Planetary and Space Science 101 (2014) 186–195

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Planetary and Space Science

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Lutetia's lineaments

S. Besse a,n, M. Küppers b, O.S. Barnouin c, N. Thomas d, J. Benkhoff a a ESA/ESTEC, Keplerlaan 1, Noordwijk, The Netherlands b ESA/ESAC, PO Box 78, 28691 Villanueva de la Cañada, Spain c Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA d Physikalisches Institut, Sidlerstrasse 5, University of Bern, CH-3012 Bern, Switzerland article info abstract

Article history: The European Space Agency's Rosetta spacecraft flew by asteroid (21) Lutetia on July 10, 2010. Received 18 April 2014 Observations through the OSIRIS camera have revealed many geological features. Lineaments are Received in revised form identified on the entire observed surface of the asteroid. Many of these features are concentric around 10 July 2014 the North Pole Crater Cluster (NPCC). As observed on (433) Eros and (4) Vesta, this analysis of Lutetia Accepted 14 July 2014 assesses whether or not some of the lineaments could be created orthogonally to observed impact Available online 30 July 2014 craters. The results indicate that the orientation of lineaments on Lutetia's surface could be explained by Keywords: three impact craters: the Massilia and the NPCC craters observed in the northern hemisphere, and (21) Lutetia candidate crater Suspicio inferred to be in the southern hemisphere. The latter has not been observed Asteroid during the Rosetta flyby. Of note, is that the inferred location of the Suspicio impact crater derived from Lineaments lineaments matches locations where hydrated minerals have been detected from Earth-based observa- Impact crater tions in the southern hemisphere of Lutetia. Although the presence of these minerals has to be confirmed, this analysis shows that the topography may also have a significant contribution in the modification of the spectral shape and its interpretation. The cross-cutting relationships of craters with lineaments, or between lineaments themselves show that Massilia is the oldest of the three impact feature, the NPCC the youngest, and that the Suspicio impact crater is of intermediate age that is likely occurred closer in time to the Massilia event. & 2014 Elsevier Ltd. All rights reserved.

1. Introduction shown that the boulders' distribution on the surface could be explained by ballistic trajectory of the NPCC impact ejecta. It has On 10th July 2010, the Rosetta spacecraft of the European Space been also suggested that NPCC is the source of most of the Agency successfully flew by the main-belt asteroid (21) Lutetia lineaments visible on the observed surface (Jutzi et al., 2013; (Schulz et al., 2012). Numerous observations of its surface were Thomas et al., 2012), if it is assumed that lineaments are created by made by remote sensing instruments, revealing its surface proper- large impacts on a surface. ties and composition. Of particular interest were the observations Lineaments are very common features that have been observed of the OSIRIS (Optical Spectroscopic and Infrared Remote Imaging on many previously imaged asteroids. The first direct observation System) camera (Keller et al., 2007), the main imaging system of lineaments was obtained by the Viking missions on the onboard the orbiter, which revealed numerous geological features Phobos (Thomas et al., 1979). These lineaments extend for several on its surface (Sierks et al., 2011). Detailed analysis of the images kilometers around the surface, and a lot of them start from the has shown that the asteroid surface is covered by numerous crater Stickney, thus suggesting impact as one of the leading craters (Vincent et al., 2012) with shallow depth-to-diameter formation mechanisms (Thomas et al., 1978). Lineaments were ratios, suggesting that Lutetia may have encountered weathering then observed on asteroids (243) Ida (Sullivan et al., 1996), (951) processes on its surface mostly by impact (Besse et al., 2012; Ernst Gaspra (Veverka et al., 1994), (433) Eros (Prockter et al., 2002; et al., 2012; Michel et al., 2009; Hirata et al., 2009; Richardson et Thomas et al., 2002), (4) Vesta (Buczkowski et al., 2012; Jaumann al., 2005). The large impact craters located at the north pole, also et al., 2012), and one large lineament was proposed on asteroid named North Polar Crater Cluster (NPCC), is one of the most (2867) Steins (Keller et al., 2010). Lineaments were also suggested interesting features of Lutetia's surface. Küppers et al. (2012) have on the surface of asteroids (253) Mathilde (Thomas et al., 1999) and (25,143) Itokawa (Barnouin-Jha et al., 2008). Lineaments have been easily spotted on the surface of asteroid (21) Lutetia given n Corresponding author. their wide distribution on the surface (Sierks et al., 2011; Thomas E-mail address: [email protected] (S. Besse). et al., 2012). http://dx.doi.org/10.1016/j.pss.2014.07.007 0032-0633/& 2014 Elsevier Ltd. All rights reserved. S. Besse et al. / Planetary and Space Science 101 (2014) 186–195 187

The observation of lineaments on asteroids has led to various the crater Stickney). Moreover, although cross-cutting relationship possible mechanisms explaining their origin. These mechanisms were described in Thomas et al. (2012), a detailed analysis of these are grouped into 5 main categories: (1) formation by impact relationships in the context of the origin of the lineaments has not (Asphaug et al., 1996; Thomas et al., 1979; Buczkowski et al., been done yet. This work aims at giving a relative age and 2008) is one of the most accepted scenario for most of the stratigraphy of the different events that created the lineaments asteroids including Lutetia and consistent with most observations, by the study of cross-cutting relationships. (2) ejecta coming from impact craters on Mars, as originally proposed by Murray et al. (1994) for Phobos, although this 2. Observations and mapping hypothesis has been recently debated (Ramsley and Head, 2013), (3) thermal stress was proposed on Eros to explain the multiple 2.1. Rosetta and OSIRIS observations orientation of lineaments (Dombard and Freed, 2002), (4) parent body inherited fabric (Buczkowski et al., 2008; Thomas et al., The Rosetta spacecraft flew by the asteroid Lutetia at a distance 2002) also proposed as a viable explanation for the multiple of 3168 km. Observations were taken continuously by the OSIRIS orientations of the lineaments on Eros, and (5) down slope Narrow and Wide Angle Camera (i.e., NAC and WAC) for a period of scouring by boulders coming from an impact crater on the object 2h(Sierks et al., 2011). These observations have different spatial itself was also proposed in the case of Phobos and the Stickney resolutions, with a pixel scale of 59 m at closest approach (CA) for impact (Head and Cintala, 1979). Nevertheless, impact craters are the NAC. Only images from the NAC are used to map the likely the source of most lineaments on asteroids, as seen in many lineaments in this analysis, with a total of 45 images used. The cases. Other mechanisms are less important and have only been phase angle varies very rapidly, from 01 20 min prior to CA, to 801 shown valid in a very few instances. at CA, and up to 1391 for the last image used in this analysis 6 min On Lutetia, the impact mechanism has been proposed as being after CA. The range of phase angles, higher than 301, is appropriate the dominant factor that created the lineaments on the surface. for mapping geological features such as lineaments. The orange In a very detailed study of the surface, Thomas et al. (2012) filter (649 nm) is used in this study as no absorption or emission mapped more than 400 lineaments on the entire visible surface features are expected in this domain. This filter is combined with a from the OSIRIS camera. Given the preferred orientations of the neutral filter to diminish the flux of small phase angle imaged lineaments, which are often oriented east–west, the authors before CA. A summary of the images used in this analysis is proposed that the NPCC crater could be the source of most of provided in Table 1. The images with the time of acquisition the lineaments. Thomas et al. (2012) also acknowledge that some between 15.40.19 (UT) and 15.46.58 (UT) were the most helpful lineaments (e.g., mostly in the Narbonensis region) have a differ- images for mapping the lineaments. ent orientation suggesting that not all the lineament orientations Analysis of morphological features on a surface is always could be explained by the NPCC alone. Jutzi et al. (2013) have sensitive to the lighting conditions, and could be subject to bias explored in more detail the hypothesis of impact for the creation in their identifications. The images used to map the lineaments of the lineaments by focusing on the NPCC (and its main crater of have been obtained through a limited period of time (i.e., less than about 34 km diameter) with numerical simulation of surface two hours) during which the position of the Sun does not change deformation. The authors found that velocity field lines after significantly. At the same time, the spacecraft moves rapidly, 50 s are reasonably in agreement with the orientation of the dramatically changing the phase angle from 261 to 1391 during lineaments on the surface, thus suggesting that the NPCC could the ten minutes around CA. However, the movement of the indeed be the impact at the origin of most of the lineaments. These spacecraft is in the plane of the incoming light from the Sun to simulations are, in some cases, capable of explaining the various the surface, thus not changing the perspectives on the surface. As orientations of the lineaments seen by Thomas et al. (2012) with it can be seen in Fig. 1 with the direction of the shadows and in the NPCC impact being the sole source. Fig. 2, numerous lineaments are found with directions that are In this analysis, we explore the impact mechanism theory in perpendicular or parallel to the direction of the Sun. This is order to complement the study of Thomas et al. (2012), and particularly true in the Achaia and Narbonensis regions where determine the origin of all the preferred orientations of the cross-cutting lineaments are observed. Thus, the mapping of the lineaments. This analysis is done from an observational point of lineaments is believed to be robust, and mostly independent of view using the visible images of the OSIRIS camera. This work bias from the illumination conditions. relies on the calculation of the pole solution of the lineaments to infer the location of the impact that may have created them. This is 2.2. The Small Body Mapping Tool (SBMT) only valid if one assumes that the lineaments are created ortho- gonally from the location of the impact (i.e., or concentric around To analyze the lineaments and their orientations, the mapping is the impact crater), as opposed to created radially (e.g., Phobos and done using the Small Body Mapping Tool (SBMT) (Kahn et al., 2011).

