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The line between comets and asteroids is somewhat blurred (see below) but when we see a big bright tail we at least like to call it a comet. This question is about exploration of the tails of big-tail-producing but otherwise small natural solar system bodies in heliocentric orbits.

Have spacecraft every been navigated through such a tail on purpose? If so, was it a challenge to predict the trajectory of the tail separately from the trajectory of the body producing it?

Sometimes there are a pair of tails (see this answer (voting to reopen the question)) responding differently to a mixture of forces, and sometimes there are many tails (see below). If this has happened, I'm wondering if there was a tail propagating algorithm used in order to target it with a spacecraft, and feedback from tail observations and subsequent tail-tracking trajectory correction maneuvers.


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    $\begingroup$ ISTR Ulysses did, but maybe not on purpose. $\endgroup$ – Organic Marble Nov 5 '20 at 23:38
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    $\begingroup$ @OrganicMarble I think "it's so easy that it's been done by accident" (or similar) is a perfect answer! $\endgroup$ – uhoh Nov 5 '20 at 23:47
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    $\begingroup$ AFAIR there is at least one historical event of the Earth passing through a tail of a comet. $\endgroup$ – fraxinus Nov 6 '20 at 8:31
  • $\begingroup$ @fraxinus ya that sounds very familliar. I remember seeing artwork or a drawing of a spectacular meteor shower in an old text, and it was more recently recognized as likely due to crossing paths with a comet, but I'm not sure if what I am remembering would count as a comet's tail per se $\endgroup$ – uhoh Nov 6 '20 at 9:02
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Ulysses, the shuttle-launched joint NASA/ESA probe to study the sun's polar regions, ran through three comet tails, more or less by chance.

enter image description here

Ulysses Catches Record for Catching Comets by Their Tails

  • ...comet Hyakutake ...On May 1, 1996, while Ulysses was cruising through space studying the solar wind, its data suddenly went wild for a few hours.

  • The once-in-a-lifetime chance encounter with a comet tail happened again in 2004 when Ulysses flew through the ion tailings of comet McNaught-Hartley

  • Ulysses racked up its third, and perhaps most scientifically revealing, comet tail encounter this past February1 when it again flew through the ion tailings of a comet named McNaught (a different comet than the one encountered in 2004, but discovered by and named after the same astronomer).

1 2007

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Rosetta collected dust from 67P/Churyumov-Gerasimenko and analyzed it under an atomic force microscope, without landing on the cometary body itself; depending on your definitions this would seem to imply having flown through its tail.

Navigation isn't much of an issue; you simply navigate close to the cometary body and hang out on the sunny side -- though I guess technically that's the comet's head.

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  • $\begingroup$ I've asked this, but I won't answer it either, at least not right away: How did ESA blast an atomic force microscope off the Earth, deploy it in deep space, capture tiny particles from a comet and position them 'under' it? $\endgroup$ – uhoh Nov 6 '20 at 2:07
  • $\begingroup$ Isn't the tail of comet always on the opposite side of the sun, i.e. the dark side? Because it's not a trail left by the comet moving, but rather gas that is blown off by the pressure from the solar wind. $\endgroup$ – corsiKa Nov 8 '20 at 22:18
  • $\begingroup$ My crude mental model is that the tail material is sublimated dirty ice coming off the sunlit side, then differentially accelerated in the direction of the shadowed side by solar wind and radiation pressure, i.e. the tail starts on the sunny side and flows to the opposite side, hence my reference to the comet's head. I don't know how accurate my mental model is. $\endgroup$ – Russell Borogove Nov 8 '20 at 23:56
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The two Vega probes comes to mind, ending their implausible sounding mission of slipping balloons into the atmosphere of Venus with a flyby of Halley's comet in 1986.

They took a heavy beating flying through the coma, which is the shell of dust and gasses surrounding the comet itself, at the start of the tail.

From a navigational point of view, the goal appears to just have been to come as close to the nucleus as possible.

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The International Cometary Explorer spacecraft passed through the plasma tail of 21P/Giacobini–Zinner in September, 1985, which I think was the first time the human race had engineered such a rendezvous. Many years ago, in my salad days, I did my PhD research on the encounter.

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  • $\begingroup$ Yes indeed, it seems you've found the first and a pretty amazing mission it was. If there are any details you can track down on the planning of the trajectory through the comet's tail, that would be great! Feel free to share any relevant details you like. Welcome to Space! (again) $\endgroup$ – uhoh Nov 6 '20 at 16:00
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    $\begingroup$ Thank you! It didn't take much searching for, it was three years of my life, and comes readily to mind! Sadly, I came into it in 1988, after the mission had flown, and much of the analysis had been done, so I don't know much about the mission planning phase, and specifically nothing about the planning for the tail encounter. We definitely flew right through the middle of the plasma tail, though; there's a huge sign change in the magnetic field as we passed from one lobe to the other. $\endgroup$ – MadHatter Nov 6 '20 at 16:15
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In 1986, Giotto closely approached Halley's comet flying through dust and gas and surviving with less damage than expected.

I couldn't tell if Giotto was flying through Halley's tail or coma, but its journey can be taken as an upper bound of how harsh flying through the tail can get.

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