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Tube Worms, Hydrothermal Vents, Life On Mars? A Comparative Morphological Analysis

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Hundreds of tubular and spiral specimens resembling terrestrial tube worms and worm tubes were photographed in the soil and atop and protruding from “rocks” on Sols 177, 199 and 299 in the vicinity of Endurance Crater, Meridiani Planum. Dozens of these putative “worms” and tubes are up to 3 mm in size. These tubular specimens display twisting, bending, and curving typical of biology and are different from abiogenic structures. Morphological comparisons with living and fossilized tube worms and worm tubes also supports the hypothesis that the Martian tubular structures may be biological as they are similar and often nearly identical to their terrestrial counterparts. The literature concerning abiotic and biotic formation of mineralized tubular formations is reviewed and the Martian tubular structures meet the criteria for biology. In addition, larger “anomalous” oval-specimens ranging from 3 mm to 5 mm in diameter were photographed and observed to have web-like appendages reminiscent of crustacean pleopods. That marine organisms may have evolved and flourished in the vicinity of Endurance Crater, Meridiani Planum, was originally predicted by NASA’s rover Opportunity crew in 2004, 2005, and 2006. This area is believed to have hosted a briny body of water that was heated by hydrothermal vents; and these are favored habitats of tube worms. Further, all these specimens were photographed adjacent to vents in the surface and the mineralogy of Endurance Crater is similar to that produced by tube worms and their symbiotes. However, if any of these specimens are alive, fossilized, mineralized or dormant is unknown. Abiotic explanations cannot be ruled out and it cannot be stated with absolute certainty they are biological.
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Journal of Astrobiology
Tube Worms on Mars 1 JournalofAstrobiology.com
Rhawn Joseph Copyright © 2021 Journal of Astrobiology, 8, 1-37, 2021
Tube Worms, Hydrothermal Vents, Life on Mars?
A Comparative Morphological Analysis
Rhawn Joseph1, Olivier Planchon2, David Duvall1,3, Rudolph Schild1,4,
1Astrobiology Research Center, CA, USA
2National Center for Scientific Research, Biogéosciences, University of Bourgogne, France
3Dept. of Zoology (emeritus), Oklahoma State University, OK, USA
4Center for Astrophysics (emeritus), Harvard-Smithsonian, Cambridge, MA, USA
Journal of Astrobiology, Vol 9, 1-37, PrePrint
Editors-in-Chief: G. Bianciardi, K. Wołowski, R. del Gaudio
Abstract
Hundreds of tubular and spiral specimens resembling terrestrial tube worms and worm tubes were
photographed in the soil and atop and protruding from “rockson Sols 177, 199 and 299 in the vicinity of
Endurance Crater, Meridiani Planum. Dozens of these putative “worms” and tubes are up to 3 mm in
size. These tubular specimens display twisting, bending, and curving typical of biology and are different
from abiogenic structures. Morphological comparisons with living and fossilized tube worms and worm
tubes also supports the hypothesis that the Martian tubular structures may be biological as they are
similar and often nearly identical to their terrestrial counterparts. The literature concerning abiotic and
biotic formation of mineralized tubular formations is reviewed and the Martian tubular structures meet
the criteria for biology. In addition, larger “anomalous” oval-specimens ranging from 3 mm to 5 mm in
diameter were photographed and observed to have web-like appendages reminiscent of crustacean
pleopods. That marine organisms may have evolved and flourished in the vicinity of Endurance Crater,
Meridiani Planum, was originally predicted by NASA’s rover Opportunity crew in 2004, 2005, and 2006.
This area is believed to have hosted a briny body of water that was heated by hydrothermal vents; and
these are favored habitats of tube worms. Further, all these specimens were photographed adjacent to
vents in the surface; and the mineralogy of Endurance Crater is similar to that produced by hydrothermal
vents and tube worms and their symbiotes. However, if any of these specimens are alive, fossilized,
mineralized or dormant is unknown. Abiotic explanations cannot be ruled out. It cannot be stated with
absolute certainty they are biological.
Key Words: NASA, Opportunity, Life on Mars, Hydrothermal Vents, Tube Worms, Spiral Worms, Worm Tubes,
Crustacean, Pleopods, Thermal Vents, Cold Water Seeps, Endurance Crater, Fossils, Mineralization.
Pictorial Abstract
Submitted: 8/6/21
Peer Reviews: 14 (5 rejecting)
Final Revision 8/24/2021
Accepted for publication by two of the three Editors-in-Chief
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1. Martian “Tube Worms” “Worm Tubes” and Endurance Crater
Elongated tubular formations resembling “worm tubes” and “tube worms” some with “caps” and
“collars” protruding from stony matrix or tubes or laying upon the surface have been photographed in
Meridiani Planum by the rover Opportunity Microscopic Imager in the area leading from Eagle Crater to
and within Endurance Crater. Morphologically the Endurance Crater “worm tubes” with open apertures
are similar to those photographed atop and possibly attached to sedimentary rock in the “Vera Rubin
Ridge” area of Gale Crater (Figure 1). Those on “Vera Rubin Ridge” have been described as
“ichnofossils” and possible indicators of biology (DiGregorio 2018; Baucon et al. 2020; Joseph et al.
2020a) vs “stick shapes” due, hypothetically, to erosion resistant mineral grains (Greicius 2019). As
detailed in this report, these Endurance Crater tubular specimens are also morphologically similar to
terrestrial tube worms and worm tubes.
