Shulou(Shulou.com)11/24 Report--

New discovery of perseverance: 22-degree halo on Mars! "

On December 15, 2021, Earth time, the perseverance rover, which was on a mission on the surface of Mars, took several rare photos, showing that Mars can also see an optical phenomenon formed by special ice clouds refracting sunlight-a 22-degree halo. This is the first time a human probe has observed this phenomenon outside the earth.

Perseverance rover shot halo (Lemmon et al. (2022) Fig.1) A team of scientists Lemmon (note, not lemons) from the Colorado Institute of Space Sciences (Space Science Institute) published the discovery in August 2022 in the famous American geophysical research journal Geophysical Research Letters.

Halo and its classification halo, also known as halo (halo) and white rainbow, are atmospheric optical phenomena. Halo is an arc, aperture or spot formed by light (sunlight, moonlight) scattered by clouds rich in ice crystal particles. according to the difference in shape and location, it can be divided into 22-degree halo, 46-degree halo, solar column, illusory sun (near / far), circum-zenith arc, circum-terrestrial arc and so on. The difficulty of observing different kinds of halos is different. generally speaking, 22-degree halos are the most common, and the brightness of other kinds of halos is weak, or because of the angle of observation, it often takes more conditions to be observed. sometimes it even becomes some "spectacle" into the news.

Why is the distribution of some kinds of halos called 22-degree halos? This is named after the "viewing angle radius" of the halo. Under good weather conditions, most of the pure ice crystals in the atmosphere are hexagonal prisms (Schaefer,1949). According to geometrical optics, when light enters from one side of the hexagonal prism and then refracts from the other side, the refraction angle is about 22 degrees. In the case of 46-degree halo, the light enters from the side of the hexagonal prism and then refracts and then emits from the top / bottom surface, or just the opposite direction from the top / bottom surface into and out of the side, with a refraction angle of about 46 degrees. Because ice crystals naturally face the sun on the side, and the light enters and exits on many sides, and rarely passes through the top / bottom surface, the 22-degree halo is much stronger and easier to observe than the 46-degree halo.

Conceptual map of the simple cause of 22-degree halo and 46-degree halo other kinds of halos are also caused by the refraction of light through a six-prism or complex six-prism combination. The shape distribution and arrangement direction of ice crystals in the atmosphere are often not random, but with certain arrangement rules or dominant components. In some specific weather conditions and places, the refracted light from a certain direction becomes stronger, and the corresponding optical phenomenon is more obvious.

When we were in middle school, we learned about an ominous omen-Bai Hong Guan Ri, in the article "Tang Jie lived up to his Mission". The celestial phenomena mentioned here are actually illusory solar arcs. It passes right through the sun and intersects with a 22-degree halo ring to create a magic sun (holiday, sun dog), hence the name. In modern times, we should understand that this is a scientific phenomenon that can be explained by optical principles, not an ominous sign.

The phantom sun is sometimes so bright that it is on a par with the real sun, as if there were several suns in the sky, hence the name. On a sunny winter day, the atmosphere is rich in small and clean ice crystals, 22-degree halos and phantom arcs are unusually clear, and the intersecting phantom sun becomes so bright that it becomes a spectacle.

The solar column is a halo in the vertical direction, like a pillar of light passing through the sun.

When the height angle of the sun is very low (below 32 degrees, the sun is in a very partial position, such as winter, dusk), you can see the circular zenith arc (circumzenital arc, also known as "solar load").

If the view is wide and clear enough, the height angle of the sun is higher (above 58 degrees, the sun is closer to the top of the head, such as midsummer, noon), and the latitude is not more than 58 degrees, you can see the horizontal arc around the earth ("solar cycle", parhelic circle).

The upper or outer tangent arc is a halo tangent above the 22-degree halo, and sometimes there is an arc nearly parallel to the 22-degree halo above the upper tangent arc, called the Parry arc, which was first discovered and described in detail by the British explorer Sir William Perry (1790-1855).

Several rare halos on Mars there are few "halos" to understand the halos on Earth, and then we turn our perspective to Mars. Why is there so little "halo" on Mars? In history, many rovers such as Curiosity and opportunity have landed and worked for long hours, but they have never photographed a solar halo. Although Mars has a thin atmosphere, it also has clouds, but the main component is not only water, but also some dry ice. Severe weather such as multiple sandstorms on Mars can stably show the meteorological conditions of ice crystal scattering are relatively rare. Most crucially, many previous studies have shown that the Martian atmosphere lacks the conditions for the formation of large-size regular hexagonal prism ice crystals, and halos require hexagonal ice crystals that are much larger than visible light waves. in order to satisfy the geometrical optics approximation.

Cooper (2020), a cloud on Mars, has obtained some evidence of hexagonal prism ice crystals, referring to data from the rover such as Curiosity, but these ice crystals are extremely rare. The halo accidentally captured by perseverance allowed scientists to determine that large-grained ice crystal clouds also exist on Mars, giving scientists a new understanding of the Martian climate and the formation and distribution of ice clouds on Mars.

references

[1]。 Lemmon, Mark T., et al. "Hexagonal prisms form in water-ice clouds on Mars, producing halo displays seen by Perseverance Rover." Geophysical research letters 49.17 (2022): e2022GL099776.

[2]。 Schaefer, Vincent J. "The formation of ice crystals in the laboratory and the atmosphere." Chemical Reviews 44.2 (1949): 291320.

[3]。 Wendisch, Manfred, and Ping Yang. Theory of atmospheric radiative transfer: a comprehensive introduction. John Wiley & Sons, 2012.

[4]。 Sheng Peixuan, etc. Atmospheric Physics (2nd Edition). Peking University Press, 2013.

[5]。 Kahn, Ralph. "The spatial and seasonal distribution of Martian clouds and some meteorological implications." Journal of Geophysical Research: Space Physics 89.A8 (1984): 6671-6688.

[6]。 Cooper, B. A., Moores, J. E., Battalio, J. M., Guzewich, S.D., Smith, C. L.A., Modestino, R. C. N., & Tabascio, M. V. (2020). Aphelion cloud belt phase function investigations with Mars Color Imager (MARCI). Planetary and Space Science, 184, 104840. Https://doi.org/10.1016/j. pss.2020.104840

This article comes from the official account of Wechat: stone popular Science Studio (ID:Dr__Stone), by Sikong.

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.