Small asteroid to hit Earth's atmosphere today
earthsky.org
earthsky.org
There are most likely hundreds of thousands to millions of a few meter sized asteroids flying around the inner solar system.
I did a large chunk of the numerical analysis in this paper: https://arxiv.org/pdf/2310.12918
I recommend figure 12 to get a sense of how far we can see at any given moment.
The definition which is commonly used as "hazardous" is about a 140m asteroid, which would cause a significantly bad day regionally, but not end civilization. That being said, 50m is still a very very bad day.
These meter-ish size ones usually just make a pretty fireball.
Some various links to data about this impact:
https://cneos.jpl.nasa.gov/sentry/details.html#?des=2024%20R...
Regarding a 100m asteroid impact:
> The pressure blast would destroy buildings up to 9 miles (15 km) from ground zero, and windows would shatter more than 60 miles away (100 km). To make matters worse, as the partially burned rock hit the ground, it would trigger seismic tremors that would spread through the planet's crust, carrying the destruction further away from the epicenter. The debris ejected into the air by the force of the impact would rain back on the ground miles away from the impact site, and the finer dust and dirt would remain hanging in the air, spreading with the wind across large distances.[3]
I can imagine a 140m asteroid causing a very, very bad day indeed for a region.
Not an expert, just curious and I can type stuff into a search engine.
[1] https://en.m.wikipedia.org/wiki/Tunguska_event
[2] https://en.m.wikipedia.org/wiki/Meteor_Crater
[3] https://www.space.com/asteroid-apocalypse-how-big-can-humani...
Definitely into science fiction territory here considering that DART resulted in a Δv measured in centimetres per second, but I'm still rather tickled by the idea of collecting a new moon for ourselves :)
Besides, why LEO? Even GSO is 11 times closer than the Moon.
Just to quantify the bad day scale: Tunguska[0] is estimated to have been 50-60m.
Can you suggest any beginner tools or resources for a layman to learn more about your field? I've taken an intro orbital mechanics course, solar system geology course and one on exoplanet detection and I'd like to keep the kinds of skills that I got from those courses fresh in my brain.
How do you recommend I do that?
Most of the state of the art in the field is algorithms from the 60s/70s, the classic software which many people use are packages like Mercury, written in either fortran or C++.
These factors are why I am attempting to release my code to the (small) community.
These are just random guesses though, so I could be completely wrong.
Velocity is important though.
A very rough calculation of mine involving a hypothetical asteroid in a elliptical orbit extending as far as Jupiter and right down to Earth, assuming no difference in orbital inclination to Earth and no significant gravitational perturbations, would result in a relative speed of 5km/s. The actual impact speed would be greater due to Earth's own gravity, adding an extra 11km/s.
Not all asteroids are from the asteroid belt, but I am under the impression that visitors from the outer solar system (which could be as fast as the upper bound that ddahlen mentions) are much more infrequent than stray asteroid belt objects, so the median impact speed would still be relatively slow.
Earth's orbital diameter is: ~30 x 10^7 km
number of seconds in a year is: ~ π x 10^7 s
so, Earth's orbital velocity is: ~30 km/s
speed of light, c, is: ~30 x 10^4 km/s
so, Earth's orbital diameter is: ~ 1,000 light seconds
and, Earth's orbital velocity is: ~ 0.0001 cJust doing some back of the envelope calculations, looks like Omuamua was moving about 165,000km/hr (relative to Earth) when it was about at Earths orbital distance.
This speed is not actually a crazy number, it is a lot faster than the majority of things which could hit us, but there are geometries of things in our solar system which can reach these relative velocities. (For example things in retrograde, IE: reverse orbits) can lead to basically escape velocity + earths velocity.
Looks like there is not a significant amount of variance in asteroid speed so mass would be the biggest deciding factor.
Tiny stuff burns up completely in the upper atmosphere, where the pressure is low, because they have low surface area per mass -- the atmosphere can stop them entirely. Their terminal velocity is low. (That is, when the velocity through air is high enough that the drag prevents gravity from speeding up the object any further.)
