The excitement among the participants who gathered for the launch of TESS, NASA's youngest celestial observer, on April 18 was understandable. Equipped with four telescopes, the satellite will orbit for two years and photograph more than 200,000 stars, dozens within 10 light years of Earth. Sara Seager, Deputy Science Director of the Mission, was watching with her family from Cape Canaveral that day, knowing exactly what was at stake. "It is fair to say that TESS will find a whole range of planets in the habitable zone," she says. In plain English: We could only find one planet that will house life until 2020.
TESS stands for Transiting Exoplanet Survey Satellite, and its mission is to identify planets orbiting the brightest stars in our neighborhood of the universe. When the orbit of a planet lies between its sun and the cameras of TESS, the star's light is momentarily dimmed, just as an airplane blocks a bit of sunlight as it passes. Back on Earth, astronomers reading the TESS data know that these small fluctuations signal the presence of a planet. They will then be able to explore more powerful instruments ̵
The mission will not capture every planet. Those with orbits longer than a month or not aligned will not be dimming their stars for the cameras. But if intelligent life – or any life – lives nearby, this mission will likely find it. "We'll know about their planets, that's for sure," says Hertz.
Astronomers have a potentially habitable checklist. "We want to find small, stony planets," says Seager, "in the Goldilocks zone of a star." This zone is exactly what it sounds like: not too big and not too small and not too close or too far from the sun. Planetary hunters like Seager are particularly interested in those two or three times the size of the Earth called super-Earths. These could be water worlds of which half or more of their mass is water, or they could be rocky worlds with swollen atmospheres of hydrogen instead of carbon dioxide and nitrogen. As Seager, who has developed a method for exploring distant planetary atmospheres, our concept of what constitutes a planet based on our earthly reference could be the exception rather than the rule. "We do not have a simple story," she says, "for what could be the most common type of planet in our galaxy."
To date, astronomers know about 3,472 exoplanets, 42 in the Goldilocks Zone. Seager, Hertz and many other astronomers hope that TESS will extend this last number. At the moment, they have to wait at least three months for the first TESS announcement. But they are hopeful. "I predict that TESS will be quite significant for the planets we will study over the next decade," says Hertz.