The "Christmas Comet" seen by Metis aboard Solar Orbiter


Visible and ultraviolet composite images of comet Leonard seen by Metis (Credits: ESA/Metis Team)
Visible and ultraviolet composite images of comet Leonard seen by Metis (Credits: ESA/Metis Team)

On the night between the 15th and the 16th of December, the Metis coronagraph aboard the Solar Orbiter mission has acquired wonderful images of the comet Leonard and of its extended tail. Recently the Leonard comet has been very popular. In fact, it has reached its maximum brightness, and hence visibility, during the month of December, thus perfectly in time to gain the nickname of “Christmas comet”.

Being discovered on the 3rd of January 2021 by the American astronomer Gregory J. Leonard, the comet is simply known as comet Leonard but its formal name is C/2021 A1. Comet Leonard is a 1 km diameter body passing inside the solar system for the first time. On the 3rd of January 2022 the comet has reached its perihelion, i.e. the minimum distance from the Sun, at 0.6 astronomical units, and then it will continue the journey along its hyperbolic orbit to get back outside the solar system.

During its journey towards the Sun, the comet passed at about 40 million km from the Solar Orbiter spacecraft. Solar Orbiter is an ESA/NASA mission developed to study the Sun. Some of the instruments onboard Solar Orbiter had the chance to observe the comet, one of these instruments is the coronagraph Metis realized by an Italian-led consortium.

Metis has been realized by the Italian Space Agency (Asi) in collaboration with the Italian National Institute for Astrophysics (Inaf) and with Cnr, many Italian Universities and different international research institutes.

Metis has acquired images of the comet during a time period of about 12 hours. “Thanks to the two channels of the instrument, the images of the comet have been acquired at the same time both in the ultraviolet and in visible light ranges,” says Marco Romoli, Metis Principal Investigator and professor at the University of Florence, “the simultaneous observation in both these bands is a peculiar key feature of Metis”.

The researchers of the Institute for Photonics and Nanotechnologies in Padova, that have participated in the realization and calibration of Metis, have also been in charge of the observation planning of the Leonard comet. To correctly plan for the comet observations and predict the expected comet and tail brightness, all the available comet observations from Earth have been taken into account.

“We have performed some simulations to plan the observation sequence and the integration times to be used with Metis. The distance of the comet from Metis, the comet expected total brightness and its distribution, the size and position of the coma have all been taken into account” says Alain Corso researcher at the Cnr-Ifn Padova. “The comet transit in the Metis field of view has been along a diagonal, with the dust and ion tails of the comet pointing towards Metis.”

In the following days, from 17 to 19 December, Solar Orbiter continued to track the comet and its evolution thanks to the images acquired by the instrument SoloHI.

The images of the comet Leonard are now being analyzed by the Metis team researchers. Thanks to the data acquired in the visible band, using also different polarization states, hints on the comet dust composition can be obtained, while from the ultraviolet images the water production rate can be derived.

Per informazioni:
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