The gravitational pull on such and object would only differ between Mars and Earth very close up and for an object moving at 20k/s, that is not many seconds to accelerate it. There is also the point that Earth has a very dense atmosphere which would actually tend to slow down such a body (as well as heating it up) while Mars has a very thin atmosphere. Also as I have pointed out before, with just a third of the gravity, material ejected into the air will go far higher and stay in the air far longer. Mars has a density of 3.9 compared to Earth's 5.5 (that of water), allowing that Mars is also believed to have an iron core. The 23% difference will be cancelled by the softer surface of Mars, allowing for more damage by an impact.
Asteroid to hit Mars
- Thread starter Orleander
- Start date
The gravitational pull on such and object would only differ between Mars and Earth very close up and for an object moving at 20k/s, that is not many seconds to accelerate it. There is also the point that Earth has a very dense atmosphere which would actually tend to slow down such a body (as well as heating it up) while Mars has a very thin atmosphere. Also as I have pointed out before, with just a third of the gravity, material ejected into the air will go far higher and stay in the air far longer. Mars has a density of 3.9 compared to Earth's 5.5 (that of water), allowing that Mars is also believed to have an iron core. The 23% difference will be cancelled by the softer surface of Mars, allowing for more damage by an impact.
Janus58. I never cared a lot for poetry. Often just a difficult way of telling us what we already know. Pope made a number of generalisations which are quite idiotic when read on their own :
Amusement is the happiness of those who cannot think.
Fools admire, but men of sense approve.
Man: the glory, jest, and riddle of the world.
Our passions are like convulsion fits, which, though they make us stronger for a time, leave us the weaker ever after.
Amusement is the happiness of those who cannot think.
Fools admire, but men of sense approve.
Man: the glory, jest, and riddle of the world.
Our passions are like convulsion fits, which, though they make us stronger for a time, leave us the weaker ever after.
Two points: Can you explain why you believe/ know that the density of water is 5.5 and what units you are using.
How "more damage" would not meam a larger crater. You have just claimed that you never said the crater on mars would be larger than that on earth
Janus58
Valued Senior Member
Either planet will start effecting the asteroid once it enters the planet's Gravitational Sphere of Influence( that region where the planet's gravitational effect exceeds that of the Sun's.)
For the Earth, the radius of this sphere is 927,000 km and for Mars, (on average) 577,000 km. (even though Mars has only 1/10 the mass of the Earth, it is (on average)50% further from the Sun, which drops the Sun's gravitational pull to 43% of that at the Earth's orbital distance.
Traveling at the estimated initial 12.5 km/sec that the astreroid will have relative to Mars, it will spend a little under 13 hrs being accelerated by Mars' gravity, and would spend a little under 21 hrs being accelerated by Earth's gravity before impact.
Janus58
Valued Senior Member
Just for the fun of it, I figured out how accurate they have to be in predicting the asteroid's trajectory in order to get that 4% chance of impact.
As I mentioned in the last post, once the asteroid enters Mars' GSI, Mars will begin to effect its trajectory. This give the asteroid a little larger target to hit. If the asteroid's initial trajectory when entering the GSI would cause the asteroid to miss Mars by a small enough margin, Mars' gravity will dflect the trajectory into an impact.
In this particular instance, the asteroid could "miss" Mars by 400 km and still impact it.
This means that the asteriod has to "hit" a cross section with an area of 4467483 km² to result in an impact. If there is a 4% chance of the asteroid hitting this cross section, then the the range of error in the asteriod's position when it reaches Mars is +/-18,800 km.
As I mentioned in the last post, once the asteroid enters Mars' GSI, Mars will begin to effect its trajectory. This give the asteroid a little larger target to hit. If the asteroid's initial trajectory when entering the GSI would cause the asteroid to miss Mars by a small enough margin, Mars' gravity will dflect the trajectory into an impact.
In this particular instance, the asteroid could "miss" Mars by 400 km and still impact it.
This means that the asteriod has to "hit" a cross section with an area of 4467483 km² to result in an impact. If there is a 4% chance of the asteroid hitting this cross section, then the the range of error in the asteriod's position when it reaches Mars is +/-18,800 km.
5.5 (that of water), as in 5.5 times that of water. You can't leave some people any opening here.
I have given reasons a number of times why I thought the an impact on Mars would produce a larger crater than the same impact on Earth.
Janus58. At those extreme distances, I think we are talking about if the asteroid is floating around that area for a few months or so we would see the effect of this gravity pull. If something is moving at 20 kms/sec, Earth is moving at 18 km/sec and Mars about 16 km/sec, I think the object is going to have to be close in before we notice any effect on it. The atmosphere itself could do serious damage to such an object as it gas pockets inside reacting with explosive force, even blowing some small objects up into smaller objects.
Also parasitic drag on any debris lofted by the impact is less in the Martian atmosphere. This doesn't affect displacement but it does affect the propagation of impact debris, mainly how far it is dispersed from ground zero and how much falls back into the resultant crater.
Sorry, got you wrong on the crater. But you must accept that 5.5( that of water) suggests that water has a specific gravity 5.5. Also it is unnecessary to mention water at all because, unless stated otherswise , it is implicit in the definition of density/specific gravity.
Janus58
Valued Senior Member
I've crunched the numbers. For an asteroid with an inital relative speed of 12.5 km/sec (the estimated relative speed of this particular asteroid upon reaching the region of Mars) Mars' gravity would add 1km/sec additional velocity and Earth's gravity would add an additional 4km/sec. The additional velocity is due to the accumulated effect of each planet's gravity, from the time the asteroid enters the GSI until impact.
BTW, the Earth's orbital speed is 30 km/sec and for Mars 24 km/sec. The relative velocity of the asteroid WRT to Mars is due to the difference between its oribital velocity and Mars'. Since the asteriod is "coming up from behind" Mars, so to speak, the relative veloicty is less than either of the two's orbital velocities.
Janus58
Valued Senior Member
This has nothing to do with the actual size of the crater, only how far the material ejected from the crater will travel.
You can't make that generalization. "Less dense" does not equal "softer". (For example, of the two, diamond is much less dense than lead and is also much harder than lead.) The hardness of the Martian surface would have more to do with its chemcial make-up than its density.
Janus58. I'm old enough to still think in miles but kilometres are used in many cases. I forgot to convert the miles into km for orbital speeds.
Mars is said to have an iron core too but has a far lower overall density than Earth. This despite lots of metal oxides on it's surface.
I doubt that much diamond would form on the surface of Mars. Diamond is hard as it is because of pressure on it, so forms lower down, so not relevant here.
Mars is said to have an iron core too but has a far lower overall density than Earth. This despite lots of metal oxides on it's surface.
I doubt that much diamond would form on the surface of Mars. Diamond is hard as it is because of pressure on it, so forms lower down, so not relevant here.
your not working for NASA are you? :bugeye:
Heh..
Janus58
Valued Senior Member
Whoever said anything about diamonds existing on Mars? It was simply an example that density and hardness do not go hand in hand.
Neither did I dispute that Mar's crust is less dense than the Earth's. Estimates place it around 70-75% of that of the Earth's. But it is also estimated that Mars' crust is more rigid than the Earth's.
The point being that you can not use density as a reliable gauge of how the surface will react to an impact.
Enmos
Valued Senior Member
Kind of like Lead vs Aluminum.
how acurate would this be
http://janus.astro.umd.edu/astro/impact/
http://janus.astro.umd.edu/astro/impact/