One of the essential ingredients of planet-building is the clumping of dust in space. Planets can build up through the gravitational attraction of objects in space which are already about 1000km across. The problem is how do these proto-planetessimals get built? The mechanism for how dust clumps together has not been well understood. After all, when materials moving at speed through space collide, they may break apart in the force of the impact, showering down collisional cascades of ever small materials – the exact opposite of planetessimal-building. Somehow, dust must clump together into grains, which then join forces to create space pebbles, then boulders, then mountains, etc.
For these materials to adhere together, an inherent stickiness may be needed, aided by the presence of greasy organic compounds (in the form of aliphatic carbon). While it is recognised that this greasy component is more readily available in interstellar space than previously suspected (1), does that adhesive property extend down to space dust? If not, what mechanism could be bringing together ever larger clumps of plain old granular dust in space?
New research work suggests that dust and gas are not happy bedfellows within a magnetic field. So, rather like oil in water, dust particles seem to come together within gas as the mixture traverses the galactic tides. Indeed, any force brought to bear on dust moving through gas seems to create this clumping effect:
“… it was previously assumed that dust was stable in gas, meaning the dust grains would ride along with gas without much happening, or they would settle out of the gas if the particles were big enough, as is the case with soot from a fire. “…dust and gas trying to move with one another is unstable and causes dust grains to come together,” says [Phil] Hopkins [Professor of theoretical astrophysics at Caltech]...These gas-dust instabilities are at play anywhere in the universe that a force pushes dust through gas, whether the forces are stellar winds, gravity, magnetism, or an electrical field.” The team’s simulations show material swirling together, with clumps of dust growing bigger and bigger.” (2)
Computer simulations looking at how dust moves through magnetized gas seems to show this clumping effect as a general mechanism. The dust grains are like boulders in a fast moving and turbulent river (the gas within a moving stream of magnetized material). As the flows wrap around these grains and pull them back and forth, the grains have a tendency to coalesce, forming ever larger clumps. This is not just applicable to planet formation in proto-planetary disks, but may also extend to interstellar space:
“As examples, we introduce several new instabilities, which could see application across a variety of physical systems from atmospheres to protoplanetary disks, the interstellar medium, and galactic outflows.” (3) Read More…
The announcement of the discovery a new object in the outer solar system may bring us a step closer to the elusive Planet X (more recently dubbed Planet Nine). This new dwarf object, known as 2015 TG387, is a distant member of the mysterious scattered disk of objects beyond the Kuiper Belt. This particular object can travel so far away from the Sun during its orbit that it moves through the inner Oort cloud of comets, beyond 2000AU:
“The newly discovered object is called 2015 TG387, is probably a small dwarf planet at just 300km across, and is incredibly far away. It is currently lying about two and a half times further away from the Sun than Pluto is. It often reaches much further away. Its orbit takes it to about 2,300 AU — that is 2,300 times as far away from the sun as we are, and vastly more than the already huge 34 AU that the distant Pluto sits at.” (1)
The object’s vast orbit is so vast that it takes about 40,000 years to do one circuit around the Sun. Yet, its orbit is highly eccentric. It distance from the Sun varies from 64AU at perihelion to 2037AU at aphelion. Incredibly, then, it skirts both the Kuiper Belt and the inner Oort cloud, transiting between these quite distinct belts of objects.
As more objects are discovered between the Kuiper Belt and the inner Oort cloud (a torus-shaped disk of comets), the classifications of these objects are becoming more complex. A significant factor is whether these objects have perihelia within 40AU, which might briefly bring them within the influential scope of the planet Neptune. Extreme scattered disk objects fall into this category. Significantly, 2015 TG387 is fully detached from this influence at perihelion, and may be considered to be an inner Oort cloud object. Read More…
In conjunction with a scientist from the University of Michigan, the Caltech team who originally coined the term Planet Nine in 2016 have written a new paper about its formation, and the subsequent layout of the outer solar system. Having set out the evidence for this proposed object in the paper (1), they note three possible scenarios for its formation:
1) The planet’s capture from the retinue of a passing star; or, alternatively, the capture of a free-floating interstellar planet
2) The planet’s semi-ejection from the inner solar system and subsequent gradual drift outwards
3) The planet’s formation in situ.
