It was Percival Lowell who suggested that anomalies in the orbit of Uranus might point to the existence of the body he called ‘Planet X.’ The discovery of Pluto in 1930 gave us confirmation of a planet beyond Neptune (since downgraded, of course), but the idea of other large bodies in the outer Solar System still has its appeal, and although we’ve found such interesting objects as Eris and Sedna, questions remain about what else might be found lurking at the fringes of the system.
Theories of the Outer System
Thus the active theorizing, which includes one study speculating on an Earth-sized planet at 100 to 170 AU, a body that would help to explain what we know about the architecture of the Kuiper Belt. Another investigation looked at a possible Mars-sized body at 60 AU, which would help us understand the distribution of various Trans-Neptunian Objects, a term that basically covers any object orbiting the Sun beyond Neptune.
Other theories abound, one of which sees a giant planet (roughly 1.5 times as massive as Jupiter) at 25,000 AU, causing perturbations in particular cometary populations in the Oort Cloud. References to these and other work can be found in a new paper by Lorenzo Iorio (INFN, Pisa), who goes on to look at what may be the most seductive of all these hypotheses, that a small star thousands of AU from the Sun may cause perturbations that affect the inner planetary regions.
Image: An artist’s concept of the view from Eris with Dysnomia in the background, looking back towards the distant sun. What other objects, perhaps larger still, might lurk in the outer Solar System? Credit: Robert Hurt (IPAC).
A Companion for the Sun
It’s fascinating to speculate, as we have here often, about the existence of a star closer to us than the Centauri trio. Thus the ‘Nemesis’ theory, that the Sun is actually a binary star whose companion may well account for cometary impact events on Earth, a signature perhaps revealed by the periodicity of such events. Iorio weighs the evidence for a brown or red dwarf in such a configuration, looking at its gravitational effects on the inner rocky planets.
[Note the addendum below]. The result is a set of interesting constraints on what may lurk beyond our currently understood system. A brown dwarf of 75 to 80 Jupiter masses, for example, cannot orbit closer than roughly 1.8 to 1.9 light years from the Sun, while the minimum distance for a red dwarf ranges from 2.1 to 5.6 light years depending on its mass. If there’s a Jupiter-sized body out there, it should be no closer than 13,500 AU (recall that Proxima is 10,000 AU from the primary Centauri stars). An Earth-sized object might be found beyond about 750 AU but no closer.
Addendum: Within the last few days, the author uploaded a second version of this work which I didn’t become aware of until this PM (thanks, Bynaus!). In the second version, these numbers change significantly. A brown dwarf is now constrained to 3,736-3,817 AU from the Sun, while an M-dwarf must be no closer than 3,793 AU to 7,139 AU. Quite different results, and obviously even more interesting in terms of interstellar targets, if indeed it turns out that any such objects do exist. Dr. Iorio’s comment re the new version: “Rewritten version amending the previous one which contained a serious error. Results changed.” Indeed!
Filling Out the Census
Using Dr. Iorio’s computations, then, we can’t say that any of these objects exist, but only that if any of them do, they are not to be found closer than these figures suggest. The closest star could be far closer than the Centauri stars, although we do not, obviously, have confirmation that such an object is there. Finding a brown dwarf or an M-dwarf within several thousand AU would change the prospects for our first interstellar probe considerably, and would surely serve as an inducement to propulsion research if planets were to be found there. [This section re-written due to the changes to the paper noted above].
All of which is a useful reminder that even as we look into the remotest parts of the universe in search of cosmic history, we still have much to consider in regions not far from our own Sun. We have plenty of work ahead in building the local census. I also think of deep space explorers like Caltech’s extraordinary Mike Brown, whose investigations keep filling in the blanks in our outer system sketchbook. What challenging projects await the students Mike Brown’s generation is now training!
The paper is Iorio, “Constraints on Planet X and Nemesis from Solar System’s inner dynamics,” available online.
A very useful paper. How ironic it would be to discover a major planet in the Kuiper belt in those times when extrasolar planets have begun to be known! After all, Eris and Sedna were discovered in the post-1994 era.
http://arxiv.org/abs/0904.1562
In the abstract of the version that is now up at arxiv, the numbers are different (smaller – and thus, I think, more interesting…) compared to this article, e.g., Brown Dwarf minimum distance = 3,736-3,817 AU = ~0.06 LJ.
Are we looking in the same place? I’m not seeing these closer figures.
The link is correct (try shift-reload?) – from the Conclusion-section of the PDF in the link above: “It turns out that the minimum distance at which a body with the same mass of the Earth could orbit is 130 AU, while for the mass of Mars it reduces to 62 AU; for the mass of Jupiter it is 886 AU. By assuming it is a brown dwarf (m ? 75 ? 80 mJup), its minimum distance is about 3,800 AU, while for a red dwarf (m ? 0.075? 0.5 M?) it is 3,793? 7,139 AU.”
