A Case for Hydrothermal Systems in Firsoff Crater

Bernanda Telalovic`1, Roanna Chan2, Jordan Epstein3, Laurie Mac4, Jeff Stanger5, Jie Zhou6 Student Imaging Program, Sydney Powerhouse Museum, NSW, Australia

1 Student, Casula High School; [email protected] 2 Student, St. George Girls High School, [email protected] 3 Student, Cranbrook School, [email protected] 4 Student, St. George Girls High School, [email protected] 5Head Teacher Science, St. George Girls High School, [email protected] 6 Student, St. George Girls High School, [email protected]

Summary: Life on Earth is thought to possibly have originated from ancient hydrothermal systems, some of which are associated with impact craters. This analogue was used to investigate the potential circumstances for past hydrothermal systems on Mars. Candidate craters are those with diameters >50km and evidence of phyllosilicates. All dust-covered and eroded craters were eliminated to avoid spectral data errors. Features found using HiRISE were found to be morphologically similar to hydrothermal systems on Earth. An analysis of the intersection of the crater depth profile with the Martian steady-state ground ice shows the intersection of the two, further supporting the existence of impact-induced hydrothermal phenomena. Firsoff Crater was imaged by THEMIS after comparing spectral and morphological data and analysed with respect to these criteria.

Keywords: Hydrothermal, Mars, Craters, Firsoff, Cryolithosphere

Introduction and Methods Ancient hydrothermal systems are considered a possible location for the origin of life on Earth and are found in association with volcanoes and impact craters [1]. An impact-induced hydrothermal system is created upon impact when a fraction of a meteorite’s kinetic energy (Ek) is converted to heat (Eh), melting the rock and ground ice [2]. In craters on Earth, hot springs seem to be concentrated around the central peak, and at the rim [3]. A central peak in large craters indicates that a considerable amount of surface was liquefied during impact, inferring a large amount of Eh absorbed by the area, thus melting the sub-surface ice (cryolithosphere) and formed hydrothermal systems. The model proposed here is that impact- induced melting of the cryolithosphere, forms long-term hydrothermal phenomena which are detectable as fossil hydrothermal features including phyllosilicate deposits.

Fig 1. Model for impact-originated hydrothermal systems [1]. Not to scale.

1 Martian craters with diameters larger than 50 km [2] were examined for a sizeable impact- related heating effect and to better suit the resolution of the Thermal Emission Imaging System (THEMIS) camera (18 m2/pixel) on-board the Mars Odyssey orbiter [4]. Candidate craters associated with evidence of phyllosilicates were of particular interest since these are often associated with hydrothermal activity [5]. The existence of phyllosilicates was investigated using data from the Compact Reconnaissance Imaging Spectrometer (CRISM) on the Mars Reconnaissance Orbiter (MRO) [6]. CRISM images were studied in the ir_phy band (infrared hydroxylated silicates (including phyllosilicates) reflectance band) and ir_hyd band (infrared bound water reflectance band). The ir_phy browse products visualise spectral data as red (Fe/Mg phyllosilicates), (Al phyllosilicates or hydrated silica) and blue (hydrated minerals). The ir_hyd browse products visualise spectral data as red (bound water or ice), green (monohydrated sulfates) and blue (bound water). Ir_phy images with localised detections of hydrated clays (seen in blue) along with ir_hyd images containing an abundance of bound water (seen in red) were taken as indicative of a possible hydrothermal occurrence (Fig. 3) which is undermined by the unreliability of the CRISM instrument due to the dust cover in the area.

Features that corresponded to Earth-established hydrothermal systems were observed using images from the High Resolution Imaging Science Experiment (HiRISE) [7] and compared to existing THEMIS images. The sizes of the features were measured using the Java Mission- planning and Analysis for Remote Sensing program (JMARS) [8]. To study the effect the impact would have had on the cryolithosphere; existing models outlined in references 9 and 10 were used to estimate the depth of the cryolithosphere. The theoretical initial depth of Firsoff was estimated to 3.3 km maximum, according to relationships proposed by Garvin et al. [11]. Superimposing the two shows the impact carried sufficient energy to melt the cryolithosphere, thus forming hydrothermal systems (see Fig 9).

FirsoffFirsoff Crater Crater (350.6°(350.6° E, E, 2.73°)

Fig. 2. A Mars Orbiter Laser Altimeter (MOLA) map showing the location of Firsoff crater and approximate elevation adapted from image available at [12]

2 Data and Analysis

Firsoff crater is located at coordinates 350.6° E, 2.73° N in the which has been dated to approximately the upper age [13], however further research needs to be done to narrow this down to a specific timeframe. The crater is at current depth of approximately 3.06 km in depth and 79 km diameter (see Fig 8). It was selected as it was the best match for the set search criteria (e.g. >50km in diameter with evidence of phyllosilicates in the area and a large central peak). Morphologically, Firsoff is akin to the Curiosity landing site crater, with a similar layered central peak raised to the level of the crater rim. Figure 2 gives a context of the crater’s location.

