Mighty asteroid morphed Mars
25 June 2008
Is the biggest impact scar in our Solar System on Mars? Scientists now think a massive asteroid smashed into the planet polishing off its rough landscape. It left the largest crater ever seen! Antenna checks out the impact...
This research was published in the journal Nature on 26 June 2008.
This research was published in the journal Nature on 26 June 2008.
Artist's impression of the asteroid impact.
Image: Jeff Andrews-Hanna
Mars's smooth northern lowlands are shown in blue. The southern highlands are heavily cratered.
Image: NASA
Mars is flatter at the top than at the bottom. The north side has a much smoother surface and thinner crust than the south of the planet. |
Scientists previously thought movement within Mars's crust was responsible for the planet's shape. So what made them think it was really caused by an asteroid impact?
The clue came from a half-hidden egg-shaped crater. This covers most of northern Mars - what's referred to as the northern lowlands. Layers of volcanic rock obscure the crater from sight...
If it was hidden, how did they confirm their suspicions?
They mapped out the shape of the crater by looking at Mars's gravitational field - the force around a planet that's caused by its mass. The way the gravitational field varies across the planet surface reflects the shape of the landscape.
Circular craters on the martian surface - the usual kind
Image: ESA
The crater turns out to be four times bigger than anything ever seen on any other planet! But an impact of this size should have melted the rock and left no evidence. It's also unusual because it's egg-shaped - most impact craters are round.
The asteroid Vesta, similar to the one thought to have hit mars.
Image: NASA
So why are the researchers now convinced it's an impact crater?
'An asteroid impact was too big to reconstruct in the lab. So we ran computer simulations to determine how the forces from various-sized impacts would spread around the planet.' explains Craig Agnor, a Solar System expert at Queen Mary University.
Cutaway artist's impression of the impact.
Image: Francis Nimmo
'We found that an asteroid about 400 miles wide hitting the planet at 40 times the speed of sound could have caused the crater that formed the northern lowlands.'
What do the experts think?
'This exciting research tells us more about the violent early Solar System. Young planets were subjected to a terrific bombardment of huge chunks of rock,' says Doug Millard, space curator at the Science Museum.
Doug Millard, space curator, Science Museum
Image: Doug Millard