Closest Not-Really-Earthlike Earthlike Planet Found Sort of!

[Nefaro]

Keep in mind the reason for the large majority of discovered exoplanets being huge gas giants, many of which orbit closely around their star - the methods being used to find them.

True, although I think there are also theories for why gas giants ought to be closer and rockies farther out.

But you're also right, the current detection technology skews a particular direction.

It's certainly shown Planetary Migration to be a common thing, and supports the very solid theory of it happening in our own system.   O0 

A big question is how often do planets or, more specifically, rocky planets get ejected from their system by the migration of their larger brethren.  We supposedly lost one when Jupiter moved inwards & then back out due to an orbital resonance with Saturn, and switching Uranus and Neptune.  Thanks for saving Earth, btw, Saturn.  I wonder whether the "ejected" planet is the predicted "Planet 9", in extremely distant orbit, or whether there was also another that is completely gone.

I think we'll slowly start seeing rocky planets being discovered in close orbits more often as better technology comes online.  The one around Proxima is right next door to us, galactically speaking, and very close to a relatively smaller dwarf star, making it easier for our current methods to detect. 

[Pete Dero]

Keep in mind the reason for the large majority of discovered exoplanets being huge gas giants, many of which orbit closely around their star - the methods being used to find them.

True, although I think there are also theories for why gas giants ought to be closer and rockies farther out.

But you're also right, the current detection technology skews a particular direction.

On of the most used method (transit of planet in front of star) tendq to favor detecting gas giants in close orbits.  The fact that many of these are detected does not mean
they are the most common configurations.  As research continues gas giants further from their stars will start showing up more often.  You need a longer observing period to see a transit happening as their orbits will be bigger and take longer to complete.

Some recent info : http://www.skyandtelescope.com/astronomy-resources/kavli-qa-how-did-planets-form/

[JasonPratt]

We supposedly lost one when Jupiter moved inwards & then back out due to an orbital resonance with Saturn, and switching Uranus and Neptune.  Thanks for saving Earth, btw, Saturn.  I wonder whether the "ejected" planet is the predicted "Planet 9", in extremely distant orbit, or whether there was also another that is completely gone.

There are some interesting if half-baked theories about Saturn having migrated in far enough at one point to drag Mars, Venus, and Earth along in its wake, leaving geographical scarring common on Mars and Earth (maybe also Venus, harder to tell) due to electrical arc discharges.

That all sounds plausible enough; the half-baked side argues that this happened during the last four or six thousand years! -- even up into the last 3000 years maybe  :o -- and that although this didn't last long (a couple of generations, perhaps less) the spectacular effects contributed to a bunch of mythical and partially historical culture around the globe.

[Nefaro]

We supposedly lost one when Jupiter moved inwards & then back out due to an orbital resonance with Saturn, and switching Uranus and Neptune.  Thanks for saving Earth, btw, Saturn.  I wonder whether the "ejected" planet is the predicted "Planet 9", in extremely distant orbit, or whether there was also another that is completely gone.

There are some interesting if half-baked theories about Saturn having migrated in far enough at one point to drag Mars, Venus, and Earth along in its wake, leaving geographical scarring common on Mars and Earth (maybe also Venus, harder to tell) due to electrical arc discharges.

That all sounds plausible enough; the half-baked side argues that this happened during the last four or six thousand years! -- even up into the last 3000 years maybe  :o -- and that although this didn't last long (a couple of generations, perhaps less) the spectacular effects contributed to a bunch of mythical and partially historical culture around the globe.

Sounds pretty far-fetched, but you can't rule anything out until disproved.

I was mentioning one of the most popular planetary migration theories for our system, in which Jupiter's early migration had a direct effect on our inner rocky planets being fairly small.  Along with numerous other notable effects.  An interesting one.


The "Grand Tack" theory ->


http://www.space.com/28901-wandering-jupiter-oddball-solar-system.html 

Wandering Jupiter

The researchers modeled a leading scenario for the formation of Jupiter and Saturn known as the "Grand Tack," wherein Jupiter arose first and migrated toward the sun until Saturn formed, which caused Jupiter to reverse course and migrate outward to its current orbit. They calculated what might happen if a set of rocky planets formed in the inner solar system before Jupiter migrated inward. [Photos of Jupiter: The Jovian Giant]

In the early solar system, the sun was surrounded by a dense disk of gas and dust. This suggests that any inner rocky planets forming might have eventually become super-Earths such as many of the exoplanets that astronomers have seen around other stars.

However, as Jupiter moved inward, its gravitational pull would have slung these nascent inner worlds into close-knit, overlapping orbits. This would have set off a series of collisions that smashed these newborn worlds into pieces.

"It's the same thing we worry about if satellites were to be destroyed in low-Earth orbit," Laughlin said in a statement. "Their fragments would start smashing into other satellites and you'd risk a chain reaction of collisions. Our work indicates that Jupiter would have created just such a collisional cascade in the inner solar system."

The resulting debris would then mostly have spiraled into the sun. A second generation of inner planets would have formed later from the depleted material that was left behind. This would explain why Mercury, Venus, Earth and Mars are younger than the outer planets, and why they are both smaller and have much thinner atmospheres than inner worlds seen in other planetary systems.

"The results imply that our terrestrial planets formed after Jupiter's early migration wiped the slate clean and set the stage for formation of gas-poor objects," Batygin said. "The fact that all of these characteristics of the solar system turn out to stem from the same process is exciting — it is as if the scattered pieces of the puzzle are finally falling together into a coherent picture."

"This kind of theory, where first this happened and then that happened, is almost always wrong, so I was initially skeptical," Laughlin said in a statement. However, "there is a lot of evidence that supports the idea of Jupiter's inward and then outward migration. Our work looks at the consequences of that. Jupiter's 'Grand Tack' may well have been a 'Grand Attack' on the original inner solar system."

[JasonPratt]

Who else thought of Orson Welles as Unicron when you got down to the Grand Attack of Jupiter?  >:D