Figure 1. (Left) Tubular specimens from Gale Crater, Mars. (Right) Tubular specimen from Endurance
Crater, Meridiani Planum, Mars.
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Figure 2. Terrestrial Tube Worms (Annelida, Serpulidae) and Worm Tubes (red arrows). C—dorsolateral
view of terrestrial tube worm removed from worm tube. D—SEM of scoops (or leaflets) outside the
worm tube entrance (indicated by white arrows). E—view of tube worm in the tube. Scale: C—1 mm, D
—0.5 mm, E—1 mm. (Modified from Kupriyanovaetal et al. 2011).
In addition to colonization by putative Martian “tube worms” Gale and Endurance Craters are
believed to have hosted lakes of water at various times in the past thereby providing a habitable
environment that promoted the evolution and fossilization of eukaryotes (Grotzinger et al. 2014; Hynek et
al. 2015; Squyres et al. 2004, 2006); and for which there is now some evidence (Baucon et al. 2020;
DiGregorio 2018; Elewa 2021; Latif et al. 2021; Joseph et al. 2020a,b; Kaźmierczak 2016, 2020). The
past watery environment of Endurance Crater (Meridiani Planum) has also been described as a salty
“brine” (Clark et al. 2005; Grotzinger et al. 2005; Squyres et al. 2004, 2006); and which is also a favored
habitat of “tube worms” (Cary et al. 1989; Roberts et al. 2010a,b; Dupré & Brosolo 2010; Monastersky
2012).
“Worm tubes” are distinct from the soft-bodied worms within (Figure 2). These tubes are
generated by mucus and non-mucus mechanisms which differ in their preservation durability (Georgieva
et al 2019). They are sensitive to touch and if disturbed or threatened by predators, the worm will retract
deep inside the tube (Tunnicliffe et al. 1990). Tube worms can also exit the tube and migrate across the
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surface or through ocean or lake water in search of nutrients or a new habitat. Figure 5 depicts a
mineralized/fossilized “worm-like” specimen immediately anterior to a “worm tube.”
As documented in this report, these specimens have the classic features of “tube worms,” spiral
worms, and “worm tubes” many of which congregate near, adjacent to or on the rims around holes in the
ground that may have served as hydrothermal vents (Figures 4-16). Some species of terrestrial tube
worms (spionid polychaetes) have paired antenna-like organs referred to as “palps” (Dupré & Brosolo
2010); and features similar to these have been observed among the “tube worms” of Endurance Crater
(Figure 17). In addition, shrimp-shaped (Figure 18) and spiral-shaped “worms” (Figures 19, 20) and
oval-shaped Martian specimens with appendages similar to the pleopods of crustaceans (Figure 4) have
been observed in close proximity to the tubular structures of Endurance Crater. On Earth crustaceans are
often observed in close proximity to tube worm colonies (Dupré & Brosolo 2010; MacAvoy et al. 2003;
Li et al. 2020). Morphological comparisons with terrestrial tube worms and their tubes also indicates a
close similarity to the Martian tubes (Figures 21-22) and the variety of “worms” photographed on the
surface of Endurance Crater (Figures 23-25). Furthermore, there are specimens that resemble worms and
tubes which have become mineralized and fossilized (Figures 26-27) and attached to “rock-like” matrix
within which and adjacent to what appear to be worm holes and small tubular specimens protruding
outward from these holes--similar to rock-dwelling tube worms on Earth (Figures 28, 29).
As documented in this report, these findings indicative of putative tube worms, worm tubes and
associated biological communities (Figures 30, 31), support the hypothesis that Endurance Crater, and its
surroundings, provided a salty marine-environment in which these and other organisms evolved and
flourished (Hynek et al. 2015; Squyres et al. 2004, 2006). Moreover, the disposition and state of
preservation of these specimens upon the surface--if they are in fact tube worms and worm tubes--is
indicative of recent rapid evaporation of these briny waters; and leaves open the possibility that some of
these Martian “tube worms” may be dormant; or, they were “pickled” by this salty brine.
2. Endurance Crater, Mineralogy, Salty Brines, Hydrothermal Vents & “Tube Worm” Symbiotes
In this report there are no attempts to make any precise taxonomic identification of these Martian
tubular specimens, other than to distinguish “worm tubes” (which may or may not be occupied) and what
appear to be soft-bodied specimens that often have a “cap” and collar. Likewise, in the ensuing discussion
of “worm tubes” and terrestrial-water dwelling “tube worms” (e.g. siboglinids, serpulids, chaetopterids)
we will not make any distinctions between those that dwell in cold water seeps, hydrothermal vents, or
near the surface of shorelines (e.g. Hove & Kupriyanova 2009).
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Tube worms are metazoan marine invertebrates belonging to the phylum Annelida and have no
“mouth” or “gut” (Ruppert & Barnes 2007). Tube worms (e.g. “Vestimentiferan”) commonly colonize
hydrothermal vents and cold water (hydrocarbon) seeps throughout the world (Berguist et al. 2003;
Freytag et al. 2001; Hessler & Smithey, 1983; Hove & Kupriyanova 1986; Sibuet & Olu 1998; MacAvoy
et al. 2003; Li et al. 2020; Georgieva et al. 2019) and form colonies of thousands of individual worms
(Brooks et al. 1989) that coexist with bacteria, mussels, and snails (Li et al. 2020). They are believed to
have few or no predators (Berguist et al. 2003) other than “crabs” (Dupré & Brosolo 2010; MacAvoy et
al. 2003). They flourish in the most extreme environments and were discovered at a depth of 2,550 meters
flourishing in the Galapagos hydrothermal vents beneath the Pacific Ocean, in 1977 (Corliss et al. 1981).
