Martian spherules

Spherules still in their originating strata

Martian spherules (also known as blueberries due to their blue hue in false-color images released by NASA) are the abundant spherical hematite inclusions discovered by the Mars rover Opportunity at Meridiani Planum on the planet Mars. They are found in situ embedded in a sulfate salt evaporitic matrix, and also loose on the surface.^[1]

Characteristics

Ranging in size from less than 100 micrometers to more than 250 micrometers, similar spherules were found in Moon soil samples collected by Apollo 12 at the Procellarum Basin, and Apollo 14 near Mare Imbrium (Sea of Rains), the dark crater that dominates the Moon's face, and their properties were consistent with expectations for creation by meteor impacts.

Origin

The origin of the spherules is under current investigation. Possible geological processes include:

accretion under water
Meteor impacts
Volcanic eruptions

The shapes by themselves do not reveal the particles' origin with certainty. "A number of straightforward geological processes can yield round shapes," said Dr. Hap McSween, an Opportunity science team member from the University of Tennessee, Knoxville. They include accretion under water, but apparent pores in the particles make alternative possibilities of meteor impacts or volcanic eruptions more likely origins, he said.

Mosaic shows some spherules partly embedded, spread over the (smaller) soil grains.

"We see these strange round objects we're calling "spherules" embedded in the outcrop, like blueberries in a muffin. The outcrop erodes away as it gets sandblasted, and the spherules (which seem to resist erosion better than the rest of the outcrop does) fall out and roll down the hill. Weird." said Dr. Steve Squyres.

Spherules appear both on the surface and deeper in the Martian soil. The difference between these and ones which were found at the surface was that they had a very shiny surface, that created strong glints and glares which made them appear shiny or polished. On March 2, Opportunity mission scientists reported that they concluded a survey of the distribution of spherules in the bedrock. They found that the spherules spread out evenly and randomly inside the rocks, and not in layers. This supports the notion that they grew in place, since if their origin was related to volcanic or meteoric episodes one would expect layers of spherules as a "record in time" for each event. This observation was added to the list of evidence for liquid water being present at this rock site, where it is thought the spherules formed.