<p><a href="http://arxiv.org/pdf/astro-ph/0111290v1.pdf" rel="nofollow noreferrer">Thommes et al. (2001)</a> ran simulations and found that, at optimal conditions (namely, a planet of ~ 10 Earth masses), migration can be complete with ~ 100,000 years. Note that this was done before in-depth research was done on the Nice model, which is very similar. However, the mechanisms are different, as are the planet masses. The difference in timescales is dramatic.</p>

<p><a href="http://arxiv.org/pdf/0712.0553v1.pdf" rel="nofollow noreferrer">Levison et al. (2007)</a> did explore their own model - the Nice Model. They found that it took 60 million years to 1.1 billion years for Jupiter and Saturn to break their resonance. The period of encounters and scattering lasted for 878-885 million years, followed by a period of eccentricity damping lasting for 0.3 million years to 4 million years.</p>

<p>What <em>was</em> relatively quick was the ejection of the hypothetical 5th giant planet. The change in the other giants' orbits, however, was not.</p>

<p>So yes, planetary migration on this scale takes a long time. A very long time.</p>

<hr>

<p>For some <em>really</em> interesting results, see the graphs of semi-major axis vs. time from the various four-, five-, and six- planet models of <a href="http://arxiv.org/pdf/1208.2957v1.pdf" rel="nofollow noreferrer">Nesvorný  &amp; Morbidelli (2012)</a>. There are some incredible oscillation among the orbits of Uranus and Neptune in some of the simulations, which is eventually slowly damped.</p>

<blockquote>
  <p><img src="https://i.sstatic.net/7juYg.png" alt="">
  <br>
  Fig. 14.— Orbit histories of the giant planets in a simulation with five initial planets. See the caption of Fig. 1 for the description of orbital parameters shown here. The five planets were started in the (3:2,3:2,2:1,3:2) resonant chain, M<sub>disk</sub> = 20 M<sub>Earth</sub> and B(1). The fifth planet was ejected at $t =$ 6.1 Myr after the start of the simulation.</p>
</blockquote>

<p>There's another relevant passage, if you're looking at setups with six giant planets:</p>

<blockquote>
  <p>The instability typically occurred in two steps, corresponding to the ejection of the two planets. Sometimes, as in Fig. 18, the ejection of the two planets was nearly simultaneous, but most of the times there was a significant delay between ejections. This was useful because the first planet’s ejection partially disrupted the planetesimal disk and reduced its capability to damp e55, which was then excited by the second planet’s ejection. While this mode of
  instability can be important, we would need to increase the statistics (>100 simulations for each initial condition) to be able to properly resolve the small success fractions in the six-planet case.</p>
</blockquote>

CC BY-SA 3.0
2016-01-24T09:18:12.613Z
Did Neptune move outwards during one single orbit which happened to enter some "gravitational keyhole" available during the time of the Jupiter and Saturn resonance? Or did it migrate slowly during thousands of orbits? Once the orbit changes, I suppose that a repeat encounter becomes less likely. Spacecrafts often use one engine burn, or gravity assist, to increase eccentricity and another burn to circularize the orbit. Neptune cannot have done that.
LocalFluff
CC BY-SA 3.0
2016-01-24T15:49:24.300Z
@LocalFluff It was over many orbits. The graphed results of semi-major axis vs. time from the various four-, five-, and six- planet models of [Nesvorny & Morbidelli (2012)](http://arxiv.org/pdf/1208.2957v1.pdf). Show the outer ice giants exhibiting orbits that oscillate slightly in their semi-major axes over millions of years after the ejection(s), slowing down very slowly. Figure 14 shows an interesting example of this. So even the initial movements took many orbits.
HDE 226868
CC BY-SA 3.0
2016-01-24T01:02:22.847Z
2016-01-25T15:48:16.560Z
2016-01-25T15:48:16.560Z
HDE 226868
<p>Current models of the configurations of the planets conclude that Neptune once migrated outwards. AFAIK this refurbishment came about by Jupiter and Saturn gradually getting into and leaving a gravitational resonance.</p>

<p>Did Neptune (and possibly a fifth giant planet) redirect itself in a sudden encounter event, like comet 67P Churyumov–Gerasimenko did in 1959, halving the perihelion of its orbit since then? Or did it happen gradually over maybe millions of years? Is planetary migration in general sudden or gradual? Is it a matter of a single encounter event, or an adaptation to a changing gravity landscape?</p>

CC BY-SA 3.0
2016-01-23T20:04:21.230Z
[A simulation of one variant of the Nice Model](https://www.youtube.com/watch?v=VXeOh3xmrQM) shows things happening relatively quickly.
HDE 226868
CC BY-SA 3.0
2016-01-23T20:15:29.693Z
@HDE226868 But did it happen during one single (inevitable) passage coincidence? Or did it grow as slowly as mountains speed towards the sky.
LocalFluff
CC BY-SA 3.0
2016-01-23T20:24:49.080Z
Models predict that there was an encounter with Saturn that swung the 5th gas giant towards Jupiter, and another encounter with Jupiter that flung it away. There were then secondary effects as the remaining four gas giants interacted with one another. I couldn't tell you the timescales off the top of my head, though.
HDE 226868
<solar-system><gravity><planetary-formation><orbital-migration>
Do planets migrate suddenly or gradually?
LocalFluff
# Do planets migrate suddenly or gradually?