All three of these scenarios require certain conditions for them to work, which means that no single formation theory stands out as particularly probable. The capture and scattering models depend upon the interjection of outside bodies (passing stars or brown dwarfs, or objects in the Sun’s birth cluster). The in situ formation of a planet so far from the Sun implies that the Sun’s protoplanetary disk was significantly larger than generally accepted. The formation of Planet Nine in its calculated position thus remains problematic, based upon standard models of planetary and solar system formation (e.g. the Nice model). Further, whatever processes which placed it in its proposed current position would have significantly affected the layout of the Kuiper belt within its overarching orbit. This factor is what the current investigation described by this paper aims to solve.
This paper then describes computer simulations of the early Kuiper belt, and how the shape and extent of the fledgling belt may have affected the complex interplay between it, Planet Nine, and the objects in the extended scattered disk (1). The research team modelled two distinct scenarios for the early Kuiper belt, each of which matches one or more formation scenarios for Planet Nine. The first is a ‘narrow’ disk, similar to that observed: The Kuiper disk appears to be truncated around 50AU, with objects found beyond this zone likely having been scattered outwards by processes which remain contentious. The second scenario is a ‘broad’ disk, where objects in the Kuiper belt would have routinely populated the space between Neptune and the proposed orbit of Planet Nine, hundreds of astronomical units out. This would match a formation scenario involving an extensive protoplanetary disk. Read More…
Brown dwarfs are notoriously hard to find. It’s not so bad when they are first born: They come into the Universe with a blast, shedding light and heat in an infantile display of vigour. But within just a few million years, they have burned their available nuclear fuels, and settle down to consume their leaner elemental pickings. Their visible light dims considerably with time to perhaps just a magenta shimmer. But they still produce heat, and the older they get, the more likely that a direct detection of a brown dwarf will have to be in the infra-red spectrum.
This doesn’t make them much easier to detect, though, because to catch these faint heat signatures in the night sky, you first need to have a cold night sky. A very cold night sky. Worse, water vapour in the atmosphere absorbs infra-red light along multiple stretches of the spectrum. The warmth and humidity of the Earth’s atmosphere heavily obscures infra-red searches, even in frigid climates, and so astronomers wishing to search in the infra-red either have to build IR telescopes atop desert mountains (like in Chile’s Atacama desert), or else resort to the use of space-based platforms. The downside of the latter is that the telescopes tend to lose liquid helium supplies rather quickly, shortening their lifespan considerably compared to space-based optical telescopes.
The first major sky search using a space telescope was IRAS, back in the 1980s. Then came Spitzer at the turn of the century, followed by Herschel, and then WISE about five years ago. Some infra-red telescopes conduct broad searches across the sky for heat traces, others zoom in on candidate objects for closer inspection. Each telescope exceeds the last in performance, sometimes by orders of magnitude, which means that faint objects that might have been missed by early searches stand more of a chance of being picked up in the newer searches.
The next big thing in infra-red astronomy is the James Webb Space Telescope (JSWT), due for launch in Spring 2019. The JSWT should provide the kind of observational power provided by the Hubble Space telescope – but this time in infra-red. The reason why astronomers want to view the universe in detail using infra-red wavelengths is that very distant objects are red-shifted to such a degree that their light tends to be found in the infra-red spectrum, generally outside Hubble’s operational parameters (1). Essentially, the JWST will be able to see deeper into space (and, therefore, look for objects sending their light to us from further back in time when the first stars and galaxies emerged). Read More…
It looks like it’ll be another long, lonely autumn for Dr Mike Brown on the summit of the Hawaiian dormant volcano Mauna Kea, searching for Planet Nine. He made use of the 8m Subaru telescope last year, and it looks like he’s back again this year for a second role of the dice (unless he does all this by remote control from Pasadena?). I can only assume, given the time of the year, that the constellation of Orion remains high on their list of haystacks to search.
