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View Full Version : A Mars for a Moon?



RalofTyr
2007-Aug-30, 05:37 AM
What if Earth had a Mars for a Moon?

What is the largest sized moon and earth-like world can have?

tony873004
2007-Aug-30, 05:47 AM
If it was in the same orbit, tides would be greater. It would be a more interesting object for observers, especially if it were not tidally locked so it could display all its faces.

It would be a more interesting target for astronauts. Perhaps we'd already have colonies there. Perhaps it would have life since it would be closer to the Sun and hence warmer.

Earth would have a longer day.

Depending on your definition of moon, it would certainly have to be less massive than Earth, otherwise Earth would be the moon. I guess the common barycenter would still have to be beneath Earth's surface, as this was almost a criteria for considering Pluto a double planet.

mfumbesi
2007-Aug-30, 09:27 AM
......Perhaps we'd already have colonies there. Perhaps it would have life since it would be closer to the Sun and hence warmer.
........

If only it were so.
I am sure by now we would have fought Martians. In an moon planet war, Imagine that. Imagine the first close-up images of our Mars moon, with creepy crawly and the likes. I wonder what the Earth governments of the 50s and 60s cold would have done. Still land on Mars or not to interfere, assuming that the Martians were lagging in technology.
This is fun....It raises issues of what do we do if complex/intelligent life is found near-by (we can send a probe and so on) and its technically possible for us/probes to go there.

astromark
2007-Aug-30, 09:50 AM
I would sagest that the Moon, (now mars) would need to be a little further away from earth than the moon is now. Simply to maintain the Eco system as we know it. If the balance of distance and orbital velocity were right it would be a grand sight. Yes we would have most certainly been going there. Look at all the questions that spring to mind at this thought. The very nature of humanity is to want to know.

mugaliens
2007-Aug-30, 12:00 PM
Pluto's moon, Charon, is almost as big it Pluto is.

Radii:

Pluto: 1195 km
Charon: 603 km


I would sagest that the Moon, (now mars) would need to be a little further away from earth than the moon is now. Simply to maintain the Eco system as we know it. If the balance of distance and orbital velocity were right it would be a grand sight. Yes we would have most certainly been going there. Look at all the questions that spring to mind at this thought. The very nature of humanity is to want to know.

I wouldn't be so sure, particularly after tidal locking occurred, as the oceans would simply be predominantly tided towards Mars, so the only real tidal effect would be the Sun.

Just think, though - in order to achieve the same rotation, they'd have to be very close. This would create a normal day on one side of the Earth, and two "days" broken by a several hour dark period on the other.

Hobo
2007-Aug-30, 12:09 PM
What if Earth had a Mars for a Moon?

What is the largest sized moon and earth-like world can have?

The moon has one the size of earth, so the earth could probably have a much bigger one.

Ronald Brak
2007-Aug-30, 12:18 PM
If the moon becomes bigger than the earth than the earth is the moon.

If a mars sized object orbited earth then the double planet should be tide locked. This could make for long days.

astromark
2007-Aug-30, 07:34 PM
"Couldn't be so sure, particularly after tidal locking occurred, as the oceans would simply be predominantly tided toward Mars, so the only real tidal effect would be the Sun.

Just think, though - in order to achieve the same rotation, they'd have to be very close. This would create a normal day on one side of the Earth, and two "days" broken by a several hour dark period on the other.[/QUOTE]

This,. Can not be right. Have another look at the orbital mass and revisit your conclusion. The gravity of a Mars size Moon at a closer distance would be terminal. Tidal forces would be devastating.

hhEb09'1
2007-Aug-30, 08:31 PM
Pluto's moon, Charon, is almost as big it Pluto is.

Radii:

Pluto: 1195 km
Charon: 603 kmCharon has about an eighth the mass (half the radius, so cubed), so that's a little like saying a small child is almost as big as a linebacker. :)
This,. Can not be right. Have another look at the orbital mass and revisit your conclusion. The gravity of a Mars size Moon at a closer distance would be terminal. Tidal forces would be devastating.They seem to mean that they're tidally locked, so no significant tidal stress. If Mars were out a bit farther than the moon, the earth and Mars could be locked, the earth would have, what, forty-day or so days?