NASA's Transiting Exoplanet Survey Satellite (TESS) did a bit of limbering up before commencing its science operations on July 25, 2018. As a part of last-minute tests before starting its search for exoplanets on that day, the unmanned space telescope demonstrated what it could do by snapping a series of images capturing the motion of a comet over the course of 17 hours.
With the looming retirement of the ailing Kepler Space Telescope, TESS is more than just a replacement. Building on the successful design of Kepler, TESS incorporates four low-power, low-noise digital cameras set in an ultra-stable platform. Since its job is to scan the entire sky for any signs of Earth-like exoplanets among 200,000 of the brightest stars, it has to operate at a very high standard.
According to NASA, this was the reason for the comet-clicking test in July. By following the comet for almost an entire day, TESS was able to show that it could collect a set of stable, periodic images over a prolonged time. For the exercise, comet C/2018 N1 was selected by mission control. This comet was first sighted by NASA's Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) satellite on June 29 of this year and is currently 29 million mi (48 million km) from Earth in the constellation of Piscis Austrinus.
The space agency released the images in the form of an animated GIF file as well as an annotated video. The composite shows the comet moving across the field of view followed by its tail of gas and water vapor being pushed behind by the solar winds. The animated image also shows a number of other astronomical objects that flicker back and forth between black and white. Part of this is due to image processing, but NASA says that some of the stars in view are variable stars and their flickering is due to changes in their brightness.
Also moving across the image are several asteroids, seeming to follow the comet like cosmic remoras. Meanwhile, there is a faint broad arc of light that looks like a camera flaw, but is in reality light from the planet Mars, which was at its closest distance to the Earth when the images were taken.
Launched on April 18 from Cape Canaveral Air Force Station atop a SpaceX Falcon 9 rocket, TESS 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. This will allow the spacecraft to remain stable with minimal corrections that would reduce its sensitivity. It also lets TESS scan the entire sky over time without glare from the Sun or the Earth.
The video below shows the animated composite.
Source: NASA