Can comets create a microclimate crater on Mars 30km deep with 0.7bars?

[darkdave3000]

How wide does it need to be?
Is it structurally stable?
What is the temperature?
Does it mix well with the general atmosphere?
and many more…
It is a long list of questions.
Until you identify the “what,” “how” is not a high priority question.

I'm not God so I need your help to figure these things out. We are all in this together right? We all want to be able to live on Mars within our life time. I think it needs to be wide enough so the rim of the crater is not a threat the the settlement in the center of the crater. The temperature increases as you dig deeper into Mars so this should not be as big as a problem as the CO2 poinsoning, but I will get on my spreadsheet and give you a figure later. I have been ill this holiday season so not my self. Maybe you can help me come up with some of these answers that you have presented your self as im unwell.

 

[Frabjous]

I'm not God so I need your help to figure these things out. We are all in this together right? We all want to be able to live on Mars within our life time. I think it needs to be wide enough so the rim of the crater is not a threat the the settlement in the center of the crater. The temperature increases as you dig deeper into Mars so this should not be as big as a problem as the CO2 poinsoning, but I will get on my spreadsheet and give you a figure later. I have been ill this holiday season so not my self. Maybe you can help me come up with some of these answers that you have presented your self as im unwell.

There is much more HARD work required on YOUR part before people will begin to be drawn to you vision. Most of us already have Muses that we are following.

 

[darkdave3000]

How wide does it need to be?
Is it structurally stable?
What is the temperature?
Does it mix well with the general atmosphere?
and many more…
It is a long list of questions.
Until you identify the “what,” “how” is not a high priority question.

I found these two sources about the temperature on Mars, seems to me we want the impact crater to be close to the Equator and the crater should at least be temporarilly hotter than usual as soon as it's form. I expect it will cool off gradually over time.

"Surface temperatures may reach a high of about 20 °C (293 K; 68 °F) at noon, at the equator, and a low of about −153 °C (120 K; −243 °F) at the poles.[25] Actual temperature measurements at the Viking landers' site range from −17.2 °C (256.0 K; 1.0 °F) to −107 °C (166 K; −161 °F). The warmest soil temperature estimated by the Viking Orbiter was 27 °C (300 K; 81 °F).[26] The Spirit rover recorded a maximum daytime air temperature in the shade of 35 °C (308 K; 95 °F), and regularly recorded temperatures well above 0 °C (273 K; 32 °F), except in winter.[27]"

https://en.wikipedia.org/wiki/Climate_of_Mars

"If we look at Mars' possible geothermal gradient (see Earth's) which is about 25 °C per km. Using the low estimate of Mars's gradient to be 1/4 that of Earth's Source, that's a bit over 6° C per km. so 55 km, 330° C. Added that to Mars' average surface temperature of -55 C, you're talking 275° C or 527° F at 55 km underground, and that's a low estimate."

https://astronomy.stackexchange.com/questions/14875/what-is-the-temperature-55-km-beneath-the-surface-of-mars#:~:text=Using the low estimate of,and that's a low estimate.

 

[Vanadium 50]

This sounds like an invitation, in the words of Sheldon Cooper, "[for us] noble, semi-skilled laborers to execute the vision of those who think and dream."

But in any event, if you have the technology to move comets around willy-nilly, why do you you want them to dig impossible holes? Wouldn't it be simpler to have them provide the atmosphere in the first place?

 

[Rive]

So what if I moved an ice rock from the asteroid belt say a 20km diameter one and crashed it into Mars as slow as possible say 2km/s?

Comparing the difficulty of landing a 20km diameter asteroid at around half of the escape velocity and digging that hole - well, just digging it would be a lot less stressful.

For us too

 

[Drakkith]

Comparing the difficulty of landing a 20km diameter asteroid at around half of the escape velocity and digging that hole - well, just digging it would be a lot less stressful.

Dear god, the fuel requirements to move a 20km diameter comet are staggering.
That's about 4x10¹⁵ kg of mass. Just to get 1 m/s of delta-V using hydrolox (isp of roughly 400) you'd need 10¹² kg of fuel. That's a billion metric tons! And that's before calculating the fuel required to get that fuel to the comet! That would take roughly 40x more fuel!

Assuming you got the comet waaaaaay out in the outer solar system where it is moving slowly, you might only need 1000 m/s of delta-V or less to get it to where you want. That amount of delta-V would require roughly 1.2x10¹⁵ kg of fuel. That's 1000x more delta-V for more than 1200x more fuel (the tyranny of the rocket equation!)

I'm not sure how much delta-V you'd need to adjust a comet's orbit, as it depends on the orbital details of both the comet and the target, but let's say that you'd need a mass of fuel of AT LEAST 30% of the comet's mass. That'll give you about 1000 m/s, which is probably about the bare minimum you'd need unless you want to go waaay out past Neptune and Pluto to snag a comet. And then wait a few hundred years for it to get to your target.

 

[Rive]

Dear god, the fuel requirements to move a 20km diameter comet are staggering.

Any Sci-Fi plot (on the 'hard' side) involving planetary rearrangement of such calibre would use some other forms of engines than chemical: fusion drive or such, at the very least.

