Mapping asteroidsĪrecibo has cataloged the features of many near-Earth asteroids ( SN: 5/7/10). NASA, JHUAPL, Carnegie Institution of Washington 5. ![]() Arecibo’s early radar observations measured the 59-day rotation rate of Mercury (shown in this false-color image of MESSENGER spacecraft data, which highlights chemical and mineralogical features on the planet’s surface). The 59-day rotation better matched the observation that Mercury’s temperature is fairly even across its surface. That’s because it also takes 88 days for the planet to complete one orbit around the sun.Īs a result, that side would be much hotter than the planet’s dark side. If Mercury had turned on its axis once every 88 days, as previously thought, then the same side of the planet would always face the sun. That observation cleared up a long-standing mystery about the planet’s temperature. In 1965, Arecibo radar measurements revealed that Mercury spins on its axis once every 59 days, rather than every 88 days ( SN: 5/1/65). Smithsonian Institution, NASA GFSC, Arecibo Observatory, NAIC 6. This 2015 image showcases the planet’s northern hemisphere. Technological advances have allowed Arecibo to get crisper views of Venus. Its radar images revealed evidence of past tectonic and volcanic activity on the planet, such as ridges and valleys ( SN: 4/22/89) and ancient lava flows ( SN: 9/18/76). In the 1970s, Arecibo’s radar vision got the first large-scale views of Venus’ surface ( SN: 11/3/79). Venus is shrouded in a thick layer of clouds, but Arecibo’s radar beams could cut through that haze and bounce off of the rocky planet’s surface, allowing researchers to map the terrain. NASA, JHUAPL, Carnegie Institution of Washington, Arecibo Observatory 7. Images of Mercury taken by NASA’s MESSENGER spacecraft in 20 confirmed that hints of water ice (yellow) seen on the planet by Arecibo reside in shadowy regions at Mercury’s poles (north pole, shown two craters labeled). Finding ice on Mercury raised the question of whether ice might exist in shadowed craters on the moon, too - and recent spacecraft observations indicate that it does ( SN: 5/9/16). NASA’s MESSENGER spacecraft later confirmed those observations ( SN: 11/30/12). But Arecibo observations in the early 1990s hinted that ice lurked in permanently shadowed craters at Mercury’s poles ( SN: 11/9/91). Mercury seems like it would be an unlikely place to find water ice because the planet is so close to the sun. ESA, Francesco Ferraro/Bologna Astronomical Observatory 8. But data from Arecibo showed that pulsars can ‘spin-up’ to rotate hundreds of times per second by siphoning material off a neighboring star (as seen in this artist’s impression pulsar in blue). Pulsars typically rotate more slowly as they age. The NANOGrav project now uses such rapid-fire radio beacons as extremely precise cosmic clocks to search for the ripples in spacetime known as gravitational waves ( SN: 2/11/16). Then, astronomers realized that old pulsars can “spin-up” by siphoning mass from a companion star, and flash every one to 10 milliseconds. ![]() That find was puzzling at first because PSR 1937+21 is older than the Crab Nebula pulsar, and pulsars were thought to rotate more slowly with age. In 1982, Arecibo clocked a pulsar, dubbed PSR 1937+21, flashing every 1.6 milliseconds, unseating the Crab Nebula neutron star as the fastest known pulsar ( SN: 12/4/82). Arecibo observations of the frequency of radio flashes from the pulsar at the center of the Crab Nebula (red star in the middle) gave support to the idea that pulsars are rapidly spinning neutron stars. That discovery strengthened the idea that pulsars are actually rapidly spinning neutron stars, stellar corpses that sweep beams of radio waves around in space like celestial lighthouses ( SN: 1/3/20). But in 1968, Arecibo saw the pulsar at the center of the Crab Nebula flashing every 33 milliseconds - faster than white dwarfs can pulsate. Clocking the Crab Nebula pulsarĪstronomers originally thought that apparently blinking stars called pulsars, discovered in 1967, might be pulsating white dwarf stars ( SN: 4/27/68). But in honor of Arecibo’s 57-year tenure as one of the world’s premier observatories, here are 10 of the telescope’s coolest accomplishments, presented in roughly reverse order of coolness. But on December 1, the 900-metric-ton platform of scientific instruments above the dish came crashing down, demolishing the telescope and spelling the end of Arecibo’s observing days.Īrecibo has made too many discoveries to include in a Top 10 list, so some of its greatest hits didn’t make the cut - like a strange class of stars that appear to turn on and off ( SN: 1/6/17), and ingredients for life in a distant galaxy. Since 1963, this behemoth radio telescope in Puerto Rico has observed everything from space rocks whizzing past Earth to mysterious blasts of radio waves from distant galaxies. The sun has set on the iconic Arecibo telescope.
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