NASA's next-generation exoplanet hunter began its science mission this week. On July 25, the unmanned Transiting Exoplanet Survey Satellite (TESS) got to work on its two-year whole-sky survey to seek out planets outside our solar system by looking at the nearest and brightest stars for signs of changes in their brightness, indicating that a planet or other orbiting body is passing in front of them.

With the Kepler Space Telescope going into near hibernation as it reaches the end of its service life, TESS coming online couldn't have happened at a better time. Launched on April 18 this year from Cape Canaveral Air Force Station atop a SpaceX Falcon 9 rocket, TESS is not only the successor to the Kepler, but a distinct upgrade. Where Kepler only looked for planets in a limited band of the sky, TESS will examine 200,000 of the brightest stars in our galaxy spread over an area that is 400 times greater than that observed by Kepler.

Though TESS has begun to accumulate scientific data, it hasn't transmitted anything back to Earth yet. That's because the spacecraft is in a lunar resonant orbit, an elliptical orbit between 108,000 km (67,000 mi) and 375,000 km (233,000 mi) that sees the spacecraft circle the Earth every 13.7 days with an inclination of 37 degrees to the Moon's orbit.

It does this to make sure the spacecraft always remains 90 degrees out of phase with the Moon, so the latter's gravitational field can't disrupt TESS's trajectory for decades to come. In addition, this orbit will give TESS a clear view of the whole sky, allow it to maintain its temperature, and keeps it well out of the radioactive Van Allen belts. Unfortunately, it also means that TESS can only transmit back to mission control when it comes closest to Earth. Once it does so, space scientists can begin analyzing the data and identify planetary candidates.

"I'm thrilled that our new planet hunter mission is ready to start scouring our solar system's neighborhood for new worlds," says Paul Hertz, NASA Astrophysics division director. "Now that we know there are more planets than stars in our universe, I look forward to the strange, fantastic worlds we're bound to discover."

The animation below shows how TESS will conduct its survey.

Source: NASA