Table 1 Summary of the images used and their parameters. Although a large number of images are available, the mapping is mostly done on a limited number of images (images 22 to 40). The additional images are used as check-up with different phase angles and resolutions. Images only with the filters F82 or F22, which are combinations of Neutral- Orange and Clear-Orange respectively (see Keller et al., 2007 for details on the filters), are used in this anaysis.

Name Time of acquisition (UT) Phase angle (degree) Resolution (m/pixel)

(1)N20100710T142438992ID20F82 14.24.58 8.58 1354 ↕ 21 images with increasing phase and decreasing resolution (22)N20100710T154000819ID20F82 15.40.19 26.40 97 ↕ 12 images with increasing phase and decreasing resolution (35)N20100710T154441262ID20F22 15.45.00 80.48 59 ↕ 4 images with increasing phase and resolution (40)N20100710T154639204ID20F22 15.46.58 109.2 68 ↕ 4 images with increasing phase and resolution (45)N20100710T155039219ID20F22 15.50.58 138.77 118 188 S. Besse et al. / Planetary and Space Science 101 (2014) 186–195

stereophotoclinometry technique (Gaskell et al., 2008), combined with stereo control points and shape from silhouette (Jorda et al., 2011, 2012). An example of one OSIRIS image projected on the shape model with the SBMT is given in Fig. 1. The use of the combination of the shape model and the image allows a direct mapping of the lineaments in 3D, thus providing all the necessary information to characterize them.

2.3. Mapping of the lineaments

The mapping of the lineaments is simply done by drawing lines directly on the shape model where the lineament appears to be located on the OSIRIS image. The position of the lineament is then recorded in the shape model reference frame, thus allowing for changing image, resolution, and phase angle easily. Over 200 linea- ments have been mapped on the surface, which is about 2 times fewer than those mapped by Thomas et al. (2012). In this analysis, a conservative approach has been used in order to map easy, and well defined lineaments. It is acknowledged that not all of the lineaments may have been mapped, however a special emphasisis has been made on looking for additional orientations of lineaments rather than multiple lineaments of the same orientation. Moreover, during the mapping of these lineaments, it has been found that Thomas et al. (2012) may have over interpreted some features as lineaments (e.g., figure 24 of Thomas et al. (2012)). In fact, some features are not mapped as lineaments in this work because they are too small to be mapped indisputably as lineaments. However, it is important to stress Fig. 1. View in the SBMT of Lutetia's shape model from Jorda et al. (2011), together with the image N20100710T154639204ID20F22 projected on its surface. The grid that both analyses came to the same result as of the preferred corresponds to the coordinate system of the asteroid with 101 intervals, the North direction of the lineaments. Lineaments have been separated into Pole is facing us (z axis). Bright areas correspond to portion of the surface not categories depending on region, and according to the geological observed by this OSIRIS image. mapping proposed by Massironi et al. (2012). The mapping of the lineaments is presented in Fig. 2,theydonotsignificantly differ from those defined by Thomas et al. (2012) (see Fig. 8), only the number is lower. Once the mapping of the lineaments is performed, and their coordinates saved in the shape model reference frame, calculation of the orientations and the poles of the lineaments can be done. The same approach, and algorithm as used for the analysis of the lineaments of Eros (Buczkowski et al., 2008)andVesta(Buczkowski et al., 2012) is used in this study. The mathematical description of the definition of the pole is described in Buczkowski et al. (2008).The curvature of the lineaments on small irregular shapes of asteroids is giving a strong constraint on the dip (i.e., the plunge) of the lineaments. In fact, the orientation alone of the lineament could not give a proper solution of the pole because a multitude of planes with variousdipscanfit through a given orientation. This fundamental dissimilarity makes all the difference with the previous work of Thomas et al. (2012) that only considered the orientation of the lineaments, and did not calculate the proper pole solution. As we shall see later, this provides significant differences in the inferred craters that could be at the origin of the lineaments. Although some lineaments are generally orientated east-west, that does not mean that they all have their poles located close to the NPCC. The orienta- tions of the lineaments are strong constrains for the longitude of the pole solution, but only the dip will define the latitude of the pole.

Fig. 2. View of the lineaments mapped in this work and overlayed on the shape 3. Origin and relationship of the lineaments model. Each color of the lineaments corresponds to a different region according to Massironi et al. (2012): Achaia is red, Narbonensis is Blue, Noricum is purple, These analyses also focuses on the assumption that lineaments Etruria is green, and Baetica is . (For interpretation of the references to color in are created orthogonal to the pole of the impact crater that created this figure caption, the reader is referred to the web version of this paper.) them. Thus, by using the same assumption as Thomas et al. (2012), the comparison of the results can be made easily. The radial The SBMT can use a variety of shape models and project images solution, as seen in the case of Phobos, is also discussed in order directly on its surface. The OSIRIS images mentioned in Section 2.1 to evaluate the two ways of creating lineaments from an impact are used together with the shape model defined from the crater. S. Besse et al. / Planetary and Space Science 101 (2014) 186–195 189

