Martian spherules (also known as hematite spherules, blueberries, & Martian blueberries) are small spherules (roughly spherical pebbles) that are rich in an iron oxide (grey
hematite
Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...
, α-Fe
2O
3) and are found at
Meridiani Planum
Meridiani Planum (alternatively Terra Meridiani) is a large plain straddling the equator of Mars. The plain sits on top of an enormous body of sediments that contains bound water. The iron oxide in the spherules is crystalline (grey) hematite (Fe ...
(a large plain on Mars) in exceedingly large numbers.
These spherules were discovered on the Martian day that NASA's
Mars Exploration Rover
NASA's Mars Exploration Rover (MER) mission was a robotic space mission involving two Mars rovers, ''Spirit (rover), Spirit'' and ''Opportunity (rover), Opportunity'', exploring the planet Mars. It began in 2003 with the launch of the two rove ...
''Opportunity'' landed at
Meridiani Planum
Meridiani Planum (alternatively Terra Meridiani) is a large plain straddling the equator of Mars. The plain sits on top of an enormous body of sediments that contains bound water. The iron oxide in the spherules is crystalline (grey) hematite (Fe ...
. (At NASA's Mission Control building that was January 24, 2004.) They are grey but look bluish next to the ubiquitous rusty reds on Mars, and since the first spherules found in Eagle Crater were 3–6 mm in diameter,
the
''Opportunity'' team quickly called them "blueberries".
Martian blueberries are either embedded or loose. That is, Martian blueberries are either embedded in the large body of sediments of
Meridiani Planum
Meridiani Planum (alternatively Terra Meridiani) is a large plain straddling the equator of Mars. The plain sits on top of an enormous body of sediments that contains bound water. The iron oxide in the spherules is crystalline (grey) hematite (Fe ...
, or they are loose blueberries that lie directly on outcrops of the sediments or lie on top soils spread over the Meridiani sediments.
The size of these spherules varies by location and elevation across the
Meridiani Planum
Meridiani Planum (alternatively Terra Meridiani) is a large plain straddling the equator of Mars. The plain sits on top of an enormous body of sediments that contains bound water. The iron oxide in the spherules is crystalline (grey) hematite (Fe ...
.
Martian blueberries are rich in the iron oxide hematite, but determining how rich they are in this iron oxide has proven difficult.
(more below). The formation of blueberries required aqueous chemistry and involved flows of acidic, salty, liquid water over the
Meridiani Planum
Meridiani Planum (alternatively Terra Meridiani) is a large plain straddling the equator of Mars. The plain sits on top of an enormous body of sediments that contains bound water. The iron oxide in the spherules is crystalline (grey) hematite (Fe ...
and over two geological epochs.
Initial discovery
Discovery from Orbit
The
Thermal Emission Spectrometer
The Thermal Emission Spectrometer (TES) was an instrument on board Mars Global Surveyor. TES collected two types of data, hyperspectral thermal infrared data from 6 to 50 micrometres (μm) and bolometric visible-near infrared (0.3 to 2.9 μm) me ...
(TES) on the orbiter ''
Mars Global Surveyor
''Mars Global Surveyor'' (MGS) was an American Robotic spacecraft, robotic space probe developed by NASA's Jet Propulsion Laboratory. It launched November 1996 and collected data from 1997 to 2006. MGS was a global mapping mission that examined ...
'' first detected crystalline gray hematite (α-Fe
2O
3) within the
Sinus Meridiani. This discovery was part of a broader effort to map Mars for minerals associated with past water.
Maps of Surface Hematite
Between 1997 and 2002, the ''
Mars Global Surveyor
''Mars Global Surveyor'' (MGS) was an American Robotic spacecraft, robotic space probe developed by NASA's Jet Propulsion Laboratory. It launched November 1996 and collected data from 1997 to 2006. MGS was a global mapping mission that examined ...
''s
TES mapped the whole planet of Mars for surface hematite levels.
Figure 1a gives the
TES's global hematite map in low resolution. It has just one large spot covering a region with high hematite levels. This green, yellow, and red spot straddles the equator and the prime meridian in the middle of Figure 1a. A higher resolution map of the high-hematite region is shown in Figure 1b.
Search for Signs of Water & Life
In the 1990s, NASA officials wanted to delineate a framework for
"faster, better, cheaper" exploration of Mars. In this context, the "Water Strategy" was outlined in 1995/1996.
