NASA's planet-hunting Kepler space telescope has woken up from yet another slumber and begun collecting science data again, the US space agency has said.
It began collecting science data on August 29 for its 19th observation campaign.
"After being roused from sleep mode, the spacecraft's configuration has been modified due to unusual behaviour exhibited by one of the thrusters," NASA said in a statement on Thursday.
"Preliminary indications are that the telescope's pointing performance may be somewhat degraded. It remains unclear how much fuel remains; NASA continues to monitor the health and performance of the spacecraft," it added.
In July, NASA placed the spacecraft, with 2,650 confirmed planets, in a hibernation-like state in preparation to download the science data collected in its latest observation campaign.
On August 3, Kepler successfully began downloading its store of science data from its Campaign 18 and then went into sleep mode after downloading Campaign 18 data on August 24.
Launched in 2009, the Kepler mission is specifically designed to survey our region of the Milky Way galaxy to discover hundreds of Earth-sized and smaller planets in or near the habitable zone and determine the fraction of the hundreds of billions of stars in our galaxy that might have such planets.
Among other findings, recently 24 new planet discoveries were made using data from the 10th observation campaign, adding to the spacecraft's growing bounty of 2,650 confirmed planets.
The Kepler space telescope, which is now 94 million miles away from Earth, has survived many potential knock-outs during its nine years in flight, from mechanical failures to being blasted by cosmic rays.
NASA in April launched another planet-hunting spacecraft, the Transiting Exoplanet Survey Satellite (Tess).
After the Kepler space telescope, Tess is the second spacecraft which will search for planets outside our solar system, including those that could support life.
NASA announced that Kepler, its alien world-hunting spacecraft, has discovered two previously unknown planetary systems including three super-Earth size planets in the much-coveted "habitable zone" capable of sustaining life.
This diagram compares the planets of our solar system to Kepler-62, one of the newly found systems. The five-planet system is a relatively close 1,200 light-years from Earth, in the constellation Lyra. The five planets of Kepler-62 orbit a 7-billion-year-old star classified as a K2 dwarf -- just two-thirds the size of our sun -- and only one-fifth as bright.
Much like our solar system, Kepler-62 is home to two habitable zone worlds, Kepler-62f and Kepler-62e. Kepler-62f orbits every 267 days and is only 40 percent larger than Earth, making it the smallest exoplanet known in the habitable zone of another star. The other habitable zone planet, Kepler-62e, orbits every 122 days and is roughly 60 percent larger than Earth.
The two habitable zone worlds orbiting Kepler-62 have three interior companions, two larger than the size of Earth and one about the size of Mars. Kepler-62b, Kepler-62c, and Kepler-62d orbit every five, 12, and 18 days, respectively, making them very hot and inhospitable for life as we know it.
This illustration from NASA depicts the relative sizes of the Kepler habitable zone planets, showing from left to right, Kepler-22b, Kepler-69c, Kepler-62e, Kepler-62f, and Earth.
This artist's concept depicts Kepler-62f, a super-Earth size planet in the habitable zone of a star smaller and cooler than the sun, located about 1,200 light-years from Earth in the constellation Lyra.
This graphic shows the planets of our inner solar system as compared with the Kepler-69 system, a two-planet system about 2,700 light-years from Earth in the constellation Cygnus. The two planets of Kepler-69 orbit a star that belongs to the same class as our sun, a G-type star.
Kepler-69c orbits a sun-like star every 242 days, while its companion planet, Kepler-69b, is just over twice the size of Earth and whizzes around its star once every 13 days.
Kepler-62f, shown here in an artist's illustration, is a super-Earth size planet in the habitable zone of a star smaller and cooler than the sun. It's located a relatively close 1,200 light-years from Earth in the constellation Lyra.
The smallest of the recently discovered habitable zone planets, Kepler-62f is about 40 percent larger than Earth in size, orbiting its host star every 267 days. NASA stresses that although we do know the size of the planet, its mass and composition are unknown.
Much like our solar system, Kepler-62 is home to two habitable zone worlds. The small shining object seen to the right of Kepler-62f is Kepler-62e. Orbiting on the inner edge of the habitable zone, Kepler-62e is about 60 percent larger than Earth.
An artist's illustration shows Kepler-62e, a super-Earth size planet about 1,200 light-years away which orbits its host star every 122 days and is about 60 percent larger than Earth.
Kepler-69c, seen here in an illustration of what the habitable zone planet might look like, is a super-Earth size planet orbiting a star much like our sun, about 2,700 light-years from Earth in the constellation Cygnus.