THE SOUTHWORTH PLANETARIUM
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Founded January 1970
2022-2023: L
Sunrise: 7:00 a.m.
Sunset: 4:04 p.m.
Civil twilight begins: 6:27 a.m.
Civil twilight ends: 4:37 p.m.
Sun's host constellation: Ophiuchus
Moon phase: Waxing gibbous (94% illuminated)
Moonrise: 2:59 p.m.
Moonset: 6:36 a.m. (12/7/2022)
Julian date: 2459920.21
"No problem can withstand the assault of sustained thinking." -Voltaire

THE DAILY ASTRONOMER Tuesday, December 6, 2022
Is "Planet Nine" a Captured Rogue?

I should preface this article with the acknowledgement that, though highly
probable*, the existence of the body now dubbed “Planet Nine” is
hypothetical. Consequently, any theory about its origin will be highly
speculative. That having been said -or written- some astronomers have
actually proposed that Planet Nine could be a rogue planet.** Paul A Mason
and James Vesper, two research astronomers at New Mexico State University,
wrote a paper (published by the American Astronomical Society in Jan 2017)
entitled “Simulation of Rogue Planet Encounters with the Solar System: Is
Planet Nine a Rogue Planet?”

They conducted 156 computer simulations involving the interaction of rogue
planets with the solar system. Mason and Vesper assumed that the rogue
planet in their simulation was similar to that of the proposed planet nine:
at least ten times the size of Earth. The analysis of these simulations
showed that

   - In 60% of the encounters, the rogue planet simply entered the solar
   system’s outer fringes and then departed. At times it took a small dwarf
   planet with it.
   - In 40% of the encounters, the Sun managed to capture the rogue planet,
   which would remain at a great distance from the Sun.

Intriguingly, the simulation suggests that the captured body would
establish a highly elongated orbit at a distance of 1000 AU (or, 1000 times
farther from the Sun than Earth.) This distance is about equal to the
presumed mean distance of Planet Nine. Even though the Sun’s gravitational
influence is tenuous at such a distance, the Sun’s gravity will still be
dominant over the nearest star system, Alpha Centauri, which is 261,935 AU
away.

An artistic depiction of the hypothetical planet Nine. As it has never been
observed -and might not exist in the first place- details about its
appearance are, well, scant. Notice the small illuminated ellipse at the
upper right. That ellipse represents Neptune’s orbit. Image credit:
Wikimedia Commons

Of course, this is all highly speculative. Unsurprisingly, astronomers have
not yet found Planet Nine. At such a distance, it must be quite faint, if
it exists. Moreover, with a mean distance of 1000 AU, its orbital period
would likely exceed 31,600 years. Such a planet’s existence would be
confirmed by noting alterations in its position over time. [Pluto was
discovered this way after a year’s searching, and it only requires 248
years to complete one orbit. Granted, that was in 1929–1930 using what
would now be regarded as an antiquated blink comparitor.] Hopefully, the
James Webb Space Telescope might help astronomers locate Planet Nine. If it
is found, astronomers will then study it as closely as possible (probes are
not a feasible option at this point) and could gain some real insight into
its origin.

It might well be a rogue planet that now belongs to us. Physics allows it.

*Though not yet observed, many astronomers believe that Planet Nine exists
because of the peculiar “clustering” of Trans-Neptunian objects

**A rogue planet is defined as one that is not gravitationally bound to any
star. It seems highly probable that the Milky Way harbors billions of these
rogue worlds. That high number is not surprising because simulations
suggest that most, if not all, solar systems will propel at least one -but
often more- planets away during the tumultuous formation process.




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