The Uranian Orbit
Uranus is one of our least explored celestial neighbors. Only once have we flown a probe nearby, snapping nearly 2000 pictures. Scientists believe there may be a hot surface underneath the massive gas atmosphere.
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MID-COLUMBIA ORBIT MAP
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In March 1781, William Herschel was doing a star survey with a home-made telescope, when he stumbled across a tiny bluish-green disk. When he returned to it several nights later, he could tell that it had moved.
Herschel originally thought it was a comet or a stellar disc, which he believed he might actually resolve. He reported the sighting to Nevil Maskelyne, Britain’s Astronomer Royal.
Finally, Russian Academician Anders Lexell computed the orbit and found it to be probably planetary.
In March 1781, William Herschel was doing a star survey with a home-made telescope, when he stumbled across a tiny bluish-green disk. When he returned to it several nights later, he could tell that it had moved. Herschel originally thought it was a comet or a stellar disc, which he believed he might actually resolve. He reported the sighting to Nevil Maskelyne, Britain’s Astronomer Royal. He made many more observations of this object. Finally, Russian Academician Anders Lexell computed the orbit and found it to be probably planetary.
Herschel agreed, determining that it must be a planet beyond the orbit of Saturn. He called the new planet the "Georgian star" (Georgium sidus) after King George III, which brought him favour with the monarch; however the name did not stick. In France, where reference to the British king was to be avoided if possible, the planet was known as "Herschel" until the name "Uranus" was universally adopted around 1850 as proposed by Johann Bode, in conformity with the other planetary names from classical mythology. Herschel was eventually awarded the Copley Medal and elected a Fellow of the Royal Society. In 1782, he was appointed "The King's Astronomer", but remains most famous for discovering Uranus.
As part of the Grand Tour, taking advantage of a rare planetary alignment, NASA's Voyager 2 spacecraft flew closely past distant Uranus, the seventh planet from the Sun, in January 1986.
At its closest, the spacecraft came within 81,500 kilometers (50,600 miles) of Uranus's cloud tops on Jan. 24, 1986.
Voyager 2 radioed thousands of images and voluminous amounts of other scientific data on the planet, its moons, rings, atmosphere, interior and the magnetic environment surrounding Uranus.
Since launch on Aug. 20, 1977, Voyager 2's itinerary has taken the spacecraft to Jupiter in July 1979, Saturn in August 1981, and then Uranus. Voyager 2's next encounter was with Neptune in August 1989. Both Voyager 2 and its twin, Voyager1, have recently left our solar system and entered interstellar space.
MORE ON VOYAGER 2
Voyager 1 and 2 were designed to take advantage of a rare planetary alignment to study the outer solar system up close. Voyager 2 targeted Jupiter, Saturn, Uranus and Neptune.
Like its sister spacecraft, Voyager 2 also was designed to find and study the edge of our solar system.
Voyager 2's images of the five largest moons around Uranus revealed complex surfaces indicative of varying geologic pasts. The cameras also detected 11 previously unseen moons. Several instruments studied the ring system, uncovering the fine detail of the previously known rings and two newly detected rings. Voyager data showed that the planet's rate of rotation is 17 hours, 14 minutes. The spacecraft also found a Uranian magnetic field that is both large and unusual. In addition, the temperature of the equatorial region, which receives less sunlight over a Uranian year, is nevertheless about the same as that at the poles.
Nation: United States of America
Objective(s): Jupiter Flyby, Saturn Flyby, Uranus Flyby, Neptune Flyby
Spacecraft Mass: 1,592 pounds (721.9 kilograms)
Mission Design and Management: NASA / JPL
Launch Vehicle: Titan IIIE-Centaur (TC-7 / Titan no. 23E-7 / Centaur D-1T)
Launch Date and Time: Aug. 20, 1977 / 14:29:44 UT
Launch Site: Cape Canaveral, Fla. / Launch Complex 41
- Imaging Science System (ISS)
- Ultraviolet Spectrometer (UVS)
- Infrared Interferometer Spectrometer (IRIS)
- Planetary Radio Astronomy Experiment (PRA)
- Photopolarimeter (PPS)
- Triaxial Fluxgate Magnetometer (MAG)
- Plasma Spectrometer (PLS)
- Low-Energy Charged Particles Experiment (LECP)
- Plasma Waves Experiment (PWS)
- Cosmic Ray Telescope (CRS)
- Radio Science System (RSS)
WHAT WE KNOW
Uranus is made up of ices: frozen water, methane, and ammonia. They form a slushy fluid under a thick hydrogen and helium atmosphere. There is probably a small, rocky core, but no surface other than that. Some scientists consider it a gas giant, while others call it an ice giant (along with Neptune).
Uranus is tilted about 90 degrees, and rotates on its side compared to the rest of the planets. That gives it very odd seasons, which are not well understood. We can see the largest clouds from Earth, but it's not enough to get a good idea of what is going on. We have only sent one spacecraft that direction, and when it flew by, the atmosphere was very smooth and quiet.
There are 27 known moons orbiting Uranus. Five of them are larger than the others, and are considered major moons. For historical reasons, the moons are named after characters from the works of Shakespeare and Alexander Pope, instead of from ancient mythology. When the Voyager 2 spacecraft went though the Uranian system, it could only look at one moon close up. If they wanted the probe to continue to Neptune, the scientists didn't have a choice: it had to be Miranda, the smallest of the major moons. They were disappointed about that, because they thought a larger moon would be more interesting. They were wrong! Miranda is one of the most fascinating moons in the whole solar system. Driven by inner heat that is no longer being generated, huge blocks of ice cracked and shifted on its surface. It is covered by fault lines and towering cliffs. Huge chunks of the surface have different geologic histories as if they were part of different objects. At one time, scientists thought it had been blown apart and rearranged, but further study ruled that out. We are fortunate to have some high-resolution images of this interesting object.
Last updated September 19, 2023. Content written by Trevor Macduff.
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