Perseverance Captures Martian Moon Shining in the Sky Before Sunrise
NASA’s Mars Perseverance rover, which just captured auroras from the Martian surface for the first time, also recently captured a predawn landscape shot that includes Deimos, the smaller of Mars’ two moons.
The Perseverance team just shared the incredible new photo, which was captured at 4:27 AM local time on March 1, the 1,433rd Martian day, or sol, of the Perseverance mission.
The image is a composite of 16 images captured using the Perseverance rover’s left navigation camera. The camera can shoot for a maximum exposure time of 3.28 seconds per frame, which was insufficient for the dim predawn conditions. The 16 shots were combined into one image onboard the rover before being sent to Earth. The composite represents a total exposure time of just over 52 seconds.
The low light combined with the long exposures results in quite a bit of digital noise, making the final shot appear hazy. Many of the white specks in the photo are digital noise, while others may be the result of cosmic rays. However, two brighter dots, labeled in the image below, are Regulus and Algebra, a pair of stars that are part of the constellation Leo. The brightest spot in the sky is, of course, the Martian moon, Deimos.
“This perspective captures the diffuse first light as night turns into early morning, well before sunrise. Stars and a moon still wheel overhead, with a dimly lit landscape extending as far as the eye can see. It’s a peaceful scene that feels like many early mornings here on Earth before much of the world awakes and starts its day. It feels almost like home, and perhaps someday we may start our mornings there too,” Nathan Williams, a planetary scientist and Perseverance engineering camera operations team member, tells PetaPixel.
“For these types of morning observations, the Navcams are warmed up (using heaters) to temperatures above -55 degrees Celsius for operational use. Because the cameras have no moving parts (e.g., no mechanical shutter), the long exposure times are achieved electronically. Besides the difference in exposure times and slightly longer warmup time, the operation of the camera was essentially identical to a daytime image acquisition.”
Williams worked on capturing this image alongside Justin Maki, an imaging scientist on the team, and Mastcam-Z deputy principal investigator. Williams explains that only “simple corrections” for sensor noise and artifacts have been made to the final image.
The RAW image data was very noisy, but the team could correct for the consistent noise using dark frame subtraction, “mathematically subtracting an image with the same exposure duration but that’s all dark except for noise.” This technique is used by astrophotographers on Earth, too, although usually with a lens cap still on their lens. For Perseverance, it is done using an image taken during the darkest period of the night.
“Subtracting that consistent noise helped a lot, but there was still a residual striped / cross-hatched pattern from the sensor, so we then normalized (divided) each row and column by its average brightness,” Williams continues.
He says the final image seen above was not color-calibrated, but instead a “simple white balance stretch like most cameras automatically do here on Earth.” They did not perform edits “to saturation, no AI, etc.”
Deimos is one of two Martian moons; the other is Phobos. Deimos has a mean radius of just 3.9 miles (6.2 kilometers) and orbits Mars every 30.3 hours. The natural satellite is 14,580 miles (23,460 kilometers) from Mars, much farther away than the larger Phobos. Phobos has a mean radius of seven miles (11 kilometers) and orbits Mars from about 3,700 miles (6,000 kilometers).
PetaPixel has recently covered images related to both of Mars’ moons. Perseverance shot a Martian eclipse of Phobos crossing in front of the Sun last September. As for Deimos, a European Space Agency (ESA) probe, Hera, caught an incredible glimpse of Deimos against a backdrop of Mars in March.
Image credits: NASA/JPL-Caltech
