On a cold, clear night in January, MIT astrophysicist George Ricker and his students stepped onto a rooftop on campus and aimed a giant camera at the highest point in the sky.

That camera, an engineering model of the four being launched with Nasa ‘s Tess mission, revealed a night thick with stars.

“In two seconds you could see things that were a hundred thousand to a million times fainter than what you could see with your naked eye,” said Ricker, the mission’s principal investigator.

The test offered a small taste of what TESS, the Transiting Exoplanet Survey Satellite, will discover after it launches as early as Monday afternoon. The spacecraft will scan almost all of the sky for neighboring stars, searching for the dips in their brightness that signal the presence of a planet.

The goal: To find planets that are smaller than Neptune, with a radius less than about four times that of Earth. Scientists will then use other telescopes to measure the masses of 50 of them.

A few worlds TESS finds may be small, rocky bodies like Earth. And a few of those might, just possibly, be habitable places for life as we know it.

“It’s very exciting,” Ricker said. “We’re getting a chance to potentially answer a question that humanity’s always been interested in: What’s in the sky? And are there other beings, other places like Earth?”

NASA has employed space-based telescopes to find answers to these questions for decades.

Hubble and Spitzer have spent part of their missions searching for exoplanets, which are planets that orbit stars other than the sun.

Kepler was a full-time planet-hunter, and it revolutionized astronomers’ understanding of exoplanets. Launched in 2009, it was particularly interested in finding Earth-sized planets orbiting sun-like stars at a distance where water on the surface could be stable in liquid form — the…