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By Adarsh Kumar, BS-MS 2019
They might have known that we Homo Sapiens have two eyes, with which when gazed upon the Heavens, we perceive miniscule sources of glare. We have a third eye, too, that has succoured us to contemplate the realms beyond envision.
An Insight
Venturing into Arecibo, Puerto Rico, we come across the Arecibo observatory owned by the National Science Foundation of the US. The Arecibo Observatory was home to one of the world's biggest individual unit radio telescope built in 1963 until recently, FAST (China) began its observations in 2016. It was a 305-meter spherical reflector consisting of perforated Aluminium panels and movable antenna structures that were positioned about 168 meters above the reflector's surface. The panels focused on incoming radio waves on the antennas and, after that, get transmitted to the central processing unit. The observatory also included an auxiliary 30-meter telescope that served as an interferometer (radio) and a medium to study the Earth's atmosphere. One of the key features of the antenna structures was that it could be moved in any arbitrary direction, which made it possible to track a particular celestial object in different suburbs of the sky and focus on it for long periods to gather valuable information info.
Major Contributions
Having such a huge dish to collect radio waves, allowed Arecibo to see objects that were nearly obscured from the general perception of vision, making it great at detecting objects like Pulsars. Arecibo was one of the very few which got the designation of ‘King’ in Pulsar hunting by scientists.
And as the title goes on, Arecibo in 1968 observed the rapid spinning motion at the central region of the Crab Nebula, faster than even white dwarves, which allowed scientists to get a clearer picture of what Pulsars are actually. Fourteen years later, Arecibo clocked a pulsar at every 1.6 milliseconds and hence unseated the Crab Pulsar as the fastest known Pulsar.
Observing rapid spins feels excellent. Well, it wasn't only limited to that. Observations in the early 1990s by Arecibo hinted that Ice skulked in the persistently shadowed craters of Mercury (Fig. 1), which was later confirmed by NASA's MESSENGER spacecraft. Unfortunately, radio telescopes like FAST China or the Green Bank Telescope aren't outfitted with radio transmitters, making Arecibo an exception again. Arecibo's transmitters allowed it to bounce radio waves off of gases in the atmosphere of asteroids and planets, revealing crucial information such as the shape, size, orbital track, etc. This feature in the 1970s allowed Arecibo's radar vision to get the first large-scale view of Venus's Surface and allowed researchers to map the planet's terrain (Fig. 2). Five years prior to this, the radar measurements by Arecibo divulged that Mercury spins on its axis once every 59 days, rather than 88 days, which helped in clearing up a long-strand mystery about Mercury's temperature shifts as 88 days is the same period which Mercury takes to orbit around the sun once.
Figure 1
Figure 2
Apart from these, Arecibo was the first of its kind to broadcast a radio message intended for an Alien audience in 1974! The message consisted of 1,679 bits of information, beamed towards a cluster of stars roughly about 25,000 light-years away. The binary code string (radio message) consisted of chemical formulas for components of DNA, a solar system schematic, a stick figure human sketch, and some other scientific data.
Recent decommission of an epic saga
In August 2020, a cable holding up the central platform snapped, making a hole in the reflector's dish. Three months from then, a second cable broke up, after which the National Science Foundation declared that the snapped cables were beyond repair and the whole structure was in Danger of Collapsing. Days after NSF's announcement, the remaining cables, weighing about 900 tonnes, broke and collapsed into the dish below, smashing it.
Before its collapse, experts indicated beforehand that the complete structure's condition is alarming. As a result, NSF evaluated multiple assessments by independent engineering companies. They found that the cables (remaining ones) could no longer carry the loads they were designed to support.
Potential replacement?
There have been some plans for the potential replacement of the Arecibo telescope, but they are still in their early phases. Nevertheless, many proposals have been made and submitted to the National Science Foundation, which calls for replacing the Giant dish with an array of 1,000 small dishes, every 9 meters across, on the platform spanning the current dish.
Regardless of its tenure, the contributions made by Arecibo have assisted us this far into the future. The data from the collapsed is safely moved and preserved to the Texas Advanced Computing Centre, where over 3 petabytes of data would be transferred from around 50 years of Arecibo sky scans!!
For students and scientists around the world to wield and recollect the sensational journey of Arecibo.
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