City-killer' asteroid 2024 YR4 could hit the moon instead of us, scientists say

[Admin]

Asteroid 2024 YR4 has a 2.3% chance of hitting Earth in the year 2032. But according to new estimates, it may have an even smaller chance of hitting the moon instead.

City-killer' asteroid 2024 YR4 could hit the moon instead of us, scientists say : Read more

 

[Aldebaran5]

" about as wide as Walt Disney World's Cinderella Castle is tall"
What is the target audience of this article anyway? 12 year old girls?

 

[COLGeek]

" about as wide as Walt Disney World's Cinderella Castle is tall"
What is the target audience of this article anyway? 12 year old girls?

How many elephants is that? I can't find my decoder ring...

 

[Unclear Engineer]

Aw, come on - pity the poor journalist trying to make an analogy for a measurement in meters that U.S. basement-dwelling gamers can relate to. If it's not the size of a football field, there is probably a frantic Internet search for the dimensions of things that might be near the same size. But, maybe they could standardize on Rapunzel hair lengths, though.

 

[Classical Motion]

I think it is possible to disrupt earth with a moon asteroid collision. If it disrupts the smooth acceleration of our tides it could do great damage. If the collision effected the center of moon g, then our tide inertia will be upset. A phase change, might take months to smooth out.

It’s not a planet killer, but it could certainly say hello.

 

[billslugg]

Moon mass = 7.3e22 kg
Moon speed in its orbit = 986 m/s
Moon's kinetic energy before asteroid strike = 3.549e28
Diameter of 2024 YR4 = 100 m
Mass of 2024 YR4 = 2.4e9 kg
Impact speed of 2024 YR4 = 1.73e4 m/s
Kinetic energy of asteroid = 3.5e17

The kinetic energy of the asteroid is but 1 part in 1e11 of the Moon's. The change in speed of the Moon would shorten the lunar month by 24 microseconds. This is insignificant to our daily lives.

 

[Classical Motion]

That's assuming the Moon is solid. What if it's hollow? And you punch a hole in it? Or the innards fall out? What if it's pressurized? Or deflates.

My supposition about the Moon is not reference on this rock. If our Moon gets disturbed, it could cause great havoc here for us.

It might be impossible to live near ocean water without a moon.

That's all. Our Moon needs protecting too.

 

[Unclear Engineer]

I am not understanding why Billslugg is comparing kinetic energy instead of momentum.

Much of the asteroid's kinetic energy will be lost to heating of the materials, which is then radiated to space. Some of it might be turned into ejecta, which might push in a somewhat different direction from the impact direction, unless that happened to be straight "down". So, the kinetic energy is not going to be conserved in the Moon's orbital motion, anyway.

Assuming an "inelastic collision", the momentum of the asteroid would be added as a vector (direction as well as speed time mass) to that of the Moon. So, depending on where it hit the Moon, it might extremely slightly slow it down, speed it up or change its direction by an amount of speed determined by the ratio of their masses times the asteroid's speed of impact, which is a velocity change of only 5.6e-10 m/s that might go in various directions, depending on where the asteroid hit.

The Moon is currently averaging 986 m/s, [Bill's figure, which is not the same as Wiki's] so the change would be by only 5.8e-13 of the Moon's current velocity and might be plus or minus.

Without going into the orbital mechanics, the difference in the time that it takes the Moon to make one orbit of Earth could roughly change by 5.8e-13 x 29.53 days = 1.5e-6 seconds.

That slight of a change is simply not going to be noticeable on Earth, other than by extremely precise astronomical observations. Tides on Earth are not so regular, anyway. Winds and eddies in ocean currents change sea levels from place to place all of the time, compared to what they would be from purely astronomical influences. And the astronomical influences, including the tilts of the Earth's axis and the Moon's orbit relative to the plane of Earth's orbit around the Sun, plus the elliptical nature of the Moon's orbit and the Earth's orbit, combine in a manner that already produces net cycles with a period of about 18.6 years. See https://www.coastalwiki.org/wiki/Long-period_lunar_tides. And, that cycle is not precisely repeating, either.