3.1. Lineaments orthogonal to the impact 250W and 45S. This solution is very favorable because it matches the pole solution of the Achaia region, and a suspected impact Applying the same methodology as used by Buczkowski et al. crater on the non-observed portion of the surface based on the (2008, 2012), the poles of the lineaments are calculated for each of analysis of the lineaments of Achaia. From now on, this suspected the five regions of Lutetia's surface: Achaia, Narbonensis, Noricum, impact crater at 250W and 45S will be referred to as Suspicio. Baetica and Etruria. The results are presented in Fig. 3, with the (3) Noricum: although it appears that the lineaments are middle panel giving the pole solutions (e.g., small crosses). The divided into two main orientations that are close to 901 apart, projection of the pole of the lineaments on Lutetia's surface always the majority of the lineaments are oriented east–west. The pole give two solutions that are antipodal. If the pole solution on the solutions are however very different indicating different dips. Two OSIRIS observed portion of the asteroid is within, or very close to solutions are preferred, 270W and 70N, and 250W and 90N. Given an impact crater, this solution is favored. If no impact crater is the high latitudes of these solutions, longitudes are changing seen, then the solution on the part not observed by OSIRIS is rapidly, and this could explain the scatter of the pole solutions. favored. As we shall see later, this implies only one solution in the Moreover, both solutions are close and consistent with the NPCC. non-observed part of Lutetia's surface. (4) Baetica: two solutions of the poles are consistent with (1) Achaia: from the projection of the lineaments on the shape impact craters. The Massilia impact crater corresponds to the model (Fig. 3, bottom panel), it is clearly visible that the linea- solution 90W and 45N, and the NPCC corresponds to the solution ments have two preferential orientations which are close to being 260W and 85N. At first, the lineaments of this region have the 451 apart. A first cluster of pole solutions is favored close to 250W same orientation but certainly have different dips that point to the and 40S. The projection of this pole on Lutetia's surface is in the two solutions, and not only the NPCC one. portion not observed by the OSIRIS instrument. As we shall see (5) Etruria: most of the lineaments are oriented east–west, and later, this solution is very attractive given the ground-based the pole solution, 85W and 45N, fits very well with the Massilia observations of 3 μm absorption bands (Rivkin et al., 2011), and crater. possible hydrated minerals. The second cluster of poles is favored All the pole solutions for each region are summarized in Table 2 at 130W and 50N. The projection on Lutetia's surface is within the together with the closest impact craters that could be at the origin Massilia crater. The second solution of this second cluster is in the of the lineaments. The projection of these solutions on Lutetia's unresolved portion of the surface (320W and 45S), where unre- surface is given in Fig. 4. solved observations before CA show a concavity located right at The orientations of Lutetia's lineaments, with the idea that they these coordinates that could certainly correspond to an impact are created orthogonally to the impact crater, could be explained crater. In both cases, the solutions point to a pole consistent with by three impacts on the surface: (1) the Massilia impact in the an impact crater. Narbonensis region which is an appropriate solution for the (2) Narbonensis: the vast majority of the lineaments have the orientation of the lineaments of the Achaia and Etruria regions, same orientations and the pole solutions are well clustered around (2) the NPCC that could explain the orientation of lineaments from

Fig. 3. Preferred orientations of the lineaments for each region. The top panel corresponds to rose diagrams, they give the directions of the lineaments weighted by the number of lineaments, and the arrow points to the average direction. The middle panel corresponds to a stereographic projection that allows the representation of the planes, and the poles at the same time. The third panel shows the lineaments that have been mapped and considered to calculate the planes, and poles for each individual region. 190 S. Besse et al. / Planetary and Space Science 101 (2014) 186–195

Table 2 Summary of the preferred directions of the poles of the lineaments pictured in Fig. 4 with their respective possibly associated crater names.

Achaia Narbonensis Noricum Baetica Etruria

Solution 1 250W/40S 250W/45S 270W/70N 85W/45N 85W/45N Solution 2 130W/50N – 250W/90N 260W/85N – Suspicio Suspicio NPCC Massilia Massilia Craters - ––––––––- - ––––––––- Massilia NPCC

Fig. 4. Coverage of the OSIRIS resolved observations of Lutetia's surface during the Rosetta flyby. The white crosses correspond to the pole solutions of the preferred lineaments orientations. The poles are correlated to the Massilia crater outlined on the right, and the NPCC outlined by the dashed line on the top. The third invoked crater, Suspicio, is in a region not imaged by OSIRIS. The red crosses correspond to the center location of the ground based observations that reported the possibility of hydrated minerals (Barucci et al., 2012; Rivkin et al., 2011). Two of these observations are located close to the Suspicio craters. (For interpretation of the references to color in this figure caption, the reader is referred to the web version of this paper.) the Noricum and Baetica region, and (3) the Suspicio impact on the radially from the impact (Thomas et al., 1979, 1978). The same portion not imaged by the OSIRIS camera that could explain the observations are made on the surface of Eros, which exhibits lineaments from the Achaia and Narbonensis regions. lineaments expending radially for several hundred of meters from It is important to note that the majority of the lineaments have the craters Psyche and Leylie (Buczkowski et al., 2008). On asteroid been mapped in the Achaia and Narbonensis regions, and the Lutetia, given that there are several large craters on the surface solutions of these two regions are not connected to the NPCC. This (Vincent et al., 2012; Marchi et al., 2012), it is possible that the is a significant difference from the previous work of Thomas et al. orientations of some lineaments could be radial to an impact (2012) that will be discussed in more detail in Section 4. crater. In fact, as it can be seen on Figs. 2 and 3, the lineaments of the 3.2. Additional observations in support of the Suspico crater Achaia and Noricum regions that are orientated east–west could be interpreted as being radially extended from the Massilia crater. The shape model obtained from lightcurves and adaptive optics For the lineaments of the Achaia region, although they have the (Carry et al., 2010), and constrained on the northern part by the right orientation, there are no direct connections between the OSIRIS observations (Carry et al., 2012) is showing hints of a large lineaments and the crater rim as seen in the case of Phobos and depression for the pole direction associated with the Suspicio Eros. The case of the Noricum region is more difficult to judge from crater (Fig. 2 and equatorial view of Carry et al. (2010), and Fig. 2 of a morphological point of view. The lineaments have the correct Carry et al. (2012)). To explain the variations between the modeled orientations, and extend radially from the Massilia crater. They are, flux, and the Spitzer observations, O'Rourke et al. (2012) suggested for some of them, connected to what could be interpreted as the the presence of significant slopes in the southern hemisphere rim of the crater, although it is very degraded and disturbed by consistent with a large impact crater. Thus, observations from subsequent impacts. Nevertheless, some of the lineaments that other instruments are supporting the possibility of a large impact have the same orientation are also extending further into the crater at the southern hemisphere of Lutetia, consistent with the Massilia crater. It has been seen, especially for the crater Psyche of proposed location of the Suspicio crater. Eros that lineaments could have extensions inside the crater (Buczkowski et al., 2008). These observations for the crater 3.3. Lineaments radial to the impact Massilia are very limited and the lack of surface coverage around the southern part of the crater rim does not allow confirmation of Although it is common to infer that lineaments are created this hypothesis of lineaments extending radially from the crater. orthogonal to the impact, it has been seen that lineaments can also Some lineaments in the Achaia and Narbonensis regions also seem extend radially from an impact crater, and most likely be related to to be radially oriented with respect to the NPCC. However, the that same impact event. This is particularly true in the case of orientations of these lineaments are not following the curvature of Phobos and Eros. On Phobos, several lineaments start from the rim the crater rim and those at the edge of the crater do not appear to of the crater Stickney, and develop for several hundred of meters extend radially. All of these morphological criteria make unlikely S. Besse et al. / Planetary and Space Science 101 (2014) 186–195 191

