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Space constitutes a three-dimensional expanse with defined positions and orientations. It’s an almost absolute vacuum, containing minimal matter and exerting extremely low pressure. Sound waves cannot travel through space due to the sparse arrangement of molecules. While not entirely empty, sparse elements like gas, dust, and matter inhabit the less dense regions of the universe, while more populous areas support celestial bodies like planets, stars, and galaxies.

Space is the region beyond a planet’s atmosphere so for Earth, it begins about 100 kilometres (62 miles) above sea level. The Kármán line is the boundary between our atmosphere and outer space. We have the capacity to observe celestial objects located up to 46.5 billion light-years distant from Earth, encompassing planets, stars, and galaxies. This expanse is referred to as the observable universe.

The prevailing scientific consensus places the age of the universe at approximately 13.8 billion years. However, certain fundamental properties, including its age, remain somewhat uncertain. Competing measurements of the rate of expansion suggest the cosmos could potentially be as young as 11.4 billion years.

So, to arrive at such a number, astronomers go hunting for ancient stars. The Milky Way galaxy alone contains hundreds of billions of stars, and the vast part of astronomy’s early history was devoted to studying and characterising stars. We can determine the age of the universe (to an extent) by analysing light and other types of radiation travelling from deep space.

SPACE REGIONS

Space is a complex realm, characterized as a partial vacuum, where different regions are delineated by the prevailing magnetic fields and dynamic influences. Geospace encompasses Earth’s atmosphere and extends outward to the boundaries of Earth’s magnetic field, yielding to the influence of the solar wind in interplanetary space. The heliopause serves as the demarcation between interplanetary space and the interstellar medium, where magnetic fields supersede the solar wind. Beyond, interstellar space spans to the galaxy’s outer limits before transitioning into the vast expanse of the intergalactic void.

GEOSPACE

The upper atmosphere and magnetosphere are parts of the region of space known as geospace that is close to Earth. The outer boundary of the geospace is the magnetopause, which forms an interface between the Earth’s magnetosphere and the solar wind. The inner boundary is the ionosphere.

Earth’s magnetic field directs the movement of sparsely dispersed electrically charged particles in geospace. These particles collectively form a medium through which storm-like disturbances, fueled by the solar wind, can generate electrical currents in Earth’s upper atmosphere. Geomagnetic storms have the potential to disrupt two key regions in geospace: the radiation belts and the ionosphere.

These disturbances lead to heightened flows of high-energy electrons, capable of causing lasting harm to satellite electronics. This interference extends to shortwave radio transmissions and disrupts the accuracy of GPS location and timing. Additionally, magnetic storms pose a threat to astronauts, even when in low Earth orbit. They give rise to spectacular aurorae visible in high-latitude regions, forming an oval around the geomagnetic poles.

INTERPLANETARY SPACE

Interplanetary space is the outer space within the Solar System also known as interplanetary medium. The interplanetary space stretches to the outermost limits of the Solar System, where it meets interstellar space and gives rise to the heliosphere—a magnetic bubble enveloping our Solar System. The boundary between interplanetary space and interstellar space is known as heliopause and is believed to be approximately 110 to 160 astronomical units (AU) from the Sun.

The solar winds emanating from the Sun, comprising a portion of the material within interplanetary space, continue their journey to the outer reaches of the Solar System, ultimately encountering interstellar space. The magnetic particles in these solar winds interact with interstellar space and form a protective sphere. The upper atmosphere of Earth undergoes a constant bombardment by solid objects originating from interplanetary space.

Although interplanetary space generally can be considered an excellent vacuum, there are certain situations in planetary dynamics where interactions with gas can significantly alter the motion of the particles.

INTERSTELLAR SPACE

The space between the stars, known as interstellar space, is not merely a void. It is filled with the interstellar medium (ISM), which consists of hydrogen (70%) and helium (28%), formed in the Big Bang that set our universe into motion. The other 2% in interstellar space is heavier gases and dust, consisting of the other elements made inside stars and spewed into space by supernovae. The substance in interstellar space is widely dispersed. While there are areas of higher density, the standard density hovers around one atom per cubic centimeter. Still, even the densest regions of interstellar space count as a vacuum, compared with our earthly air.

