Evidence for a ninth planet in the Solar System

Well the BIG news of the last few weeks is that there is now almost certainly a ninth planet in our solar system. The evidence is based on the apparent shepherding of half a dozen Kuiper Belt objects, including Sedna. I say apparent because there is a very very small probability that the group could have formed naturally without the help of a planet. But it’s very small. So the telescopes, including the big Subaru one,  are pointing in the direction where that planet is likely to be.

Calculations show that mass-wise it’s about the weight of Neptune.

Now let’s look at Bode’s Law which states that:

The law relates the semi-major axis a of each planet outward from the Sun in astronomical units:

a=0.4+0.3 \times 2^m

for m=-\infty,0,1,2...

Earth is one astronomical unit away from the Sun. For the outer planets, each planet is predicted to be roughly twice as far from the Sun as the previous object.

This bears out the current known planetary distribution – note as Pluto crosses Neptune’s orbit, it is accepted they are in the same slot for the purposes of Bode’s law.

So where would this new planet sit in the Bode’s law regime of things?

Well estimates say that the new planet’s closest approach is 200 astronomical units (aus) and its farthest is between 600 and 1200 aus.

 Bode’s formula gives:
  • Mercury – 0.4 (actual – 0.39)
  • Venus – 0.7 (actual – 0.72)
  • Earth – 1 (actual – 1.00)
  • Mars – 1.6 (actual – 1.52)
  • Ceres – 2.8 (actual -2.77)
  • Jupiter – 5.2 (actual 5.20)
  • Saturn – 10.0 (actual 9.54)
  • Uranus – 19.6 (actual 19.2)
  • Neptune / Pluto – 38.8 (actual Neptune – 30.06 and Pluto – 39.44)

According to Bode’s Law the next planets out, if there are any, should appear at (in aus):

  • 77.2
  • 154.0
  • 307.6
  • 614.8
  • 1229.2

Clearly ninth planet would fit in with those marked in bold i.e. 307.6 and 614.8 aus.

So what has happened in 77.2 aus and 154.0 aus slots?

I argued in a previous post that Eris would fit the 77.2 aus (at 67.8 aus from the Sun), particularly if it had, as yet undiscovered, companions in that slot like we are seeing with the Neptune-Pluto pairing. See here for more details.

So what is going on in the 154.0 slot? That kind of needs answering.

That’s the kind of question that can lead to interesting science fiction stories. Go forth and write!


One thought on “Evidence for a ninth planet in the Solar System

  1. Very interesting point about Bode’s Law – we know so little about the Kuiper Belt (the fact that Planet X – a Neptune-sized body – is inferred through maths, rather than observed) suggests that we may yet find hidden gems there. 🙂

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