Officially classified C/2020 F8 (SWAN) but nicknamed comet SWAN, the new comet was first spotted in April 2020 by Australian amateur astronomer Michael Mattiazzo using data from the Solar Wind ANisotropies (SWAN) instrument aboard the NASA/ESA Solar and Heliospheric Observatory (SOHO).
Comet SWAN makes its closest approach to Earth on May 13, 2020, at a distance of 85 million km (53 million miles); its closest approach to the Sun, called perihelion, will happen on May 27, 2020. Image credit: NASA / ESA / SOHO.
SWAN captures images in ultraviolet light, including a specific ultraviolet wavelength called Lyman alpha. This is a wavelength that is characteristically emitted by hydrogen atoms.
The instrument’s primary goal is to map changes in the solar wind, the variable flow of charged particles that is continuously released by the Sun into interplanetary space. In addition, it has become an effective discoverer of comets too because these objects are also sources of hydrogen.
In the case of a comet, the hydrogen comes from the water vapor the icy core releases into space when heated by the Sun. And there is more, as solar radiation can break water molecules into a single hydrogen atom and a hydrogen-oxygen pair.
The result is a cloud of hydrogen that surrounds the comet, giving off a bright spot of Lyman-alpha light that can be spotted in the SWAN maps.
Almost every day, SWAN records a complete map of the sky. These raw sky maps are full of stars, making it difficult to pick out new comets, which may arrive at random from any direction. To make the job easier, successive maps are automatically subtracted from one another, removing the stars and leaving only variable or moving sources visible.
Comet SWAN is only the 12th discovery from this instrument and is the 3932nd comet discovered by SOHO.
Currently moving from the southern to the northern skies, the comet is just faintly visible to the naked eye, but current estimates suggest that, by the end of May 2020, it could be significantly brighter — if it survives that long.
Comets are fragile objects, and can often break apart as they approach the Sun. In April 2020, the much anticipated comet ATLAS suffered this fate, breaking into at least 30 fragments.
Comet SWAN is now entering the ‘danger zone’ and will reach its closest point to the Sun on May 27 — at this time, the solar heating will be at its maximum.
“By April 15 the comet was ejecting about 1,300 kg of water vapor every second — a fast rate of ejection when compared to other comets,” said SWAN team comet expert Dr. Michael Combi, a researcher at the University of Michigan.
“This is already three times more than comet 67P/Churyumov-Gerasimenko at its best, when it was visited by ESA’s Rosetta mission between 2014 and 2016,” said Dr. Jean-Loup Bertaux, former principal investigator and proposer of the SWAN instrument.
