Scientists who worked with the Curiosity rover used part of their navigation equipment – an accelerometer like the one in your mobile phone – to make an important measure of Mars's mysterious geology.
Curiosity is currently circling around Mount Sharp, a mountain of 5 miles (3 miles) in the center of the Gale Cretaceous. However, it is unclear whether the mountains are the result of a crater that was once filled up and loses on erosion, or the mountain is more like a great deal of deposited material. Curiosity does not have a scientific instrument for determining the nature of the mountain – but has navigation equipment for measuring force. So the scientists became creative.
"I realized that you can download the app on your phone and, not very precisely, but you can measure it [the force of Earth’s gravity] because your phone has accelerometers, "said Gizmodo, lead author of the study, Kevin Levis, an assistant at Johns Hopkins University. He thought he could do the same thing with the Curiosity accelerometers and make some interesting science.
Gravimetry, or precise measurements of changes in a local gravitational field, is a useful way to understand the walls below the surface, because the force of gravity of the object increases with its mass. Apollo 17 had a gravimetric experiment for studying the Moon, for example – but curiosity does not have a gravimeter. However, it has a navigation system that includes a gyroscope and accelerometer for measuring speed, acceleration and orientation changes.
The navigation system is not as sensitive as a gravity meter, but scientists did it. They received information about the acceleration that the rover experienced, and then customized them to explain things like the Curiosity location on Mars, as well as the potential effects of temperature and elevation on the equipment.
Their analysis revealed surprise – the average density of the walls below curiosity was lower than expected. This meant that the dirt is much porous, which means there are more holes than the scientists expected. They were also able to conclude that the sediment would not be very deep, otherwise it would have been more compact or filled.
It seems that all of these points imply that the Sharp Mountain was not the result of erosion that created a high peak, but it formed through a sediment that penetrated the already formed crater, resulting in a huge deposit, according to a paper published today in the journal Science.
"My first impression was that it is a smart engineering trick for the use of rover instruments that are not designed as scientific instruments to actually be science," said Gismodo Kirsten Siebach, a Mars geologist and assistant at Rice University. She noted that the value of the porosity of the rock is surprisingly high. She said that the paper confirmed some previous observations on Gale's crater, but is in contrast to others.
"It makes us better understand what could behave like rocks of low porosity on Mars," she said.
Such measurements come with inherent limitations, such as the introduction of potential bias when attempting to select data to be used and uncertainties in the use of an instrument for a task that was not intended.
But it's science, and work reveals new information that brings us closer to finding out what really can happen inside the crater, and should be considered along with other experiments, simulations, and data. And there are still many experiments to build evidence: Mars InSight will be able to teach scientists about the geology of the planet in general, based on how heat flows through the planet, while Mars 2020 will have a radar penetrating the country to collect information about the underground at its landing site, Crater Lake.
It is not the first time that we have heard from scientists who are redirecting navigation equipment to science – but this is especially ingenious.
Levis said: "One of the things I really like in this study is that it is my type of science – finding new ways for existing data to be used by MacGiver – a brand new scientific instrument."