Mars' moons

[BibleBeliever]

A quick google search told me that:

 

"Mars' moons were discovered in August of 1877 by Asaph Hall at the US Naval Observatory using the large 26-inch Alvan Clark refractor. "

 

So How did Jonathan Swift in his book 'Gullivers Travels' published in 1726 have this to say about them...

 

"They have likewise discovered two lesser stars, or satellites, which revolve about Mars; whereof the innermost is distant from the centre of the primary planet exactly three of his diameters, and the outermost, five; the former revolves in the space of ten hours, and the latter in twenty-one and a half; so that the squares of their periodical times are very near in the same proportion with the cubes of their distance from the centre of Mars; which evidently shows them to be governed by the same law of gravitation that influences the other heavenly bodies." Page 108 of the Gutenberg eBook

 

I have heard that the earth, many years ago, was on a 360 day orbit and Mars was on a 520 day orbit, and that every 52 years (if I remember correctly) Mars came so close to earth that it caused some major disruptions thereby getting the name 'Mars God of war" If this was true then could the two moons have been seen with the naked eye?

 

I'm not trying to imply anything, I just found it interesting and wondered if any of you had read similar things or could point out where the information I have is wrong.

 

Thanks.

[Michaelangelica]

Good question

 

Remember Swift was a satirist. He could have been sending up the Science of the time?

It's fair to say that Kepler had an unusual aptitude for seeing patterns, to the extent that he sometimes saw patterns that weren't even there

(as witness his perception that the planets were arranged in accord

with the dimensions of circumscribed Platonic solids).

A good example is that when he learned of Jupiter's four moons, andcompared this with

the Earth's one Moon, he concluded that Mars must have two moons (by

the geometrical progression 1,2,4...).

 

This suggestions seems to

have been taken up by other people, including Voltaire and the English

author Jonathan Swift, whose Gulliver's Travels (written in 1726)

contains the remarkable description of the astronomical prowess of

the fictional Laputan astronomers:

Galileo's Anagrams and the Moons of Mars

[BibleBeliever]

Fair enough, and the information he wrote about the position and revolution of the moons is just junk?

 

Is there any evidence for the old orbit of earth?

[CraigD]

Fair enough, and the information he [swift] wrote about the position and revolution of the moons [of Mars] is just junk?

I wouldn’t call it junk, but fiction. Swift never seriously claimed that the fanciful places and people he wrote about actually existed.

 

In this case, his fiction happened to agree with the actual number of satellites of Mars, but his orbital distances were wrong: He gave distances of 3 and 5 Mars diamaters, while the actual distances are about 1.4 and 3.5. He showed good knowledge of Kepler’s third law, though, which, IMHO, made him a pretty good science educator for his day. ;)

[CraigD]

Is there any evidence for the old [360 day] orbit of earth?

To the best of my knowledge, there’s little evidence, either empirical (fossils, etc) or theoretical, that the Earth’s orbital period has significantly increased, decreased, or stayed the same in during the last 4.5 billion years. Before that, current best theory holds that Earth was more a loose swarm of rubble than a recognizable planet.

 

Theoretically, as the Sun loses mass due to fusion and the solar wind (at a rate of about 5200000000 kg/s, or 0.0000000000000001%/year. For this to have resulted in an increase in the Earths orbital period from 360 to 365.25 (1.4%) would thus have taken 14 million billion years, 300000 times the age of the Earth, so such a change can’t be accounted for as due to the Sun’s steady loss of mass.

 

Orbital mechanics are complicated, though, with the giant planets shifting a lot of mass around in ways that can affect themselves, one another, and the inner planets. This is so complicated that even the best computer models can only simulate many very different but possible orbital histories, not determine which one actually occurred.

 

So, until some clever person discovers a way of directly observing the solar system’s distant past or measuring the length of an Earth year using some archeological means, all I think we can about the history of large changes in the Earth’s orbital period is “we don’t know”.

[Tormod]

every 52 years (if I remember correctly) Mars came so close to earth that it caused some major disruptions thereby getting the name 'Mars God of war"

 

This definitely is not true. The distance between Mars and the Earth was at it's minimum in 2003 - after 60,000 years.

 

Astronomers Ready for Close Encounter of a Mars Kind

 

At such a distance the graviational impact from Mars is not even measurable from Earth.

 

The Moon isn't that much smaller than Mars, but it is much closer (only about 380,000 kilometers away) and it's impact on the earth is only enough to cause tidal stress and lunatics. ;)

[BibleBeliever]

Thanks for the reply's, Like I said it was something I heard and I wanted to see how close it was to the truth. You've helped a lot.

[Chacmool]

Here is an interesting consideration of whether Earth's year was once 360 days long. It is presented in the form of a trial, where you get to make the final decision.

[Pyrotex]

...Is there any evidence for the old orbit of earth?

One can test the reality of the concept that "once upon a time" Mars orbit was so close to Earth's that it caused disasters on Earth by the following logic.

 

First, how close would Mars have to come to Earth to cause detectable troubles? The Moon at 1/4 million miles gives us large tides. Mars at (very) approximately 16 times the mass of the Moon, could cause the same tides at 4 times the distance, say, 1 million miles. If you want earthquakes and such, then Mars would have to come much closer. But let's take 1 million miles.

 

Planetary orbits are fragile and delicate structures. They last so long (to our minds) and seem so permanent because nothing much happens in our solar system, other than the occassional comet or asteroids, and they have insignificant masses compared to, say, the Moon.

 

A close pass of one million miles by Mars, would radically alter the orbits of both planets. Very likely, one or the other would be slung out of the solar system forever, or at the very least, shot out on a very elongated elliptical orbit, similar to those of comets.

 

In other words, if it ever happened at all, it could happen only ONCE, and would leave the solar system totally unlike what we observe now.

