Submitted by marketrent t3_y9u9o9 in science
Reply to comment by NedCarlton in As many as a fifth of all asteroids in the asteroid belt may have been formed out on the fringes of the solar system. Findings suggest that both Ryugu and the CI chondrites originate from the same region of space, and could even have shared the same parent body. by marketrent
> great protector
Is it settled science it does more good than harm?
Some fragments eventually find their way into the inner Solar System, leading to meteorite impacts with the inner planets.
Asteroid orbits in the belt continue to be appreciably perturbed whenever their period of revolution about the Sun forms an orbital resonance with Jupiter- with some swept into new orbits dangerous to earth.
Jupiter is considered the great protector because it removed 99% of the Asteroid Belt in the early days of the Solar System. Those early days produced heavy bombardment, as craters on the Moon and Mars demonstrate. But since then things have been "relatively" benign.
Nice, but the subject I was questioning was if 'the asteroid belt' is also a great protector.
Well it’s great belt for ass whooping
The asteroid belt has minimal mass (3% of our Moon). So it doesn't affect its own members much, or stop anything else from passing through.
Jupiter is 850,000 times more massive than the entire belt, so it strongly affects their orbits. For example, any asteroid that has a simple ratio to Jupiter's orbit gets pulled in the same direction every time it is closest. This pulls it out of that orbit, creating gaps in the belt. Conversely other asteroids are trapped in resonant orbits to Jupiter - the Trojans and Hildas.
So the main belt is not a protector of earth but a danger as the orbits of belt asteroids can be changed by Jupiter's massive gravity – and by occasional close encounters with Mars or other objects. These encounters can knock asteroids out of the main belt, and hurl them into space in all directions across the orbits of the other planets- like earth.
Exactly. Japan sent a probe to the asteroid Ryugu and brought back samples. The samples indicate its material formed in the outer Solar System. but now it's orbit crosses Earth's (that's why the picked it to visit).
More generally, there are 30,000 known asteroids whose orbits come closer than 1.3 times the Earth's distance to the Sun. That compares to over a million other asteroids. These "near Earth asteroids)" have an orbit half-life of 10 million years, which is very short compared to the age of the Solar System.
So these asteroids need to be constantly resupplied, otherwise there would be none left. The giant planets, which is mostly Jupiter since it is heavier than everything else combined, are the main cause of orbit changes.
The near Earth asteroids are the ones most likely to hit Earth, which is why NASA has a search program for them, and why they just tested changing an orbit by hitting it. What we have going for us is space is really empty. Earth only takes up one part in 500 million of our orbital region. So the chance of any given random rock hitting us is low. On the other hand, there are many rocks. Dust and sand-sized ones hit us every day. That's what meteors in the night sky are.
Earth's orbit is 500million times it's diameter?
No. Our orbit is 23,455 times the size of the Earth. But there is a second dimension, above and below our orbit.
This plot shows the size of asteroid orbits relative to ours on the horizontal scale, and the tilt in degrees relative to the Earth's orbit. You can see the tilts go up to 30-40 degrees.
Any tilt above zero means when they cross our orbit's distance, they can be crossing above or below where the Earth will pass. They can only hit us if they cross our distance exactly on our path, and the Earth also happens to be at that point in our orbit at the same time.
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