So, life on Earth is already adapted to much larger changes in the tides.

 

[Classical Motion]

The earth has adapted to changing tides. And will. But as far as we know, we have always had that anchor.

What kind of tide pattern would result with no moon at all?

With the positions of the land, would a tide pattern EVER occur?

It might result in a continuous non pattern. Chaos oceans. With extreme currents.

 

[billslugg]

That's assuming the Moon is solid. What if it's hollow? And you punch a hole in it? Or the innards fall out? What if it's pressurized? Or deflates.

It doesn't make any difference what is inside the Moon, what shape it is or what it is made of. Its mass is measured by how long it takes an object to orbit it. If you want to challenge the mass number, I recommend you call NASA at 202-358-0001 and just rip them a new one.

 

[Classical Motion]

A displacement of mass can displace the center of gravity.

 

[billslugg]

Correct, mass distribution affects the CG, but CG is irrelevant to the mass calculation. For finding the change in speed, one can use either momentum or energy as both are conserved. I ignore losses to melting, etc.

 

[Clark]

" about as wide as Walt Disney World's Cinderella Castle is tall"
What is the target audience of this article anyway? 12 year old girls?

Yes, NASA's critical audience is children around the age of 10-12, as that is the age when kids are inspired. A prime opportunity to spark a lifelong interest in science, technology, engineering, and math (STEM) fields by engaging them with exciting space exploration concepts, potentially inspiring them to pursue careers in these areas later in life.

 

[Unclear Engineer]

Correct, mass distribution affects the CG, but CG is irrelevant to the mass calculation. For finding the change in speed, one can use either momentum or energy as both are conserved. I ignore losses to melting, etc.

Bill, I know we are talking about miniscule effects, but I think it is important to represent the physics correctly.

Although "energy is conserved" if you account for where it ends up, in several different forms, the total kinetic energy of the impactor is not all added to the kinetic energy of the Moon, The only way for kinetic energy to be added by other than momentum addition would be for ejecta from the explosion going faster than the lunar escape velocity so that its momentum creates an equal but opposite momentum effect on the mass of the Moon.

That was a significant factor in the DART experiment, mainly because the mass, and thus the escape velocity of the struck asteroid is so small that a lot of the asteroid's (very loosely bound) mass was ejected back along the path of the incoming impactor. Think of that as a rocket motor, with the energy coming from the impactor kinetic energy being turned into heat energy, which causes the "propellant" ejecta of gas, dust and rocks to shoot out at high speeds from the cavity formed by the impact.

But, in the case of the Moon, that is much less likely, because the Moon had much higher gravity, and most of the ejecta will not reach lunar escape velocity. And, the kinetic energy of the impactor that goes into the splat of ejecta in all directions more or less parallel with the Moon's surface will all impact the Moon's surface pretty quickly, turning its kinetic energy into heat and vibration energy of the Moon's surface and interior- having no effect on the speed of the Moon along its own orbital path. What impactor kinetic energy that does not add directly to the momentum of the Moon along its orbital path (or maybe make it rock a little from side to side - 'librate"), will escape the Moon as thermal energy being radiated back into space, perhaps very slowly. (Yes, emitting infrared photons in one direction will theoretically produce "thrust" too, but not enough for me to bother to calculate. If you want to calculate it, remember that those photons are emitted (roughly) isotopically into the hemisphere above the local surface of the impact location.)

 

[Unclear Engineer]

If you want to think about how asteroid impacts on the Moon might change its orbit, consider whatever made the South Pole-Aitkin Basin. From Wikipedia ( https://en.wikipedia.org/wiki/South_Pole–Aitken_basin ) :

"Simulations of near vertical impacts show that the bolide ought to have excavated vast amounts of mantle materials from depths as great as 200 km below the surface. However, observations thus far do not favor a mantle composition for this basin and crustal thickness maps seem to indicate the presence of about 10 kilometers of crustal materials beneath this basin's floor. This has suggested to some that the basin was not formed by a typical high-velocity impact, but may instead have been formed by a low-velocity projectile around 200 km in diameter (compare to the 10 km diameter Chicxulub impactor) that hit at a low angle (about 30 degrees or less), and hence did not dig very deeply into the Moon. Putative evidence for this comes from the high elevations north-east of the rim of the South Pole–Aitken basin that might represent ejecta from such an oblique impact. The impact theory would also account for magnetic anomalies on the Moon."

