Mars developed in as little as two to four million years after the birth of the solar system, far more quickly than Earth, according to results of a new study published in this week's issue of the journal Nature.
Mars is planetary embryo that never collided with other embryos to form an Earthlike planet.
The red planet's rapid formation helps explain why it is so small, say the study's co-authors, Nicolas Dauphas at the University of Chicago and Ali Pourmand at the University of Miami.
Their research was funded by the National Science Foundation (NSF).
Mars probably is not a terrestrial planet like Earth, which grew to its full size over 50 to 100 million years via collisions with other small bodies in the solar system, said Dauphas, a geophysicist.
"Earth was made of embryos like Mars, but Mars is a stranded planetary embryo that never collided with other embryos to form an Earthlike planet," Dauphas said.
The new work provides evidence for this idea, which was first proposed 20 years ago on the basis of planetary growth simulations.
It likely will change the way planetary scientists view Mars, said Pourmand, a marine geologist and geophysicist. "We thought that there were no embryos in the solar system to study, but when we study Mars, we are studying embryos that eventually made planets like Earth."
There had been large uncertainties in the formation history of Mars because of the unknown composition of its mantle, the rock layer that underlies the crust.
"Now we can shrink those uncertainties to the point where we can do interesting science," Dauphas said.
Dauphas and Pourmand were able to refine the age of Mars by using the radioactive decay of hafnium to tungsten in meteorites.
Hafnium 182 decays into tungsten 182 in a half-life of nine million years. This relatively rapid decay means that almost all hafnium 182 will disappear in 50 million years, providing a way to assemble a fine-scale chronology of early events in the solar system.
"To apply that system you need two gradients," Pourmand explained. "You need the hafnium-tungsten ratio of the mantle of Mars and you need the tungsten isotopic composition of the mantle of Mars."
The latter was well known from analyses of martian meteorites, but not the former.
Previous estimates of the formation of Mars ranged as high as 15 million years because the chemical composition of the martian mantle was largely unknown.
Scientists still wrestle with large uncertainties in the composition of Earth's mantle because of processes such as melting.
"We have the same problem for Mars," Dauphas said.
Analyses of martian meteorites provide clues about the mantle composition of Mars, but their compositions also have changed.
Solving some lingering unknowns about the composition of chondrites, a common type of meteorites, provided the data needed.
As essentially unaltered debris left over from the birth of the solar system, chondrites serve as a Rosetta stone for deducing planetary chemical composition.
Cosmochemists have intensively studied chondrites, but still poorly understand the abundances of two categories of elements they contain, including uranium, thorium, lutetium and hafnium.
Dauphas and Pourmand analyzed the abundances of these elements in more than 30 chondrites, and compared those to the compositions of another 20 martian meteorites.
"Once you solve the composition of chondrites you can address many other questions," Dauphas said.
Hafnium and thorium both are refractory or non-volatile elements, meaning that their compositions remain relatively constant in meteorites.
They also are lithophile elements, those that would have stayed in the mantle when the core of Mars formed. If scientists could measure the hafnium-thorium ratio in the martian mantle, they would have the ratio for the whole planet, which they need to reconstruct its formation history.
The relationships between hafnium, thorium and tungsten dictated that the hafnium-thorium ratio in the mantle of Mars must be similar to the same ratio in chondrites.
To derive the martian mantle's hafnium-tungsten ratio, they divided the thorium-tungsten ratio of the martian meteorites by the thorium-hafnium ratio of the chondrites.
"Why do you do that? Because thorium and tungsten have very similar chemical behavior," Dauphas said.
Once Dauphas and Pourmand had determined this ratio, they were able to calculate how long it took Mars to develop into a planet.
A computer simulation based on these data showed that Mars must have reached half its present size only two million years after the formation of the solar system.
"New application of radiogenic isotopes to both chondrite and martial meteorites provides data on the age and mode of formation of Mars," said Enriqueta Barrera, program director in NSF's Division of Earth Sciences. "That is consistent with models that explain Mars' small mass in comparison to that of Earth."
A quickly-forming Mars would help explain the puzzling similarities in the xenon content of its atmosphere and that of Earth's.
"Maybe it's just a coincidence, but maybe the solution is that part of the atmosphere of Earth was inherited from an earlier generation of embryos that had their own atmospheres, maybe a Marslike atmosphere," Dauphas said.
The short formation history of Mars further raises the possibility that aluminum 26, which is known from meteorites, turned the red planet into a magma ocean early in its history.
Aluminum 26 has a half-life of 700,000 years, so it would have disappeared too quickly to contribute to the internal heat of Earth.
If Mars formed in two million years, however, significant quantities of aluminum 26 would remain. "When aluminum 26 decays it releases heat and can completely melt the planet," Pourmand said.
The research was also funded by the National Aeronautics and Space Administration and the Packard Foundation.Media Contacts
Cheryl Dybas | EurekAlert!
APEX takes a glimpse into the heart of darkness
25.05.2018 | Max-Planck-Institut für Radioastronomie
First chip-scale broadband optical system that can sense molecules in the mid-IR
24.05.2018 | Columbia University School of Engineering and Applied Science
The more electronics steer, accelerate and brake cars, the more important it is to protect them against cyber-attacks. That is why 15 partners from industry and academia will work together over the next three years on new approaches to IT security in self-driving cars. The joint project goes by the name Security For Connected, Autonomous Cars (SecForCARs) and has funding of €7.2 million from the German Federal Ministry of Education and Research. Infineon is leading the project.
Vehicles already offer diverse communication interfaces and more and more automated functions, such as distance and lane-keeping assist systems. At the same...
A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.
The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...
At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.
At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...
There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?
At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
25.05.2018 | Event News
02.05.2018 | Event News
13.04.2018 | Event News
25.05.2018 | Event News
25.05.2018 | Machine Engineering
25.05.2018 | Life Sciences