[
Shirley, D. L. and McCleese, D. J., 1996, "Mars Exploration Program Strategy: 1995-2020," ''AIAA 96-0333, 34 th Aerospace Sciences Meeting and Exhibit, Reno, Nv.'' (available online at:
https://web.archive.org/web/20130511200249/http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/23620/1/96-0064.pdf).
] High priority goals for NASA in the mid-1990s were to gather some evidence for surface water using satellite surveys and to land robotic rovers on the surface to collect detailed local evidence of water and signs of life.
In early the 2000s, the hematite map of Figure 1b and the confirmation (from the topography mapping done by the ''
Mars Global Surveyor
''Mars Global Surveyor'' (MGS) was an American Robotic spacecraft, robotic space probe developed by NASA's Jet Propulsion Laboratory. It launched November 1996 and collected data from 1997 to 2006. MGS was a global mapping mission that examined ...
'') that this area is a flat plain and relatively easy to land on were the decisive pieces of evidence for choosing the Meridiani Planum as one of the landing sites for NASA's two bigger
Mars Exploration Rover
NASA's Mars Exploration Rover (MER) mission was a robotic space mission involving two Mars rovers, ''Spirit (rover), Spirit'' and ''Opportunity (rover), Opportunity'', exploring the planet Mars. It began in 2003 with the launch of the two rove ...
s (MERs), named ''
Opportunity
Opportunity may refer to:
Places
* Opportunity, Montana, an unincorporated community, United States
* Opportunity, Nebraska, an unincorporated community, United States
* Opportunity, Washington, a former census-designated place, United States
* ...
'' and ''
Spirit''.
The decisiveness for NASA of the hematite map of Figure 1b for choosing the landing site for ''
Opportunity
Opportunity may refer to:
Places
* Opportunity, Montana, an unincorporated community, United States
* Opportunity, Nebraska, an unincorporated community, United States
* Opportunity, Washington, a former census-designated place, United States
* ...
''
was because NASA was using high hematite levels as proxy evidence for large amounts of liquid water flowing in the region in the past. (Hematite only forms in the presence of liquid water in geological settings). In 2003, this high-hematite region was a high-priority place to start to search for signs of life on Mars.
New name: Meridiani Planum
The hematite map of Figure 1b covered part of a larger area called the
Sinus Meridiani by 19th-century Mars map-makers. In 2004, senior scientists for the upcoming MER
''Opportunity'' mission introduced the new place name
Meridiani Planum
Meridiani Planum (alternatively Terra Meridiani) is a large plain straddling the equator of Mars. The plain sits on top of an enormous body of sediments that contains bound water. The iron oxide in the spherules is crystalline (grey) hematite (Fe ...
for (roughly) the high hematite area in Figure 1b.
Discovery of Spherules on the Ground
NASA'S rover ''
Opportunity
Opportunity may refer to:
Places
* Opportunity, Montana, an unincorporated community, United States
* Opportunity, Nebraska, an unincorporated community, United States
* Opportunity, Washington, a former census-designated place, United States
* ...
'' successfully made the "hole-in-one" landing into
Eagle Crater at Meridiani Planum on January 24(PST), 2004. On the first sol (Martian day), the rover immediately discovered thousands and thousands of small (4–6 mm diameter) spherules lying all over the place inside
Eagle Crater.
Figure 2 shows a thumbnail of the view from
''Opportunity'''s Pancam (panoramic camera) on the first sol. (The actual image is very large, 7838 x 2915 pixels). The lead of the
Pancam
Each Pancam is one of two electronic stereo cameras on Mars Exploration Rovers ''Spirit'' and ''Opportunity''. It has a filter wheel assembly that enables it to view different wavelengths of light and the pair of Pancams are mounted beside tw ...
team, Jim Bell, soon wrote about this view: "Scientists are intrigued by the abundance of rock outcrops dispersed throughout the crater, as well as the crater's soil, which appears to be a mixture of coarse gray grains and fine reddish grains." Figure 3 is a detail of Figure 2 showing the grey spherules more clearly (click to enlarge).
Tests quickly found that the grey spherules are rich in grey hematite.
These tests included doing the "berry bowl" experiment (more below).
