**4. Blueberries as cosmic spherules**

There are two possible methods for depositing large number of hematite spherules from the top: (1) meteorite deposition and (2) volcanic deposition. Out of these two models, we suggest that the meteorite model is more consistent with all the observations of blueberries on Mars because, at present, there are no active volcanoes on Mars. Later, in this chapter, we will see evidence that some of the blueberries are very young as they have recently landed on the rovers and heat shield. This also favors the meteorite theory over volcanic deposition. According to the meteorite theory, meteorites of various sizes enter the Mars atmosphere at high speed and low temperature. When meteorites enter the Martian atmosphere, they feel friction and ram pressure, which heats up the meteorite. On Earth, commonly observed shooting stars suggest that heating can achieve very high temperatures, which make the meteorites glow. Under Martian conditions, the smaller meteorites can be completely melted. The liquid melts and then breaks down immediately into

#### **Figure 9.**

*Image of "Heat Shield Rock," an iron meteorite observed on Mars. Several blueberries and microberries are observed in the close vicinity of the meteorite. Image taken from Sol 352, courtesy of NASA/JPL/Cornell.*

smaller spherical drops whose size is determined by the surface tension of the liquid and the atmospheric drag force. Smaller drops soon achieve terminal velocity due to lower mass, which causes the temperature of the liquid drop to fall and become solid. Depending on the size of the meteorite and the time of flight, some of the drops will hit as solid balls and others as liquid drops that form microberries on collision with the ground [22]. Larger meteorites need more time to melt completely because of their mass. In bigger meteorites, melting begins at the meteorite surface, and as soon as the surface liquid reaches a critical depth, the liquid falls away as drops. This prediction suggests that the fusion crust on a meteorite should be also limited in thickness, and meteorites should also show imprints on the surface matching the size of the liquid drop, which was removed from the surface.

On sol 339, the Opportunity rover observed an iron meteorite on Mars, which was named "Heat Shield Rock." **Figure 9** shows an image of Heat Shield Rock, which is mainly iron with kamacite as the primary Fe-bearing mineral and around 7 wt.% nickel [23, 24]. A first look at the immediate surroundings of the meteorite confirms the presence of large number of microberries and blueberries near the meteorite. The surface of the fusion crust shows regmaglypts and several circular imprints. The circular imprints give an estimate of the size of the molten drops that fell off from the meteorite. This size matches with the size of blueberries lying on the ground. Several microberries and miniberries also form on meteorite impact with the ground from the liquid layer, which is still attached to the meteorite before impact. These microberries and miniberries will be distributed near the meteorite. A larger concentration of smaller blueberries and nano–dust particles forming a halo can be seen in the immediate surroundings of the meteorite (**Figure 9**). The image also shows several spherules on top of the meteorite. This image provides very strong direct evidence that Martian blueberries are cosmic spherules formed from the ablation of a meteorite. In addition, the same image also provides a strong evidence that blueberries are not concretions as iron meteorites do not carry enough water for concretion formation.

The formation of blueberries through molten meteorite drops also explains why all the observed blueberries on Mars are limited in size and are mostly perfect spheres with no internal structure and fine grain size. The size and shape of the blueberries are determined by the phenomenon commonly known

**9**

**Figure 10.**

*Hematite Spherules on Mars*

tional to [25]:

*DOI: http://dx.doi.org/10.5772/intechopen.82583*

different types of liquids to give equation:

Earth gravity, ρ1 = 1000 kg/m3

molten iron [26], *g*2 = 3.675 m/s2

as surface tension. On Earth, we can use raindrops as analogues: their sizes and shapes are controlled by the surface tension of water. The size of a raindrop can be estimated by assuming that the water drop will break up if the atmospheric drag force is greater than the surface tension force. When the gravitational force equals the atmospheric drag force, the raindrops achieve terminal velocities. These conditions give the estimated diameter of the raindrop (D) to be propor-

where σ is the surface tension of the liquid, *g* is the acceleration due to gravity, and ρ is the density of the liquid. The above equation can be simplified using two

where subscripts 1 and 2 represent two different types of liquids. By assuming that the melting of iron meteorites forms spherules, we can estimate the diameter (D2) of Martian spherules. Using σ1 = 0.073 N/m surface tension of water, *g*1 = 9.8 m/s2