I would expect that type of event to have had some serious effects on both the Moon's rotation and its orbit, particularly a low-angle hit on the pole. But, it is thought to have occurred about 4.2-to-4.3 billion years ago. So, the Moon's current nearly circular orbit and tidally locked rotation seem to indicate that there is a tendency for such perturbations to get forced towards the parameters we see today. Perhaps the tilt of the Moon's orbit is a residual of such impacts? Hard to say, if the origin of the Moon is really due to a giant impactor on Earth throwing the material that made the Moon into orbit around the Earth.

 

[Classical Motion]

I believe I have a simulation that can show you another type of orbit. Instead of thinking of an ellipse, think of a one turn helix. A stretched out one turn helix is hard to see. And even harder when you close the helix.

But if you go to Wikipedia, “Orbit of the Moon”, scroll down to Precession, and look at Animation of Moon orbit around earth.

Watch it very closely.

Can you see it?

 

[Unclear Engineer]

Classical Motion, a circular orbit looks like a helical orbit if you change the frame of reference from one that is stationary on the center of mass of the object orbited to a frame of reference where the center of mass is in motion.

So, if you look at the orbit of the Moon around the Earth, with the Earth as the frame of reference, it looks circular. But, if you look at the orbit of the Moon as you watch the Earth orbit a stationary Sun, then the Moon's motion looks like a helix. (Flattened, because the plane of the Moon's orbit around Earth is only about 5 degrees different from the plane of the Earth's orbit around the Sun.)

 

[Dale Holley]

That's assuming the Moon is solid. What if it's hollow? And you punch a hole in it? Or the innards fall out? What if it's pressurized? Or deflates.

My supposition about the Moon is not reference on this rock. If our Moon gets disturbed, it could cause great havoc here for us.

It might be impossible to live near ocean water without a moon.

That's all. Our Moon needs protecting too.

Would've, could've, should've, don't worry about what might be till it's a fact

 

[Helio]

I found a NASA page that shows the trajectory margin of error....

https://cneos.jpl.nasa.gov/news/news210.html

The JWST will improve this range when it images it in March and May, IIRC.

The article states it is a level 3 on the Torino scale. [I thought this scale was replaced with another.]

 

[Helio]

Regarding the Torino scale, can someone explain what seems odd to me. I added a purple square to address what looks like an issue. What if an asteroid has an estimated KE of about 1E7 Mt and a probability estimate of about 1E-3?

The Tornio Scale would suggest it might be a 2 or a 6? How strange. The other scale numbers seem to make sense? Please correct me and I'll be happy to get another cup of coffee as my excuse.

 

[ChrisA]

I think it is possible to disrupt earth with a moon asteroid collision. If it disrupts the smooth acceleration of our tides it could do great damage. ...

And by your argument, if I stood on a sheet of newspaper I could see farther. Everyone knows that if you are taller you can see further, so the added height gained should help.

So yes an impact on the Moon should affect the tides but the amount is too tiny to measure and other effects, I think are larger, for example, Jupiter's gravity or a small breeze blowing offshore.

 

[Classical Motion]

I didn’t realize I was in an argument or a competition. As I stated my comment doesn’t refer to this particular rock. I was just submitting that if a collision happened on the moon it could very well effect earth. IF it disturbed the moon’s orbit. An asteroid doesn’t have to hit earth, to effect earth. That’s all. We are two targets. So change the probability.

Isn’t most of the comments here on the forum, … could have, should have, and would have?

Are these not science questions? It’s what we all suppose to. Could it? Should it? Would it?

Science.