The Solar and Heliospheric Observatory (SOHO) involves the European Space Agency and NASA so that the Sun can be scanned on a permanent basis. Its instruments also help detect the comets which pass near our star.
The operational adventure of SOHO started with its launch in 1995. The following year, the space observatory reached the Lagrange point of gravitational balance L1 between the Earth and the Sun. From there, 1.5 million kilometres from our planet, it scans the Sun and has since surpassed its two-year operational life by far! On 15 June 2020, the data which it collected enabled it to discover its 4000th comet.
Finding Comets by Watching the Sun
Loaded with instruments, SOHO has carried out many measurements and, even if other observatories dedicated to the Sun have since been sent into space, the fruit of this co-operation between ESA and NASA continues its mission. The images from its LASCO instrument (Large Angle and Spectrometric COronagraph) show what happens in the immediate environment of our day star. Very useful for examining eruptions and the solar corona, LASCO also sees the so-called sun-grazing comets, those which during their orbit cross near our star. SOHO has proved itself to be very productive at this little game, since it reached the landmark on 15 June of 4000 comets discovered.
The discoveries of comets with SOHO are frequently made by “citizen scientists,” people who voluntarily study closely the freely accessible data of space missions. Thus, Trygve Prestgard noted the presence of this comet, registered as SOHO-4000, on 15 June. A student of Geophysics at the University of Grenoble in France, he knew SOHO’s “meter” was approaching 4000, but he did not think it would be himself who would be lucky enough to happen on this symbolic figure.
The video from NASA’s Goddard Center below brings together “4 of our favorite comets discovered by SOHO.” It concludes with SOHO-4000.
According to the first estimates, SOHO-4000 has quite a small core of 5 to 10 m wide. As SOHO-3999 and SOHO-4000 approached the Sun only 1.5 million kilometres apart, astronomers do not rule out that they may have been linked until very recently.