of iron gives D2 = 2.6 D1. According to the U.S. Geological Survey (USGS) website, raindrops that are spherical in shape are usually 1–2 mm in size (**Figure 10**). Larger drops with diameter of 3 mm are sometimes formed but are not spherical in shape [27, 28]. When the raindrop reaches a diameter of 4.5 mm, it opens up like a parachute and immediately breaks up into smaller drops and microdrops. One of the important features of the meteorite model is that it puts a size limit on the diameter of hematite spherules on Mars. Accordingly, hematite spherules on Mars would be spherical in shape if the diameter is less than 5.2 mm. Larger spherules are not expected to be perfect spheres and no spherules are expected to reach the size of 12 mm, which corresponds to immediately breaking up into smaller spherules and microspherules by opening up like a parachute. The meteorite theory correctly predicts the size limit of millimeter-size blueberries and also predicts the formation of a large number of

One of the puzzling observations on Mars is that there are very large numbers of blueberries (**Figure 3**) and the vast majority of spherules are isolated spheres. The Opportunity rover observed doublets and triplets [3, 5, 13, 15] as shown in **Figure 11** but these instances were very rare. It is important to note that the observation of large numbers of blueberries and microberries does not suggest a large number of meteoritic

perfectly spherical microberries and nanophase material.

*Raindrop shapes with various sizes. (Courtesy USGS website).*

as density of water, σ2 = 1.46 N/m surface tension of

as Mars gravity, and ρ2 = 7860 kg/m3

(1)

(2)

as

as the density

*Mineralogy - Significance and Applications*

smaller spherical drops whose size is determined by the surface tension of the liquid and the atmospheric drag force. Smaller drops soon achieve terminal velocity due to lower mass, which causes the temperature of the liquid drop to fall and become solid. Depending on the size of the meteorite and the time of flight, some of the drops will hit as solid balls and others as liquid drops that form microberries on collision with the ground [22]. Larger meteorites need more time to melt completely because of their mass. In bigger meteorites, melting begins at the meteorite surface, and as soon as the surface liquid reaches a critical depth, the liquid falls away as drops. This prediction suggests that the fusion crust on a meteorite should be also limited in thickness, and meteorites should also show imprints on the surface matching the size of the liquid drop, which was removed from the surface.

*Image of "Heat Shield Rock," an iron meteorite observed on Mars. Several blueberries and microberries are observed in the close vicinity of the meteorite. Image taken from Sol 352, courtesy of NASA/JPL/Cornell.*

On sol 339, the Opportunity rover observed an iron meteorite on Mars, which was named "Heat Shield Rock." **Figure 9** shows an image of Heat Shield Rock, which is mainly iron with kamacite as the primary Fe-bearing mineral and around 7 wt.% nickel [23, 24]. A first look at the immediate surroundings of the meteorite confirms the presence of large number of microberries and blueberries near the meteorite. The surface of the fusion crust shows regmaglypts and several circular imprints. The circular imprints give an estimate of the size of the molten drops that fell off from the meteorite. This size matches with the size of blueberries lying on the ground. Several microberries and miniberries also form on meteorite impact with the ground from the liquid layer, which is still attached to the meteorite before impact. These microberries and miniberries will be distributed near the meteorite. A larger concentration of smaller blueberries and nano–dust particles forming a halo can be seen in the immediate surroundings of the meteorite (**Figure 9**). The image also shows several spherules on top of the meteorite. This image provides very strong direct evidence that Martian blueberries are cosmic spherules formed from the ablation of a meteorite. In addition, the same image also provides a strong evidence that blueberries are not concretions as iron meteorites do not carry enough

The formation of blueberries through molten meteorite drops also explains why all the observed blueberries on Mars are limited in size and are mostly perfect spheres with no internal structure and fine grain size. The size and shape of the blueberries are determined by the phenomenon commonly known

**8**

**Figure 9.**

water for concretion formation.

