[BRIEF NOTE] The new Solar System

[rfmcdonald]

In the course of an examination of the possibility of a high-speed mission to the dwarf planet of Haumea, one of many Kuiper belt of icy bodies beyond the orbit of Neptune, Centauri Dreams makes the point that our understanding of the structure of the Solar System has changed radically, from a solar system with nine planets to one with eight planets and huge numbers of dwarf worlds.

As Poncy did, I’ll use outer planet specialist Mike Brown’s illustrations of what has happened to our Solar System in the last few decades. The first illustration shows the Solar System most of us grew up with, a system with nine planets that were more or less clearly defined, with what was assumed to be a certain amount of debris and cometary material further out.

Now, of course, we see a new Solar System. Depending on how we define planets, we can declare that we have numerous such objects in the outer system — call them ‘dwarf planets’ — along with, much further out, the enormous, spherical system known as the Oort Cloud. Think about this: The number of objects with a diameter beyond 500 kilometers has doubled in just ten years from thirty-five to more than seventy as we’ve continued our investigation of trans-Neptunian objects. It is fully assumed that within another decade or two, we’ll know of hundreds more of these objects.

Let me quote [space proponent Joel] Poncy on this:

If we now recap all sizable Solar System planetary objects larger than 500 km, we get 19 objects closer than the orbit of Uranus, orbit-able after a decade or so of cruise with current technologies. Uranus itself can be flown by but not orbited for a decent travel time. We have already more than 40 objects at Uranus and beyond and this number will grow considerably by 2020. This is even starting to change the appellation ‘Outer System,’ which was previously used to name the part beyond the frost line at 4 AU, and is now sometimes used to designate the part beyond 30 AU.

Consider, too, that we once thought of the the Solar System as being enclosed in a well defined heliosphere that separated it from true interstellar space. Now we have objects like Sedna, with an aphelion (942 AU) that is well beyond the heliosphere. In moving to its perihelion at 76 AU, Sedna moves from interstellar space into the heliosphere and then gradually works its way back out again. The new Solar System is packed with objects that defy all the definitions we once brought to the term.

The images, and much else, are available at the blog site.