Shining alien objects with brilliant, flashing tails thrashing across the sky, comets are fragile, ephemeral invaders from afar that make the long and treacherous journey from their dark, distant, and frozen domain, in our Solar System’s outer limits, to enter the warm, golden inner regions closer to our fiery Star. These icy visitors from far, far away are beautiful, frozen strangers that rampage across alien og seeds Earth’s skies, captivating observers with their silvery, mesmerizing brilliance. Even though comet impacts on our planet are synonymous with mass extinctions–such as the demise of the dinosaurs 65 million years ago–research presented in August 2015 at the Goldschmidt geochemistry conference held in Prague, Czech Republic, shows that ancient comet impacts may well have triggered the substantial synthesis of peptides–the first building blocks of life on Earth. This discovery may have important implications for the evolution of life on our own planet–as well as the genesis of life elsewhere.
Dr. Haruna Sugahara, of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) in Yokahama, and Dr. Koichi Mimura, from Nagoya University performed a series of experiments to replicate the ancient conditions associated with comet impacts on the primordial Earth during the era when life first appeared, about 4 billion years ago.
The scientists took frozen combinations of water ice, silicate (forsterite), and amino acids at cryogenic conditions (77 Kelvin), and then used a propellant gun to trigger the shock of a comet crash. After studying the mixture after the impact with gas chromatography, they discovered that some of the amino acids had merged to form short peptides of up to 3 units in length, termed tripeptides.
Basing their conclusion on the data derived from this experiment, the scientists estimated that the amount of peptides manufactured would be approximately the same as that thought to be churned out by normal terrestrial processes, including hydration and dehydration cycles, as well as lightning storms.
“Our experiment showed that the cold conditions of comets at the time of the impacts were key to this synthesis, as the type of peptides formed this way are more likely to evolve to longer peptides,” Dr. Sugahara explained in an August 18, 2015 Physics Organization (phys.org) News Letter.
Strange, Frozen Invaders From Afar
Comets are bright, frozen invaders from afar that hold within their mysterious, icy hearts the most pristine, primordial ingredients that contributed to the birth of our Solar System about 4.56 billion years ago. This very ancient mix of icy material has been preserved in the pristine “deep freeze” of our Solar System’s most distant, darkest domains. Comets are brilliant and breathtaking, but for decades they were too dismissively referred to as “icy dirt balls” or “dirty snowballs”, depending on the observer’s point of view. These icy aliens travel in from their remote home, located beyond the outermost of the eight major planets, the ice-giant Neptune. Many astronomers think that by gaining an understanding of the ingredients that compose these ephemeral, delicate celestial objects, they can likewise acquire an understanding of the mysterious ingredients that contributed to the special recipe that formed our Solar System.
Comets are relic icy planetesimals, the leftovers of a vast population of primordial objects that contributed to the construction of the four giant, majestic, gaseous planets of the outer Solar System: Jupiter, Saturn, Uranus, and Neptune. Alternatively, the asteroids are the leftover rocky, terrestrial planetesimals that merged together long ago to form the quartet of rocky and metallic inner planets: Mercury, Venus, Earth, and Mars. Planetesimals of both the rocky and icy kind crashed into each other in the “shooting gallery” that characterized our newborn Solar System, and then merged together to form ever larger and larger objects–from pebble size, to boulder size, to mountain size–and, then, ultimately to planet size.
The brilliant, icy comets come rampaging into the bright and balmy inner Solar System, far from their frozen homes that are situated in two frigid, dim and distant domains that harbor a myriad of their icy cousins. The Kuiper Belt–the reservoir of comet nuclei closest to Earth–is located beyond the orbit of Neptune, and it is the distant home of short-period comets. Short-period comets invade the inner Solar System more often than every 200 years. The much more distant domain harboring comet nuclei, the very remote Oort Cloud, is a vast sphere of icy objects that is believed to encircle our entire Solar System. The Oort Cloud is the remote home of the long-period comets, that come flying into the melting heat of the inner Solar System, shrieking, sparkling, glowing with their thrashing tails of silvery fire. Long-period comets are those that enter into Earth’s general neighborhood every two hundred years–or more! Because our planet dwells closer to the Kuiper Belt, the short-period comets are much more frequent visitors, and have played a more important role than their long-period cousins in Earth’s history. Nevertheless, Kuiper Belt Objects (KBOs) are sufficiently remote, small, and faint to have lurked beyond the reach of our scientific technology until 1992. Astronomers have never actually directly observed the extremely remote Oort Cloud, but its likely existence has been inferred indirectly from the way that long-period comets orbit our Sun. The Oort Cloud is commonly believed to extend half way to the nearest star beyond our Sun.
Each time an invading comet comes rampaging into the toasty, brightly lit, inner Solar System, its sheds part of its mass as a result of the sublimation of some of its ices to gas. Therefore, these fragile invaders are doomed to destruction. For example, the famous Halley’s Comet is believed to have a lifetime of less than 100,000 years. The comets that we see today, as they streak brilliantly across our sky, are destined to evaporate and vanish as a consequence of the sublimation of their ices to gas. However, these doomed visitors from afar will be replaced by a new generation of fresh, icy comets, that eventually will wander into our Solar System’s warm, and mercilessly Sun-drenched, inner regions.
A comet’s core is termed its nucleus, and it is primarily composed of ice and dust that is captured within a cage of dark organic material. The ice is mostly frozen water. However, other types of ice may exist as well, such as methane, ammonia, carbon monoxide, and carbon dioxide ices. The nucleus may contain a small, rocky hidden heart.
As the doomed, but glowing, comet invades the inner Solar System near its searing-hot parent-Star, the ice that envelopes its nucleus changes to gas, and it forms a lovely, bright cloud termed a coma. Radiation rushing out from our Sun shoves the tiny dust motes away from the coma, resulting in the brilliant, dusty tail that comets are so famous for. Charged particles emanating from our Star alter some of the comet’s gases into ions, forming an ion tail. Because the tail of a comet is formed by our Star’s ferocious heat, as well as its rushing solar wind, cometary tails always thrash away from our Sun.