Nasa's newest planet-hunting spacecraft is poised for an evening launch from Cape Canaveral, Florida.
The Tess satellite will scan almost the entire sky, staring at the brightest, closest stars in an effort to find any planets that might be encircling them.
The mysterious worlds beyond our solar system, called exoplanets, could harbour life.
Scientists expect Tess to discover thousands of rocky and icy planets and gas giants, maybe even water worlds and places defying imagination - possibly even a twin Earth.
Bigger and more powerful observatories of the future will scrutinise these prime candidates for potential signs of life.
A SpaceX rocket is scheduled to blast off with Tess at 6:32pm local time. The name Tess is short for Transiting Exoplanet Survey Satellite.
This evening, we will launch our latest planet hunter, @NASA_TESS, for a two-year mission to search the skies for planets outside our solar system. Starting at 1pm ET, our experts will answer your questions during a Science @reddit_AMA: https://t.co/oV4MP2kAg0 pic.twitter.com/LTcgNwTuxc— NASA (@NASA) April 16, 2018