Why "Potentially Hazardous" asteroids, and not just "Very Near Earth" asteroids?

I'm not clear on why these asteroids are considered, or at least *termed*, "potentially hazardous" objects, if they are known to not be on a collision course with the Earth. I thought maybe it was because when they are first discovered their trajectories can't be calculated precisely enough to say they're not going to collide, but then there are those that are discovered and have an initial trajectory known to be safe, but they're still put on the "potentially hazardous" list.

I understand that the term is given to objects coming within 0.05 AU (NASA), but why are they considered "potentially hazardous" if they have zero chance of hitting us, or sometimes of even getting close to any satellites? Why not just call them "very near Earth" objects, and dispose of the potential for misguided fear?

reply to post by 00nunya00

There isn't "zero chance".

This ``potential'' to make close Earth approaches does not mean a PHA will impact the Earth. It only means there is a possibility for such a threat. By monitoring these PHAs and updating their orbits as new observations become available, we can better predict the close-approach statistics and thus their Earth-impact threat.

neo.jpl.nasa.gov...

reply to post by 00nunya00


I guess because your "zero chance of hitting us" isn't quite zero.

For instance, the gravity of another large object might change it's trajectory slightly....

Peace

In Space... No one can hear you ask for directions...

they're like balls spinning around a bunch of whirlpools in a large cosmic tub, swaying this way and that.. coming to some equilibrium, but still at the right time, it can deviate.

it's inevitable we'll be hit. wonder if we'll be around to see it however.

reply to post by 00nunya00


The thing is that those objects constantly orbit the Sun, and their orbit can at times bring them very close to Earth. Like with the notable example of the Apophis asteroid, these close encounters can change the asteroid's orbit slightly, increasing the likelyhood of impacting the Earth. en.wikipedia.org...

Originally posted by operation mindcrime
reply to post by 00nunya00

 

I guess because your "zero chance of hitting us" isn't quite zero.

For instance, the gravity of another large object might change it's trajectory slightly....

Peace

Okay, so then what I'm getting at is, when we look at these "PHA"s like the 2012DA14 or whatever it is (coming in Feb, 0.06 LDs or whatever) and people start saying "there's no chance it's going to hit us, stop being a ninny over such a silly thing" then those people who are naysaying are the ones who are actually wrong, right? If even NASA can't say that they will, indeed, miss us, then why is there so much hate over people worrying about pretty close PHAs like the upcoming Feb one?

reply to post by 00nunya00

then those people who are naysaying are the ones who are actually wrong, right

Not exactly. The object will not hit us on its next close approach.
What may or may not happen next time around cannot be accurately enough calculated to rule out the possibility entirely.

Originally posted by Phage
reply to post by 00nunya00

 

then those people who are naysaying are the ones who are actually wrong, right

Not exactly. The object will not hit us on its next close approach.
What may or may not happen next time around cannot be accurately enough calculated to rule out the possibility entirely.

*Zero* chance of hitting us on the coming/current close approach? Okay, so then that means every object on there will have another approach of Earth at some time in the future?

reply to post by 00nunya00

That would be a fair statement.

reply to post by Phage


Right on, thank you for helping me understand this designation! (I'm glad you're back to your old avatar setup too, BTW; hang-glider Phage was just not right, for some reason, can't say why.)