A close-up of Jupiter is the Great Red Spot taken by the JunoCam instrument on NASA’s Juno probe, and the color-enhanced by citizen scientist Jason Major.
Jupiter is the Great Red Spot has been for hundreds of years, but the source of the characteristic color remains a mystery. New laboratory experiments are in work to produce a color — and others found in Jupiter’s turbulent cloud tops — here on Earth, and researchers have found that radiation and temperature play an important role in the change of the color of some of the transparent material found in the clouds.
A primary suspect in the colors of Jupiter’s clouds is ammonium hydrosulfide, a kind of salt. Formed by ionized ammonia and bisulfide, decomposes rapidly in typical atmospheric conditions and the temperature on Earth, making it a challenge to investigate its properties.
“Models predict that ammonium hydrosulfide is the third most common cloud component [Jupiter], behind ammonia and water,” Mark Loeffler, an astrochemist at Northern Arizona University, told Space.com by e-mail. Loeffler worked with a fellow chemist, Reggie Hudson, NASA’s Goddard Space Flight Center in Maryland, in an attempt to re-create the color of Jupiter, the clouds in the laboratory. [Jupiter is the Great Red Spot: An Iconic Monster Storm in Photos]
The scientists have run around 200 experiments on ammonium hydrosulfide in an attempt to change the color of the Great Red Spot. After hitting the salt with simulated cosmic rays, compared them with the observations of NASA’s Hubble Space Telescope.
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“This work took a bit, because there is not much published on this connection, and there appeared to be a lot going on in the sample,” Loeffler said.
The Great Red Spot is the big mystery
With the wind as high as 400 mph (644 km/h), Jupiter is the Great Red Spot is brewing for at least 150 years. The astronomers in the 1600s identified with an unclear function on the Jupiter with the place, but scientists are not sure that it was the same storm. In the past few years, the storm is shrunk to the width of one Earth. It was previously estimated on the three Earths wide. At the same time, observations showed that the color of the stain change, suggesting that the composition may also move.
Although ammonium hydrosulfide is present in Jupiter’s atmosphere, Loeffler said, that it does not exist as a gas. Instead, it must be reduced as the grains of salt that are mixed with, or a layer of another material.
By itself, ammonium hydrosulfide is transparent and colorless. But in Jupiter’s clouds, the salt is not in isolation. Cosmic radiation, the high-energy radiation travel through space, bombarding the planet and the clouds. These rays, which come from outside the solar system and even outside the Milky way, you can change the color of many salts, such as previous experiments have shown.
To determine how ammonium hydrosulfide reacted to radiation, Loeffler and Hudson first had to cool the sample holder to temperatures where the salt would remain stable as a solid. Then, they sprayed ionized ammonia and hydrogen sulfide in the sample holder, where the two components react to produce salt. In addition, the researchers used a particle accelerator to bombard the sample holder with protons to represent cosmic radiation has an influence on the cloud. Throughout the process, the researchers monitored the ice and the collected images in both visible and ultraviolet light. Most of the nearly 200 repetitions of that experiment lasted what Loeffler called ‘a long day’, although some ran over night.
Loeffler summarized the process in a single word: “fun.”
The researchers found that varying the temperature of the “cosmic rays” affect the color of the salt. At low temperatures of minus 263 degrees Celsius (min 505 degrees Fahrenheit) and minus 223 degrees C (minus 370 degrees F), the salts were orange or reddish orange. At higher temperatures of minus 153 degrees celsius (minus 244 degrees F) and minus 113 degrees C (minus 172 degrees F), the salts turned green. The researchers attributed that greenish tint of sulfur. Only a small fraction of sulfur is identified in the clouds, but on a much smaller ratios than those found in the salts produced in the lab.
That provides an interesting challenge, Loeffler said, because the Great Red Spot is thought to be a temperature closer to those that the production of the greening of the salts, although the clouds are clear red.
“It would be nice if the red colors we see at low temperatures may be responsible for] the Great Red Spot, but which are likely to be cold,” Loeffler said.
So what is the role of ammonium hydrosulfide play in the colours of Jupiter legendary storm? The researchers are still not sure. The visible color of the ammonium hydrosulfide (or red or green or something in between) is determined by the wavelength of the light that the compound is broadcasting, but the complete profile of the light of the compound contains wavelengths than just the visible range.
So the researchers compare the full wavelength profile of ammonium hydrosulfide at different temperatures, and a dose with the complete profile of the light of Jupiter is the Great Red Spot. Although the ammonium hydrosulfide ice at low doses and low temperatures makes a “reasonable match” is what is observed on the planet at some wavelengths, it does not correspond to all the wavelengths, scientists have seen in Jupiter’s storms. Ices irradiated at higher temperatures to make a better match, but the wavelengths that create the greenish color are of course not consistent with what the Hubble telescope has seen.
“After comparison with this new low-temperature data, it seems evident that the best fit of a single [ammonium sulfide] ice is one that has been irradiated and heated to higher temperatures, so that the removal of the [sulphur] radical,” the researchers said.
He points to a 2016 study he worked on, Loeffler said, the warming-up of the green samples to temperatures that match those found in the cloud layer of clear, unirradiated ammonium sulfide get rid of the non-bound sulphur ions and the greenish color. That study, together with other papers from 1976, focusing on only one of the temperature when the sample was irradiated. Together with the new study, which will appear in the March 1 issue of the journal Icarus, these are the only documents that report the results of the work in the laboratory for ammonium hydrosulfide, according to the authors of the new study.
That’s because the instability of the salt makes it a challenge to work with, Loeffler said.
“Also, the material smells bad, like rotten eggs, and a cleaner,” he said. “For the safety, all the excess material must be ventilated from the room, so no one breathes.”
Worse still, he said, destroy the monsters lab components. “It’s really not the best material to work with,” Loeffler said.
But that does not deter the scientists. Now that they have studied how the ammonium hydrosulfide changes over a range of doses and temperatures, the couple plans to other substances in their experiments, which can contribute to the colors of the Great Red Spot.
Originally published on Space.com.