Robin George Andrews writes:

We like to think of ourselves as unique. That conceit may even be true when it comes to our cosmic neighborhood: Despite the fact that planets between the sizes of Earth and Neptune appear to be the most common in the cosmos, no such intermediate-mass planets can be found in the solar system.

The problem is, our best theories of planet formation — cast as they are from the molds of what we observe in our own backyard — haven’t been sufficient to truly explain how planets form. A new study, however, published in Nature Astronomy in February, demonstrates that by taking magnetism into account, astronomers may be able to explain the striking diversity of planets orbiting alien stars.

It’s too early to tell if magnetism is the key missing ingredient in our planet-formation models, but the new work is nevertheless “a very cool new result,” said Anders Johansen, a planetary scientist at the University of Copenhagen who was not involved with the work.

Until recently, gravity has been the star of the show. In the most commonly cited theory for how planets form, known as core accretion, hefty rocks orbiting a young sun violently collide over and over again, attaching to one another and growing larger over time. They eventually create objects with enough gravity to scoop up ever more material — first becoming a small planetesimal, then a larger protoplanet, then perhaps a full-blown planet.

Yet gravity does not act alone. [Continue reading…]