In Pursuit of Semi-Earth Worlds

In the vast cosmic expanse, stars coalesce into celestial archipelagos known as galaxies. Our sun, a radiant member of the Milky Way galaxy, resides within this cosmic tapestry. The Milky Way itself assumes the form of a flattened pie, its central bulge protruding gracefully. Here, nestled in the galactic plane, our sun and its retinue of eight planets[1], including Earth, find their abode.

To traverse the cosmic distances between stars and galaxies, astronomers employ the light year—a unit defined as the distance light travels during one terrestrial year. This remarkable span amounts to an awe-inspiring 9.461 trillion kilometers.

While numerous minor galaxies orbit in proximity to our Milky Way, the Andromeda galaxy stands as our nearest grand spiral companion. Its luminous presence, visible from our earthly vantage, spans an astonishing 2.5 million light-years—an ethereal beacon that captivates our unaided eyes.

 

The Andromeda Galaxy

 

Stars and planets diverge fundamentally: stars radiate heat and light through nuclear reactions within their cores, akin to colossal cosmic furnaces. In contrast, planets—like Earth—rely on the luminosity of the stars they orbit. To estimate the average number of planets in the Universe, we must ascertain the count of stars (such as our sun) around which Earth revolves and the number of galaxies (like the Milky Way) within our cosmic neighborhood.

Observations reveal thousands of millions of galaxies, with estimates ranging from 100 billion to 200 billion[2]. The Milky Way, a medium-sized galaxy, harbors over 100 billion stars. Considering the entire Universe, the star count averages around 10,000 billion. When each star potentially hosts planets, the grand total of cosmic worlds becomes staggering and almost unfathomable.

The quest for habitable planets centers on identifying worlds capable of supporting life akin to Earth’s. Essential criteria include the presence of water—the lifeblood of existence—along with a safe orbital distance from their host star (avoiding extreme heat or cold). Additionally, the star’s age must allow sustained energy for life to flourish over billions of years, mirroring Earth’s conditions.

Driven by urgency, this search arises from Earth’s dwindling resources and the impending environmental challenges. Notably, physicist Stephen Hawking urged humanity to leave Earth by 2600 to safeguard our civilization. Meanwhile, the discovery of semi-Earth planets continues, fueled by improved surveillance technology. Perhaps, in the future, we’ll encounter intelligent life among these cosmic neighbors, thanks to advanced observatories, satellites, and Mars landers.

In our vast Universe, the possibility of intelligent life extends beyond our solar system. To explore this potential, the Planetary Habitability Laboratory (PHL) meticulously catalogs semi-Earth planets. These worlds are categorized by mass, size, and their proximity to their host star. Among them are small, rocky ‘Miniterrans,’ akin to Mercury and our moon, as well as Earth-like ‘Subterrans’ like Mars. Additionally, rocky ‘Terrans’—such as Venus—coexist with larger ‘Superterrans’ like Uranus, Jupiter, and Saturn. Some planets, resembling Earth in composition, form from compressed gases due to their own gravity—like Jupiter, composed of hydrogen, helium, and other elements.

 

Other tables have also been prepared by the laboratory based on the distance between each discovered planet and the star around which it revolves. Some planets are so close to their star (or sun) that they are too hot to hold the water required for life in its liquid form, while others are in warm regions (not too hot or cold); these planets appear to be habitable. Finally, some planets are very far from their sun, orbiting in extremely cold regions, making them difficult to colonize, even if they contain water in the form of ice.

 

More than 3,700 planets' locations around their stars, as well as their mass and size, have been documented by the laboratory. On November 15, 2017, it was discovered that 21 of them, as shown in the table below, were similar to Earth in terms of mass, size, and location in a warm orbit around their stars.

 

As shown in the table below, NASA's Kepler Observatory has monitored and documented 4,302 planets, including 14 Earth-like planets.

 

For comparison, the laboratory has created a classification table for the solar system's planets that is similar to the two tables above, with only Earth, Mars, and the Moon located in the warm, habitable area around the Sun, Venus and Mercury in the hot zone, and the rest of the planets in very cold areas away from the Sun.

 

 

These statistics were relevant as of November 15, 2017, and are subject to change, replacement, addition, or deletion as monitoring and exploration progress, and we do not rule out the possibility of discovering more promising planets teeming with life in the future.

Does the Quran address the concept of life extending beyond our planet into the vast expanse of the Universe?

In Surah Ash-Shuraa (42:30) of the Quran, Verse 30 draws attention with its profound message: "And among His Signs is the creation of the heavens and the earth, and of whatever living creatures He has spread forth in both."

This verse subtly suggests the existence of life beyond our planet.

Moreover, the Quran clarifies that these beings—scattered across other planets—are genuine creatures akin to those inhabiting Earth. Their shadows resemble those of ordinary living beings, dispelling any misconception that they might be angels. In Islamic tradition, angels are created from heavenly light by God.

Surah Ar-Raad (13:15) reinforces this cosmic unity: “And unto Allah (Alone) falls in prostration whoever is in the heavens and the earth, willingly or unwillingly, and so do their shadows in the mornings and in the afternoons.”

Additionally, Surah An-Nahl (49:16) affirms the coexistence of angels and other Earth-like creatures on distant planets: “And to Allah prostrates whatever is in the Heavens and whatever is on Earth of a moving creature, and the angels do so; they disdain not from it.”

 

Considering water's essential role in sustaining life, the Quran underscores this fact. “We made from water every living thing” (Surat Al-Anbya': 21:30). This understanding aligns with the biological reality that water is indispensable for all known forms of life.

 

 

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[1] . In our solar system, eight planets gracefully orbit the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. However, the once-considered ninth planet, Pluto, was reclassified as a dwarf planet due to its shared orbit and relatively small mass. Thus, the official count of solar system planets remains at eight.

[2] . Ailsa Harvey, Elizabeth Howell, How many galaxies are there?  Science & Astronomy, published February 01, 2022.