Mineralogical Analysis of CRISM Data

Firsoff’s location places it in a mild dust region as observed by the Thermal Emission Spectrometer (TES) [14] (see also Fig 4). The CRISM spectroscopic analysis is only reliable in low dust zones, since dust can affect the accuracy of detections. It is for this reason that the infrequent CRISM data could not be taken as reliable evidence for the sediment composition of the area. CRISM images of the crater and surrounding area have been analysed nonetheless to get an estimate as to there being any significant variations.

C1 image no. C4 image no. 00017697 000172F1

C2 image no. C3 image no. 000170B5 0000C384

Fig 3. CRISM images of surrounding area, images on the left in each pair are ir_hyd (detecting bound water), right hand images are ir_phy (detecting hydrated clays, glass, phyllosilicates). C1 images are within Firsoff crater. The background image was taken scaled in JMARS as a part of the MOLA 12ppd coloured Elevation map.

In Fig 3, image C3, located in a crater adjacent is the only convincing outlier in the trend established by scattered and unreliable CRISM readings (since the presence of dust can affect the accuracy of the readings). C3 shows semi-localised hydrated sulfates, clays, and glass or water ice readings (in blue) in the area of the central peak. This can be taken as corroborating evidence to the possible hydrothermal activity in this region of Mars. The ir_hyd images show a prevalent abundance of bound water in the area, curiously not corresponding to any specific feature, noting that this can be attributed to false readings due to the dust cover of the area (See Fig 4). The exception is C3 ir_hyd which does correspond to some features within the area, therefore being slightly more reliable. By this exemption it can be inferred that there is possibly some areas of bound water within the surface Martian regolith, which is further supported by analysis of the data from the High Energy Neutron Detector (HEND) instrument (which has a range of detection to a depth of 1-2 m [9]). Research conducted using the Gamma-Ray Spectrometer on the Mars Odyssey spacecraft (the Los Alamos project) [15, 9] currently places Firsoff crater in an area of approximately 6% of water sediment composition,

3 which can mostly be attributed to bound water in minerals, thereby contributing to the amount of water that contributed to the possible hydrothermal systems.

A B C

6.25 km 6.25 km 6.25 km

Fig 4. THEMIS image I18460009 (A above), compared to image I07902037 (B above), taken 2 years later and the recent THEMIS image taken for the purpose of the research outlined in this paper (C above). (See Fig. 7 for context)

The morphological change of the dust deposit over time within Firsoff crater in Fig 4 indicates the presence of aeolian erosion which would have been acting on the features. The dust deposit confirms the data from TES and accounts for the unreliability of CRISM data.

Earth Analogues

Adjacent to the dust feature shown in Fig. 4 and 6, previous studies [13, 16] have associated layered conical mounds with a hydrothermal activity by proposing them as possible fossil mud volcanoes. These mounds lie on top of areas containing Equatorial Layered Deposits (ELDs) which may be sedimentary deposits associated with mud volcanism. The mounds are proposed as mud volcanoes by analogy with terrestrial analogues [13, 17]. Some correlation of these mounds with linear fractures or faults is suggested to support their hydrothermal origin. A large number of what appear to be fossil orifices or vents and mud breccia on many of the mounds is consistent with the mud volcano interpretation. These interpretations, although tentative, add support to the possibility of hydrothermal activity when considered in conjunction with the other information presented. An Earth analogue of layering associated with mud volcanism can be made with the El Arraiche mud volcano field [18] where sediment flow deposits are found on the flanks of the mud volcanoes, much like those shown in Fig 5 (B). Comparisons were also made between layered hydrothermal salt deposits observed as a product of volcanism in Pamukkale, Turkey as is shown in Fig 5.

A Layering and B decrease in altitude. C

Fig 5. HiRISE image ESP_026270_1820 (B) and corresponding height profile (derived from JMARS, red arrow on HiRISE image indicates location and direction of height profile) (A) compared to hydrothermally-originated salt deposits at Pamukkale, Turkey – C [19]

4 The height profile in Fig 5 (B) shows layered formations bearing resemblance to terrestrial hydrothermal salt deposits (A). Since the layering and mounds are placed within the crater basin, it can be inferred that post-impact activity has been the origin of these features. The shape of the features and their superposed nature implies a continuous phenomenon that would deposit these minerals in such a fashion. Therefore impact-induced hydrothermal activity, in the form of mud volcanoes or a simple process of deposition, analogous to that at Pamukkale and the mud volcanoes at El Arraiche, can be a possible explanation for the origin of these features, since it would encapsulate an elongated process of mineral deposition.

25 km C

A

B

Fig 6. Model of Haughton Crater (Canada) left, red dots (A) indicate confirmed impact- originated hydrothermal features [11]. THEMIS of Firsoff crater, right, shows chaotic terrain (B) near the rim and a dust deposit (C).