Medium objects have a higher terminal velocity get deeper into the atmosphere before exploding. Fragments from these (which now have higher surface area per mass) can then be slowed further by the atmosphere and make it to the surface, but not so dramatically. Bits of the Chelyabinsk impactor fall into this category.
Big objects have a high terminal velocity. They make it to the ground largely intact... and without being slowed as much by the atmosphere. That gives you craters and bad days for being a dinosaur.
https://en.wikipedia.org/wiki/The_Moon_Is_a_Harsh_Mistress
The moon colony uses this to win its freedom.
However, The Expanse is also a great book
For the first few seasons of the show I thought they did a good job, even though (or maybe because?) the show departs from the books in a lot of ways. But they tried to cram way too much into the last season and just made it seem like jibberish.
The delta-v required for a heavy asteroid may make it more practical to send a fleet of nukes though.
Example of it being different process: bullets are accelerated by gun powder, but stopped by various armor.
Example of increased dificulty: interception rockets have higher demands on speed and agility. (If somebody tries to evade, you have to be faster)
The problem of intercepting an asteroid heading towards you is exactly the same problem as intercepting an asteroid heading along any other orbit. Again, if you can redirect an asteroid, you can redirect an asteroid.
A more apt analogy would be a sword fight, where the counter to someone swinging their sword is swinging your own sword to redirect it.
Important limitation can be earlyness of detection, and equipment delivery/deployment speed, and redirection rate/speed.
Attacker could work with slow equipment deployment and redirection rate (maybe take years), but defender will need certain ratios between detection esrlyness and speedy deployment of equipment to start the deflection.
And if I’m mr Evil, I would pass the commet through some gravity assists to increase the speed - to bring the example closer to the bullet case.
In case it's not clear what I mean, one streak is greenish and the other is yellow/red. The triangle is black and one edge of it is colored red and seems to connect the centers of the streaks.
I'll take an educated guess:
(1) they are two different elevations
(2) they are essentially heatmaps of strike probability elongated because of the earth's rotation
(3) the triangle is a right triangle situated in a plane perpendicular to the earth's surface so that the red line indicates the angle.
It's funny that they'd have a strike location on the surface given that they said it won't hit the surface. But maybe it's a standard way to do the graphic, in which case it represents where it would strike if it were big enough even though it's not.
0: https://x.com/esa/status/1831307613205615044
1: https://x.com/esa/status/1831337534950924348The asteroid entered the atmosphere at a speed of approximately 11 miles per second (around 40,000 miles per hour) and burned up, creating a spectacular green flash visible to observers on the ground. Despite the cloud cover from Typhoon Yagi, the event was still visible and was captured on video by local residents.
This event marks only the ninth recorded instance of an asteroid being detected before it impacted Earth.
TIL. It seems like it's basically luck if someone is looking through a telescope in the right place at the right time?
NASA's Center for Near Earth Object Studies does a lot of neat work related to this. For example, Sentry [1], the NEOWISE mission [2], etc.
[1] https://indico.cern.ch/event/423169/contributions/1890157/at...
[2] https://ui.adsabs.harvard.edu/abs/2002SPIE.4845...13S/abstra...
[3] https://www.jpl.nasa.gov/missions/near-earth-object-surveyor
https://www.techbriefs.com/component/content/article/33153-q...
Their main telescope has a very large field of view (20 square degrees), and takes only 30 seconds per exposure, giving it many chances to get "lucky".
I would have a hard time believing "not at all".
Vaguely related this is my favorite amateur astronomer spotting accident ever, capturing supernova an hour before it happened which hasn't been done before:
https://www.popsci.com/amateur-astronomer-photographs-birth-...
makes me wonder when the sky becomes so difficult to see through if we are going to lose all that enthusiastic effort
Is this roughly the same for orbiting bodies? If so, it would seem that things on a collision course would be harder to detect, as they're indistinguishable from bodies far away that don't move. Possibly orbital mechanics change this significantly, but over the course of a few days the earth's trajectory is pretty much straight.
Some interesting stories about how these surveys work today and how they will work in ~10 years. Right now, it’s so rare to spot a weird thing in the sky that the alarms are all verified by grad students in graveyard shifts. When the new observatories come online, there won’t be enough grad students in the world :) so it’ll all be ML.
