The German magazine Der Spiegel has reported that a major announcement is imminent:  there is an Earth-like planet orbiting the red dwarf star Proxima Centauri; the Sun's closest stellar neighbour at 4.24 light years distance. The magazine claims that the discovery was made by the European Southern Observatory (ESO) using the La Silla Observatory's reflecting telescope in Chile, based upon a leak from an astrophysicist who has been working with the La Silla team (1).

ESO's 3.6m Telescope at La Silla, Chile

This alleged discovery is in keeping with the current work being carried out at La Silla, as described in January earlier this year:

"What good news that the Pale Red Dot project is now planning a two-month observing campaign to search for potential Earth-analogs around Proxima Centauri using HARPS, the High Accuracy Radial velocity Planet Searcher spectrograph at the ESO La Silla 3.6m telescope. Nightly monitoring began on January 18th." (2)

"The research (8) reveals that if the planet’s temperature were down to its sun alone, its surface would be, on average, a chilly -40C. “It seems cold, but then if you look at the same numbers for Earth you would get minus 20, minus 30C,” says [Guillem] Anglada-Escudé [from Queen Mary, University of London]. “What keeps Earth warm is basically that it has an atmosphere and an ocean,” he adds, pointing out that should the newly discovered world also boast an atmosphere, its temperature would likewise be higher." (7)

"If Voyager 1 was traveling in the direction of the red dwarf Proxima Centauri at a constant velocity of 60,000 km/hr, it would take 76,000 years (or over 2,500 generations) to travel that distance. But if it could attain the record-breaking speed of Helios 2‘s close approach of the Sun – a constant speed of 240,000 km/hr – it would take 19,000 years (or over 600 generations) to travel 4.243 light years. Significantly better, but still not in the ream of practicality." (13)

A new Trans-Neptunian Object has been discovered whose quirkiness is breaking into new territory.  This object, currently named 'Niku' after the Chinese adjective for 'rebellious', is seriously off-piste and heading in a highly inclined, retrograde motion around the Sun (1).   Does this sound familiar?   The retrograde motion is something which Zecharia Sitchin claimed for the rogue planet Nibiru.  Niku...Nibiru.  It sounds like the team who discovered this object, based at the Harvard-Smithsonian Center for Astrophysics (2), are having a bit of fun with us.  Rest assured, this is not Nibiru, or anything like it.  That said, something in the past interacted with this object to fling it into its strange orbital path, and at the moment the identity of that strongly perturbing influence is a definitive 'unknown'.

Additionally, Niku's discovery has prompted the astrophysics team to consider a new cluster of objects (high inclination TNOs and Centaurs) which appear to share the same orbital plane.  This, in itself, is an unexpected and exciting development.  Could the influencing factor be the mysterious Planet Nine (3)?

"...The new TNO appears to be part of another group orbiting in a highly inclined plane, so [Matthew] Holman’s team tested to see if their objects could also be attributed to the gravitational pull of Planet Nine.  It turns out Niku is too close to the solar system to be within the suggested world’s sphere of influence, so there must be another explanation. The team also tried to see if an undiscovered dwarf planet, perhaps similar to Pluto, could supply an explanation, but didn’t have any luck. “We don’t know the answer,” says Holman." (1)

In which case, the next logical question to ask is what knocked these objects off their perch in the inner Oort Cloud, sending them into this highly inclined cluster of orbital paths in the vicinity of the Edgeworth-Kuiper Belt?  Is this a hint that the orbital path of Planet Nine, itself inclined to the ecliptic by about thirty degrees (5), might extend far enough out into the outer solar system to skirt the inner edge of the Oort Cloud?  If so, then this could explain this perturbing effect, but also extend the aphelion distance of Planet Nine out far further than currently thought.  The implication of this, if we follow this argument to its natural conclusion, is that Planet Nine's mass would then be far greater than the ten Earth masses currently anticipated for it.  Otherwise, it would be incapable, at these greater average distances, of pulling up the anomalous cluster of Sednoids (6) into the extended scattered disk beyond in the first place.