Fig. 5. Cross-cutting relationships of lineaments with other lineaments, and of lineaments with craters. (a) Achaia region, the lineament at the bottom (arrow) is avoiding degraded craters, and the lineament at the top (arrow) is cutting the rim of a very degraded crater. These lineaments originate from the Massilia impact, thus suggesting a relatively old age for the impact. (b) cross-cutting lineaments (arrows) of the Achaia region suggesting that the lineaments orientated top to bottom (linked to Suspicio) are cutting through the lineaments orientated left to right (and linked to Massilia). Note that at the bottom, two lineaments are cutting through the rim of a less degraded crater than the one presented in Fig. 5a. This is another suggestion that the Suspicio impact is more recent than the Massilia impact. (c) lineaments of the Noricum region that cut through well defined crater rims (top and right arrows). The arrow at the bottom suggests that these somehow younger lineaments are also capable of deforming crater rims. The lineaments of the Noricum region are linked to the NPCC, suggesting a relatively younger age when compared to Massilia and Suspicio. that some of the lineaments of the regions Noricum, Achaia, and side to side, which have poles connected to the Massilia impact Narbonensis could be considered as extending radially from the crater. This superposition of lineaments clearly indicates that the two major impact craters: Massilia and NPCC. ones potentially created by the Suspicio crater were created after those linked to the Massilia impact, thus confirming that Massilia 3.4. Cross-cuting relationship is the older feature. At the bottom of the investigated region in Fig. 5b, two lineaments are cutting through the largest crater of Given that three impact craters are candidates for explaining the area. The crater has a rim that is better observed than those the orientation of the lineaments, and also because they belong to mentioned in Fig. 5a, suggesting that it is a younger impact crater. different regions of the asteroids surface that are thought to have Given that the pole direction of the lineaments that cut this rim different ages (Marchi et al., 2012), it is possible to examine the are linked to the Suspicio crater, this confirms the stratigraphically cross-cutting relationships. It can be done between the lineaments younger age of the Suspicio impact with respect to the Massilia and the craters, and the intersections of the lineaments them- impact. Moreover, the Narbonensis region, which is characterised selves in order to get a first order stratigraphic history. Although mostly by the Massilia impact crater, exhibits numerous linea- this analysis gives an estimate of the possible younger and older ments connected to the Suspicio crater. If this event was before impacts, it could not give an absolute age of each event. Fig. 5 Massilia, it is difficult to explain how the lineaments will have presents three examples of cross-cutting relationships that allow been preserved in the Narbonensis region. giving a stratigraphic relationship between the impacts that have The Noricum region has a variety of lineaments that have been possibly created the lineaments. In the Achaia region, Fig. 5a, it is interpreted has being related to the NPCC event (Thomas et al., observed that lineaments are cutting through very degraded 2012; Jutzi et al., 2013). Fig. 5c highlights a portion of these craters as pointed by the arrow at the top. At the same time, these lineaments and show that most of them are generally cutting lineaments are following the edges of other slightly less degraded through several craters of varying rim degradation states (as craters, as pointed with the arrow at the bottom of Fig. 5a. The fact shown by the arrows), to the point that the lineament at the that lineaments cutting through the rims of fresh craters are not bottom of the image is probably disturbing the rounded shape of seen in this region suggests that the lineaments were created a the crater. Although it is difficult to say if the NPCC event is long time ago, and are relatively old. In the region investigated in younger or older than the Suspicio crater in this context, it appears Fig. 5a, all the lineaments have the same orientations and the pole that it is surely younger than the Massilia impact. Nevertheless, is directed toward Massilia. This agrees with the conclusions of given the thick ejecta blanket around the NPCC (Vincent et al., previous observations (Marchi et al., 2012; Sierks et al., 2011) 2012), and the young tens to hundreds millions years modeled age suggesting that Massilia is a very old structure on Lutetia's surface. of the Baetica region, it is appropriate to propose that the NPCC Another portion of the Achaia region is investigated in Fig. 5b impact is probably younger than the Suspicio impact. It is noted where cross-cutting lineaments are observed (see arrows). The that, although the ages of young large impacts may be system- lineaments orientated top to bottom have pole solutions linked to atically underestimated because of the main-belt asteroid distri- the Suspicio crater. These cross-cut the lineaments oriented from bution (Küppers et al., 2012), this will not change the proposed 192 S. Besse et al. / Planetary and Space Science 101 (2014) 186–195 chronological order of the impact events on Lutetia. It will only ejecta when too close to the crater. The scattered location of the change the modeled ages of the impact with an older NPCC event. lineaments associated with Massilia is more important than those associated with the NPCC or the suggested impact crater Suspicio. Given that Massilia is the largest impact crater observed on the 4. Discussion surface, it is expected to find related lineaments on different regions of the surface. Thus, Massilia is most likely an impact The results of the origin of the lineaments presented in Section 3 crater, and probably the largest and oldest impact crater seen on are quite different from those proposed by previous analyses (Sierks the entire surface of Lutetia. et al., 2011; Thomas et al., 2012; Jutzi et al., 2013). As mentioned The lineaments related to the Suspicio crater have a large previously, it is believed that these differences are mainly due to spatial distribution, and are seen in the two largest regions (e.g., two aspects of this work: Achaia and Narbonensis). It is therefore proposed that the Suspicio crater should have a diameter of several kilometers in size, which 1. The different technics used to analyze the lineaments, and the is consistent with a large depression visible on the shape model fact that this analysis is the first to take into account the pole of derived from ground based observations (Carry et al., 2012, 2010). the plane that passes through Lutetia's lineaments, as already Consequently, with three major impacts on the surface, Massilia, done for other asteroids (Buczkowski et al., 2012, 2008; Suspicio and NPCC, Lutetia's surface has been seriously deformed Jaumann et al., 2012). and resurfaced. This resurfacing varies depending on the age of the 2. The different assumptions used in this work. Thomas et al. impact and the distance from the impact crater. For instance, ejecta (2012); Jutzi et al. (2013)) assumed that Massilia was degraded blankets of the NPCC are clearly visible but do not affect the entire by aging effects such that the influence on the shape and surface (Vincent et al., 2012). In fact, the age modeling of the surface structure of the surface is now almost completely lost, including by Marchi et al. (2012) suggested a timescale of almost 4 billion removal of lineaments potentially created by the impact. This years between the youngest (i.e., Baetica) and the oldest region analysis uses an alternative such that preservation of the linea- (i.e., Achaia). This is consistent with the relative stratigraphy derived ments is not a problem. from cross-cutting relationships in Section 3.4.

