Around 4.5 billion years ago an object the size of Mars is believed to have collided with Earth throwing massive amounts of material into orbit, which coalesced to form the Moon (although some astronomers believe a string of smaller impacts were responsible). In such a violent impact, Earth’s early atmosphere would have been tested to the max, but how devastating a loss it suffered is not exactly known.
To help better understand the atmospheric consequences of similar giant collisions involving young planets, a team of UK researchers has enlisted the help of 3D supercomputer simulations. Using an Earth-like planet as the target, the team ran over 100 detailed scenarios that showed the effect an incoming impact would have across a range of angles and speeds.
“We know that planetary collisions can have a dramatic effect on a planet's atmosphere, but this is the first time we've been able to study the wide varieties of these violent events in detail,” lead author Dr Jacob Kegerreis, of Durham University, UK, said in a statement. “In spite of the remarkably diverse consequences that can come from different impact angles and speeds, we've found a simple way to predict how much atmosphere would be lost.”
From the behavior of the 100 million simulated particles, the researchers concluded that perhaps unsurprisingly, head-on collisions and higher speeds led to much greater erosion of the planet’s atmosphere. Those impacts that hit at a shallower angle, like the one believed to have formed our Moon, resulted in much less atmospheric loss.
To put a number on it, between 10 and 50 percent of the Earth’s atmosphere was lost in the Moon-forming collision, according to the simulations. Even then, the planet was relatively lucky to maintain even this amount; a factor at play in other simulations as well.
“At the moment it appears that the amount of atmosphere a planet loses due to these collisions depends upon how lucky or unlucky they are in terms the type of the impact they suffer,” co-author Dr Vincent Eke, also of Durham University, said in a statement.
In the future the researchers hope to expand their work, which is due to be published in the Astrophysical Journal, to include impactors of different masses and compositions.
“This lays the groundwork to be able to predict the atmospheric erosion from any giant impact, which would feed into models of planet formation as a whole,” Kegerreis added. “This in turn will help us to understand both the Earth's history as a habitable planet and the evolution of exoplanets around other stars.”