Nasa is about to make a major step in its hunt for other worlds.
The agency is about to launch a satellite to detect more Earth-like worlds that are orbiting around stars far beyond our solar system.
TESS – the Transit Exoplanet Survey Satellite – will launch on a SpaceX rocket in Florida, carrying with it the hopes of scientists looking to find yet more exoplanets and with it the potential for discovering life.
The agency hopes that the satellite can spot thousands of new planetary candidates. Scientists can then add them to their shortlist of places that could harbour life – using different technology to sniff out whether they have extraterrestrial life.
The rocket was set to lift off from Cape Canaveral Air Force Station at 6:32 p.m. EDT, starting the clock on a two-year, $337 million mission in one of astronomy's newest fields of exploration.
NASA's latest space-bound astrophysics instrument will be carried aloft by a Falcon 9 rocket from the fleet of billionaire entrepreneur Elon Musk's private launch service, Space Exploration Technologies, or SpaceX.
TESS is designed to build on the work of its predecessor, the Kepler space telescope, which discovered the bulk of some 3,700 exoplanets documented by astronomers during the past 20 years and is about to run out of fuel.
NASA expects to pinpoint thousands more previously unknown worlds, perhaps hundreds of them Earth-sized or "super-Earth"-sized -- no larger than twice as big as our home planet.
Those are believed the most likely to feature rocky surfaces or oceans, and are thus considered the best candidates for life to evolve, as opposed to gas giants like Jupiter or Neptune.
Astronomers said they hope TESS will help catalog about 100 more rocky exoplanets for further study.
Roughly the size of a refrigerator with solar-panel wings and equipped with four special cameras, TESS will take about 60 days to reach a highly elliptical, first-of-a-kind orbit looping it between Earth and the moon every two and a half weeks.
Like Kepler, TESS will use a detection method called transit photometry, which looks for periodic, repetitive dips in the visible light from stars caused by planets passing, or transiting, in front of them.
But unlike Kepler, which fixed its gaze on a range of stars within a tiny fraction of the sky, TESS will scan a broader swath of the heavens to focus on 200,000 pre-selected stars that are closer and thus among the brightest as seen from Earth.
That makes them better suited for sensitive follow-up analysis for the exoplanet candidates TESS locates.
The TESS survey will concentrate on stars called red dwarfs, smaller, cooler and longer-lived than our sun. Red dwarfs also have a high propensity for Earth-sized, presumably rocky planets, making them potentially fertile ground for closer examination.
And because the planets circling them are bigger relative to the size of the star, and orbit at a closer distance, the slight disruptions of visible light from their transits are more pronounced, scientists said.
Measuring blips in starlight can determine the exoplanet's size and orbital path. Further observations from ground telescopes can supply its mass and ultimately the planet's density and composition -- whether largely solid, liquid or gas.
TESS itself will not detect life beyond Earth. But its most promising discoveries will undergo closer scrutiny by a future generation of larger, more powerful telescopes that will search for telltale signs of water and atmospheric gases that on Earth are indicators of life.
Additional reporting by agencies