NASA’s Kepler telescope has discovered an Earth-like exoplanet orbiting a Sun-like star 1,400 light-years away, in the constellation Cygnus. The discovery, announced on Thursday night (IST), marks the finding of an exoplanet that most closely resembles Earth among all the Earth-like planets found yet.
When astronomers say Earth-like, they usually mean in terms of size. Kepler-452b is 60% larger than Earth, has a diameter of about 14,000 km – 10% more than Earth’s is 12,700 km – and is 10% brighter, too. But more importantly, like Earth, Kepler-452b is in its star’s habitable zone – the distance away from the star where the conditions are just right for liquid water to form on the surface.
The press statement released for the occasion also said, “While its mass and composition are not yet determined, previous research suggests that planets the size of Kepler-452b have a good chance of being rocky.” A rocky planet is better suited to harbour life because it could have a hot core that could keep the planet warm from within, as well as have minerals that could make for nutrients.
However, the optimism overlooks previous research that has suggested that planets that are as big as Kepler-452b are seldom dense enough to be rocky, and tend toward being gassy like Jupiter. In fact, a statistical analysis conducted in 2014 showed that “the majority of 1.6 R⊕ planets are too low density” to be entirely rocky, where R⊕ stands for Earth’s radius. Kepler-452b’s radius is 1.63-times Earth’s.
Nonetheless, many of Kepler-452b’s features are tantalisingly similar to Earth’s and don’t discourage the admittedly distant hope, but hope nonetheless, that alien life might exist on it. Its revolution around its host star takes 385 Earth-days and, more favourably, it is 6 billion years old. That means it’s around for 1.5 billion years more than Earth – 1.5 billion more years in which life could’ve taken its time to form.
Speaking at the presser, Jon Jenkins, who led the data analysis team that helped find the planet, said “We can think of Kepler-452b as an older, bigger cousin to Earth, providing an opportunity to understand and reflect upon Earth’s evolving environment.”
Kepler-452b also joins a small but expanding coterie of 31 exoplanets that are very similar to Earth and are orbiting in habitable zones around their stars. And before its newly acquired distinction as the exoplanet most similar to Earth, Kepler-452b was preceded by Kepler-186f. The latter is 500 light-years away and not much bigger than Earth. However, the star it orbits is a red-dwarf, which emits much less energy than our Sun, a G2-class star, implying a cooler planetary surface.
With the find, the total number of exoplanet candidates spotted by the Kepler space telescope stands at 4,696 and the confirmed tally at 1,030. Named for the German mathematician Johannes Kepler, the telescope was launched in March 2009. It spots exoplanets when they pass against the face of their host stars, leading to a characteristic dip in brightness.
From 2012 until early 2013, a part of the telescope’s stabilisation system failed, forcing a reorientation of the mission’s goals by November that year to look for exoplanets only along the plane of Earth’s orbit around the Sun and those orbiting red-dwarf stars.