“Repeating linear slope” is an alluring feature on the slopes of Mars. But how can we get there and not bring earthly microbes?
3-D computer model of dark stripes of “repetitive linear slopes” on the walls of the Garni crater. The data came from the camera HiRISE MRO.
Life, as we know, needs liquid water. So imagine the excitement when in 2015, hydrated minerals (compounds that form in the presence of water) were noticed on Martian slopes, which are called “repetitive linear slopes” (RSL).
Their first high-resolution image was made by Mars Reconnaissance Orbiter (MRO) by NASA in 2006. These features appear and disappear within a few months. Arise when the sun shines most strongly on these slopes. The theory is that these RSLs can be seasonal streams of water flowing down the slopes. We have signs of life, but will it work for Mars?
Here life would have more extreme conditions, since the water is very salty. And this salt concentration is much higher than the known limit for terrestrial microbes. But still there are still regions in which there is an opportunity for life, as well as potential sources of water for future Martian research.
“The discovery of a large salt water field on Mars could be the key to further human exploration or even the colonization of the Red Planet,” write Javier Martin-Torres and Maria Paz Zorzano. “Are we ready for the next intelligence momentum?” And how do we get to these points, so as not to bring germs? And most importantly: how to colonize Mars and not pollute the planet? ”. All these questions concern the risk of contamination of Mars terrestrial microbes. And although the rovers are thoroughly sterilized, some persistent microbes remain.
NASA and other organizations adhere to the principles of planetary protection during missions, especially for “certain areas” that are relevant to the search for life. And until we get to these points, a new study states that it is better for us to figure out how to reduce the risk of pollution. Of course, we also need to understand how to stop the pollution and the Martian microbes (if they exist) of any sample that we deliver to Earth in the future.
Duplicate slope at Raga Crater on Mars. Such features are proposed as “special areas” in which life may be present. Picture taken with MRO HiRISE camera.
Not everyone agrees that RSL can have life.
Richard Zurek is the chief scientist for the MRO mission and NASA's Mars exploration program. He warns that the amount of water in the RSL is more like “seeping drops” than streams. In addition, microbes will have to contend with a very cold and salty low-pressure environment, if they were able to survive this “brine” at all. Such an environment would be critical for terrestrial microbes, so he is skeptical of these regions.
“MRO measurement covers over 100 meters. It is like a football field. And you can't sometimes tell if there are hot or cold spots, ”he said, adding that individual characteristics are often found only a couple meters across.
For this region, the MRO has captured target areas in which there are many RSLs. Another limitation is that different MRO tools have different resolutions, so the observations are difficult to compare. “It’s hard to get adequate temperature measurement,” he says. Scientists are still trying to figure out where salt water originates. MRO can only feel the temperature of the first few centimeters of the Martian regolith (soil). There is no certainty about how much water is needed to create an RSL.
Complicating and the fact that the MRO peers through the atmosphere, which prevents to see the true contrast on the slopes. Therefore, it is unclear how much RSL is darker than the surrounding terrain.
There are several oblique bands on Mars that may or may not be related to RSL. This is credited with Gale crater (landing site of the Curiosity rover). The rover's camera catches dark stripes at a great distance. But for now no one knows whether this is related to RSL. Then the question arises: should the rover be distracted from the main work in order to study them. Curiosity is now probing various layers of Mount Sharpe in search of signs of ancient habitable conditions.
“Is it possible to cancel everything, in order to search for these dark stripes, which may turn out to be just a dry mudflow?” Zurek asks.
NASA's Curiosity Rover can take the RSL at close range, but this will distract him from the main Sharp survey mission.
Therefore, all the work goes to the HiRISE MRO camera, which is in excellent condition, despite the fact that it has been working on Mars for more than 10 years.
Another Icarus article confirmed 239 candidates and RSL locations in the Mariner Valley - a huge Martian canyon. This valley shelters half of all known RSL sites, and they grow depending on the season.
“If RSL is caused by water, then such an active season for hundreds of locations suggests that water will recharge them,” it says in a document led by David Stillman. He adds that the simulation shows a melting point of at least -16 degrees Fahrenheit, which is necessary to create a stream of salt water. “The mechanisms for recharging RSL with water every year remain unknown. But a better understanding of this will help to quickly find life on Mars and provide information about water resources, ”the study says.
Zurek says that there is still a lot of unknown information about water activities, especially regarding how RSLs are formed in the Martian environment (low pressure, very cold). There are already laboratory studies that are trying to recreate this temperature cycle. But this is difficult to do, since the composition of the soil cannot be predicted without an understanding of the exact salt concentration.
“There's still a lot of work. In addition, you need to identify specific places where they can be, ”added Zhurek. MRO has managed to capture only 3% of the planet in high resolution. One of the spots is Gale Crater, which tells you whether the dark bands are RSL features. This will become clear over the next Martian year (equivalent to two years).
Zurek added that the MRO still has time to collect more data, since the orbiter will work at least until 2023. It will become connected for the Mars rover 2020, which will land on the planet in 2021.