Raditladi (crater)

Background

During its first flyby of Mercury in January 2008 MESSENGER spacecraft discovered a large impact crater approximately 2000 km west of the Caloris basin on the part of Mercury's surface previously not seen by spacecraft. This crater (or basin) was subsequently (on 8 April 2008) named Raditladi after Leetile Disang Raditladi (1910–1971), a Motswana playwright and poet. Raditladi is one of the youngest features on Mercury.

Geology

The central part of Raditladi is occupied by a large peak ring with a diameter of 125 km. This dark spot is associated with the hollows.

Extensional troughs

Visible on the floor of Raditladi inside the peak ring are concentric narrow troughs, formed by extension (pulling apart) of the surface. The troughs are arranged in a circular pattern approximately 70 km in diameter. They are thought to be graben. The geometrical center of the system of graben coincides with the center of Raditladi and is offset from the center of the peak ring complex.

Extensional troughs on Mercury are quite rare, having been seen in only a few other locations:

• Rachmaninoff, which is similar in many other ways to Raditladi
• as part of Pantheon Fossae and other troughs in the Caloris basin
• on the floor of Rembrandt, a large basin discovered during MESSENGERs second Mercury flyby. Understanding how these troughs formed in the young Raditladi basin could provide an important indicator of processes that acted relatively recently in Mercury's geologic history. There are two main theories of graben formation. The first is that they represent a surface manifestation of ring dikes or cone sheets. Both types of structures form when magma from a deep reservoir intrudes into the overlying rocks along conical or cylindrical fractures. The second hypothesis holds that the graben formed as a result of the floor uplift caused by the weight of the smooths plains outside the crater. Such plains are indeed present to the north and east of Raditladi, although their thickness and age are not known.

Age

The relative age of any surface feature can be determined from the density of impact crater on it. The density of craters on the floor of Raditladi is about 10% of that on the plains west of Caloris. The crater density is the same on the ejecta covered plains outside the basin. The smooths plains and hummocky plains also have the same crater density and therefore the same apparent age. The low crater density indicates that Raditladi is much younger than Caloris—it may have formed within the last billion years, whereas the age of Caloris is 3.5–3.9 billion years.

The young age of Raditladi shows that the effusive volcanic activity on Mercury lasted for much longer that had been thought, possibly extending to the last billion years.

Gallery

MESSENGER's first view of Mercury with name labels.jpg|Position of Raditladi on Mercury Raditladi Basin topography JMARS Colorized Shade 2km.jpg|Topography of Raditladi Raditladi crater MESSENGER WAC IGF to RGB.jpg|Exaggerated color image of Raditladi Central peak ring of Raditladi crater EW0231179208G.jpg|Central peak ring. Concentric troughs are visible.

References

References

1. It is one of 110 peak ring basins on Mercury.Chapman, C. R., Baker, D. M. H., Barnouin, O. S., Fassett, C. I., Marchie, S., Merline, W. J., Ostrach, L. R., Prockter, L. M., and Strom, R. G., 2018. Impact Cratering of Mercury. In ''Mercury: The View After [[MESSENGER]]'' edited by Sean C. Solomon, Larry R. Nittler, and Brian J. Anderson. Cambridge Planetary Science. Chapter 9.
2. "Mercury: Raditladi". USGS.
3. (2011). "The transition from complex crater to peak-ring basin on Mercury: New observations from MESSENGER flyby data and constraints on basin formation models". Planetary and Space Science.
4. (2009). "The curious case of Raditladi basin". Lunar and Planetary Science.
5. (2008). "Reflectance and Color Variations on Mercury: Regolith Processes and Compositional Heterogeneity". Science.
6. (2008). "Mercury Cratering Record Viewed from MESSENGER's First Flyby". Science.
7. (2009). "Evidence for intrusive activity on Mercury from the first MESSENGER flyby". Earth and Planetary Science Letters.
8. (2001). "Geologic evolution and cratering history of Mercury". Planetary and Space Science.
9. (2009-03-31). "The Curious Case of Raditladi Basin". [[Johns Hopkins University]] [[Applied Physics Laboratory]].