On March 4, NASA released a high-definition image of Mars taken by the tianwen-1 spacecraft. In two of the black and white images, some fine white strips caused some netizens' curiosity: isn't it snow? Why is it white? Zheng Yongchun, a researcher at the National Astronomical Observatory of the Chinese Academy of Sciences, believes that these white parts are likely to be reflected light from the slopes of Martian sand dunes, and may also contain frost formed after carbon dioxide solidifies.
According to the information released by the National Space Administration, the black-and-white image was taken by a high-resolution camera at an altitude of 330km to 350km from the surface of Mars, with a resolution of about 0.7m. The small craters, ridges, sand dunes and other landforms on the surface of Mars in the imaging area are clearly visible.
Zheng Yongchun told ScienceDaily that sand dunes have been formed on the surface of Mars by wind, and the reflected light on the slope will appear white in the photo. Many of the small white bars in the photo are crescent shaped, and the arc direction of the crescent reflects the direction of the wind. The reason why it looks white is that the camera is overexposed. Because the surface of Mars is uneven in light and shade, in order to get a clear picture of the dark places, it is possible to overexpose the bright places. In fact, these places are not so white.
At the same time, Zheng Yongchun believes that the white part of the picture may also contain frost formed after carbon dioxide solidifies.
The reporter learned that carbon dioxide will condense and turn into white dry ice at minus 78.5 ℃. In previous photos taken by foreign Mars probes, frost particles composed of carbon dioxide mixed with water ice appeared.
However, Zheng Yongchun said that whether there is solidified carbon dioxide in the pictures taken by tianwen-1 is inconclusive for the time being. Because this kind of phenomenon only appears in the low temperature season, and the National Space Administration did not disclose the specific location of the picture, it is unable to determine what season the region is in.
In fact, there are many materials on the surface of Mars that may appear white in the photos, such as exposed rock layers, salts, minerals, etc. Zheng Yongchun said that these substances are not excluded in this photo, but should be rare.