# Rogue Planets in the Sun's Galactic Neighbourhood

Models of planetary system formation predict that in the early phase of condensation of planets from a protoplanetary disc, gravitational interactions between bodies will cause some to be ejected into interstellar space. These planets wander the galaxy unattached to any star and, because they are heated only by their own gravitational contraction, are faint emitters in the infrared and very difficult to detect. A few have been discovered via micro-lensing events, but this does not permit follow-up observations.

A new paper, “A rich population of free-floating planets in the Upper Scorpius young stellar association”, reports a search for rogue planets in the closest star forming region to the Sun which found such objects to be up to seven times as abundant as expected from existing models, suggesting they are common in the galaxy.

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I am reading Starship Century and , of course, I am thinking about interstellar travel at fraction-of-light-speeds. I was thinking that, since the vacuum of space has some ‘stuff’ present, there would be a need for significant protection at the front end of interstellar ships. They would encounter particles at speeds which would impart great momentum and damage. Hitting a rogue planet or an asteroid, by contrast, presents bigger problems

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Fortunately, they are very rare. Estimates are that there are fewer than ten rogue planets within ten light years of Earth, so the threat of an impact is negligible. Objects in space tend to be distributed according to a power law, so tiny objects are far more common than those of macroscopic size. But when you’re travelling at relativistic speeds, even a mote of dust can make for a Really Bad Day.

A one milligram dust particle hitting a ship travelling at 10% of the speed of light releases energy comparable to 100 kg of TNT. Or, to be precise, Units Calculator says:

`(1/2) milligram ((0.1 c)^2) = 97.435108 kg tnt`

(I did not use the relativistic formula for mass because at 10% of the speed of light the difference from the classical formula can be ignored. It really only becomes significant at 2/3 the speed of light and greater.)

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Reminds me of the movie, Passenger.

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One of the few benefits of old age (aside from discounts on haircuts - rare since Covid) is that I can re-watch most movies and remember hardly any of what happened. I know I saw it & hardly remember it. I see I would have to rent it on Prime. Not available for free streaming. I will say I have no trouble remembering to spend as little as possible with Amazon.

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In the movie, they have a mechanism to deflect debris.

I know what you mean about Amazon. I’m a little cheesed now because in the last year I’ve become partly disabled, and that spectre of a company has enabled me to shop and resupply a lot of “stuff” easily.

Memory? Huh?

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