Image of protostar suggests planets form earlier

In early November, astronomers using the Atacama Large Millimeter Array telescope in Chile released an astonishing image.

This is an image of a protoplanetary disk – the ring of gas and dust that astronomers think surrounds most forming stars (also called protostars). This is amazing for a few reasons. It is the first image to show the detailed concentric rings indicative of planet formation in a protoplanetary disk. This visualization of real-time planet formation looks startlingly like artistic renderings of protoplanetary disks often used in interpreting fuzzy astronomical images.

More interesting, perhaps, is that the protostar HL Taurus (often referred to as HL Tau) is less than 1 million years old – too young, scientists thought, to have a forming system of planets. That there are orbiting bodies well on their way to planethood implies that planets can form far earlier than originally thought. This earlier history for planet formation means that initial thinking on the chemistry and physics that drive planet formation will need to be reconsidered.

HL Tau is a sun-like protostar about 450 light-years from Earth in the constellation Taurus. But being in the pre-star phase of its evolution and surrounded by a large disk of gas and dust renders it only visible at infrared wavelengths. Being similar in mass and type to our sun, it is one of the best analogues for the early solar system, and astronomers study the chemistry of the gas and dust surrounding this and other protostars like it to better understand how our own planetary system evolved.

This image is particularly fascinating for me, since my colleagues and I recently submitted for publication to The Astrophysical Journal one of the most detailed chemical analyses of HL Tau – taken with the powerful Very Large Telescope, also in Chile. Our analyses of our very high-resolution observations of carbon monoxide absorption lines in the gas surrounding this object revealed patterns in the oxygen isotopes that are consistent with the as-yet-unexplained patterns seen in the most primitive meteorites. This hints at early solar system processes that could have contributed to this unusual chemistry.

Now it seems that what we once considered primitive, pre-planetary processes could in fact be affecting planets directly as they form. These revelations will likely change how we interpret our astronomical observations and how we understand the early chemistry affecting planet formation, organic compounds and, eventually, life.