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A comet that shattered before it appeared in Earth’s night sky last year has nonetheless given us a rare and wonderful gift.
As its disembodied tail continued its journey through the solar system, a spacecraft orbiting the Sun may have passed through its tail, quite by accident. The European Space Agency’s solar orbiter has now given us a unique glimpse into the tail of a disintegrated comet.
The results were presented at the 2021 Royal Astronomical Society National Astronomical Meeting.
Comet C / 2019 Y4 (ATLAS) was discovered in December 2019 and comet watchers were immediately thrilled. Its course around the Sun had to bring it close enough to the Earth to be visible to the naked eye. Before it reached that point – and long before its expected perihelion – the comet disintegrated.
(NASA / ESA / STScI / D. Jewitt, UCLA / CC BY 4.0)
Above: Image from the Hubble Space Telescope of Comet C / 2019 Y4 (ATLAS) on April 20, 2020, providing the sharpest view to date of the comet’s solid core rupture.
In April of last year, images from the Hubble Space Telescope showed the fragments of the comet, shattered as its ice sheets sublimated in the increasing heat as it approached the Sun. This is not really a rare event, but rather dashed our hopes of seeing comets.
There were also other hopes for C / 2019 Y4 (ATLAS). Shortly after its launch, the Solar Orbiter team noticed that its trajectory would bring it through the tail of the comet. The spacecraft was not designed for this type of encounter, and its instruments weren’t supposed to be on at this point, but the scientists thought why not try and see what they could?
When the comet disintegrated, the team figured that since they had already prepared, they might as well continue with their plans, even if there was nothing to detect. However, when Solar Orbiter made his scheduled rendezvous with the comet tail, he did indeed detect something.
Now, scientists have reconstructed the encounter to find out exactly what the probe detected.
“We identified a magnetic field structure observed in early June 4, 2020, associated with complete magnetic field reversal, local flux deceleration and high plasma density, and dust and ion events. energies, ”wrote a team led by physicist Lorenzo Matteini of University College London.
“We interpret this structure as a magnetic field draping around a low-field, high-density object, as expected for a comet magnetism. Within and around this large-scale structure, several ion-scale fluctuations are detected which are consistent with small-scale wave and structure fluctuations generated by instabilities of cometary pickup ions. “
In other words, Solar Orbiter’s instruments detected the comet’s tail magnetic field, embedded in the ambient interplanetary magnetic field. This allowed them to learn more about the ion tail of C / 2019 Y4 (ATLAS).
Comets, you see, have two tails. There is the dust tail; this is made up of dust ejected by the comet while the icy material sublimates, generating a dusty atmosphere called coma around the comet nucleus. Radiant pressure from the Sun and solar wind pushes dust away, forming a tail.
The ion tail, on the other hand, is produced when solar ultraviolet light ionizes molecules in a coma. The resulting plasma generates a magnetosphere; it is also repelled by the solar wind, and this is the ion tail.
The team’s results showed that the magnetic field of the ion tail persists for some time after the comet decays. The magnetic field embedded in the solar wind bends and wraps around the magnetic field of the ion tail.
The probe’s measurements, they said, are consistent with an encounter with a cometary magnetic and plasma structure embedded in the solar wind, either associated with a fragment of the shattered comet or with part of the tail that was previously disconnected. .
“This is a pretty unique event and an exciting opportunity for us to study the composition and structure of cometary tails in unprecedented detail,” said Matteini.
“I hope that with the Parker Solar Probe and Solar Orbiter now orbiting the Sun closer than ever, these events could become much more frequent in the future!”
The results were presented at the 2021 National Astronomy Meeting.
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