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!
Move over, lasers: Scientists can now create holograms from neutrons, too
21.10.2016 | National Institute of Standards and Technology (NIST)
Finding the lightest superdeformed triaxial atomic nucleus
20.10.2016 | The Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.
"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...
In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.
A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...
By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.
"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...
COMPAMED has become the leading international marketplace for suppliers of medical manufacturing. The trade fair, which takes place every November and is co-located to MEDICA in Dusseldorf, has been steadily growing over the past years and shows that medical technology remains a rapidly growing market.
In 2016, the joint pavilion by the IVAM Microtechnology Network, the Product Market “High-tech for Medical Devices”, will be located in Hall 8a again and will...
'Ferroelectric' materials can switch between different states of electrical polarization in response to an external electric field. This flexibility means they show promise for many applications, for example in electronic devices and computer memory. Current ferroelectric materials are highly valued for their thermal and chemical stability and rapid electro-mechanical responses, but creating a material that is scalable down to the tiny sizes needed for technologies like silicon-based semiconductors (Si-based CMOS) has proven challenging.
Now, Hiroshi Funakubo and co-workers at the Tokyo Institute of Technology, in collaboration with researchers across Japan, have conducted experiments to...
14.10.2016 | Event News
14.10.2016 | Event News
12.10.2016 | Event News
21.10.2016 | Health and Medicine
21.10.2016 | Information Technology
21.10.2016 | Materials Sciences