[impact streak cover some human infrastructures]
I get the odds of landing in someone roof are tiny in this rural area -probably smaller than meeting a grizzly in NYC- however I won't call a grizzly "harmless". Perhaps the panic induced by not calling it harmless would cause more harm.
https://www.nasa.gov/solar-system/asteroids/asteroid-fast-fa... https://physics.stackexchange.com/questions/47754/minimum-si...
> Space rocks smaller than about 25 meters (about 82 feet) will most likely burn up as they enter the Earth’s atmosphere and cause little or no damage.
(This one is 1m, so it's a pretty good margin.)
BTW, I was watching the meteors from the attic, where my dad had a music studio, so lots of transducers around. The radio waves theory from the article would make sense.
Note though, this will likely have a huge range of uncertainty on it, as 8 hours of observation is not a lot.
I have mixed feelings about this. One the one hand, I'm super excited that we can go from discovery to wide dissemination within a few hours. On the other hand, what's the chance of something like this happening with a much bigger asteroid.
Lower.
As size increases there are fewer bigger asteroids to begin with, and they are also easier to spot.
Bigger asteroids are easier to see.
another metric that affects the ... impact ... of such an event is also the speed of the asteroid. Unlike size, I suspect higher speeds would make it harder to spot (and once spotted there would be less time to take action)
Though warning times will be shorter the higher the relative speed is.
If we are only surveying a portion of the sky at a time and a faster asteroid spends less time traversing that portion, the likelihood of detection is lower.
Assuming you are not. What kind of "streak" you are thinking about? Are you thinking about comets with their tails? Or motion blur?
Because if motion blur I would expect an asteroid on a collision course to have none. (at least in the short timeframe before the collision) Because "Constant bearing, decreasing range" is how a collision looks like from a first person perspective.
(Of course, if it's going to hit you, the faster it's going, the more straight at you its path is at the same distance. But for the same amount of "not straight at you", faster leaves a bigger streak.)
The same as it's always been, which is to say you can live your life without worrying about it.
If our technology advances such that we can observe/find more and more of these, that doesn't affect the chances that a particularly sized asteroid hits the earth or not.
Maybe under classical rules, but we know know that the act of observation collapses the range of possible outcomes, potentially locking us into a collision by an asteroid that previously existed only as a probability cloud.
Everything of asteroid size, or on the Torino Scale [0] is in the realm described by classical mechanical physics, and it will merrily follow it's existing trajectory whether or not we know about it in advance.
So, the only question is whether or not it's better to know it's arriving some hours/days/weeks in advance.
* Certainly better in cases like this (observable but harmless).
* Definitely would be better in cases like the Chelyabinsk meteor [1] which caused a fair amount of damage and some injuries, if people would be given a warning to avoid being near windows, etc.
* Absolutely better in cases of regional devastation to global catastrophe where we have time and resources to alter the trajectory to reduce or eliminate harm. Even just enough lead time to only move many of the people out of the impact damage region is a definite benefit.
* YMMV in cases of in cases of regional devastation to global catastrophe where we lack time and resources to alter the trajectory or move people. Is it better to know you'll die in X hours or be surprised?
So, I'd say everything below Torino-5 is definitely a good discovery (I think this is a Torino-0], and everything above depends on circumstances. Overall, a very good idea.
In very simplified terms, say its roughly spherical, the amount of light grows with the second exponent, so twice bigger object reflect 4 times as much light - but it is also potentially 8 times as heavy (eq. volume grows with third exponent) & thus more dangerous.
Trade-offs. :)
That assumes that the detection is photon constrained and not "nobody is looking in most directions" constrained.
It doesn't matter even if the asteroid is carrying a lit magnesium torch if nobody is looking for it systematically.
I'm not saying that it is the case. In fact I'm asking: are we photon constrained or are we constrained by the rate we are scanning the sky?
[1] https://www.nasa.gov/solar-system/asteroids/asteroid-fast-fa...
Negligible. As I noted upthread, objects large enough to be do significant damage if they hit Earth and are on trajectories that could bring them close to Earth are routinely spotted years in advance.