A leader of NASA's Mars Curiosity rover team has offered a couple of explanations for an anomalous bright spot that showed up on pictures from the Red Planet — but they're not the conventional explanations.
Let's get this straight first: It's not an alien spotlight, according to Justin Maki, an imaging scientist at NASA's Jet Propulsion Laboratory who is the lead for Curiosity's engineering cameras. Maki isn't giving any weight to the not-completely-serious claims that are being bandied about by UFO websites.
At the same time, Maki isn't immediately dismissing the phenomenon as a double-shot of cosmic rays or data dropouts. In his view, that spot of light could have entered Curiosity's right-hand navigation camera, even though there's no sign of the spot in the stereo imagery from the left-hand camera.
Maki and his colleagues think it could be a well-placed flash of reflected sunlight, or light shining through a chink in Curiosity's camera housing. Here's his explanation, passed along via email:
"Bright spots appear in single images taken by the Navigation Camera on NASA's Curiosity Mars rover on April 2 and April 3. Each is in an image taken by this stereo camera's right-eye camera [with links to the April 3 and April 2 pictures] but not in images taken within a second of each of those by the left-eye camera [again, with links to April 3 and April 2]. In the two right-eye images, the spot is in different locations of the image frame and, in both cases, at the ground surface level in front of a crater rim on the horizon.
"One possibility is that the light is the glint from a rock surface reflecting the sun. When these images were taken each day, the sun was in the same direction as the bright spot, west-northwest from the rover, and relatively low in the sky. The rover science team is also looking at the possibility that the bright spots could be sunlight reaching the camera's CCD directly through a vent hole in the camera housing, which has happened previously on other cameras on Curiosity and other Mars rovers when the geometry of the incoming sunlight relative to the camera is precisely aligned.
"We think it's either a vent-hole light leak or a glinty rock."
NASA spokesman Guy Webster told NBC News that both pictures were taken during the Martian afternoon. He said a member of the rover team is checking for other examples of light leaks and Martian sunglint.
Even if the flash is the glint from a shiny rock, the crater's rim looks far enough away that Curiosity's course is unlikely to be changed to investigate. Unless, of course, it turns out to be a Martian flashing a mirror.
There are lots more amazing pictures from Curiosity, now that it's settled in a rocky area called the Kimberley for a detailed geological survey. The Planetary Society's Emily Lakdawalla is keeping close track of the vistas on her blog and her Twitter account. Check out these highlights, including Damia Bouic's "Road to Kimberley" panorama and a wide shot of the Kimberley terrain:
Update for 10:20 p.m. ET April 8: In a news release from JPL, Maki doesn't exclude the possibility that the bright spots might be cosmic-ray hits.
"In the thousands of images we've received from Curiosity, we see ones with bright spots nearly every week," Maki said. "These can be caused by cosmic-ray hits or sunlight glinting from rock surfaces, as the most likely explanations."
He noted that the rover team usually determines the source of a bright spot by checking both the left and the right views from the navigation camera. If it doesn't show up in both views, it's probably a cosmic ray glitch. "In this case, it's not as straightforward because of a blocked view from the second camera on the first day," he said.
Maki put a bit of additional emphasis on the cosmic ray scenario in a follow-up email to NBC News: "Two different cosmic ray hits occurring in two different images that happened to be pointed in the same general direction one day apart could certainly happen from time to time," he said.
If the flash is coming from a glinty rock, that rock could be on a ridge about 175 yards (160 meters) from the rover's location on April 3, NASA said.