Table 2
Active area (km2) and active fraction of the surface (%) for 21P usingthe slow-rotator model at some interesting heliocentric distances.
| Date UT | rh | Active area | Active fraction |
|---|---|---|---|
| (au) | (km2) | (%) | |
| (a) 2018 Jun. 22 | –1.49 | 4.9 ± 0.1 | 17.5 ± 11.6 |
| (b) 2018 Aug. 17 | –1.07 | 12.0 ± 0.2 | 42.5 ± 28.0 |
| (c) 2018 Sep. 09 | –1.01 | 9.0 ± 0.2 | 32.0 ± 21.3 |
| (d) 2018 Sep. 15,16,17 | +1.02 | 6.9 ± 0.1 | 21.5 ± 14.0 |
| (e) 2018 Nov. 09 | +1.31 | 0.90 ± 0.04 | 3.3 ± 2.2 |
Notes. (a) The firstmeasurement during our monitoring campaign, (b) the maximum activity during our monitoring campaign, (c) the last measurement before perihelion passage, (d) the mean of the first measurements after perihelion passage with similar heliocentric distances of 1.02 au, and (e) the last and minimum measurements during our monitoring campaign. Large errors in the active fractions of the surface come from the large uncertainties in the radius of the nucleus, which we adopted as 1.5 ± 0.5 km (see Sect. 3.3 for details).
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