It has been documented that some species of tube worm will grow a posterior extension (root/bush)
that tunnels into the (often carbonate-rich) sediment; roots which are permeable and take up hydrogen
sulfide (Freytag et al. 2001; Julian et al. 1999). It is also well established that tube worms live
autotrophically with hydrogen sulfide as their energy source and form symbiotic relationships with
chemoautotrophic bacterial endosymbionts (Cary et al. 1993; Childress & Fisher 1992; Di Meo et al.
2000; Nelson & Fisher 1995; MacAvoy et al. 2003; Zimmermann et al. 2014). Endurance Crater is rich
in sulfides (Wray et al. 2009; Flahaut, et al. 2015; Squyres & Knoll 2005; Squyres et al. 2004, 2006).
Tube worms obtain nutrition from symbiotic sulfide-oxidizing chemoautotrophs; the sulfide fueling
autotrophic carbon fixation sustaining the tube worm host (Childress & Fisher 1992; Zimmermann et al.
2014). It has also been determined that elevated levels of CO2 enhance chemoautotrophic symbioses and
diffusion to the symbiotes (Childress et al. 1993), whereas the atmosphere of Mars is largely CO2.
It has been estimated that tube worms may release up to 90% of the sulfate produced during sulfide
oxidation back into the sediment via their “roots” (Dattagupta et al. 2008) and sulfate is a common
feature of Endurance Crater (Wray et al. 2009; Flahaut, et al. 2015; Squyres et al. 2004, 2006). The
microbial community dwelling with tube worms within the substrate, also produce calcium carbonate,
thereby cementing together microbial mats, and providing layers of calcium-laden rock which is also
colonized by tube worms (Childress & Fisher 1992; Feng et al. 2013).
Evidence of calcium-laden microbial mats and microbialites have been observed in Meridiani
Planum (Bianciardi et al. 2014; Rizzo & Cantasano 2016; Joseph et al. 2020b); the calcium carbonate
presumably secreted by algae/cyanobacteria for which there is evidence (Kaźmierczak 2016). Analysis of
spectra and surface and orbital investigations have also provided evidence of carbonate and calcium
carbonate on Mars (Boynton et al. 2009; Krall et al. 2014; Sutter et al. 2012; Wray et al. 2016).
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The carbonates produced by associated tube worm communities and symbiotes are also high in Mg,
calcite, dolomite and aragonite (Feng et la. 2013; Hila ́rio et al. 2011); and this biological “cement” is
commonly found in the substrate of ancient (Peckmann et al., 2005) and modern colonies of tube worms
(Feng and Roberts, 2010; Haas et al. 2009). Hydrothermal chimneys also consist of anhydrite (Kuhn et al.
2003). Likewise, Endurance Crater is enriched with anhydrite, sulfate, carbonate, Mg spectites, Mg/CA/
Fe carbonates (Arvidson et al. 2005, 2006; Bandfield et al. 2003; Bishop et al. 2002; Ehlmann &
Edwards, 2015; Ehlmann e al. 2008; Flahaut et al. 2014; Gendrin et al. 2005; Glotch et al. 2006; Morris
et al. 2010; Squyres et al., 2006; Wray et al. 2009, 2016) and possibly calcium carbonate (Kaźmierczak
2016) and dolomite (Flahaut et al. 2014). The white “rock-like” matrix associated with the tubular
specimens in this report, may also have an anhydrite carbonate composition. On Earth, carbonates occur
generally as high-Ca variants calcite or aragonite and dolomite (Wray et al 2016); and all these Martian
minerals are directly associated with tube worm-symbiotic biological activity on Earth (Peckmann et al.,
2005; Feng & Roberts, 2010; Haas et al. 2009).
Terrestrial tube worms, therefore, often colonize extreme environments but rely on
chemoautotrophic sulfur-oxidizing symbionts (Scott & Fisher 1995; Nelson & Fisher 2000). However,
those that dwell in hydrothermal vents have a relatively short life span and grow rapidly, whereas those
flourishing in cold seeps grow slowly and may lived up to 300 years (Pflugfelder et al. 2009).
Tube worms also flourish in highly salty brines (Cary et al. 1989; Roberts et al. 2010a,b; Dupré &
Brosolo 2010; Monastersky 2012) which may be enriched with Mg calcite (Roberts et al. 2010a; Feng &
Roberts, 2010). This is significant as the waters that have periodically filled the lakes, rivers, and streams
of Endurance Crater, Mars, have also been characterized as exceedingly salty brines (Clark et al. 2005;
Grotzinger et al. 2005; Squyres et al. 2004, 2006). Moreover, Mg and calcite have been detected on Mars
(Boynton et al. 2009; Sutter et al. 2012; Leshin et al. 2013; Archer et al. 2014).
