousand five hundred objects in all
Most of them stars. But some are too small.

We found some brown dwarfs – they’re smaller and dimmer
Their cores do some fusion but only a glimmer
The faintest of objects we care about most –
They’ve got to be planets, and without a host

A hundred rogue planets! Each off on its own.
Where did they come from?  And where are they going?
There’s two possibilities with implications
The difference relates to the objects’ formation

Maybe they’re simply the shrimpiest stars
The wee little cousins of Suns just like ours
That form all alone out of small clouds of gas
Collapsing like stars, just from not-so-much mass.

Or maybe each rogue formed around its own star
And then was ejected to space – au revoir!
Two gas giant planets – their gravity kicks
So strong that they hit like a pile of bricks.
One planet is kicked, it’s thrown and ejected
It wanders alone (and feels kind of rejected)

For more on gas giants going unstable (and destroying their rocky planets), see here. Credit: Eric Ford.

These free-floaters, all of them, are just titanic
Bigger than Jupiter (which is gigantic)
Smaller rogues must be all over the place
They’re simply too faint to detect off in space.

Scaling from exo-ma-planets, we find
With data from all sorts of methods, combined
For each mega-Jupiter there’s got to be
Ten or more Neptunes out there floating free!

There also must be lots of free-floating Earths
Wandering far from their systems of birth
But could they have life?  Well, it’s awfully chilly
They’d need a nice blanket but that might look silly
A pretty thick atmosphere could slow the heat flow
Ponds – even lakes – just might lurk down below

Artist’s conception of a free-floating gas giant planet in Upper Scorpius. Credit: J.-C. Cuillandre, COSMIC-DANCe / CFHT / Gaia DPAC

The best place for free-floating life in the dark?
A system of moons may provide just the spark
Jupiter’s moons experience tides
And friction makes heat comes up from their insides.
Free-floating gas giant moons are the place!
They’d stay nice and warm in the cold depths of space

To wrap this all up: we’ve sort of gone rogue
We hope that free-floaters will now become vogue
There’s still lots of mystery, lots to be learned
Let’s see what comes next.  Now: poem adjourned!

[A last goofy rhyme that I feel like I’ve earned:
Free-floating people do not get sunburned!]


Additional Resources
— Our paper, ‘A rich population of free-floating planets in the Upper Scorpius young stellar association,‘ (authors: Nuria Miret-Roig, Herve Bouy, Sean Raymond et al), published in Nature Astronomy
Twitter for Nuria Miret-Roig
Website of Herve Bouy
Website for the Cosmic-DANCE project
— The official press releases: ESO, NOIRLab
How planets die: When good Jupiters go bad!
More astronomy poems

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