At that time, humanity began to adopt a habit that it still maintains today: they gathered around bonfires to share their food. The Paleolithic period was in full swing and the comet we know today as C/2022 E3 (ZTF) was very close to Earth, as close as it is now, returning following 50,000 years.. The first sapiens out of Africa, even the Neanderthals that still existed, might not have made out a dim new dot, glowing in those ancient, star-filled night skies. These days, on the other hand, we will see that ball of ice, rock, gases and dust that comes to visit us once more with new eyes, but for the last time. Its transit through the solar system affected it in such a way that it will never return.
Almost a year ago, On March 2, 2022, the 16 cameras attached to the 4-foot-diameter Samuel Oschin Telescope at the Palomar Observatory in San Diego, California, observed something different.. It was first thought to be an asteroid, that is, a rock that wanders through space, tens to hundreds of kilometers in diameter. But the next day, when looking in more detail, something striking emerged: the comma. A layer of gases that surrounds the body, like a sphere, and that, when “blown” by the solar wind, forms the tail. It was a comet.
Thus it was that it took the name of C/2022 E3 (ZTF): the C, for a non-periodic comet, which takes more than 200 years to return to approach the Earth; 2022, for the year of discovery; the E, for the fortnight of its discovery (the first of March); 3, by the order of appearance among the objects of that fortnight; and ZTF, for having been observed by the search project Zwicky Transient Facility. But This scientific denomination coexists with another popular one: the green comet.
The funny thing is that no one, at least with their own eyes, will see it green. “What looks greenish is the coma and not the tail, but only with photography. At first glance it is a diffuse whitish cloud”, he clarifies. Eduardo Fernandez Lajusdoctor in astronomy, specialized in eclipsing binary systems. The color is due to dicarbon moleculespresent in the surrounding layer of gases, which emit green light when broken into two carbon atoms by sunlight.
Y Although everyone wants to witness the phenomenon, the news, at least in Argentina, is not very good. C/2022 E3 (ZTF) will not be seen with the naked eye, except for those who live in La Quiaca, in the middle of the field and have good visual acuity. The rest of the Argentines will have to resort to help: binoculars or, better yet, a telescope.
The truth is that the comet will be seen much better from the northern hemisphere. In our latitudes, the planet Earth itself blocks observation at its closest moment, on February 1, when it is regarding 42 million kilometers away. This is 110 times farther than the Moon, at just over a quarter of the distance to the Sun.
“The comet will be visible at the beginning of February, with binoculars. By the 10th we will have it at 15 degrees above the northern horizon (from the center of the country). Although it will appear higher with each passing day, it will also become dimmer, because it is moving away from the Sun and the Earth”, explains Fernández Lajus. “Brightness is a combination of the distance from the Sun and the Earth. But it can fragment its tail and dim its brightness. Comets are very capricious and hard to predict.”
For these reasons, those who live further north will have better conditions for their observation. In turn, the first night of February, the Moon will be halfway between the first quarter and the full moon, so its brightness will not help the observation. The ideal would be to wait until 3 in the morning, when the Moon hides, to take advantage of the dark night. This is how elusive it is from our country C/2022 E3 (ZTF). This ball of dust, snow and rocks that visits us at 57 km/s. That is, you might travel from Ushuaia to La Quiaca in just over a minute.
“In May 2020, the comet passed as close to Saturn as it now does to Earth, and we assume that this changed its trajectory”Explain Romina Di Sisto, doctor in astronomy and researcher at Conicet. Di Sisto is a specialist in planetary science and professor of the chair of celestial mechanics. She knows so much regarding the subject that the Minor Planet Center, the world organization in charge of asteroids, decided in 2017 that asteroid 1988 RQ12 be called Rominadisisto. In summary, if some rock is approaching the Earth, we would have to ask it if it hits us or not.
Di Sisto describes that it is logical to assume that C/2022 E3 (ZTF) had a periodic orbit around the Sun and the calculations would show that it last visited it 50,000 years ago.. “But that passage close to Saturn caused a deviation in its trajectory, which became hyperbolic, that is to say: it will leave the solar system forever,” he adds. It will then be the last opportunity to see this “clod” of the solar system.
Since the beginning of humanity, comets caused fear, “forecast” the fall of empires or “affirmed” the blessing of the gods with the emperor in turn, generated legends and amazed our species. That new star that displayed its tail among the stars might only be a sign of “something” that the universe wanted to tell us. But three centuries ago, an astronomer would give his last name to the most famous comet of all and, much more important, would teach us that they were not a divine message, but one more object in this universe governed by physical laws that we might understand.
Edmund Halley was the first to realize that not all of these bodies were different and that some might be the same, back. In 1705 he predicted the appearance of Halley’s Comet for 1758. There were still 53 years to go, but Edmund’s calculations were clear: the period of the comet was 76 years. When the scientist put forward his idea, he was already 49 years old and knew that it was almost impossible to see his greatest discovery (at 102 years old) come true. He was not wrong in either omen. In 1742, at the age of 85, Edmund Halley died, and 17 years later, a few months following his calculations, a splendid comet unfurled his tail across the firmament.
Today Halley’s heir astronomers unravel the secrets of the “green” comet, from C/2022 E3 (ZTF), on its last visit to Earth. Perhaps it is worth looking for it among the stars, if only as a distant farewell to this “messenger from heaven.”
