Planets forming around HL Tauri

The image of HL Tau, taken in October 2014 by the state-of-the-art Atacama Large Millimeter/submillimeter Array (ALMA) located in Chile’s Atacama Desert, sparked a flurry of scientific debate. 

ALMA (ESO/NAOJ/NRAO)

While those who observed the original image claimed that planets were most likely responsible for carving the gaps, some remained skeptical. It had been suggested that the gaps, especially the outer three, could not represent forming planets because they are so close together. It was argued that planets massive enough to carve such gaps should be scattered violently by the force of gravity and ejected from the system early on in its development.

But a recent study led by Daniel Tamayo is the first to suggest the gaps are evidence of planetary formation because the gaps are separated by amounts consistent with what’s called a special ‘resonant configuration.’ In other words, these planets avoid violent collisions with each other by having specific orbital periods where they miss each other, similar to how Pluto has avoided Neptune for billions of years despite the two orbits crossing one another.

The HL Tau system is less than a million years old, about 17.9 billion kilometres in radius and resides 450 light years from Earth in the constellation Taurus.