P-type asteroid

Taxonomy

An early system of asteroid taxonomy was established in 1975 from the doctoral thesis work of David J. Tholen. This was based upon observations of a group of 110 asteroids. The U-type classification was used as a miscellaneous class for asteroids with unusual spectra that did not fit into the C and S-type asteroid classifications. In 1976, some of these U-type asteroids with unusual moderate albedo levels were labeled as M-type.{{cite conference | book-title=Proceedings, 18th Lunar and Planetary Science Conference |date=March 1987

Around 1981, an offshoot of the M-type asteroid branch appeared for minor planets that have spectra that are indistinguishable from M-type, but that also have low albedo not consistent with the M type. These were initially labeled X-type asteroids, then type DM (dark M) or PM (pseudo-M), before acquiring their own unique classification as P-type asteroids (where the P indicates "pseudo-M").

Properties

The P-type asteroids are some of the darkest objects in the Solar System with very low albedos (pv{{cite book | url-access=limited | book-title=Proceedings, 35th Lunar and Planetary Science Conference

The density of the only two well-characterized P-type asteroids, 87 Sylvia and 107 Camilla P-type asteroids appears to be low, at – lower even than C-type asteroids. It is not clear what this tells us about their compositions. Both Sylvia and Camilla have moons and indications that they have been be disrupted, but they are also quite massive, at over kg, and so are unlikely to have much internal porosity affecting their densities.

The outer part of the main asteroid belt beyond 2.6 AU from the Sun is dominated by low-albedo C, D and P-type asteroids. These are primitive asteroids that may have had their materials chemically altered by liquid water. There are 33 known P-type asteroids. In addition to this, P-type asteroids are thought to be found in the outer asteroid belt and beyond.{{cite journal | doi-access=free}} The distribution of P-type asteroids peaks at an orbital distance of 4 AU.{{cite book

References

References

1. P. Vernazza et al. (2021) VLT/SPHERE imaging survey of the largest main-belt asteroids: Final results and synthesis. ''Astronomy & Astrophysics'' 54, A56