5 ms·

Do meteors ever hit the atmosphere at low speed?

by FPGAhacker 4y ago

tejtm 4y ago
relatively...yes
jacquesm 4y ago
11.2 km/sec at a minimum. (Earth's escape velocity!)
- anamexis 4y ago
  It's not immediately obvious to me – why would escape velocity also be the minimum speed at which an object could enter the atmosphere?
  - digitalsushi 4y ago
    Indeed. What if the object was traveling at the same speed as Earth as it revolves around the Sun, and their paths intersect at a very acute angle? That is to say, they met at a traffic 'zipper' ... Could an object collide with earth at a lower speed?
    - titzer 4y ago
      Yes, but it is rare because most objects in such orbits tend to either be gobbled by Earth right away, settle into L2, L3, or L4, or enter a high orbit.
    - vikingerik 4y ago
      No - because as they approach, Earth's gravitational field accelerates it. Escape velocity is the velocity needed to reach an unbounded height from the surface, so reverse that timewise and any object free-falling towards Earth will have escape velocity upon reaching it.
  - teraflop 4y ago
    Even if an object is moving in a parallel orbit to Earth's around the sun, if you "zoom in" to the point where it enters the Earth's sphere of influence, the influence of the sun is relatively small. It's roughly as if Earth and the object are free-falling together in empty space, with a small relative velocity. And Earth's escape velocity is the same velocity that would be reached by a stationary object "dropped" from infinitely far away. So relative to the Earth it will accelerate and hit the atmosphere with at least escape velocity. (This is only an approximation, but it's a pretty good one because there's such a large difference between Earth's mass and the sun's.) Another way to look at this is to simply observe that Newtonian physics is time-symmetric (neglecting effects like friction that dissipate energy). If you have a trajectory that arrives at the edge of Earth's atmosphere with a certain velocity, you can reverse it to get a trajectory that leaves with the opposite velocity (i.e. equal speed).
  - vikingerik 4y ago
    It's not the minimum possible, but it is the minimum typical case. Escape velocity is the upwards velocity needed at the surface to reach an unbounded height with velocity zero. Run that in the other direction and you see an object that starts from infinity will reach Earth at escape velocity. For that not to happen, you'd need something to perturb the object, slowing its fall or deflecting its velocity in some direction other than down. This can happen from the Moon, but it's not common given its small mass and gravitational field relative to Earth.
  - VLM 4y ago
    Have to hold multiple concepts in head at the same time. If you're "far away" with gravitational potential energy and get "close" to the atmosphere that potential will have to go somewhere and it'll go into speed. Its like how, without a parachute on earth, falling 40 M means about 100 KM/h impact speed. And parachutes don't work outside the atmosphere so its retrorockets or hit pretty fast. Going from up there to down here means a certain velocity on the fall in. Conceptually there is a calculatable difference between the speed "from infinity if the earth were not orbiting the sun" vs "from entering the earth's sphere of influence where the earth gravity matters more than the sun's gravity" but it turns out not to matter much. You're probably going to be coming in very fast from falling into the sun's gravity well. But even if the stars align and you hit the earth's influence at zero m/s (LOL good luck) you'll still hit the atmosphere "around escape velocity" after some rounding.
adolph 4y ago
Velocity is relative to a frame of reference. My understanding is that if an object has a low velocity compared to Earth it will more likely drift away due to earth-moon gravity interactions. An example is Apollo 10 third stage and lunar module ascent stage which are in solar orbits to this day. https://en.wikipedia.org/wiki/Apollo_10 https://en.wikipedia.org/wiki/Apollo_10
alexpotato 4y ago
While the odds of what I'm about to describe are astronomically (pun intended) low, I can see the following occurring: - earth moves in its orbit - meteor is moving in a straight line - that line is perfectly parallel to a point on the earth's orbit - the earth and the meteor basically link up and the speeds match so precisely that the meteor just goes into orbit
- MichaelZuo 4y ago
  There's also the very low possibility of something just skipping along the upper atmosphere and ricocheting back into space.
- glenstein 4y ago
  Well presumably meteors travel at different speeds in outer space, and some meteors could be regarded as high speeds and others at low speeds. I don't think you necessarily have to be in synchronization with Earth's orbit to be considered low speed relative to some reasonable perspective.
- IIAOPSW 4y ago
  You haven't accounted for the massive gravity well that is the sun. The difference in potential energy from infinity to the radius of Earths orbit is GMm/r. Set that equal to momentum (.5mv^2) and you get sqrt(2GM/r). Plug in the numbers and you'll see you can't really have a meteor that stumbled in from outside the solar system with a similar velocity to Earths orbit by the time it came down to Earths orbit. Put another way, if it was moving slow enough for the speeds to basically match, it would also be in an orbit around the sun similar to our own, and you'd have to account for the missing potential energy it had before entering our stars gravity well. If you want to argue it came from within the solar system, it would have to have already been in an Earth like orbit this whole time, so why don't we see it?
  - titzer 4y ago
    Orbital mechanics is considerably more complex than this because there are several over massive planets orbiting the Sun. Granted, the odds are very low of getting kicked into a trajectory that will just barely kiss Earth's orbit (at the right time), but it can happen. Not everything orbits in a conic. Also, extrasolar meteors are probably a lot more rare than the above comment would suggest.
vba616 4y ago
Yes, relatively speaking. First likely hit I found: "Meteors enter the atmosphere at speeds ranging from 11 km/sec...to 72 km/sec ... The wide range in meteoroid speeds is caused partly by the fact that the Earth itself is traveling at about 30 km/sec (67,000 mph) as it revolves around the sun. On the evening side, or trailing edge of the Earth, meteoroids must catch up to the earth’s atmosphere to cause a meteor, and tend to be slow. On the morning side, or leading edge of the earth, meteoroids can collide head-on with the atmosphere and tend to be fast." https://www.amsmeteors.org/meteor-showers/meteor-faq/ https://www.amsmeteors.org/meteor-showers/meteor-faq/
- AYBABTME 4y ago
  I wonder, if a meteor was moving very slowly (relatively) and basically just gently falling to earth, if we'd notice.
  - buck4roo 4y ago
    Yes. They are the largest source of extraterrestrial mass. https://www.sciencealert.com/5-200-tons-of-micrometeorites-are-raining-down-on-earth-s-surface-every-year https://www.sciencealert.com/5-200-tons-of-micrometeorites-a...
    - killjoywashere 4y ago
      And one has been caught on film (we think) https://www.universetoday.com/110963/norwegian-skydiver-almost-gets-hit-by-falling-meteor-and-captures-it-on-film/ https://www.universetoday.com/110963/norwegian-skydiver-almo.... There’s also a nice coffee table book about them: https://www.amazon.com/Search-Stardust-Micrometeorites-Terrestrial-Imposters/dp/076035264X https://www.amazon.com/Search-Stardust-Micrometeorites-Terre...
      - wldcordeiro 4y ago
        Damn nearly getting cut in half by a meteor while skydiving!

