Reading excerpt “Excursions to the Outer Solar System”: Between Worlds

Another possibility would be a still unknown planet-size body in the more outer regions of the Solar System, which determines the orbits of this object by the effect of its own gravity. Speculation about such an unknown planet has been expressed frequently during the past few decades. In the past few years, discussions have resumed about a ninth planet, said to be in regions beyond 200 AU from the Sun. There is no evidence of such a body, but the evidence seems to be mounting.

Perhaps, according to the third attempt at clarification, it is not a question of a body that still exists, but of a large planet (possibly a gas giant) that formed with other planets, but then ejected from the Solar System. had gone. through conversation with them. This may be enough to stretch the DO into its current state.

Although these objects are very difficult to identify, we have already identified some. The most famous of them is the item »Sedna«, the next destination of our journey. This entity defines a new “subclass” of discrete objects. All DOs whose circumference is greater than 75 AU, as in sedna, are called “sednoids”. Currently only a few sednoids are known (see Table 9.1).

9.2 Sedna

Sedna is a strange world we encounter about 500 AU away¹ (Figure 9.1, not included in this excerpt). Light from the Sun takes about three days to reach this distant object. We have already seen in the previous section that this “isolated object” has a highly eccentric orbit (Figure 9.2, not included in this sample). At its closest point to the Sun, it reaches our central star by 76 AU, but then continues its journey into the outer Solar System to the nearly unimaginable 922 AU.