Asteroid or Meteoroid?

[1dave]

The size of what classifies as an asteroid is not extremely well defined, as an asteroid can range from a few meters wide – like a boulder—to objects that are hundreds of kilometers in diameter. The largest asteroid is asteroid Ceres at about 952 km (592 miles) in diameter, and Ceres is so large that it is also categorized as a dwarf planet.

Read more at: phys.org/news/2015-06-difference-asteroids-meteorites.html#jCp

"Science" should use well defined terms, but it hasn't here.

I was just studying Wolf Creek Crater in Australia that is touted to be the "second largest METEOR impact crater on earth" - Barringer Crater in Arizona being the largest.


Note the areas blown clear by the shock waves that accompanied the meteor!

Wolf Creek:

The hole that it gouged out of the Devonian age quartzite rocks varies in diameter from 950 to 870 metres. The only bigger crater undoubtedly made by a meteorite impact is the Meteor Crater in Arizona.

Travelling at cosmic velocity, about 15km per second (that’s 40 times faster than a bullet from a high-powered rifle, or like crossing Australia in less than five minutes), the massive chunk of iron would have exploded on impact with the earth. Most of the meteorite, which was probably getting on for 100,000 tonnes in weight, would have been vapourised, along with huge quantities of the quartzite rock into which it ploughed.

Very little of the meteorite remains today, but sufficient has been collected for us to be sure that this was what made the crater. Like all iron meteorites, this one contained small quantities of nickel. In the weathered shale balls this nickel has been incorporated into what turned out to be a nickel-iron carbonate mineral not found anywhere else and which was new to science. This was named “reevesite” after Frank Reeves.

Barringer:

The Meteorite

The meteorite weighed 300,000 tons and traveled at a speed of 26,000 miles per hour (12 kilometers per second). When it struck the earth in what is now northern Arizona, it exploded with the force of 2 ½ million tons of TNT, or about 150 times the force of the atomic bomb that destroyed Hiroshima. Most of the meteorite was melted by the force of the impact, and spread across the landscape in a very fine, nearly atomized mist of molten metal. Millions of tons of limestone and sandstone were blasted out of the crater, covering the ground for a mile in every direction with a blanket of shattered, pulverized and partially melted rock mixed with fragments of meteoritic iron.

To my mind, 300,000 tons - about 50 meters (164 feet) in diameter - is a BIG boulder!
Still a meteoroid, not an asteroid. Hmm.

let's start at the beginning.

1. The supernovas.



2. Gravitational forces gather the material spewed out into cometary knots.

They are generally larger than the size of the Solar system (i.e. the orbit of Pluto), with masses comparable to that of the Earth.

3. These masses are traveling away from the original star at tremendous velocities and condensing as they go. As they collide with other interstellar debris and enter solar systems they become comets (not yet accepted by scientists).

4. As comets approach the sun they are heated, the ices they contain expand into vapors and blast pieces away.

5. The larger pieces of dying comets become asteroids, the smaller pieces become meteoroids.

All that is left is to draw a dividing line!

Bigger than a bread box? Watermelon? Superbowl stadium?

Come on hot-stuff big-shot astronomers, draw the damned line!

[1dave]

Personally, I would place the divisions at something like:
- is it Differentiated and larger than 100 miles in diameter? Then it is a planetoid.
- Is it smaller than 100 miles in diameter but larger than 100 feet? Then it is an asteroid.
- Is it smaller than 100 feet in diameter? Then it is a meteoroid.

[1dave]

Thanks to @shotgunner for bringing this to my attention:

www.iflscience.com/space/stone-found-in-egypt-has-minerals-we-have-never-seen-before-on-earth-or-in-space/



QUESTION: What percent of space rocks that have struck earth have scientists examined?

Stone Found In Egypt Has Minerals We Have Never Seen Before On Earth Or In Space

By Alfredo Carpineti

A newly published study sounds like the beginning of a great sci-fi story: A stone recovered in 1996 in Southern Egypt is puzzling scientists because, although definitely from outer space, it doesn’t look like any regular meteorite or asteroid, and the latest analysis shows that the micro-minerals within are unlike anything we have ever encountered here or in the cosmos.

Regular meteorites are made mostly of silicon with a bit of carbon (similar to the composition of our planet) but the Hypatia stone, as it is called, is the opposite, as reported in the journal Geochimica et Cosmochimica Acta.

The stone has a huge amount of carbon compounds and almost all of them have transformed into micro-diamonds. Some of the carbon compounds are of particular interest because they are known as polyaromatic hydrocarbons (PAH), a major component of interstellar dust. And there is even more unusual stuff, like pure aluminum.

"The aluminum occurs in pure metallic form, on its own, not in a chemical compound with other elements," first author Georgy Belyanin, from the University of Johannesburg, said in a statement. "As a comparison, gold occurs in nuggets, but aluminum never does. This occurrence is extremely rare on Earth and the rest of our solar system, as far as is known in science."

The stone also features a mineral called moissanite, a silicon carbide compound, in an unexpected form and nickel-phosphorus grains with very little iron, another combination never observed on Earth before. All these factors suggest that the object’s formation predates the origin of the Solar System. The stone just doesn’t fit with what we know of our local (space) rocks.

"What we do know is that Hypatia was formed in a cold environment, probably at temperatures below that of liquid nitrogen on Earth (-196 Celsius)," Professor Jan Kramers, the lead researcher on the project, explained. "In our solar system, it would have been way further out than the asteroid belt between Mars and Jupiter, where most meteorites come from."

"Comets come mainly from the Kuiper Belt, beyond the orbit of Neptune and about 40 times as far away from the sun as we are," he continued. "Some come from the Oort Cloud, even further out. We know very little about the chemical compositions of space objects out there. So our next question will dig further into where Hypatia came from."

We look forward to that. In the meantime, if you're curious, here's a fun fact: the stone was named after Hypatia of Alexandria, the great philosopher, mathematician, and astronomer of the fourth century. She was murdered and dismembered by a mob of Christian monks likely due to Cyril of Alexandria’s jealousy. He was later made a saint by the Catholic Church.

The statement about where meteroids are opinions, not facts.