This expanse between stars is referred to by astronomers as the interstellar medium.

You’ll know when you’ve arrived in interstellar space when there would be a magnetic field that does not originate from our Sun and also an increase of cold particles around you. Within the heliosphere, solar particles are heated but exist in lower concentrations. Outside of the bubble, they are very much colder but more concentrated.

INTERGALACTIC SPACE

Intergalactic space is the physical space between galaxies. These are the expansive voids that lie between galaxies. To illustrate, if one were to journey from the Milky Way to the Andromeda galaxy, they would have to traverse 2.5 million light-years of intergalactic expanse.

Surrounding and stretching between galaxies, there is a rarefied plasma that is organized in a galactic filamentary structure. This material is called the intergalactic medium (IGM) and it’s mostly made up of ionized hydrogen (hydrogen that has lost its electron). The intergalactic medium (IGM) has a density ranging from 5 to 200 times the average density of the Universe, which is less than one atom per cubic meter. This medium becomes visible to our telescopes on Earth because it heats up to temperatures in the tens of thousands to millions of degrees. At these high temperatures, electrons can escape from hydrogen nuclei during collisions. The energy released from these collisions can be detected in the X-ray spectrum.

While the most-remote regions of the IGM will be eternally isolated from neighbouring galaxies as the universe expands, more “suburban” regions play an important role in galaxy life. The InterGalactic Medium (IGM), influenced by a galaxy’s gravitational pull, gradually accretes onto the galaxy at a pace of approximately one solar mass annually—mirroring the rate of star formation within the Milky Way’s disk.

WHAT IS SPACE MADE OF?

Scientists have delved into approximately four percent of the observable cosmos, encompassing exoplanets, stars, and visible galaxies. Within this realm, they’ve determined that around five percent of our universe is composed of ordinary matter, also known as baryons — the fundamental particles comprising atoms, which in turn form molecules, ultimately constituting everything we perceive through our senses.

About 27 per cent is dark matter — a mysterious substance that interacts with our universe only through its gravitational pull — and the rest, 68 per cent, is dark energy, a cosmic field that permeates everything.

NORMAL MATTER

Normal matter accounts for roughly five percent of the total mass-energy in the universe. This category encompasses atoms, ions, electrons, and the structures they create. It encompasses stars, which emit the majority of the light we observe from galaxies, as well as interstellar gas in both the interstellar and intergalactic mediums, planets, and all the tangible objects we encounter in our daily lives. Normal matter commonly exists in four states (or phases): solid, liquid, gas, and plasma.

DARK MATTER

Dark matter isn’t merely dark, but completely invisible. It appears to allow all forms of light to pass through it as if it were entirely transparent. Nevertheless, dark matter does possess mass, which becomes evident through its gravitational influence. Observations of galaxies reveal that stars and gas move as if there is a considerably greater mass, not visible to us, exerting its pull. According to our observations, galactic dark matter is concentrated in a “halo” encircling the conventional matter within the galaxy. Astronomers also study dwarf galaxies, which are fainter and therefore more challenging to observe, yet they contain a higher proportion of dark matter compared to their larger counterparts.

DARK ENERGY

Dark energy, although also invisible, is distinct from dark matter. Dark matter brings galaxies together, while dark energy propels them apart. We have a grasp of the quantity of dark energy present due to its impact on the universe’s expansion. This phenomenon is often attributed to “dark energy,” an enigmatic form of energy speculated to pervade space. There are two proposed forms for dark energy: the cosmological constant, which is a steady energy density evenly spread throughout space, and scalar fields, which are dynamic quantities with varying energy density in both time and space.

CELESTIAL BODIES

Celestial bodies are natural objects that exist beyond Earth’s atmosphere, scattered throughout the vast expanse of the universe. They encompass a wide array of entities, including planets, moons, asteroids, comets, and stars. Each of these celestial bodies plays a unique role in the cosmic ballet, contributing to the intricate tapestry of the universe.

