<p>There are several potential explanation for the cause of the late heavy bombardment. One of them includes a passing star that disturbed the Oort cloud. A "stellar system collision" would have destroyed the solar system, though. While galaxies are mostly empty and a galactic collision won't involve that many actual collisions (if any), the gravitational interactions between the galaxies actually changes star orbits around the galactic centers. Similarly a "stellar system collision" would heavily change planetary orbits, even if there were no collisions at first.</p>

<p>Another hypothesis is a totally "interior" one: A 2:1 orbital resonance between Jupiter and Saturn changed the orbits of Neptune and Uranus, potentially even causing them to swap positions. Neptune's new orbit then affected many Kuiper belt objects, either sending them way out to form or join the Oort cloud, or sending them in as part of the late heavy bombardment.</p>

CC BY-SA 3.0
2013-10-09T06:06:01.020Z
2013-10-09T06:06:01.020Z
Wormbo
<p>If a star was ping-pong ball size, even the dense cores of colliding galaxies would be like ping-pong balls flying past, 540 miles apart.</p>
<p>A star is about 5 light-seconds across and the average separation between stars is about 6 light years, or about 220 million light seconds. So stars make up about 1 part in 2.5e15 of the galactic plane, and the odds of any two arbitrary  stars colliding when galaxies pass through each other are about 1 in 250 quadrillion.</p>
<p>Assuming the galactic  centers of mass pass through each other, the odds of any of 2 trillion stars colliding, with each pair having that probability, is 1 in 125,000.</p>
<p>Only 1 in 125,000 galaxy collisions sees even a single pair of stars touch (modulo tidal effects).</p>
<p>The moon was pummeled in the bombardment. The earth would look that beat up were it not for erosion. But stars don't collide because their sizes are too small compared to the vast interstellar distances involved.</p>

CC BY-SA 4.0
2024-04-01T13:15:35.583Z
2024-04-02T10:32:46.400Z
2024-04-02T10:32:46.400Z
Miss Understands
<p>I was thinking about the impending collision between M31 and the milky way galaxy, and I've heard that since a galaxy is mostly space most of the contents of both galaxies would be just fine. Could a similar effect be responsible for the late heavy bombardment era? Just instead of galaxies, stellar systems?</p>

<planet><solar-system><star-systems><impact><collision>
Did the Late Heavy Bombardment Period Happen Because of a Stellar System Collision?
Sarah Szabo
# Did the Late Heavy Bombardment Period Happen Because of a Stellar System Collision?

(Asked by: username_0 on 2013-10-08)

I was thinking about the impending collision between M31 and the milky way galaxy, and I've heard that since a galaxy is mostly space most of the contents of both galaxies would be just fine. Could a similar effect be responsible for the late heavy bombardment era? Just instead of galaxies, stellar systems?

**Tags:** planet, solar-system, star-systems, impact, collision

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## 2 answers

### Answer by username_1 on 2013-10-09. Score: 12

There are several potential explanation for the cause of the late heavy bombardment. One of them includes a passing star that disturbed the Oort cloud. A "stellar system collision" would have destroyed the solar system, though. While galaxies are mostly empty and a galactic collision won't involve that many actual collisions (if any), the gravitational interactions between the galaxies actually changes star orbits around the galactic centers. Similarly a "stellar system collision" would heavily change planetary orbits, even if there were no collisions at first.

Another hypothesis is a totally "interior" one: A 2:1 orbital resonance between Jupiter and Saturn changed the orbits of Neptune and Uranus, potentially even causing them to swap positions. Neptune's new orbit then affected many Kuiper belt objects, either sending them way out to form or join the Oort cloud, or sending them in as part of the late heavy bombardment.


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### Answer by username_2 on 2024-04-01. Score: 2

If a star was ping-pong ball size, even the dense cores of colliding galaxies would be like ping-pong balls flying past, 540 miles apart.

A star is about 5 light-seconds across and the average separation between stars is about 6 light years, or about 220 million light seconds. So stars make up about 1 part in 2.5e15 of the galactic plane, and the odds of any two arbitrary stars colliding when galaxies pass through each other are about 1 in 250 quadrillion.

Assuming the galactic centers of mass pass through each other, the odds of any of 2 trillion stars colliding, with each pair having that probability, is 1 in 125,000.

Only 1 in 125,000 galaxy collisions sees even a single pair of stars touch (modulo tidal effects).

The moon was pummeled in the bombardment. The earth would look that beat up were it not for erosion. But stars don't collide because their sizes are too small compared to the vast interstellar distances involved.


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