What amateurs learned about the asteroid Eurybate

The participatory scientific experiment that invites astronomy enthusiasts to observe the temporary disappearance of a star has borne fruit.





Through Chloe Durand Parenti

In 2027, the Lucy probe will fly over the Trojan asteroid called Eurybate.
©NASA

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ifNeeding to prove that citizen science was no gimmick, the recent campaign of observations of the occultation of a star by asteroid 3548 Eurybate is a good example of the results that can be obtained by well-monitored amateurs. On the night of Saturday October 22 to Sunday October 23 at around 4 a.m., from the Canary Islands to northern Sweden, more than three hundred more or less modest observation instruments were pointed at the star HD 5159323 in the constellation Gemini Hope, whether or not to see it disappear behind one of the target asteroids of the American space mission Lucy.

In France alone, the French Astronomical Association (AFA), which carried out most of the project in support of NASA, claimed to have received no fewer than 246 reports of observations! Despite the gloomy weather that disturbed many volunteers that night, 18 European observers saw the star disappear while 44 others saw it shine continuously.

eight seconds late

This made it possible for the first time to refine the trajectory of this small Trojan body of Jupiter, namely that it shares the orbit of the gas giant planet around the sun. Just to make sure his meeting with the Lucy probe, whose mission is to overfly it in 2027, isn’t a missed opportunity! In fact, when the shadow of 3548 Eurybate passed over France as expected, it appeared eight seconds late and, more importantly, fifteen kilometers further west than expected. The knowledge made it possible to significantly narrow the margins of error regarding the location of the asteroid on the firmament. “Thanks to these measurements, this uncertainty range, which was about 23 kilometers, is reduced to a few kilometers,” astronomer Josselin Desmars of the Paris Observatory told the journal. Heaven & Space the AFA.

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Finally, the vast majority of participants who actually saw Eurybate’s occultation of the star, after taking the trouble to time their observations, were also able to specify its shape and dimensions. Indeed, scientists can draw the contours of the cosmic object at the origin of the occultation, very accurately determining the period when the star disappeared from the lenses of different observers in different places. Each different occultation period corresponds to a different zone of the asteroid.

We now know that the face of the asteroid observed on the morning of October 23 is about 72 kilometers long and 64 kilometers wide, with a kind of concave growth on one of its edges. It should look like this:

A few hundred people, including simple motivated amateurs, will no doubt have allowed the American probe Lucy to get a little closer to Eurybate to give us a true picture of it within a few years.


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