Two Fascinating Space Articles That Might Stir Your Imagination

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The Difference Between Meteoroids, Meteors and Meteorites.

The names 'meteoroids', 'meteors' and 'meteorites' can be confusing. I hope that this short article will explain how they differ.

The information in my articles has been gained by reading many books on the subject. I won't pretend to be an expert, but I hope you find some of my reads interesting.

Long before the solar system existed, there was an area in space that had a massive concentration of interstellar gas and dust; we know it now as a molecular cloud. This large area of space had a higher density than the surrounding areas.

Inside this cloud would eventually become the birthplace of our local star, the Sun.

Extremely low temperatures caused the gas and dust to bond together, and these clumps grew larger as time went by. Then gravity started to pull the denser areas inwards; this growing object was the beginning of a protostar, the early stage in the formation of a star.

Gravity continued to collapse the material into an object that was getting larger, hotter and denser. When a critical temperature of around 15 million degrees Celsius (27 million degrees Fahrenheit) was reached, nuclear fusion took place in its core, and a main-sequence star was born, namely our Sun.

The Sun holds about 99.86% of the total mass in the solar system.

The nuclear fusion process in the newborn Sun caused stellar winds to stream outwards, stopping more debris from falling in.

Circling the newborn Sun was the leftover material contained in a disc-shaped cloud called a 'solar nebula'; it was inside this solar nebula that all the other celestial objects in the solar system formed, including planets, dwarf planets and moons.

The Sun is estimated to be about 4.57 billion years old; for all of that vast time, smaller rocky, icy and metallic bodies called asteroids have circled the Sun.

Asteroids can sometimes collide with each other, causing fragments to break away; it is these fragments that we call meteoroids. When icy comets come close to the Sun, the heat can melt the ice, dislodging small rocks, which also become meteoroids.

Meteoroids can be as small as grains of sand and can reach 100 metres (328 feet) in diameter; larger space objects are called asteroids.

Sometimes the Earth passes through an area in space that has a higher density of meteoroids; some can enter the Earth's atmosphere. When they do, they are known as 'meteors'. The smaller ones will burn up completely as they pass through the atmosphere. If the meteors are large enough, parts of them will land in the ocean or on dry land.

Objects that do land in the oceans or on land become meteorites. Over 90% of them are made of rock, and the remainder consists wholly or partly of iron and nickel.

The largest meteorite ever found is the Hoba meteorite, located in Namibia; this large chunk of iron is estimated to weigh over 60 tonnes.

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Atoms Are Small. But How Small?

This is a simplistic explanation of atoms; they are very complex.

Atoms are the smallest particles of chemical elements.

They are the basic building blocks of everything that can be seen or touched, including me, you and every other living thing on our planet.

Apart from a hydrogen atom, which has just one proton and one electron, other types of atoms are made up of various numbers of protons, neutrons and electrons.

A chemical element is a pure substance made of atoms that have the same number of protons in their nucleus, and the number of protons is known as the atomic number.

The mass of an atom is the total number of protons and neutrons combined. To give you an idea of the size of an atom and how small they are, take a human being of, say, 70 kilograms (154 pounds) in weight; the total number of atoms making up that person's body is estimated to be 7 octillion. An octillion is a 1 followed by 27 zeros.

During our lives, vast numbers of atoms keep joining and leaving our bodies.

The most common elements by mass that make up about 99% of the human body are oxygen, carbon and hydrogen. When we die, all the elements of which we were made will dissipate over time, eventually becoming part of other objects or even other living things in the future.

Under normal conditions, atoms cannot be destroyed; they just keep on being recycled.

A molecule is an electrically neutral group of two or more atoms held together by chemical bonds; they can be simple or complex. To give an example, a water molecule consists of one oxygen atom and two hydrogen atoms bonded together. A carbon dioxide molecule consists of one carbon atom and two oxygen atoms bonded together.

The term 'matter' is used for anything that has mass and takes up space; it is all around us. Matter is the air you breathe, the shoes you wear, the water in your glass and everything you can touch and smell. It is what we are.

The three most commonly known states of matter are solid, liquid and gas. The difference in the structure of each state is described by the density and arrangement of its particles.

It took roughly 380,000 years after the birth of the Universe for electrons to become bound to atomic nuclei, thus forming the first atoms. These new atoms were mainly hydrogen and helium. Hydrogen is still the most abundant element in the universe today.

As I said, a simple hydrogen atom contains just one proton at its centre and one electron. So you could say that an atom is mostly empty space.

To give an idea of how far the electron could be from the nucleus of a hydrogen atom, imagine this: scale up the atom so that the proton is the size of a golf ball. At that scale, the electron could be as far as 2 kilometres (1.2 miles) from the centre of the atom, giving the atom a diameter of roughly 4 kilometres (2.5 miles).

An atom can be about 0.1 to 0.5 nanometres in diameter. There are 1,000,000,000 nanometres in one metre. Yes, atoms are extremely small.

British spelling!

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