A recent article neatly sums up the current state of play with the hunt for Planet Nine (1), bringing together the various anomalies which, together, seem to indicate the presence of an undetected super-Earth some twenty times further away than Pluto (or thereabouts). Given how much, I’ve written about this materials already, it seems unnecessary to go over the same ground. I can only hope that this time, Dr Brown and his erstwhile colleague, Dr Batygin, strike lucky. They have their sceptical detractors, but the case they make for Planet Nine still seems pretty solid, even if the gloss has come off it a bit recently with the additional OSSOS extended scattered disk object discoveries (2). But there’s nothing on Dr Brown’s Twitterfeed to indicate what his plans are regarding a renewed search for Planet Nine.
Even if the Planet Nine article’s discussion about a new hunt for the celestial needle in the haystack is misplaced, it does make a valid point that super-Earths, if indeed that is what this version of Planet X turns out to be, are common enough as exo-planets, and weirdly absent in our own planetary backyard. So a discovery of such an object way beyond Neptune would satisfy the statisticians, as well as get the bubbly flowing at Caltech. Dr Brown did seem to think that this ‘season’ would be the one. We await with bated breath…
Meanwhile, the theoretical work around Planet Nine continues, with a new paper written by Konstantin Batygin and Alessandro Morbidelli (3) which sets out the underlying theory to support the result of the 2016 computer simulations which support the existence of Planet Nine (4). Dr Morbidelli is an Italian astrophysicist, working in the south of France, who is a proponent of the Nice model for solar system evolution (named after the rather wonderful French city where he works). This model arises from a comparison between our solar system’s dynamics, and those of the many other planetary systems now known to us, many of which seem bizarre and chaotic in comparison to our own. Thus, the Nice model seeks to blend the kinds of dynamical fluctuations which might occur during the evolution of a star’s planetary system with both the outcomes witnessed in our own solar system, and the more extreme exoplanets observed elsewhere (5). It invokes significant changes in the positions of the major planets during the history of the solar system, for instance. These migrations have knock on effects which then drive other disturbances in the status quo of the early solar system, leading to the variations witnessed both here and elsewhere. For instance, Dr Morbidelli lists one of the several factors which brought about the Nice model:
Last month, scientists working on the Outer Solar System Origins Survey (OSSOS) published a large dataset of new Kuiper Belt Objects, including several new extended scattered disk objects discovered way beyond the main belt (1). These four new distant objects seemed to have a more random set of properties, when compared to the rather more neat array of objects which had previously been constituted the Planet Nine cluster. This led to scepticism among the OSSOS scientific team that there was any real evidence for Planet Nine. Instead, they argued, the perceived patterns of these distant objects might be a function of observational bias (2).
Whilst reporting on these new discoveries and their potential implications, I predicted that the debate was about to hot up, bringing forth a new series of Planet X-related articles and papers (3). Indeed, leading outer solar system scientists were publishing related materials in quick succession (4,5), each finding new correlations and patterns which might indicate the presence of an unseen perturbing influence.
Now, Caltech’s Konstantin Batygin has published an article analysing the impact of the discovery of these new extended scattered disk objects on the potential for a Planet Nine body. The short conclusion he draws is that although the objects are, on the face of it, randomly distributed, their property set is largely consistent with Caltech’s original thesis (6). They are either anti-aligned to the purported Planet Nine body (as the original cluster is thought to be), or aligned with it in a meta-stable array.
It’s a year since proposed the existence of Planet Nine (1). Despite the fact that its discovery remains elusive, there have been a great many academic papers written on the subject, and no shortage of serious researchers underpinning the theoretical concepts supporting its existence. Many have sought evidence in the solar system which indirectly points to the perturbing influence of this mysterious world; others have provided data which have helped to constrain the parameters of its orbit (by effectively demonstrating where it could NOT be). Throughout 2016, I have been highlighting these developments on the Dark Star Blog.
