Monsters in the tails of comets are sculpted by the sun

Scientists are a little closer to understanding why some comets have strange dust bands in their tails. The main culprit of this cosmic mystery? Our own sun

Comets are small mbades of ice and dust left behind by the formation of the solar system 4.6 billion years ago. As comets approach the sun, the heat of the sun releases gases trapped in these comets, which also releases dust, according to a statement from NASA's Goddard Space Flight Center in Maryland. This creates two tails: a charged particle ion tail that tracks the solar wind and a tail of dust.

Dust separators have intrigued scientists since at least 1744, when this year's Big Comet would have six tails – something no one could explain at the time. It was well before the era of photography, but comet scientists at NASA found a similar effect on the film with comet McNaught in 2007. [The Greatest Comets of All Time]

McNaught displayed bands of dust, or streaks, extending behind the comet for at least 160 million kilometers (160 million kilometers) – more than the equivalent distance between the Earth and the sun.

According to the release, the research has so bothered the researchers that when McNaught's first images from space were transmitted by the STEREO mission (Observatory of Solar Earth Relations), the team thought that something was wrong. Was not going. But the tail was real, and this was confirmed in the sightings of the NASA-Europe Ulysses Spacecraft the following month. Later in 2007, observers from the southern hemisphere of the Earth could see the groups themselves, extending into the sky and giving a spectacle to the naked eye.

"McNaught was a huge deal when he came, because it was so ridiculously shiny and beautiful in the sky," said Karl Battams, an experienced professional comet observer from the Naval Research Laboratory part of the company. STEREO team. "His streaks were dusty fingers that stretched out over an immense expanse of sky.Structurally, it's one of the most beautiful comets we've seen in decades," added Battams.

A decade later, a separate research team finally found clues about McNaught's strange behavior. Oliver Price, a PhD student in Planetary Science at University College London in the UK, has seen something unique happening in the pictures.

"My supervisor and I have noticed strange phenomena in the images of these streaks, a disruption of the lines otherwise clear," he said in the same statement from NASA. "I began to investigate what could have happened to create this strange effect."

It turns out that this flaw is due to the activity of our sun. It seemed to be located in a region of the solar system, located at a certain radius of the sun, called a heliospheric current sheet. It is an area with complex shapes where the solar wind polarity – the constant flow of charged particles that flows from our sun – can change direction.

This realization, however, intrigued even more Price and his supervisor. Scientists have long known that the sun would have an effect on the ions (positively charged molecules) of the comet's tail, but seeing the sun alter the structure of a tail of dust was quite new.

"The dust in McNaught's tail – [with particles] Scientists have estimated that cigarette smoke is too heavy for the solar wind to move, "said NASA officials. . "

McNaught's images from space, unfortunately, did not follow the comet all the way, as it circled the sun. The comet was traveling too fast to stay in the images taken by STEREO and SOHO (Solar and Heliospheric Observatory). Price said that the datasets on McNaught were excellent, but that they were scattered by cameras throughout the solar system, making it difficult to see what was actually happening in the queue.

He decided to try a new technique of image processing. It gathers all the collected data with a simulation of the appearance of the tail. The simulation included factors such as the location of the dust grains, their size and age, and the time elapsed since they left the comet. This work created a temporal map; NASA officials have stated that this type of map "superimposes information from all the images taken at a given moment".

Concretely, it meant that Price could see the dust evolve for two weeks. He confirmed that it was the heliospheric current layer that caused the streaks. It took two days for the comet to browse the current sheet. As this happened, the dust was constantly moving under the effect of changing magnetic field lines. It seems that the dust was not too heavy to move, after all.

"It's as if the feathers of the striation were crumpled when it crossed the current leaf," said Geraint Jones, a member of the team, Planet Science Specialist at University College London. "If you imagine a wing with a lot of feathers, while the wing pbades through it, the lighter ends of the feathers get deformed.For us, this is an obvious proof that the dust is electrically charged and that the solar wind affects the movement of this dust ".

Scientists say the behavior of the dust tail can be extrapolated to dust that forms bodies such as asteroids, moons and planets at the beginning of the solar system. This new McNaught badysis therefore means that the role of our sun at the beginning of the solar system has yet to be explored.

A study based on Price research has been published online and will appear in the February 2019 issue of Icarus.

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