/ The most mysterious worlds of every galaxy /
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The most known planets to us orbit a star and these planets, including here also Earth, benefit from the star’s warmth and light and it is the light emitted from these stars which makes it possible for us to see them. But there are also invisible planets, hidden from our gaze, which float, abandoned, through the cosmos forever. These dark, lonely worlds have no star to orbit, no light in which to bask, no warmth to be radiated by. They are the rogue, interstellar, nomad planets, objects that does not orbit a star directly. Such objects have been ejected from the planetary system in which they formed or have never been gravitationally bound to any star or brown dwarf. Our Milky Way alone may probably have billions to trillions of rogue planets.
The researchers estimated from their observations that there are nearly two Jupiter-mass rogue planets for every star in the Milky Way. One study even suggested a much larger number, up to 100,000 times more rogue planets than stars in the Milky Way, though this study encompassed hypothetical objects much smaller than Jupiter.
Interstellar planets generate little heat and are not heated by a star, however, in 1998, David J. Stevenson theorized that some planet-sized objects adrift in interstellar space might sustain a thick atmosphere that would not freeze out. He proposed that these atmospheres would be preserved by the pressure-induced far-infrared radiation opacity of a thick hydrogen-containing atmosphere and during planetary-system formation, several small protoplanetary bodies may be ejected from the system. Such an ejected body would receive less of the stellar-generated ultraviolet light that can strip away the lighter elements of its atmosphere. Even an Earth-sized body would have enough gravity to prevent the escape of the hydrogen and helium in its atmosphere.
In an Earth-sized object that has a kilobar atmospheric pressure of hydrogen and a convective gas, the geothermal energy from residual core radioisotope decay could maintain a surface temperature above the melting point of water, allowing liquid-water oceans to exist. These planets are likely to remain geologically active for long periods. If they have geodynamo-created protective magnetospheres and sea floor volcanism, hydrothermal vents could provide energy for life.
These bodies would be difficult to detect because of their weak thermal microwave radiation emissions, although reflected solar radiation and far-infrared thermal emissions may be detectable from an object that is less than 1000 astronomical units from Earth. Around five percent of Earth-sized ejected planets with Moon-sized natural satellites would retain their satellites after ejection.
Large numbers of rogue planets criss-crossing our galaxy raise intriguing questions:
• Could life have formed and survived, or settled on such worlds?
• Perhaps technologically advanced civilisations could overcome the inconveniences of eternal darkness and an ice age with no comparison in Earth’s long and varied history?
• Maybe they harnessed nuclear power or became entirely non-biological?
• That may sound like science fiction, but what are the chances of Earth running into such a planet by chance?
This is not inconceivable.
Only in the last couple of years, rogue asteroids such as Oumuamua and rogue comets such as Borisov whizzed through our solar system. It is unlikely a rogue planet would pass by us that close up. But it’s not beyond the realms of probability. Earth has so far escaped banishment from the Sun. But one day, in about 4 bilion years, Earth too could go rogue. Because as the Sun ages, swells up and blows half of itself into space, Earth will either be swallowed by it, or be forced away. But it is unlikely to escape its gravitational attraction altogether.
So, as the dead Sun is degraded to a smouldering white dwarf, the Earth will face a similar fate to those other dark, cold worlds.
Not entirely alone, but far away from the once warm and bright orbit of its star.
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Rogue planets or brown dwarfs (which this might be) aren’t exactly rare, cosmologically speaking, but they tend to be very difficult to see. And yet, the way we found this particular planet/brown dwarf suggests we might locate other similar stellar objects through an application of the same technique. This one is either a brown dwarf or a planet — initially, it was thought to be a brown dwarf, but later mass estimates suggest it’s 12.7x the mass of Jupiter, which puts it right on the cusp of the planet/brown dwarf distinction. Brown dwarfs are typically thought to begin at 13 Jupiter masses (MJ), which is why SIMP J01 (etc) was originally thought to be a brown dwarf. In fact, it’s not clear this is a settled issue — some of the write-ups on this story explicitly refer to SIMP J01365663+0933473 as a brown dwarf, while others call it an enormous planet, scorching surface temperatures of about 825 degrees Celsius. The National Radio Astronomy Observatory site refers to a discovery late last year that suggests the planet is only 200 million years old and is too young to be a star.
“This object is right at the boundary between a planet and a brown dwarf, or ‘failed star’, and is giving us some surprises that can potentially help us understand magnetic processes on both stars and planets,” The Sun quoted Melodie Kao, the lead author of the study at Arizona State University, as saying.
First, it’s relatively close, at just 20 light years away. It possesses an enormous magnetic field some 200x stronger than Jupiter’s. It has 12.7x Jupiter’s mass, but it wouldn’t actually be much larger than Jupiter itself. Brown dwarfs, even those vastly more dense than Jupiter (60-90MJ), aren’t actually all that much larger than our fifth planet, and brown dwarf sizes only appear to vary by 10-15 percent. This object, for example, is just 1.22x the diameter of Jupiter, despite its mass. Astronomers at the National Science Foundation’s Karl G. Jansky Very Large Array used the radio telescope to detect the rogue planet, making this the first time we’ve identified a planetary-mass object using radio astronomy.
The planet Nibiru, the 12th planet in the writings of Zecharia Sitchin, based on his extra-terrestrial interpretation of Sumerian mythology, could be considered a rogue planet, since it supposedly possesses a highly elliptical, 3657-year orbit. However there is no scientific evidence for such a planet.
