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--------------------------------- 2608 - MARS - cosmic rays seen on Mars?
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- If you were on Mars as the stars rose, you would see a completely different world than the one on display in night images beamed home by InSight's cameras. Essentially, in the images that we have so far, there's very little content that you would actually see with your eyes.
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- The images come from a device called the Instrument Context Camera, one of two perched on the InSight lander. One of those instruments, the seismometer, is the reason for the meteor search. This instrument is tuned to feel shuddering waves traveling through Mars. Scientists can then parse that data to understand the interior structure and activity of the Red Planet.
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- Those ground waves could be spawned by mars quakes, the Martian equivalent of earthquakes. But they can also occur when meteorites slam into the planet's surface. The scientists' need meteor data for their calculation of how often such impacts occur on Mars in order to interpret the seismometer's data.
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- NASA's “Spirit rover“, which roamed the Red Planet from 2004 to 2010, spent the summer of 2005 sky watching. That opportunity came thanks to the weather, which cleared so much dust off Spirit's solar panels that they were overproducing energy, creating a bounty of energy for use.
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- This extra energy allowed Spirit to spend some nights sky watching, but scientists never spotted a meteor in that data. Given the scale of observations gathered that's pretty inconclusive. It could mean that fewer meteors arrive at Mars than scientists expected or that the team simply had bad luck.
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- InSight, which arrived in November 2018, took up the task as a low-priority project. The first images came from the lander's Instrument Deployment Camera, which is attached to the arm of the rover and can be pointed at specific locations. But for months now, that camera has had more pressing concerns than shooting stars.
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- Here is the reason: InSight's second key science instrument, a heat probe nicknamed the mole, has been troublesome. The mole is meant to dig itself about 16 feet (5 meters) below the surface, measuring heat transport in the Martian rock as it does.
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- The mole's dig has been slow going, however. In general, the probe has struggled to get traction in the rock. The instrument has even popped partway out of its burrow on a few occasions. Difficulties faced by the mole mean that the Instrument Deployment Camera has focused on providing engineers with visual evidence of what's happening with the probe and rescue attempts. There's no time for stargazing.
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- The scientists looking for meteors recruited the Instrument Context Camera instead. Like its companion, this camera was left over from the Curiosity rover, based on designs from 1999, then upgraded to see in color.
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- Unlike the Instrument Deployment Camera, the Instrument Context Camera is stuck in place, and is equipped with a fisheye lens that distorts its view. It's not a natural sky watcher. It has the advantage that it's a larger field of view, so we see about a third of the horizon. It has the big disadvantage that it's not looking very high up in the sky. Obviously, if you were here on Earth looking for meteors, you wouldn't focus on the horizon.
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- Daytime images from the camera make its stargazing challenges evident. Mars itself fills most of the camera's field of view. Despite the seeming uniformity of the night images, the ground takes up most of the Instrument Context Camera's view, with no stars to see. Just a curving swath of sky remains above the red rock to be filled with stars after sunset.
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- Meteors would follow a curved path as seen by the fisheye lens. The carbon-dioxide-rich atmosphere would give a meteor an orange glow. But most pinpricks of light in the InSight images come from an entirely different celestial phenomenon: cosmic rays, fragments of atoms that careen across the universe in all directions.
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- Unlike the terrestrially pedestrian stars and meteors, cosmic rays are very difficult to photograph from Earth. Our atmosphere blocks many such particles from reaching the surface. A lucky camera on Earth set to take a long-exposure image may catch a cosmic ray here or there.
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- Mars doesn't have Earth's atmosphere to burn up cosmic rays, leaving the Red Planet primed to host a cosmic-ray detector. The universe is awash with cosmic rays. You don't think much about these flying protons because they mostly just pass through you and the environment.
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- While they won't affect InSight's other data, the cosmic ray images could feed scientists' curiosity about these particles, particularly their frequency at Mars. The length of a streak speaks to the type of particle involved. Longer streaks are typically high-energy protons or muons. The angle at which the cosmic ray is traveling tells us it is coming from the Sun.
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- InSight's night images capture the shadows of cosmic rays. That's because, for each 5-minute exposure, the camera also captures an instantaneous view to subtract out of the main image, as a sort of calibration image. If a cosmic ray hits during that instantaneous image, but not during the main image, the result is a dark spot, marking the shadow of where a cosmic ray will appear in the instantaneous image.
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- Time is running out for getting photos from the Instrument Context Camera because the infamous Martian dust-storm season will soon begin, blotting out the horizon.
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- Within a couple of weeks we won’t be able to see even a bright star that low in the sky.
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- So much for sky watching on the planet Mars. Bet you never thought you would see this. Check out the NASA web site to see the photos.
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- February 7, 2020 2608
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