April 6, 2020

05.06.11: Attack of the Rogue Planets?

Do dark worlds abound? (Credit: NASA/Artist’s Concept).

They’re out there, Man… I don’t know why, but Sunday morning our thoughts always turn toward ideas of cosmic death and destruction here at ye’ ole Astroguyz HQ… a recent study published in the journal of Nature suggests a startling possibility; that free-floating gas giant planets may be common in our galaxy; more common, in fact, than stars by a ratio of 2:1 in favor of the dark worlds. The news comes by way of exoplanet searches carried out by MOA (Microlensing Observations in Astrophysics) and OGLE (the Optical Gravitational Lensing Experiment) that watch for gravitational lensing events as the unseen body bends the light of a background star. Of the 474 events observed during the monitoring of 50 million stars from 2006 to 2007, 10 events stood out as having no corresponding host star, as evidenced by a tiny but discernable lensing event. Tentative estimates may put the number of “rogue planets” in the Milky Way galaxy in the (cue Carl Sagan) “hundreds of billions…” could one of these hidden worlds lurk nearby?

Not so fast, says Phil Plait, AKA the Bad Astronomer himself; he calculates by dividing the volume of our galaxy by the estimated number of hidden worlds that on average, one star-free world may exist for every 100 cubic light years, or perhaps within a 3 light year radius of our own solar system. And let’s be clear, we’re NOT talking Nibiru, Nemesis, Tyche, or the current Planet X in vogue at the moment… as the preface to ye’ ole Hitchhiker’s Guide says, space is Big, and Dr. Plait points out that the threat from a rogue world passing by and causing mayhem is pretty low. Keep in mind, this average distribution doesn’t factor in that population density probably varies throughout the Milky Way (it certainly does for stars) and that many of these worlds many blur the line between planet and brown dwarf… and no, these worlds don’t solve the dark matter deficit of our galaxy, not by a long shot. Still, it’s an interesting thought experiment to think of what might be out there, and the discovery of a rouge world in our galactic neighborhood would be big news. In fact, the jury isn’t entirely in on whether there is a brown dwarf star closer than Alpha Centauri, but as the recent NEO-Wise infrared survey is sorted out and the James Webb Space Telescope reaches first light in the next few years, we may be able to point at the sky some Sunday evening and say; “Thar be rogue world(s), matey…”

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