3. Tube Worms and Meridiani Planum’s Briny Salty Lakes
It is established that Meridiani Planum (Hynek et al. 2015; Squyres et al 2004) and Gale Crater,
like other areas of Mars, hosted a series of lakes in which a variety of organisms may have flourished and
became fossilized (Bianciardi et al. 2021; Joseph et al. 2020a,b, Rizzo et al. 2021; Squyres et al 2004;
Kaźmierczak 2016, 2020; Grotzinger et al. 2014). Squyres et al (2004), who led NASA’s Mars rover
Opportunity team that explored Meridiani Planum, reported that eukaryotic "filamentous
microorganisms" may have colonized this area in the distant past. Hofmann and Farmer (2000) predicted
that mineralized fossils of filamentous tubular microorganisms may be abundant on Mars. What appear to
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be mineralized fossils of tube worms have been photographed in Endurance Crater (Figures 26-27).
Hynek et al. (2015), who examined hundreds of sites where salt deposits have been observed from
space by the Mars Reconnaissance Orbiter or Mars Express, has reported that deposition in Meridiani
Planum probably formed from a fluvio-lake process and an active hydrological cycle involving rivers and
flooding streams that cut into valleys and formed a massive lake. According to Hynek et al. (2015) this
lake was habitable and may have been inhabited by a variety of organisms; including, as postulated by
Squyres et al (2004) filamentous eukaryotic organisms. In addition, it has been hypothesized that the area
encompassing Eagle and Endurance Crater long ago hosted subsurface aquifers heated by thermal vents
(NASA 2009; Squyres et al. 2004), a favored habitat of tube worms.
After Opportunity entered Endurance Crater on Sol 134 (June 12, 2004) cirrus clouds were
observed (NASA 2009) which on Earth contain ice crystals and super cooled water droplets (Franks
2003). The implication is that when temperatures rise, water may rain down upon or percolate up upon
the surface of Endurance Crater, only to eventually seep back and pool beneath the surface or evaporate
and again form clouds of frozen water droplets.
For the next 201 days Opportunity explored Endurance Crater (Squyres et al. 2004, 2006; Squyres
& Knoll 2005). The outcrops of Endurance (and Eagle) Crater (also known as the “Burns formation”)
were found to include and largely consist of sulfate-rich sandstone--the lowest portions of which were
covered by small dune-like ripples of fine grained sand (Figure 3). The ripples of sand are believed to
have been deposited by high levels of ground water (Andrews-Hanna et al., 2010) and the waxing and
waning of one or more vast lakes (Squyres et al., 2004; Grotzinger et al., 2005, 2006; Metz et al., 2009).
Figure 3. Endurance Crater. False color Pancam panorama of the dune field on the floor of Endurance
crater. Image acquired on Sol 211 using Pancam's 753 nm, 535 nm, and 432 nm filters, L2, L5, and L7.
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According to Squyres and colleagues (2004) the overall environmental conditions of Endurance
crater and the surrounding terrain are indicative of “episodic inundation by shallow surface water,
followed by evaporation, exposure, and desiccation...” and “that the area over which these aqueous
processes operated was at least tens of thousands of square kilometers in size.” They go on to conclude:
“Because liquid water is a key prerequisite for life, we infer that conditions at Meridiani may have been
habitable for some period of time in martian history.”
Detailed analysis of the mineralogy and chemistry of this outcrop suggests that this area once
hosted large shallow sulfate-enriched salty seas, lakes and streams that are chemically similar to sulfate-
enriched brines commonly found in terrestrial lakes throughout the world (reviewed by Clark et al. 2005;
Grotzinger et al. 2005). Terrestrial sulfate-enriched brines also host colonies of tube worms (Cary et al.
1989; Roberts et al. 2010a,b; Dupré & Brosolo 2010; Monastersky 2012).
On Sol 199 and 299 the Opportunity’s Microscopic Imager photographed tubular specimens
ranging in size from approximately 1 mm to 3 mm in size, lying upon the surface and jutting out from
white matrix “rocks” the composition of which is unknown. Ovoid specimens with what appear to be
pleopods were also observed (Figures 4, 30, 31).
When the rivers, lakes and streams of Mars vanished from the surface is a matter of speculation.
However, there is considerable evidence of rivers and lakes of ice and water-ice sequestered in the
southern and northern polar caps and beneath the surface (Byrne et al. 2009; Orsei et al. 2018, 2020;
Lauro et al. 2020), and that may extend deep into surrounding terrain (Arnold et al. 2019; Sori et al.
2019) some of which are heated by thermal anomalies (Arnold et al. 2019; Sori et al. 2019). It is believed
there are sources of water beginning at a depth of 1 meter below the surface of Endurance Crater which
may also host subterranean aquifers (Clark et al. 2005) that in the past were heated by hydrothermal vents
that had been colonized by eukaryotes (Squyres et al., 2004). Based on the evidence presented here, it is
probable that these underground aquifers are still inhabited by tube worms and other organisms.
4. Composition of Tube Worm Fossils: Biology vs Abiogenic Mineralization
It is believed tube worms first evolved near or in thermal sources within lakes and seas during or
just prior to the “Cambrian Explosion” (Landing 1993; Nanglu et al. 2016) and that the mineralization of
tubular organisms is most likely to occur when exposed to heated sources of water (Gotze et al. 2020)
thereby enhancing their preservation as fossils. Some of the Martian tubular formations reported appear
to be almost entirely mineralized and fossilized (Figures 26-27). On Earth, tubular specimens that
appear to be entirely abiotic and composed of crystals and minerals have been shown to be biological in
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origin with minerals forming on the outside of cell walls (Gotze et al. 2020). The onset of metazoan
biomineralization is considered a key innovation in the evolution of annelids (Yang et al. 2020).
