Hacker News Reader

Comment by rcthompson | Hacker News Reader

There's an extra large jump from Mars to Jupiter, but that's because there's an asteroid belt between them, which might be an aborted planet. If you put the average distance of the asteroid belt as planet number 5, I bet it would look even more linear.

View on HN

The asteroid belt doesn't have nearly enough mass to be/have been a planet[0]. Largest thing there is Ceres, followed by Vesta, of which only the first qualifies as a dwarf planet.

There was an hypothesis about it being the remnants of a destroyed planet[1], but that was mostly an idea to support the Titius-Bode law[2], which was disproved a few hundred years ago.

[0] Currently about 3x Ceres mass, though it may have about Earth mass early in its history. See https://en.wikipedia.org/wiki/Asteroid_belt#Formation and https://en.wikipedia.org/wiki/Asteroid_belt#Evolution

[1] https://en.wikipedia.org/wiki/Phaeton_(hypothetical_planet)#...

[2] https://en.wikipedia.org/wiki/Titius%E2%80%93Bode_law

> ... the Titius-Bode law[2], which was disproved a few hundred years ago

Er... the Wikipedia page you're citing at [2] has this to say:

"Results from simulations of planetary formation support the idea that a randomly chosen stable planetary system will likely satisfy a Titius–Bode law."

and

"96% of these exoplanet systems adhere to a generalized Titius–Bode relation to a similar or greater extent than the Solar System does."

"Disproved" in science often means "superseded by more accurate theory".

True, but the article doesn't mention a more accurate theory. It implies that the rule works better than we have theoretical reasons to expect. (But as I commented above, the article contradicts itself to some degree.)

The Wikipedia article is contradictory. As you quoted, it says that the law works well in simulation and in observation, and yet it's just a coincidence. Of course it's not exact, but it looks like a very good first approximation.

The qualifier "dwarf" doesn't mean that the celestial body is too small to be considered a planet, it means that it hasn't cleared the neighborhood around its orbit. (Blame the IAU if you find this counterintuitive). This means that your conclusion is wrong: the asteroid belt actually has enough mass to be a planet.

Other than not having enough mass, what would cause a celestial body to not clear its orbit? The only other factor that occurs to me is time, is there anything else? If not, does that mean Ceres may eventually become a planet?

If the asteroid belt originally had the mass of Earth, then I'd say it's fair to count it as a planet in this context, assuming that the orbits of the planets were established fairly early and have stayed about the same since then.

Is it possible that this was a planet, but most of the mass was ejected out of the system?

Some models[1] suggest that Neptune and Uranus formed closer to the sun, and then migrated to their current orbits later (explanations vary between Jupiter and Saturn pulling them out, or some extrasolar mass).

1: https://en.wikipedia.org/wiki/Neptune#Formation_and_migratio...

That's why the second graph on the page is 'Our Solar System with Ceres' showing exactly that.

??? Adding a point in between two other points literally can't make something more linear, it can only make it less linear.

I mean that the asteroid belt would be counted as a 5th planet, and Jupiter would be 6, and so on.

Ah, I understand now. Increasing the index of the outer planets is what would make the fit better, and the asteroid belt is a good way to justify it (and happens to be consistent with some other theories about the solar system).

The x-axis is the planet (+aborted planet) count. You’d be shifting all later planets over by one.

Reply on news.ycombinator.com