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.
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?
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.)
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.
[1] https://www.nasa.gov/solar-system/asteroids/asteroid-fast-fa...