'Seventeen new planets, including one Earth-sized world discovered'

Astronomers have discovered 17 new planets, including a potentially habitable Earth-sized world, by combing through data gathered by NASA's Kepler space telescope which was launched in 2009, and retired in October 2018.

According to the researchers, including Michelle Kunimoto from the University of British Columbia in Canada, the Kepler satellite, over its original four-year mission, looked for planets, especially those lying in the potentially habitable "Goldilocks Zone" of their stars, where liquid water could exist on a rocky planet's surface.

The current findings, published in The Astronomical Journal, include one such rare planet named KIC-7340288 b.

This planet, the researchers said, is just one and a half times the size of the Earth -- small enough to be considered rocky, instead of gaseous like the giant planets of the Solar System, and in the habitable zone of its star.

"This planet is about a thousand light years away, so we're not getting there anytime soon!" said Kunimoto.

"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," she added.

The study noted that the planet has a year that is 142 and a half days long, orbiting its star at 0.444 Astronomical Units (AU, the distance between Earth and the Sun) -- just bigger than Mercury's orbit in our Solar System.

The planet gets about a third of the light that the Earth gets from the Sun, the scientists noted.

Of the other 16 new planets discovered, the researchers said, the smallest is only two-thirds the size of the Earth -- one of the smallest planets to be found with Kepler so far.

The remaining planets, they said, range in size up to eight times the size of the Earth.

In the current study Kunimoto used what is known as the "transit method" to look for the planets among the roughly 2,00,000 stars observed by the Kepler mission.

"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," she explained.

"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," Kunimoto added.

In addition to the new planets, the researchers were also able to observe thousands of known Kepler planets using the transit method, which they said will be used to reanalyse the exoplanet census as a whole.

"We'll be estimating how many planets are expected for stars with different temperatures," said Jaymie Matthews, another co-author of the study.