Phobos is spiralling inward

[PB666]

https://earthsky.org/space/mars-moon-phobos-slowly-falling-apart

.02 meter per year at a distance 6000 km means that in 300,000,000 [corrected] years mars and phobos will collide. Make a long story short. I'm relatively certain it will make more than a poof of dust.[at least on phobos]

Mars, colony, not so wise.

Ok, so the question of course is how.

Edited November 11, 2015 by PB666

[peadar1987]

https://earthsky.org/space/mars-moon-phobos-slowly-falling-apart

.02 meter per year at a distance 6000 km means that in 300,000 years mars and phobos will collide. Make a long story short. I'm relatively certain it will make more than a poof of dust.

Mars, colony, not so wise.

Ok, so the question of course is how.

How what? How is it spiralling inwards? Tidal interactions, as it orbits more quickly than Mars rotates, Mars is constantly robbing it of orbital velocity and converting it to its own rotation

[Steel]

.02 meter per year at a distance 6000 km means that in 300,000 years mars and phobos will collide

Your maths is out by a factor of 10^3. It's actually 300,000,000 years. But equally Phobos will hit the Roche limit much sooner (a quick estimate puts that around 25,000,000 years from now) than that and then to all intents and purposes just becomes a cloud of orbital debris.

Edited November 11, 2015 by Steel

[sgt_flyer]

Once phobos will get through the roche limit, it will break apart. once it has broken apart, all those fragments will slowly drift apart (as they will be on slightly different orbits), creating a small asteroid belt around mars, until those fragments themselves impact mars's ground. Of course, if we ever build some colony on mars, it would be better to build nothing under Phobo's orbital path - as that's where the impacts will occur (unless we can find a way to stabilise phobos orbit before it's ripped apart by mars's gravity.)

Still, if we ever manage to create a huge colony on mars, it'll mean we'll have develloped some proper interplanetary mean of travel - so phobos would likely be heavily prospected for materials for things such as in orbit construction

[KerbMav]

I think a colony on Mars should be built near the poles anyway ... more ice nearby, "thicker" atmosphere, i.e. more atmosphere between the colony and the Sun due to inlination ... ?

[More Boosters]

I think a colony on Mars should be built near the poles anyway ... more ice nearby, "thicker" atmosphere, i.e. more atmosphere between the colony and the Sun due to inlination ... ?

And even less sunlight.

[KerbMav]

Always a catch ...

[PB666]

Your maths is out by a factor of 10^3. It's actually 300,000,000 years. But equally Phobos will hit the Roche limit much sooner (a quick estimate puts that around 25,000,000 years from now) than that and then to all intents and purposes just becomes a cloud of orbital debris.

thanks, it did seem like to coincidentally soon.

At what point does phobos start disrupting objects on the surface such as landslides and rock falls? or Not.

Edited November 11, 2015 by PB666

[magnemoe]

Anyway, changing Phobos orbit is trivial compared to teraforming mars.

[SpaceK]

Even if your computation was right, that would not disqualify a Mars colony. 300000 years ago, homo sapiens did not even exist, and homo erectus (maybe) just began controlling fire. It's unlikely that we couldn't do anything against a random captured astroid trying to hit our then-highly developed cities on one of the core planets of our interstellar empire in 300000, especially since we have some good ideas on how to reroute an asteroid already today (I'm not sure if homo erectus seriously considered colonizing Mars).

If our species survives, that is.

[Steel]

At what point does phobos start disrupting objects on the surface such as landslides and rock falls? or Not.

Even by the time it hits the Roche limit (which is ~5000 km) the force on objects on the surface will not be noticeably more than it is today, so it shouldn't be a problem

[Hcube]

Ahem i'm afraid 6000km/0,02m per year is 3*10^8 years and not 300,000 years. OP was off by just 3 orders of magnitude...

I'm pretty sure that in 300,000,000 years from now, humans (or what will be left of humans) will have other kinds of problems

[SargeRho]

I don't think Phobos is much of a threat to a Martian colony. Since it's going to crash, mine it away before it does?

[Tex_NL]

https://earthsky.org/space/mars-moon-phobos-slowly-falling-apart

.02 meter per year at a distance 6000 km means that in 300,000 years mars and phobos will collide. Make a long story short. I'm relatively certain it will make more than a poof of dust.

Mars, colony, not so wise.

Ok, so the question of course is how.