The different interpretation proposed in this manuscript about 4.2. Can lineaments originating from Massilia and Suspicio survive the origin of the lineaments of Lutetia has several implications for billion years time scale? the history and the evolution of Lutetia's surface. Multiple aspects of these implications are discussed in the following paragraphs. Given the stratigraphic relationship of the impact craters, and the modeled ages of these possible impacts, the survival of 4.1. Age relationship and implication for Lutetia's history the lineaments is an important factor. Through time, lineaments could be altered, space weathered chemically and physically to a Based on various cross-cutting relationships between linea- point where they would no longer be detectable. Large impact ments and craters, a simple stratigraphic relationship appears to craters are a natural source for resurfacing planetary surfaces, as be coherent with the three potential impact craters candidates to described by Asphaug et al. (1996). Although the physical scale of explain the origin of the lineaments. In this relative stratigraphy, the simulated impacts by Asphaug et al. (1996) is smaller than Massilia is the oldest impact given the general degraded state of Massilia, the simulations have shown that previous fractures that the impact crater and the lineaments visible on its floor. Observa- created the lineaments could reactivate them. Thus the lineaments tions of the NPCC, and its ejecta blankets have already classified could appear fresher, and could survive for billion of years. this event as most probably the youngest feature that have change Moreover, this will only refresh the lineaments, and not change the state of Lutetia's surface (Marchi et al., 2012; Sierks et al., the stratigraphic relationship discussed in Section 3.4. Küppers 2011). Although there is no doubt that the Suspicio impact is et al. (2012) argued that the lifetime of boulders, and by inference younger than the Massilia impact, its relative stratigraphy to the lineaments, is underestimated and could survive for billion NPCC is more difficult to evaluate. Nevertheless, given that linea- of years instead of a few hundred millions. Analysis of other ments in the Noricum region are cutting fresher craters than the asteroids' lineaments on Eros and Vesta (Buczkowski et al., 2012, lineaments in the Achaia region, it is proposed that the Suspicio 2008) proposed that the lineaments could have survived cata- crater is older than the NPCC. The proposed relative stratigraphy strophic impact events. In fact, part of Eros' lineaments are from the older impact crater to the younger is: Massilia, Suspicio, thought to originate from the parent body inherited fabrics, and NPCC. meaning that lineaments could potentially survive the disruption Massilia is interpreted as being an impact crater resulting from of an asteroid. More recently, lineaments on Vesta have been a collision of Lutetia's surface with a projectile of about 8 km linked to the Veneneia and Rheasilvia basin, which are both (Sierks et al., 2011). However, Thomas et al. (2012) suggested hundreds of kilometers in diameter. The age model of both further analyses to confirm the impact origin of the Massilia crater impacts is respectively at least 2 and 1 billion years old (Schenk given the state of degradation of the crater. They suggested that it et al., 2012; Schmedemann et al., 2013). This suggest that linea- is possible that Massilia is the remnant of pre-existing structure ments could survive a time scale appropriate for the estimated age from a parent body and may not be an impact crater. However, this of the oldest impacts on Lutetia's surface. analysis has shown that Massilia could be the source of lineaments on Lutetia's surface, which is consistent with an impact origin. 4.3. Why are the lineaments not mainly related to NPCC? Furthermore, the lineaments whose poles are associated with Massilia are distributed in all regions except Noricum and Narbo- There are two possible reasons why few lineaments are related nensis. In fact Noricum is the nearby region from the impact, and to the NPCC: (1) The NPCC did not generate lineaments, and/or its lineaments associated to Massilia in the Achaia region are gen- contribution is overestimated, or (2) The lineaments associated to erally located further away from the impact. the NPCC are not visible. The lack of lineaments in some regions could be explained by The very detailed analyses of Jutzi et al. (2013) and Thomas their proximity to the impact itself. It is possible that lineaments et al. (2012) have clearly emphasized the role of the NPCC in the are either not created in the proximal regions, or are covered by creation of the lineaments. Although this analysis confirms that S. Besse et al. / Planetary and Space Science 101 (2014) 186–195 193 the NPCC could be responsible for some of the lineaments, the Given the rotation properties of Lutetia (Barucci et al., 2005), previous analyses do not explain why lineaments would not be permanently shadowed regions on the surface are unlikely. created by the Massilia impact. This could be related to the large The Suspicio crater might increase the chances of permanently size of the impact with respect to the diameter of the asteroid. shadowed regions, but the crater would have to be very deep to In fact, very few lineaments are observed on asteroid Mathilde, sustain shadows. This possibility is very unlikely given that cross- which has a very large impact crater (Thomas et al., 1999), cutting relationships have shown that this crater is relatively old although this could also be due to the lower resolution of the (see Section 3.4), and thus the topography should not be favorable observations. More hydrocode simulations, as done by Jutzi et al. for permanent shadows. (2013), are required to infer any relationship between the creation Another possibility is that the crater could have exposed to the of the lineaments and the size of the impactor with respect to the surface a subsurface layer that contains these hydrated minerals. size of the body. However, if lineaments are seen associated to This layer could be homogenous on the entirety of Lutetia, and in Massilia, which is two times larger than the NPCC, then the large some way, related to the formation history and differentiation of size of the impact crater could not be the reason why few the asteroid. However, it is more likely that any subsurface layer of lineaments are associated to the NPCC. On the other hand, it is hydrated minerals would be unhomogeneous, given that observa- unlikely that the NPCC is too small since lineaments associated tions of hydrated minerals are limited and they are not excavated with very small craters (e.g., few kilometers) have been found by any northern craters. This would be consistent with the on Eros. proposal of Barucci et al. (2012), who proposed that the composi- Jutzi et al. (2013) suggested that the orientation of the linea- tion of the southern hemisphere of Lutetia is primordially different ments could be defined as rapidly as during the first minute of the from that of the northern hemisphere. impact. Thus, even if the impact is as young as 10 Myr (Marchi Finally, the last relationship between the hydrated minerals et al., 2012), the fact that there are few lineaments associated with and the impact crater could be the topography. Topography can the NPCC can not be because they have yet to form. However, significantly change the local illumination conditions that affect given that the NPCC is most likely the youngest large impact on spectral shape. In particular, slopes will sort the size of the grains, the surface, the heavily micro-shattered inside the asteroid from which is a very important factor in changing the shape of previous large impacts (i.e., Massilia, Suspicio) may have not been absorption bands (Clark, 1999). favorable for the generation of another set of lineaments. Although Therefore, although this analysis draws some relationships Jutzi et al. (2013) used a shattered internal asteroid structure and between the presence of hydrated minerals and possible impact still found lineaments associated with the NPCC, it could be that features, the presence of hydrated features should be confirmed the shattered effect has been underestimated in the simulations. before drawing conclusions on the possible history of asteroid Therefore, the wave propagation from the impact could be much Lutetia. more attenuated than anticipated by Jutzi et al. (2013), and not permit the creation of another generation of lineaments. Although observational bias is still a possibility for the small 5. Conclusions number of identifications of lineaments associated to the NPCC, the effect of bias should be minimal and thus not affect our results. This analysis of Lutetia's lineament orientations is based on the However, the lack of lineaments associated with the NPCC could assumption that lineaments are created orthogonal to the impact also be due to the thick regolith developed through time. If so, the crater, as seems to be common on other asteroids. Another creation of lineaments could be prevented or hindered by large important assumption used in this work is the fact that preserva- regolith movements that could have filled or covered the linea- tion of lineaments over very large time scales (e.g., billion years) is ments. Thus, the lineaments could be present but below the possible, as suggested for other asteroids (e.g., Eros and Vesta). The detection limits. Lineaments associated to the NPCC are found in same technique as used for the analysis of lineaments on asteroids the Noricum region, where regolith may be less important due to Eros (Buczkowski et al., 2008) and Vesta (Buczkowski et al., 2012) strong local slopes. is employed to determine the direction of the pole of the plane It is difficult to argue in favor of one particular explanation for that passes through the lineament. This pole is used as the the lack of lineaments associated to the NPCC. It is possible that a solution for the possible location of the impact crater that created combination of all the reasons could lead to their small number. the lineaments. The results are different from previous studies Additional numerical simulations will be needed to identify if one (Jutzi et al., 2013; Thomas et al., 2012; Sierks et al., 2011) in that of these factors is more likely than the others. Of particular the NPCC is not seen as the major event that created the interest is the fracturing of the asteroids interior from previous lineaments. The main results are summarized in these three impacts that was taken into account in Jutzi et al. (2013) analysis, points: but could be explored in greater detail with varying level of shattered interior.  The analysis of the lineaments shows that three impact craters are very good candidates for the origin of the lineaments. On 4.4. Hydrated features on the far-side the northern hemisphere, observed during the Rosetta flyby, the two largest impacts, Massilia and NPCC, are very good Surprisingly, the location of the Suspicio crater is located near candidates. Another candidate inferred from the orientation of the reported detection of possible hydrated minerals (Rivkin et al., the lineaments is located in the southern hemisphere, and 2011). The antipodal solutions of the poles located within Massilia tentatively named Suspicio. and the NPCC could also be, to a certain extent, associated to the  Cross-cutting relationship between lineaments and craters, and hydrated features reported by Rivkin et al. (2011) in the southern between lineaments themselves show that Massilia is the most hemisphere. However, as discussed previously, only the Suspicio ancient impact, and NPCC the younger. Although cross-cutting solution is favored in the unobserved hemisphere of Lutetia. relationships suggest the Suspicio event occurred between the Although these hydrated minerals have yet to be confirmed by two other impacts, the likelihood of Suspicio being closer in other observations, and were not observed in the northern hemi- time to Massilia is high. sphere (Coradini et al., 2011), the association with possible impact  The spatial location of the Suspicio crater is very close to features derived from the lineaments' orientation is interesting. observations of hydrated minerals (Rivkin et al., 2011). 194 S. Besse et al. / Planetary and Space Science 101 (2014) 186–195