Do meteors ever hit the atmosphere at low speed?

tejtm 4y ago

relatively...yes

jacquesm 4y ago

11.2 km/sec at a minimum. (Earth's escape velocity!)

anamexis 4y ago
It's not immediately obvious to me – why would escape velocity also be the minimum speed at which an object could enter the atmosphere?
- digitalsushi 4y ago
  Indeed. What if the object was traveling at the same speed as Earth as it revolves around the Sun, and their paths intersect at a very acute angle? That is to say, they met at a traffic 'zipper' ... Could an object collide with earth at a lower speed?
  - titzer 4y ago
    Yes, but it is rare because most objects in such orbits tend to either be gobbled by Earth right away, settle into L2, L3, or L4, or enter a high orbit.
  - vikingerik 4y ago
    No - because as they approach, Earth's gravitational field accelerates it. Escape velocity is the velocity needed to reach an unbounded height from the surface, so reverse that timewise and any object free-falling towards Earth will have escape velocity upon reaching it.
- teraflop 4y ago
  Even if an object is moving in a parallel orbit to Earth's around the sun, if you "zoom in" to the point where it enters the Earth's sphere of influence, the influence of the sun is relatively small. It's roughly as if Earth and the object are free-falling together in empty space, with a small relative velocity. And Earth's escape velocity is the same velocity that would be reached by a stationary object "dropped" from infinitely far away. So relative to the Earth it will accelerate and hit the atmosphere with at least escape velocity. (This is only an approximation, but it's a pretty good one because there's such a large difference between Earth's mass and the sun's.) Another way to look at this is to simply observe that Newtonian physics is time-symmetric (neglecting effects like friction that dissipate energy). If you have a trajectory that arrives at the edge of Earth's atmosphere with a certain velocity, you can reverse it to get a trajectory that leaves with the opposite velocity (i.e. equal speed).
- vikingerik 4y ago
  It's not the minimum possible, but it is the minimum typical case. Escape velocity is the upwards velocity needed at the surface to reach an unbounded height with velocity zero. Run that in the other direction and you see an object that starts from infinity will reach Earth at escape velocity. For that not to happen, you'd need something to perturb the object, slowing its fall or deflecting its velocity in some direction other than down. This can happen from the Moon, but it's not common given its small mass and gravitational field relative to Earth.
- VLM 4y ago
  Have to hold multiple concepts in head at the same time. If you're "far away" with gravitational potential energy and get "close" to the atmosphere that potential will have to go somewhere and it'll go into speed. Its like how, without a parachute on earth, falling 40 M means about 100 KM/h impact speed. And parachutes don't work outside the atmosphere so its retrorockets or hit pretty fast. Going from up there to down here means a certain velocity on the fall in. Conceptually there is a calculatable difference between the speed "from infinity if the earth were not orbiting the sun" vs "from entering the earth's sphere of influence where the earth gravity matters more than the sun's gravity" but it turns out not to matter much. You're probably going to be coming in very fast from falling into the sun's gravity well. But even if the stars align and you hit the earth's influence at zero m/s (LOL good luck) you'll still hit the atmosphere "around escape velocity" after some rounding.

