# The probable trajectory of the ninth planet in night sky?

#### sami_m

What would be the propable trajectory and position of the ninth planet that has been suggested few days ago (20.1.2016 by Konstantin Batygin and Michael E. Brown) ?

if i understood correctly, the exact position of the planet is unknown and has not been evaluated.

the orbital elements and physical properties they used in one of their simulation looks like to be (page 9 second column)

$m > 10 m_{earth}$ mass
$i = 30 °$ inclination, this would mean that the estimated trajectory is a great circle that is in the 30° angle to the celestial equator. But i dont know what is the direction of the perihelion, aphelion or ascending node?
$e = 0.6$ eccentricity
$a = 700 Au , b = 550 Au$ semimajor axis and semiminor axis
$ω = 150 °$ argument of perihelion (from what direction?)

but i dont know how to estimate error limits. Also the discussion section says that the analysis is not yet complete and other possibilities may not be excluded.

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#### Janus

Staff Emeritus
Gold Member
There are are a couple of parameters missing from that list if you wanted to locate the planet or plot its trajectory:
The longitude of the ascending node
The mean anomaly at a given epoch. (basically, you have to know at what point of its orbit it is in on some date to know where it will be at some other date.)

Also, the inclination is measured with respect to the ecliptic, not the celestial equator.

BvU

Staff Emeritus
If we knew the exact orbital parameters, we wouldn't call it "Planet Nine". It would be observed in a telescope and would have a real name.

#### sami_m

If we knew the exact orbital parameters, we wouldn't call it "Planet Nine". It would be observed in a telescope and would have a real name.
they dont mention there the orientation of the orbit, is it because , if the perihelion is of the orbit is slowly migrating, then the orientation can be anything now?

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