(Asked by: username_0 on 2016-01-23)

Current models of the configurations of the planets conclude that Neptune once migrated outwards. AFAIK this refurbishment came about by Jupiter and Saturn gradually getting into and leaving a gravitational resonance.

Did Neptune (and possibly a fifth giant planet) redirect itself in a sudden encounter event, like comet 67P Churyumov–Gerasimenko did in 1959, halving the perihelion of its orbit since then? Or did it happen gradually over maybe millions of years? Is planetary migration in general sudden or gradual? Is it a matter of a single encounter event, or an adaptation to a changing gravity landscape?

**Tags:** solar-system, gravity, planetary-formation, orbital-migration

> **Comments:**
> **username_1**: [A simulation of one variant of the Nice Model](https://www.youtube.com/watch?v=VXeOh3xmrQM) shows things happening relatively quickly.  
> **username_0**: @username_1 But did it happen during one single (inevitable) passage coincidence? Or did it grow as slowly as mountains speed towards the sky.  
> **username_1**: Models predict that there was an encounter with Saturn that swung the 5th gas giant towards Jupiter, and another encounter with Jupiter that flung it away. There were then secondary effects as the remaining four gas giants interacted with one another. I couldn't tell you the timescales off the top of my head, though.  

---

## 1 answers

### Answer by username_1 on 2016-01-24. Score: 6

[Thommes et al. (2001)](http://arxiv.org/pdf/astro-ph/0111290v1.pdf) ran simulations and found that, at optimal conditions (namely, a planet of ~ 10 Earth masses), migration can be complete with ~ 100,000 years. Note that this was done before in-depth research was done on the Nice model, which is very similar. However, the mechanisms are different, as are the planet masses. The difference in timescales is dramatic.

[Levison et al. (2007)](http://arxiv.org/pdf/0712.0553v1.pdf) did explore their own model - the Nice Model. They found that it took 60 million years to 1.1 billion years for Jupiter and Saturn to break their resonance. The period of encounters and scattering lasted for 878-885 million years, followed by a period of eccentricity damping lasting for 0.3 million years to 4 million years.

What *was* relatively quick was the ejection of the hypothetical 5th giant planet. The change in the other giants' orbits, however, was not.

So yes, planetary migration on this scale takes a long time. A very long time.

---

For some *really* interesting results, see the graphs of semi-major axis vs. time from the various four-, five-, and six- planet models of [Nesvorný & Morbidelli (2012)](http://arxiv.org/pdf/1208.2957v1.pdf). There are some incredible oscillation among the orbits of Uranus and Neptune in some of the simulations, which is eventually slowly damped.

> ![](https://i.sstatic.net/7juYg.png)
>   
> Fig. 14.— Orbit histories of the giant planets in a simulation with five initial planets. See the caption of Fig. 1 for the description of orbital parameters shown here. The five planets were started in the (3:2,3:2,2:1,3:2) resonant chain, Mdisk = 20 MEarth and B(1). The fifth planet was ejected at $t =$ 6.1 Myr after the start of the simulation.

There's another relevant passage, if you're looking at setups with six giant planets:

> The instability typically occurred in two steps, corresponding to the ejection of the two planets. Sometimes, as in Fig. 18, the ejection of the two planets was nearly simultaneous, but most of the times there was a significant delay between ejections. This was useful because the first planet’s ejection partially disrupted the planetesimal disk and reduced its capability to damp e55, which was then excited by the second planet’s ejection. While this mode of
> instability can be important, we would need to increase the statistics (>100 simulations for each initial condition) to be able to properly resolve the small success fractions in the six-planet case.

> **Comments:**
> **username_0**: Did Neptune move outwards during one single orbit which happened to enter some "gravitational keyhole" available during the time of the Jupiter and Saturn resonance? Or did it migrate slowly during thousands of orbits? Once the orbit changes, I suppose that a repeat encounter becomes less likely. Spacecrafts often use one engine burn, or gravity assist, to increase eccentricity and another burn to circularize the orbit. Neptune cannot have done that.  
> **username_1**: @username_0 It was over many orbits. The graphed results of semi-major axis vs. time from the various four-, five-, and six- planet models of [Nesvorny & Morbidelli (2012)](http://arxiv.org/pdf/1208.2957v1.pdf). Show the outer ice giants exhibiting orbits that oscillate slightly in their semi-major axes over millions of years after the ejection(s), slowing down very slowly. Figure 14 shows an interesting example of this. So even the initial movements took many orbits.  

---

