Two Planets Found Sharing One Orbit

dweezil-n0xad writes "Buried in the flood of data from the Kepler telescope is a planetary system unlike any seen before. Two of its apparent planets share the same orbit around their star. If the discovery is confirmed, it would bolster a theory that Earth once shared its orbit with a Mars-sized body that later crashed into it, resulting in the moon's formation."

Re:Time for another IAU meeting

[Anonymous Coward]

Quick, we need to redefine the meaning of "planet" yet again.

Yeah... because it's been changed so many times, right? And for no good reason to boot, right?

Truth is, the term "planet" has only really been defined once, a few years ago. before that, we had an intuitive idea of what a "planet" was; we included Pluto, as it appeared to be a comparatively unique object, but then we found that Pluto isn't unique and that there is no reason to believe that we wouldn't have millions (at least!) of planets, since there'll be that many objects that all share Pluto's characteristics and that'll have the same right to be called "planet".

Not a good solution, obviously, so we looked for something different and came up with a better, precise definition. And yes, that meant that Pluto lost its "planet" status... but that's happened before; Ceres was considered a planet when it was first found. Until, that is, people noticed that it was just one of a ton of objects that would then also have to be called "planets" if Ceres was one. Sound familiar? It's basically exactly Pluto's situation.

Now maybe you don't see keeping the number of planets down as a worthwhile goal, but personally, I think that if you're thinking that the four major rocky planets in the inner solar system and the four gas giants in the outer solar system do not stand out from millions of asteroids and Kuiper belt objects, then you're deluded. They do.

Doesn't mean the remaining objects aren't interesting, mind you, but that's just you attaching too much significance to the label "planet" in the first place.

Keplerian Occultations

[kenwd0elq]

The problem with the planet detection methods used by the Kepler team is that it is all calculated based on occultations; the slight dimming of the star's light as a planet passes between that star and the Kepler satellite. This only works if the planet in question is 1) HUGE or 2) very close to the star or 3) the Earth just HAPPENS to be in the plane of the planet's orbit around the star. That's why we're discovering so many enormous planets with orbital periods in the range of only a few days. But the nice thing about the Kepler data seems to be that it's eliminating many of the "it could NEVER have happened that way!" explanations. With upwards of 500 billion stars in the Milky Way galaxy and we've looked only at a few thousand, it looks more and more that ANYTHING is possible when it comes to planetary formation.