One of the things we need to learn about the Alpha Centauri stars is whether Proxima Centauri is gravitationally bound to Centauri A and B. Much hinges on the issue, for if Proxima is merely passing in the night, then whatever disruptive effect it may have upon an outer halo of comets around the Centauri stars would be a one-shot affair. On the other hand, if Proxima is a stable part of this system, then it may send comets laden with volatiles into whatever planetary systems are around Centauri A and B. Proxima might be, in other words, the difference between dry rocky worlds and planets with abundant water, with all that implies about the possibilities for life.
We’ve seen the same kind of thinking applied to our own Solar System in the form of the star dubbed ‘Nemesis.’ As the theory goes, Nemesis could be a red or perhaps a brown dwarf that could account for what seems to be a periodicity in terms of extinction events on Earth. Disrupting cometary orbits in the Oort Cloud, such an object might send comets into the inner system on a 26-million year cycle. The Telegraph is one of a variety of media looking into the story (Astrobiology Magazine is another), and speculating on whether or not some evidence for Nemesis has turned up in the orbit of Sedna, the dwarf planet discovered in 2003 whose orbit continues to cause ripples in the planetary sciences community.
The Telegraph quotes the object’s discoverer, Mike Brown (Caltech), on the matter:
“Sedna is a very odd object – it shouldn’t be there! It never comes anywhere close to any of the giant planets or the sun. It’s way, way out there on this incredibly eccentric orbit. The only way to get on an eccentric orbit is to have some giant body kick you – so what is out there?”
Did someone say ‘eccentric’? Sedna gives new meaning to the term, with a perihelion of 76 AU and an aphelion of a whopping 975 AU, making for an orbital period lasting as long as 12,000 years. Brown himself says his own surveys would not have picked up anything as distant and slow-moving as Nemesis would have to be, all of which leaves the prospects for an unseen companion still very much alive.
In a 2006 paper, Rodney Gomes (Observatório Nacional, Brazil) and colleagues note that Sedna and the object 2000 CR105 stand out from the thousand or so trans-Neptunian objects thus far discovered because their trajectories cannot be accounted for by the planetary configuration we know about. The authors call them ‘the first discovered true inner Oort cloud objects.’ They may be evidence of a distant planetary-mass solar companion, one the authors characterize as follows:
A small mass companion (roughly Earth to Neptune mass) could have formed within the planetary region, been ejected to its current heliocentric distance by gravitational scatterings of Jupiter and Saturn. Such a body may have been ejected from the Solar System after producing the DDP [distant detached population], or it could remain as the largest member of the standard scattered disk population. Or its perihelion could have been raised by perturbations of passing stars which would have needed to have been passing at a closer distance than would be reasonable to hypothesize subsequent to the dispersal of the Sun’s birth cloud/cluster, but not as close as required for direct stellar perturbations producing the observed high perihelion scattered disk objects. A Jupiter mass or larger object on a highly inclined orbit beyond 5000 AU would most likely have formed as a small, distant binary-star like companion, e.g., by fragmentation during collapse or capture.
With WISE (Wide-Field Infrared Explorer) on the case, it may not be too long before we have evidence one way or the other. Chances are a red dwarf no more than 25,000 AU out would have been spotted by now, but a brown dwarf might still elude detection. John Matese (University of Louisiana at Lafayette), one of the authors of the above paper, has been studying Nemesis possibilities for more than two decades, and now opts for an object about three to five times the size of Jupiter as a possible cause of the cometary commotion. WISE will need until perhaps mid-2013 before two sky scans and telescopic follow-ups of any Nemesis-like detection can be completed.
For more, see Gomes et al., “A Distant Planetary Mass Solar Companion May Have Produced Distant Detached Objects,” Icarus 184, No. 2 (October, 2006), where the authors say the object in question could be an Earth-mass planet at 1000 AU, a Neptune-mass planet at 2000 AU, or a Jupiter-mass object at 5000 AU or farther (abstract). So maybe we’re not talking about a ‘death star’ at all, but a huge Planet X of the kind Percival Lowell was once so intent on finding. Lowell, thanks to the indefatigable Clyde Tombaugh, had to settle for tiny Pluto, but we’ve yet to rule out much larger objects in the dark realms beyond the Kuiper Belt. WISE should settle the matter conclusively in about three years.