Although the detection of hydrated minerals still has to be Kryszczynska, P., Polinska, M., Fulchignoni, M., Roy, R., Naves, R., Poncy, R., confirmed, several ideas are discussed as to the origin of this Wiggins, P., 2010. Physical properties of the ESA Rosetta target asteroid (21) Lutetia. II. Shape and flyby geometry. A & A 523, A94. http://dx.doi.org/10.1051/ absorption band. One likely explanation could be changes in 0004-6361/201015074 arXiv:1005.5356. the local phase angles, and physical properties of the surface Carry, B., Kaasalainen, M., Merline, W.J., Müller, T.G., Jorda, L., Drummond, J.D., Berthier, J., due to the possible presence of a large impact crater. O'Rourke, L., Ďurech,J.,Küppers,M.,Conrad,A.,Tamblyn,P.,Dumas,C.,Sierks,H., 2012. Osiris Team, 2012. Shape modeling technique KOALA validated by ESA Rosetta at (21) Lutetia. Planet. Space Sci. 66, 200–212. http://dx.doi.org/10.1016/j. This analysis does not associate the orientations of the linea- pss.2011.12.018 arXiv:1112.5944. ments to pre-existing orientations related to an hypothetical Clark, R.N., 1999. Spectroscopy of Rocks and Minerals, and Principles of Spectro- parent body as recently suggested (Giacomini et al., 2014). In this scopy. In: Manual of Remote Sensing, vol. 3. John Wiley and Sons, New York, pp. 3–58 (Chapter 1). respect, this analysis agrees with Lutetia being a planetesimal Coradini, A., Capaccioni, F., Erard, S., , G., De Sanctis, M.C., Filacchione, G., Tosi, F., (Vernazza et al., 2011; Weiss et al., 2012; Sierks et al., 2011). This Barucci, M.A., Capria, M.T., Ammannito, E., Grassi, D., Piccioni, G., Giuppi, S., analysis presents an alternative interpretation of the origin of the Bellucci, G., Benkhoff, J., Bibring, J.P., Blanco, A., Blecka, M., Bockelee-Morvan, D., lineaments on asteroid Lutetia that differ from previous numerical Carraro, F., Carlson, R., Carsenty, U., Cerroni, P., Colangeli, L., Combes, M., Combi, M., Crovisier, J., Drossart, P., Encrenaz, E.T., Federico, C., Fink, U., Fonti, S., Giacomini, L., modeling (Jutzi et al., 2013), depending on the assumption used Ip, W.H., Jaumann, R., Kuehrt, E., Langevin, Y., Magni, G., McCord, T., Mennella, V., for the creation and preservation of the lineaments. Mottola, S., Neukum, G., Orofino, V., Palumbo, P., Schade, U., Schmitt, B., Taylor, F., Tiphene, D., Tozzi, G., 2011. The surface composition and temperature of asteroid 21 Lutetia as observed by Rosetta/VIRTIS. Science 334, 492. http://dx.doi.org/ Acknowledgments 10.1126/science.1204062. Dombard, A.J., Freed, A.M., 2002. Thermally induced lineations on the asteroid Eros: evidence of orbit transfer. Geophys. Res. Lett. 29, 1818. http://dx.doi.org/ The ESA fellowship program supported the research of S. Besse. 10.1029/2002GL015181. We thank Emily Baldwin for english corrections of the manuscript. Ernst, C.M., Barnouin, O.S., Gaskell, R.W., 2012. The morphology of craters on 433 Eros. In: Lunar and Planetary Institute Science Conference Abstracts, p. 2393. We thank J.B. Vincent for providing the projection of Lutetia's Gaskell, R.W., Barnouin-Jha, O.S., Scheeres, D.J., Konopliv, A.S., Mukai, T., Abe, S., surface. We are grateful to Antonella Barucci and an anonymous Saito, J., Ishiguro, M., Kubota, T., Hashimoto, T., Kawaguchi, J., Yoshikawa, M., reviewer for helpful comments that improved the quality and Shirakawa, K., Kominato, T., Hirata, N., Demura, H., 2008. Characterizing and navigating small bodies with imaging data. Meteorit. Planet. Sci. 43, 1049–1061. clarity of the manuscript. OSIRIS was built by a consortium of the http://dx.doi.org/10.1111/j.1945-5100.2008.630 tb00692.x. Max-Planck-Institut für Sonnensystemforschung, Katlenburg- Giacomini, L., Massironi, M., Aboudan, A., Bistacchi, A., Barbieri, C., 2014. 3D Study Lindau, Germany; CISASUniversity of Padova, Italy; the Laboratoire of Lutetia Lineaments: New Clues to Understand the Asteroid Origin. LPI Contributions. d'Astrophysique de Marseille, France; the Instituto de Astrofísica Head, J.W., Cintala, M.J., 1979. Grooves on Phobos: Evidence for Possible Secondary de Andalucia, CSIC, Granada, Spain; the Research and Scientific Cratering Origin. Technical Report. Support Department of the ESA, Noordwijk, Netherlands; the Hirata, N., Barnouin-Jha, O.S., Honda, C., Nakamura, R., Miyamoto, H., Sasaki, S., Instituto Nacional de Técnica Aeroespacial, Madrid, Spain; the Demura, H., Nakamura, A.M., Michikami, T., Gaskell, R.W., Saito, J., 2009. A survey of possible impact structures on 25143 Itokawa. Icarus 200, 486–502. Universidad Politéchnica de Madrid, Spain; the Department of http://dx.doi.org/10.1016/j.icarus.2008.10.027. Physics and Astronomy of Uppsala University, Sweden; and the Jaumann, R., Williams, D.A., Buczkowski, D.L., Yingst, R.A., Preusker, F., Hiesinger, H., Institut für Datentechnik und Kommunikationsnetze der Tech- Schmedemann, N., Kneissl, T., Vincent, J.B., Blewett, D.T., Buratti, B.J., Carsenty, U., Denevi, B.W., De Sanctis, M.C., Garry, W.B., Keller, H.U., Kersten, E., Krohn, K., Li, J.Y., nischen Universität Braunschweig, Germany. The support of the Marchi, S., Matz, K.D., McCord, T.B., McSween, H.Y., Mest, S.C., Mittlefehldt, D.W., national funding agencies of Germany (DLR), France (CNES), Italy Mottola, S., Nathues, A., Neukum, G., O'Brien, D.P., Pieters, C.M., Prettyman, T.H., (ASI), Spain (MEC), Sweden (SNSB), and the ESA Technical