As part of the communal effort to locate this missing object, a collaboration between astronomy and mediaeval history seeks to determine whether it may have played a part in the long-term schedule of returning comets (1).  Comets can be perturbed slightly by even long-distant tugs by planets, and these miniscule alterations will be a continuous process as the positions of the known planets adjust relative to the comet over time.  Computer simulations can model these adjustments and attempt to predict the dates of return of comets which have had their orbital periods slightly adjusted by the planets over time.  Perusing the historical records of comet sightings and comparing these to the modelled schedule of their perihelion appearances may turn up anomalies.  Such anomalies may then be an indication of the presence of a further influencing gravitational effect, which has not been taken into account in the calculations.  In other words, Planet X.

Although the current project, conducted by academics from Queen's University in Belfast, is focussing upon comet appearances contained within European records over the last 1000 years, it could potentially be extended into earlier historical periods, from ancient cultures which were fascinated by astronomy.  The ancient Chinese were particularly fond of astronomy, for instance:

"Unlike any other country, China is the only place where astronomical observations took place uninterrupted for 4000 years and this surveillance led to many important astronomical discoveries. Special care was taken in China to record the appearance of unexpected events in the sky, such as eclipses, comets or star explosions." (3)

New Object Adds Grist to the Planet Nine Mill

Objects with this kind of orbital property were predicted to exist if Planet Nine lurks out there somewhere, influencing this distant minor bodies.  Without taking into account the existence of an additional planet, it was impossible to calculate Caju's spectacularly complex orbit using computer simulations (2).

The authors couldn't entirely rule out the possibility that Caju had been semi-ejected into its extreme orbit during the period of instability during the Late, Heavy Bombardment, some 3.9 billion years ago, though:

Other perturbing mechanisms were also considered in the calculations, including the intrusion of another star, or migratory movements of the giant planets.  however, the highly inclined orbit exhibited by this strange object only really started to fall into place when Planet Nine  was invoked.  The presence of Planet Nine permits 2015 BP519 to start out with a relatively low inclination and then easily attain its current-day inclination.  Things will become clearer ion the future if the Dark Energy Survey manages to add more objects to the ETNO tally, particularly if they're highly inclined to the ecliptic, like Caju.  Such a grouping would add an additional layer of evidence for a Planet X object above and beyond the physical clustering of ETNOs first pointed out by Scott and Trujillo in 2014 (4).

Image credit: ESO/M. Kornmesser

The Nice model predicts that dynamical instabilities in the early solar system would have caused some of the minor bodies in the inner solar system to be expelled, and this theory allows for the capture of exiled asteroids in Neptune's net, thus settling into the Kuiper Belt as a captured Trans-Neptunian Object.

This is the first object to provide a definitive link between the solar system's two belts.

The discovery of 1I/'Oumuamua last year has provided an anomaly rich with speculative potential.  This probable interstellar visitor wasn't a comet, but an asteroid.  This shocking finding has heightened speculation about how much ejected material is floating around in interstellar space: the chances of the first observed visitor to the solar system being an asteroid which originated from within another star's ice-line seems remote, given how tightly this should have been held onto compared with more loosely-bound comets, rich with icy volatiles (1).  The implication is that a substantial mass of materials is ejected from the inner zones of star systems during planet-formation. 

Image credit: Paul Weigert/Western University. 

You can see the retrograde orbit in action here:

gizmodo.com article

The interstellar asteroid phenomenon has also caused astronomers to reconsider what they might be looking for when they consider interstellar visitors.  Rather than assuming that some comets with hyperbolic orbits might be interstellar in origin, they can start to wonder whether interstellar visitors need to look like comets at all.  Perhaps the entire mix of objects in our midst needs to be considered.  Stars form in clusters, in close proximity to one another in stellar nurseries.  They pair up in dense cores which may go on to become binary stars, or split into singular star systems.  There is plenty of opportunity for materials to be exchanged during these early times, and now, it seems, further opportunities for asteroid materials to get picked up by the Sun, too. 

One very peculiar object in the solar system is now the focus of this thinking.  Could it be that a 3km wide object located near to Jupiter's orbit has an interstellar origin?  2015 BZ509 is in a resonant orbit with the gas giant but, unlike Jupiter's many familial Trojans, its orbit is retrograde in character (2).  This asteroid, dubbed "Bee-Zed", is orbiting the Sun in the wrong direction (3).  Such an object could not have started out this way - defying the solar system's natural protoplanetary spin.  It must have arrived in Jupiter's domain by another means, and been captured into its strange co-orbital orbit, defying death by keeping a wary distance from the gas giant itself.  It was initially realised that its orbit has been stable for at least a million years, and appears to be safe enough from Jupiter.  Perhaps there is a chance of it having a future collision with one of the gas giant's many Trojans, as many have probably yet to be discovered. 

As to the origins of Bee-Zed, it may have been a captured comet from the Oort cloud (4), for instance, or a Halley-family comet which entered into the resonant relationship through an interaction with Saturn (2). There's also a possibility that it arrived from interstellar space.  Recent computer simulations have shown that Bee-Zed's current co-orbital, retrograde orbit near Jupiter has actually been stable for the entire life-time of the solar system.  This implies that it could have been captured from interstellar space into its current retrograde orbit at a very early stage of the solar system's life (5).  The argument for this early immigration runs like this:

"...planet formation models cannot produce such a primordial large-inclination orbit with the planets on nearly coplanar orbits interacting with a coplanar debris disc that must produce the low-inclination small-body reservoirs of the Solar system such as the asteroid and Kuiper belts." (5)

And breath again.  This argument has been countered on statistical grounds, and without further study of this relatively tiny rock, no one is going to be quite sure either way (4).  What arguments like this do highlight, however, is the potential for a mixing of the cosmic waters.  The concept that all of the bodies in the solar system originated in the solar system is starting to look simplistic.  As a result, the super-computer simulations of how the solar system formed may have to take into account the potentially rogue nature of some of these bodies.  But which ones?  If some of the asteroids in our midst are immigrants from other star systems, then the solar system's family represents a mixed-race within the Cosmos.  Perhaps the same may be said of some of the larger objects in the solar system, too? 

Another possibility is that Bee-Zed was unsettled into its retrograde motion by a Planet X object (4):

"Planet Nine... would inevitably “pollute” the solar system with retrograde objects much like BZ509 as it drifts through the outer solar system. “So do you need to draw [BZ509] from the interstellar medium? No—Planet Nine would give it to you for free,” [Konstantin] Batygin says. “The interstellar interpretation is one possibility; Planet-Nine-induced dynamics provide an alternative.”" (4)

Expect a paper from the Caltech duo soon...

Written by Andy Lloyd, 22nd May 2018

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