Question about PHA's

[Pgdome]

Good Day:

I recently joined so pardon any already covered topics. I have a question regarding potentially hazardous asteroids that was prompted by my nephew (14) who is contemplating becoming an astronomer or cosmologist. He tends to get worked up and overly focuses on PHA's as they could potentially impact earth that are typically listed on numerous sites. I've tried to explain to him that there is an astronomically low chance for these objects to strike earth and there is a specific definition of these objects that classify them such as size, speed and the percentage of AU from earth. I informed him that most of these objects, at their nearest approach, are millions of km's away. He of course responded that why do scientists classify them as potentially hazardous if they are so low risk. Which prompts this question, in light of PHA's having a specific definition, what would make these PHA's that are many lunar distances away from earth, potentially become truly hazardous? Would it be due to potential collisions with other objects not seen? Or does the Sun and its activity have the potential to affect the object's trajectory? Or a variable orbit? I'm really curious myself and after some reading could not establish any particular reason that would impact trajectory but also something to relay to my nephew that has an overactive imagination and looks at too much clickbait online. Thanks in advance. 

[MinYoongi]

2 hours ago, Pgdome said:

Good Day:

I recently joined so pardon any already covered topics. I have a question regarding potentially hazardous asteroids that was prompted by my nephew (14) who is contemplating becoming an astronomer or cosmologist. He tends to get worked up and overly focuses on PHA's as they could potentially impact earth that are typically listed on numerous sites. I've tried to explain to him that there is an astronomically low chance for these objects to strike earth and there is a specific definition of these objects that classify them such as size, speed and the percentage of AU from earth. I informed him that most of these objects, at their nearest approach, are millions of km's away. He of course responded that why do scientists classify them as potentially hazardous if they are so low risk. Which prompts this question, in light of PHA's having a specific definition, what would make these PHA's that are many lunar distances away from earth, potentially become truly hazardous? Would it be due to potential collisions with other objects not seen? Or does the Sun and its activity have the potential to affect the object's trajectory? Or a variable orbit? I'm really curious myself and after some reading could not establish any particular reason that would impact trajectory but also something to relay to my nephew that has an overactive imagination and looks at too much clickbait online. Thanks in advance. 

Because they could potentially be brought off their course which would make an impact theoretically more likely.
 

[Pgdome]

Thanks for the response, so the potential is there to be brought off course through interacting with another object or could solar dynamics play a part as well? 

[Archmonoth]

On 11/6/2021 at 6:54 AM, Pgdome said:

Good Day:

I recently joined so pardon any already covered topics. I have a question regarding potentially hazardous asteroids that was prompted by my nephew (14) who is contemplating becoming an astronomer or cosmologist. He tends to get worked up and overly focuses on PHA's as they could potentially impact earth that are typically listed on numerous sites. I've tried to explain to him that there is an astronomically low chance for these objects to strike earth and there is a specific definition of these objects that classify them such as size, speed and the percentage of AU from earth. I informed him that most of these objects, at their nearest approach, are millions of km's away. He of course responded that why do scientists classify them as potentially hazardous if they are so low risk. Which prompts this question, in light of PHA's having a specific definition, what would make these PHA's that are many lunar distances away from earth, potentially become truly hazardous? Would it be due to potential collisions with other objects not seen? Or does the Sun and its activity have the potential to affect the object's trajectory? Or a variable orbit? I'm really curious myself and after some reading could not establish any particular reason that would impact trajectory but also something to relay to my nephew that has an overactive imagination and looks at too much clickbait online. Thanks in advance. 

Your nephews imagination sounds bright, awesome of you to encourage their learning and investigation of solar activity!

 

Perhaps this helps: In my imagination asteroids are like dust bunnies, full of ice and loosely gathered stones from other impacts. Their density is very low, and can be shaped like pancakes or icicles. They are likewise as flimsy; they fall apart if you put them in water, or a gust from a solar flare perturbs them. If they are heavy enough they will fall towards the Sun, and the journey is like a river, full of turns and bends, smashing up against the sides of gravitational currents from moons and planets. 

 

The Sun eats about 3000 asteroids a year, and sometimes the heavier ones become comets with regular orbits, avoiding the Sun by a small degree. 

 

The solar systems has been spinning for quite some time, so many of the dust bunnies have already been cleared away, leaving only the dust balls which dwell in shadows of gravitational pits from planets, or simply too far from the Sun to be disturbed easily. 

 

Your nephew might be correct and an asteroid could hit us, but the frequency of such an occurrence might be hundreds of millions of years apart, since something significant needs to disrupt the tranquil chandelier which is the current asteroid belt. 

 

Anyways, the dust bunnies are attracted to larger masses like Jupiter and the Sun, and if they get close to earth, the Moon will generally clear them away before reaching Earth. 

 

I hope this helps with your nephew!

[Drax Spacex]

I was surprised to learn just how many PHAs there are.    But there may be more soon as I would expect an increase in demand for public housing to provide decent and safe rental housing for eligible low-income families, the elderly, and persons with disabilities.  Healthy single people are on their own.  There are approximately 1.2 million households living in public housing units, managed by some 3300 PHAs.

Since PHA is not in https://www.spaceweatherlive.com/en/acronyms-and-abbreviations.html, it would be helpful to the casual forum reader to define what PHA means either in the topic name or in the first post.

Edited November 8, 2021 by Drax Spacex
Snarkiness

[Pgdome]

Yeah sorry about that, I meant to highlight definition I provided at the beginning of the post but didn't associate the reference.  Think the terminology came from a specific Astronomy site while doing research. Thanks everyone for the responses, much clearer understanding and was able to communicate it over Thanksgiving. Thanks again.