Tube worms are members of the phylum Annelida (Ruppert & Barnes 2007) and may have first
evolved over 500 million years ago (Landing 1993; Nanglu et al. 2016). Employing Earth as an analog, if
the putative Martian specimens are in fact worms, then their ancestors may have evolved over half a
billion years ago (Joseph et al. 2020a). However, there is no general agreement as to the ancestral history
of annelid tube worms with some species dated to the early Jurassic and mid Cretaceous to the Silurian
period (Georgieva et al. 2019; Hove & Kupriyanova 2009) and with the main tube-building vent and
seep annelid lineage, the vestimentiferans, dated to the Palaeozoic just prior to the Cambrian Explosion
(Georgieva et al 2019; Landing 1993; Nanglu et al. 2016).
The tubes of the worms are the most likely to be preserved unless the worm is also mineralized.
The tubes are distinct from the soft-bodied worms within and are generated by mucus and non-mucus
mechanisms which differ in their preservation durability. As summarized by Georgieva et al (2019): the
more robust non-mucus annelid tubes “can be divided into three broad categories: calcium carbonate
tubes, agglutinated tubes comprised of inner organic layers and outer exogenous material (e.g. sediment
grains), and tubes comprised purely of an organic secretion.” Calcareous tubes often consist of calcite or
aragonite (Vinn et al. 2008) whereas “organic” tubes have a high protein carbohydrate content (Merz
2015). Chitin is also a common component of these tubes (Georgieva et al 2019) which indicates the
contribution of fungi (Gotze et al. 2020); and there is evidence of fungi on Mars (Dass 2017; Joseph
2016; Joseph et al. 2021). All these different types of tube occur in cold water seeps and hydrothermal
environments (Georgieva et al 2019; Kupriyanova et al. 2010).
Be they robust or mucous-based, fossilized tubes are often broken or only pieces remain, and
these remnants may become highly mineralized. Many of the Martian tubular fossils may have been
broken, or are partially buried in the soil (Figure 11, 22, 23). Therefore, it is impossible to make detailed,
fine structure comparisons between what we presume to be fossils of Martian vs terrestrial tube worms.
Assuming these specific Martian specimens are “tube worms” it is unknown if they evolved and
flourished in cold or hot water seeps or vents or near lakes shores. Tubes formed at hydrothermal vents
are preserved primarily by iron sulphides and upon fossilization details of outer tube ornamentation and
textures may be retained (Cook & Stakes 1995; Georgieva et al. 2015). By contrast, at cold-water seeps,
aragonite often serves to retain the finely multi-layered structure of the tube walls (Haas et al. 2009).
Many of the specimens resembling “tube worms” and “worm tubes” observed in Endurance
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Crater are markedly well preserved--though photo quality is often poor. If they are in fact tube worms,
these findings may support an iron-rich hydrothermal origin--a supposition reinforced by a lack of
evidence for aragonite. Or perhaps they flourished just beneath the surface of the lakeshore.
If biological, then given their state of preservation, they must have been recently formed. Some of
the putative Martian “tube worm” specimens with collars and caps may be dormant. Moreover, many of
these specimens were photographed next to holes/vents in the ground (Figures 4, 5) and it is believed
there may be near-surface water at a depth of 1 meter and that Endurance Crater may host subterranean
aquifers (Clark et al. 2005) that long ago were heated by hydrothermal vents and colonized by eukaryotes
(Squyres et al., 2004). Hence, if biological, it is possible that these tubular organisms bubbled up to the
surface along with subsurface waters in the recent past, and then when the waters evaporated or seeped
back beneath the surface, they were left behind and became dormant, or died and became fossilized.
Figure 4. Endurance Crater (1M145849709EFF3505P2976M2M1). Blue arrow points to a hole/vent.
Numerous spiral and tubular shaped “worm-like” formations are circled in red. The red box frames an
oval-specimen with web-like appendages reminiscent of crustacean pleopods.
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Figure 5. Endurance Crater (M145852935EFF3505P2906M2M1). Blue arrow points to a hole/vent. Note
fossilized/mineralized tubular specimens on either side of arrow. Red arrows point to tubular specimens.
Numerous spiral shaped “worm-like” specimens can be viewed circled in red at the entrance to the hole.
Note “twisted” specimen at bottom center with appendages. White arrow points to elongated structure
that may be a fossilized/mineralized worm that had occupied the “worm tube” directly beneath it.
5. Morphological Biological Observations: Spirals, U-loops, Tortuosity, Bending, Twisting, Curving
It is not likely these Martian specimens are abiogenic; though this possibilty cannot be ruled out.
Nevertheless, biological vs abiogenic tubular formations are easily distinguished. Biological formations
show a significantly greater degree of tortuosity, bending, and direction changes (Gotze et al. 2020;
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Williams et al. 2015). By contrast, abiogenic mineral filaments and fibers are typically straight (low
tortuosity) with little evidence of bending, twisting, turning or direction changes (Gotze et al. 2020;
Hofmann et al. 2009).
As depicted in the photographs presented here, these Martian tubular specimens show typical
biological features including flexibility, spirals, U-loops, tortuosity, bending, twisting, and curving
directional changes. Therefore, the Martian tubular structures meet the criteria for biology (Gotze et al.
2020; Hofmann & Farmer, 2000; Hofmann et al. 2009; Williams et al. 2015).
