A Rain of Icy Particles Is Affecting the Giant Planet’s Weather
The planet SaturnSaturn is the sixth planet from the sun and has the second-largest mass in the Solar System. It has a much lower density than Earth but has a much greater volume. Saturn's name comes from the Roman god of wealth and agriculture.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>Saturn is easily recognizable for its opulent ring system that can easily be seen through a small telescope. Astronomers have now found that the rings are not as placid as they look. The icy rings particles are raining down onto Saturn’s atmosphere. This is heating the upper atmosphere. It took a collection of 40 years’ worth of Saturn observations, gleaned from four NASAEstablished in 1958, the National Aeronautics and Space Administration (NASA) is an independent agency of the United States Federal Government that succeeded the National Advisory Committee for Aeronautics (NACA). It is responsible for the civilian space program, as well as aeronautics and aerospace research. Its vision is "To discover and expand knowledge for the benefit of humanity." Its core values are "safety, integrity, teamwork, excellence, and inclusion." NASA conducts research, develops technology and launches missions to explore and study Earth, the solar system, and the universe beyond. It also works to advance the state of knowledge in a wide range of scientific fields, including Earth and space science, planetary science, astrophysics, and heliophysics, and it collaborates with private companies and international partners to achieve its goals.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>NASA planetary missions to come to this conclusion. Hubble Space TelescopeThe Hubble Space Telescope (often referred to as Hubble or HST) is one of NASA's Great Observatories and was launched into low Earth orbit in 1990. It is one of the largest and most versatile space telescopes in use and features a 2.4-meter mirror and four main instruments that observe in the ultraviolet, visible, and near-infrared regions of the electromagnetic spectrum. It was named after astronomer Edwin Hubble.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>Hubble Space Telescope observations were used to tie together all the evidence, collected in ultraviolet light. These results may be applied to determine if similar ring systems encircle planets orbiting other stars. Their rings would be too far away to be seen, but ultraviolet light spectroscopy of the planets could yield clues.
Hubble Space Telescope Finds Saturn’s Rings Heating Its Atmosphere
The secret has been hiding in plain view for 40 years. But it took the insight of a veteran astronomer to pull it all together within a year, using observations of Saturn from NASA’s Hubble Space Telescope and retired Cassini probe, in addition to the Voyager 1 and 2 spacecraft and the retired International Ultraviolet Explorer mission.
The discovery: Saturn’s vast ring system is heating the giant planet’s upper atmosphere. The phenomenon has never before been seen in the solar system. It’s an unexpected interaction between Saturn and its rings that potentially could provide a tool for predicting if planets around other stars have glorious Saturn-like ring systems, too.
The telltale evidence is an excess of ultraviolet radiation, seen as a spectral line of hot hydrogen in Saturn’s atmosphere. The bump in radiation means that something is contaminating and heating the upper atmosphere from the outside.
The most feasible explanation is that icy ring particles raining down onto Saturn’s atmosphere cause this heating. This could be due to the impact of micrometeorites, solar wind particle bombardment, solar ultraviolet radiation, or electromagnetic forces picking up electrically charged dust. All this happens under the influence of Saturn’s gravitational field pulling particles into the planet. When NASA’s CassiniThe Cassini–Huygens Mission, generally called Cassini, was a joint mission between NASA, the European Space Agency and the Italian Space Agency to study the Saturn system. Launched in 1997, Cassin provided astronomers with a massive amount of data about Saturn and its rings, its magnetosphere, and its moons. Cassini reached the end of its journey in 2017 when it deliberately dived into Saturn's atmosphere, where it disintegrated like a meteor.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>Cassini probe plunged into Saturn’s atmosphere at the end of its mission in 2017, it measured the atmospheric constituents and confirmed that many particles are falling in from the rings.
“Though the slow disintegration of the rings is well known, its influence on the atomic hydrogen of the planet is a surprise. From the Cassini probe, we already knew about the rings’ influence. However, we knew nothing about the atomic hydrogen content,” said Lotfi Ben-Jaffel of the Institute of Astrophysics in Paris and the Lunar & Planetary Laboratory, University of Arizona, author of a paper published on March 30 in the Planetary Science Journal.
“Everything is driven by ring particles cascading into the atmosphere at specific latitudes. They modify the upper atmosphere, changing the composition,” said Ben-Jaffel. “And then you also have collisional processes with atmospheric gasses that are probably heating the atmosphere at a specific altitude.”
Ben-Jaffel’s conclusion required pulling together archival ultraviolet-light (UV) observations from four space missions that studied Saturn. This includes observations from the two NASA Voyager probes that flew by Saturn in the 1980s and measured the UV excess. At the time, astronomers dismissed the measurements as noise in the detectors. The Cassini mission, which arrived at Saturn in 2004, also collected UV data on the atmosphere (over several years). Additional data came from Hubble and the International Ultraviolet Explorer, which launched in 1978, and was an international collaboration between NASA, ESA (European Space AgencyThe European Space Agency (ESA) is an intergovernmental organization dedicated to the exploration and study of space. ESA was established in 1975 and has 22 member states, with its headquarters located in Paris, France. ESA is responsible for the development and coordination of Europe's space activities, including the design, construction, and launch of spacecraft and satellites for scientific research and Earth observation. Some of ESA's flagship missions have included the Rosetta mission to study a comet, the Gaia mission to create a 3D map of the Milky Way, and the ExoMars mission to search for evidence of past or present life on Mars.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>European Space Agency), and the United Kingdom’s Science and Engineering Research Council.
But the lingering question was whether all the data could be illusory, or instead reflected a true phenomenon on Saturn.
The key to assembling the jigsaw puzzle came in Ben-Jaffel’s decision to use measurements from Hubble’s Space Telescope Imaging Spectrograph (STIS). Its precision observations of Saturn were used to calibrate the archival UV data from all four other space missions that have observed Saturn. He compared the STIS UV observations of Saturn to the distribution of light from multiple space missions and instruments.
“When everything was calibrated, we saw clearly that the spectra are consistent across all the missions. This was possible because we have the same reference point, from Hubble, on the rate of transfer of energy from the atmosphere as measured over decades,” Ben-Jaffel said. “It was really a surprise for me. I just plotted the different light distribution data together, and then I realized, wow— it’s the same.”
Four decades of UV data cover multiple solar cycles and help astronomers study the Sun’s seasonal effects on Saturn. By bringing all the diverse data together and calibrating it, Ben-Jaffel found that there is no difference to the level of UV radiation. “At any time, at any position on the planet, we can follow the UV level of radiation,” he said. This points to the steady “ice rain” from Saturn’s rings as the best explanation.
“We are just at the beginning of this ring characterization effect on the upper atmosphere of a planet. We eventually want to have a global approach that would yield a real signature about the atmospheres on distant worlds. One of the goals of this study is to see how we can apply it to planets orbiting other stars. Call it the search for ‘exo-rings.’”
Reference: “The Enigmatic Abundance of Atomic Hydrogen in Saturn’s Upper Atmosphere” by Lotfi Ben-Jaffel, Julianne I. Moses, Robert A. West, Klaus-Michael Aye, Eric T. Bradley, John T. Clarke, Jay B. Holberg and Gilda E. Ballester, 30 March 2023, Planetary Science Journal.
DOI: 10.3847/PSJ/acaf78
The Hubble Space Telescope is a project of international cooperation between NASA and ESA. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.
Source: SciTechDaily