88P/Howell

 

This comet was discovered by Ellen Howell on August 29th 1981 on plates taken with the 46-cm Schmidt at Mount Palomar that has, over the years been used so prolifically for comet and NEO discoveries. The comet was magnitude 15 and diffuse. At discovery the perihelion distance was 1.62AU and the period 5.94 years. Since then the comet has been seen at each return: in 1987, 1993, 1998 and 2004 and is expected again in 2009.

 

It was rapidly realised that 88P/Howell had had a Jupiter encounter in 1978, shortly before discovery. Further investigation has shown that its eventual discovery has been the result of a process of slow migration of perihelion over the course of the 20^th Century. Prior to 1907 the comet had perihelion at 2.01AU and was significantly fainter. However, encounters with Jupiter in 1907 (0.19AU), 1978 (0.58AU) and 1990 (0.53AU) have made the perihelion distance reduce progressively to 1.84AU, then 1.61AU (at discovery) and finally to 1.41AU. The perihelion distance will continue to reduce slightly reaching a minimum of 1.35AU in 2020, after which the reverse process will start, with more encounters increasing the perihelion distance progressively to 1.86AU at the start of the 22^nd Century.

 

The reduced perihelion distance means that at a favourable return, such as 2009, the comet can now reach about magnitude 10. The current period is 5.50 years, making alternate returns very good and very bad.

 

The comet was quite well covered at its 2004 return, although observations were only made well after perihelion due to the circumstances of the apparition. The light curve is made up of data from Ramón Naves & Montse Campàs (MPC 213), Julio Castellano (MPC 939), Francesc Baldris (MPC A01), Josep Lluis Salto (MPC A02), Filip Fratev (MPC A61), José Antonio Reyes & Sensi Pastor (MPC J76), Joaquín Sánchez (MPC J78) and Toni Climent (MPC J97).

 

The light curve shows a steady fade, although this is logical as the coverage starts six months after perihelion. The CCD data presented here shows a much slower fade than the total visual magnitude data for which Seichii Yoshida finds m1 = 5.5 + 5 log Delta + 25 log r (with a 33 day perihelion asymmetry and maximum brightness after perihelion).

 

The value of Afrho shows a rapid decline from approximately 120-cm at T+180 days, to about 15-cm at T+260 days. The dust production rate declines as r^-9, somewhat faster than normal in Jupiter family comets, but not extraordinarily fast.