Star-grazers

Ansdell and her team of astrophysicists attempted to decipher what these little dippers are, and their results are published in Monthly Notices of the Royal Astronomical Society. After ruling out instrumentation errors or data processing artefacts, a detailed analysis of the shapes of the dips suggested that the little dippers are likely caused by star-grazing comets, analogous to comet ISON, as well as the 2011 sun-grazing comet, C/2011 W3 Lovejoy.

“If you look at the shape of the dips, one side is steep,” says Ansdell. “When you see a steep ingress and then a slow egress, it indicates that there is some sort of trailing tail. When you see the opposite, there’s potentially a leading tail.”

These probable exocomet transiting events are difficult for computer algorithms to detect because their dips aren’t periodic and they don’t have the standard ‘exoplanet’ dip shape. Jacobs, a self-proclaimed ‘treasure hunter for light curves’, is now an expert at scanning light curves by eye and analyzing the data of a star in a few minutes.

“You can see things that computers aren’t trained to see,” says Jacobs. He signed up to sort through the data and was familiar with the shape of the dip caused by exocomets. “I had [previously] flagged some exocomets in the Kepler field,” he says, “We kind of knew what they looked liked.” It was only on the second time scanning through the 20,000 stars of K2 data that he noticed the two ‘little dippers’.”

The presence of exocomets around these older stars, where objects should be on more stable orbits unless perturbed by something, means that they are potentially harbouring outer gas giant planets like Jupiter. Sun-grazing comets in our Solar System are the result of gravity perturbations by the gas giants in the outer Solar System flinging the comets onto eccentric orbits that graze the Sun (and sometimes even fall into the Sun, where they are vaporized). However, detecting outer planets around other stars is difficult because of the long timescales of their orbits and the requirement for multiple periodic detections to confirm their existence.

However, the presence of star-grazing exocomets could indicate the presence of Jupiter-like exoplanets in these systems. “If these are analogous, then that would indicate that there is a Jupiter-like planet in their outer regions,” says Ansdell.