**6. Discussion**

The various observations of Martian blueberries strongly support the theory that the spherules are cosmic spherules formed from the ablation of meteorites. The images shown in **Figures 9** and **14**–**18** can only be explained by the meteorite model. In the meteorite ablation model, the cosmic spherules are formed from the liquid phase. Hence, they will be perfect spheres, hard, and size limited. The interior of the spherules will be glassy or extremely fine grained, and will not show nucleation or inclusions of basaltic grains of Martian surface. The blueberries, microberries, and nanophase material will be located only on the top soil and missing from the deeper soil. To date, all observations (listed in **Table 1**) made on Mars are consistent with the meteorite ablation model. To the best of our knowledge, no hematite concretions have been found on Mars and concretions made of pure hematite do not exist on Earth. The cosmic spherule mechanism also suggests that hematite found on the surface of Mars is extra-Martian and not native to Mars.

#### **Figure 18.** *Images of REMS-UV sensor on Curiosity rover showing a cosmic spherule impact.*

A big iron meteorite or a few meteor shower events can produce a large number of spherules on Mars. About a billion spherules of 4 mm in diameter can be produced by a 4 m diameter meteorite. Because the spherules are heavy, the distribution of spherules at the Meridiani is expected to be sharply defined, immobile, and elliptical due to trajectories of the meteors. The age of the hematite deposit on Meridiani has been suggested by reference [3] to be in excess of 3.5 Ga. Opportunity rover did discover several large iron meteorites in the Meridiani Planum [23, 29]. Some scientists [30] have argued that the six iron meteorites found at Meridiani are the result of a single rare event of a large meteorite impact.

Mössbauer data from the Opportunity rover concluded that blueberries at Meridiani Planum are made of hematite [18]. It is possible to form hematite in a CO2 atmosphere at temperatures above 900°C from high-FeO glass-rich basalts [31]. One possible redox reaction for the formation of hematite from iron meteorite is 2Fe + 3CO2 = Fe2O3 + 3CO. For meteorites that have some iron, it is possible to form hematite-coated spherules. Cooper et al. in Ref. [32] determined that at 700°C and FeO concentration > 1.9 wt%, the Fe migration is favored over Ca and Mg migration. The evidence for the formation of hematite particles at 60 km altitude on Earth has been suggested by [33].

It is interesting to note that Earth's Moon has no atmosphere and meteorites on the Moon do not get heated due to drag force. The spherules formed on Moon are mostly due to impact heating and are known as impact glass spherules. On Earth, millimeter-sized cosmic spherules are found in abundance [34–37]. The large amount of cosmic spherules on Mars could be due to its proximity to the asteroid belt [23]. Mars also has low gravity and thin atmosphere that are favorable conditions for forming large spherules.

A direct evidence of a cosmic spherule on Mars is shown in **Figure 18**. In 2012, NASA's "Curiosity" rover landed in Gale Crater. **Figure 18** shows images of the REMS-UV sensor, which is placed within the rover deck facing the sky. The sol 418 image shows that a small cosmic spherule has landed on the UV sensor, which was not observed in a previous image (Sol 282). The image taken on sol 585 shows that the spherule has rolled slightly to the right revealing the original impact spot.

**15**

**7. Conclusion**

*†*

**Table 1.**

Spirit rovers) (recent events)

*Other chemical phases are also possible.*

location)

Some of the important observations of Martian blueberries cannot be explained by a concretion model. These observations include the following: (1) spherules are size limited, (2) they are located only on the top soil, (3) they show no internal structure, and (4) they lack grains of the host matrix. In addition, the distribution of spherules suggests that they fell from above, as shown in **Figure 8**. The observations of spherules collected by the heat shield and rovers suggest that these spherules are very young and cannot be explained by the process of aqueous alteration, which requires a significantly longer period of time. The observations of spherules and nanophase materials near the meteorites are direct evidence that spherules are meteoritic in nature. The meteorite ablation model producing cosmic spherules on Mars explains all the observations and properties of Martian blueberries. According to this mechanism, while traveling through Martian atmosphere, a meteorite gets very hot, reaches melting temperatures, and forms liquid molten drops that reach terminal speeds due to drag force and cool down to solid spherules and microspherules. The maximum size of the spherules is limited by the surface tension of the molten material and atmospheric drag force. The spherules are expected to be mostly perfect hard isolated spheres, with no internal structure and nucleation, and

*Observations and physical properties of Martian blueberries and their comparison with a meteorite model.*

