[Just thinking (OP)]

How are small meteors landing on the ground? There are a few reasons for this but first most meteors do not make it to the ground. Most often any meteor of a size ranging from the size of a grain of sand to around two meters in diameter would not get throw the atmosphere as they completely burn up and vaporize from the shear friction of our atmosphere. So how are they finding these small pieces of space rock one reason a small rock may be fond is due to the velocity that the rock made its entry the speed can vary from as slow as 3 hundred kilometres per hour to over 100,000 kilometres per hour. The lower end of these velocities is the ones that are most often found. For these smaller meteors to reach the ground they must make their entry at a very shallow angle just like a spacecraft will make it's re entry allowing it to slow down gradually in the thinner upper atmosphere. The chances of a meteor entering this very thin slice of the earth atmosphere is very slim as there is so much moor of the earth exposure for the meteors to enter with the results of total burn up. So a list of reasons for meteors making it to the ground. 1: meteor plays catch up and enters from the rear of earth orbit of the sun 2: meteor makes shallow entry 3: meteor starts of quite large slows down and brakes up 4: meteor of larger size impacts the earth and shatters on impact. So do you know any other reasons for a piece of space rock to be lying around?

[Halc]

its entry the speed can vary from as slow as 3 hundred kilometres per hour

28000 km/hr seems to be the lower limit, and even then only for objects that are already in orbit about Earth, making them technically moons not meteors. Any meteor not already in orbit will enter at a minimum speed of about 40000 km/hr. Coming from behind Earth's orbit (or any other direction) does not change this figure. At best it might get a negative gravity boost from passing in front of the moon before coming in.

So do you know any other reasons for a piece of space rock to be lying around?

Meteors cannot totally burn up. They're made of matter and it might break up into little hot bits, but the pieces still need to come down. The small stuff found on Earth is probably chunks abraded from larger incoming objects.

[evan_au]

As mentioned, size matters - pieces of a large meteor are likely to make it to ground level than a sand-sized object hitting the upper atmosphere.
- And speed does matter - some meteor showers hit Earth almost head-on, while others "catch up" from behind.
- Material composition is also important:
- Carbonaceous chondrites make up a lot of objects in space, but few make it to the ground. They have a lot of carbon in them, and they tend to burn up
- Rocky objects (silicates) are more likely to make it through Earth's atmosphere
- Metallic objects (nickel/iron) are thought to be rare in space, but they have an even better chance of making it to the ground.

Another category is not so easy to recognise, as they are almost invisible: microspherulites. These are tiny glassy balls that may be:
-  melted droplets of a rocky meteorite,
- the glassy inclusions in carbonaceous chondrites.
- They are also found in meteorite impact layers (like the K-T boundary), where they may be a mixture of the incoming meteorite and rocks from the impact site.
- These are arriving continually - a study of the grit in people's guttering found many of these.
- Their small size means that they have a very low terminal velocity, so they don't leave a crater when they land.

See: https://en.wikipedia.org/wiki/Microspherulite#Aerial_environment

[Just thinking (OP)]

Any meteor not already in orbit will enter at a minimum speed of about 40000 km/hr. Coming from behind Earth's orbit (or any other direction) does not change this figure. At best it might get a negative gravity boost from passing in front of the moon before coming in.

The earth is travelling at 100,000 kilometres per hour as it orbits the sun and if a meteor was to enter from the rear it will indeed have a velocity of almost - that velocity. And my estimate for the speed of the slowest arrivals to the ground are just that the speed of the meteor on touch down not the start of the entry.

[Just thinking (OP)]

Any meteor not already in orbit will enter at a minimum speed of about 40000 km/hr. Coming from behind Earth's orbit (or any other direction) does not change this figure. At best it might get a negative gravity boost from passing in front of the moon before coming in.

The earth is travelling at 100,000 kilometres per hour as it orbits the sun and if a meteor was to enter from the rear it will indeed have a velocity of almost - that velocity. And my estimate for the speed of the slowest arrivals to the ground are just that the speed of the meteor on touch down not the start of the entry.

Carbonaceous chondrites make up a lot of objects in space, but few make it to the ground. They have a lot of carbon in them, and they tend to burn up
- Rocky objects (silicates) are more likely to make it through Earth's atmosphere
- Metallic objects (nickel/iron) are thought to be rare in space, but they have an even better chance of making it to the ground.

Material composition is also important:
- Carbonaceous chondrites make up a lot of objects in space, but few make it to the ground. They have a lot of carbon in them, and they tend to burn up
- Rocky objects (silicates) are more likely to make it through Earth's atmosphere
- Metallic objects (nickel/iron) are thought to be rare in space, but they have an even better chance of making it to the ground.

Thanks, Evan I completely overlooked compositions that is a big one that can make a great difference. Another interesting topic I was thinking about is identifying meteors v space junk during burn up.

[evan_au]

Hunting for micrometeorites?
See some examples here: https://www.sciencefriday.com/articles/up-on-the-roof-a-handful-of-urban-stardust/
...but most of us don't have an electron microscope or an in probe for chemical analysis...

[Just thinking (OP)]

Thought I might just mention terminal velocity can have something to say about this topic. the maximum speed of a falling object starting from a standstill at the border of space and atmosphere is around the speed of sound as the object accelerates to the ground it enters the thicker atmosphere and by the time it reaches the ground, it will be travelling at a speed of no more than 250 kilometres per hour. This same atmospheric breaking can on occasions occur with meteors making for a slow touchdown.

[Just thinking (OP)]

Hunting for micrometeorites?

That would be fun as you mentioned before a good location would be on the roof and gutters. Just tack this opportunity to mention its a bit off topic but about 20 or 30 years ago my late brother told me that he went outside one early morning to pick up the newspaper in his front yard and there was this burnt crispy thick fabric on his lawn and was crumbling when he picked it up and there were a few pieces laying there. He threw it all in the bin later with great regret as we both agreed that it was most likely space junk maybe some insulation or space clothing?

[Bored chemist]

Thought I might just mention terminal velocity can have something to say about this topic.

Then you should say that it depends enormously on the size and weight of the object.
https://en.wikipedia.org/wiki/Kinetic_bombardment

[Just thinking (OP)]

Then you should say that it depends enormously on the size and weight of the object.

That's very true and the entry velocity and the angle of entry and the composition. The bigger they are the slower they are and the more shallow the entry the more chance of making it to the ground whether in one piece or fragmented. There have been meteors that are meters in size and many tons that only penetrated the ground a few meters this is consistent with not much greater speed than terminal velocity.

[alancalverd]

Back in the balmy days of 15% interest rates and general governmental incompetence, someone wrote to the Chancellor of the Exchequer

"I note that MH Government is encouraging entrepreneurs. I would like to own a small business. What should I do?"

"Buy a big one and wait."

[Just thinking (OP)]

"Buy a big one and wait."

One step forward two steps back.