spaceSpace and Physics

Scientists Brush Off Concerns About NASA's Next Planet-Hunting Telescope


Jonathan O'Callaghan

Senior Staff Writer

TESS will launch on March 20, 2017 at the earliest. NASA/JPL-Caltech

An upcoming NASA mission that will look for new exoplanets has a bit of an issue with its cameras – but scientists are hopeful it won’t be a major cause for concern.

The mission is called the Transiting Exoplanet Survey Satellite (TESS), which is going to launch on a Falcon 9 rocket no earlier than March 20 this year. Boasting four CCD cameras, the telescope will find planets via the transit method, noticing the dip in light as they pass in front of their host stars.


However, in July last year NASA revealed the focus of the four cameras will “drift” slightly when the spacecraft cools to its operating temperature in space. This out-of-focus area only affects the edge of images, but it’s still not ideal.

In the 231st meeting of the American Astronomical Society in Washington this week, scientists involved in the mission delved more into the problem, saying they did not expect it to affect the mission. The nature of TESS’s mission, using photometry to measure the light of distant stars, means that the focus is not too important.

“This is a photometry mission, not an imaging mission,” George Ricker, principal investigator for TESS, said at the AAS meeting as reported by SpaceNews.

“What this means is that it’s not important to have a sharp focus across the entire field of view. This was never part of the design. But it is important that the focus be stable, and that’s what we’ve been able to establish.”

Most of the known exoplanets so far have been found by NASA's Kepler telescope. NASA/JPL-Caltech

The spacecraft is expected to find about 5,000 exoplanets, about 50 of which should be similar in size to Earth. Its discoveries will add to those already made by NASA’s Kepler telescope, and provide new targets of interest for upcoming missions like the James Webb Space Telescope (JWST).

TESS will be placed in a 13.7-day orbit around Earth, one that keeps it not only stable but allows a high data transfer rate to the ground. This wide orbit also means it won’t need to use its on-board thrusters much, and the mission could last for decades, helping us greatly increase the number of known exoplanets.

This isn’t the only telescope that has had a focusing issue. When the Hubble Space Telescope was launched in 1990, mission controllers were horrified to discover that its primary mirror had been polished to the wrong shape, causing its images to appear blurry. It wasn’t until a Space Shuttle servicing mission in 1993 that the issue was fixed.

Fortunately, it looks like TESS’s problem won't cause any similar issues. Still, given the excitement around exoplanets at the moment, you can understand the concern for what is set to be the next great planet hunter.


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