Here are some of the most notable celestial bodies:

PLANETS

Planets are celestial bodies that orbit stars, with Earth being one in our solar system. They vary in size, composition, and atmospheric conditions. Notable examples include Jupiter, a gas giant with a prominent storm called the Great Red Spot, and Mars, a terrestrial planet with potential for past microbial life.

MOONS

Moons are natural satellites that orbit planets, providing insight into celestial body interactions. Earth’s moon, Luna, influences tides and has been a subject of human exploration. Notable moons include Europa, suspected to harbor a subsurface ocean, and Titan, Saturn’s largest moon, with an atmosphere and liquid lakes.

ASTEROIDS

Asteroids are small, rocky celestial bodies that orbit the Sun, primarily found in the asteroid belt between Mars and Jupiter. They range from a few meters to hundreds of kilometers in diameter. Some, like Bennu and Ryugu, are studied for potential impacts on Earth and clues about the early solar system.

Learn more about Asteroids here.

COMETS

Comets are icy bodies that originate from the distant reaches of the solar system. As they draw near the Sun, they undergo sublimation of their ices, resulting in the formation of a luminous coma and tail. Notable comets include Halley’s Comet, which returns every 76 years, and Comet 67P/Churyumov-Gerasimenko, studied closely by the Rosetta spacecraft. They offer insights into early solar system conditions.

Learn more about Comets here.

STARS

Stars are luminous celestial objects, primarily composed of hydrogen and helium, undergoing nuclear fusion in their cores. They emit light, heat, and energy, sustaining life on planets like Earth. Our Sun, a G-type main-sequence star, is crucial for Earth’s climate and biology. Diverse stars exhibit varying sizes, colors, and lifecycles.

NEBULAE

Nebulae are vast clouds of gas and dust in space, often serving as stellar nurseries where stars are born. They come in various forms, including emission nebulae, which emit light, reflection nebulae that scatter starlight, and dark nebulae, which obstruct visible light. Famous examples include the Orion Nebula and the Eagle Nebula’s Pillars of Creation.

GALAXIES

Galaxies are colossal systems of stars, gas, dust, and dark matter bound together by gravity. They vary in shape, size, and content. The Milky Way, our home galaxy, contains billions of stars and hosts our solar system. Other notable galaxies include Andromeda, the nearest spiral galaxy, and the elliptical galaxy Messier 87, imaged by the Event Horizon Telescope.

BLACK HOLES

Black holes are enigmatic cosmic objects with intense gravitational pull, so strong that not even light can escape. They form from the remnants of massive stars that collapse under their own gravity. Studying them reveals profound insights into spacetime and the boundaries of physics. Notable is the supermassive black hole at the center of our Milky Way galaxy.

Learn more about Black Holes here.

PULSARS

Pulsars are highly magnetized, rapidly rotating neutron stars, remnants of massive stellar explosions. They emit beams of electromagnetic radiation, appearing as regular pulses when observed from Earth. These precise cosmic timekeepers have provided crucial insights into fundamental physics and the extreme conditions within neutron stars. The Crab Pulsar is a well-known example.

QUASARS

Quasars are intensely luminous and energetic centers of distant galaxies, powered by supermassive black holes. They emit colossal amounts of energy, making them visible over vast cosmic distances. Their study unveils the early universe’s conditions and offers insights into galaxy formation and the dynamics of extreme cosmic phenomena.

In conclusion, the vast expanse of outer space continues to captivate our imaginations, offering a realm of infinite possibilities and mysteries yet to be unravelled. From the pioneering days of space exploration to the cutting-edge missions of today, humanity’s journey beyond Earth’s atmosphere stands as a testament to our insatiable curiosity and boundless ambition.

The remarkable achievements of astronauts and cosmonauts, the tireless work of space agencies, and the innovation of private companies have propelled us into a new era of space exploration, pushing the boundaries of human knowledge and technological capability. Yet, as we marvel at the wonders of the cosmos, we must also recognize the challenges and responsibilities that come with venturing into this frontier. Questions of sustainability, ethical resource utilization, and international cooperation will play pivotal roles in shaping the future of space exploration.