What is the rate of ejecta deposited between planets?

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Discussion Overview

The discussion revolves around the rate of ejecta deposited between planets, particularly focusing on the estimated amounts of rocks ejected from Mars and their impact on Earth. Participants explore various estimates and seek to understand the mechanisms behind planetary ejecta, including the implications of these rates for other celestial bodies like moons.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant cites an estimate of approximately 500 kilograms of rocks ejected from Mars landing on Earth each year and questions the existence of a matrix showing ejecta amounts between planets.
  • Another participant suggests searching Google Scholar for estimates of planetary ejecta hitting Earth, indicating the complexity and diversity of the topic.
  • Concerns are raised about the extreme nature of claims regarding "billions of tons" of ejecta and the 500 kg/year figure, with a request for references to support these claims.
  • A participant calculates that assuming 10^9 metric tons with a surface density of 2000 kg/m^3 results in a significant volume of material ejected annually, but questions the validity of these figures specifically for Martian material.
  • Another participant mentions an average rate of 50,000 tonnes/year for all meteoritic material, contrasting it with a lower figure found on Wikipedia.
  • One participant reflects on the mechanisms of ejection, noting that collisions are necessary for material to be ejected and speculating on the rarity of such events, particularly for Mars and the Moon.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the accuracy of the estimates for ejecta rates and the mechanisms involved. There is no consensus on the validity of the figures presented or the processes that lead to planetary ejecta.

Contextual Notes

Participants highlight the need for clarity on definitions and parameters when discussing ejecta rates, as well as the potential for significant variability in estimates based on different sources.

swampwiz
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I was reading this (which is notable for its non-science content, but I am only referring to this part):
https://www.nationalreview.com/2020/11/wokeists-assault-space-exploration
... it is estimated that every year, approximately 500 kilograms of rocks ejected from Mars via meteoric impact land on our planet.
Is there a matrix that shows the amount that goes between the planets? (And here, I consider a moon to be a "planet".)
 
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No one has any idea?
 
It is not that simple. Try this search on google scholar 'estimates of planetary ejecta hitting earth'

Lots of good hits. You need to decide your parameters, the diversity of topics is not small.
 
swampwiz said:
I was reading this (which is notable for its non-science content, but I am only referring to this part):
https://www.nationalreview.com/2020/11/wokeists-assault-space-exploration

Is there a matrix that shows the amount that goes between the planets? (And here, I consider a moon to be a "planet".)
I would like to see references for their claims for the "billions of tons" and the 500kg/yr
They both seem extreme.
 
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Let’s assume 10^9 metric tons. Surface density of 2000kg/m^3. That gives a 793m cube removed per year. That seems big, but not obscenely big. It could even be right. One is integrating over a lot of impacts.

I would also check out LPSC extended abstracts.
 
caz said:
Let’s assume 10^9 metric tons. Surface density of 2000kg/m^3. That gives a 793m cube removed per year. That seems big, but not obscenely big. It could even be right. One is integrating over a lot of impacts.

I would also check out LPSC extended abstracts.
I could believe the figures for ALL meteorites, but just for Martian material, a bit hard to swallow

The rate for ALL meteoritic material is an avg of 50,000 tonnes / year
Wiki at ~ 15,000 tonnes / yr is very low compared to other sites
 
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davenn said:
I would like to see references for their claims for the "billions of tons" and the 500kg/yr
They both seem extreme.

The numbers all seem to be huge but intuition can be very misleading.
The mechanism for ejection from a planet has to be a collision as some other mass comes in and collides with the surface. I would imagine there would have to be unusual circumstances for this to happen as most of the Kinetic Energy of the incident mass would be shared.

If the incident mass were to arrive from the Kuiper belt, say, it could have enough energy to eject a similar size mass into a much lower orbit - to collide with another inner (rocky) planet. But you would think that there would be far fewer rocks ejected than arriving. These events would all be pretty newsworthy on Earth but probably no one would be aware of an ejection event.

Having a rarified atmosphere and moderate gravity, Mars would perhaps be a better candidate for supplying rocks to Earth than the other way round. The Moon, even better.
 

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