A study carried out by geologists at Brown University (Rhode Island) provides a possible compatibility between the hot and humid scenario that is deduced from Martian geology and the cold and frozen past that some atmospheric models suggest .
Even assuming that Mars was generally frozen , the research reveals that it is feasible that daily maximum temperatures in summer could rise above freezing enough to contribute to the melting of ice at the edges of glaciers.
That meltwater, discharged in relatively small amounts year after year, could have been enough to sculpt the characteristic erosion channels and channels seen on the red planet today, according to the researchers, who have published their study online in the journal Icarus .
Lead authors are Ashley Palumbo, student at Brown University, Jim Head, professor in Brown’s Department of Earth, Environmental and Planetary Sciences, and Robin Wordsworth, professor at the Harvard School of Engineering and Applied Sciences.
According to Palumbo, the research was inspired by the Earth’s climatic dynamics , particularly in Antarctica: “A similar phenomenon can be seen in the Antarctic Dry Valleys, since the seasonal rise in temperature is enough to form lakes and keep them liquid , despite because the average annual temperature is well below freezing. So we wanted to see that something similar could have happened on Mars millions of years ago. “
The researchers started from a state-of-the-art climate model for the red planet, which envisions an atmosphere composed largely of carbon dioxide (as is the case today).
That scenario results in a cold and icy early Mars , in part because solar energy production is believed to have been much weaker in the early history of the solar system.
The researchers ran the model taking into account a wide range of parameters for variables that may have been important about 4 billion years ago, when the characteristic networks of channels and valleys formed in the southern highlands of the planet.
Although scientists generally agree that the atmosphere of Mars was denser in the past , it is unclear what its actual thickness was.
Similarly, while most experts agree that the atmosphere was made up primarily of carbon dioxide, small amounts of other greenhouse gases may be present. Palumbo and his colleagues analyzed the model with various feasible atmospheric thicknesses and with additional degrees of warming from the greenhouse effect.
It is also not known precisely what the variations in the orbit of Mars would be 4 billion years ago , so the researchers tested a series of plausible orbital scenarios and also tested different degrees of tilt of the axis, which influences the amount of light. solar received by the upper and lower latitudes of the planet, as well as in different degrees of eccentricity, that is, the distance at which the planet’s orbit deviates from the circle, which can increase seasonal changes in temperature.
The study envisioned scenarios in which ice covered the region near the current location of the valley networks . While the average annual temperature of the planet in those scenarios remained well below freezing, the model produced maximum summer temperatures in the southern highlands that rose above freezing .
For the visible traces of water flowing from this mechanism to be explained, it is necessary that the volume of water during the duration of the formation of the network is sufficient for the water to rise to the surface at required speeds. to carry out an erosive action.
A few years ago, Jim Head and Brown University student Eliot Rosenberg published an estimate of the minimum amount of water it would take to carve the largest of the valleys. Using that as a guide, along with estimates of necessary runoff rates and duration of valley network formation from other studies.
Palumbo showed that assuming the Martian orbit was highly eccentric, these criteria were met. That required degree of eccentricity is within the range of possible orbits for Mars 4 billion years ago. Taken together, according to Palumbo, the results offer a scenario that allows the geological evidence of the water that flowed in the early days of Mars to be compatible with the atmospheric evidence of a cold and icy planet.
Credit: NASA / JPL-Caltech / Arizona State University