adolph 4y ago

Velocity is relative to a frame of reference. My understanding is that if an object has a low velocity compared to Earth it will more likely drift away due to earth-moon gravity interactions. An example is Apollo 10 third stage and lunar module ascent stage which are in solar orbits to this day. https://en.wikipedia.org/wiki/Apollo_10 https://en.wikipedia.org/wiki/Apollo_10

alexpotato 4y ago

While the odds of what I'm about to describe are astronomically (pun intended) low, I can see the following occurring: - earth moves in its orbit - meteor is moving in a straight line - that line is perfectly parallel to a point on the earth's orbit - the earth and the meteor basically link up and the speeds match so precisely that the meteor just goes into orbit

MichaelZuo 4y ago
There's also the very low possibility of something just skipping along the upper atmosphere and ricocheting back into space.
glenstein 4y ago
Well presumably meteors travel at different speeds in outer space, and some meteors could be regarded as high speeds and others at low speeds. I don't think you necessarily have to be in synchronization with Earth's orbit to be considered low speed relative to some reasonable perspective.
IIAOPSW 4y ago
You haven't accounted for the massive gravity well that is the sun. The difference in potential energy from infinity to the radius of Earths orbit is GMm/r. Set that equal to momentum (.5mv^2) and you get sqrt(2GM/r). Plug in the numbers and you'll see you can't really have a meteor that stumbled in from outside the solar system with a similar velocity to Earths orbit by the time it came down to Earths orbit. Put another way, if it was moving slow enough for the speeds to basically match, it would also be in an orbit around the sun similar to our own, and you'd have to account for the missing potential energy it had before entering our stars gravity well. If you want to argue it came from within the solar system, it would have to have already been in an Earth like orbit this whole time, so why don't we see it?
- titzer 4y ago
  Orbital mechanics is considerably more complex than this because there are several over massive planets orbiting the Sun. Granted, the odds are very low of getting kicked into a trajectory that will just barely kiss Earth's orbit (at the right time), but it can happen. Not everything orbits in a conic. Also, extrasolar meteors are probably a lot more rare than the above comment would suggest.

vba616 4y ago

Yes, relatively speaking. First likely hit I found: "Meteors enter the atmosphere at speeds ranging from 11 km/sec...to 72 km/sec ... The wide range in meteoroid speeds is caused partly by the fact that the Earth itself is traveling at about 30 km/sec (67,000 mph) as it revolves around the sun. On the evening side, or trailing edge of the Earth, meteoroids must catch up to the earth’s atmosphere to cause a meteor, and tend to be slow. On the morning side, or leading edge of the earth, meteoroids can collide head-on with the atmosphere and tend to be fast." https://www.amsmeteors.org/meteor-showers/meteor-faq/ https://www.amsmeteors.org/meteor-showers/meteor-faq/

AYBABTME 4y ago
I wonder, if a meteor was moving very slowly (relatively) and basically just gently falling to earth, if we'd notice.
- buck4roo 4y ago
  Yes. They are the largest source of extraterrestrial mass. https://www.sciencealert.com/5-200-tons-of-micrometeorites-are-raining-down-on-earth-s-surface-every-year https://www.sciencealert.com/5-200-tons-of-micrometeorites-a...
  - killjoywashere 4y ago
    And one has been caught on film (we think) https://www.universetoday.com/110963/norwegian-skydiver-almost-gets-hit-by-falling-meteor-and-captures-it-on-film/ https://www.universetoday.com/110963/norwegian-skydiver-almo.... There’s also a nice coffee table book about them: https://www.amazon.com/Search-Stardust-Micrometeorites-Terrestrial-Imposters/dp/076035264X https://www.amazon.com/Search-Stardust-Micrometeorites-Terre...
    - wldcordeiro 4y ago
      Damn nearly getting cut in half by a meteor while skydiving!