Was it sculpted by several small impacts, via mantle convection in the planet's interior, or by one giant impact? Now scientists at the California Institute of Technology have shown through computer modeling that the Mars dichotomy, as the divided terrain has been termed, can indeed be explained by one giant impact early in the planet's history.
"The dichotomy is arguably the oldest feature on Mars," notes Oded Aharonson, associate professor of planetary science at Caltech and an author of the study. The feature arose more than four billion years ago, before the rest of the planet's complex geologic history was superimposed.
Scientists had previously discounted the idea that a single, giant impactor could have created the lower elevations and thinner crust of Mars's northern region, says Margarita Marinova, a graduate student in Caltech's Division of Geological and Planetary Sciences (GPS) and lead author of the study, which appears June 26 in the journal Nature. This special issue of the journal features a trio of papers on the Mars dichotomy.
For one thing, Marinova explains, it was thought that a single impact would leave a circular footprint, but the outline of the northern lowlands region is elliptical. There is also a distinct lack of a crater rim: topography increases smoothly from the lowlands to the highlands without a lip of concentrated material in between, as is the case in small craters. Finally, it was believed that a giant impactor would obliterate the record of its own occurrence by melting a large fraction of the planet and forming a magma ocean.
"We set out to show that it's possible to make a big hole without melting the majority of the surface of Mars," Aharonson says. The team modeled a range of projectile parameters that could yield a cavity the size and ellipticity of the Mars lowlands without melting the whole planet or making a crater rim.
After cranking 500 simulations combining various energies, velocities, and impact angles through the GPS division's Beowulf-class computer cluster CITerra, the researchers narrowed in on a "sweet spot"--a range of single-impact parameters that would make exactly the type of crater found on Mars. Although a large impact had been suggested (and discounted) in the past, Aharonson says, computers weren't fast enough to run the models. "The ability to search for parameters that allow an impact compatible with observations is enabled by the dedicated machine at Caltech," he adds.
The favored simulation conditions outlined by the sweet spot suggest an impact energy of around 1029 joules, which is equivalent to 100 billion gigatons of TNT. The impactor would have hit Mars at an angle between 30 and 60 degrees while traveling at 6 to 10 kilometers per second. By combining these factors, Marinova calculated that the projectile was roughly 1,600 to 2,700 kilometers across.
Estimates of the energy of the Mars impact place it squarely between the impact that is thought to have led to the extinction of dinosaurs on Earth 65 million years ago and the one believed to have extruded our planet's moon four billion years ago.
Indeed, the timing of formation of our moon and the Mars dichotomy is not coincidental, Marinova notes. "This size range of impacts only occurred early in solar system history," she says. The results of this study are also applicable to understanding large impact events on other heavenly bodies, like the Aitken Basin on the moon and the Caloris Basin on Mercury.
The Caltech study comes at a time of renewed interest in the ancient crustal feature on Mars, Aharonson notes. Also in this issue of Nature, Jeffrey Andrews-Hanna and Maria Zuber of MIT and Bruce Banerdt of JPL examine the gravitational and topographic signature of the dichotomy with information from the Mars orbiters. Another accompanying report, from a group at UC Santa Cruz led by Francis Nimmo, explores the expected consequences of mega-impacts.
Elisabeth Nadin | EurekAlert!
Astronomers find unexpected, dust-obscured star formation in distant galaxy
24.03.2017 | University of Massachusetts at Amherst
Gravitational wave kicks monster black hole out of galactic core
24.03.2017 | NASA/Goddard Space Flight Center
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
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In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
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