Odd. I just downloaded again and I get this in the conclusion section:
The distance to alpha Cen AB and Proxima Cen is only a little over a parsec (4.3 lightyears, if I recall my scifi correctly). If the effect of one M dwarf can be measured out to 5.6 LY (presumably the high-mass limit, meaning ~0.7 Msun), then shouldn’t the effect of two roughly solar-mass stars at 4.3 LY be visible in the data?
I think I know what happens: if you follow my link it will lead you to v(ersion)2, dated April 14th. The numbers you find are in v1, from April 9th. In case you can’t see v2, I have now downloaded the file – if you send me an e-mail, I’ll send it to you.
BTW: Nice find, and congratulations for your great site/blog. I visit it at least every other day.
Thanks, Bynaus. I just was able to download the second version. I’m adjusting the main entry accordingly.
I see the same as Bynaus:
“It turns out that the minimum distance at which a body with the same mass of the
Earth could orbit is 130 AU, while for the mass of Mars it reduces to 62 AU; for the mass of Jupiter it is 886 AU.”
Many thanks to Bynaus (and also Pat) for helping me sort this issue out. The post above is now amended to reflect the changes Dr. Iorio made to his work within the last few days. Re E’s question, the changes to the calculations in this paper may obscure the issue, since Dr. Iorio now thinks an M-dwarf is possible far closer to our system than he previously had stated. I have no idea how the Centauri stars might play out in his new calculations (good question!).
Earth, or even Mars, sized bodies at those distances would be excellent candidates for future economic exploitation. They may be the easiest places in the solar system to mine 3He, if they exist and if their atmospheres have retained enough of that gas (this would depend on the temperature of their atmospheres at the exobase.)
Hi Paul F. Dietz;
I like the idea of building subterranean living quarters for we humans on such Earth sized and Mars sized bodies. Assumming that such civilizations would require 10 TeraWatts of power as does current human civilization here on Earth, and that each such planet has about as much hydrogen as Earth does or approximately 10 EXP 18 tons, then the lifetime of the civilization’s dwelling place could be about 2.5 x 10 EXP 15 years assumming that 400 tons of hydrogen fusion to Helium could power the civilization.
The civilization might be constucted within a highly insulated dewar type of containment feature. If the Oort Cloud or outer Kuiper Belt contains several to numerous such bodies, missions to such bodies would be great precursor operations to eventually going further out to other luminous stellar systems.
Wouldn’t a nearby M-dwarf have been detected already by the various telescopic surveys? Maybe even brown dwarfs would be discovered by
their infrared signature if they were that close.
If something is perturbing the objects out in the Kuiper belt I think they
would be of lower mass then brown dwarfs but possibly more massive
then Jupiter.
Gas giants expelled from the early inner solar system?
Or rogue planets slowly wandering between star systems?
Interstellar space maybe more crowded then previously understood.
ah yes, the nemesis theory. its an interesting thought, and its not implausible. if it exists, it will probably be found sooner or later by observation and analysis. it would go to show how much more we have to learn about our stellar neighborhood, even with our advanced knowledge. nemesis could hypothetically be a useful way station for interstellar travel…
it would be pretty epic if we found an earth-like planet in or near the kuiper belt. that could also be a way-station or colony that could be useful in interstellar travel, and also in mining trans-neptunian objects.
Hi All
Paul F. Dietz, what a happy thought! Surely easier than mining it from the Gas Giants, though the trip times are punitive. In the 1970s there was some speculation that Titan had retained a primary atmosphere of H2/He and thus could provide He3 for “Daedalus” style engines. That didn’t obtain, but Earth-to-Mars mass objects cast into the Outer Reaches (the OOC as I’ve dubbed it) should have kept any H2/He atmospheres they might have formed with.
Another possibility, discussed 10 years ago now by David Stevenson, is that a sufficiently warm planet might retain liquid water oceans under a primary atmosphere because of hydrogen’s quite effective greenhouse effect. The Solar System is getting more interesting as time goes on.
Would it be possible for brown dwarves or giant isolated planets to be located nearer than this if they were NOT gravitationally bound to the sun? ( I can’t access the full paper, so apologies if it is in there). As I understand it, brown dwarves form as “stars” on their own. In fact that is what differentiates them from “planets”.
This is interesting, about finding local brown dwarves
http://adsabs.harvard.edu/abs/2009AAS…21345907M
Quote:
“Abstract
The Wide-field Infrared Survey Explorer (WISE) is a Medium-class Explorer program mission (MIDEX) designed to map the entire sky in four bands between 3 and 25 microns with vastly greater sensitivity than previous all-sky surveys at these wavelengths. WISE will be launching in late 2009. All-sky surveys are the optimal tool for finding rare objects, such as objects which bridge the gap in effective temperature and mass between the coolest currently known brown dwarfs (T 650 K) and the giant planets (T<150 K). Studies of these ultra-cool brown dwarfs will yield insights into the initial mass function, the minimum mass for brown dwarf formation, and the atmospheric characteristics of a possible new spectral class, the Y dwarfs. WISE is also likely to find the nearest star to the Sun; this object is not likely to be a star at all, but rather a low temperature brown dwarf……”
So some scientists at least believe that it is LIKELY that one or more brown dwarves are nearer than the Centauri system. Interesting times.
keith bradshaw quotes the abstract on the WISE mission:
Hadn’t seen that particular quote before, but it’s heartening to think that a nearby brown dwarf may be more than idle speculation!