6. Ruling Out Abiotic Mineralization
It has been hypothesized that due to high porosity and large cavities within hydrated theoleitic
basalts, bacteria, archaea and circulating fluids will precipitate and crystalize various minerals, beginning
with Fe-rich compounds and organic carbon secondary to microbial activity (Gotze et al. 2020). It is
believed that host rocks provide Ca, leading to the crystallization of Ca-rich zeolites which, under certain
conditions (e.g. hydrothermal vents) and in association with various silicates, clays, calcites and quarts,
may envelop and surround the surface of a biological filament core (Gotze et al. 2020).
Many of these minerals and metals have been detected or identified on Mars (Williams et al. 2013;
Treiman et al. 2016) and have been found in mixtures of clay and embedded in basaltic and
phyllosilicate-bearing Martian rocks (Bristow et al. 2015; Vaniman et al. 2014). Some of the Martian
tubular structures appear to be worms and worm tubes that have been mineralized (Figures 26-27).
On Earth, crystallization of various hydrated minerals, coupled with biological activity, are known
to generate tubular “filamentous fabrics” within vesicles, cavities and subterraneous environments and
occasionally in basaltic brecci (Gotze et al. 2020; Hofmann et al. 2008). These terrestrial subterraneous
tubules are fashioned via bio-mineralization, and range in size from microscopic to macroscopic, and are
affected by gravity but have no relationship to stalactite growth (Gotze et al. 2020; Ottens et al. 2019).
By contrast, all the tubular specimens presented in this report were photographed on the surface,
albeit some near holes/vents in the ground or jutting out from small holes or attached to the top-side of a
white rock-like matrix (Figures 4,5,6, 11, 12, 15-17, 22, 24) the composition unknown. Even those that
appear to be mineralized/fossilized specimens on the surface and attached to “rocks” are atypical of
mineralized/crystalized abiogenic tubules which generally form in subsurface environments in a top-
down direction due to the influence of gravity.
Gotze et al. (2020) reports that terrestrial tubes suspected to be abiogenic contain organic matter in
the central filamentous core. Based on a detailed chemical analysis Gotze et al. (2020), determined “that
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the innermost filamentous core often consists of thread-like, mostly Fe-rich sheet silicates” and that the
“detected relics of organic matter and the partly analyzed excess carbon indicate that these inner filaments
might be the result of biochemical activities... resulting from the mineralization of microbial fabrics based
on filaments, followed by the abiotic precipitation of a complex assemblage of minerals... Alternative
explanations of origin would require modes of filament formation currently unknown to science.” As
summed up by Gotze et al. (2020): terrestrial tubules “are similar to microbial filaments and... are most
likely initiated by microbial communities active in these cavities.” As noted, Squyres et al. (2004, 2006)
have argued that filamentous eukaryotes may have flourished in Meridiani Planum.
Gotze et al. (2020) also found evidence for fungal chitin in these mineralized tubes (see also
Sterflinger 2000) similar to the chitin of wood mold fungus Aureobasidium pullulans and Basidiomycetes
(Di Mario et al. 2008; Gupta et al. 2015). Basidiomycetes have been repeatedly identified in Meridiani
Planum (Armstrong 2021; Dass, 2017; Joseph 2016; Joseph et al. 2020c,d; 2021), which is also the
general vicinity in which these Martian tubular formations have been discovered. Fungi play a significant
role in the formation of terrestrial tubules (Gotze et al. (2020).
According to Gotze et al. (2020) these fungal filaments may have served as a nucleus (biogenic
template) that enabled and initiated the mineralization processes. These living (or dead) organic surfaces
are believed to act as “seeds” around which minerals form and then calcify. That is, the cell walls of these
organisms may act to bind metal ions and there follows mineral growth surrounding these tubular
filaments (Hofmann & Farmer, 2000).
Studies have shown that these tubular formations can form, biologically, in the most extreme
environments (Johannessen et al. 2019; Krepski et al. 2013). According to Hoffman et al. (2008), these
tubular formations “are a logical target in the search for past life on Mars.”
7. Mars vs Earth Morphological Comparisons: Tube Worms and Worm Tubes
On Earth various tubular features and fine ornamental details are generally not well preserved,
especially those fossilized at seeps vs those in hydrothermal vents (Little et al. 1998; Georgieva et al
2019). As to the Martian specimens, because of poor image quality and resolution, it is only possible to
identify biological features such as twisting, turning, and bending, the presence of a “cap” and/or collar,
and to differentiate between “worm tubes” and “worms” which may be hidden within a tube or jutting out
from a rock-crevice or laying on the surface or beneath or next to a rock. Therefore to further assist in
identifying these Martian specimens, we have elected to compare and contrast these Martian specimens
with living and fossilized worm tubes and tube worms from Earth.
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I. COMPARISONS: TERRESTRIAL VS MARTIAN TUBE WORMS & WORM TUBES
Figure 6. Earth. D—0.5 mm. Open tube of Annelida, Serpulidae with animal removed from the tube.
Arrows indicate scoops/leaflets at the entrance of tube. (From Kupriyanovaetal et al. 2011).
Figures 7 & 8. Mars, Endurance Crater. Fibrous open “worm tubes” with numerous scoops/leaflets at the entrance
of the tube. Note: oval structures at the upper mouth and left-lower mouth in the specimens to the left and right
respectively. Possibly these tubes are occupied and a tube worm may be extending outside the mouth of the tube in
the specimen to the right (see Figure 9). ---2.5 mm. (Left: 1M145405702EFF3500P2957M2M1 / Right:
1M145852648EFF3505P2957M2M1)
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Figure 9. Mars, Endurance Crater. Fibrous open “worm tubes” that are possibly occupied by tube worms,
indicated by white arrows pointing to oval structures. Darkening contrast has been applied to the figures
in the right column. Specimen in the bottom row may depict the cap and collar of a tube worm protruding
from the tube. Red arrows point to what may be mouth palps.
