Sungrazing Comets as Source of Pickup Ions at Earth Orbit and Ulysses

Most of the sungrazing comets observed by LASCO at SOHO belong to the Kreutz group of comets and follow trajectories that are tightly clumped in space. Statistical analysis of 9 years of SOHO observations suggests that the true apparition rate of these comets is as high as one every other day. Practically all these comets break up before perihelion passage. Their material is dissociated and ionized, and subsequently transported away from the Sun as pickup ions in the solar wind. Their mean mass flux is about 3.1 · 10 g·s. Since the breakup occurs between 40 and 4 solar radii and the ionization is almost immediate, the expected location of these ions in the phase space is close to the location of the inner source of pickup ions. Assuming radial propagation, the cometary pickups should be observable at Earth between August and January, with peak probability at the end of September. At Ulysses, they should be observable approximately between −25 and 40 degrees ecliptic latitude during the fast latitude scans, the first of which occurred in 1995 and the second in 2001. The population of cometary pickup ions should be augmented by about 40% by solar wind protons as a result of charge exchange with the cometary neutral hydrogen and oxygen atoms and subsequent reionization of the newly-created Energetic Neutral Atoms, streaming with respect to the solar wind. In total, the average flux of the pickup ions related to the sungrazing comets at 1 AU should be about 1.6 · 10 g·s·sr within the detection area (and null outside it). This value is comparable to the flux of the inner source-pickup ions.