On April 10th, amateur astronomer Michael Mattiazzo (Australia) reported the discovery of an unknown comet in images obtained by the SOHO/SWAN instrument. Now designated C/2020 F8 (SWAN), the object is currently located in Piscis Austrinus, slowly moving north-east and brightening. Follow-up observations have shown the comet to display a particularly condensed coma, as well as a faint ion tail (several arcminutes long). Based on his own ground-based images, Michael estimated the comet to be V= +9.7 mag on April 10th. However, more recent estimates suggest the object to currently be around V= +8 mag! Due to the brightness of the comet, in addition to its condensed appearance, it is possible that it might be undergoing an outburst.
Figure 1: Comet C/2020 F8 (SWAN) comet as imaged by Rob Kaufman (cropped). Notice the obvious green colour, as well as the highly condensed nature, of the coma! The image was taken from Bright (Victoria, Australia) and was acquired using a Canon DSLR (EOS 800D) along with a 55mm F/5.6 lens. (c) Rob Kaufman.
The available observations suggest that the comet is still on its inbound journey towards perihelion, and will hence (most likely) keep brightening, while progressively moving towards less favourable skies (poorer solar elongation). According to Seiichi Yoshida’s website, the object could reach V= +4 mag near perihelion on May 31st (q= 0.43 AU), but will be at relatively poor solar elongation. Other sources suggest that it may reach a peak brightness within the range of V= +2 to +3 mag! As of currently, it is difficult to make any reliable estimations regarding the comet’s peak magnitude, and hence these values should be taken with caution.
Figure 2: C/2020 F8 (SWAN) as imaged by Rolando Ligustri using the Siding Spring Observatory (Australia) facilities. Notice the comet’s vast green coma and faint ion tail! (c) Rolando Ligustri
Due to the poor resolution of SOHO/SWAN images, in addition to the numerous automated all-sky surveys (e.g. ATLAS, CSS and PANSTARRS), SWAN comet discoveries are rare. Indeed, over the past 25 years, only 14 comets carry the name “SWAN” (including co-discoveries)*. In many cases, these comets were located at poor solar elongation at the time of discovery (a “blind spot” for most surveys).
Figure 3: Cropped view of C/2020 F8 (SWAN) as seen in one of the discovery SOHO/SWAN (“comet tracker map”) frames. The poor resolution of the images makes it impossible to discern any of the obvious cometary features captured by ground-based images. Image credit: ESA/NASA/LATMOS SOHO/SWAN.
Note that C/2020 F8 is not the first SOHO/SWAN discovery made by Michael Mattiazzo. Indeed, Michael is credited for the (co)discovery of seven other SWAN comets, his first being C/2004 H6 (SWAN). His others include: C/2004 V13, C/2005 P3, P/2005 T4, C/2006 M4, C/2015 C2, and C/2015 P3 (SWAN). Among these, C/2006 M4 reached mag +4.5 a month after it had passed perihelion (August 21st, 2006), making it the only SWAN comet to be visible to the naked-eye!**
Figure 4: Composite image showing: A SOHO/LASCO C3 image extract of C/2004 V13, and cropped image extracts of C/2006 M4, C/2015 C2 and C/2015 P3, from photographs taken by Doug Neal (Kennewick, WA, USA) and Rob Kaufman (Bright, Victoria, Australia). (c) Doug Neal, Rob Kaufman.
To conclude, C/2020 F8 (SWAN) is a relatively bright (V= +8 mag) comet, possibly in outburst, that is currently on its way to perihelion. Based on its orbit and current brightness, the comet is estimated to reach a peak brightness between 2 – 4 mag in late-May or June, but will likely be somewhat difficult to observe due to poor solar elongation. However, estimating the peak brightness of any comet is very difficult, and hence these values are to be taken with alot of caution. It is still a very new discovery, with relatively few observations currently available. Indeed, it is equally possible that the brightening may eventually stagnate, or that the comet may even start disintegrating. This would not be extremely surprising knowing that perihelion distance is only of q= 0.43 AU. As of currently, we can only wait!
*This does not include 273P/Pons-Gambart, which was temporarily designated C/2012 V4 (SWAN) before it was found to be the return of lost comet D/1827 M1 (Pons-Gambart).
**Comet C/2012 E2 (SWAN) reached mag +1 before it disintegrated on March 14th, 2012. However, it was too close to the Sun to be observed from Earth. More information on this comet can be found here.