Figure 10. Eudistylia vancouver photographed in tidepools. Red circle: worm protruding from tubes.
(Left) Tube worm gill plumes and worm protruding from tube (from https/theoutershores.com/
2015/02/11/northern-feather-duster-worm). (Right) Operculum, Annelida, Serpulidae (From Kupriyanova
et al. 2012).
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Figure 11. Endurance Crater. 1M145852876EFF3505P2957M2M1. Specimens resembling tube worms
and worm tubes upon the surface, and “worms” protruding from small holes in the white matrix which
may consist of anhydrite which in turn is associated with the chimneys of active and collapsed
hydrothermal vents and their surroundings (Kuhn et al. 2003). Note oval specimens in the lower right
with what appear to be pleopods. ___ 5 mm
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Figure 12. Tube worm operculum and collars. (Middle) Mars, Endurance Crater, Tube Worms? (Right)
Terrestrial Tube Worms (Annelida, Serpulidae) C. Pseudochitinopoma amirantensis. Operculum, —300
μm, From Kupriyanova et al. 2012.
Figures 13. Endurance Crater. 1M144251471EFF3352P2977M2M1. Martian specimens resembling
“tube worms” with caps, operculum and collars.
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Figures 14. (Right) Endurance Crater. Specimen with cap and denticulate collar emerging from Tube (red arrows)
(Left) Hyalopomatus jirkovi tubes with denticulate collars. A—dorsal and B—lateral views, C.D,H—operculum E
—dorsal and F—lateral views, G—operculum, I, J—fragment of the tube. Scale: A, B, I,—1 mm, C, D, G—0.2
mm, E, F—0.5 mm, H—0.3 mm, J—3 mm. From Kupriyanova et al. 2012.
Figures 15. Endurance Crater. Worm tubes and (circled in red) tube worms with denticulate collars? (Right:
1M145850659EFF3505P2977M2M1. Left 1M145852935EFF3505P2906M2M1).
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Figures 16. (Left: 1M145850153EFF3505P2977M2M1 / Right: M145405241EFF3500P2957M2M1D).
Center: Close-up view of the operculum of a worm in the tube; —1 mm, Kupriyanova et al. 2012
Figures 17. Endurance Crater. 1M143896318EFF3336P2957M2M1. Martian specimens with “antenna?”
Figures 18. Endurance Crater. 1M145405241EFF3500P2957M2M1 1M145404757EFF3500P2957M2M1
Martian specimens resembling “shrimp.”
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Figure 19. Spiral tube worm. From Kupriyanova et al. 2011.
Figures 20. Endurance Crater. (1M145850719EFF3505P2936M2M1). Martian spiral “tube worms?”
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Figure 21. From left to right: detail of grooved possibly multi-layered worm tube walls. Scale bars: A,C,
= 1 mm; D,E = 0. 5 mm. (Reprinted from Georgieva et al. 2019).
Figures 22. Endurance Crater. Martian tubular specimens, including those that appear to be mineralized and jutting
out from a matrix that may consist of anhydrite and/or calcite and calcium carbonate. (Top:
1M145852935EFF3505P2906M2M1 / Bottom: 1M145852721EFF3505P2957M2M1).
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M145851070EFF3505P2977M2M1 / 1M145405702EFF3500P2957M2M1
1M145851070EFF3505P2977M2M1 / 1M145405241EFF3500P2957M2M1
Figures 23. 1M145850485EFF3505P2977M2M1 / 1M145852648EFF3505P2957M2M1. An assortment
of “tube worms” and “worm tubes?”
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Figure 24. Endurance Crater. 1M145852648EFF3505P2957M2M1. Specimens resembling a “tube
worm” (left bottom) and numerous “worm tubes” some embedded or jutting out from a white matrix the
composition of which is unknown but that may consist of anhydrite and/or calcite and calcium carbonate.
Anhydrite is typically white or gray, and is the mineral that makes up the chimneys of hydrothermal vents
and surrounding substrate (Kuhn et al. 2003). However, these chimney vents are fragile and will easily
collapse. The Ca-bearing sulfates of outcrops of Endurance Crater / Meridiani Planum have been found
to consist of approximately 10% anhydrite (Glotch et al. 2006). ___ 5 mm
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Figure 25. Endurance Crater. 1M145851070EFF3505P2977M2M1 Putative tube worms, worm tubes,
spiral worms and “shrimp” and “snail” -shaped specimens.
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Figures 26. Endurance Crater. 1M145853288EFF3505P2957M2M1. Specimens resembling (#1):
Mineralized/fossilized tube worms and tubes, and (# 2,3,5,6) tube worms”and “worm tubes” in white
matrix and (#4) soil. The white chalky substrate may consist of anhydrite talc; though the actual
consistency of this material is unknown.
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Figures 27. Endurance Crater. 1M145853288EFF3505P2957M2M1. Specimens resembling mineralized
tube worms and tubes embedded in white matrix and soil. (Bottom) Contrast added.