Still: once they have the tool they would rather carve that hole from above, than all that mess with smashing comets onto the surface and cleaning up all the rubble later on...

The whole topic (as seemingly intending to be serious) is just plain ridiculous.

 

[Vanadium 50]

the fuel requirements to move a 20km diameter comet are staggering.

Oh, you naysayers with your facts and numbers and equations. Bah!

 

[Drakkith]

So what if I moved an ice rock from the asteroid belt say a 20km diameter one and crashed it into Mars as slow as possible say 2km/s? The Asteroid Belt does not have as much potential difference in gravitational energy as compared to kuiper belt objects as you know so we should be able to manage a lower delta V in this case.

You are correct. Let's look as some numbers.

Let's first assume the icy object is in a near-circular orbit at 3.0 AU. Orbital velocity at this distance from the Sun is 17.2 km/s. To bring the periapsis down to intersect Mars' orbit, 1.66 AU or less, requires slowing the object down from 17.2 km/s to 14.5 km/s, for a delta V of 2700 m/s. Upon reaching Mar's orbit the object's velocity has increased to 26.1 km/s, compared to Mars' 22 km/s, a difference of about 4 km/s. Now, upon reaching Mars' sphere of influence the object will begin accelerating towards Mars, increasing its speed relative to Mars even more.

A slow moving object falling from the edge of Mars' sphere of influence gains about 4 km/s delta V. But our object is already moving at 4 km/s, so we wouldn't gain quite that much. Let's say 3 km/s. So now you have to slow your impactor down from 7 km/s to 2 km/s, a delta V of 5 km/s.

Added together, we need a total delta V of 2.7 + 7 - 2 = 7.7 km/s.

Now let's grab a comet from way out in the outer solar system. If you grab one whose periapsis is already within 1.66 AU, then you're in luck. You don't need to spend the delta V to slow it to bring its orbit down to meet Mars'. But let's look at that anyways. For an object in a near-circular orbit at 30 AU (Right around Neptune's orbit):
Speed: 5.44 km/s
Once we slow it down so the periapsis is at 1.66 AU:
Speed at apoapsis: 1.76 km/s
Speed at periapsis: 31.8 km/s
Mars' speed at apoapsis (where we want to intercept it): 22 km/s

So we need to spend about 3.68 km/s delta V to slow it down and our intercept velocity is much higher. Assuming our object is whipping around and catching up to Mars from behind, that's a difference in velocity of almost 10 km/s. Add in another 2 km/s at least to account for when the object 'falls' to Mars inside the sphere of influence, and we're looking at 3.68+10+2 - 2 = 13.68 km/s of delta V if you want to crash a 20 km diameter icy object into Mars at only 2 km/s.

How much fuel would we need? Let's assume a 'perfect' rocket of negligible mass compared to the mass of the fuel and payload.

Case 1
Object from asteroid belt, mass 4x10¹⁵ kg:
Required delta V: 7.7 km/s.
Engine ISP: 450 (liquid hydrogen-oxygen engine)
Fuel mass: 19x10¹⁵ kg (19 petatons, or 19 million gigatons)

Engine ISP: 20,000 (DS4G ion engine)
Fuel mass: 160x10¹² kg (160 gigatons)

Case 2
Object from 30 AU, same mass as above:
Required delta V: 13.68 km/s
Engine ISP: 450
Fuel Mass: 84x10¹⁵ kg (84 petatons, 84 million gigatons)

Engine ISP: 20,000
Fuel Mass: 290x10¹² kg (290 gigatons)

Well, on the plus side, an ion engine cuts your fuel usage from 18x the mass of the object to about 0.05x the mass of the object.

*Note: I used apoapsis and periapsis instead of aphelion and perihelion because that's what I'm used to seeing, as I've played a lot of Kerbal Space Program and that's what they use. The -apsis words are generic and apply no matter what body you're orbiting.

I used this Delta-V calculator for all the delta V calculations and Universe Sandbox for the object's various velocities.

 

[russ_watters]

Any Sci-Fi plot (on the 'hard' side) involving planetary rearrangement of such calibre would use some other forms of engines than chemical: fusion drive or such, at the very least.

Still: once they have the tool they would rather carve that hole from above...

That's the plot of Star Trek.

No, the movie.

No, the other one.

 

[256bits]

The whole topic (as seemingly intending to be serious) is just plain ridiculous.

I thought @snorkack gave the answer in post #2?

 

[jrmichler]

So would raining down smaller ice rocks at slower speeds say a cluster of 20 x 1km diameter at 8km/s

This idea was used by Robert L. Forward in his SF novel Martian Rainbow. Since he specialized in hard science fiction, you might find that book a good read.

 

[DaveC426913]

As long as we're putting forward reading material for Areoforming, might I suggest Kim Stanley Robinson's Mars Trilogy?

He made a pit on Mars, but he simply dug it with autonomous excavation equipment. (A couple of big plusses with this method are: 1] technology is less advanced than moving comets around, and 2] that you don't have to wait centuries for the crater to cool and solidify.)