On April 19, local time, the National Academy of Sciences, the Academy of Engineering and the School of Medicine released the "Ten Year Plan" for planetary science and astrobiology in the United States from 2023 to 2032, suggesting that NASA carry out research on Uranus and its satellites and list it as the "highest-priority new Flagship mission".
U.S. Ten-Year Plan for Planetary Science and Astrobiology from 2023 to 2032, image courtesy of the National Academies of Sciences, Engineering, and School of Medicine
In the aforementioned plan, a team of U.S. planetary scientists proposed that Uranus should be the focus of NASA exploration. NASA will use the Ten Year Plan to explain and seek funding to Congress, and if the proposal comes to fruition, NASA will launch a $4.2 billion orbiter and atmospheric probe to Uranus in the early 2030s to try to understand the formation and composition of the ice giant. Previously, only NASA's Voyager 2 probe flew by Uranus in 1986.
Uranus and its "neighbor" Neptune are between rocky planets (such as Earth) and gas giants (such as Jupiter and Saturn), "which represents a unique type of planet that we know very little about," said Ravit Helled, a planetary scientist at the University of Zurich who was one of 130 scientists involved in the program report.
Artistic representation of giant objects in the solar system, from nasa's Jet Propulsion Laboratory
Uranus was the first planet to be discovered through a telescope, discovered by astronomer William Herschel in 1781, when he thought it might be a comet or star. Two years later, based on astronomer Johann Elert Bode's observations, Uranus was generally considered a planet. Herschel tried unsuccessfully to name Uranus after King George III. The scientific community was more receptive to Bode's suggestion, naming it Uranus, the ancient Greek god of the sky.
Since then, Uranus has been considered one of the eight planets in the solar system. As the seventh planet in the solar system from the inside to the outside, it ranks third in diameter in the solar system, with a radius of 15,759.2 miles (about 25,362 kilometers), four times wider than The Earth. The average distance between Uranus and the Sun is about 1.8 billion miles (about 2.9 billion kilometers), or 19.8 astronomical units, and one astronomical unit (AU) refers to the average distance from the Sun to Earth. This means that it takes 2 hours and 40 minutes for solar rays to travel from the Sun to Uranus.
Infrared composite image of the two hemispheres of Uranus obtained with the Keck telescope adaptive optics system, image from the Keck Observatory
Due to its distance from the Sun, Uranus, as an ice giant, is very cold and windy, surrounded by 13 faint halos and 27 known moons. It rotates at an angle of nearly 90 degrees and is the only planet in the solar system with an equator at almost right angle to its orbit. This unique tilt angle makes Uranus look like a rolling ball spinning around the sun, while also leading to extreme seasons on Uranus. For nearly a quarter of every Uranus year (about 84 Earth years), the Sun shines directly on the poles of Uranus, leading the entire hemisphere of Uranus to a dark winter of up to 21 Earth years.
According to NASA, Uranus formed about 4.5 billion years ago, when gravity drew swirling gas and dust in to form the ice giant. Like Neptune, Uranus may have formed closer to the Sun and was only moved farther away about 4 billion years ago. Most of the planet's mass (80% and above) is made up of "ice," or water, methane, and ammonia. It has a small rocky core with temperatures up to 9,000 degrees Fahrenheit (4,982 degrees Celsius) near the core. Uranus' atmosphere consists mainly of hydrogen and helium, as well as small amounts of methane, water and ammonia. It is methane that gives Uranus its signature blue color, which absorbs the red part of the sun's rays, giving it a blue-green color.
Voyager 2 took images of Uranus on Jan. 14, 1986, from a distance of about 7.8 million miles (about 12.7 million kilometers), from nasa's Jet Propulsion Laboratory
Scientists have found that Uranus's environment is not suitable for life. The planet's temperature, pressure, and composition characteristics are likely to be too extreme and unstable, making it difficult for organisms to adapt. In addition, Uranus has an unusual, irregularly shaped magnetosphere. The magnetic field usually coincides with the direction of the planet's rotation, but Uranus's magnetic field is oblique.
Combining the above characteristics, the low energy of Uranus's interior, active atmospheric dynamics and complex magnetic fields are important puzzles that need to be explored at present. Scientists have speculated that a huge impact during the formation of the solar system may have caused the planet's extreme axial tilt. In the limited data obtained by Voyager 2's flyby of Uranus, Uranus's large icy moons show unexpected evidence of geological activity, suggesting that its moons may have oceans. Meanwhile, Voyager 2 saw some discrete clouds as it flew over Uranus in 1986. Recent observations have shown that Uranus exhibits dynamic clouds near the vernal equinox, including features of rapid changes in light.
Image of "crescent-shaped" Uranus taken on January 24, 1986, when Voyager 2 flew by Uranus, from NASA's Jet Propulsion Laboratory and the United States Geological Survey
In response, the "Ten Year Plan" proposes to make the Uranus Orbiter and Probe (UOP) a new flagship mission with the highest priority, and preferably launched in 2023-2032. The UOP mission will provide an atmospheric probe to make years of orbital travel to the Uranus system to deepen awareness of ice giants. Its scientific exploration goals will involve the origin of Uranus, its internal and atmospheric composition, magnetospheres, moons and halos. The mission could be launched on existing launch vehicles, preferably in 2031 and 2032, and could use Jupiter's gravitational assistance to shorten the launch time.
Robin Canup, a planetary scientist at the Southwest Research Institute, said the decision to study Uranus over Neptune could be attributed to "celestial opportunism." If the mission is launched by a Falcon Heavy rocket in 2031 or 2032, the orbiter could be assisted by Jupiter's gravity, reaching Uranus 13 years later, and longer if Neptune is chosen. "This mission (UOP) is technically ready," Canup says, "and we propose to start immediately." "But whether this can be achieved depends on whether NASA can develop a reasonable budget that will be affected by the pandemic and the soaring cost of the mission."
Further research on Uranus may also expand understanding of exoplanets. Scientists believe that the two sets of halos surrounding Uranus, the dense arrangement of moons and some strange objects may have comets or objects from outside Neptune called the Kuiper Belt region.