Nomads of the Dark: Rogue Planets Explained Quiz

If a planet is ejected from a solar system, its gravitational field travels with it; if it had moons with stable orbits before ejection, then those moons can remain gravitationally bound to the planet as it drifts through the galaxy.

If a large population of rogue planets exists, and if most were created by ejection, then this provides evidence that planetary orbits are often unstable during formation; therefore, studying them helps us understand how many planets were "lost" during the birth of our own solar system.

If a rogue planet is not in a closed orbit around the star it lensed, and if the star and planet are moving in different directions through the galaxy, then the alignment is a one-time "chance encounter" that will never repeat.

If an object is between 13 and 80 Jupiter masses, it is a brown dwarf because it can fuse deuterium; if it is below 13 Jupiter masses, it is a planet; however, both types of objects can be found wandering the galaxy without a host star.

If NASA is launching a wide-field infrared telescope to monitor millions of stars in the galactic bulge for microlensing spikes, and if this mission is the Nancy Grace Roman telescope, then it is the primary tool for finding rogue planets.

If a planet has been ejected from a star system and is moving through the vast gaps between solar systems, then it is located in the interstellar medium (ISM).

If every object with mass exerts a gravitational force according to the law of universal gravitation, then even a drifting planet contributes its mass to the total gravity of the galaxy, helping to hold the galaxy together.

If a planet has no star, it cannot receive solar energy; however, if it has internal radioactive elements, formation heat, or a moon causing friction, and if it has a thick atmosphere to trap that heat, it can remain significantly warmer than the surrounding space.

If current microlensing surveys like OGLE and MOA detect frequent short-duration events, and if we extrapolate those findings to the whole galaxy, then the data suggests there are billions or even trillions of rogue planets, outnumbering the stars.

If a barycenter is the balance point between two or more orbiting masses, and if a rogue planet is alone in interstellar space, then it lacks a local orbital balance point with a host star.

If a planet is defined as an object orbiting a star, and if some planetary-mass objects are found drifting in interstellar space without a parent sun, then those objects are classified as rogue planets because they orbit the galaxy's center of mass directly.

If planets cool down over billions of years, and if infrared telescopes detect heat, then we have the best chance of seeing a rogue planet directly while it is still "glowing" from its initial gravitational contraction in a young cluster.

If a rogue planet is not bound to a star, we cannot predict its location or wait for a repeat orbit; if the planet has no star, we lose the "standard" light source used in transits, and its small mass creates a very brief signal.

If multiple large planets interact gravitationally in a young, crowded system, their tugs can accelerate one planet to escape velocity; if the planet reaches escape velocity, it is ejected into interstellar space.

If the time a background star spends being magnified depends on the mass of the foreground lens, and if 2 hours is an extremely short duration compared to the weeks-long events caused by stars, then the lens must be a very low-mass object like a terrestrial planet.

If a rogue planet is young, it still possesses internal heat from its formation; if it has internal heat, it emits infrared radiation that can be detected by sensitive thermal telescopes even without a nearby star to provide light.

If a planet has no host star, it cannot transit or cause a stellar wobble (radial velocity); if it is young and hot, it can be seen directly in the infrared, and if it passes in front of a background star, it can be detected via microlensing.

If the duration of a lensing event is proportional to the size of the area where gravity can effectively bend light (the Einstein radius), and if the Einstein radius depends on the mass of the lens, then a low-mass planet will have a smaller "lens" area, resulting in a shorter time window of magnification.

If a rogue planet has no host star and emits almost no visible light, then we cannot use transits or radial velocity; if that planet passes in front of a distant star, its gravity will bend and magnify that star's light, which is the process of microlensing.

If stars form from the gravitational collapse of gas clouds (nebulae), then they can form in isolation; however, if computer simulations show that most rogue planets are ejected from young solar systems due to gravitational instabilities, then they did not form in empty space but were "kicked out" of their original homes.