NASA's planet-hunting satellite TESS launches

Over 60 days, TESS will establish an orbit around Earth and test its instruments. Then, the two-year mission will officially begin.

TESS will pick up the search for exoplanets as the Kepler Space Telescope runs out of fuel.

Kepler, which has discovered more than 4,500 potential planets and confirmed exoplanets, launched in 2009. After mechanical failure in 2013, it entered a new phase of campaigns to survey other areas of the sky for exoplanets, called the K2 mission. This enabled researchers to discover even more exoplanets, understand the evolution of stars and gain insight about supernovae and black holes.

Soon, Kepler's mission will end, and it will be abandoned in space, orbiting the sun and never getting any closer to Earth than the moon.

TESS will survey an area 400 times larger than what Kepler observed. This includes 200,000 of the brightest nearby stars. Over the course of two years, the four wide-field cameras on board will stare at different sectors of the sky for days at a time.

TESS will begin by looking at the Southern Hemisphere sky for the first year and move to the Northern Hemisphere in the second year. It can accomplish this lofty goal by dividing the sky into 13 sections and looking at each one for 27 days before moving on to the next.

The satellite itself is not much bigger than a refrigerator. The cameras sit on top, beneath a cone that will protect them from radiation.

TESS will look for exoplanets using the transit method, observing slight dips in the brightness of stars as planets pass in front of them. Bright stars allow for easier followup study through ground- and space-based telescopes.

"TESS is helping us explore our place in the universe," said Paul Hertz, Astrophysics Division director at NASA Headquarters. "Until 20 years ago, we didn't know of any planets beyond our own solar system. We've expanded our understanding of our place in the universe, and TESS will help us keep expanding."

The cameras can detect light across a broad range of wavelengths, up to infrared. This means TESS will be able to look at many nearby small, cool red dwarf stars and see whether there are exoplanets around them. Red dwarf stars have been found to host exoplanets within the habitable zone, and many astronomers believe they could be the best candidate for hosting Earth-size exoplanets with conditions suitable for life.

NASA expects TESS to allow for the cataloging of more than 1,500 exoplanets, but it has the potential to find thousands. Of these, officials anticipate, 300 will be Earth-size exoplanets or double-Earth-size Super Earths. Those could be the best candidates for supporting life outside our solar system. Like Earth, they are small, rocky and usually within the habitable zone of their stars, meaning liquid water can exist on their surface.

"One of the biggest questions in exoplanet exploration is: If an astronomer finds a planet in a star's habitable zone, will it be interesting from a biologist's point of view?" said George Ricker, TESS principal investigator at the Massachusetts Institute of Technology's Kavli Institute for Astrophysics and Space Research in Cambridge. "We expect TESS will discover a number of planets whose atmospheric compositions, which hold potential clues to the presence of life, could be precisely measured by future observers."

These exoplanets will be studied so that NASA can determine which are the best targets for missions like the James Webb Space Telescope. That telescope, whose launch was just pushed back to 2020, would be able to characterize the details and atmospheres of exoplanets in ways scientists have not been able to do.

"We learned from Kepler that there are more planets than stars in our sky, and now TESS will open our eyes to the variety of planets around some of the closest stars," Hertz said. "TESS will cast a wider net than ever before for enigmatic worlds whose properties can be probed by NASA's upcoming James Webb Space Telescope and other missions."

NASA believes that TESS will build on Kepler's momentum and open the study of exoplanets in unprecedented ways.

"TESS is opening a door for a whole new kind of study," said Stephen Rinehart, TESS project scientist at NASA's Goddard Space Flight Center. "We're going to be able 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. I don't think we know everything TESS is going to accomplish. To me, the most exciting part of any mission is the unexpected result, the one that nobody saw coming."

More than a decade ago, Massachusetts Institute of Technology scientists first proposed the idea of a mission like TESS. They have been instrumental in bringing the mission from idea to reality and will continue to be involved once the mission launches. A science team devoted to TESS at MIT aims to measure the masses of at least 50 small exoplanets that have a radius of less than four times that of Earth -- an ideal dimension that could suggest habitability.

"Mass is a defining planetary characteristic," said Sara Seager, TESS deputy director of science at MIT. "If you just know that a planet is twice the size of Earth, it could be a lot of things: a rocky world with a thin atmosphere, or what we call a 'mini-Neptune' -- a rocky world with a giant gas envelope, where it would be a huge greenhouse blanket, and there would be no life on the surface. So mass and size together give us an average planet density, which tells us a huge amount about what the planet is."

TESS Objects of Interest, an MIT-led effort, will look for objects in TESS' data that could be exoplanets and catalog them.

"TESS is kind of like a scout," said Natalia Guerrero, deputy manager of TESS Objects of Interest. "We're on this scenic tour of the whole sky, and in some ways we have no idea what we will see. It's like we're making a treasure map: Here are all these cool things. Now, go after them."

TESS data will also be publicly available so that anyone can download them and search for exoplanets. A data pipeline has been established so that TESS can fulfill its mission. It will collect about 27 gigabytes per day -- that's about 6,500 song files -- and send data back every two weeks.

NASA's Pleiades, an incredibly powerful supercomputer, will be able to keep up and process the 10 billion pixels over three to five days.

The more people that look through the data, the better, the scientists believe. This could be how planets that support life are found.

"There's no science that will tell us life is out there right now, except that small rocky planets appear to be incredibly common," Seager said. "They appear to be everywhere we look. So it's got to be there somewhere."