One of the proposed explanations--a massive asteroid impact--now has strong support from computer simulations carried out by two groups of researchers. Planetary scientists at the University of California, Santa Cruz, were involved in both studies, which appear in the June 26 issue of Nature.
"It's a very old idea, but nobody had done the numerical calculations to see what would happen when a big asteroid hits Mars," said Francis Nimmo, associate professor of Earth and planetary sciences at UCSC and first author of one of the papers.
Nimmo's group found that such an impact could indeed produce the observed differences between the Martian hemispheres. The other study used a different approach and reached the same conclusion. Nimmo's paper also suggests testable predictions about the consequences of the impact.
The so-called hemispheric dichotomy was first observed by NASA's Viking missions to Mars in the 1970s. The Viking spacecraft revealed that the two halves of the planet look very different, with relatively young, low-lying plains in the north and relatively old, cratered highlands in the south. Some 20 years later, the Mars Global Surveyor mission showed that the crust of the planet is much thicker in the south and also revealed magnetic anomalies present in the southern hemisphere and not in the north.
"Two main explanations have been proposed for the hemispheric dichotomy--either some kind of internal process that changed one half of the planet, or a big impact hitting one side of it," Nimmo said. "The impact would have to be big enough to blast the crust off half of the planet, but not so big that it melts everything. We showed that you really can form the dichotomy that way."
Nimmo's group includes UCSC graduate student Shawn Hart, associate researcher Don Korycansky, and Craig Agnor of Queen Mary University, London. The other paper is by Margarita Marinova and Oded Aharonson of the California Institute of Technology and Erik Asphaug, professor of Earth and planetary sciences at UCSC.
The quantitative model used by Nimmo's group calculated the effects of an impact in two dimensions. Asphaug's group used a different model to calculate impacts in three dimensions, but with lower resolution (i.e., less detail in the simulation).
"The two approaches are very complementary; putting them together gives you a complete picture," Nimmo said. "The two-dimensional model provides high resolution, but you can only look at vertical impacts. The three-dimensional model allows nonvertical impacts, but the resolution is lower so you can't track what happens to the crust."
Most planetary impacts are not head-on, Asphaug said. His group found a "sweet spot" of impact conditions that result in a hemispheric dichotomy matching the observations. Those conditions include an impactor about one-half to two-thirds the size of the Moon, striking at an angle of 30 to 60 degrees.
"This is how planets finish their business of formation," Asphaug said. "They collide with other bodies of comparable size in gargantuan collisions. The last of those big collisions defines the planet."
According to Nimmo's analysis, shock waves from the impact would travel through the planet and disrupt the crust on the other side, causing changes in the magnetic field recorded there. The predicted changes are consistent with observations of magnetic anomalies in the southern hemisphere, he said.
In addition, new crust that formed in the northern lowlands would be derived from deep mantle rock melted by the impact and should have significantly different characteristics from the southern hemisphere crust. Certain Martian meteorites may have originated from the northern crust, Nimmo said. The study also suggests that the impact occurred around the same time as the impact on Earth that created the Moon.
Tim Stephens | EurekAlert!
DGIST develops 20 times faster biosensor
24.04.2017 | DGIST (Daegu Gyeongbuk Institute of Science and Technology)
New quantum liquid crystals may play role in future of computers
21.04.2017 | California Institute of Technology
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
20.04.2017 | Event News
18.04.2017 | Event News
03.04.2017 | Event News
24.04.2017 | Physics and Astronomy
24.04.2017 | Materials Sciences
24.04.2017 | Life Sciences