A rogue planet on a collision course with Earth is something science-fiction stories have in common with doomsday theories (such as the 2012 Mayan calendar prophecies). Astronomy, however, has revealed nothing to lend credence to these fantastical scenarios. Researchers had used powerful telescopes to rule out the existence of any planet the size of Mars or greater within 7 billion miles of Earth and any planet the size of Jupiter or greater within 100 billion miles.1 (For comparison, Neptune orbits the Sun at a mean distance of 2.8 billion miles.)
While these findings may provide reassurance for those developing investment strategies for their grandchildren, it is quite another matter when attempting to use very distant planets to understand the stability of advanced life over the past several million years. Some astronomers have hypothesized that an extremely distant planet in the solar system may be responsible for causing the mass extinction events noted in the fossil record (such events took place at regular intervals throughout a 27-million-year period).2 To address these considerations, astronomer Kevin Luhman analyzed the database from the Wide-Field Infrared Survey Explorer satellite to search for possible thermal emission signals from gas giant planets and brown dwarfs that may be lurking in the outer limits of the solar system.3 (Brown dwarfs are bodies ranging in size from 12–75 Jupiter masses.)
Luhman determined that no planet the size of Saturn or greater exists within 2.6 trillion miles (0.44 light-years) of the Sun and no planet the size of Jupiter or greater exists within 7.6 trillion miles (1.30 light-years).4 Such a stringent limit on distant solar system bodies effectively rules out the possibility that a distant planet could be responsible for the mass extinction events noted in the fossil record.
This limit also implies that, over the past several million years, advanced animals on Earth have been relatively undisturbed by events in the extreme outer realms of the solar system. One can only hope this limit will also put an end to speculations that a hypothesized Planet X will bring about the end of civilization or usher in the apocalyptic events prophesied in Scripture.
A Unique Planetary System
Such a lack of large planets and brown dwarfs may be an exceptional feature for planetary systems. In spite of the fact that planets orbiting at great distances from their stars are extremely difficult to detect, astronomers have found a substantial number.5 Researchers have also discovered several free-floating planets and brown dwarfs (bodies unattached to any star).6
Large planets cannot form at great distances from their stars because the circumstellar disks from which they form do not extend far enough. However, the nearly ubiquitous high-eccentricity orbits observed for exoplanets located more than a 100 million miles from their host stars (Earth’s distance from the Sun = 92.8 million miles; see the exoplanet catalog) implies that many planets will be ejected from their planetary systems. Given the expected large population of ejected planets, there exists a high likelihood that many stars will capture these free-floating bodies into very wide orbits.7
Our solar system’s lack of planets with high-eccentricity orbits, lack of wide orbit planets, and lack of any large body within a light-year of the Sun all suggests that our planetary neighborhood is special. At RTB, we propose that the uniqueness of our solar system indicates that it was designed intentionally, in order to make possible the existence of enduring advanced life on Earth. We can thank God that the closest we’ll be to a rogue planet is the pages of a sci-fi novel.