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Nomad Planets: Stepping Stones To Interstellar Space?
An anonymous reader writes "Ian O'Neill suggests in an opinion piece at Al Jazeera that brown dwarves and nomad planets (planets not orbiting any star) could be a much needed stepping stone on our way to foreign stars. Quoting the article: 'In February, a fascinating paper was published in the Monthly Notices of the Royal Astronomical Society detailing calculations on how many "nomad planets" the Milky Way must contain after estimating our galaxy's mass from how much gravity it exerts on surrounding space. Scientists from the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) had uncovered something surprising — there are likely many more planets in the Milky Way than stars. ... Louis Strigari and his Kavli team calculated that there must be 100,000 planets for every star in the Milky Way (PDF). That's a lot of planets! But how can this be? Every star can't have tens of thousands of planets ranging from Pluto-sized to Jupiter-sized. This planetary "excess" actually suggests the existence of planets that were born without a star — nomad planets. ... we need all the help we can get if we are to venture to another star, so these ultracool brown dwarfs could become much-needed "stepping stones" for future starships to refuel on their light-years of journey time. There may be the possibility that these sub-stellar objects may even become more desirable targets for interstellar travellers. After all, there may be dozens of these invisible objects between here and Proxima just waiting to be uncovered by the sophisticated infrared telescopes of the future; they'd certainly make for more accessible scientific curiosities.'"
I don't think I'd want to stop at some random dwarf star. What is it you don't want on a long trip? Yes, to slow down and enter another gravity well. Doing so would make for a hell of a long trip. The time spent accelerating back along your path (people used to call it decelerating, but apparently that isn't a correct term), the fuel used escaping from the new gravity well, and the time and fuel used accelerating again. Worth it? Maybe if your design requires all that refueling. But the time involved is going to be the killer. It would probably triple (or more) the duration of the trip.
Sounds like they're hypothesising that all the "dark matter" is actually made of planets, or did i miss something...
DM cannot be made of planets because it cannot be made of atoms (it was not part of the plasma which filled the universe ~380k years after the Big Bang) nor does it have the same distribution as matter in a galaxy (rather than a disc it forms a spherical halo). The "gravitational effect" the summary misleading refers to is not the gravitational field of the galaxy but the local gravitational field of the object which bends light creating a lens effect. If the object passes between us and a distant star then the field will bend more light towards us causing the star to get brighter which is how you can detect them without seeing them.
Well, the paper actually claims that there are between 2x and 100000x the number of nomad planets as there are stars. This kind of conservative claim is almost certainly right! Their ability to count on the press to distort their claims by citing only the upper bound and not the lower bound is canny and borderline unethical. Kudos to them for an excellent piece of press-release science!
Even if you could overcome these effects and could reach speeds 100 times faster than is currently possible, it would take 500 years just to reach the nearest star system.
The humans will be forever locked on Earth unless FTL is possible. Exploration robots can be sent to faraway planets even without FTL, but they will be back many thousands of years after the launch. Humans will not be able or willing to take such a trip; they won't be humans anymore by the time they land.
This is similar to exploration of Americas. People could sail across the Atlantic ocean on Egyptian reed rafts, in theory - and perhaps a few did, but it made no impact on the rest and, if done, inflicted heavy human losses on the way there and back. Americas were not accessible until wind-driven, large ships were built that could do the trip in a reasonable time, with a reasonable chance of success, and that could carry a decent amount of commercial cargo. The same applies to the Moon right now; humans can go there and back, but such a trip is too expensive and too risky, and has very few clear reasons to even bother with.
If human of Planet Earth can think of nomad planets being vehicles to cruise the universe, you think sentient aliens from other planets wouldn't think of he same thing?
Perhaps they already are doing that
As I see it, there are a couple of big problems with nomad planets. Available energy is hard to use. The environment would probably be very close to 4K (the temperature of the cosmic microwave background). I guess that there would probably be some sort of fusion, fission, or gravitational resources available for many of these places. But I doubt much energy will be available without serious technology.
Alternately, you might have life adapted to this environment with extremely slow metabolism (here, I include Earth nonlife examples such as electronics/integrated circuit systems and clockwork mechanisms). Such adaption has a price. The beam of a flashlight or the warmth of a human body even through an insulated suit might be lethal to them.
But over a long enough time, there's probably a nomad planet traveling close to you at a decent rate of speed and traveling in a direction you want to go.