The moniker "blueberries" was coined for the grey hematite spherules by the original
''Opportunity'' science team due to these spherules appearing bluish relative to the underlying rusty-red soils in the "natural color RGB images" analyzed.
Blueberry Formation
Blueberries are either embedded in the large body of sediments of
Meridiani Planum
Meridiani Planum (alternatively Terra Meridiani) is a large plain straddling the equator of Mars. The plain sits on top of an enormous body of sediments that contains bound water. The iron oxide in the spherules is crystalline (grey) hematite (Fe ...
or they are loose blueberries that lie directly on outcrops of the sediments or lie on top soils spread over the Meridiani sediments.
The loose blueberries and soils are eroded out of the underlying sediments.
Both today's embedded blueberries and the loose blueberries were formed in the sediments of
Meridiani Planum
Meridiani Planum (alternatively Terra Meridiani) is a large plain straddling the equator of Mars. The plain sits on top of an enormous body of sediments that contains bound water. The iron oxide in the spherules is crystalline (grey) hematite (Fe ...
by "diagenetic" processes, i.e., processes that change sediments by water-rock interactions.
The diagenetic processes not only formed embedded blueberries but also changed an original large body of sediments. Thus, blueberry formation was (broadly) a three-step process:
* Formation of the original body of sediments;
* Diagenetic transformation of the original sediments to produce today's sediments and embedded blueberries;
* Erosion of top layers of the sediments to form top soils and loose blueberries.
Each of these broad steps involved multiple sub-step processes, described in the following sub-sections:
Noachian River Flows

Prior to the formation of Meridiani's defining sediments, in the wet
Noachian
The Noachian is a system (stratigraphy), geologic system and early geologic timescale, time period on the planet Mars characterized by high rates of meteorite and asteroid Impact event, impacts and the possible presence of abundant surface water. ...
(named for the biblical Noah) more than about ~3.7 billion years ago, liquid water was present and plentiful enough to form river channels that bought and deposited large quantities of basaltic silt to the current Meridiani region.
The dried river valleys are easily seen in thermal inertia images taken in orbit by
''Mars Odyssey'' and reproduced in Figure 4 (click on it for higher resolution).
The river valleys seen in Figure 4 terminate abruptly as they flow into the Meridiani's massive formation of sediments.
Formation of Today's Sediments & Embedded Spherules
From around the late-
Noachian
The Noachian is a system (stratigraphy), geologic system and early geologic timescale, time period on the planet Mars characterized by high rates of meteorite and asteroid Impact event, impacts and the possible presence of abundant surface water. ...
/early-
Hesperian
The Hesperian is a system (stratigraphy), geologic system and geologic timescale, time period on the planet Mars characterized by widespread Volcanology of Mars, volcanic activity and catastrophic flooding that carved immense outflow channels acr ...
to sometime around 3.5 billion years ago, the layered sediments deposited in the earlier
Noachian
The Noachian is a system (stratigraphy), geologic system and early geologic timescale, time period on the planet Mars characterized by high rates of meteorite and asteroid Impact event, impacts and the possible presence of abundant surface water. ...
epoch were transformed.
This transformation probably included a significant additional deposition of high-sulfur-content material of volcanic origin.
The change certainly included aqueous geochemistry that was acidic and salty, as well as rising & falling water levels: Features providing evidence include cross-bedded sediments, the presence of
vug
A vug, vugh, or vugg () is a small- to medium-sized cavity inside rock. It may be formed through a variety of processes. Most commonly, cracks and fissures opened by tectonic activity ( folding and faulting) are partially filled by quartz, calc ...
s (cavities), and embedded hematite spherules that cut across sediment layers, additionally the presence of large amounts of
magnesium sulfate
Magnesium sulfate or magnesium sulphate is a chemical compound, a salt with the formula , consisting of magnesium cations (20.19% by mass) and sulfate anions . It is a white crystalline solid, soluble in water but not in ethanol.
Magnesi ...
and other sulfate-rich minerals such as
jarosite
Jarosite is a basic hydrous sulfate of potassium and ferric iron (Fe-III) with a chemical formula of KFe3(SO4)2(OH)6. This sulfate mineral is formed in ore deposits by the oxidation of iron sulfides. Jarosite is often produced as a byproduct dur ...
and chlorides.
Jarosite formation requires aqueous acidic conditions below pH 3.
