What you need to know about TESS, NASA’s new planet-spotting satellite

NASA is gearing up to launch a satellite into space that'll be better than any other at finding Earth-like planets.

TESS, short for Transiting Exoplanet Survey System, will travel aboard a SpaceX Falcon 9 rocket, scheduled for launch Monday at 6:32 p.m. local time from Cape Canaveral, Florida. The satellite is designed to scour the night sky for planets outside of our solar system — exoplanets, as scientists call them — with a particular interest in those similar enough to Earth that they just might be able to sustain life too. NASA hopes to find around 20,000 exoplanets, 50 of which will be about the size of Earth.

TESS is set to replace the first planet-searching satellite, the Kepler space telescope, which NASA sent it into orbit in 2009 and has begun to run out of fuel.

“The point of Kepler was to carry out a census: What are the statistics of the exoplanet population?” Stephen Rinehart, the project scientist for TESS at NASA, told VICE News.

So while Kepler’s goal was to figure out whether planets were common — and, it turns out, they are — Tess has a more specific purpose. With TESS, “we can start talking about what individual planets are like rather than as parts of broad demographic groups, or as statistics,” Rinehart said.

TESS is much better suited, in other words, for figuring out whether a planet the satellite identifies outside of the Milky Way is like Earth — and therefore could, in theory, sustain life.

TESS will still be looking for planets the same way Kepler did: It’ll track the path of planets as they cross between Earth and the stars they orbit, which is called a transit. When a planet crosses a star, the star becomes briefly dimmer.

By watching these planets’ orbits closely, NASA hopes to figure out how dense the planets are. As the planets orbit around their sun, they’ll exert some gravitational force on the star. By observing those stars closely, scientists can spot them wobbling as the planets circle — and based on how much they wobble, scientists can estimate the density of the planet, which gives them a sense of what the planet’s made of.

Earth-like planets are rocky, whereas Jupiter-like gaseous giants have a mass that’s more diffuse.

“If I know the density, then I can talk about whether it’s a gas-like planet like Jupiter or a waterworld, or something really weird and exotic,” Rinehart said.

TESS will also be pioneering a new type of Earth orbit, one that’ll limit the amount of fuel it needs to stay up and running. George Ricker, the principal researcher on the TESS mission, calls it the "Goldilocks orbit": It’s just the right distance between the Earth and the moon.

After it launches, TESS will do a moon fly-by before finding the elliptical orbit from which it will observe the skies. Once in its standard orbit, the satellite will circle the earth every 13.7 days; when it’s closest to the Earth, it’ll be 67,000 miles above us.

SpaceX has prepped for the launch: TESS is packed away in the Falcon 9 payload. The company successfully ran a test-fire on Wednesday, which sent the rocket up in the air above the pad and landed it back down safely.

After sending TESS into space, the company hopes to land the Falcon 9 rocket on a drone ship landing pad in the ocean. That went OK for the Falcon Heavy rocket: SpaceX landed two out of three of the Falcon Heavy’s boosters during a test launch in February. The third, which attempted a landing on a drone ship, exploded.

Cover image: This undated photo made available by NASA shows technicians with the Transiting Exoplanet Survey Satellite (TESS). (NASA via AP)