Ice giant Uranus on radar to explore
By Amanda Jermyn

Uranus, shrouded in mystery, named for the Greek sky god, is the seventh planet from the Sun, located between Saturn and Neptune. As this distant planet becomes more accessible with modern technology, gradually the veils are being lifted, revealing all manner of astronomical treasures. Uranus was discovered in 1781 by astronomer William Herschel, and was the first planet found with the aid of a telescope.

Because of its great distance from the Sun (about 20 times the distance from Earth to Sun) Uranus takes a whopping 84 Earth years to complete one orbit. One of the odd features of this planet is that its rotation axis is tilted far more than that of any other planet in the solar system, so it appears to be rotating on its side. While other planets appear like tilted spinning tops, Uranus seems more like a rolling ball. As a result, it experiences unusual seasonal changes: Each pole receives about 42 years of continuous sunlight followed by 42 years of continuous darkness. Scientists suspect it was left spinning on its side after a collision early in its history with a planetary object twice the size of Earth.

With a diameter four times that of Earth, Uranus is one of two ice giants of the solar system, the other being Neptune. It consists of a rocky core wrapped in an icy mantle which in turn is covered by a gaseous outer layer. The mantle, comprising the bulk of the planet, is not made of ice in the conventional sense but is rather a super dense fluid composed of water and ammonia. The gaseous outer layer is mostly hydrogen and helium, with small amounts of methane, ammonia and water. It gets its blue-green color from the methane in its atmosphere. A recent image taken by Larry Sromovsky of the University of Wisconsin-Madison with the Gemini 8.1 meter (319 inch) telescope shows an intriguing bright patch that is thought to be an eruption of methane ice high in its atmosphere.

Uranus has 27 known moons, named for characters from the works of Shakespeare and Alexander Pope. It also has two sets of rings, an inner set consisting of mostly narrow dark rings, and an outer brightly colored set. While the earliest of these were discovered in 1977 and the most recent in 2005 by the Hubble Space Telescope, William Herschel, discoverer of the planet, thought he saw a reddish ring around Uranus in 1789. However, because no one else observed this, he assumed he had imagined it.

According to an article in the journal Nature Physics, oceans of liquid diamond, with solid diamond icebergs, may be floating on both Neptune and Uranus. This could help explain the large discrepancy between the alignment of the magnetic and geographic poles on both planets. If Earth’s magnetic field were that far off it would place the magnetic north pole in Texas instead of off an island in Canada.
So far the only spacecraft to visit Uranus was Voyager 2 in 1986. In 2011 an orbiter and probe mission was recommended to NASA, with a proposed launch date between 2020 and 2023. With huge advances in technology in the interim one can only wonder what strange and wondrous features such a mission might reveal.

Join the Springfield STARS Club on Tuesday, January 24th at 7:30pm at the Springfield Science Museum for a talk by Richard Sanderson on the topic: “Believe It or Not: Science in the Age of Misinformation.” Sanderson is curator of physical science at the Springfield Science Museum and manages the museum’s Seymour Planetarium and observatory. He is also an astronomy writer who has been published in international journals such as Sky & Telescope and Astronomy. He is co-author of the 2006 book, “Illustrated Timeline of the Universe.” Sanderson is a past president of the Springfield STARS Club and co-founder of the Connecticut River Valley Astronomers’ Conjunction, now in its 30th year. Refreshments will be served, and the public is welcome free of charge.