Note, also, that two of the lead authors of this new paper are astronomers from Harvard who, when scrutinising astrometry data on Pluto and other trans-Neptunian objects, have previously argued for either the existence of a second perturbing planet, or a significantly more massive Planet Nine body (7).  I asked one of them, Dr Matthew Holman, whether the proposed Planet Nine body - this time with greater mass and orbital period - might have been capable of drawing down Niku from the inner Oort Cloud, to which he responded:

"I really have not figured out the explanation for the common plane, prograde and retrograde, that these objects seem to share, but it's not clear to me that if something like a Planet Nine is perturbing them that it would need to have such a large aphelion.  The gravitational influence of the disk and bulge of the galaxy are strong enough [to] reduce the pericenters of inner Oort cloud objects into the region of the planets." (8)

"It seems likely that Drac was gravitationally disturbed from its home in the inner Oort Cloud by a passing star, or some other disturbance in its local space.  It then fell toward the inner Solar System where it found its new home near the Kuiper Belt." (4)

"2008 KV42 may even provide evidence of Planet Nine. The Kozai effect inside the mean-motion resonances with Planet Nine may cause a periodic exchange between its inclination and its eccentricity. When the elongated perpendicular centaurs get too close to a giant planet, orbits such as that of 2008 KV42 are created." (9)

"And Drac, which had been such a disappointment? Once we started looking we realized that our gravitational simulations create Drac, too. Sometimes, when the elongated perpendicular Centaurs do get too close to giant planet [sic], that planet pulls their orbit a little close, and also swings the orbit around randomly.  Another Drac is born.  The Planet Nine hypothesis requires the existence of objects with orbits like Drac, which otherwise had no plausible explanation." (10)

iopscience.iop.org article

As more rocky exoplanets are discovered orbiting neighbouring stars, questions are now being raised amongst academics about whether there are sufficient numbers of warm protoplanetary disks observed around young stars to statistically account for them all. 

"The high occurrence rate inferred for Earth-mass planets around mature solar-type stars based on exoplanet surveys (roughly 20%) stands in stark contrast to the low incidence rate (less than 2-3%) of warm dusty debris around solar-type stars during the expected epoch of terrestrial planet assembly (roughly 10 Myr). If Earth-mass planets at AU distances are a common outcome of the planet formation process, this discrepancy suggests that rocky planet formation occurs more quickly and/or is much neater than traditionally believed, leaving behind little in the way of a dust signature. Alternatively, the incidence rate of terrestrial planets has been overestimated or some previously unrecognized physical mechanism removes warm dust efficiently from the terrestrial planet region." (1)

The solution to this glaring dilemma advocated by Scott Kenyon, of the Harvard-Smithsonian Center for Astrophysics, and his colleagues, is that the speed with which planets form from the dusty disks surrounding very young stars is much quicker than thought - allowing more planets to form in the potentially shortened time these disks are in place.  Either the low incidence of warm dust disks needs to be explained, or the large quantity of rocky planets must be accounted for in other ways.  Bear in mind that the number of rocky planets being discovered is likely to be the tip of the proverbial iceberg, as the technology to detect small planets continues to improve year on year.

They also consider whether there are other ways for dust to be removed from planetary environments around new stars, perhaps by 'gas drag'.  As an online commentator noted:

"Gas drag will definitely moderate the movements of dust particles so instead of colliding and scattering and/or shattering, they flow together. This enables gravity wells to very quickly clean up the dust and other debris within a solar system type nebula." (2)

I'm quite convinced that the planet-forming process is not limited to accretion within swirling dust disks around young stars, but that it is an ongoing process within a variety of environments.  As planetary scientists think hard about the anomalies being thrown up by exoplanet observations, I hope that progress will be made towards a new model of planet formation:  One that may lead to the formation of planets beyond the traditional planetary zones of stars.