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Figure 28. Endurance Crater. 1M145853288EFF3505P2957M2M1. Specimens resembling tube worms
and worm tubes embedded and protruding from white matrix that may consist of calcium carbonate
Figure 29. Earth. Tube worms and worm tubes embedded and protruding from a large rock along the
shoreline of the ocean. Copyright Dr. Jessica Winder, "Jessica's Nature Blog"$https://natureinfocus.blog
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Figure 30. 1M145849709EFF3505P2976M2M1. Note “pleopods” that resemble those of crustaceans.
Figure 31. 1M145852935EFF3505P2906M2M1. Note “pleopods” that resemble those of crustaceans.
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II. DISCUSSION
8. “Tube Worms” and Worm Tubes: Evidence Favors Biology
Almost all the “tubular” specimens depicted in this report show varying degrees of curvature,
twists, bends, and directional changes: the hallmarks of biology. There is no obvious evidence of
crystallization or mineralization in the majority of specimens; though what appear to be mineralized
tubular formations attached to “rocks” were also photographed (Figures 26, 27). As pointed out by an
anonymous referee, some of the tubular specimens jutting out from matrix (Figures 12, 15 ) may be
mineralized formations; e.g. gypsum or jarosite crystals inter-grown within a pyrite or sulfur matrix. If
these latter specimens are mineralized, they nevertheless appear very similar to terrestrial tube worms.
Several of the ovoid specimens have appendages resembling the pleopods of crustaceans (Figures
30, 31). There is no resemblance to micrometeorites or tektites. If they are biological, is unknown.
9. Fossilization and Dormancy?
An examination of all available sequential photos shows no evidence of “tubular” or “ovoid”
specimen movement and no indication of active biology. Therefore, it can be deduced that if biological,
then most of these worm-like specimens are (a) dormant, (b) and/or recently fossilized, mineralized, or
(c) “pickled” by their salty briny habitat. Given their remarkable degree of preservation upon the surface,
it is reasonable to assume these colonies must have flourished in the recent past.
There is evidence of underground aquifers 1 meter beneath the surface (Clark et al. 2005). Based on
the findings and photos presented here, it is probable these underground aquifers are inhabited by tube
worms and other organisms; and that these waters periodically flow to the surface forming salty ponds
and shallow lakes only to eventually evaporate and seep back beneath the surface leaving the remains of
these organisms adjacent to holes/vents which may lead to and from these subsurface pools of water.
However, anhydrite is a common feature of hydrothermal chimneys and surrounding substrate (Kuhn et
al. 2003) and this mineral has been detected in the outcrops of Meridiani Planum (Glotch et al. 2006).
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III. CONCLUSIONS
Given the the mineralogy of Endurance Crater which is similar to the habitat of terrestrial water-
dwelling tube worms and their symbiotes, and as based on this review of the literature and the
morphological comparisons depicted here, there is every reason to suspect these tubular specimens are
biological as they resemble worm tubes and tubular and spiral worms. The Martian specimens display
bending, twisting, spirals and direction changes and differ from abiogenic tubular formations which are
generally linear in shape. Some specimens resemble shrimp whereas the larger oval-shaped forms have
appendages similar to crustacean pleopods. If they are crustaceans, this supports the hypothesis that
Endurance Crater provided a marine environment which enabled these and other organisms to flourish.
These tubular specimens were photographed in proximity to holes/vents in the surface at distances
ranging from a few mm to a few centimeters. It is believed there is water beginning at a depth of 1 meter
below the surface of Endurance Crater which may also host subterranean aquifers (Clark et al. 2005) that
in the past were heated by hydrothermal vents that had been colonized by eukaryotes (Squyres et al.,
2004). Thermal vent chimneys are fragile and easily collapse and they and their surroundings consist of
anhydrite (Kuhn et al. 2003); a mineral found in these same Meridiani Planum outcrops (Gotch et al.
2006). Therefore, given the evidence reviewed in this report, it is probable that these holes in the surface
are remnants of collapsed thermal vents around which colonies of organisms flourished. It is equally
probable tube worms dwelling beneath the surface were recently propelled above ground by an outflow of
water that pooled upon the surface forming shallow lakes only to eventually recede and evaporate.
However, it is impossible to determine the exact nature of these specimens without direct physical
examination and extraction coupled with detailed biochemical analysis. Similarities in morphology are
not proof of life. Abiogenic explanations cannot be ruled out. Despite the numerous specimens that
resemble “tube worms” and “worm tubes” it cannot be stated with certainty that tube worms colonized
the putative watery-briny environment of Endurance Crater.
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... Specimens resembling algae [26][27][28][93][94][95][96], domical concentric stromatolites, lichens, fungi, [27][28][29]30,97], and tube worms [31][32][33][34]98] have been photographed by the NASAs Mars rovers. Of course, similarities in morphology are not proof of life. ...
... Spectral and geological-morphological observations of the Syrtis Major Volcanic Plains that include vent-like and conical-chimney-like structures [140] , supports the impact and magma scenarios. Likewise, evidence of "vents" and minerals associated with hydrothermal and tube worm-symbiotic activity discovered within Endurance Crater and surrounding outcrops [98,138] is consistent with both scenarios for the formation of hydrothermal vents. ...
... The lakes of Endurance Crater have also been described as a salty "brine" [106][107][108][109]. Brines and hydrothermal vents are a favored habitat of "tube worms" and their symbionts [152][153][154][155]. Vents/holes surrounded by tubular specimens have been observed within Endurance Crater, the latter of which have been tentatively identified as fossilized/mineralized tube worms and their tubes [98,138]. ...
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