On Earth, examining ice core samples is one of many methods that scientists are using to reconstruct the history of our past climate change. The same is true of the northern polar ice cap of Mars, which consists of many layers of frozen water that have accumulated over eons. Examining these layers could give scientists a better understanding of how the Martian climate has changed over time.
This remains a challenge as we can currently only study the Mars polar caps from orbit. Fortunately, a team of UC Boulder researchers was able to use data from the high-resolution imaging science experiment (HiRISE) aboard the Mars Reconnaissance Orbiter (MRO) to record the evolution of the northern polar ice caps over the past million years.
The research was led by Andrew Wilcoski and Paul Hayne, Ph.D. Student and assistant professor at the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado Boulder. The study describing its results recently appeared in the Journal for Geological Research (JGR), a publication by the American Geophysical Union (AGU).
The HiRISE instrument before it was integrated into the MRO. Photo credit: NASA
For their study, Wilcosky and Hayne attempted to determine the current state of the NPRC (Martian North Polar Residual Cap), which is crucial for understanding the North Polar Layered Deposits (NPLD). Using the high-resolution images captured by the HiRISE instrument, Wilcosky and Hayne examined the harsh features of the NPRC – including ripples and ridges of varying sizes and shapes.
They then modeled the growth and recession of NPRC over time based on its interaction with solar radiation and how the rate of growth and loss is affected by the amount of atmospheric water vapor. What they found was that in addition to the formation of uneven terrain (waves and ridges) in an ice sheet due to exposure to sunlight, the ice also sublimates unevenly.
Basically, Mars’ axial tilt, which is responsible for experiencing seasonal changes similar to Earth, causes one side of these features to sublime (the sun-facing side) while the other side does not. As a result, these features are exaggerated, resulting in pronounced ridges and valleys that grow stronger over time.
Overall, the model used by Wilcoski and Hayne indicated that the rough features observed by the MRO should be 10 m (33 ft) in diameter and 1 m (3.3 ft) deep. In addition, their results showed that as the features age, the spatial wavelength (the distance) between each ripple increases – from 10 to 50 m (164 ft). As they say in their study:
“Our results show that the size of the hills and depressions on the surface of the ice cap suggest that these roughness features took 1–10,000 years to form. Our results also suggest that the formation of features on the surface may depend on when in the course of a year (e.g. summer or winter) water vapor is present in the atmosphere. “
A composite image showing alternating layers of ice and sand around the northern polar region, captured by the MRO’s HiRISE camera. Photo credit: NASA / JPL / University of Arizona
These results are consistent with the images acquired with the Martian North Polar Residual Cap (NPRC) HiRISE instrument. They indicated that the harsh features observed around the northern polar ice of Mars over the past 1,000-10,000 years have formed, providing scientists with a starting point for reconstructing the climatic history of Mars.
Such is the nature of the red planet. Today scientists have a pretty good understanding of the nature of the Martian landscape and how it changes over the course of the year. You also have an idea of what it looked like billions of years ago thanks to immaculately preserved surface features that indicate the presence of flowing and stagnant water (rivers, streams, and lakes) in the past.
In the meantime, however, as the climate passed from one to the other, much remains to be learned. In the coming years, robotic missions could be sent to Mars to directly examine the ice sheets and possibly even return samples to Earth. In the next decade, when astronauts set foot on Mars, the opportunity to explore the ice caps could also be offered.
Further reading: EOS (AGU), JGR Planets
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