Figures 5 and 6 show Microscopic Imager close-ups of the sediment rock matrix that appeared in a prestigious paper.
Figure 5 illustrates the four physical constituents of sediment outcrop: (i) the sedimentary layers containing a lot of basaltic sand particles; (ii) the embedded hematite spherules; (iii) fine-grained, sulfate-rich cement (in most parts of the outcrop); (iv) vug cavities (that are thought to be molds for crystals of, for example, hydrated sulfates).
Figure 6 images a similar sediment outcrop surface to Figure 5. However,
''Opportunity'''s Rock Abrasion Tool abraded this surface. Such abrasions showed that (a) the sediment layers are very soft and easy to cut, and (b) the hematite spherules have uniform internal structures.
The diagenetic transformation (i.e., change by water-rock interactions) to today's sediments involved a significant shift in water flows in the region. The inflows from rivers became less, and the dominant water movements in the sediments became vertical with rising and falling aquifer levels.
At least one model of global Martian hydrology accounts for the historical shift in water flows at Meridiani Planum.
This model links Meridiani's change in water flows to activity in the volcanic Tharsis region. With the vertical aquifer flows, it is believed that (playa) lakes repeatedly formed and disappeared as the aquifer levels rose and fell.
(The dry area around Utah's
Great Salt Lake
The Great Salt Lake is the largest saltwater lake in the Western Hemisphere and the eighth-largest terminal lake in the world. It lies in the northern part of the U.S. state of Utah and has a substantial impact upon the local climate, partic ...
is a playa.)
McLennan and his students constructed a geochemical model that generates hematite within a context like the Meridiani sediment.
The hematite formed into spherules by
concretion
A concretion is a hard and compact mass formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or spherical in shape, although irregular shapes a ...
(when minerals came out of solution).
The concretion process to form spherules of hematite probably occurred by diffusion of the hematite through the sedimentary rock matrix.
Formation of Soils & Loose Spherules, Crater Degradation
The period of rising and falling aquifer levels ceased, and no water flowed on Meridiani Planum thereafter.
Although, when this happened is poorly understood. Estimates include around 3.5 billion years ago
and about 3 billion years ago.
The only water left at the plain is bound in rocks.
Erosion with water flows in earlier eras was much faster than in this arid epoch.
However, erosion did not stop. Other much slower erosional processes continued and became the primary agents of change to the plain. This slower change was and is driven by meteorite impacts, the wind, and gravity. Over the hard-to-grasp eon of around three billion years, meteorite impacts and the wind formed the sandy top soils and loose hematite spherules and sorted these into the layered soil bedforms that we can now see.

The meteorite, gravity, and wind-driven processes work like this:
* Over billions of years, meteorite impacts created many craters on the plain.
* There were enough small (5 to 30 m diameter) craters created in the eon of around three billion years to cover, on average, the whole plain once.
Although, each small crater degraded and disappeared in about 25 million years or less, and only about 0.7% of the plain's area is presently covered in small craters.
* Each meteorite impact produces large numbers of blocks of sediment material in the crater rim and as ejecta around the crater.
* Most of the initial sediment blocks project above the surrounding material (by a few centimeters or more) and are exposed to saltating sand (i.e., wind-driven, bouncing sand).
* Meridiani sediment matrix is soft and easy-to-erode.
It erodes about 30 to 300 times faster than other regions of Mars (such as Gusev Crater).
(Although, this arid erosion is much slower than erosion with water flows.)
* The saltating sand erodes the soft, easy-to-erode parts of the sediment matrix in the projecting blocks.
* These blocks are either completely eroded or erode until they become smooth and no longer project into saltating sand.
* This block erosion creates dust particles and turns embedded spherules into loose spherules.
* The dust particles are blown off the plain and become part of the global dust.
* The sulfates preferentially turn into dust and are transported off the plain by the wind.
* The larger basalt sand particles, spherules fragments, and hematite spherules remain in place on the plain.
* Wind, gravity, and size-sorting created the soil bedforms from the basaltic sands, spherule fragments, and spherules.
* With the aid of gravity and wind, the original (small) crater holes are gradually filled in (with material from eroded rim blocks and other local erosion material), and the plain is returned to a flat state.
Phil Christensen outlined these processes in 2004, soon after
''Opportunity'' landed.