""The large masses of these two substellar objects suggest that they could be formed as stars with their binary hosts: a large molecular cloud collapsed and fragmented into four pieces; the larger two successfully became stars and formed the HD 87646 binary, and the other smaller ones failed to form stars and became the substellar objects in this system. This scenario might be relevant for the binary stars but seems problematic for the two substellar objects on orbits within one AU because it is unclear whether fragmentation on such a small scale can occur," the paper reads (1)

"Other hypothesis offered by the scientists is that the two newly discovered giant objects were formed like giant planet in a protoplanetary disk around HD 87646A. However, they added that such massive disks are rare in close binaries, and further investigation is needed to confirm this explanation." (3)

Given the large number of substantial exoplanets and brown dwarfs discovered over the last couple of decades, finding a couple more in a close binary system may not seem so surprising.  We've got used to the fact that the classical planet-forming model, which described how the solar system came about so well, simply does not apply to the diversity of planetary systems emerging from the ballooning exoplanet data (now >500). 

According to the core accretion model, the nature of the close binary system should create problems for giant planet formation, because gravitational perturbations inhibit the growth of planetessimals in the protoplanetary disk, meaning that the formation of a planetary core is slowed down.  The dust disk will essentially dissipate before the planetary core can amass gaseous material around it to form a gas giant of brown dwarf. 

Furthermore, given the sheer size of these brown dwarf companions, the initial disk would have to be massive to have formed them.  This isn't generally seen in young close binary systems, meaning that the disk should have dissipated way faster than the time required for giant planet formation (1).  This is a similar issue to that recently raised for rocky planet formation (4).

Image Credit: Janella Williams, Penn State University

Another theory of planet formation relies on disk instability, which doesn't suffer the same problems in this case as the core accretion model.  The authors are, however, cautious of advocating this mechanism for the complex HD 87646 case as it's not clear whether disk instability can be triggered in the presence of a close stellar companion (1).  The planet-forming mechanism in this case remains a mystery, although the authors do offer ideas about the migration and scattering of these companion objects post-formation. 

An alternative which would not have been considered by mainstream astrophysicists is the radical model of planet formation proposed by the French engineer François Berguerand, whom advocates the action of a passing star to draw out a spindle of stellar matter from a young star.  This spindle of dense matter then separates out into gaseous planets (5).  This close binary system would seem to provide the perfect opportunity for the drawing out of such matter to create the substantial brown dwarf companions for the primary star.  I've written to François for comment.

Most star systems have lost their dust disks by 300-400 million years (8).  Rare circumstellar dust disks around older stars are then thought to arise as a result of collisional cascades between rocky objects, like asteroids and comets, in planetary systems (9) in what are otherwise dynamically calm environments.  As a result of this hypothesis, older star systems which exhibit dust disks are considered good candidates for the presence of terrestrial planets (10).  The solar system should perhaps also exhibit this kind of dust disk, given its perceived general stability.  the fact that it doesn't is thought to be due to the decimation of the Kuiper Belt which took place around 3.9 billion years ago:

"Intriguingly, our solar system looks unusual... because it has rocky planets as well giant planets that are relatively calm in terms of their orbital dynamics, but no debris disk.

"“So, why don’t we have this dust?” [Sean] Raymond [of the Observatory of Bordeaux, France] said. “Well, it turns out that for more than half a billion years after its formation, the solar system did have a bright debris disk!  As is the case for other stars, the dust was produced by icy planetesimals occasionally colliding and grinding themselves away.  This population of planetesimals was the primordial Kuiper belt, and we think it contained about 50 Earth masses of material, at least 100 times more mass than it does today.”

"However, the Kuiper belt was almost completely cleared out during a period instability about 3.8 billion years ago that is linked with the “Late Heavy Bombardment,” when asteroids were slung around the solar system, leaving planets with scars often still visible today." (11)

I consider this event to be the result of the infiltration into the planetary zone of a rogue sub-brown dwarf object which, I believe, still remains undiscovered in the outer reaches of the solar system.  Its presence has indeed eliminated much of the Kuiper Belt, and created the 'Kuiper Cliff' at about 50AU. 

