Years after NASA’s Kepler Space Telescope was retired from its Earth-sized planet-hunting duties, the data it gathered is still providing astronomers a chance to discover new planets. From the Kepler mission alone, a total of 4,776 candidates and confirmed planets are reported. University of British Columbia (UBC) PhD student Michelle Kunimoto has just added another 17 to this number.
As described in a paper published in The Astronomical Journal, Kunimoto conducted an independent search of all ∼200,000 stars observed in the initial four-year Kepler mission, to find evidence of planets “transiting” across the stars.
"Every time a planet passes in front of a star, it blocks a portion of that star's light and causes a temporary decrease in the star's brightness," Kunimoto said in a statement. "By finding these dips, known as transits, you can start to piece together information about the planet, such as its size and how long it takes to orbit."
Using the same three-transit minimum detection criteria as the Kepler team, Kunimoto discovered 17 new planetary candidates. Amongst these was the officially named KIC-7340288 b planet. At around 1.5 times the size of Earth, this planet is small enough to be considered rocky, as opposed to gaseous like the outer planets of the Solar System. Furthermore, it also lies within the habitable zone of its star, where the planet’s surface temperatures could allow liquid water to form.
"This planet is about 1,000 light-years away, so we're not getting there anytime soon!" Kunimoto exclaimed. "But this is a really exciting find, since there have only been 15 small, confirmed planets in the Habitable Zone found in Kepler data so far."
With an orbital period of only 142.5 days, the planet is located 0.444 Astronomical Units (1 AU is the distance between Earth and our Sun) from its star, around the same distance as Mercury is from the Sun. However, the planet receives about a third of the light Earth gets from the Sun.
The other 16 planets in this new discovery range in size from around two-thirds the size of Earth, one of the smallest planets found from Kepler so far, up to eight times the size of Earth. KIC-11350118 c, the smallest planet discovered in Kunimoto’s search, is actually associated with a known system, called KOI-4509. Already detected around the star is an Earth-sized planet with an orbital period of 12 days.
Kunimoto’s discovery was also not her first, having previously found four planets during her undergraduate degree. In future research Kunimoto and her colleagues hope to carry out independent searches of data from other missions, such as Keplerʼs follow-up K2, and the more recent Transiting Exoplanet Survey Satellite. This will contribute to their other work in calculating occurrence rate statistics of particular planets.
"We'll be estimating how many planets are expected for stars with different temperatures," Jaymie Matthews, UBC professor and Kunimoto's PhD supervisor, added. "A particularly important result will be finding a terrestrial Habitable Zone planet occurrence rate. How many Earth-like planets are there? Stay tuned."