Mars has two moons; Phobos and Deimos. Now,
Pascal Rosenblatt and his team think that the planet used to have way more
moons, as they publish in this week’s Nature.
Fear and Panic; Phobos and Deimos
Scientists
used to think that Phobos and Deimos, Mars’s moons, are two asteroids that got stuck
in Mars’s gravity. This also made sense, since the asteroid belt is close to
Mars. Moreover, the moons have an irregular shape and are not made of the same
stuff as Mars. These are also clear signs that Phobos and Deimos originally
were asteroids. There’s only one problem. When an asteroid gets caught in the
gravity field of a planet, its orbit is usually elliptical, oval shaped. This
is because the asteroid is shooting through a bit before being pulled back by
the planet, this creates the oval shape. But, Phobos’s and Deimos’s orbits are
circle shaped. And Mars’s gravity is way too weak to turn an oval orbit into a circular
orbit. The chances that the circular orbits happened by accident are so small that
it is more likely that Phobos and Deimos formed in another way, closer to Mars.
A big boom results in some moons
Pascal
Rosenblatt and his team believe that Phobos and Deimos are formed out of debris
that was formed when a giant asteroid hit Mars. That debris then formed a ring
around Mars, and with computer simulations, Rosenblatt and his team found out
that a couple of moons were formed out of that debris. All those moons, except
two, orbited too close to Mars and crashed into the surface. The other two
moons slowly moved into higher orbits and eventually became what we now know as
Phobos and Deimos. We have, of course, no way to check this. Since we can’t
just travel back in time and take a look. But if Phobos and Deimos are made out
of a little bit of Mars and a bit of asteroid, it would pretty much prove this
theory right.
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| The Borealis basin is the orange area on the left |
Solving our puzzle
But there’s
also another thing this new theory can explain. If an asteroid collided with
Mars, there must be a crater. Rosenblatt and his team might even have found
this crater already; the Borealis basin, a crater that covers around forty
percent of the surface of Mars. The collision that created this crater must
also have created a lot of debris, out of which the two moons and more could
have easily formed. And at the same time, this new theory about Mars’s moons is
another piece in the puzzle that is our solar system, and we might even be able
to solve the complete puzzle one day.
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