By contrast, what we have in the case of HR 2562 is an inner brown dwarf, surrounded by an outer circumstellar disk.  This would then imply that the bulk of the system's rocky material - asteroids, terrestrial planets, planetessimals - lies beyond the the reach of a substantial inner sub-stellar companion. 

Or is it actually an example of the way a sub-stellar companion can 'sweep out' a region of space?  In the case of our solar system, this is what I believe has occurred between the Kuiper Belt and the inner Oort Cloud (i.e. between 50 and 2000AU).

My friend and fellow researcher Lee Covino sent me an article recently which, on the face of it, appeared to have little to do with my Dark Star stuff.  It was about Ultra-Diffuse Galaxies (UDGs), particularly a mass of these objects in the Coma cluster (1).  The evident lack of stellar mass in these galaxies, compared with their implied total mass, shows that these galaxies have a much lower quantity of normal 'baryonic' matter than the universe average (2), which implies, say cosmologists, the dominant prevalence of Dark Matter. 

Image Credit: M. Markevitch & D. Clowe

Perhaps the normal mechanism whereby stars form en masse within a central galactic core was somehow interrupted, some wonder:

"We suggest that UDGs like DF17 may be "pure stellar halos", i.e., galaxies that formed their stellar halo components, but then suffered an early cessation in star formation that prevented the formation of any substantial central disk or bulge." (3)

In which case, one might ask, what happened to all that material which did not end up firing up stars, like in 'normal' galaxies?  There's a ton of missing mass in the universe, and it's a big puzzle:

So, an alternative possibility is that a huge quantity of unaccounted 'normal' baryonic matter is out there, but not to be found in visible stars, nor in enormous gas /dust clouds.  This missing matter (which is 'dark', but not actually exotic) would therefore be diffuse, and broken into bite-sized cosmic chunks which slip under the observable radar.  Like cool, free-floating gas giant planets moving through the vast gaps between stars, for instance.  These might be as large as failed stars - ultra-cool brown dwarfs, up to old red dwarfs.  Could this help solve the mystery of the missing 90% of the mass of the universe?

The problem then is that the sheer number of these would have to be truly enormous to account for the missing mass of galaxies.  Perhaps 1000s of these free-floating planetary objects for every visible star; with a distribution which tends to place these dark, lower mass objects into the outer peripheries of the galactic environment.  Such a suggestion has been considered historically as an alternative explanation to Dark Matter: 

"Brown and black dwarfs are a much more difficult proposition. These objects, which are essentially freely wandering Jupiter-like objects, are so dim that it may be impossible to ever detect them. Although there are no sound theoretical reasons for believing that they exist in the required numbers, it is possible that such objects were produced in large numbers by the star formation process in globular clusters long ago, when galaxies were just beginning to form. The black and brown dwarfs may then have diffused out of their star clusters and formed very large halos around galaxies. Because of their low luminosities, they would be extremely difficult to detect, even if there were quadrillions of them around every galaxy." (4)

An allied concept is that the comets conventionally thought to arrive from the Sun's distant Oort Cloud are instead interstellar interlopers.  In other words, one might argue that comets are, essentially, travellers between the stars which occasionally trespass into stellar environments.  Astronomers can determine from the trajectory of long-period comets whether they originated within the solar system, or entered the solar system from the interstellar space between the stars.  Interstellar comets should have hyperbolic trajectories, which would allow them to pass cleanly through the solar system. 

"The results [from LINEAR] are surprising in three ways.  Firstly, the flux of comets through the inner solar system is much lower than some previous estimates.  Secondly, the expected rise in comet numbers to larger perihelia is not seen.  Thirdly, the number of comets per unit absolute magnitude does not significantly rise to fainter magnitudes.  These results imply that the Oort cloud contains many fewer comets than some previous estimates, that small long-period comets collide with the Earth too infrequently to be a plausible source of Tunguska-style impacts, and that some physical process must have prevented small icy planetessimals from reaching the Oort cloud, or have rendered them unobservable." (9)

Previous Blog

Next Blog