[ Later, more in-depth research confirmed them and added details to Christensen's outline.]
Blueberry Composition
Early Blueberry Composition Results
Early on, ''Opportunity'''s Mössbauer spectrometer took data that determined that the iron mineral component of these spherules is dominated by hematite. However, the Mössbauer spectrometer provided no information about the mineral components of these spherules that do not contain iron.
The "berry bowl" experiment took alpha particle X-ray spectrometer
:''APXS is also an abbreviation for APache eXtenSion tool, an extension for Apache web servers.''
An alpha particle X-ray spectrometer (APXS) is a spectrometer that analyses the chemical element composition of a sample from scattered alpha parti ...
(APXS) readings of two sampling targets just centimeters apart: One had no (zero or one) spherules in the spectrometer's field of view (FOV), while the other had around 25 spherules in the FOV. Figure 8 shows the adjacent "berry bowl" sampling targets. The APXS results indicated there was noticeably more iron in the target with ~25 spherules relative to the target with 0 or 1 spherules. Based on this and similar experiments, several unreviewed conference abstracts claimed (deliberately not cited here)
that hematite dominated the composition of the spherules and some published papers cited these conference claims. However, there were reasons to be cautious. The instruments detected mixed signals from sampling targets that included signals not only from the spherules but also from dust and rock (in the "berry bowl" experiment) or dust and soils (in other composition data collections). In 2006, Morris et al. showed that the methods used by some researchers to pick out the spherule composition signal from the dust and soil signals were flawed and that such methods could do no more than constrain the iron oxide content of the spherules to between 24 wt% and 100 wt% (that is, almost no constraint at all).
Later Blueberry Composition Results
A 2008 paper published the result of a clever experiment that showed ''Opportunity'''s mini-TES (thermal emission spectrometer) could not detect any silicate minerals in the spherules. This non-detection constrained silicate levels in spherules to less than 10 wt% and probably below 8 wt%. This result is helpful since the APXS data shows a strong anti-correlation between silicates and iron oxide in the spherules -
so low silicate levels indicate high iron oxide levels.
A recent paper used the mini-TES's non-detection of silicates and some improved data analysis methods to find over 340,000 allowable standard oxide chemical compositions for the spherules (allowable = consistent with the silicate non-detection). The lowest and highest weight percentages for the iron oxide content in these allowable spherule compositions were, respectively, 79.5 wt% and 99.8 wt%. While, for the large majority of the allowable compositions, the iron oxide contents in the spherules were between 85 wt% and 96 wt%; further, the nickel content was always close to 0.3 wt%, a group of five standard oxides (MgO, Na2O, P2O5, SO3, and Cl) each had content above trace-level with a combined group content of 6.8 +/- 2.4 wt%, the SiO2 levels ranged between 8 wt% and 0 wt%, and the other eight APXS standard oxides had either 0 wt% content or only trace level content.
Size of Blueberries
The ''Opportunity'' science team published three papers that studied variations in hematite spherule size.[Squyres, S. W., et al., 2009, "Exploration of Victoria Crater by the Mars Rover Opportunity," ''Science'', 1058-1061. https://doi.org/10.1126/science.1170355] They found spherule size variation by location and elevation.
In the earliest paper, a team of ''Opportunity'' rover scientists reported on studies of all the soil
materials found between the landing site in Eagle Crater to the location on sol 552 of the rover's traverse (between Endurance Crater and Victoria Crater
Victoria is an impact crater on Mars located at 2.05°S, 5.50°W in the Meridiani Planum extraterrestrial plain, lying situated within the Margaritifer Sinus quadrangle (MC-19) region of the planet Mars. This crater was first visited by the Mars E ...
).
They found that in a sample of 696 blueberries, disregarding any non-spherical blueberries from the sample, the blueberries' average major axis to be about 2.87 mm (just over one-tenth inch). They also discovered that blueberries found within soils are typically smaller than blueberries found in the outcrops. They noted the size of the blueberries tends to decrease with decreasing latitude.
