What's going on with comet Wirtanen?


Wirtanen's Lightcurve

Lightcurve of comet WIrtanen

Lightcurve of comet Wirtanen (colored dots), compiled from observations reported to the Minor Planet Center. Predicted magnitudes are current estimates from sources using different techniques, and are highly uncertain. These will be updated as more recent observations help in constraining the projections.


Updates


26 Jun 2018

Update/Correction on Wirtanen's recovery

On June 1, we reported that Wirtanen had been recovered (see June 1 report below). It turns out that the object that we reported in the May 8 images was a random asteroid (133655), that had nearly the same expected brightness and proper motion as Wirtanen, but was following ~77 arcsec behind the comet's predicted position.

On Jun 18, 19 and 20, Lori Feaga et al. (UMD) obtained observations of Wirtanen from the DCT. Astrometry from these observations, which were obtained under better conditions (2 airmass during astronomical twilight) than the May data, linked well to measurements from 2014. This confirmed that the June ID was actually Wirtanen, and proved that the May ID was not.

The June 18-20 images were obtained when Wirtanen was at a heliocentric distance of 2.28 AU, geocentric distance of 1.98 AU, and had an r' magnitude of 20.6. It shows a short tail (~5 arcsec) to the SSW (in the anti-solar direction, which also coincides with the direction opposite to the comet's velocity vector).

May
8 image of comet 46P/Wirtanen

To re-visit the May 8 observations, we used Wirtanen's new orbit solution to look for the comet in those data, and found that it was close to the newly-predicted positions but barely detectable in individual frames. It became visible when all images were coadded, and is in fact, seen in the coadded image that we presented in our report from June 1.

May
8 image of comet 46P/Wirtanen

The new data indicate that Wirtanen is currently 1-1.5 mag fainter than predicted in both May and June. It is not yet clear how this will translate to the brightness around close approach to the Earth.

The updated orbit solution confirms that Wirtanen will make its close approach to the Earth at a distance of 0.0775 AU on December 16, 2018, at 13:29 UT. Additional astrometry is requested to continue to refine the orbit and constrain the effects of any non-gravitational forces.


1 Jun 2018

Comet Wirtanen has been recovered!

46P/Wirtanen was recovered on May 8, 2018 in images obtained by Nick Moskovitz (Lowell Observatory), in collaboration with Tony Farnham and Matthew Knight (University of Maryland). Six images of the comet were obtained at the Discovery Channel Telescope operated by Lowell Observatory. They were acquired during astronomical twilight at 4.5-5.1 airmass. A coadded version of the images is shown below.

At the time of the recovery, Wirtanen was at a heliocentric distance of 2.61 AU, geocentric distance of 2.80 AU, and had an r' magnitude of 20.3. There is no obvious coma visible in the images, but the comet's brightness suggests that it is already exhibiting activity.

The updated orbit solution confirms that Wirtanen will make its close approach to the Earth at a distance of 0.078 AU on December 16, 2018, but with only limited 2018 observations, the exact time of close approach has an uncertainty of several hours. Additional astrometry is requested to refine the orbit and constrain the effects of non-gravitational forces.

Recovery image
of comet 46P/Wirtanen