Working out a planet's attributes

undormant · 2012-03-25 12:18:26

Hi there,

I am new to this forum, well, I used to post last year before the forum went down but can't access that account now since I have changed my email address etc. I used to be Rokku, a bit of a lurker and Terraforming is my fave section of discussion.

There isn't really a good section to put this in so I'll ask for advice here if that's ok.

I am trying to write a novel and am having trouble working out the planets attributes. If anyone can tell me if I have any details wrong on a technical level can they please help me out and let me know?

I've had this discussion with some other people and we have so far come to the conclusion that:

It has a 30 hour day (an hour being the same length as one of our hours by the way) and takes 400 Earth days to go around it's sun therefore in the Goldielocks zone.

It has very similar amount of ocean percentage-wise and a very similar axial tilt.

We agreed that if Purple was twice the size of Earth but I wanted Earth-like gravity that Purple would have to be 4 times as dense as Earth materials-wise. I'm not sure what this translates as when talking about mass.

All of that kind of makes sense to me. It's when adding moons it gets a bit more complicated. Purple has 4 moons, all twice the size of our moon, they have gravity of about the same as Earth, therefore they have an Earth similar mass(?). As a sidenote they are all like Earth in terms of oceans and atmosphere etc. I guess the main question is: Can Purple hold 4 moons of this description in orbit without much trouble?

Ok so I had the moons as being Circumference (equatorial) 20,000 km and again with Earth gravity on the surface. Our Moon is about 10,000 km so willing to go down to that if it makes it work. Willing to go to 0.8 Earth gravity maybe.

The moons would be tidal locked to Purple like our system, I would want the moons to line up so they appear slightly behind each other at all times, but that would require moon 2 to be moving faster than moon 1, and moon 3 to be moving faster than moon 2 etc not sure that's natural.

I need the gravity on all bodies to be Earth-like, but I need the physical size of these bodies to be as stated, is it mathematically possible?

Hope someone can help. Thank you for your patience!

R

karov · 2012-03-25 13:57:05

http://www.transhuman.talktalk.net/iw/Geosync.htm

undormant · 2012-03-26 09:15:58

That's useful as the Roche Limit is interesting, but is there a law or mathematical equation whereby I can figure out if a body can hold another body in orbit?

R

karov · 2012-03-26 14:36:43

Hill radius / sphere. Wiki or google for it.

Terraformer · 2012-03-29 12:38:19

Is this planet natural, or artificial? If the former, you're constrained by what can actually happen.

undormant · 2012-04-07 01:08:11

Well in this story the planet is natural and it's moon have been captured by technology.

However, if I write a natural system it would be useful to know it's limits.

R

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#1 2012-03-25 12:18:26

Working out a planet's attributes

#2 2012-03-25 13:57:05

Re: Working out a planet's attributes

#3 2012-03-26 09:15:58

Re: Working out a planet's attributes

#4 2012-03-26 14:36:43

Re: Working out a planet's attributes

#5 2012-03-29 12:38:19

Re: Working out a planet's attributes

#6 2012-04-07 01:08:11

Re: Working out a planet's attributes

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