Of all the interesting targets the WISE (Wide-Field Infrared Explorer) mission might find, I’ve focused primarily on two in Centauri Dreams: A small star, doubtless a brown dwarf, that might be found closer to us than the Alpha Centauri trio, and a large planet out in the Oort Cloud that might be disturbing cometary orbits. That latter scenario turned up again last March in Finding the Real Planet X, when we looked at various theories about large objects in the outer system, including the thinking of John Matese and Daniel Whitmire (University of Louisiana at Lafayette).
Parameters of a Perturber
Matese has studied the possibility of small stars near our Sun for two decades, but his view now, as revealed in a paper just published in Icarus, is that an object three to five times larger than Jupiter may be the perturber we’re looking for. Matese and Whitmire’s paper on the matter has been available as a preprint since April, but its publication in Icarus has caught the eye of the press, as in this story in The Independent. Think of all the time Percival Lowell devoted to finding a large ‘Planet X’ that wasn’t there (although the detection of Pluto did come out of the search), while a truly massive Planet X at a far greater distance may now turn up in WISE data.
And the Planet X we’re talking about is not ‘Nemesis’ — that would be the name for the small star once considered a possibility as a binary companion to the Sun. Matese and Whitmire prefer ‘Tyche,’ the good sister of Nemesis in mythology, as the name for the gas giant they hope to find in WISE’s data. We’ll have to wait a bit to find out, but not all that long. WISE, whose transmitter has now been turned off, has completed its principal and extended missions and is in hibernation as of early February. The first release, covering 57 percent of the data gathered, will be in April, with the full dataset becoming available in 2012. Matese and Whitmire have calculated that the object should have a temperature of roughly 200 Kelvin, and WISE should be able to see it.
Tyche sounds like a gas giant, according to Whitmire, but even assuming it to be so, we won’t know if it qualifies as a ‘ninth planet’ of our system until the International Astronomical Union considers the matter. After all, we live in a world where Pluto lost its status due to reconsideration of small icy worlds, and it may be that a massive gaseous world out in the Oort Cloud at 15,000 AU would raise questions about its origin. Is it likely that such a planet would have formed around another star, and if so, shouldn’t there be a new, separate designation?
The Planet and the Tides
We’ll see what happens when and if Tyche is discovered. Beyond the possibility of a new planet, the paper on this work becomes absorbing in its study of the effects of the galactic tide (drawing objects toward the center of the galaxy) in pulling comets out of the Oort Cloud. In their analysis of earlier work on the matter, the authors conclude, “…the data are of sufficiently high quality to unambiguously demonstrate the dominance of the galactic tide in making comets discernable at the present epoch.” Where Tyche fits into that picture is that a certain percentage of long-period comets evidently enter the Solar System at an angle that the galactic tide theory cannot explain, offering evidence of perturbation by our unseen companion.
From the paper (here I’m quoting the preprint, as I don’t yet have the Icarus paper. Be aware that this section may have been amended in the final draft):
We have described how the dynamics of a dominant galactic tidal interaction, weakly aided by an impulsive perturbation, predicts specific properties for observed distributions of the galactic orbital elements of outer Oort cloud comets. These subtle predictions have been found to be manifest in high-quality observational data at statistically significant levels, suggesting that the observed OOC comet population contains an ≈ 20% impulsively produced excess. The extent of the enhanced arc is inconsistent with a weak stellar impulse, but is consistent with a Jovian mass solar companion orbiting in the OOC.
Not only that, but such a body would have roiled the system enough to produce some of the stranger things we’ve found recently:
A putative companion with these properties may also be capable of producing detached Kuiper Belt objects such as Sedna and has been given the name Tyche. Tyche could have significantly depleted the inner Oort cloud over the solar system lifetime requiring a corresponding increase in the inferred primordial Oort cloud population. A substantive difficulty with the Tyche conjecture is the absence of a corresponding excess in the presumed IOC daughter population.
In other words, the Tyche work can explain the behavior of comets from the outer Oort Cloud, but it has trouble with the inner Oort (IOC). Even as we go to work on the dynamics of cometary motion in that region, we should know soon whether this analysis is purely theoretical or has planetary implications. The Independent says Matese and Whitmire think WISE will find Tyche in short order, quoting the latter: “If it does, John and I will be doing cartwheels. And that’s not easy at our age.”