[Janus]

One can test the reality of the concept that "once upon a time" Mars orbit was so close to Earth's that it caused disasters on Earth by the following logic.

 

First, how close would Mars have to come to Earth to cause detectable troubles? The Moon at 1/4 million miles gives us large tides. Mars at (very) approximately 16 times the mass of the Moon, could cause the same tides at 4 times the distance, say, 1 million miles. If you want earthquakes and such, then Mars would have to come much closer. But let's take 1 million miles.

At 6.42e23 kg, Mars is more like 8.7 times the mass of the moon.

For tides equal to those of the Moon, Mars would have to be about 2.05 times the distance of the Moon, as tidal forces decrease by the cube of the distance.

 

Planetary orbits are fragile and delicate structures. They last so long (to our minds) and seem so permanent because nothing much happens in our solar system, other than the occassional comet or asteroids, and they have insignificant masses compared to, say, the Moon.

 

A close pass of one million miles by Mars, would radically alter the orbits of both planets. Very likely, one or the other would be slung out of the solar system forever, or at the very least, shot out on a very elongated elliptical orbit, similar to those of comets.

 

In other words, if it ever happened at all, it could happen only ONCE, and would leave the solar system totally unlike what we observe now.

 

Let's use your 1,000,000 mile(1,600,000 km) closest approach. Let's also assume a maximum deflection trajectory (a parabolic path). This means that Mars would be moving at escape velocity at closest aprroach. which is 0.5 km/sec at 1 million miles. That means that we can set our maximum change of relative velocity between Earth and Mars as 1 km/sec (it will actually be smaller, but we'll be generous).

 

this velocity change will be shared between the two planets, and since the Earth is a little over 9 times the mass of Mars, this means that Mars would undergo a change of 0.9 km/sec and the Earth 0.1 km/sec.

 

Maximum orbital change will occur when these velocity changes occur in the same direction as the planets present orbital velocities. How much orbital change does this result in?

 

For the Earth:

 

A gain of .1 km/sec will cause a gain of in the average distance from the Sun of about 2.3 million km. This might seem a lot, but it less than the Earth moves in and out from the Sun due to its present eccentricity of orbit.

 

Mars: For Mars, you first you need to determine what type of orbit will casue the close approach needed. It turns out that it is one with a perhelion at Earth orbit and aphelion at 163 million km or about 14 million km further than than Earth orbit.

 

Given this, you can determine that the 900 m/sec change in its velocity would result in a change of about 11 million km iin its average distance from the Sun

[Boerseun]

I have heard that the earth, many years ago, was on a 360 day orbit and Mars was on a 520 day orbit, and that every 52 years (if I remember correctly) Mars came so close to earth that it caused some major disruptions thereby getting the name 'Mars God of war"

To the best of my knowledge, Mars got named after the Roman god of war, because of its visibly red colour. Their perception of the planet reminded them of blood and gore, hence the name. Same with Mercury being named after the messenger of the gods, because of its swift orbit. There's a lot of poetry to be found amongst the planets.

[Pyrotex]

At 6.42e23 kg, Mars is more like 8.7 times the mass of the moon....Mars: For Mars, you first you need to determine what type of orbit will casue the close approach needed. It turns out that it is one with a perhelion at Earth orbit and aphelion at 163 million km or about 14 million km further than than Earth orbit....

Thanks Janus, for keeping me honest. I was doing order-of-mag estimates in my head , being too lazy to look up the numbers. You're right about the tidal forces ~ inverse cube.

 

Okay, 1,000,000 miles was too big, that's all. I should have used a "Calvin" orbit with a near-miss between Earth and Mars of 10,000 miles.

 

Yeah! That would shake things up! Wake up some shepherds! Sling-shot some planets! Bwahahahaha! :D :) :D :lol: :D

[jackson33]

the moon is thought to have formed, while the earth was at about a 14k mile orbit. either from part of earths mass of from its own. its also thought it has slowly increased this 24k mile orbit to its current 240k mile orbit, inching out each year. isn't it possible Mars formed much closer to earth and changed orbits as well. we both are heading the same direction with near the same speeds around the sun. wouldn't it be possible that at some point mars broke off any connection to the earth, slowing its speed to achieve the current orbit. the first billion or two of the solar system could have seen many planets or objects that fell into the sun or left the solar system.

 

infinite, i have no reference and offer as food for thought. not even opinion...

if i had time a good SF novel could be written, with the duel planets earth/mars, the intelligent life figuring out the split was eminent and moved their life form to the one, now called earth. looking forward to knowing how this couldn't have happened, say 200 mya...

[Janus]

Thanks Janus, for keeping me honest. I was doing order-of-mag estimates in my head , being too lazy to look up the numbers. You're right about the tidal forces ~ inverse cube.

 

Okay, 1,000,000 miles was too big, that's all. I should have used a "Calvin" orbit with a near-miss between Earth and Mars of 10,000 miles.

 

Yeah! That would shake things up! Wake up some shepherds! Sling-shot some planets! Bwahahahaha! :singer: :D :) :D

 

 

I've been crunching some numbers, and it looks like that even with a 10,000 "near miss" Mars would have be moving at nearly escape velocity(about 342 meters/sec shy of the 42426 km/sec) from the Sun to begin with in order to be ejected from the Solar system by a slingshot around the Earth.

 

The best actual gain of speed I found is at a deflection angle of 79° with a speed gain of 3.1 km/sec. This would result in an increase in the average orbital distance of about 39 miilion km.

 

These numbers seem about right when compared to the Galileo probe which needed two gravity boosts from the Earth and one from Venus to get to Jupiter. On one of those Earth boosts, it passed within 5000 miles of the Earth's center and got a boost of 4.4 km/sec.