15

We actually have a very good idea of this because the Mars Reconnaissance Orbiter has been orbiting Mars for over a decade. The MRO is, basically, a spy satellite around Mars and is continually taking high-resolution photos of the surface. It has revisted much of the surface, taking pictures multiple times over the years. As a consequence, we have a very ...


7

The linked article is copied from a university press release. Arecibo's article is more matter-of-fact but naturally also emphasizes the value of their own work. NASA Goldstone can do planetary radar and remains operational. As this page says: Arecibo has twice the range and can see three times the volume of Goldstone, while Goldstone, whose greater ...


7

Fairly good. Two stars of mass $M$ falling from infinity straight towards each other until they merge at distance $2R$ will get kinetic energy $GM^2/R$. This is a lot, for two suns it is $1.8978\times 10^{41}$ J. However, compared to the binding energy of even a single star, $\approx 3GM^2/5R$ this is less(the sun has binding energy $2.2774\times 10^{41}$ J, ...


6

JPL and ESA provide tools to search for small bodies meeting user-defined criteria. I tried: H <= 24 MOID <= 1e-4 au with each and got these results in common: (89959) 2002 NT7, an H=16.5 (~1.4 km) asteroid with a 2.29 year period. MOID≈4000 km but closest approach between 1900 and 2200 is 0.37 au; orbit rather highly inclined (i=42.3°). (292220) ...


5

There are problems with this: What happens when an asteroid hits the atmosphere The asteroid will be travelling fast, more than 10 km per second. In front of it the atmosphere will be compressed and heat up, this causes the "meteor" (a streak of light in the sky). It also causes puts a lot of stress on the asteroid. If the asteroid is very small (sand ...


4

The database of the meteoritical society might be what you are looking for. You can do a search by year. Based on this data, I drew this quick plot of number of recorded meteorites per year Now there are a couple things to see here. First is that we find as roughly as many meteorites as we did ten or twenty years ago. So these events are not more common ...


4

Something to consider might be a large very dark (low albedo) asteroid. I would say it is quite possible a large dark asteroid (e.g. P-type) "could" be headed for us, and we would not know it until it hit us (e.g. distance 0). I think you are asking for the closest distance. It appears the main method of detecting asteriods is with telescopes, but we are ...


3

Further to Mark Olson's answer, while an asteroid impact is popularly thought of as the reason for extinction events on Earth, the reality is more prosaic, with volcanism and glaciation being the most common causes. In all cases, including impact events, the loss of species is primarily the result of a dramatic change to the global environment. The K–Pg ...


3

There is this source that claims 2800 kg of meteor material lands on the moon everyday. They break down that amount to determine an average area per strike. There have been other studies like this one and this report. I sure can't vouch for the accuracy of this first report but it's from a reputable (NASA) source.


3

How ancient they are, I'd have to say as old as the solar system. Collision frequency: Collision amongst Asteroid Belts From ref 1 below: Based on the particle in a box model which assumes a homogeneous distribution in the interactive volume, the intrinsic collision probability is computed to be around $5 \times 10^{-18} km^{-2}yr^{-1}$. However Wetherill(...


2

On the Near Earth Object Program web page from NASA, it lists about 80 objects that passes near the Earth over the next 4 months. Many of them pass within 0.01 AU, the closest one will pass on Oct 24 and be only 0.0038 AU (or 1.5 times the Earth Moon distance) away. From Wikipedia: Scientists estimate that several dozen asteroids in the 6 to 12 meter ...


2

Wired: May 19, 1910: Halley’s Comet Brushes Earth With Its Tail The 1910 pass of Earth was especially close and, thanks to expansive newspaper coverage, eagerly anticipated by the general public. In fact, Earth’s orbit carried it through the end of the comet’s 24-million-mile-long tail for six hours on May 19, earning the story the day’s banner headline ...


2

The answer is that they don't come very close. As Wikipedia notes, It is rare for a comet to pass within 0.1 AU (15,000,000 km; 9,300,000 mi) of Earth. Even better, though, is an actual list of some of the closest approaches of comets to Earth. The closest one listed, Comet Lexell in 1770, came 0.0151 AU away from Earth. The list only shows 20 comets ...


2

Comets are part of the meteor calculation. Space junk is a minor concern. Most satellite and rocket bodies are fairly flimsy and are destroyed by the atmosphere. Sometimes chunks do come down. But by the time they reach Earth they are not falling fast enough to form a significant crater. However being directly hit could be fatal. According to Mark ...


1

This recent paper by Napier et al. indeed concludes that centaur comets break up into many pieces large enough to cause mass extinction events on Earth. Since objects orbit in the same way regardless of mass, I suppose that dangerously big comet debris are more common in meteor streams, and that major impacts are more common during meteor showers. Small ...


1

The American Meteor Society FAQ page notes that about 95% of observed meteors are probably of cometary origin. But they're apparently so fragile that they're only about 1/3 of observed fireballs, and 0% of known meteorites. Also, since the Earth passes through streams of cometary debris several times a year, and yet there's been only one plausible mass ...


Only top voted, non community-wiki answers of a minimum length are eligible