Yesterday brought the tragic news that the famous 304.80 m radio dish at the Arecibo Observatory in Puerto Rico will have to be demolished after the failure of two support cables. It’s the end of an era, but a good excuse to revisit some of the most important scientific contributions made possible by the famous facility.
Strategically built inside a sinkhole, the Arecibo Observatory has been at the centre of all sorts of scientific breakthroughs for the past 57 years. The radio dish has made invaluable contributions to planetary and stellar science, the study of small-bodied objects like asteroids, cosmology, and even the search for extraterrestrial intelligence.
Here are some key highlights from Arecibo’s illustrious career. RIP.
A Revised Year on Mercury
Arecibo’s first major discovery came in 1967, when data gathered by the radio telescope showed that a year on Mercury is 59 days long, not 88 days as previously assumed.
Sending a Message to Aliens
A cool thing about the Arecibo Observatory is that, in addition to receiving radio signals, it can also transmit them. This capability was put to the test in 1974 when the facility beamed a transmission, known as the Arecibo message, to globular star cluster M13. This region of space is approximately 25,000 light-years away, so we’ll have to be patient about receiving a response.
Written in binary, the message was short, depicting things like DNA, the human form, and even a digital representation of the Arecibo Observatory itself. In case you’re wondering, here’s what the transmission looks like:
You can find a full explanation of the Arecibo message here.
The First Detection of Binary Pulsar
Pulsars — rapidly spinning stars that shoot beams of electromagnetic radiation from their highly magnetic poles — were first discovered in 1967. Researchers using the Arecibo Observatory in 1974 did one better by discovering the first binary pulsar, in which a pulsar orbits another star. The discovery earned Joseph Taylor and Russell Hulse the 1993 Nobel Prize in Physics.
The First Radar Maps of Venus
Arecibo spotted its first asteroid in 1989, an object named 4769 Castalia. The observatory would go on to find many more and collect important data about potentially dangerous near-Earth objects. One of the more regrettable aspects of the dish having to be shut down is that Arecibo will no longer scour the skies in search of potential threats.
Finding Ice at Mercury’s Poles
The closest planet to the Sun, Mercury, has ice at both its north and south poles, which we learned in 1992 thanks to observations made by Arecibo. The deposits are presumably water ice, evidence of volatile materials on Mercury’s surface. This ice “persists in shadowed craters despite the high temperatures, 800°F, at the surface,” according to the National Astronomy and Ionosphere Centre, which is the formal name of the Arecibo Observatory.
The First Extrasolar Planets Ever Discovered
In 1992, astronomer Aleksander Wolszczan used the Arecibo telescope to spot three exoplanets around a pulsar named PSR B1257+12. These were the first planets ever discovered outside of our solar system, and a big step forward in our understanding of the cosmos.
Refining Our Understanding of Gravitational Waves
Gravitational waves — ripples in the fabric of spacetime caused by tremendous events like colliding black holes or supernovae — were finally confirmed by scientists in 2016, after being predicted by Albert Einstein a century ago. This monumental discovery, made by the Laser Interferometer Gravitational-wave Observatory (LIGO), might not have been possible had it not been for Arecibo, as NAIC explains:
Indeed, the first evidence for the existence of gravitational waves came from long-term Arecibo observations of a pulsar in a decaying orbit with another neutron star, where the rate of orbital shrinkage matched the rate expected from the loss of energy carried away by emitted gravitational waves.
First Repeating Fast Radio Burst
Scientists first detected fast radio bursts (FRBs) in 2007, but two major factors prevented them from fully understanding these enigmatic, millisecond-long pulses. The first is that all of them (until recently) originated in galaxies far, far away. The second is that FRBs were fleeting, one-off events. That changed in 2016, when scientists working at the Arecibo Observatory spotted the first repeating FRB. Since that time, we have detected other repeaters and even FRBs originating from our own galaxy. Recent evidence suggests these pulses are coming from highly magnetic neutron stars known as magnetars.
The Curious Case of the Vanishing Pulsars
In one of the more unexpected astronomical discoveries, scientists used the facility to detect two rather odd pulsars that stopped blinking for intermittent periods. The discovery, made in 2017, suggests pulsars don’t always blink, and that they have an “on state” and an “off state.” What’s more, this research suggests there may be more intermittent pulsars than “normal” pulsars.
Hunting for Aliens
Despite these incredible discoveries, Arecibo is probably most famous for its use in SETI — the search for extraterrestrial intelligence. The observatory has been used by such groups as [email protected], the SETI team at the University of California, Berkeley, and the SETI Institute’s Project Phoenix. The dish was even featured in the 1997 film Contact. No radio signals from aliens have ever detected by Arecibo (nor by any other observatory, for that matter), which is, in and of itself, an interesting observation — one that’s forcing us to ask: Where is everybody?