The Binary Institute:
http://www.binaryresearchinstitute.org/
has been wondering if the Sun has a companion. I don’t know how this article would tie in with their research.
Also, please don’t try to make He-3 a reason to go exploring in space (strip mining the Moon, etc.). No one has yet to build a working fusion reactor and last I heard, the usual formula of _current year_ + 50 is still accurate. There’s even less work being done on a He-3 reactor.
We should go into space and explore, not to go after a mythical energy source.
Hi All
FrankH, ITER should fire up in 2016 and by 2031 they’re hoping for enough physical data to build a working demo power-reactor by 2048. But you’re right – they won’t be burning He3 and probably no time soon via a tokamak. However the Future’s task is to surprise us and one possible game-changer would be the development of Bussard Polywell fusors able to burn a whole range of fusion fuels. The earliest will probably burn D-T or D-D and use the neutron flux to heat water or lithium, but later designs will try for D-He3, He3-He3 or Bussard’s beloved p-B11. If Richard Nebel and crew have ongoing success with WB-7.2 and its successors then the world’s power balance could change rapidly.
As for the Binary Institute, the proposed orbit of the companion (a 24,000 year period as I recall) has a minimum semi-major axis of ~840 AU or so. That seems to be just a bit too close according to Iorio’s work if it’s more than a Jupiter mass. If it’s currently at aphelion then it might squeek in under the data. So maybe?
I’m sure I remember reading that any nearby (ie closer than Proxima) M-class stars or brown dwarfs above a certain temperature would already have been detected in the various IR surveys. The only possibility left is BD’s at low temperature, and that very low temperature consideration constrains the mass to something like <20M(j).
Anyway, considering that at least one major calculation error in this paper has been detected, how do we know there are not more?
I would not bet on polywell ever working with advanced fuels. I have not be at all impressed with the supposed rebuttals of Rider’s demolition of the entire class of reactor concepts (basically, non-thermal ion distributions thermalize too fast to be be useful with anything but DT; the recirculating energy needed to maintain the distribution is too high to be practical.) To my knowledge, no paper rebutting Rider has ever appeared in the peer reviewed literature.
I’d love to see Bussard’s Polywell get extra funding, in part because it isn’t a Big Science project, it’s a real engineering attempt at making a working, economically viable fusion reactor.
Keith Bradshaw mentions that a BD would be visible in an IR survey, but I think that a 4.6BY old BD would be very cool and dim. Maybe cool enough to have gone undiscovered in IR surveys to date, especially since its motion in the sky would not be as noticeable as a planet’s.
Hi All
Not the place for an argument, but Bussard answered Rider’s critique some time ago, basically showing that the Polywell design avoided thermalising the ions. The original Farnsworth-Hirsch design can’t avoid electrode losses and bremmstrahlung, but the Polywell’s magnetic shielding changes the picture significantly. But even the colliding beam designs that Rider’s specific analysis targetted seem to have intricacies that Rider’s analysis was too broadbrush to address, as the colliding beam researchers pointed out in various journals. And designs like Focus Fusion are equally too complex in their plasma geometries for Rider’s analysis to apply to readily.
The complexity of the plasma flow in such designs is beyond any closed form integration and currently beyond numerical computation. The only way to know for sure is to build the damn things and run them until they work or they break. There’s no other way. Even “well known” systems like tokamaks have plasma behaviour beyond computation and that’s why ITER is being built. Every new plasma machine is an unknown country as far as performance and fusion potential go.
Not the place for an argument, but Bussard answered Rider’s critique some time ago, basically showing that the Polywell design avoided thermalising the ions.
Bussard never published any such rebuttal in the peer reviewed literature, as far as I know (even though such a publication would surely have helped them raise money, which is a red flag in my mind). What I heard of it on the net did not seem sufficient. Moreover, it failed to address the other of the showstoppers Rider identified: the loss of energy from the ions to the cold electrons (or, if the electrons are hot, the loss of energy from them to radiation).
Paul
Experimentation not argumentation was my point.
Hmm. Proxima centauri is within the range given for a possible M-dwarf solar companion. But obviously proxima is gravitationally bound to the other two Centauri stars, and not our sun.
Shouldn’t that mean that the potential orbits of such putative solar companions are further constrained? There must be a zone in space around the Centauri system where any M-dwarf solar companion would be “stolen” from the sun by the greater combined gravity of Alpha Centauri A and B.