Direc- Raymond, C.A., Roatsch, T., Russell, C.T., Schenk, P., Schmidt, B.E., Scholten, F., torate is gratefully acknowledged. We thank the Rosetta Science Stephan, K., Sykes, M.V., Tricarico, P., Wagner, R., Zuber, M.T., Sierks, H., 2012. Vesta's shape and morphology. Science 336, 687. http://dx.doi.org/10.1126/ Operations Centre and the Rosetta Mission Operations Centre for science.1219122. the successful flyby of 21 Lutetia. Jorda, L., Gaskell, R., Lamy, P., Kaasalainen, M., Groussin, O., Faury, G., Gutierrez, P., Sabolo, W., Hviid, S., 2011. Shape and physical properties of Asteroid (21) Lutetia from OSIRIS images. In: EPSC-DPS Joint Meeting 2011, p. 776. References Jorda, L., Lamy, P.L., Gaskell, R.W., Kaasalainen, M., Groussin, O., Besse, S., Faury, G., 2012. Asteroid (2867) Steins: Shape, topography and global physical properties from OSIRIS observations. Icarus 221, 1089–110 0. http://dx.doi.org/10.1016/j. Asphaug, E., Moore, J.M., Morrison, D., Benz, W., Nolan, M.C., Sullivan, R.J., 1996. icarus.2012.07.035. Mechanical and geological effects of impact cratering on Ida. Icarus 120, Jutzi, M., Thomas, N., Benz, W., El Maarry, M.R., Jorda, L., Kührt, E., Preusker, F., 2013. 158–184. http://dx.doi.org/10.1006/icar.1996.0043. The influence of recent major crater impacts on the surrounding surfaces of Barnouin-Jha, O.S., Cheng, A.F., Mukai, T., Abe, S., Hirata, N., Nakamura, R., Gaskell, R.W., (21) Lutetia. Icarus 226, 89–100. http://dx.doi.org/10.1016/j.icarus.2013.05.022. Saito, J., Clark, B.E., 2008. Small-scale topography of 25143 Itokawa from the Kahn, E.G., Barnouin, O.S., Buczkowski, D.L., Ernst, C.M., Izenberg, N., Murchie, S., Hayabusa laser altimeter. Icarus 198, 108–124. http://dx.doi.org/10.1016/j. Prockter, L.M., 2011. A tool for the visualization of small body data. In: Lunar icarus.2008.05.026. Barucci, M.A., Belskaya, I.N., Fornasier, S., Fulchignoni, M., Clark, B.E., Coradini, A., and Planetary Institute Science Conference Abstracts, p. 1618. Capaccioni, F., Dotto, E., Birlan, M., Leyrat, C., Sierks, H., Thomas, N., Vincent, J.B., Keller, H.U., Barbieri, C., Koschny, D., Lamy, P., Rickman, H., Rodrigo, R., Sierks, H., 2012. Overview of Lutetia's surface composition. Planet. Space Sci. 66, 23–30. A'Hearn, M.F., Angrilli, F., Barucci, M.A., Bertaux, J.L., Cremonese, G., Da Deppo, V., http://dx.doi.org/10.1016/j.pss.2011.11.009. Davidsson, B., De Cecco, M., Debei, S., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, Barucci, M.A., Fulchignoni, M., Fornasier, S., Dotto, E., Vernazza, P., Birlan, M., Binzel, R.P., P.J., Hviid, S.F., Ip, W.H., Jorda, L., Knollenberg, J., Kramm, J.R., Kührt, E., Küppers, M., Carvano,J.,Merlin,F.,Barbieri,C.,Belskaya,I.,2005.Asteroidtargetselectionforthe Lara, L.M., Lazzarin, M., Moreno, J.L., Marzari, F., Michalik, H., Naletto, G., Sabau, L., new Rosetta mission baseline. 21 Lutetia and 2867 Steins. A&A 430, 313–317 Thomas, N., Wenzel, K.P., Bertini, I., Besse, S., Ferri, F., Kaasalainen, M., Lowry, S., http://dx.doi.org/10.1051/0004-6361:20041505. Marchi, S., Mottola, S., Sabolo, W., Schröder, S.E., Spjuth, S., Vernazza, P., 2010. E- Besse, S., Lamy, P., Jorda, L., Marchi, S., Barbieri, C., 2012. Identification and physical Type Asteroid (2867) Steins as Imaged by OSIRIS on Board Rosetta. Science 327, properties of craters on Asteroid (2867) Steins. Icarus 221, 1119–1129. http://dx. 190. http://dx.doi.org/10.1126/science.1179559. doi.org/10.1016/j.icarus.2012.08.008. Keller, H.U., Barbieri, C., Lamy, P., Rickman, H., Rodrigo, R., Wenzel, K.P., Sierks, H., Buczkowski, D.L., Barnouin-Jha, O.S., Prockter, L.M., 2008. 433 Eros lineaments: A'Hearn, M.F., Angrilli, F., Angulo, M., Bailey, M.E., Barthol, P., Barucci, M.A., global mapping and analysis. Icarus 193, 39–52. http://dx.doi.org/10.1016/j. Bertaux, J.L., Bianchini, G., Boit, J.L., , V., Burns, J.A., Büttner, I., Castro, J.M., icarus.2007.06.028. Cremonese, G., Curdt, W., da Deppo, V., Debei, S., de Cecco, M., Dohlen, K., Buczkowski, D.L., Wyrick, D.Y., Iyer, K.A., Kahn, E.G., Scully, J.E.C., Nathues, A., Fornasier, S., Fulle, M., Germerott, D., Gliem, F., Guizzo, G.P., Hviid, S.F., Ip, W.H., Gaskell, R.W., Roatsch, T., Preusker, F., Schenk, P.M., Le Corre, L., Reddy, V., Jorda, L., Koschny, D., Kramm, J.R., Kührt, E., Küppers, M., Lara, L.M., Llebaria, A., Yingst, R.A., Mest, S., Williams, D.A., Garry, W.B., Barnouin, O.S., Jaumann, R., López, A., López-Jimenez, A., López-Moreno, J., Meller, R., Michalik, H., Miche- Raymond, C.A., Russell, C.T., 2012. Large-scale troughs on Vesta: a signature of lena, M.D., Müller, R., Naletto, G., Origné, A., Parzianello, G., Pertile, M., planetary tectonics. Geophys. Res. Lett. 39, 18205. http://dx.doi.org/10.1029/ Quintana, C., Ragazzoni, R., Ramous, P., Reiche, K.U., Reina, M., Rodríguez, J., 2012GL052959. Rousset, G., Sabau, L., Sanz, A., Sivan, J.P., Stöckner, K., Tabero, J., Telljohann, U., Carry, B., Kaasalainen, M., Leyrat, C., Merline, W.J., Drummond, J.D., Conrad, A., Thomas, N., Timon, V., Tomasch, G., Wittrock, T., Zaccariotto, M., 2007. OSIRIS Weaver, H.A., Tamblyn, P.M., Chapman, C.R., Dumas, C., Colas, F., Christou, J.C., the scientific camera system onboard Rosetta. Space Sci. Rev. 128, 433–506. Dotto, E., Perna, D., Fornasier, S., Bernasconi, L., Behrend, R., Vachier, F., http://dx.doi.org/10.1007/s11214-006-9128-4. S. Besse et al. / Planetary and Space Science 101 (2014) 186–195 195