The ''Opportunity'' team found many fragmented blueberries and suggested the fracturing occurred after spherule formation. They believe the fracturing either be from meteoric impacts or the "same process" that "fractured the outcrop". However, the team notes this would not explain the presence of the smallest hematite spherules detected. The smallest are close to perfectly spherical and therefore cannot be explained by fracturing or erosion. The ''Opportunity'' team also found that blueberries uncovered by the Rock Abrasion Tool
The Rock Abrasion Tool (RAT) is a grinding and brushing installation on NASA’s twin Mars Exploration Rovers, '' Spirit'' (MER-A) and '' Opportunity'' (MER-B), which landed on Mars in January 2004. It was designed, developed and continues to be o ...
aboard Opportunity were 4.2 +/- 0.9 mm (0.16 inches) major axis length at Eagle Crater and 4.5 +/- 0.6 mm at Endurance crater, about 2.2 +/- 0.5 mm (0.087 inches) at Vostok and about 3.0 +/- 0.2 mm (0.12 inches) at Naturaliste (crater)
'' Opportunity'' is a robotic rover that was active on the planet Mars from 2004 to 2018. Launched on July 7, 2003, ''Opportunity'' landed on Mars' Meridiani Planum on January 25, 2004, at 05:05 Ground UTC (about 13:15 Mars local time), thr ...
. Those found in "the plains" south of Endurance Crater were smaller (1-2mm or 0.04-0.08 inches) than those of Eagle and Endurance craters.
The second paper studying spherule size extended the study area 2–3 km further south on the plains to Victoria Crater. This paper reported similar observations to the first but went further to suggest the observed size variation might be due to sampling different sediment stratigraphic levels at different locations. Additionally, it suggested simple variations in diagenetic conditions were linked to changes in spherule size.
The third paper made systematic size measurements of hematite spherules embedded in the walls of Victoria Carter
Victoria Mary Carter is a former New Zealand politician. She is now a professional company director and businesswoman.
Early life
Carter, born in England, came to New Zealand with her mother, journalist Valerie Davies. Her stepfather was jo ...
at different heights. (Victoria Crater
Victoria is an impact crater on Mars located at 2.05°S, 5.50°W in the Meridiani Planum extraterrestrial plain, lying situated within the Margaritifer Sinus quadrangle (MC-19) region of the planet Mars. This crater was first visited by the Mars E ...
is a large and deep crater.) These measurements showed a clear variation of spherule size with elevation within the sediments of Meridiani Planum
Meridiani Planum (alternatively Terra Meridiani) is a large plain straddling the equator of Mars. The plain sits on top of an enormous body of sediments that contains bound water. The iron oxide in the spherules is crystalline (grey) hematite (Fe ...
. The smaller spherules were higher up, the larger ones lower down. The lowest spherules near the bottom of Victoria Crater
Victoria is an impact crater on Mars located at 2.05°S, 5.50°W in the Meridiani Planum extraterrestrial plain, lying situated within the Margaritifer Sinus quadrangle (MC-19) region of the planet Mars. This crater was first visited by the Mars E ...
had similar diameters to the spherules in Eagle Crater, and the elevations of these distant locations were nearly equal.
No papers were written on spherule size that covered areas of the rover's traverse south from Victoria Crater
Victoria is an impact crater on Mars located at 2.05°S, 5.50°W in the Meridiani Planum extraterrestrial plain, lying situated within the Margaritifer Sinus quadrangle (MC-19) region of the planet Mars. This crater was first visited by the Mars E ...
to the enormous Endeavour Crater
Endeavour is an impact crater located in the Meridiani Planum extraterrestrial plain within the Margaritifer Sinus quadrangle (MC-19) region of the planet Mars. Endeavour is about in diameter. Using ''Mars Reconnaissance Orbiter'' data, phy ...
. However, searches of the archive of the images taken by the rover's Microscopic Imager show some of the largest blueberries photographed are close to the rim of Endeavour Crater
Endeavour is an impact crater located in the Meridiani Planum extraterrestrial plain within the Margaritifer Sinus quadrangle (MC-19) region of the planet Mars. Endeavour is about in diameter. Using ''Mars Reconnaissance Orbiter'' data, phy ...
(see Figure 11).
Numbers of Blueberries & Loose Spherule Surface Density
There are no peer-reviewed published estimates of the number of loose hematite spherules on Meridiani's soils or embedded hematite spherules in the plain's sediments. However, the reader can sense how mind-boggling big those numbers are with a photograph of an area of soil with a typical surface density of the hematite spheres. Such a photograph ''has'' been published.
