A NASA spacecraft blasted off on Wednesday, April 18th, 2018, to seek out Earth-like worlds and search for clues to alien life.

The Transiting Exoplanet Survey Satellite, or TESS, will search 200,000 of the closest, brightest stars for previously undiscovered planets. Scientists expect to find thousands including hundreds of rocky worlds comparable in size to our own Earth.

TESS, which is about the size of a refrigerator, has four wide-field digital cameras on board. Together, they will continuously scan large strips of sky, checking each sector for at least 27 days at a time.

The robotic spacecraft lifted off on a SpaceX Falcon 9 rocket from Cape Canaveral, Florida, during a launch window that opens at 6.32pm local time on April 16th. It went into orbit around the Earth, and will spend two years watching almost the entire sky, covering a field of more than 20 million stars.

The onboard cameras are designed to monitor nearby stars for tiny fades in their light caused by planets passing in front of them during their orbits.

TESS will follow in the footsteps of NASA’s Kepler spacecraft which has discovered thousands of exoplanets since it was launched in March, 2009. TESS will focus on stars less than 300 light-years away and up to a hundred times brighter than Kepler’s targets.

The mission’s project scientist Stephen Rinehart, of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said: “TESS is opening a door for a whole new kind of study.

“We’re going to be able to study individual planets and start talking about the differences between planets. The targets TESS finds are going to be fantastic subjects for research for decades to come. It’s the beginning of a new era of exoplanet research.”

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Scientists from the Massachusetts Institute of Technology (MIT) aim to weigh up at least 50 small planets that are less than four times the diameter of the Earth, using TESS data.

TESS’s thousands of discoveries of likely exoplanets will be followed up by observations from ground-based telescopes. These will measure each planet’s size, mass and the time it takes to orbit its star.

A new generation of powerful telescopes, including NASA’s Hubble replacement the James Webb Space Telescope, and the European Extremely Large Telescope in Chile, will be able to study the closer planets’ atmospheres for signs of life including water.

MIT’s Professor Sara Seager, deputy director of science for TESS, told Skymania: “When a planet goes in front of its star, the starlight shines through the atmosphere, and believe it or not, we are able to pick up the atmosphere features of the planet as imprinted on the star.

“Astronomers take a spectrum of the star by itself, when the planet is not transiting, and then one during transit and essentially subtract.”

We asked Professor Seager what might be clues to a planet being habitable. She told us: “Well, everyone pretty much agrees that water vapour on a small rocky planet is an indicator of habitability,because all life as we know it needs liquid water.

“On Earth, microbes have created all sorts of chemicals. Oxygen is number one to look for, then we have other small gases like methane, nitrous oxide, maybe hydrogen sulphide, and then we have a whole host of others.

“On the other hand we want to be prepared for the unexpected. We don’t want to miss anything just because we weren’t smart enough.”

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