Arecibo Observatory's Greatest Triumphs

Yesterday brought the tragic news that the famous 1,000-foot 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 center 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.

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.

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:

00000010101010000000000001010000010100000001001000100010001001011001010101010101010100100100000000000000000000000000000000000001100000000000000000001101000000000000000000011010000000000000000001010100000000000000000011111000000000000000000000000000000001100001110001100001100010000000000000110010000110100011000110000110101111101111101111101111100000000000000000000000000100000000000000000100000000000000000000000000001000000000000000001111110000000000000111110000000000000000000000011000011000011100011000100000001000000000100001101000011000111001101011111011111011111011111000000000000000000000000001000000110000000001000000000001100000000000000010000011000000000011111100000110000001111100000000001100000000000001000000001000000001000001000000110000000100000001100001100000010000000000110001000011000000000000000110011000000000000011000100001100000000011000011000000100000001000000100000000100000100000001100000000100010000000011000000001000100000000010000000100000100000001000000010000000100000000000011000000000110000000011000000000100011101011000000000001000000010000000000000010000011111000000000000100001011101001011011000000100111001001111111011100001110000011011100000000010100000111011001000000101000001111110010000001010000011000000100000110110000000000000000000000000000000000011100000100000000000000111010100010101010101001110000000001010101000000000000000010100000000000000111110000000000000000111111111000000000000111000000011100000000011000000000001100000001101000000000101100000110011000000011001100001000101000001010001000010001001000100100010000000010001010001000000000000100001000010000000000001000000000100000000000000100101000000000001111001111101001111000

You can find a full explanation of the Arecibo message here.

In 1981, Arecibo provided the first radar maps of Venus—a planet perpetually covered in clouds. The dish would provide even more detail of Venus in the following years.

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.

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 Center, which is the formal name of the Arecibo Observatory.

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.

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.

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.

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.

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 SETI@Home, 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?