DO STAR NEAR-MISSES MAKE SUPER-JUPITERS FALL?
How fragile is life?
Many disasters can strike a biosphere.
A famous “equation” the Drake equation, is meant to estimate the probability of life in the galaxy. It overlooked many factors. One of them is interstellar near-misses. It is not a question of stars colliding, but of the disruption of solar systems.
A star zoomed through our Solar System just 70,000 years ago, astronomers have just discovered.
No other star is known to have approached this close to us.
The international team of astronomers found that the intruder came five times closer than our current nearest neighbour – Proxima Centauri (at .8 light year whereas Proxima Centauri is 4.2 light year away).
The star, a red dwarf known as Scholz’s star, cruised through the outer Oort Cloud, a region not as much stuffed with comets as the inner Oort Cloud. Scholz’s Star is 8% of the mass of the Sun, and it is accompanied by a brown dwarf which is nearly as massive (6% of Sun mass). It goes without saying that going through the comet cloud would have adverse consequences for advanced life on Earth. But worse could happen.
(Brown dwarves just miss the mass necessary mass to have enough heat and pressure to get fusion going in their cores).
Something struck me when extrasolar planets were discovered. How frequent were the super-Jupiters grazing their home stars? Of course, there was a detection bias (with the technology used by the French Corot, and the more recent USA Kepler, the probability to detect a super-Jupiter close by was overwhelming).
However, a question loomed: how do you get a gas giant that was obviously formed far from the home star, so close to the home star? One could imagine a cloud breaking the planet, but that makes little sense (as cloud and planet have similar angular momentum, and the planet would suck the cloud).
Collisions. Or more exactly, near-misses.
Previous work suggests that flybys within 0.25 pc occur infrequently (~0.1 Myr−1).
Sedna, a dwarf planet, whose orbit varies between 70 (seventy) and 1,000 (thousand) Astronomical Units (AU, the distance between Sun and Earth). Maybe a remnant from a near collision (torn from a Red Dwarf clutches).
In any case, Scholz’s star came within 52,000 AUs of the Sun. And it passed very fast (the slower the pass, the greater the disruption).
If it had passed within 100 AUs, the disruption would have been considerable (Neptune is at 30 AUs; at 90 AUs, the pull from a passing star, in the worst case would 1/10 of that of the Sun, and would make the orbit of Neptune ellipse, significantly eccentric)
So what happens if a gas giant gets a severely eccentric orbit? Well, it can cut through the others’ orbits, and the whole system becomes unstable. A few large collisions and near misses later, one could get some gas giants to graze their suns, as observed.
As usual, I just suggest the idea. Others can figure out the details, program their computers, and check….
Let’s make a little computation. Suppose that the probability of a star coming within 52,000 AUs was once every 100,000 years (a probability tellingly estimated BEFORE it came to be known Scholtz’s star zoomed by).
Let’s consider the disruption radius to be 100 AUs. The probable number of near-misses disrupting the inner system during the past extent of the Solar System would then be:
1/25,000)x(10^4)x5 = 2.5.
That’s quite a bit… And, now that we know about Scholz’s Star’s recent flyby, no doubt that the probability of near misses will skyrocket. All the more as the Sun is presently in the pretty empty zone, the Local Bubble, 300 light years across.
I have explained in the pat that life depended not just upon having a planet in the Habitable Zone (the Water Zone), but also in the Radioactive Belt.
Many are the causes of disasters on the way to advanced life, as I have enumerated in:
Being lucky with stellar flybys is another factor to consider: a nudge to the outer gas giants, and it’s curtains for advanced life. Bacteria don’t count. I am suggesting that, in star systems long established, star near-misses is a much serious problem than rogue asteroids or comets.