34

First let's try to understand why planets migrate inwards. Planets are formed in a protoplanetary disk; a huge disk of gas and dust that accretes on to a newly forming star at the centre. Gravitational interactions between the planets and the gas in the disk play a very important role in planetary formation and evolution. As planets orbits within the disk, ...


11

What governs the Earth's orbital period is its orbital angular momentum and the mass of the Sun. Two events have certainly changed the Earth's orbital period (a) whatever collision formed the Moon and (b) the continuous process of mass loss from the Sun. A third possibility (c) is that tidal torques from the Sun have increased the angular momentum of the ...


8

There is no direct evidence of change of orbits of the gaseous planets of the Solar System. But one could wonder about the stability of the Solar System, and if such events could happen again. Theory: The Solar System is a chaotic system, as most of gravitational systems involving $N$ bodies. The KAM theorems (for Kolmogorov, Arnold and Moser, the three ...


8

I want to point out that the Moon's orbit isn't circular now. A 0.055 mean eccentricity isn't that circular. But, onto your question. I think you're making a bad assumption on the "must have started very elliptic. Individual objects that are ejected from a planet need to follow their orbital path. So any object flung from the earth would need ...


7

Since the very early solar system, there have not been large-scale movements of the planets. In the early solar system, while the planets were still embedded in a protoplanetary disk, there were large movements. (notably the hypothesised "Grand Tack" of Jupiter) However once Jupiter reached it's current position of 5.2AU it remained there, and the Earth ...


7

The current explanation for this is something called the frost line (which changes over time). At greater distances from the Sun, a body will receive less and less radiation, and so it will be colder than if it were closer to the Sun. Eventually, conditions become cold enough for volatiles to condense into grains. These volatiles make it possible for large-...


7

The solar system is chaotic, but it is also stable! The fixed and linkages between the bars of a double pendulum allow for very rapid energy transfer between the arms. This makes the chaotic motion develop rapidly. The interactions between planets are gravitational and much much weaker, moreover, the planets are heavier and it takes a lot more energy to ...


6

Thommes et al. (2001) 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 ...


6

I found an article by Ian O'Neill posted on May 2, 2008 at universetoday.com with the title Could Jupiter Wreck the Solar System? which says But here’s the kicker: There is only a 1% chance that these gravitational instabilities of the inner Solar System are likely to cause any kind of chaos before the Sun turns into a Red Giant and swallows Mercury, Venus, ...


6

Surely not a gas giant... Mercury is a rock of 0.05 $\rm m_{\oplus}$, such a mass could never grow into a gas giant (For detail see Piso & Youdin (2014), fig. 6, where you can see that below a planet mass of 5 $\rm m_{\oplus}$ the growth time of a significant atmosphere for a planet exceeds the lifetime of protoplanetary discs, i.e. is not possible). I ...


5

The configuration of the solar system is thought to have been more or less settled after the first 10-20 million years or so. However, what governs the Earth's orbital period is it's orbital angular momentum and the mass of the Sun. Two events have certainly changed the Earth's orbital period (a) whatever collision formed the Moon and (b) the continuous ...


5

Earth's orbital eccentricity varies over time from being nearly circular (low eccentricity of 0.0034) and mildly elliptical (high eccentricity of 0.058). It takes roughly 100,000 years for Earth to undergo a full cycle. In periods of high eccentricity, radiation exposure on Earth can accordingly fluctuate more wildly between periods of perihelion and ...


5

Definitely. In the early solar system, there were probably several more planets than there are today. Gravitational interactions between the planets caused some to be flung into the sun, while others were sent spiralling into the sun until it settled out into the more or less stable configuration we have today. With the Kepler spacecraft and other exoplanet ...


5

This is plausible, and might even be a good idea if used right. First off, NASA has been working on plans for an asteroid redirect mission, called ARM. While it remains to be seen whether this will be approved, and they plan to put it into lunar orbit, this is a hypothetical scenario anyways so I'll ignore that. Now, putting an asteroid into earth orbit is ...


