Guest Editorial

The Arecibo Observatory has had a prominent role within the International Astronomical Union, both scientifically and from a human capital perspective, and its loss will be keenly felt.

With its unparalleled sensitivity for more than 50 years, it provided unique insights into the structure of the Milky Way Galaxy, star forming regions, and evolved stars by observing a variety of atomic and molecular lines, most notably observations of the 21 cm line of neutral hydrogen.

Discoveries with the Arecibo Observatory helped lay the foundation for the emerging era of multi-messenger astronomy, highlighted by the discovery that the orbits of a pair of neutron stars were decaying, as expected if the binary system was emitting gravitational waves as predicted by the Theory of General Relativity. Precise timing of radio pulsars provided equally novel advances in areas such as the equation of state of nuclear matter and advances toward the direct detection of nanohertz gravitational waves.

Both observations with and transmissions from the Arecibo Observatory injected new elements into the search for life in the Universe, primarily in the area of searching for signatures of other technologies, and, for half a century, Arecibo stood as the defining marker for interstellar transmissions.

Within the Solar System, the Arecibo Planetary Radar (often affectionately known as “El Radar”) helped change our view of the planets Mercury and Venus, crucially providing the first views of the surface of Venus. More recently, the Arecibo Planetary Radar obtained crucial information about near-Earth asteroids, leading not only to scientific discoveries but precise orbit determinations for the purposes of planetary defense.

These scientific discoveries only happened, though, because of the immense amount of talent that was cultivated at the Arecibo Observatory. Numerous scientists and engineers, from the island of Puerto Rico and internationally, developed their skills at the Arecibo Observatory, leading to further discoveries through the field of astronomy.

While the members of the Radio Astronomy Commission of the International Astronomical Union are saddened by its loss, there is no doubt that data acquired by the Arecibo Observatory will continue to be critical to new discoveries for many years to come. The National Science Foundation is also exploring new scientific roles and opportunities for the observatory.

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