Author: Sathish Marimuthu, Research Scholar, Centre for Nanotechnology Research (CNR), VIT Vellore
“I’d bet almost anything that life from another planet if formed independently from life on Earth, would be more different from all species of Earth life than any two species of Earth life are from each other”.
- Neil deGrasse Tyson
The universe contains billions of planets, In which some of the planets theoretically have the potential to harbour life. But so far, we haven't found any aliens in the universe. We may be searching in the wrong locations, which may be the cause. What if life on other planets isn't similar to life as we know it?
The Building block...
One of the elements that is most prevalent in the universe, it is none other than carbon. It serves as the foundation for all life on Earth. Because it can create four connections with another element like oxygen, and form long chains of atoms known as polymers, carbon is very unique. Carbon forms compounds that are both soluble in water and water-insoluble. These two solubility profiles are necessary to sustain living systems.
This discussion of carbon’s diverse features leads to the question: Are there other atoms that display chemical diversity on par with carbon that could serve as the molecular basis for life?
There is another element that has the same effect. In addition to sharing a chemical composition with carbon, silicon is one of the substances that makes up the majority of the universe mass. Silicon has a potential to serve as the basis for biological extraterrestrial life and that life may exist inside our solar system.
Silicon has similar chemistry to carbon. It has a valence of four and forms Si-Si and Si-H bonds. It also forms bonds with heteroatoms such as oxygen.
Are they among us?
In our Solar system, the moon of Saturn may be a potential home for silicon-based extraterrestrial life. The atmosphere of Titan, the largest of these moons, is made up of 95% nitrogen and 5% methane. Titan gets about 1% of the sunlight that Earth does, thus it has no oxygen and whatever water it does have is frozen solid. However, life forms built on silicon wouldn't need any water. Instead, they might rely on liquid methane to serve as the galaxy's life-giving fluid.
Essential Conditions for Si based life...
The lack of oxygen would also be essential for such life to emerge. Here's why. When carbon unites with oxygen, or oxidizes, as it does during a fire, it turns into a gas, carbon dioxide. Now, when silicon oxidizes, it becomes silicon dioxide, or silica, which is a solid and not a gas. If Titan had oxygen in its atmosphere, silicon would immediately turn into rock, and no life could possibly begin in that state. But Titan's atmosphere doesn't contain any oxygen, giving silicon-based life a chance.
Most scientists agree that silicon-based life would need extreme heat to thrive. Therefore, it is probable that you would have to go far below Titan's surface to uncover it. A living thing would reside someplace in the Titan's core, where it is heated, due to the tremendous cold on its surface.
As the authors of the Life paper state, “Silicon and carbon are ‘false twins.’ Their similarities are superficial and insufficient to mitigate their crucial differences. Chemistry that is stable and normal for carbon is unstable and exotic for silicon, and, similarly, chemistry that is unstable and impossible for carbon is stable and routine for silicon. Silicon’s distinct chemical characteristics and reactivity make it a challenging choice for life.” 
There are plenty of other planets in the universe. Some of them may have the ideal environment for non-carbon-based life to flourish but the environment on Earth denies silicon any opportunity to develop into a living form. As the authors of the Life paper conclude, “Silicon-based life that uses Si exclusively as a scaffold element is often portrayed in science fiction. . . . However, silicon-based life that uses Si exclusively as a scaffold element is almost certainly impossible.”
 Peng, S. (2015). Silicon-Based Life in the Solar System. Silicon, 7(1), 1-3.
 Petkowski, J. J., Bains, W., & Seager, S. (2020). On the potential of silicon as a building block for life. Life, 10(6), 84.