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Neptunes apperance4/1/2023 ![]() Lower-resolution data contribute to the long-term record of planetary atmosphere evolution, but to routinely achieve angular resolutions better than approximately 1” requires adaptive optics approaches. Meanwhile, ground-based telescope technologies have also advanced to the point that some rival space-based observation, particularly at near-IR wavelengths. Note that while Table 1 presents a summary of major dedicated programs, there are other data sets from smaller Hubble programs and from other operating spacecraft missions, some of which use the outer planets as a calibration source. The Outer Planet Atmospheres Legacy (OPAL) program began in 2014 to routinely monitor these planets and now observes each gas giant once per year, with examples in Figure 2. However, there have been few multi-year, many observation, programs dedicated to the outer planets, as shown in Table 1, and those are usually centered around specific predictable events or to provide support context imaging for other operating missions, such as Galileo, Cassini, and Juno (e.g., ). Indeed, an intensive observing campaign around the impacts of the Comet Shoemaker-Levy 9 fragments into Jupiter showed the power of having a large telescope that could image a planet for long periods of time. Although Hubble’s prime science area is astrophysics, early scheduling included dedicated planetary observing time. First, the launch of the Hubble Space Telescope allowed detailed planetary imaging without the blurring effects of the Earth’s atmosphere. History of High-Resolution ImagingĪs deep space mission technology evolved, other telescope technologies also continued to mature. Lastly, we examine long-term cycles on these planets, some of which are only now being realized after decades of observations. Section 4 discusses comparisons of the zonal winds, waves, and cloud structure of the gas giants, Jupiter and Saturn, and of the ice giants, Uranus and Neptune. In Section 3, we summarize the overall cloud appearance (banded structure, colors, and major discrete features) for each of these planets individually. First, we review the history of high-resolution imaging from space-based to Earth-based observations for each of these planets. We limit our discussion to atmospheric weather-layer studies in the near-UV to the near-IR range, as longer wavelengths are discussed in other papers in this volume likewise, aurorae and upper atmosphere phenomena are also covered separately, and not included here. ![]() Here, we review what has been learned from a long baseline of high-spatial-resolution imaging data, where we define high resolution as 50 milliarcsec or better. Additionally, Hubble, and much of the ground-based AO imaging, can acquire data at near-infrared (IR) wavelengths that were not available to Voyager and which provide greatly enhanced imaging contrast, an especially important tool for understanding ice giant atmospheres. Future facilities will enable even greater spatial resolution and, combined with our existing long record of data, will continue to advance our understanding of atmospheric evolution on the giant planets.Ī unique aspect of Hubble is its access to ultraviolet (UV) wavelengths blocked by the Earth’s atmosphere. With several decades of data already obtained, we can now begin to investigate seasonal influences on dynamics and aerosol properties, despite orbital periods ranging from 12 to 165 years. Temporal variations in winds, cloud structure, and color over timescales of days to years have been measured for all four planets. This coverage allows comparisons of atmospheric properties between the planets, as well as in different regions across each planet. These facilities offer a powerful combination of high spatial resolution, often <0.05”, and broad wavelength coverage, from the ultraviolet through the near infrared, resulting in compelling studies of the clouds, winds, and atmospheric vertical structure. The Hubble Space Telescope, particularly the Wide Field Camera 3 (WFC3) and Advanced Camera for Surveys (ACS) instruments, and large ground-based telescopes with adaptive optics systems have enabled high-spatial-resolution imaging at a higher cadence, and over a longer time, than can be achieved with targeted missions to these worlds. However, these missions are infrequent Uranus and Neptune have only had a single flyby by Voyager 2. Each of the giant planets, Jupiter, Saturn, Uranus, and Neptune, has been observed by at least one robotic spacecraft mission.
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