This is an unexpected opportunity at the launch of the European mission, but on December 17, the Solar Orbiter probe crossed the tail of comet Leonard. The latter was already far away, but the very sensitive instruments devoted in particular to the solar wind were able to study its composition.
And this time, all the instruments were calibrated!
The Last Show of Comet Leonard
Many amateur and professional astronomers followed comet C/2021 A1 Leonard in December, which offered a nice spectacle, even if it was not (unless there were exceptional conditions) visible to the naked eye.
At University College London, Samuel Grant, who works on the interactions between the solar wind and comet tails, uses software simulation to estimate particle directions. ” I’ve used it on Leonard and Solar Orbiter, with several solar wind speed variations. The two crossed paths ! The European probe, relatively close to the Earth after its gravitational assistance on November 27, therefore did not cross the comet closely: it was 44 million kilometers away… But, carried by the solar wind, the particles that ejected were indeed measured, with a peak on December 17.
Turbulence!
Unsurprisingly, the clearest detection of this passage in Leonard’s “wake” was made thanks to the instrumental suite devoted to the analysis of the solar wind (SWA), via its charged particle sensor HIS (for Heavy Ion Sensor). The instrument manager was adamant and explained that the ion detections on this occasion were directly related to the comet. SWA-HIS thus captured oxygen, various carbonaceous molecules and even water.
But Solar Orbiter has many other instruments on board, and the readings from the MAG magnetometer are also being analyzed… And of course there are the other sensors that have observed Leonard thanks to their optical suites. The Metis coronagraph, in particular, was able to observe the comet in the ultraviolet and visible spectrum. This should help determine how fast the comet was ejecting its water and dust.
Measures, measures and more measures
The Solar Orbiter data, if they take advantage of the passage “in” the flow generated by comet Leonard, are in fact added to a veritable anthology of European and American measurements in December. The Soho probe observed it, as did STEREO-A, and even the Parker solar probe, between two dives within the very heart of the solar “atmosphere”. What better way to understand these distant objects, a large part of which was formed at the dawn of the Solar System and does not survive a single passage near the Sun…
In addition, calibrating instruments helps prepare for the future. In particular, ESA is preparing Comet Interceptor, a small mission that will take off before scientists have determined its objective: it will be placed on hold, before maneuvering to fly as close as possible to a comet plunging towards its destiny.
Finally, for Solar Orbiter, whose instruments are now 100% operational, it was a new opportunity to carry out measurements on a comet. The teams were excited to pass in the wake of comet C/2019 Y4 Atlas in 2020, but it was still too early in its mission for the instruments to perform optimally.
Source:
ESA
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