*Hematite Spherules on Mars*

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

**Observations Agreement with** 

1. Millions of blueberries found on Mars (population) Yes 2. All blueberries are less than 6.2 mm in diameter (size limitation) Yes 3. Predominantly perfect spheres (shape) Yes 4. Blueberries show no grain structure (internal structure) Yes 5. Blueberries show no nucleation (mechanism) Yes 6. Coexistence of old and fresh blueberries (age difference) Yes 7. Coexistence of blue and yellow berries (chemical difference) Yes 8. All blueberries limited to top soil and missing in deeper soil (location) Yes 9. Interior of blueberries missing grains of host soil (pure phases) Yes 10. Hematite (composition) Yes†

11. Large amount of microberries observed only on top surface (population and

18. Blueberries found on man-made objects (heat shield and Opportunity and

12. Blueberries appear embedded in soil (location) Yes 13. Hard (mechanical strength) Yes 14. Circular burn spot on solar panel (hot impact) Yes 15. Rare observation of doublets and triplets (mechanism) Yes 16. Doublets and triplets are made of different-sized spherules (mechanism) Yes 17. All blueberries on Wopmay rock are fully exposed (mechanism) Yes

19. Blueberries on heat shield and rovers are shiny (young age) Yes 20. Blueberries found on and near iron meteorites (mechanism) Yes

**meteorite model**

Yes

Yes

*Mineralogy - Significance and Applications*

A big iron meteorite or a few meteor shower events can produce a large number of spherules on Mars. About a billion spherules of 4 mm in diameter can be produced by a 4 m diameter meteorite. Because the spherules are heavy, the distribution of spherules at the Meridiani is expected to be sharply defined, immobile, and elliptical due to trajectories of the meteors. The age of the hematite deposit on Meridiani has been suggested by reference [3] to be in excess of 3.5 Ga. Opportunity rover did discover several large iron meteorites in the Meridiani Planum [23, 29]. Some scientists [30] have argued that the six iron meteorites found at Meridiani are

Mössbauer data from the Opportunity rover concluded that blueberries at Meridiani Planum are made of hematite [18]. It is possible to form hematite in a CO2 atmosphere at temperatures above 900°C from high-FeO glass-rich basalts [31]. One possible redox reaction for the formation of hematite from iron meteorite is 2Fe + 3CO2 = Fe2O3 + 3CO. For meteorites that have some iron, it is possible to form hematite-coated spherules. Cooper et al. in Ref. [32] determined that at 700°C and FeO concentration > 1.9 wt%, the Fe migration is favored over Ca and Mg migration. The evidence for the formation of hematite particles at 60 km altitude on

It is interesting to note that Earth's Moon has no atmosphere and meteorites on the Moon do not get heated due to drag force. The spherules formed on Moon are mostly due to impact heating and are known as impact glass spherules. On Earth, millimeter-sized cosmic spherules are found in abundance [34–37]. The large amount of cosmic spherules on Mars could be due to its proximity to the asteroid belt [23]. Mars also has low gravity and thin atmosphere that are favorable condi-

A direct evidence of a cosmic spherule on Mars is shown in **Figure 18**. In 2012, NASA's "Curiosity" rover landed in Gale Crater. **Figure 18** shows images of the REMS-UV sensor, which is placed within the rover deck facing the sky. The sol 418 image shows that a small cosmic spherule has landed on the UV sensor, which was not observed in a previous image (Sol 282). The image taken on sol 585 shows that the spherule has rolled slightly to the right revealing the original

the result of a single rare event of a large meteorite impact.

*Images of REMS-UV sensor on Curiosity rover showing a cosmic spherule impact.*

Earth has been suggested by [33].

tions for forming large spherules.

**14**

impact spot.

**Figure 18.**


#### **Table 1.**

*Observations and physical properties of Martian blueberries and their comparison with a meteorite model.*

## **7. Conclusion**

Some of the important observations of Martian blueberries cannot be explained by a concretion model. These observations include the following: (1) spherules are size limited, (2) they are located only on the top soil, (3) they show no internal structure, and (4) they lack grains of the host matrix. In addition, the distribution of spherules suggests that they fell from above, as shown in **Figure 8**. The observations of spherules collected by the heat shield and rovers suggest that these spherules are very young and cannot be explained by the process of aqueous alteration, which requires a significantly longer period of time. The observations of spherules and nanophase materials near the meteorites are direct evidence that spherules are meteoritic in nature. The meteorite ablation model producing cosmic spherules on Mars explains all the observations and properties of Martian blueberries. According to this mechanism, while traveling through Martian atmosphere, a meteorite gets very hot, reaches melting temperatures, and forms liquid molten drops that reach terminal speeds due to drag force and cool down to solid spherules and microspherules. The maximum size of the spherules is limited by the surface tension of the molten material and atmospheric drag force. The spherules are expected to be mostly perfect hard isolated spheres, with no internal structure and nucleation, and located only on the top surface layer. The meteorite mechanism also suggests that hematite found on the surface of Mars is extra-Martian.
