Near Earth Asteroids

[Shadowy Man]

"Spiral" was a poor word choice. The point is that, with a very flattened trajectory relative to Earth (see attached screenshot from https://ssd.jpl.nasa.gov/tools/orbit_viewer.html ), a tiny change in initial conditions can introduce much uncertainty. Earth's own gravity will have an effect on the impact.

View attachment 49367

What do you mean by “very flattened trajectory”?

 

[Swammerdami]

"Spiral" was a poor word choice. The point is that, with a very flattened trajectory relative to Earth (see attached screenshot from https://ssd.jpl.nasa.gov/tools/orbit_viewer.html ), a tiny change in initial conditions can introduce much uncertainty. Earth's own gravity will have an effect on the impact.

View attachment 49367

What do you mean by “very flattened trajectory”?

At the time of (near) collision the asteroid's trajectory (i.e. orbit) will be very close to the Earth's trajectory/orbit. Therefore the speed at which the asteroid and the Earth approach each other will be quite small compared with their orbital speeds. This slow approach both amplifies the effect (relative to Earth) of imprecision in position AND gives the Earth's gravity more time to influence the asteroid's trajectory.

 

[Shadowy Man]

"Spiral" was a poor word choice. The point is that, with a very flattened trajectory relative to Earth (see attached screenshot from https://ssd.jpl.nasa.gov/tools/orbit_viewer.html ), a tiny change in initial conditions can introduce much uncertainty. Earth's own gravity will have an effect on the impact.

View attachment 49367

What do you mean by “very flattened trajectory”?

At the time of (near) collision the asteroid's trajectory (i.e. orbit) will be very close to the Earth's trajectory/orbit. Therefore the speed at which the asteroid and the Earth approach each other will be quite small compared with their orbital speeds. This slow approach both amplifies the effect (relative to Earth) of imprecision in position AND gives the Earth's gravity more time to influence the asteroid's trajectory.

Ok. I see what you’re saying. Just wasn’t familiar with that particular terminology.

Presumably with the orbital elements we could calculate the relative velocity at orbital intersection.

 

[Jimmy Higgins]

How much damage will occur if it misses the Earth, but we get clipped by the error bar as it passes? Perhaps Musk could heroically go out in person to cut the error bars off and hurl them into deep space.

Not much. That is what happened with the Tunguska Event.

 

[Elixir]

How much damage will occur if it misses the Earth, but we get clipped by the error bar as it passes? Perhaps Musk could heroically go out in person to cut the error bars off and hurl them into deep space.

First they go after the gay bars and now you want them to go after the error bars?
Let’s just go straight to prohibition!

 

[Bomb#20]

Unless it it already in earth orbit, which it is not, there’s no way a “spiral” is a descriptor of an incoming trajectory. It will basically be a collision of two objects orbiting the sun whose orbits intersect at a point. The earths gravity will have some effect on the incoming trajectory but at the speed it will be coming it wouldn’t have time for that to make large changes in its trajectory. At least that’s my intuition without running the numbers.

I think that's right, but here's the rest of the story. 2024 YR4 currently has a 4-year orbital period; it had close approaches in 2016 and 2020, and another is scheduled for 2028. But according to this NASA website, the most likely upcoming collision possibilities are in 2032, 2039, 2043, 2047, 2074, and 2079. The ones after 2032 aren't multiples of 4 years. So NASA is evidently expecting the earth's gravity to have a huge effect on the outgoing trajectory. It could reduce the orbital period by as much as six months.

 

[Shadowy Man]

Unless it it already in earth orbit, which it is not, there’s no way a “spiral” is a descriptor of an incoming trajectory. It will basically be a collision of two objects orbiting the sun whose orbits intersect at a point. The earths gravity will have some effect on the incoming trajectory but at the speed it will be coming it wouldn’t have time for that to make large changes in its trajectory. At least that’s my intuition without running the numbers.

I think that's right, but here's the rest of the story. 2024 YR4 currently has a 4-year orbital period; it had close approaches in 2016 and 2020, and another is scheduled for 2028. But according to this NASA website, the most likely upcoming collision possibilities are in 2032, 2039, 2043, 2047, 2074, and 2079. The ones after 2032 aren't multiples of 4 years. So NASA is evidently expecting the earth's gravity to have a huge effect on the outgoing trajectory. It could reduce the orbital period by as much as six months.

