mardi 23 février 2016

Plan(et) 9 from ou[te]r Spaceolar System

The man who killed planet nine ...
For those of a certain age, it will always be tough to accept that Pluto isn't a planet anymore, just as no adult Chicagoan can call the Sears Tower the "Willis Tower" without queasiness. We were taught from childhood to rank tiny Pluto, which circles the sun at an average distance of 3.5 billion miles, as every bit the equal of Neptune, Uranus, or even Jupiter. Thus the news, in 2006, that a bunch of killjoy astronomers had demoted it seemed like an insult to underdogs everywhere.  
Mike Brown, a professor of astronomy at Caltech, was the man who inadvertently caused this interplanetary crisis when he discovered Eris, an object even farther from the sun than Pluto, but considerably more massive. Briefly ballyhooed as the 10th planet, it soon provoked chaos within astronomy circles, calling into question the very meaning of the word "planet"—never precisely defined before—and finally taking Pluto down with it. Not for nothing did Mr. Brown name his discovery after the goddess of strife and discord.
By JAMES KENNEDY Updated Nov. 26, 2010 12:01 a.m.

... may have helped to revive it

Caltech researchers have found evidence of a giant planet tracing a bizarre, highly elongated orbit in the outer solar system. The object, which the researchers have nicknamed Planet Nine, has a mass about 10 times that of Earth and orbits about 20 times farther from the sun on average than does Neptune (which orbits the sun at an average distance of 2.8 billion miles). In fact, it would take this new planet between 10,000 and 20,000 years to make just one full orbit around the sun.
The researchers, Konstantin Batygin and Mike Brown, discovered the planet's existence through mathematical modeling and computer simulations but have not yet observed the object directly.
01/20/2016 Written by Kimm Fesenmaier


Let's call it Telisto ...
As far as the denomination of such a still undiscovered major body of the our planetary system, several names have become more or less popular over the years in either the specialized literature and in popular accounts; given the remarkable distance envisaged by Batygin & Brown (2016) for it, we reiterate the name Telisto [from τηλιστος ´ : farthest, most remote]. Nonetheless, in the following we will dub it PX or X for simplicity.
(Submitted on 16 Dec 2015 (v1), last revised 31 Jan 2016 (this version, v3))

... if it is located far enough?

The hunt for a planet X started in 1915 Lowell (1915), and some important limitations were provided by different approaches. The direct imaging survey of the far solar system by infrared space telescopes IRAS and WIZE did not detect any massive objects of Jupiter size inside 25000 AU and of Saturn size inside 10000 UA Luhman (2014). In 1993, Standish (1993) demonstrated that no anomalous residuals can be seen in the residual of the outer planet orbits. However since this work, no direct confrontation has been performed between the perturbations induced by a planet X on the orbits of the main planets of our solar system and the best fitted planetary ephemerides. The only estimates were made indirectly, based on the results of the ephemerides, but without refitting the whole parameters of these ephemerides (Iorio 2012, 2016). 
Since 1993, very accurate observations of Saturn orbit were obtained thanks to the tracking of the Cassini spacecraft during its exploration of the Saturnian system. As described in (Folkner et al. 2014), (Hees et al. 2014) and (Fienga et al. 2016), the ten year positions of Saturn allow significant improvement in our knowledge of Saturn’s orbit, as well as of Jupiter, Uranus, and Neptune orbits. These Cassini data have already been used very successfully to put some strict limits on the possibility of an anomalous Pioneer acceleration (Anderson et al. 2002; Fienga et al. 2010). Furthermore, thanks to the Cassini flyby of Jupiter, a supplementary accurate position of Jupiter is also used to build the ephemerides. Finally, the flyby of the New Horizons spacecraft of the Pluto-Charon system should bring some supplementary information and constraints for the existence of a super-Earth. 
We use here the dynamical model of the INPOP planetary ephemerides (Fienga et al. 2008, 2009, 2010, 2011, 2016) for testing the possibility of an additional planet, focussing on the proposed nominal planet P9 of Batygin & Brown (2016). In the dynamical model of INPOP planetary ephemerides, we add a super-Earth object of 10 M with different orbital characteristics, in agreement with the proposed orbit of P9. We then build new ephemerides including these objects and perform a global fit of the perturbed planet orbits to the whole data set that is used to construct the INPOP and DE430 JPL ephemerides (Folkner et al. 2014). 
Allowed zone for P9. The red zone (C14) is excluded by the analysis of the Cassini data up to 2014 (Sec.4). The pink zone (C20) is how much this zone can be enlarged by extending the Cassini data to 2020 (Sec.4). The green zone is the most probable zone for P9 (v ∈ [108◦ : 129◦ ]), with maximum reduction of the residuals at v = 117.8 ◦ (blue dot P9). The white zone is the uncertainty zone where the P9 perturbation is too faint to be detected.
The Cassini data provides an exceptional set of measures that acts as a very sensitive device for testing the possibility of an additional massive body in the solar system. With the data accumulated until 2014.4, we can exclude the possibility that P9 is in the section of the orbit depicted in red in Fig[ure above], with a true anomaly v in [−130;−100]∪[−65; 85]. We thus contradict the affirmation of Iorio (2016), who states that a body of 10 M is excluded if it resides closer to 1000 AU of the Sun. Iorio (2016) does not properly consider how much the presence of an additional body can be absorbed by the fit of all the other parameters in the solar system ephemerides. The global fit that we present here avoids this drawback. Moreover, we found that the presence of P9 could significantly decrease the Cassini residuals if v is in the interval [108;129], with a most probable position at v = 117.8+11-10. 
Since the Cassini data is at present the most precise sensor for testing the possibility of an additional body in the solar system, it is essential that Cassini continues to provide ranging data, since there will not be very soon an additional spacecraft around one of the planets beyond Saturn. Extending the Cassini data up to 2020 will already allow to state for the existence of P9 for v ∈ [−132;106.5]. Juno will soon arrive around Jupiter and will thus allow us to improve the orbit of Jupiter. This may not directly improve the constraints on P9, because Jupiter is less sensitive than Saturn to the perturbations of P9. Nevertheless, constraining Jupiter more tightly will allow us to improve the determination of P9, because less flexibility will exist for absorbing the perturbations due to P9.
(Submitted on 19 Feb 2016 (v1), last revised 22 Feb 2016 (this version, v2))

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