At the close of 2016, two further papers were published about Planet Nine. The first of these delves more deeply into the possibility that Planet Nine (Brown’s new name for Planet X, which seems to have caught on among astronomers keen to distance this serious search from, well, the mythological planet Nibiru) has a resonance relationship with some of the objects beyond the Edgeworth-Kuiper Belt which it is perturbing. These kinds of resonance relationships are not unusual in planetary orbital dynamics, so such a suggestion is not that odd, even given the eccentricities of the bodies involved here. The new research, from the University of California, Santa Cruz, bolsters the case for this kind of pattern applying to Planet Nine’s orbit:
“We extend these investigations by exploring the suggestion of Malhotra et al. (2016) (2) that Planet Nine is in small integer ratio mean-motion resonances (MMRs) with several of the most distant KBOs. We show that the observed KBO semi-major axes present a set of commensurabilities with an unseen planet at ~654 AU (P~16,725 yr) that has a greater than 98% chance of stemming from a sequence of MMRs rather than from a random distribution.” (3)
Their randomised ‘Monte Carlo’ calculations provide a best fit with a planet of between 6 and 12 Earth masses, whose eccentric orbit is inclined to the ecliptic by about 30 degrees. They are unable to point to a specific area of the sky to search, but provide a broad-brush region which they favour as most probable. Dr Millholland has also helpfully provided a 3D manipulable 3D figure of the cluster of extended scattered disk objects allegedly affected by the purported Planet Nine, alongside their extrapolated orbit for it (4). Read More…
Dr Konstantin Batygin and Dr Mike Brown argue in their latest paper that the retrograde Kuiper Belt Objects Niku and Drac could have once been extended scattered disk objects (1). If you have been following these blogs during 2016, it will come as no surprise to you to hear that the influence which perturbed them into their anomalous current orbits was Planet Nine, the 10+Earth-mass planet lurking several hundred-plus Astronomical Units away, whose gravitational influence seems to be influencing the objects in and beyond the Kuiper Belt beyond Neptune (2):
“Adopting the same parameters for Planet Nine as those previously invoked to explain the clustering of distant Kuiper belt orbits in physical space, we carry out a series of numerical experiments which elucidate the physical process though which highly inclined Kuiper belt objects with semi-major axes smaller than a < 100 AU are generated. The identified dynamical pathway demonstrates that enigmatic members of the Kuiper belt such as Drac and Niku are derived from the extended scattered disk of the solar system.” (1) Read More…
Astronomers have announced the discovery of the third most distant object in the solar system, designated 2014 UZ224 (1). At a distance of 91.6AU, it is pipped to the title of ‘most distant solar system object’ by V774104 at 103AU (2), followed by the binary dwarf planet Eris at 96.2AU(3). The new scattered disk object lies approximately three times the distance of Pluto away, and may be over 1000km in diameter – potentially putting it into the dwarf planet range. Its 1140 year orbit is notably eccentric, which is becoming more expected than otherwise with this category of trans-Neptunian object.
The find is a fortunate byproduct of the Dark Energy Survey, which seems to be rather good at picking out these dark, distant solar system objects. It was first spotted in 2014, with follow-up observations which have firmed up its orbital properties, but clearly delayed the announcement of its existence until now. These follow-up observations were rather scatty over time, and so the Dark Energy team, led by David Gerdes of the University of Michigan, developed software to establish its orbital properties: Read More…
Almost nine months after the release of their paper about the likely existence of Planet Nine (1), Drs Mike Brown and Konstantin Batygin have secured a sizeable chunk of valuable time on the Subaru telescope, based in Hawaii. If they’re right about where it is, and luck is on their side, then they may detect the elusive planet within weeks. Brown and Batygin think they’ve narrowed it down to roughly 2,000 square degrees of sky near Orion, which will take approximately 20 nights of telescope time to cover with the powerful 8.2-meter optical-infrared Subaru telescope at the summit of Maunakea, Hawaii, which is operated by the National Astronomical Observatory of Japan (2). Mike Brown is quite gung-ho about it, as can be gleaned from these extracts from a recent interview with the L.A. Times:
“”We are on the telescope at the end of September for six nights. We need about 20 nights on the telescope to survey the region where we think we need to look. It’s pretty close to the constellation Orion…We’re waiting for another couple of weeks before it’s up high enough in the sky that we can start observing it and then we’re going to start systematically sweeping that area until we find it.
“”It makes me think of the solar system differently than I did before. There’s the inner solar system, and now we are some of the only people in the world who consider everything from Neptune interior to be the inner solar system, which seems a little crazy.”” (3)
Let’s hope they’re on the money. They have quite a lot to say about some of the correspondence that comes their way from members of what might loosely be termed ‘the Planet X community’.