Since when is this new? Somebody probably ran out of topics and decided to revive this. It has been known for decades Phobos' orbit is unstable.

What's next? Oh no, our moon is slowly drifting away! What happened? What can be done about it? Well, you better get used to it. Our moon has been drifting away for millions of years and nothing can be done about it to prevent it.

Edited November 11, 2015 by Tex_NL

[r4pt0r]

Once phobos will get through the roche limit, it will break apart. once it has broken apart, all those fragments will slowly drift apart (as they will be on slightly different orbits), creating a small asteroid belt around mars, until those fragments themselves impact mars's ground.

This is something that has confused me. why wouldn't the bits stay coalesced, shouldn't their combined mass draw enough gravity to keep them together?

Or is this sort of like a way smaller scale event horizon sort of thing, and they are getting essentially spagettified, because Mars pulling them apart is stronger than the weak pull of the separate bits?

[Robotengineer]

Why not Nuke-It-Nowâ„¢?

[PB666]

Since when is this new? Somebody probably ran out of topics and decided to revive this. It has been known for decades Phobos' orbit is unstable.

What's next? Oh no, our moon is slowly drifting away! What happened? What can be done about it? Well, you better get used to it. Our moon has been drifting away for millions of years and nothing can be done about it to prevent it.

Well you almost got there, but you could have explained precisely why phobos is spiralling inward and the moon is spiraling outward.

[Steel]

This is something that has confused me. why wouldn't the bits stay coalesced, shouldn't their combined mass draw enough gravity to keep them together?

Or is this sort of like a way smaller scale event horizon sort of thing, and they are getting essentially spagettified, because Mars pulling them apart is stronger than the weak pull of the separate bits?

If their combined mass kept them coalesced then they wouldn't have been ripped apart in the first place. The tidal force beyond the Roche limit is strong enough to overcome the bodies own gravity and so the resulting pieces are spread due to differences in their orbits

[r4pt0r]

If their combined mass kept them coalesced then they wouldn't have been ripped apart in the first place. The tidal force beyond the Roche limit is strong enough to overcome the bodies own gravity and so the resulting pieces are spread due to differences in their orbits

ahh, ok I think I understand that

[Hcube]

Well you almost got there, but you could have explained precisely why phobos is spiralling inward and the moon is spiraling outward.

I'm not sure but i'd say it's because Phobos orbits Mars faster than Mars rotates and the Moon orbits the Earth slower than the Earth rotates. I just eyballed that on a sheet of paper with tidal forces and it seems reasonable. I'd like to know wether i'm completely wrong, so if someone can confirm.... ^^

[pincushionman]

This is assuming, of course, that we don't just intentionally crash Phobos before we even start, so it's out of the way and we can use Deimos as a tether for a space elevator.

[Rakaydos]

This is assuming, of course, that we don't just intentionally crash Phobos before we even start, so it's out of the way and we can use Deimos as a tether for a space elevator.

Go Kevlar space elevater! dont need no nanotubes on mars.

[Kerbart]

Even by the time it hits the Roche limit (which is ~5000 km) the force on objects on the surface will not be noticeably more than it is today, so it shouldn't be a problem

I have no clue how celestial body disintegration works, but I'm betting dollars to doughnuts that it's not this scenario:

• Monday: Phobos is still there
  
• Tuesday: where once was Phobos is now a ring of debris around Mars

I interpret the Roche limit as “under this limit the planet will no longer exist†but I suspect that as Phobos is approaching the limit it's already starting to shear and perhaps breaking up in large pieces?

[Steel]

I have no clue how celestial body disintegration works, but I'm betting dollars to doughnuts that it's not this scenario:

• Monday: Phobos is still there
  
• Tuesday: where once was Phobos is now a ring of debris around Mars

I interpret the Roche limit as “under this limit the planet will no longer exist†but I suspect that as Phobos is approaching the limit it's already starting to shear and perhaps breaking up in large pieces?

The Roche Limit is just the threshold whereby the larger body's gravitational tidal forces become stronger than the forces holding the smaller body together. Obviously for a non-uniform body with a non-negligible size the effects of these tidal forces will be seen before or after the limit, but its a good indication of the rough distance that the body will cease to be a body any more.

Because Phobos is so non-uniform getting a good idea of when it will break up is difficult, if we look at this NASA article there seems to be evidence that the process of disintegration is already starting.

[Findthepin1]

I wonder if when humans attempt to land on Phobos, the whole moon just shatters when somebody puts the flag down.