as surface tension. On Earth, we can use raindrops as analogues: their sizes and shapes are controlled by the surface tension of water. The size of a raindrop can be estimated by assuming that the water drop will break up if the atmospheric drag force is greater than the surface tension force. When the gravitational force equals the atmospheric drag force, the raindrops achieve terminal velocities. These conditions give the estimated diameter of the raindrop (D) to be proportional to [25]:

$$D \propto \sqrt{\frac{\sigma}{g\rho}}\tag{1}$$

where σ is the surface tension of the liquid, *g* is the acceleration due to gravity, and ρ is the density of the liquid. The above equation can be simplified using two different types of liquids to give equation:

$$\frac{\partial D\_{\times}}{\partial D\_{1}} = \sqrt{\frac{\sigma\_{\times} \mathbf{g}\_{1} \rho\_{1}}{\sigma\_{1} \mathbf{g}\_{2} \rho\_{2}}} \tag{2}$$

where subscripts 1 and 2 represent two different types of liquids. By assuming that the melting of iron meteorites forms spherules, we can estimate the diameter (D2) of Martian spherules. Using σ1 = 0.073 N/m surface tension of water, *g*1 = 9.8 m/s2 as Earth gravity, ρ1 = 1000 kg/m3 as density of water, σ2 = 1.46 N/m surface tension of molten iron [26], *g*2 = 3.675 m/s2 as Mars gravity, and ρ2 = 7860 kg/m3 as the density of iron gives D2 = 2.6 D1. According to the U.S. Geological Survey (USGS) website, raindrops that are spherical in shape are usually 1–2 mm in size (**Figure 10**). Larger drops with diameter of 3 mm are sometimes formed but are not spherical in shape [27, 28]. When the raindrop reaches a diameter of 4.5 mm, it opens up like a parachute and immediately breaks up into smaller drops and microdrops. One of the important features of the meteorite model is that it puts a size limit on the diameter of hematite spherules on Mars. Accordingly, hematite spherules on Mars would be spherical in shape if the diameter is less than 5.2 mm. Larger spherules are not expected to be perfect spheres and no spherules are expected to reach the size of 12 mm, which corresponds to immediately breaking up into smaller spherules and microspherules by opening up like a parachute. The meteorite theory correctly predicts the size limit of millimeter-size blueberries and also predicts the formation of a large number of perfectly spherical microberries and nanophase material.

One of the puzzling observations on Mars is that there are very large numbers of blueberries (**Figure 3**) and the vast majority of spherules are isolated spheres. The Opportunity rover observed doublets and triplets [3, 5, 13, 15] as shown in **Figure 11** but these instances were very rare. It is important to note that the observation of large numbers of blueberries and microberries does not suggest a large number of meteoritic

**Figure 10.** *Raindrop shapes with various sizes. (Courtesy USGS website).*

**Figure 11.** *Observed doublet and triplet blueberries on Mars.*

events on Mars. A single small meteorite can produce a large number of spherules. For example, a 2-inch diameter meteorite is equivalent to 2048 spherules with diameter of 4 mm. In addition, a small meteorite entering the Martian atmosphere will distribute thousands of spherules over a large area on Mars along its trajectory. A very large number of spherules could also be formed during a meteorite shower event. Another important observation is that the population of doublets and triplets is very low in comparison to isolated spherules, which can be explained by the meteorite ablation mechanisms. The doublets can be formed when two liquid drops come in contact. However, in the liquid phase, this simply forms a bigger drop and immediately splits up into smaller drops. Similarly, two solid spherules will simply stay as two individual spherules and not form a doublet. For a doublet to form, the recombination of two spherules must occur near the liquid-solid phase transition. This significantly reduces the probability of the formation of a doublet or triplet. The meteorite model also predicts that doublets and triplets are more likely to have spherules of different diameters than the same diameter. This is because the doublet is more likely to form when one drop is moving faster than the other drop. Because the terminal speeds of drops are proportional to their masses, the doublets and triplets would be composed of spherules of different sizes as shown in **Figure 11**.

Because meteorites can fall on Mars at any time, there are other requirements that need to be satisfied for a meteorite ablation model. The first requirement is that new young cosmic spheres should be observed along with older spherules. The second is that cosmic spherules of other compositions should also be observed. **Figure 12** shows very shiny younger spherules among the older spherules.

**11**

*Hematite Spherules on Mars*

cosmic spherule mechanism.

**Figure 13.**

**5. Further evidence of cosmic spherules**

the older blueberries seen on the ground.

and shape match the nearby spherules.

younger age because the rovers landed on Mars in 2004.

