I never knew...
Uranus was a gas giant...
Boffins have long hypothesised the existence of a large, but thus far unseen, celestial body in our Solar System, somewhere beyond the orbit of Pluto, but NASA's WISE survey has found no sign of the mysterious "Planet X". A nearby star stands out in red in this image from the Second Generation Digitized Sky Survey by WISE …
Hmm ... Register Units?
About 8 mReg?
(Being 8/1000 of the distance from here to Regulus. Although mysteriously, the Register-star is in the constellation of Leo (probably eating its entrails...), and will be obscured by 163 Erigone on the morning of March 20th - expect articles to go missing or be delayed around that time.)
How many brontosaurus's is that?
+1 to Psyx.
However, I believe the theory as to how the Oort cloud formed, and therefore what it is composed of, precludes objects that large existing in any great number.
There are likely such objects in the inner Oort region* but I believe the area of interest is the outer Oort Cloud as the data that pointed to this hypothetical planet's existence was based on long period comets originating in the (outer) Oort Cloud.
It is my understanding that the Oort Cloud consists almost entirely of small comets flung out during the creation of the solar system and if such a large planet/dwarf star were to exist, it would have been captured, rather than flung out.
Does that sound right? It's all hypothetical anyway as we can't detect anything smaller/dimmer than about Jupiter out there anyway!
* - Well, by definition, there must be as it was proposed to exist to accommodate the dwarf planet Sedna when it was realised that it was too far out to be part of the Kuiper Belt but too close in to be part of the (hypothetical) Oort Cloud.
> the effects of gravity fall off exponentially
As any fule kno, gravity obeys an inverse square law, F = GMm/r^2
If it was exponential, it would have some constant k to the power of r in the denominator.
Sorry to nitpick, but 'exponential' has a useful exact meaning which is literally diluted by using it wrongly.
I seem to recall something about the circumference of ignorance, said by someone whose words were worth listening to.
In any case, I feel that scientific progress in astronomy is an exciting field these days. In 2000, we thought planetary systems were rather scarce. Since then, we've had confirmation that at least one-third of the systems that we have surveyed have planets in them. We've gone from hypothesizing Earth-like planets to actually finding planets in the Goldilocks zone.
Now we realize that our "backyard" is bigger than we thought it was ? No problem, we'll work that out too. It should provide a good learning experience as well, teach us how to survey and map a system for when we arrive at a new solar system - sometime in this millennia or the next.
Exciting times !
No it does not. That is not how black holes work. Look it up. Their effect on the neighborhood is no different to a star or planet. They just have the size to go with their name.
As a thought experiment, try getting stuck in (or proposing the earth get effected by) a black hole. Try it. Propose any means you wish. You may find some small problems actually achieving it.
"I'd think that a smaller planet would also be a risk of upsetting the potential comments of the Oort cloud though."
Luckily, the rocks have a pretty good founding in physics and know that a small planet is not going to plough through widely scattered debris in a sphere over a light year in diameter and cause anything approaching chaos, because small planets don't have much gravity and the oort cloud isn't some kind of Star Wars asteroid field with rocks every 200m.
Seriously: The Oort cloud is far larger with far less debris than you think it is.
One thing the Nemesis hypothesis has always been very clear on is the size of the orbit - in order to get the period right it needs a semi-major axis of around 95,000 AU. These chaps can make meaningful assertions up to only 42% of that distance and less than 7.5% of the volume of space, and this is somehow "proof"?
Yes, Nemesis is unlikely but it is a legitimate minority opinion, dismissing it as crackpot science is in itself a demonstration of scientific ignorance, since the whole idea is surprisingly and annoyingly difficult to conclusively disprove. In their eagerness to "prove" the falsehood of the theory they are guilty of far worse junk science.
But a star that close to the Sun, even if it is class Y brown dwarf it would have showed up like a bright beacon to the IRAS and/or ISO missions, let alone any of the terrestrial IR-sensitive telescopes. Also the theoretical orbital parameters for Nemesis (consistent with the extinction pattern) has been worked out a long time ago, and we know in what part of the sky we should be looking, but nothing is there!
BTW, the extinction pattern data is based on a very small sample set that is statistically not significant. Basically the uncertainties outweigh the conclusions.
... but presumably the proposed Nemesis is supposed to have a highly elliptical orbit? In which case - assuming it isn't currently at/near an extrema, the liklihood of spotting it might be higher, although of course it's slower moving out there and less likely to dwell in range. Also, might it not be likely to share the same orbital plane as the (inner) Oort cloud? - perhaps relaxing your 0.4^3~=0.07 to about ~ .4^2 ~= 0.16.
While the authors may well be over confident, it seems to me that without further detail, your 0.4^3 is perhaps to be a rather too stringent a bound on probability.
presumably the proposed Nemesis is supposed to have a highly elliptical orbit? In which case - assuming it isn't currently at/near an extrema, the liklihood of spotting it might be higher...
Orbital mechanics have the effect that the closer in a body to whatever it is orbiting the faster it travels, before slowing down as it moves further away from that body again - if you think about it it's simple conservation of energy, as kinetic energy is traded for potential and vice versa. The net effect is that arguing for a highly elliptical orbit pushes out the average distance at any given time quite considerably, since the body spend most of its time traveling slowly through the more distant part of its orbit, before quickly sweeping through the closer portion and returning to a greater distance.
In any event, for the theory to hold it almost needs the reverse, while the orbit doesn't have to be perfectly circular it can't be highly eccentric. The projected orbit is huge - a radius of 1½ light years. The more eccentric it becomes the further the hypothetical body moves away from the Sun at it's outermost limit and if it gets too far the Sun ceases to be gravitationally dominant. Even if in one particular pass it doesn't come close enough to anything else to be perturbed out of orbit, you would expect precession of the argument of perihelion over cosmological time, which would have the effect of flinging it out in a slightly different direction on each orbit. That increases the chances of an eccentrically orbiting body being lost forever.
Given they've got the orbit worked out they also know based on the extinction events where on the orbit the planet ought to be. So you don't have to do a whole sky survey. If those calculations show it outside the range of experimental observation, there would have been no point in conducting the exercise in the first place, at least vis-a-vie testing the Nemesis hypothesis.
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