The Transiting Exoplanet Survey Satellite (TESS) will be able to scan about 90% of the sky.

• A. It will scan about 50% of the sky
• B. It will scan about 5% of the sky
• C. It will scan about 90% of the sky
• D. It will scan all of the sky

Answer: (C)

Sky coverage for a space telescope is limited by where it can safely point and how long it can observe. You can’t look too close to the Sun, and a finite mission lifetime means only so many sky regions can be observed. TESS uses four wide-angle cameras to sweep large swaths of the sky and cycles through new sectors as it orbits, gradually filling in the observable portions. Over about two years, this design yields coverage of most of the sky, with only a small fraction remaining inaccessible due to solar glare and geometry. That’s why about 90% is the best estimate for how much of the sky TESS can scan. The other options either underestimate the scope or imply complete sky coverage, which isn’t possible given the Sun’s glare and the mission’s time constraints.