The astronomical world was abuzz late last year when a spectacular new image taken with the Atacama Large Millimeter/submillimeter Array (ALMA) was released. It appeared to show very clear gaps in the disk of dust surrounding the star HL Tau. Some scientists pointed to this as evidence of early planetary formation, but others questioned how the supposed configuration could be stable. Now a team led by Daniel Tamayo at the University of Toronto says not only is it plausible this image shows very early planetary formation, it’s actually quite a good fit.

HL Tau is a very young star possibly less than 100,000 years old, but likely closer to 1 million. It is positioned about 450 light years from Earth in the constellation Taurus. The ALMA image taken in October 2014 was actually a calibration image used to test the array in its highest power configuration. They just didn’t expect the image of HL Tau would be so much better than previous observations.

Tamayo, like other scientists, was originally skeptical that the image of HL Tau captured by ALMA could show planets. While we know that large planets would probably carve out gaps in the protoplanetary dust cloud, these gaps are awfully close together. In our solar system, the large gas giants are far enough apart in their orbits that they aren’t perturbed by each other’s gravity.

Tamayo’s first simulation of HL Tau with Saturn-sized reference planets (above) predicted violent interactions that ejected planets and drastically altered orbits. In short, it doesn’t match the image. Then he modeled the system with a “resonant” configuration, and it all started to make sense.

In a resonant system, two planets might have orbits that are very close together (or even crossing), but they orbit at a rate such that they are never in the same region at the same time. This is how Pluto and Neptune, which have crossing orbits, have managed to avoid direct interaction with each other for billions of years. Tamayo’s HL Tau resonant model (seen below) is a very good match for what we see with ALMA. Even if all five planets are the size of Saturn, they could have remained stable in the theorized configuration.

So the gaps visible in the ALMA image are explainable by planets, according to Tamayo’s team. However, there’s one big caveat. The resonant model takes into account the gravitational influence of the disk of dust and gas. Once that disk has dissipated, it’s likely the system wouldn’t remain resonant and will eventually fly apart as in the non-resonant simulation above. In fact, many exoplanetary system seem to have highly eccentric orbits similar to that simulation. This indicates many solar systems could have experienced a similarly violent early life. Our solar system might have gotten off easy.