So, what would happen if a comet the size of our moon collided with Venus?

[psksvp]

Hello

what if a big comet(let's say, as big as our moon), made mainly of ice(95%), hit venus,

1) Would this change the orbit of venus, and if it did, would there be any effects on Earth and any other planets.

2) Would the atmosphere of venus changed, if yes, what would be the possibility of the changes.

psksvp

 

[Nereid]

Welcome to Physics Forums, psksvp!

An object as big (=mass) as the Moon hitting Venus would have a dramatic effect! And it wouldn't matter whether it was made of ice, rock, or iron (except for the fine details).

In some ways such an impact would be similar to that which we think created our own Moon - a Mars-sized object hit the early Earth, creating our present Earth and (after some time) Moon (it coalesced from the debris of the collision that didn't stay with the Earth or was ejected from the newly formed Earth-Moon system).

The extent to which the Venusian (or rather, the new Venus') orbit would be changed would depend on the details of the impact, especially on where is was coming from and how fast (and its mass, of course, but as you said 'as big as our moon', I assume this is fixed, at the mass of the Moon).

As for effects on other planets, well, any significant change in the mass of any planet, or orbit, will affect all the others' orbits. However, the effect would be minimal for the gas giants, and maximal for Mercury and Earth (and any Apollo, Aten, and Amor asteroids).

Perhaps the biggest effect on Earth would be the impacts of debris from the collision which ended up hitting us; the extent of such impacts would depend heavily on the details of the 'comet'-Venus impact (and the composition of the 'comet').

The atmosphere of Venus would be totally changed - it would get an entirely new atmosphere!

 

[varsha]

The atmosphere of Venus would be totally changed - it would get an entirely new atmosphere!

in what ways? it'll be because of the merging of a cold body(the comet's made of 95%of ice) with something hot(venus's atmosphere) right? any other ways?

and oh, welcome psksvp!

 

[psksvp]

What I am trying to guess is, with that much ice, there could be O2 produced as a result?? and about the orbit of Venus, what if the Venus's orbit get bigger after the collision, the gravitation field of Venus would effect the Earth??(My Guess would be the Earth's orbit get put out also).

Thank you.

psksvp

 

[varsha]

that's a possibility-effecting the orbit of the earth. but how do you say that O2 may be formed as a result of the merge?

 

[berkeman]

that's a possibility-effecting the orbit of the earth. but how do you say that O2 may be formed as a result of the merge?

I think he means all the O2 from the ice contribution and the heat of the collision.

 

[varsha]

ok...got it. any other changes in the atmosphere?

 

[psksvp]

My question was, with the conditions I've described, is it possible that O2 is produced?

 

[Nereid]

The atmosphere of Venus would be totally changed - it would get an entirely new atmosphere!

in what ways? it'll be because of the merging of a cold body(the comet's made of 95%of ice) with something hot(venus's atmosphere) right? any other ways?

Let's do a simple calculation ... what is the mass of a body, made of ice, with a diameter equal to that of the Moon? For simplicity, let's assume its density is 1 g/cc (=1,000 kg/m³). This is pretty simple to work out, right?

What is the mass of the Venusian atmosphere? We need some inputs; maybe http://zebu.uoregon.edu/~soper/Venus/atmosphere.html might help (the data are provided in a somewhat unusual form, but reasonably straight-forward to work out an OOM - order of magnitude - for the mass of the Venusian atmosphere, right?).

So, what % of the impactor (a Moon-sized ice comet - the difference between 100% and 95% is irrelevant, for our OOM calculation) would Venus need to retain, as atmosphere, for it equal the mass of the present-day Venusian atmosphere?

 

[Nereid]

What I am trying to guess is,

Let's not guess - how about we work it out, together?

with that much ice, there could be O2 produced as a result??

OK, so how does one get O₂ from H₂O? As berkeman said, somehow the energy of the collision dissociates the water into H and O, which somehow get separated sufficiently to prevent any significant recombination, right?

Well, there's no lack of energy to do the dissociation! I'd worry about the separation though - what could prevent all but a tiny fraction of the H and O from recombining?[qutoe]and about the orbit of Venus, what if the Venus's orbit get bigger after the collision, the gravitation field of Venus would effect the Earth??(My Guess would be the Earth's orbit get put out also).[/QUOTE]Again, let's not guess, let's do an OOM calculation!

"Venus's orbit get bigger" is pretty much the same as 'Venus gains angular momentum', or 'Venus gets some deltaV'. The best we could do would be if the impactor added as much deltaV to Venus as it could. How much would that be? Well, we have the mass of the impactor, the mass of Venus (we can look that up easily, right?), so all we need is the impactor's relative velocity. Let's assume it's directed in the best possible way (which is what? in the same direction as Venus is traveling in its orbit? opposite? orthogonal? something else??), and is as high as an incoming KBO could be (what I mean is, if you 'drop' an object, initially at rest wrt the Sun, from a distance of a typical KBO, how fast would it be going when it hit Venus?).

What are the equations that we need?

 

[varsha]

well, the mass of venus is about four-fifths that of earth.that is 4.86900x10 raised to 24 kilograms.
diameter of the moon is 3476 km.(got this from the net)
what we need is the relative velocity of the impactor as u said.