The shard-like asteroid from deep space which shot through the solar system last years, known as ‘Oumuamua, set many an astronomer’s heart racing. The peculiar body was determined to be the first confirmed interstellar asteroid to have been observed (1). It’s possible, though, that other comets which pursue so-called hyperbolic orbits (moving fast enough to escape the solar system) also have an interstellar origin, rather than having originated from the Oort Cloud. A team of Spanish astrophysicists, who have more than a passing interest in the topic of Planet X, have performed powerful computer simulations to build up a picture of the trajectories and spatial origins of various hyperbolic comets (2). The objects they chose to consider have inbound velocities greater than 1km/s
Following adjustment for the Sun’s own movement through space towards the Solar Apex, interstellar visitors would likely have a more or less random distribution to their radiants (the position in the sky from which they came, rather like meteor showers striking the Earth’s atmosphere). The Spanish team carried out statistical analysis on the emerging sky maps of these radiants, and looked for patterns or clusters of these origin points. Statistically significant patterns did indeed emerge from the data. A particularly large source was located in the zodiacal constellation Gemini. Such a clustering might indicate a number of possibilities, which the astrophysicists explore in their paper.
One possibility is a close flyby of a star in the past which could have disrupted the outer edges of the distant Oort Cloud, sending comets in-bound towards the Sun. Looking at the tracking of candidate flybys in the (by Cosmic standards) relatively recent past, Carlos de la Fuente Marcos, Raul de la Fuente Marcos & S. J. Aarseth argue that there is a possible correlation between this cluster of hyperbolic orbit radiants in Gemini, and a close flyby of a neighbouring binary red dwarf system known as Scholz’s star some 70,000 years ago (2). At a current distance of about 20 light years, Scholz’s star may be a close neighbour to the Sun relatively speaking, but even so it took a while for it to be discovered. This was probably because of a combination of factors: Its proximity to the Galactic plane, its relative dimness, and its slow relative movement across the sky (3). Its distance was less than a light year 70,000 years ago, and its rapid movement away from us in the intervening time helps to explain why it was difficult to detect as a neighbouring binary star: Its retreating motion is mostly along our line of sight, making it difficult to differentiate from background stars. Read More…
Not so long ago, brown dwarfs (failed stars caught in an awkward in-betweener zone between stars and planets) were hypothetical bodies. Their low stellar masses allow for only a very short period of light-emission in their early years, after which they cool and darken considerably.
“[A] brown dwarf has too little mass to ignite the thermonuclear reactions by which ordinary stars shine. However, it emits heat released by its slow gravitational contraction and shines with a reddish colour, albeit much less brightly than a star.” (1)
It was recognised early on that if they existed at all, they would be very difficult to spot – and so it proved. In recent years, the ability to detect these objects has improved considerably, including more effective infra-red sky surveys. As they have become more common, the frontier of sub-stellar bodies has dropped in mass into the ultra-cool stellar bodies known as sub-brown dwarfs – many of which would equally properly be designated as rogue gas giant planets. These objects tend to have masses below 13 times that of Jupiter (13Mj) (2). These objects have always interested me greatly, and very early on in my own research efforts I was advocating the potential importance of sub-brown dwarfs in the hunt for additional planets orbiting our own Sun at great distances (3). I used the term ‘Dark Star’ to describe these ultra-cool objects; a term suggested by a friend of mine. Some can be found orbiting stars (usually beyond 50AU) while others are free-floating entities in their own right.
One of the pair of Caltech scientists who announced in January that there was a very high probability that a ‘super-Earth’, dubbed ‘Planet Nine’, exists beyond Neptune (1,2), has noted that a newly discovered eccentric Kuiper Belt Object cuts down the possibility that they were wrong still further.
“The object [uo3L91] shares some of the same behavior as the other six Kuiper Belt bodies, suggesting it has also been pushed by a large planet that is between 200 and 1,200 times the distance from the Sun to Earth. The object was discovered by the Canada France Hawaii Telescope, which is conducting the Outer Solar System Origins Survey (OSSOS); information about its movements were presented recently by astronomer Michele Bannister at the SETI Institute.” (3)