angular momentumasteroidsearthinertia
The concept in my mind is that an asteroid is on a vector similar to Earth's, but slightly slower (e.g., 50kmh slower). As Earth passes it, it enters the atmosphere at a sharp angle, and since Earth was passing it, it just barely touches down due to Earth's gravity and atmospheric drag.
Given a large asteroid (e.g., 500 meters wide), is there any reason something like this couldn't happen? And, is there any evidence that it has happened?
As mentioned in NotAstronaut's answer, objects smaller than 25 meters will typically burn up in the atmosphere. One can very easily see why this should be the case using Newton's impact depth formula. This is based on approximating the problem by assuming that the matter in the path of the object is being pushed at the same velocity of the object, so as soon as the object has swiped out path containing the same mass as its own mass, it will have lost all of its initial momentum. All its kinetic energy will then have dissipated there, so if this happens in the atmosphere it will have burned up before reaching the ground.
This is, of course, a gross oversimplification, but it will yield correct order of magnitude estimates. We can then calculate the critical diameter as follows. The mass of the atmosphere per unit area equals the atmospheric pressure at sea level divided by the gravitational acceleration, so this is about $10^4\text{ kg/m}^2$. If an asteroid of diameter $D$ and density $\rho$ is to penetrate the atmosphere, its mass of $1/6\pi \rho D^3$ should be larger than the mass of the atmosphere it will encounter on its way to the ground, which is $5/2 \pi 10^3 D^2\text{ kg/m}^2$. Therefore:
$$ D > \frac{1.5\times 10^4}{\rho} \text{ kg/m}^2$$
If we take the density $\rho$ to be that of a typical rock of $3\times 10^3 \text{ kg}/\text{m}^3$, then we see that $D>5\text{ m}$, which is reasonably close order of magnitude estimate to the correct answer.
According to the American Meteor Society, the sonic boom of an asteroid or meteor (sometimes referred to as a 'fireball') is due to
If a very bright fireball, usually greater than magnitude -8, penetrates to the stratosphere, below an altitude of about 50 km (30 miles), and explodes as a bolide, there is a chance that sonic booms may be heard on the ground below. This is more likely if the bolide occurs at an altitude angle of about 45 degrees or so for the observer, and is less likely if the bolide occurs overhead (although still possible) or near the horizon.
And from CalTech's CoolCosmos page
When an object travels faster than the speed of sound in Earth's atmosphere, a shock wave can be created that can be heard as a sonic boom.
The reason for asteroids causing sonic booms in the lower atmosphere, is according to the article How the Falling Meteor Packed a Sonic Punch (Klotz, 2013) is due to
Because the meteor is supersonic, the waves, which travel at the speed of sound, can’t get out of the way fast enough. The waves build up, compress and eventually become a single shock wave moving at the speed of sound.
Looking a bit further in to what a sonic boom (Using a jet as an example) is and how it occurs is illustrated in the following diagram
So, if a meteor, asteroid is going faster than the speed of sound for particular part of the atmosphere, then a sonic boom will occur. Going back to the American Meteor Society's description of the likely cause of a sonic boom, they stated that if a meteor comes in
below an altitude of about 50 km (30 miles)
then a sonic boom is likely to occur, one of the reasons is that the speed of sound is slower, due to the temperature of the atmosphere at that height and lower. Below is a graph showing the speed of sound plotted against temperature as a function of atmospheric elevation:
Best Answer
If the asteroid is in parallel to the orbit of the earth and at rest it will feel the gravitational attraction and will fall with velocity growing as $g\cdot t^2.$ This force will be there whatever the angle and velocity of the asteroid, centrifugal forces may make it miss the earth in a parabolic orbit, or be caught in an elliptical as the path of the satellites. To avoid falling on the earth with great velocity it would need not only to have a small velocity relative to earth but also an acceleration equal or larger and opposite to the acceleration of gravity.