*DOI: http://dx.doi.org/10.5772/intechopen.82583*

*Coexistence of yellow berries along with blueberries.*

This observation is in agreement with the meteorite ablation model. However, it is very difficult to explain the coexistence of old and new spherules on Mars with the concretion model, which will require evidence of water appearing, disappearing, and reappearing on Mars. **Figure 13** from sol 319 shows the coexistence of both blue and yellow berries. In this false color image, the color indicates a change in optical reflectance, which indicates different chemical compositions for the blue and yellow berries. In the next section, we will look at the evidence that strongly supports the

The observations on Mars made by rovers shown in this section can only be explained by a meteorite model. There is a very small probability that man-made objects such as the rovers and heat shield will collect cosmic spherules from recent meteoritic events. However, for the meteorite model to be correct, there are few conditions: (1) the sizes of the spherules must obey the predicted size limit and (2) the spherules must look shiny in comparison to older blueberries, indicating

**Figure 14** from sol 339 shows a piece of the heat shield of the Opportunity rover. Because blueberries are spherical, they are most likely to collect at the bottom of a slope on the heat shield. The photograph clearly shows several fresh-looking blueberries collected on the heat shield. The size and texture can be compared with

The images taken by the Opportunity rover of itself are shown in **Figure 15** (top image: sol 322; bottom image: sol 323), which show few blueberries collected by the rover. The size of these shiny spherules are similar to the size of the older, dull-looking blueberries lying on the ground as seen in the top right corner of the image shown in **Figure 15**. Further strong evidence in support of meteorite model is shown in **Figure 16**. If the spherules are formed by molten drops of falling meteorites, then they are expected to be very hot. **Figure 16** shows the image (1M156679326EFF3981P2979M2M1) taken on sol 321 of the solar panel by the microscopic imager on Opportunity. The image shows a burned impact mark at location 'B' along with few microspherules nearby shown as 'A.' The burn mark size

The other Mars rover "Spirit" landed in the Gusev Crater area. According to the MGS satellite image, this site is not rich in hematite. Hence, Spirit rarely observed spherules on the ground. The images from the Spirit rover taken on sol 330 show a few spherical objects on the solar panels marked by green circles (**Figure 17**, left).

**Figure 12.** *Coexistence of younger and older spherules on Mars.*

*Mineralogy - Significance and Applications*

*Observed doublet and triplet blueberries on Mars.*

**Figure 11.**

events on Mars. A single small meteorite can produce a large number of spherules. For example, a 2-inch diameter meteorite is equivalent to 2048 spherules with diameter of 4 mm. In addition, a small meteorite entering the Martian atmosphere will distribute thousands of spherules over a large area on Mars along its trajectory. A very large number of spherules could also be formed during a meteorite shower event. Another important observation is that the population of doublets and triplets is very low in comparison to isolated spherules, which can be explained by the meteorite ablation mechanisms. The doublets can be formed when two liquid drops come in contact. However, in the liquid phase, this simply forms a bigger drop and immediately splits up into smaller drops. Similarly, two solid spherules will simply stay as two individual spherules and not form a doublet. For a doublet to form, the recombination of two spherules must occur near the liquid-solid phase transition. This significantly reduces the probability of the formation of a doublet or triplet. The meteorite model also predicts that doublets and triplets are more likely to have spherules of different diameters than the same diameter. This is because the doublet is more likely to form when one drop is moving faster than the other drop. Because the terminal speeds of drops are proportional to their masses, the doublets and triplets would be composed of spherules

Because meteorites can fall on Mars at any time, there are other requirements that need to be satisfied for a meteorite ablation model. The first requirement is that new young cosmic spheres should be observed along with older spherules. The second is that cosmic spherules of other compositions should also be observed. **Figure 12** shows very shiny younger spherules among the older spherules.

**10**

**Figure 12.**

*Coexistence of younger and older spherules on Mars.*

of different sizes as shown in **Figure 11**.

**Figure 13.** *Coexistence of yellow berries along with blueberries.*

This observation is in agreement with the meteorite ablation model. However, it is very difficult to explain the coexistence of old and new spherules on Mars with the concretion model, which will require evidence of water appearing, disappearing, and reappearing on Mars. **Figure 13** from sol 319 shows the coexistence of both blue and yellow berries. In this false color image, the color indicates a change in optical reflectance, which indicates different chemical compositions for the blue and yellow berries. In the next section, we will look at the evidence that strongly supports the cosmic spherule mechanism.
