45P/Honda-Mrkos-Pajdusakova Home Page
What is interesting about comet H-M-P?
- H-M-P has made several recent approaches to the Earth
H-M-P's 5.3 year orbit currently puts it on a 3-apparition cycle. Over this cycle, one apparition is poor, with the comet on the other side of the Sun at perihelion, but the next two are timed such that the Earth is well-positioned for pre-perihelion observations and post-perihelion observations, respectively.
- H-M-P gets closer to the Sun than Wirtanen or T-G-K
The 0.53 AU perihelion distance of H-M-P has an effect on its activity. Because it receives ~4x as much energy as the other two comets, it is likely to be more evolved. Also, since the activity peaks near perihelion, it is ramping up or ramping down when H-M-P approaches the Earth at 1 AU. This, combined with the fact that it tends to exhibit a diffuse coma, likely keeps it from appearing as bright as the other comets.
- H-M-P's is difficult to observe at perihelion
The current configuration of H-M-P's orbit, with perihelion at 0.53 AU, places the comet at a small solar elongation (<30°) around perihelion. Most Earth-based telescopes are not able to observe this close to the Sun, which leads to a lack of data for this comet at perihelion.
With the 2011 and 2017 close approaches to the Earth, there is a rapid transition from observable to unobservable (in 2011; vice versa in 2017) as the comet is well-positioned for observations when it is outside Earth's orbit, and then rapidly gets lost in the Sun's glare when it passes Earth.