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Hey Cancer, quit trying to destroy the universe!


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Astronomers think they've recorded a dying star devouring its doomed jpvian planet. It probably wasn't inhabited -- jovian, after all, and cooked for a long period before the final plunge -- but raise a glass in tribute anyway.

 

https://www-cf.npr.org/2023/05/03/1173082322/this-star-ate-its-own-planet-earth-may-share-the-same-fate

 

Dean Shomshak

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Not much new there, other than the number-crunching.  It must have happened very early, because the whole system -- planet, moons, rings -- is canted over by about 100 degrees.  Knocking the planet sideways after the other stuff had formed would not alter the moon orbits etc. to remain coplanar with the planet's equator, which is what we see; the entire planetary accretion disk ensemble had to have that tilt almost from time zero.  This isn't a late-in-life invasion; this is the doctor dropping the baby as it's being delivered.

 

Meanwhile, no one seems ever to comment in the same innuendo-laden way about Venus going the other way.  Its rotation axis is dead perpendicular to the fundamental plane of the Solar System, but the planet, ah, seems to have resisted the peer pressure to turn around like everyone else.

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A thought I had a while back: Does the Solar System contain any "normal" planets?

 

Mercury is strange. It has the most elliptical orbit of any planet, a slow rotation putting its day and year into a 3:2 resonance, and may have lost much of its mantle in an early collision.

 

Venus is strange. Its rotation is so slow that its day is longer than its year, something true of no other planet. Also backwards or, what amounts to the same thing, its axis is tipped almost 180 degrees.

 

Earth is strange, and not just for having oceans and life. It has the largest moon in proportion to the planet's own size in the Solar System. (Not counting dwarf planets like Pluto/Charon.)

 

Mars...? Middling size, beween Earth and Mercury. Not as geologically dead as Mercury, but not as active as Earth or Venus. The only terrestrial planet to have two moons, both tiny captured asteroids, but these are probably temporary by astronomical standards. Distinctive, but would it be strange if it turned out Earth or Venus also had such tiny temporary moons? So Mars might be a "normal" terrestrial planet.

 

Jupiter: Biggest planet, by far, and undoubtedly the first to form. Not anomalous, really, but unique.

 

Saturn is strange for its uniquely large ring system. OK, so that's temporary, and other planets may have had or will someday have equally large ring systems. But there's evidence that it also doesn't have a core -- that the pressure of its atmosphere disintegrated and dissolved any core it formed with (though this did not happen with the larger Jupiter). That's a permanent weirdness.

 

Uranus is strange for being tipped on its side and, as the linked article mentions, its atmosphere is colder than it should be.

 

Neptune is about the same size, mass and composition as Uranus, but its axis is sensibly near-perpendicular to the ecliptic. It has some oddball moons -- Triton has a close-in retrograde orbit, while little Nereid is so elliptical it's cometary. I've seen the speculation that Triton is a captured Kuiper Belt Object, whose capture probably disrupted the orbit of Nereid. But then, it's the gas giant that's closest to the Kuiper Belt just like Mars is the terrestrial closest to the asteroid belt, so neither planet's satellites should be entirely unexpected.

 

So, only two "normal" major planets out of eight. Which means that actually, it's normal for planets to be in some way strange.

 

Dean Shomshak

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Lots of those lead to strong suspicions that evolutionary processes (both known and unknown) have had profound effects on the Solar System over its entire history.  The Nice model was originally investigated as a way to understand the cause of the Late Heavy Bombardment, but it has consequences for Solar System dynamics that go well beyond that.  Mars has been messed with by Jupiter over its entire history.   There are suggestions that another ice giant planet was originally part of the Solar System but was ejected at early times, with a few dynamical relics left behind; roughly half a dozen free-floating planets are known from gravitational microlensing, and it's not known if these things formed independent of any star or if they are planets formed in but subsequently ejected from "ordinary" star systems.  Frankly, it is impossible to understand what little we know about the population of trans-neptunian objects without including drastic evolution (and that evolution includes a lot of losses: accretions onto planets, or ejection from the Solar System) of that population by gravitational interactions with Neptune and perhaps others of the gas giants.

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