5

As has already been said, the major sources of change to Earth's orbit are interactions with other planets and passing stars. We're ruling out mass loss of the Sun, so the next consideration is probably tidal interactions between the Earth and Sun. This paper suggests that the Earth is receding from the Sun by about 15cm/yr for this reason. This is 150 km ...


4

Yes, it's possible to have many nested levels, all stable. Each nested orbit needs to be inside the Hill sphere of its central body in order to be stable. You can't nest any further when the Hill sphere gets too close to the Roche limit. Below the Roche limit the satellite disintegrates. The exact number of nested levels depends very greatly on the ...


4

I am by no means an authority on this area but prompted by user /u/called2voyage I will refer the 1994 Astronomical Journal paper by Shahid-Saless (Colorado) and Yeomans (JPL) Relativistic Effects on the Motion of Asteroids and Comets. To paraphrase their abstract: They study the predicted effects arising from relativistic perturbations on the motions of ...


4

The primary driver of ice ages over the history of the Earth is much more Earth science than astronomy. The modern ice age cycle (last 2.6 million years or so) is only possible with relatively low levels of CO2 in the atmosphere and land masses near the North Pole where glaciers can form. Other factors in the modern ice age period are thought to be the ...


3

In a solar system model by Varadi Runnegar and Ghil Earth's inclination varies between 0 and about 0.05 radians (or about 3 degrees) The variation is rather chaotic, but you may note that there seems to have been a qualitative change in the pattern about 60-70 million years ago


3

Since the late heavy bombardment, the Earth's orbit couldn't have changed much. After all, life has been here ever since. Most scientists think that the answer to the faint young sun paradox is a thicker CO2 atmosphere and not the Earth being closer in. In earlier solar system history, the Earth may have been "shepherded" in by Jupiter when it migrated ...


3

Watched the video, and I thought it was really cool seeing the modeling of different young solar-systems. The orbital resonances they were talking about were for smaller objects that form debris fields in resonance with a giant planet. Since they only looked at models for the inner planets, the closest example to the bit in the video with our current ...


3

Exoplanets is an almost over populated field of research now, so yes they are monitored. But maybe not too much beyond what is needed to confirm their existence. I think you have to humble yourself in the enormity of time. There are some transient events in astronomy, but mostly, watching the sky is like watching a rock. Nothing much changes. Phoebes is ...


3

Kepler orbits apply only to 2-body systems. They apply only, if the masses aren't too large and the orbits aren't too close. Otherwise relativistic effects occur, as for the Sun - Mercury system. Kepler orbits only apply, if the bodies are sufficiently spherical. As soon as a third body comes into play, the system can become chaotic. Too many conditions, ...


3

In short, most of the trojans stay orbiting arround L4 or L5. These can be called tad-pole orbit asteroids. There are some trojan asteroids, however, that their orbit never get's too close to L4 nor L5 to get trapped and have a tad-pole orbit, or they do but they have too much energy to get trapped. These trojan asteroids have larger orbits, following a ...


3

This is unpredictable. The solar system is a chaotic system and it's long-term behavior can't be predicted. But it's also a very stable chaotic system and the planetary orbits have been stable for 4 billion years and will remain stable for some millions of years into the future. See the Wikipedia article for an overview. When we numerically integrate the ...


3

As pm-2ring already commented, the direction of the axis has a period of about 8.85 years. It's worth noting, though, that in reality the moon's orbit does not correspond very closely to an ellipse, because it is rather heavily perturbed by the Sun. Relative to this reality, the concept that the moon's orbit around the earth has a 'major axis' results ...


3

The direction of the semimajor axis of the Moon's orbit actually changes quite quickly. In fact it does a cycle around the ecliptic in approximately 8.85 years. This is known as the apsidal precession. That Wikipedia article also explains the Moon's nodal precession, the precession of the Moon's orbital plane, which has a period around 18.6 years (...


3

Dating the age of the asteroid belt is a problem that has to date no general solution. Rocks are usually dated in the laboratory via isotopical analysis. This is possible for meteorites, but what to do about those rocks that remain in space? Several methods to date the asteroid belt are known to me, apart from ad-hoc assumptions that it has the same age ...


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