steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
I keep seeing articles about how Voyager 1 is leaving the solar system, or about to leave the solar system, or may just have left the solar system. An example is a science blog post titled More evidence that Voyager has exited the solar system.

These articles are talking about a real and interesting phenomenon, but I find the description of it as "leaving the solar system" misleading.

What they are primarily talking about is Voyager leaving the sun's heliosphere, the region of space affected by the charged particles of thesolar wind. Outside the heliosphere is the interstellar medium. Passing the heliopause between the heliosphere and the interstellar medium is crossing a significant boundary between a kind of space that is heavily influenced by the sun and one that isn't. So it is a significant event that Voyager 1 is passing this boundary, and in the process giving us evidence about the location of the boundary and what conditions are like at it and on either side of it.

Voyager 1 is currently about 122 astronomical units (au) from the sun, or 122 times earth's distance from the sun. That's a long ways away, but there are still many objects in the solar system whose orbits take them out that far; not only many comets, but also Sedna, which goes as far as 940 au from the sun at its most distant. And the Oort cloud, a hypothesized reservoir of comets that have never yet come close to the sun, is hypothesized to be between around 5000 and 50,000 au from the sun. All these orbits are still orbiting the sun, and thus still part of the solar system. It seems misleading to me to say that Voyager 1 is leaving the solar system when it's still well within the orbits of many things orbiting the sun.

But crossing the heliopause is still neat and noteworthy.
steorra: Part of Saturn in the shade of its rings (Default)
[personal profile] steorra
There's something I want a word or phrase for, and I don't think there is one.

My main interest within astronomy is in the solar system. The objects in the solar system that I find most interesting are those that are big enough to be round (i.e., in hydrostatic equilibrium), but small enough to be solid - thus excluding the Sun and gas giants.

The objects that fit in my category of interest cut across several of the usual categories. It includes the terrestrial planets, but not the gas giants. It includes all dwarf planets. It includes relatively large moons (most moons with a diameter greater than about 400 km), but not small moons.

I've been calling them "solid round solar system bodies", but that's an awkward phrase and I'd really like a tidier one.

I was brainstorming with a friend the other day and the best we could come up with was something like "terrestrial worlds" or "terrestrial bodies". If I poke around on the internet to see how those phrases have been used before, they both seem to have several uses, none of which is quite what I'm looking for. One of the main issues with "terrestrial" is that it's sometimes used not to distinguish solid objects from gaseous objects, but to distinguish rocky solid bodies from icy solid bodies. But there are other uses of "terrestrial worlds" or "terrestrial bodies" that include both rocky and icy ones; the meaning I found closest to what I want included the terrestrial planets, Pluto, and the moons larger than Pluto, but for no apparent reason didn't include the round moons or dwarf planets (such as Ceres) that are smaller than Pluto.

What do you guys think? Is "terrestrial worlds" or "terrestrial bodies" a good term for the concept I want to name? Can you think of a better one?


Jun. 21st, 2011 12:42 pm
steorra: Part of Saturn in the shade of its rings (Default)
[personal profile] steorra
Lights in the Dark a neat blog of solar system photos by someone who, among other things, processes raw NASA images by e.g. combining images from different colour filters to produce a single colour image. This picture of Titan and Rhea is what led me there.
jeweledeyes: Sailor Venus thinks you're a loser (Kowalski science)
[personal profile] jeweledeyes
A Big Surprise from the Edge of the Solar System
NASA's Voyager probes have reached the edge of the solar system and found something surprising there--a froth of magnetic bubbles separating us from the rest of the galaxy.

I, for one, was astounded by this!



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