# B Is the Earth in its original orbit?

1. Jan 4, 2017

### scincemaniac

We know that the dinosaur was wiped out by a big meteor. Imagine a bullet hitting a hard surface,the Impact from the bullet should have moved the surface backwards right? So imagen that the meteor represent the bullet hitting the earth and with that kind of impact it should have moved the earth from its real orbit. Although this is just a theory that I have made and I want to share to everybody and see what do you think about it

2. Jan 4, 2017

### Bystander

... and, have you done the math for this simple model? Conservation of momentum and all?

3. Jan 4, 2017

### DDH

The question in the title isn't well defined as "original orbit"? can mean anything. The answer depends completely on the interpretation of the reader of those words.
But let's put that aside as you explained what you really meant in your post.

The analogy in your post is understandable but it distorts a real understanding of the proces. The mass difference between the bullet and a steel plate is much, much smaller than the difference of a big meteorite and planet earth, even when the meteorite is 6 miles/10 kilometers in diameter. To use a better analogy, what would happen to the trajectory of such a big meteorite when you fire a bullet at it? Yes, it would alter the trajectory of the meteorite but only on a microscopic scale.
The same applies to the trajectory of earth when a big meteorite strikes earth.

Let's assume earth and the meteorite are both perfect spheres and both consist of the same (uniform) material. For simplicity assume the radius of earth is 6000 km and the radius of the meteorite is 6 km. The meteorite is therefor 1/1000th that of earth. The volume of a sphere is 4/3 pi r3. The mass of the meteorite would therefor be 1/1,000,000,000 of the mass of the earth. You can find the formula for momentum on internet. Calculate what would happen to earth's momentum when the meteorite strikes earth head on. Then ask yourself what the effect will be om the momentum when earth and the meteorite deform when striking each other.

4. Jan 4, 2017

### scincemaniac

Thanks mate this is useful for me to continue on my study :)

5. Jan 4, 2017

### Staff: Mentor

Quick estimate: 10 km/s at 1/1,000,000,000 the mass of the earth changes our velocity by ~10µm/s. Orbits are closed ellipses, so the largest deflection from this velocity change is of the order of 6 months with a different velocity, for a difference of 10µm/s * 6 months = 160 meters. Completely negligible. Our orbit changes much more due to the gravitational forces of other planets (e. g. Jupiter: ~50,000 km as yearly variations).

6. Jan 4, 2017

### newjerseyrunner

We've also been struck by things far far bigger than the asteroid that killed the dinosaurs. The current theory of how the moon formed was that an object the size of Mars collided with earth. A lot of energy gets dispersed as shockwaves and heat. You envision a bullet hitting a bowling bowl and pushing it right? What about hitting a bullet-proof water balloon? The Earth is almost entirely liquid, not solid. We live on an eggshell, not a solid marble.

7. Jan 5, 2017

### newjerseyrunner

SciShow Space released this video yesterday on the topic

8. Jan 10, 2017

### Chronos

The geological and paleontological record suggests earth has enjoyed a remarkably stable climate for billions of years. That is sufficient to assume earth's orbit has been marvelously consistent for billions of years.

9. Jan 10, 2017

### sophiecentaur

Goldilox in more ways than one, then.

10. Jan 10, 2017

### Gary Weller

No. While we have maintained a consistently survivable climate for billions of years, we could not possibly be in the exact same orbit as we were prior to the KT ELA. No matter how infinitesimal the difference, it's not possible. If we pass closer to Jupiter one year than the next, we are certainly being affected to some degree. More specific to your question, Math and Physics would say that the meteor MUST have changed Earth's orbit, again no matter how infinitesimally. We are still within the habitable zone and will likely remain that way until the death of Sol.

11. Jan 10, 2017

### Staff: Mentor

The solar luminosity increases slowly and the habitable zone shifts outwards. Within ~2 billion years we'll be outside the habitable zone, while the sun will continue to shine for ~5 billion years.

12. Jan 10, 2017

### Gary Weller

I'm well aware of that. I should have specified "until the death throes of Sol".