Rogue Planets Ahoy!

According to an article in Nature astronomy, astronomers have identified over 70 rogue planets in an amazing discovery.

The planets are considered “rogue” because they orbit no stars and pass through space on journeys through the voids between stellar systems. They are also known by the less glamorous title of Free-Floating Planets or FFPs.

While these have been known about for several years (and one made a “guest appearance” in my third Joe Ballen novel, Transformation Protocol), such planets are difficult to detect, and few have been identified, up until now.

Why are Rogues so hard to detect?

Most exoplanets (the ones we know about at least) orbit nearby stars and have been discovered through methods that rely on very precise readings of how they affect their host star. These include measuring the tiny dimming of a star’s light (known as the transit method) or the “wobble” of a star caused by a large planet pulling on it (radial velocity method). Without a star of their own, rogue planets are extremely difficult to detect, and the team working on the problem had to comb through terabytes of data gathered over 20 years.

According to Hervé Bouy, lead scientist of the project and astronomer at the Laboratoire d’Astrophysique de Bordeaux, there could be several billions of these giant planets adrift in the Milky Way galaxy.

That in itself is impressive enough, but it also makes me wonder about something else. There’s a problem in astronomy we’ve known about for many years and as yet have no answer for. The galaxies we see are spinning so fast that, according to our best theories, they should spin apart in a relatively short time, so something must be holding them together. The current leading theory is dark matter, an invisible type of exotic matter that has mass, but rarely, if ever, interacts with any other form of matter.

But astronomers can only estimate the amount of matter in a galaxy from visible matter, i.e. stars. They allow for planets in planetary systems, but if rogue planets are as numerous as they now appear to be, could they account for the “missing mass” needed to hold everything together?

Rule of the Numerous Small

Isaac Asimov once mentioned that the universe tends to operate by the Rule of the Numerous Small, the idea being that there are always far more small things than there are large ones. Like the exoplanets we’ve discovered, these rogue planets will be among the largest, simply because bigger objects are easier to detect than smaller ones. So, if there are several billions of these large rogues, how many smaller ones must there be? I look forward to following the research!

2 Responses

  1. I’m not trying to start an alarmist, doomsday scenario by asking this, but, had there been any serious look at the possibility/ probability of one of these planets interacting with the Sol System? End of the world stuff aside, imagine the things we could learn from such an encounter.

  2. Hi Michael, Thanks for getting in touch.
    I’ve not seen anything looking at this scenario, and I think it’s probably statistically unlikely. Space is big (to quote Douglas Adams!) and most of it empty. So even with billions of rogue planets out there, the chance of one intersecting with our solar system is probably negligible.
    If one did arrive, again much of our solar system is empty so it may pass through without making itself known very much, though if it passed through the inner solar system, I imagine there’s be some gravitational effects on the smaller planets like ours.
    It’s certainly interesting to speculate on what we might learn from a non-disastrous encounter. Such a planet could potentially provide us with a huge amount of knowledge about planetary formation mechanisms, and how general our theories of geological development are. If you want to go further, there’s also the small possibility that such a planet could carry life, buried deep under frozen oceans.
    As with our recent encounter with Oumuamua, these things can and do happen. We’d probably need some further developments in space capability to reach any such object. Definitely worth pondering though!

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