April 5 – By Jove

Today’s factismal: The radio emissions of Jupiter were reported to the public 61 years ago today.

One of the most amazing accidents in science was the discovery of radio waves from Jupiter by  Franklin and Burke in 1955. At the time of the discovery, no-one thought that other planets would give off radio waves.We knew that the sunspot cycle was identical to the Earth’s geomagnetic cycle, thanks to Edward Sabine’s work in 1852 but the idea that a mere planet could give off radio waves powerful enough to be heard on Earth seemed laughable.

After all, radio was something that took either a station designed to send Amos and Andy broadcasts or a star – or so people thought. Radio astronomy had just started to come into its own in the 1950s, with the construction of large antennas like Arecibo, that were used to listen for stars using light waves outside of the visible spectrum (i.e., radio waves). The discovery of strong radio signals coming from the Crab Nebula only served to whet the astronomers’ appetites for more.

An image of the Crab Nebula at radio frequencies (Image courtesy NASA)

An image of the Crab Nebula at radio frequencies (Image courtesy NASA)

One such radio observatory was built by the Carnegie Institution where Franklin and Burke worked. Shaped like a giant X, the telescope was designed to scan across the skies, looking for signals from the stars. But on one March morning, they got not one but two signals from the Crab Nebula. At first, they dismissed the extra signal as being from a farmhand’s car as he returned home late from a date. But the signal showed up every day. Even more interestingly, it showed up four minutes later each day.

Jupiter at radio wavelengths (Image courtesy NASA)

Jupiter at radio wavelengths (Image courtesy NASA)

The regularity ruled out a farmhand and his car. And the four minutes change in timing told them what it was: a radio signal from Jupiter. Because Jupiter is moving across the sky, each day it appears in a slightly different place. And signals from the different place would show up four minutes later each day. Once again, serendipity and prepared minds had led to a new discovery. Since then, radio signals have been observed from many planets, and have proven to be a valuable tool for exploring how planetary magnetic fields change over time.

If you’d like to replicate their discovery and maybe make some of your own, then why not give NASA’s Project JOVE a try? They’ll tell you how to build your own radio telescope using a kit, and give you a forum to discuss your findings. Just turn your dial to:

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