Küppers, M., Moissl, R., Vincent, J.B., Besse, S., Hviid, S.F., Carry, B., Grieger, B., Sierks, H., Da Deppo, M., Davidsson, B., Debei, S., De Cecco, M., De Leon, J., Ferri, F., Fornasier, Keller, H.U., Marchi, S., 2012. OSIRIS Team, 2012. Boulders on Lutetia. Planet. Space S., Fulle, M., Hviid, S.F., Gaskell, R.W., Groussin, O., Gutierrez, P., Ip, W., Jorda, L., Sci. 66, 71–78. http://dx.doi.org/10.1016/j.pss.2011.11.004. Kaasalainen, M., Keller, H.U., Knollenberg, J., Kramm, R., Kührt, E., Küppers, M., Marchi, S., Massironi, M., Vincent, J.B., Morbidelli, A., Mottola, S., Marzari, F., Lara, L., Lazzarin, M., Leyrat, C., Moreno, J.J.L., Magrin, S., Marchi, S., Marzari, F., Küppers, M., Besse, S., Thomas, N., Barbieri, C., Naletto, G., Sierks, H., 2012. Massironi, M., Michalik, H., Moissl, R., Naletto, G., Preusker, F., Sabau, L., Sabolo, W., The cratering history of asteroid (21) Lutetia. Planet. Space Sci. 66, 87–95. http: Scholten, F., Snodgrass, C., Thomas, N., Tubiana, C., Vernazza, P., Vincent, J.B., //dx.doi.org/10.1016/j.pss.2011.10.010 arXiv:1111.3628. Wenzel, K.P., Andert, T., Pätzold, M., Weiss, B.P., 2011. Images of asteroid 21 Lutetia: Massironi, M., Marchi, S., Pajola, M., Snodgrass, C., Thomas, N., Tubiana, C., Baptiste a remnant planetesimal from the early solar system. Science 334, 487. http://dx. Vincent, J., Cremonese, G., da Deppo, V., Ferri, F., Magrin, S., Sierks, H., Barbieri, C., doi.org/10.1126/science.1207325. Lamy, P., Rickman, H., Rodrigo, R., Koschny, D., 2012. Osiris Team, 2012. Geological Sullivan, R., Greeley, R., Pappalardo, R., Asphaug, E., Moore, J.M., Morrison, D., Belton, – map and stratigraphy of asteroid 21 Lutetia. Planet. Space Sci. 66, 125 136. http: M.J.S., Carr, M., Chapman, C.R., Geissler, P., Greenberg, R., Granahan, J., Head III, J.W., //dx.doi.org/10.1016/j.pss.2011.12.024. Kirk, R., McEwen, A., Lee, P., Thomas, P.C., Veverka, J., 1996. Geology of 243 Ida. Michel, P., O'Brien, D.P., Abe, S., Hirata, N., 2009. Itokawa's cratering record as Icarus 120, 119–139. http://dx.doi.org/10.1006/icar.1996.0041. observed by Hayabusa: implications for its age and collisional history. Icarus Thomas, N., Barbieri, C., Keller, H.U., Lamy, P., Rickman, H., Rodrigo, R., Sierks, H., – 200, 503 513. http://dx.doi.org/10.1016/j.icarus.2008.04.002. Wenzel, K.P., Cremonese, G., Jorda, L., Küppers, M., Marchi, S., Marzari, F., Murray, J.B., Rothery, D.A., Thornhill, G.D., Muller, J.P., Iliffe, J.C., Day, T., Cook, A.C., Massironi, M., Preusker, F., Scholten, F., Stephan, K., Barucci, M.A., Besse, S., 1994. The origin of Phobos' grooves and crater chains. Planet. Space Sci. 42, El-Maarry, M.R., Fornasier, S., Groussin, O., Hviid, S.F., Koschny, D., Kührt, E., – 519 526. http://dx.doi.org/10.1016/0032-0633(94)90093-0. Martellato, E., Moissl, R., Snodgrass, C., Tubiana, C., Vincent, J.B., 2012. The O'Rourke, L., Müller, T., Valtchanov, I., Altieri, B., González-Garcia, B.M., Bhattacharya, geomorphology of (21) Lutetia: Results from the OSIRIS imaging system B., Jorda, L., Carry, B., Küppers, M., Groussin, O., Altwegg, K., Barucci, M.A., onboard ESA's Rosetta spacecraft. Planet. Space Sci. 66, 96–124. http://dx.doi. Bockelee-Morvan, D., Crovisier, J., Dotto, E., Garcia-Lario, P., Kidger, M., Llorente, org/10.1016/j.pss.2011.10.003. A., Lorente, R., Marston, A.P., Sanchez Portal, M., Schulz, R., Sierra, M., Teyssier, D., Thomas, P., Veverka, J., Bloom, A., Duxbury, T., 1979. Grooves on PHOBOS—their Vavrek, R., 2012. Thermal and shape properties of asteroid (21) Lutetia from distribution, morphology and possible origin. J. Geophys. Res. 84, 8457–8477. Herschel observations around the Rosetta flyby. Planet. Space Sci. 66, 192–199. http://dx.doi.org/10.1029/JB084iB14p08457. http://dx.doi.org/10.1016/j.pss.2012.01.004. Thomas, P., Veverka, J., Duxbury, T.C., 1978. Origin of the grooves on PHOBOS. Prockter, L., Thomas, P., Robinson, M., Joseph, J., Milne, A., Bussey, B., Veverka, J., Nature 273, 282–284. http://dx.doi.org/10.1038/273282a0. Cheng, A., 2002. Surface expressions of structural features on Eros. Icarus 155, Thomas, P.C., Joseph, J., Carcich, B., Veverka, J., Clark, B.E., , J.F., , A.W., 75–93. http://dx.doi.org/10.1006/icar.2001.6770. Chomko, R., Robinson, M., Murchie, S., Prockter, L., Cheng, A., Izenberg, N., Ramsley, K.R., Head, J.W., 2013. The origin of Phobos grooves from ejecta launched Malin, M., Chapman, C., McFadden, L.A., Kirk, R., Gaffey, M., Lucey, P.G., 2002. from impact craters on Mars: tests of the hypothesis. Planet. Space Sci. 75, – 69–95. http://dx.doi.org/10.1016/j.pss.2012.10.007. Eros: Shape, topography, and slope processes. Icarus 155, 18 37. http://dx.doi. Richardson, J.E., Melosh, H.J., Greenberg, R.J., O'Brien, D.P., 2005. The global effects org/10.1006/icar.2001.6755. of impact-induced seismic activity on fractured asteroid surface morphology. Thomas, P.C., Veverka, J., Bell, J.F., Clark, B.E., Carcich, B., Joseph, J., Robinson, M., Icarus 179, 325–349. http://dx.doi.org/10.1016/j.icarus.2005.07.005. McFadden, L.A., Malin, M.C., Chapman, C.R., Merline, W., Murchie, S., 1999. – Rivkin, A.S., Clark, B.E., Ockert-Bell, M., Volquardsen, E., Howell, E.S., Bus, S.J., Mathilde: Size, shape, and geology. Icarus 140, 17 27. http://dx.doi.org/ Thomas, C.A., Shepard, M., 2011. Asteroid 21 Lutetia at 3 μm: observations with 10.1006/icar.1999.6121. IRTF SpeX. Icarus 216, 62–68. http://dx.doi.org/10.1016/j.icarus.2011.08.009. Vernazza, P., Lamy, P., Groussin, O., Hiroi, T., Jorda, L., King, P.L., Izawa, M.R.M., Schenk, P., O'Brien, D.P., Marchi, S., Gaskell, R., Preusker, F., Roatsch, T., Jaumann, R., Marchis, F., Birlan, M., Brunetto, R., 2011. Asteroid (21) Lutetia as a remnant of – Buczkowski, D., McCord, T., McSween, H.Y., Williams, D., Yingst, A., Raymond, C., Earth's precursor planetesimals. Icarus 216, 650 659. http://dx.doi.org/10.1016/ Russell, C., 2012. The geologically recent giant impact basins at Vesta's south j.icarus.2011.09.032. pole. Science 336, 694. http://dx.doi.org/10.1126/science.1223272. Veverka, J., Thomas, P., Simonelli, D., Belton, M.J.S., Carr, M., Chapman, C., Davies, M.E., Schmedemann, N., Kneissl, T., Ivanov, B.A., Michael, G.G., Neukum, G., Nathues, A., Greeley, R., Greenberg, R., Head, J., 1994. Discovery of grooves on Gaspra. Icarus Sierks, H., Wagner, R., Krohn, K., Le Corre, L., Reddy, V., Ruesch, O., Hiesinger, H., 107, 72. http://dx.doi.org/10.1006/icar.1994.1007. Jaumann, R., Raymond, C.A., Russell, C.T., 2013. Crater retention ages from Vincent, J.B., Besse, S., Marchi, S., Sierks, H., Massironi, M., OsirisTeam, 2012. (4) Vesta matching independent Ar-Ar ages of HED meteorites. In: EGU General Physical properties of craters on asteroid (21) Lutetia. Planet. Space Sci.66, Assembly Conference Abstracts, p. 5741. 79–86. http://dx.doi.org/10.1016/j.pss.2011.12.025. Schulz, R., Sierks, H., Küppers, M., Accomazzo, A., 2012. Rosetta fly-by at asteroid Weiss, B.P., Elkins-Tanton, L.T., Antonietta Barucci, M., Sierks, H., Snodgrass, C., (21) Lutetia: an overview. Planet. Space Sci. 66, 2–8. http://dx.doi.org/10.1016/j. Vincent, J.B., Marchi, S., Weissman, P.R., Pätzold, M., Richter, I., Fulchignoni, M., pss.2011.11.013. Binzel, R.P., Schulz, R., 2012. Possible evidence for partial differentiation of Sierks, H., Lamy, P., Barbieri, C., Koschny, D., Rickman, H., Rodrigo, R., A'Hearn, M.F., asteroid Lutetia from Rosetta. Planet. Space Sci. 66, 137–146. http://dx.doi.org/ Angrilli,F.,Barucci,M.A.,Bertaux,J.L.,Bertini,I.,Besse,S.,Carry,B.,Cremonese,G., 10.1016/j.pss.2011.09.012.