Figures 12 and 13 are true-color and false-color versions of the photo. The spherules are easier to see in the published false-color version (Figure 23). Click on it to enlarge it. The sampling target of Figures 12 & 13 had 29% coarse hematite coverage. The range of coverage among similar targets was 10% to 40%. These targets were sampled over a wide area, between Sol 70 (2004-04-04) and Sol 999 (2007-11-15).
The parts of the plain ''Opportunity'' studied are ''not'' special: Compared to the rest of Meridiani Planum, they do not have high surface hematite levels. To see this, look at the plain's surface hematite map (Figure 1b) and the small blue line (labeled OT ) indicating the route of ''Opportunity'''s Traverse of the plain.
The mind-bogglingness of the number of loose hematite spherules hits when Figures 12 & 13 are extrapolated to the plain's whole surface area (about 150,000 km2): 150,000 km2 is close to 2/3's the area of the main island of Japan (Honshu
, historically known as , is the largest of the four main islands of Japan. It lies between the Pacific Ocean (east) and the Sea of Japan (west). It is the list of islands by area, seventh-largest island in the world, and the list of islands by ...
) and also 72% the area of the main island of the UK (Great Britain
Great Britain is an island in the North Atlantic Ocean off the north-west coast of continental Europe, consisting of the countries England, Scotland, and Wales. With an area of , it is the largest of the British Isles, the List of European ...
), it is also bigger than the land areas of 30 of the 50 states of the USA.
The number of embedded spherules (in the plain's sediments) is probably much higher than the number of loose spherules (on soils). Since (1) the estimates of the erosion depth of original sediment needed to produce the loose spherules are less than 1 meter, while (2) the typical depths of the plain's sediments are several hundred meters.
Shiny Blueberries without Dust
The image at right (Figure 14) shows shiny hematite blueberries. The shininess and the position of these blueberries are unusual. The rover ''Opportunity'' dug a trench into the top soils that lie over the Meridiani Planum's sediments. Figure 14 shows a wall to the newly dug trench with (partially uncovered) soil-embedded blueberries.
Soil-embedded blueberries are rare. Size-sorting tends to position loose blueberries on or very near the surface of soil bedforms. Almost all photographed blueberries were exposed to the atmosphere and are now covered in a layer of Mars's dust. The layers of dust take away the shininess of the blueberries. The blueberries inside the trench are dust-free because the interiors of soil beds are largely dust-free. Without the dust, these blueberries are shiny.
Blueberries on Earth
Earth analogs
Researchers from the University of Utah
The University of Utah (the U, U of U, or simply Utah) is a public university, public research university in Salt Lake City, Utah, United States. It was established in 1850 as the University of Deseret (Book of Mormon), Deseret by the General A ...
have explored the similarities between the blueberries and spherical concretions discovered within "Jurassic Navajo Sandstone" in southern Utah. They have concluded Mars must have had previous ground water activity to form the blueberries. However, they do note the spherules are more spherical in the Martian sample due to the lack of "joints, fractures, faults, or other preferential fluid paths", unlike the Utah sample. A team of researchers from Japan studied the spherules found in Utah as well as spherules that were later discovered in Mongolia, in the Gobi
The Gobi Desert (, , ; ) is a large, cold desert and grassland region in North China and southern Mongolia. It is the sixth-largest desert in the world. The name of the desert comes from the Mongolian word ''gobi'', used to refer to all of th ...
. They found evidence that the concretions found in these locations are first formed as "spherical calcite concretions" in sandstone. Acidic water rich in iron then dissolve the calcite leaving behind the iron rich (hematite) spherule. This leads to the conclusion that the blueberries may have formed early in Mars's history when the atmosphere was more dense by the same process.
See also
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References
External links
Science Magazine special issue on MER Opportunity initial results
from JPL relating to Mars spherules
Morphological Investigations of Martian Spherules, Comparisons to Collected Terrestrial Counterparts
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Sedimentary Concretions vs. Impact Condensates: Origin of the Hematitic Spherules of Meridiani Planum, Mars
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Ironstone Concretions - Analogs to Martian Hematite Spherules
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relations to Martian Spherules.
on Moqui marbles and Martian spherules
relations to cyanobacteria and terrestrial stromatolites.
{{DEFAULTSORT:Martian Spherules
Mars, Spherules
Rocks on Mars