How Does Earth Move Through Space?

[1dave]

I hope to be among those being "TWINKLED."

[RWA3006]

Ed, Dave, I've shared the same thoughts for a long time.

[Deleted]

...and now we find out that most all those solar system models we were shown in school were wrong - Venus is not Earth’s closest neighbor: Calculations and simulations confirm that on average, Mercury is the nearest planet to Earth—and to every other planet in the solar system. (OK, the orbits are still sort of correct, except that Mercury is nearer to us than Venus most of the time)

[parfive]

I'll gladly pay you Tuesday for a hamburger today.

[1dave]

As it turns out, by some phenomenon of carelessness, ambiguity, or groupthink, science popularizers have disseminated information based on a flawed assumption about the average distance between planets. Using a mathematical method that we devised, we determine that when averaged over time, Earth’s nearest neighbor is in fact Mercury.

That correction is relevant to more than just Earth’s neighbors. The solution can be generalized to include any two bodies in roughly circular, concentric, and coplanar orbits. By using a more accurate method for estimating the average distance between two orbiting bodies, we find that this distance is proportional to the relative radius of the inner orbit. In other words, Mercury is closer to Earth, on average, than Venus is because it orbits the Sun more closely. Further, Mercury is the closest neighbor, on average, to each of the other seven planets in the solar system.
Simple but wrong

To calculate the average distance between two planets, The Planets and other websites assume the orbits are coplanar and subtract the average radius of the inner orbit, r1, from the average radius of the outer orbit, r2. The distance between Earth (1 astronomical unit from the Sun) and Venus (0.72 AU) comes out to 0.28 AU. The table at the bottom of the article shows the calculated distance between each pair of planets using that method.

Although it feels intuitive that the average distance between every point on two concentric ellipses would be the difference in their radii, in reality that difference determines only the average distance of the ellipses’ closest points. Indeed, when Earth and Venus are at their closest approach, their separation is roughly 0.28 AU—no other planet gets nearer to Earth. But just as often, the two planets are at their most distant, when Venus is on the side of the Sun opposite Earth, 1.72 AU away. We can improve the flawed calculation by averaging the distances of closest and farthest approach (resulting in an average distance of 1 AU between Earth and Venus), but finding the true solution requires a bit more effort.
A better approach

To more accurately capture the average distance between planets, we devised the point-circle method. The PCM treats the orbits of two objects as circular, concentric, and coplanar. For our solar system, that’s a pretty reasonable assumption: The eight planets have an average orbital inclination of 2.6° ± 2.2°, and the average eccentricity is 0.06 ± 0.06. An object in a circular orbit maintains constant velocity, which means that over a sufficiently long period, it is equally likely to be in any position in that orbit. We consider a planet’s position at any given time as a uniform probabilistic distribution around a circle defined by the average orbital radius, as shown in figure 1a. The average distance between two planets can therefore be described as the average distance of every point on the circle c2, defined by r2, to every point on the circle c1, defined by r1.

Figure 1. (a) The uniform probabilistic distribution of two circularly orbiting bodies, with orbital radii r1 and r2. (b) Radial symmetry is used to simplify the average distance between the distributions.

Venus is on average 1.14 AU from Earth, but Mercury is a much closer 1.04 AU.

[1dave]

physicstoday.scitation.org/do/10.1063/PT.6.3.20190312a/full/media/sizes/full/figure5.png


Figure 7: Example of long-term evolution of the planetary orbits: Mercury (white), Venus (green), Earth (blue), Mars (red). Time is indicated in thousands of years (kyr). (a) In the vicinity of the current state, the orbits become distorted under the influence of planetary perturbations, but without allowing close encounters or collisions. (b) In about 1% of cases, the orbit of Mercury may be distorted enough to allow a collision with Venus or the Sun in less than 5 Gyr. (c) In one of the trajectories, the eccentricity of Mars increases sufficiently to allow for a close encounter or collision with Earth. (d) This leads to a destabilisation of the terrestrial planets that also allows a collision between Venus and Earth. Adapted from (Laskar and Gastineau, 2009)

[1dave]

www.skyandtelescope.com/astronomy-news/will-mercury-hit-earth-someday/

First, the bad news: the inner solar system is unstable. Given enough time, Jupiter's gravity could yank Mercury out of its present orbit.

Two new computer simulations of long-term planetary motion — one by Jacques Laskar (Paris Observatory), the other by Konstantin Batygin and Gregory Laughlin (University of California, Santa Cruz) — have both reached the same disturbing conclusion.

Says Laughlin, "The solar system isn't as stable as we'd thought." Both teams have found that Jupiter's gravity can increase Mercury's orbital eccentricity over time. Mercury's path around the Sun is already nearly as elliptical as Pluto's. But Jupiter can make Mercury's orbit so out of round that it overlaps the path of Venus. A close encounter between them could send the innermost planet careening off wildly.

"Once Mercury crosses Venus's orbit," Laughlin says, "Mercury is in serious trouble."

So is Earth.

At that point, the simulations predict Mercury will suffer generally one of four fates: it crashes into the Sun, gets ejected from the solar system, it crashes into Venus, or — worst of all — crashes into Earth.

To call this catastrophic is a gross understatement. Such an impact would kill all life on our planet. Nothing would survive. By contrast, the asteroid that doomed the dinosaurs 65 million years ago was likely just 6 miles in diameter; Mercury is 3,032 miles across. The last time an object about that size hit the Earth, the resulting debris formed our Moon.

Think we'll escape the chaos by fleeing to Mars? Think again. Even Mars might not be safe. In one of the computer simulations, the Red Planet was tossed into the cold of interstellar space.

Now, the good news: there's only about a 1% chance that Mercury will go crazy before the Sun bloats into a red giant billions of years from now. "If you're an optimist," says Laughlin, "then you say the glass is 99 percent full."

Laskar, who discovered that Mercury could go wild back in 1994, will publish his paper in Icarus; Batygin (who's still an undergraduate) and Laughlin will publish theirs in The Astrophysical Journal.

Ken Croswell is the author of a new book about the solar system, Ten Worlds: Everything That Orbits the Sun (Boyds Mills Press, 2007).

[HankRocks]

Mar 17, 2019 0:33:11 GMT -5 parfive said:

I'll gladly pay you Tuesday for a hamburger today.

 I yam what I yam and that's all what I yam

[susanwaring]

Feb 10, 2019 1:45:06 GMT -5 johnw said:

1dave  Hi Dave, this has been an interesting discussion and we have had some fine conversations to support  opinions on this basic of all questions  being "how did it all start." I have made my opinion on this subject known since it is what I can believe and make infinite sense of and "see" how it could be. Other people have  concepts and beliefs and so they should since each have their own path to follow. We could go on as long as we need, but since you started this thread and now want to end it. I believe it fitting that it end like so. 




                       Α Ω

[joshuamcduffie]

[1dave]

Feb 10, 2020 19:57:34 GMT -5 joshuamcduffie said:

FINALLY the truth leaks out.