Mars shines brilliantly in the sky this summer, and at the Planétarium. To mark the opening of two new shows, A Day on Mars, and Asteroid: Mission Extreme, let’s explore some connections between the Red Planet and it’s wandering interplanetary neighbours.
It only takes a quick glance at Mars to realise that its history has been impacted, quite literally, by asteroids. Just a few decades of observation by orbiting probes has been enough to reveal the formation of new impact craters.
Scientists even predict that a twenty-kilometre object will strike Mars “soon”. And that object is Phobos, one of the two Martian moons. Phobos orbits Mars so quickly, the tidal forces it generates are accelerating the planet’s rotation. As a result of this transfer, the tiny moon is losing both energy and altitude, and it’s approaching Mars by 2 centimetres per year. That’s about how quickly fingernails grow. Not very fast, but it’s enough to send Phobos plunging into the Martian atmosphere within 50 million years. Of course, astronomers are used to talking in terms of billions of years, so “soon” is a relative description!
Up in the air
But will Mars then be impacted by an actual asteroid? The origin of the two Martian moons is still being debated. Three models compete: asteroid capture; formation in orbit; and agglomeration of impact debris. Observation of the surfaces of both moons tends to favour the first hypothesis: Their chemical composition is similar to certain asteroids that have been studied. However, their orbits are nearly circular and parallel to Mars’ equator, which supports agglomeration, either when the planet was forming, or following a major impact that ejected Martian debris into space.
The answer is on its way
Only by studying samples of the two moons are we likely to solve the mystery of their origin. Phobos-Grunt, a Russian mission with this objective, was launched in 2011 but a malfunction prevented it from leaving Earth orbit. Luckily though, debris fragments from celestial objects sometimes make their way here, without us having to go and collect them. While we wait for an actual piece of Phobos to fall from the sky, scientists, as well as visitors who view our meteorite collection, can examine rocks that originate from asteroids, the Moon and even Mars!