The model in Fig 1 outlines a higher probability of hydrothermal activity at the central peak, however the chaotic terrain interpreted as mud volcanism [13] corresponds to confirmed impact-originated hydrothermal features of Haughton Crater [3], both being located in the near-rim basin of the craters. The diameter of Haughton Crater (approx. 20 km) is less than the estimated 79 km diameter of Firsoff (measured by JMARS) and it can be inferred that much more Eh was derived from the Ek of the impactor, creating a greater possibility of hydrothermal activity.

Observed layered mounds in Firsoff Crater can likewise be linked to hydrothermal alteration, by an analogy with the hydrothermally altered ejecta blanket of Lonar crater, India. Due to size of this crater (1.8 km in diameters [20]) and the confirmation of hydrothermal activity through mineralogical studies bears implications that Firsoff, a significantly larger crater could support hydrothermal alteration in this manner. This research becomes more substantial when it is recognized that both Lonar and Firsoff crater were formed in a basaltic terrain [20] (since most of the Martian regolith has a basaltic composition, [21]), thereby inferring a possible connection between the chemical processes analysed at Lonar crater, but on a much larger scale, noting that reliable mineralogical data of Firsoff is required to sufficiently compare the two.

A Model for Cryolithosphere Intersection

To study how the impact would have modified the cryolithosphere, a theoretical model has been used from Mellon et al [10] (taking into account climate and seasonal sublimation occurrences) which predicts the steady-state ground ice upper boundary (the depth of cryolithosphere that is unaffected by seasonal sublimation processes) ranges from

5 approximately 5 m to 240 m for the geographic location of Firsoff crater. Other research conducted by Kuzmin et al [22] places the theoretical depth of the cryolithosphere at the upper boundary of steady-state ice at approximately 500 m to liquid water cryolithosphere of around 1.5 km lower boundary for the geographic location of Firsoff crater.

Empirical evidence of the existence of ground ice within the region can be found when looking for lobate ejecta of nearby craters, as Firsoff’s own ejecta has been severely eroded. Lobate / fluidised ejecta can only be formed in the presence of a liquid such as water liquefied by impact. Fig 7 shows the existence of one such crater whose ejecta has not been eroded since impact, therefore substantiating the theoretical predictions made by Mellon et al and Kuzmin et al.

Firsoff

A B

Fig 7. Nearby crater with clear lobate ejecta (A) and location of this crater with relation to Firsoff (B). Both images were taken from JMARS 12ppd MOLA elevation map. Both images were taken in JMARS

Similarly, if it can be found that the original depth of Firsoff crater was sufficient to intersect the theoretical value of the depth of the cryolithosphere, it can thus be inferred that enough Eh would have dissipated into the surrounding area to initiate impact-induced hydrothermal activity. To estimate the original depth of the crater, research done by Garvin et al [11] was used, and employing their formula for calculating the original depth of complex crater (those with central peaks), d=0.36D0.49 (1) gave a theoretical max depth of d=3.3 km, where d is the theoretical original depth and D is the diameter, derived from the depth profile of Firsoff from JMARS in Fig 8.

Fig 8. Current height profile of Firsoff crater derived from the 12 ppd MOLA elevation map in JMARS (A) and location of profile (red line in B). Both images were taken in JMARS.

6 Superimposing the theoretical depth of ground ice to the current crater depth profile gives evidence of intersection between the theoretical values of the depth of cryolithosphere predicted by both Mellon et al [10] and Kuzmin et al [22], shown in Fig 9.

Fig 9. Theoretical values of the depth of cryolithosphere superimposed onto a height profile of Firsoff as seen in Fig 8. Note that since the original depth of the crater was estimated at 3.3 km, therefore the original depth would have intercepted the steady-state ground ice to a greater degree.

As can be seen from Fig 9 the depth profile of Firsoff intercepts both models for cryolithosphere depth and it can thus be inferred that the Ek of the impact would have generated enough heat to melt a portion of the cryolithosphere, initiating hydrothermal systems within the crater. Since the crater’s original depth has an estimated maximum of 3.3 km, it can be assumed that the interception with the steady-state ground ice at the time of impact would have been significantly more, also substantiated by the general consensus among researchers that the amount of steady-state ground ice in the history of Mars was greater than current predictions [23].

Conclusion

The evidence from spectral analysis, cryolithosphere and Earth analogues provides a case for the existence of impact-originated hydrothermal systems in Firsoff Crater, warranting further research into the age of the crater and corresponding changes in the cryolithosphere. Applying this model to other similar craters on Mars would strengthen the proposition that specific types of craters on Mars have ancient hydrothermal system as per the Earth analogue model.

Acknowledgements

Our thanks to the Australian Space Research Program, the Mars Student Imaging Program, Dr Carol Oliver, Prof Malcolm Walter, Dr Graziella Caparelli, and many others who helped during this research.

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