The lonely planets – the English “rogue planets” seem much more exciting – have yet to reveal many of their secrets. Their origin, for example. It is possible that some of the solitary planets were formed by the agglomeration of gas and dust, and that there simply was not enough material available to form a star. But it’s also possible that they originated in a galaxy, having been thrown away from a massive planet by the force of gravity.
It is also not known if life could exist. You might think not, without the energy from the heat of the sun. But there is one conceivable scenario that could make life possible: geothermal action – the heat from within the planet’s interior – and a dense atmosphere could combine to create an energy cycle so that life can thrive there. With a core of liquid metal, a lonely planet can even have a magnetic field, which can protect life from cosmic rays.
What we do know is how to find solitary planets: using the micro-lens, a variation of the gravitational lens. The space around us seems to extend in a straight line. But objects with mass exert gravity, and when it is large enough, the space near such an object visibly deviates. This means that a beam of light that is simply moving straight ahead appears to an observer to be deflecting towards such a heavy object. This effect is very strong for black holes. Albert Einstein predicted it as early as 1912, but the effect was not observed for the first time until 1979.
You can think of the micro lens as this small scale effect. You see it, for example, when a lonely planet moves in front of another object. This provides science with an interesting method of detecting objects that are faint or do not emit radiation at all.
Countless lonely planets
Recent Japanese research has revealed ten solitary planets. It may not seem like much, but the Japanese have only explored a small part of the universe. Estimates range from a lonely planet for four stars to as many as 100,000 lonely planets per star. So even by the most conservative estimate, our Milky Way galaxy is teeming with solitary planets.
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