We are Stardust

Dr M. N. Saha presented the famous Saha ionization theory (Saha’s equation) in 1920. In his two research papers published in the Philosophical Magazine, he showed that the Sun is composed of the same 92 elements known to be present on Earth at that time. In the subsequent year, he also published a paper in the Proceedings of the Royal Society, repeating his analysis of other stars and finding similar results. The Sun is a 2^nd or 3^rd generation star formed by the gas and dust of other stars that have already died. Everything that surrounds us is composed of atoms created inside the stars. We are made up of stardust. This idea invites us to think that life on Earth is not an isolated phenomenon. But this idea could be incomplete. The role of stars does not stop there. Not only do they create matter, atoms that make living things, but they may also be responsible for creating, evolving and extinguishing life anywhere in the Universe. The question is, how can so distant stars be associated with our lives? What kind of cosmic link binds us to them? The answer is hidden in the study of cosmic radiation, where astronomy meets particle physics and biology.

We need to study the link between life and distance stars in cosmic radiation. Many astronomical telescopes today are dedicated to finding answers to the above questions. With the help of these telescopes, we can detect and investigate what the stars are made of, what elements they are composed of, and what elements are being formed in these stars. The stars do not live forever; they are born, evolve and die. The same will happen to our Sun; it will die in five thousand million years. The Universe is filled with the region where hydrogen and other heavier atoms in dust form accumulate. These are the places where stars are born. The incredible energy inside stars allows for the creation of new and heavier atoms by nuclear fusion: helium, carbon, oxygen, and silicon up to iron formed in these gigantic stellar ovens. The stars explode at the end of their lives as Supernova and nova. They release all those atoms into space. This stellar dust and gas is the raw material to form new stars and planetary systems. Our Sun is also formed in an enriched media, the medium already created by the elements that come from other stars. Therefore, atoms that form living things were ones inside the distanced stars.

Figure 1: The Crab Nebula is the leftover, or remnant, of a massive star in our Milky Way that died 6,500 light-years away. Image credit: NASA, ESA, J. Hester and A. Loll

Science has gone a step further; the latest findings suggest that the relationship between stars and life in the Universe is even deeper. Many cosmic rays (energetic particles) are ejected during stars’ death. The effect of these rays on life is disturbing. Cosmic rays cannot be detected using telescopes that detect electromagnetic waves from radio to x-rays and gamma rays. We need new and advanced instruments to catch these rays, hence a new way of doing astronomy. In the province of Mendoza in Argentina, the largest observatory in the world for the detection of cosmic rays (the Pierrot Jar Observatory) is established. In observation of cosmic rays, we do not look for the light or photon; rather, we look for the particles. These particles are mostly protons (about 90%); from the remaining 10%, most are helium nuclei, and 1% are electrons and other nuclei such as iron and nitrogen.

In interstellar space, we find places with gas (mostly hydrogen) and little amount of dust (primarily carbon and silicon). The dust is covered with an ice mantle mainly made of water and other molecules such as carbon monoxide, carbon dioxide, and ammonia. The cosmic rays discharge over these molecules and dust frozen surfaces. This creates very rich chemistry able to synthesize the first blocks to create a life, for example, amino acids and molecules related to sugar. The same interstellar places also host the formation of stars and planets. Inside a star, those molecules can not survive due to extreme temperature and density conditions. But these molecules can hide and stay safe in the asteroids and comets. The millions and millions of asteroids fall over already formed planets with more stable conditions carrying seeds of life within them. The Rosetta Space Mission from European Space Agency detected sixteen organic molecules basics for life origin on a comet in our solar system. It is concrete proof of life creating molecules coming from outer space. Other planets also receive asteroids and comets from outer space. If the condition on those planets (exoplanets) is similar to Earth, the starting point for life will be similar. This shows that the life is a phenomenon on the cosmic scale.

Figure 2: Pillars of Creation. Interstellar cloud of gas and dust taken by the Hubble Space Telescope in 1995.

We on Earth live in a constant shower of cosmic particles from different stars. When highly energetic cosmic rays penetrate our atmosphere and hit a molecule, it creates millions and millions of new particles. The atmosphere absorbs many of them, but some reach the ground. We study the connection between cosmic rays and life in astrobiology. Far from Earth, cosmic rays create molecules involved in the life creation process; they also affect the life already present on Earth. The Sun drives life processes in the atmosphere by providing light energy, but distant stars are also responsible for some crucial phenomena. As discussed earlier, cosmic ray shower creates trails of ions in the atmosphere. These ions help facilitate embryonic seeds’ formation, which helps stabilize particles and cloud droplet precursors for life. Cosmic rays are essential for cloud formation and the evolution of the atmosphere. They also help the formation of amino acids, ammonia, methane, and water in the atmosphere. Once life is created, cosmic rays also affect the steady mutation of DNA, promoting the complexity of life and human existence. Therefore, these rays accelerate the evolution process of life. This way, stars not only produce atoms we are made up of, but when they die, they also flood space with particles that travel for millions of years and arise the spark of life anywhere in the Universe.