I admit to having little specific information. I was speaking generally about impacts/near miss scenarios, particularly addressing the word “spiral”, which has been rendered moot by swammerdami

 

[Elixir]

Unless it it already in earth orbit, which it is not, there’s no way a “spiral” is a descriptor of an incoming trajectory. It will basically be a collision of two objects orbiting the sun whose orbits intersect at a point. The earths gravity will have some effect on the incoming trajectory but at the speed it will be coming it wouldn’t have time for that to make large changes in its trajectory. At least that’s my intuition without running the numbers.

I think that's right, but here's the rest of the story. 2024 YR4 currently has a 4-year orbital period; it had close approaches in 2016 and 2020, and another is scheduled for 2028. But according to this NASA website, the most likely upcoming collision possibilities are in 2032, 2039, 2043, 2047, 2074, and 2079. The ones after 2032 aren't multiples of 4 years. So NASA is evidently expecting the earth's gravity to have a huge effect on the outgoing trajectory. It could reduce the orbital period by as much as six months.

As of February 10, 2025, the probability of asteroid 2024 YR4 impacting Earth on December 22, 2032, is 2.3%

That seems like a pretty significant chance.
I guess if we don’t look up …
If we add the chances of impact in the other 5 dates Bomb mentioned, are we above 10% yet?

 

[Shadowy Man]

Unless it it already in earth orbit, which it is not, there’s no way a “spiral” is a descriptor of an incoming trajectory. It will basically be a collision of two objects orbiting the sun whose orbits intersect at a point. The earths gravity will have some effect on the incoming trajectory but at the speed it will be coming it wouldn’t have time for that to make large changes in its trajectory. At least that’s my intuition without running the numbers.

I think that's right, but here's the rest of the story. 2024 YR4 currently has a 4-year orbital period; it had close approaches in 2016 and 2020, and another is scheduled for 2028. But according to this NASA website, the most likely upcoming collision possibilities are in 2032, 2039, 2043, 2047, 2074, and 2079. The ones after 2032 aren't multiples of 4 years. So NASA is evidently expecting the earth's gravity to have a huge effect on the outgoing trajectory. It could reduce the orbital period by as much as six months.

If it has a 4 year orbital period that means it orbits farther out on average than the earth. Which means that when it gets to earth it will be on a faster part of its orbit. I’ll have to look up the orbital elements to be able to calculate the speed when it’s at 1AU.

 

[Loren Pechtel]

The impact is estimated to have the energy of an 8 - 50 megaton H-bomb, though with little, if any, radioactive fallout. As the map posted by crazyfingers shows, the point of impact, if any, is tightly constrained. Many targets have high populations but limited financial or geopolitical value.

The map doesn't make any sense though. Why would there be so much east-west uncertainty and simultaneously so little north-south uncertainty? There has to be a story there. I'd bet on it being an artifact of the computer model they're using.

Because the uncertainty isn't equal in all directions. Astronomers are very good at measuring angles, very poor at measuring distance. Normally, over time as the Earth moves the distance number improves as they can pick the curve that makes sense.

In this case, it's probably not east-west uncertainty. Rather, it's time uncertainty and Earth is moving. They know where much better than they know when--will it pass in front, behind, or go smack?

 

[Loren Pechtel]

If they know the direction the asteroid is moving to a high degree of precision, but have more uncertainty about its speed (or its distance), then that would result in a projected impact whose location is determined by the rotation of the Earth, and whose probability of occurring is determined by Earth's movement along her orbit; Both of these vary by a FAR greater amount in the East-West direction than they do in the North-South direction.

Rotation??? Earth's rotation is on the order of 1 km/sec. Compared to the 30 km/sec of our orbit.

 

[bilby]

If they know the direction the asteroid is moving to a high degree of precision, but have more uncertainty about its speed (or its distance), then that would result in a projected impact whose location is determined by the rotation of the Earth, and whose probability of occurring is determined by Earth's movement along her orbit; Both of these vary by a FAR greater amount in the East-West direction than they do in the North-South direction.

Rotation??? Earth's rotation is on the order of 1 km/sec. Compared to the 30 km/sec of our orbit.

So what? The precise point of impact still depends on what part of the surface is pointing towards the incoming object when it arrives.

