Over the past two decades, thousands of planets have been found that are orbiting stars other than the Sun. They are called exoplanets, and most were discovered using data from the now retired Kepler space telescope. And thanks to the work of a graduate student from the University of British Columbia, those same data were used to find even more.
By searching through the entire collection of Kepler data, graduate student Michelle Kunimoto was able to identify a total of 17 candidate exoplanets that had never previously been discovered, including one located in the habitable zone.
Her work was published in The Astronomical Journal.
How many planets are still hiding in the data?
The original goal of the Kepler space telescope was to find planets outside our Solar System through use of the transit method, which allows astronomers to detect the presence of a planet when it passes in front of its parent star and temporarily dims the star’s light. And although Kepler officially retired in late 2018, there’s still a lot that can be learned from the rich data it captured.
The original data analysis program carried out by the Kepler team led to the discovery of more than 2,000 planets. However, follow-up analyses carried out by independent teams have shown that there are hundreds of planets that the original analysis missed.
The reason for this is that different algorithms used to search the data may be better suited to detecting different types of planetary systems, or recognizing false positives like companion stars or noise in the data that may be masquerading as candidate planets. Teams from around the world — including citizen scientists — have used unique methods to find new planets long after Kepler’s original mission ended.
Kunimoto and her collaborators used an algorithm and data analysis pipeline that was different from previous searches through the data, and particularly well-suited to finding multiplanet systems — that is, stars that host multiple planets. They also used different requirements than the Kepler team for how noisy the data could be, which allowed them to dig deeper into the data and identify planets that the Kepler team missed.
Whole new worlds
Kunimoto searched nearly 200,000 stars total, and initially detected over 100,000 signals. However, many of these were false positives, and she had to develop a sophisticated vetting routine that would allow her to distinguish these thousands of false alarms from genuine planets. For example, one criterion Kunimoto used was that the signal had to be seen at least three times. This allowed her to significantly reduce the number of signals detected, paring it down from over 100,000 to just 4000 potential planets.
Of the nearly 4,000 candidate planets Kunimoto found in the data, many had previously been identified and confirmed by the Kepler team. However, a total of 17 planets candidates had never before been seen — by the original Kepler analysis, or by any other teams.
“This is a big discovery and definitely one that I’m […] excited about,” said Kunimoto.
Perhaps most exciting is the fact that one of the 17 planets Kunimoto identified is a potentially-rocky super-Earth located in its parent star’s habitable zone — the range of distances away from the parent star where liquid water could exist on the surface of a planet. Very few planets similar to this one have been discovered previously, which makes Kunimoto’s discovery especially important for the search for life on other worlds.
“[T]his is a really exciting find,” Kunimoto explained, “since there have only been 15 small, confirmed planets in the Habitable Zone found by Kepler so far.”
In the future, Kunimoto plans to apply her data analysis routine to data from the K2 and TESS missions. And with any luck, it’ll only be a matter of time before the number of known exoplanets becomes even larger.