The Earth, with a diameter of 12,750 km grew to almost twice the size of Mars, with a 6,794 km diameter, via collisions with smaller planetary embryos, according to a new study which says that Mars is a planetary embryo that escaped such collisions.
Credit: National Aeronautics and Space Administration/Jet Propulsion Laboratory
SYDNEY: Mars developed in as little as two to four million years after the birth of the Solar System - far more quickly than the Earth - according to measurements of different isotopes in Martian meteorites.
Previous model simulations of Mars' growth couldn't explain the planet's small size - with a diameter about half the size of Earth's. Research published today in Nature, now supports the theory that Mars grew as a planetary embryo in the early stages of the Solar System, rather than growing from collisions of larger embryos - which is the generally held theory for the formation of the Earth.
"Earth was made of embryos like Mars, but Mars is a stranded planetary embryo that never collided with other embryos to make an Earthlike planet," said co-author and geophysicist Nicolas Dauphas from the University of Chicago.
"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," said Ali Pourmand, another co-author and a geophysicist from the University of Miami Rosenstiel School of Marine & Atmospheric Science.
Accretion and our planets
The planets formed as matter slowly lumped together due to gravity, in a process known as accretion, from the disk of matter - the protoplanetary disk - around our newly-formed Sun.
The Earth is predicted to have taken 10-50 millions of years to form (different rates are predicted by different models, but radioisotope data confirm this range).
Jupiter and the other giant planets may have taken a few millions of years to accrete as solids, before gaining more gas from the disk, although faster mechanisms for gravitational collapse have been suggested.
These processes, mapped by computer modeling, can be confirmed by studies of radioactive isotope levels in meteoroids that split from a parent body. Comparing radioisotope abundances, and other chemical data such as metal ore structures, can reveal information about the parent body they came from, in this case Mars.
Confirming a 'quick' birth
Scientists compare the ratio of isotopes to early Solar System levels and these ratios also provide an indication of the time at which the planet underwent melting or core formation.
As the core of a planet forms, different elements move to the outer silicate layers and the inner metal layers, so amounts of these elements in a sample indicate the layer and may indicate this transition.
Scientists can then date the material using the amount of radioactive isotopes of these elements left: as these unstable isotopes decay they can calculate for how long these decay has taken by comparing the decrease in concentration of a radioactive isotope compared to a known ratio of a non-radioactive isotope.
Dauphas and Pourmand have confirmed the 'quick' birth of Mars, with data showing it could have grown to half its size in just 1.8 million years.
Forming time of Planets ?
I dont believe this article.
You cant tell the Forming age of a Planet by what is on the Planets Surface.
The Radiation of Meteors or whatever only shows the time elapsing from their Source a Supernova.
If that is found on the suface of a Planet the planet must have existed then.
And when has this radioactive Meteor or whatever plunged into the surface of the planet?.
If the Biggest event of the known history of Earth according to this articles doctrine of accretion,
happened 65 million years ago,
why are the Earth and the Planets not constantly bombarded with matter from Supernovas so the Earth and the Planets will grow bigger and bigger?
Is it not wery obvious that the Sun and the Solary System with Planets,
has take many Billions of Years to Form.
Beginning of the Sun as Saturnus with the Rings,
how long will it take before Saturnus becomes a Sun,
and the Rings Planets ?.
No - this theory of a Big Bang is an error - the Universe has always and will always exist bouth in Time and the 3 Dimentions.
Arne Strand. Sweden.