**Abstract**

In 2004, the observation of large amounts of hematite spherules on Mars by the NASA's Mars Exploration Rover "Opportunity," which landed in Eagle crater on Meridiani Planum, created tremendous excitement among the scientific community. The discovery of hematite was significant as it suggests past presence of water on Mars. Furthermore, the hematite spherules were widely suggested to be concretions that formed by precipitation of aqueous fluids. Among the various observed mysteries of Martian hematite spherules, also known as "blueberries," one regarding to their size limit was very puzzling. All of the millions of blueberries observed on Mars were smaller than 6.2 mm in diameter. Because the concretions on Earth are not limited in size, the formation of the Martian blueberries became difficult to explain. In this chapter, we will discuss the observed properties of Martian hematite spherules and explain why a cosmic spherule formation mechanism provides a possible solution to the puzzling observations on Mars.

**Keywords:** Martian hematite spherules, Martian blueberries, cosmic spherules, concretions

## **1. Introduction**

In 1996, NASA launched the Mars Global Surveyor (MGS) spacecraft to perform global mapping of Mars. One of the instruments on the MGS is the thermal emission spectrometer (TES), which would map the mineralogy of the Martian surface using infrared spectroscopy. TES imaging revealed the presence of crystalline gray hematite on Mars in Sinus Meridiani. **Figure 1** shows the global distribution of minerals on Mars [1, 2]. The distribution of hematite is shown in pink and labeled as H in the areas of Aram Chaos and Sinus Meridiani. The bottom image shows the distribution of hematite in Sinus Meridiani. According to [1] and [3], the hematite covers an area of over 175,000 km2 . The hematite boundary is abrupt and immobile and all the hematite is very possibly confined to a thin layer. According to [3], this layer could be only 100 microns, because TES gives surface measurements. The age of hematite is estimated over 3.5 Ga. The unnamed crater shown in the bottom image (**Figure 1**) shows no hematite, indicating that it was formed after the hematite deposit. Similarly, the inflow from top may be newer than hematite. The authors suggested that these hematite deposits were formed by chemical precipitation from aqueous fluids, and TES data provide evidence that liquid water has been stable for millions of years on early Mars.

The Mars Exploration Rover "Opportunity" landed in Eagle crater on Meridiani Planum in the western part of the Sinus Meridiani region on January 24, 2004. Within a few days of landing on Mars, the Opportunity rover sent pictures of large numbers of spherules, as shown in false-colored images in **Figures 2** and **3** [4].

#### **Figure 1.**

*Global distribution of hematite on Mars using the thermal emission spectrometer on the Mars Global Surveyor Spacecraft (top image). Bottom image is a close-up view of hematite abundance in Sinus Meridiani. (Image courtesy of USGS, NASA/JPL).*

**Figure 2.**

*Observations of hematite spherules at Meridiani, Mars, by the Opportunity rover. (Image courtesy of NASA/ JPL).*

The spherules were studied using instruments on board the Opportunity rover. The Mössbauer spectrometer was used to confirm the mineralogy of the spherules as hematite. A rock abrasion tool (RAT) was used to cut some of the spherules and concluded that spherules are also very hard. The rover instruments provided ground validation data confirming the presence of hematite on Mars as predicted by the orbital TES data obtained by the MGS spacecraft. The gray hematite spherules

**3**

*Hematite Spherules on Mars*

**Figure 3.**

*NASA/JPL).*

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

appeared blue in the false-colored data from Mars and were therefore nicknamed "blueberries." The discovery of Martian blueberries quickly became an exciting scientific discovery as leading scientists concluded that hematite spherules were concretions and that their discovery proved the presence of water in Mars history. The idea that the Martian hematite spherules are concretions has been largely accepted by most planetary scientists for the past several years [3, 5–15]. Several scientists also found concretion terrestrial analogues in southern Utah, in the Jurassic Navajo Sandstone [16], and in Lake Brown, Australia [17]. In the next section, we will discuss the observed properties of the Martian hematite spherules, which will

*Observations of hematite spherules at Meridiani, Mars, by the Opportunity rover. (Image courtesy of* 

Within a few days of operations, the Opportunity rover surprised the science community by sending pictures of a large number of spherules on Mars, now commonly known as blueberries [18]. The follow-up investigation [11, 13] by the NASA science team found several interesting observations of blueberries. Some of these observations are as follows: (i) the primary carriers of hematite at the landing site are blueberries and their fragments; (ii) the hematite was located mostly on the surface of the landscape; (iii) the deeper soil is mostly basaltic sand and is free of hematite; (iv) the blueberries are mostly perfect spheres; (v) the typical diameters of the blueberries are 4–6 mm; (vi) the blueberries are hard; (vii) the blueberries are made of very fine grain material; and (vii) the blueberries have no internal structure. In addition, all the hematite spherules appear to be located within the

**Figure 4** shows the result of the RAT used on the Martian surface to cut open some of the soil-embedded spherules. The spherules were found to be hard and difficult to cut. The spherules showed no internal structure with grain size below the detection limit (31 μm) of the Microscopic Imager (MI). Further investigation of the spherules found that there are two types of blueberries: larger blueberries with average size of 4 mm in diameter and microberries with average size of 0.79 mm in diameter. All blueberries were smaller than 6.2 mm in diameter with a median size of 4.2 mm.

lead us to the controversy of the origin of these spherules.

upper 10 mm thickness of the surface soil.

**2. Observed properties of Martian hematite spherules**

#### **Figure 3.**

*Mineralogy - Significance and Applications*

**2**

**Figure 2.**

*JPL).*

**Figure 1.**

*courtesy of USGS, NASA/JPL).*

The spherules were studied using instruments on board the Opportunity rover. The Mössbauer spectrometer was used to confirm the mineralogy of the spherules as hematite. A rock abrasion tool (RAT) was used to cut some of the spherules and concluded that spherules are also very hard. The rover instruments provided ground validation data confirming the presence of hematite on Mars as predicted by the orbital TES data obtained by the MGS spacecraft. The gray hematite spherules

*Observations of hematite spherules at Meridiani, Mars, by the Opportunity rover. (Image courtesy of NASA/*

*Global distribution of hematite on Mars using the thermal emission spectrometer on the Mars Global Surveyor Spacecraft (top image). Bottom image is a close-up view of hematite abundance in Sinus Meridiani. (Image* 

*Observations of hematite spherules at Meridiani, Mars, by the Opportunity rover. (Image courtesy of NASA/JPL).*

appeared blue in the false-colored data from Mars and were therefore nicknamed "blueberries." The discovery of Martian blueberries quickly became an exciting scientific discovery as leading scientists concluded that hematite spherules were concretions and that their discovery proved the presence of water in Mars history.

The idea that the Martian hematite spherules are concretions has been largely accepted by most planetary scientists for the past several years [3, 5–15]. Several scientists also found concretion terrestrial analogues in southern Utah, in the Jurassic Navajo Sandstone [16], and in Lake Brown, Australia [17]. In the next section, we will discuss the observed properties of the Martian hematite spherules, which will lead us to the controversy of the origin of these spherules.