 

[Shadowy Man]

Ok, so according to the JPL Small Body Lookup website, Asteroid 2024 YR4 will have a relative velocity of about 13.5-14 km/s (~30,000 mph) at the potential impact on December 22, 2032.

The date, time, and distance from Earth will all be refined as more observations bring down the uncertainty in the ephemerides. If you look at my linked page you will see that the uncertainties are large at this time. Compare, say, to something like Apophis (2004 MN4), whose ephemerides uncertainties are multiple orders of magnitude smaller. On April 13th, 2029, Apophis will come within ~38000 km of Earth with a relative velocity of 7.4 km/s.

 

[steve_bank]

List of asteroid close approaches to Earth - Wikipedia

en.wikipedia.org

 

[Bomb#20]

I think that's right, but here's the rest of the story. 2024 YR4 currently has a 4-year orbital period; it had close approaches in 2016 and 2020, and another is scheduled for 2028. But according to this NASA website, the most likely upcoming collision possibilities are in 2032, 2039, 2043, 2047, 2074, and 2079. The ones after 2032 aren't multiples of 4 years. So NASA is evidently expecting the earth's gravity to have a huge effect on the outgoing trajectory. It could reduce the orbital period by as much as six months.

As of February 10, 2025, the probability of asteroid 2024 YR4 impacting Earth on December 22, 2032, is 2.3%

That seems like a pretty significant chance.
I guess if we don’t look up …
If we add the chances of impact in the other 5 dates Bomb mentioned, are we above 10% yet?

Not even close, The odds for all the other dates add up to about 1 in 100,000. (And according to the site's latest update 2074 is no longer a potential collision.)

Based on how erratic the pattern of potential collision dates is, it looks to me like NASA thinks by far the most likely scenario is that the 2032 interaction will alter the period of the orbit from its current exact resonance with Earth's orbit to some random-ass period like three years and 354 days, which means 2024 YR4 is going to take up repeatedly returning to the point where our orbits cross on dates other than Dec. 22, when the Earth gets there every year, which means we probably won't see it again for maybe a thousand years.

 

[steve_bank]

Events with very low probabilities do happen.

Tunguska event - Wikipedia

en.wikipedia.org

The Tunguska event was a large explosion of between 3 and 50 megatons[2] that occurred near the Podkamennaya Tunguska River in Yeniseysk Governorate (now Krasnoyarsk Krai), Russia, on the morning of 30 June 1908.[1][3] The explosion over the sparsely populated East Siberian taiga felled an estimated 80 million trees over an area of 2,150 km2 (830 sq mi) of forest, and eyewitness accounts suggest up to three people may have died.[2][4][5][6][7] The explosion is generally attributed to a meteor air burst, the atmospheric explosion of a stony asteroid about 50–60 metres (160–200 feet) wide.[2][8]: p. 178  The asteroid approached from the east-south-east, probably with a relatively high speed of about 27 km/s; 98,004 km/h (Mach 80).[2] Though the incident is classified as an impact event, the object is thought to have exploded at an altitude of 5 to 10 kilometres (3 to 6 miles) rather than hitting the Earth's surface, leaving no impact crater.[9]

 

[Swammerdami]

The asteroid 2024 YR4 has an orbital period of almost exactly 4 years and, moreover, is currently aligned to nearly collide with Earth once every 4 years. Furthermore its minimal distance to the Sun is not much less than 1 AU.

I can understand why those parameters made it so easy to detect: It came very close December 21. But is there some reason why NEOs with such orbits (year an integer multiple of Earth's year & perigee near Earth) are the most likely colliders? Is the prior orbit of the Tunguska asteroid known or guessable?

 

[bilby]

https://xkcd.com/3049

 

[Shadowy Man]

But is there some reason why NEOs with such orbits (year an integer multiple of Earth's year & perigee near Earth) are the most likely colliders?

is this a true statement? What statistics have you seen that suggest this?

 

[Elixir]

But is there some reason why NEOs with such orbits (year an integer multiple of Earth's year & perigee near Earth) are the most likely colliders?

is this a true statement? What statistics have you seen that suggest this?

If it is true, I’d surmise it’s that other orbits that cross earth’s, do so at greater angles to earth’s travel, giving them less time in or around earth’s orbital path.