Charon tectonics

Abstract

New Horizons images of Pluto's companion Charon show a variety of terrains that display extensional tectonic features, with relief surprising for this relatively small world. These features suggest a global extensional areal strain of order 1% early in Charon's history. Such extension is consistent with the presence of an ancient global ocean, now frozen.

Keywords: Charon; Geological processes; Image processing; Pluto; Tectonics.

Fig. 1

This is the last LORRI image that captures the whole disk of Charon and what is referred to as the New Horizons encounter hemisphere, roughly centered at 350° longitude, 40° latitude. Informal names of some features are provided, for more informal named features see Moore et al. (2016a). This is the C_LORRI_FULLFRAME_1 observation (LOR_029914776, ~2.4 km/pixel) which has been deconvolved to bring out features.

Fig. 2

Charon terrain model in orthographic projection created from the PELR_C_LORRI and PEMV_C_COLOR_2 observations.

Fig. 3

Polar stereographic view of Charon’s north pole created from the PELR_C_LORRI and PEMV_C_COLOR_2 observations.

Fig. 4

Charon tectonic features mapped in this work overlain on a mosaic of LORRI images.

Fig. 5

The same tectonic structures as mapped in Fig. 4 but without the underlying mosaic.

Fig. 6

Serenity Chasma. White arrows point to the north and south rims of Serenity Chasma on this mosaic of several LORRI images (primary image is LOR_0299175682, deconvolved to bring out features). The surface beyond the northern rim of Serenity Chasma displays a series of small-relief mostly east-west faults parallel to the chasma rims, and the inset to the lower right is a Galileo image (GO_0023:[G28.GANYMEDE.C055244]3639R.IMG) of dark terrain on Ganymede’s Nicholson Regio, which may be showing similar faulting patterns; note scale difference.

Fig. 7

Perspective view of Mandjet Chasma as taken by LORRI (LOR_0299168968, deconvolved to bring out features) looking westward to the limb, North is to the lower right. Mandjet starts in the lower left of the frame and extends to the limb in the upper right (denoted by brackets). The scarp along the left side of the frame south of Mandjet bounds Vulcan Planum.

Fig. 8

Topographic map of the mid-latitude scarps and crustal block region. What appear to be coherent crustal blocks bounded by scarps in this region are outlined with a dashed line. An elevated region that does not have the steeper sides of the crustal blocks in this region is outlined with a solid line. It may be a Vulcan Planum outlier. This is a mosaic of LORRI images from the C_LEISA_HIRES observation overlain by topography created from the PEMV_C_COLOR_2 and PEMV_C_MVIC_LORRI_CA observations.

Fig. 9

These images show the northern limb of Charon and its polar region to be irregular and displaying a large amount of relief. In the center and right, just below the limb in both images, scarps can be seen with dark features at their crests (the same scarp is identified with an arrow in each image). These are not shadows as these scarps face the Sun. The upper image is a mosaic of LORRI images from the C_LEISA_LORRI sequence. The dark Mordor Macula can be seen in the lower right. The lower image is a deconvolved version of LOR_0299175565 taken after the C_LEISA_LORRI sequence when the spacecraft was closer to Charon. The diameter of Pirx crater is called out in both images.

Fig. 10

LORRI coverage for one rotation before New Horizon’s closest approach. Numbers below each image show the approximate center east longitude on Charon for each image. The upper left image without a label is the image at 350° reprojected to match the image at 351° in order to help match features. These images are interlaced deconvolved versions of the images from the following LORRI sequences: PC_MULTI_MAP_A_18_L1AH (351°), PC_MULTI_MAP_B_1 (336°), PC_MULTI_MAP_B_2 (314°), PC_MULTI_MAP_B_3 (295°), PC_MULTI_MAP_B_4 (280°), NAV_C4_L1_CRIT_33_02 (266°), PC_MULTI_MAP_B_6 (239°), NAV_C4_L1_CRIT_34_02 (223°), PC_MULTI_MAP_B_8 (202°), PC_MULTI_ MAP_B_9 (183°), PC_MULTI_MAP_B_10 (167°), NAV_C4_L1_CRIT_35_03 (153°), PC_MULTI_MAP_B_12_L1AH_02 (126°), NAV_C4_L1_CRIT_36_02 (110°), NAV_C4_L1_ CRIT_37_02 (86°), PC_MULTI_MAP_B_15_02 (70°), PC_MULTI_MAP_B_16_02 (54°), PC_MULTI_MAP_B_17_02 (45°), PC_MULTI_MAP_B_18_02 (35°), PCNH_MULTI_ LONG_1D1_02 (17°) PC_MULTI_LONG_1d2a_02 (2°), and C_LORRI_FULLFRAME_1 (350°). The two bottom right images are both from the time near closest approach. The image on the left is a deconvolved mosaic of LORRI images from the C_LORRI sequence and the image on the right is MVIC image MC0_0299176432.

Fig. 11

These images are the same as in Fig. 10. The diagrams show the locations of assumed features. Argo Chasma is labeled ‘A.’ The large bright-rimmed crater near Argo is labeled ‘c.’ There are three large unnamed lineations, ‘x,’ ‘y,’ and ‘z’ on the non-encounter hemisphere that can be observed in several images.

Fig. 12

Example tectonic features in the inset of Figs. 13–16. This image is a mosaic of the LORRI images from the C_LEISA_LORRI_1 sequence.

Fig. 13

The strike of groove segments mapped on Fig. 4. The inset shows grooves west of Alice crater; Sun from the north.

Fig. 14

The strike of ridge crest segments mapped on Fig. 4. The inset shows a typical ridge in Serenity Chasma; Sun from the north.

Fig. 15

The strike of scarp crest segments mapped on Fig. 4. The inset shows a north-facing scarp just south of Alice crater; Sun from the north.

Fig. 16

The strike of graben segments mapped on Fig. 4. The inset shows Tardis Chasma, a typical graben on Charon; Sun from the north.

Fig. 17

A colorized terrain model of Serenity Chasma can be seen with numbered profiles marked, starting with profile 1 on the left.

Fig. 18

Profiles from Fig. 17 with flexural fits superimposed. Each profile is labeled with the best-fit elastic thickness T_e. Flexural fitting procedure and parameter values adopted are the same as in (Peterson et al., 2015) except for the surface gravity.

Fig. 19

A comparison of profile 3 (Fig. 17) from Serenity Chasma compared to similar profiles from Ithaca Chasma, Tethys (Giese et al., 2007); Arden Corona, Miranda (Pappalardo et al., 1997); and graben on Ariel (Peterson et al., 2015).

Fig. 20

These traces show the local maximum (top of footwall) and minimum (bottom of footwall) topography along the southern wall of Serenity Chasma (profiles shown in Fig. 17). The difference between these two levels is also plotted as the vertical offset across the scarp.