NASA’s planet-hunter TESS catches a comet flying by on its first day on the job

NASA’s latest planet-hunting probe has beamed back a stunning sequence of images showing a comet in motion 48 million kilometers from Earth. Taken over the course of 17 hours on 25 July, the day the Transiting Exoplanet Survey Satellite (TESS) started science operations, these images helped demonstrate the satellite’s ability to collect a prolonged set of stable periodic images covering a broad region of the sky — critical factors in finding transiting planets orbiting nearby stars. Over the course of these tests, TESS took images of C/2018 N1, a comet discovered by NASA’s **Near-Earth Object Wide-field Infrared Survey Explorer** (NEOWISE) satellite on 29 June. The comet, located about 48 million kilometres from Earth in the southern constellation **Piscis Austrinus** , is seen to move across the frame from right to left as it orbits the Sun. The comet’s tail, which consists of gases carried away from the comet by an outflow from the Sun called the solar wind, extends to the top of the frame and gradually pivots as the comet glides across the field of view.

In addition to the comet, the images showed a treasure trove of other astronomical activity. The stars appear to shift between white and black as a result of image processing. The shift also highlights variable stars - which change brightness either as a result of pulsation, rapid rotation, or by eclipsing binary neighbours. Asteroids in our solar system appear as small white dots moving across the field of view. Stray light from Mars, which is located outside the frame, can be seen as a faint broad arc of light, moving across the middle section of the frame from left to right. The images were taken when Mars was **at its brightest** near opposition, or its closest distance, to Earth. This also happened to be a short period near the end of the commissioning phase, prior to the start of **TESS's science operations** . They present just a small fraction of TESS’s active field of view.