Animation shows Ceres’ colors, terrains, 215 years after discovery
Using images taken by the Dawn spacecraft, members of the mission’s framing camera team created an animation simulating the various features and terrains that a viewer would see if he or she actually had the opportunity to fly over Ceres.
The animation comes on the 215th anniversary of Ceres‘ discovery by astronomer Giuseppe Piazzi, director of the Palermo Observatory in Sicily, on Jan. 1, 1801.
Piazzi initially thought his discovery – which he found using an instrument known as a Ramsden Circle – was a comet, as noted in a letter he wrote to astronomers Johann Elert Bode and Barnaba Oriani.
Two hundred years ago, Piazzi could not have envisioned a spacecraft visiting the object he discovered to take close-up photographs of its craters and map its features.
Questions about the nature of the object, which Piazzi named Ceres Ferdinandea after both the Roman goddess of agriculture, who was also patron deity of Sicily, and King Ferdinand of Sicily, were raised beginning at the time of its discovery and continue even today.
The name “Ferdinandea” fell into disuse, much like other homages to patron politicians, such as Galileo’s reference to the four big moons of Jupiter as the “Medicean stars” and William Herschel’s initial moniker for Uranus, “Georgium Sidus”, after England’s King George III.
Piazzi initially announced he had discovered a comet but did not publicize data from his observations, for which he was criticized by some astronomers.
He reported discovering Ceres, which he described as being faint with a color similar to that of Jupiter while he was working on a catalog of star positions.
After observing it again several nights later and noticing it had slightly moved, he realized it could not be a star.
Much like Herschel when he first discovered Uranus, Piazzi described his discovery as a comet, though his writings to Bode and Oriani indicate he wasn’t certain about this.
“I have presented this star as a comet, but owing to its lack of nebulosity, and to its motion being so slow and rather uniform, I feel in the heart that it could be something better than a comet, perhaps. However, I should be very careful in passing this conjecture to the public,” Piazzi wrote.
For a while in early 1801, his observations were curtailed by illness, bad weather, and Ceres’ movement behind the Sun, making it no longer visible at night.
The first indication Ceres was something other than a comet came from astronomer Jerome de Lalande, with whom Piazzi shared his observation data upon request.
Johann Karl Burckhardt, a student of de Lalande, calculated Ceres’ orbit and found it to be circular rather than highly elliptical, as typical of comets.
At the same time, Bode and Oriani strongly advocated the theory that the spacing of the Solar System’s planets from the Sun follows a specific pattern, a position that became known as the Titius-Bode hypothesis.
The position of Uranus, discovered in 1781 by Herschel, seemed to confirm that theory because the planet was located just where the proposal predicted it should be.
However, the Titius-Bode hypothesis also indicated there should be a planet between Mars and Jupiter. Assuming this world was yet to be discovered, a group of German astronomers created an organization known as the “Celestial Police” in 1800, just before Ceres’ discovery, to search for it.
Each of the group’s 24 astronomers searched 15 degrees of the sky in the ecliptic plane. Piazzi was not initially part of this group and was invited only after Ceres’ discovery.
Recognizing that Ceres was found just where the theory proposed it should be, Bode and Oriani each calculated an orbit for it believing it was their missing planet.
According to Ileana Chinnici, who published a booklet about Ceres for the Palermo Observatory to commemorate the 215th anniversary of its discovery, astronomers continued researching Ceres only because of their strong conviction that it was the “missing planet” orbiting between Mars and Jupiter.
“They ‘believed’ in the existence of the planet and were driven by the endeavor to confirm it,” Chinnici emphasized. “This shows how powerful are ideas, models, theories – yesterday as well as today,”
Mathematician Carl Friedrich Gaus, just 24 years old, calculated an orbit for Ceres with location predictions different from those made by other astronomers. Using these calculations, various astronomers, including Piazzi, successfully located Ceres again in late 1801 and early 1802.
Within a year of Ceres’ discovery, more objects were found orbiting between Mars and Jupiter, beginning with Pallas in March 1802.
The notion that these objects could not all be planets was initially put forward by Herschel, who coined the term “asteroid”, meaning “star-like”, because even with the most powerful telescopes of the time, these objects appeared as points of light, much like stars, and could not be resolved into disks.
Piazzi opposed the downgrade, which he attributed to a perceived desire by Herschel to be the only living person who had discovered a planet. “If an Asteroid Ceres must be called, so must also be called Uranus,” he stated.
Eventually, thousands of asteroids were discovered orbiting between Mars and Jupiter. Other than Ceres, none was large enough or massive enough to be spherical. Vesta and Pallas, the two next largest objects in the belt, are nearly spherical, both appearing to have had a big portion lobbed off by an impacting body.
The Hubble Space Telescope eventually confirmed Ceres is round, which led to its being reclassified again, this time as a dwarf planet.
With the technology of the late 20th and early 21st centuries, astronomers began peeling back the layers of mystery surrounding Ceres. NASA’s International Ultraviolet Explorer found hydroxide on the dwarf planet in 1992, and the European Space Agency’s (ESA) Herschel Observatory, a space telescope that studies objects in the far-infrared, discovered water vapor coming off Ceres in 2013.
NASA’s Dawn mission, launched in 2007, entered orbit around Ceres in March 2015 after spending a year orbiting and studying Vesta, supported by the Hubble Space Telescope, which observed the dwarf planet in ultraviolet light.
Dawn‘s findings transformed Piazzi’s point of light into something he could hardly have imagined, emphasized Dawn mission director and chief engineer Marc Rayman.
Ceres is a highly-cratered world with diverse terrains that include a cone-shaped mountain and reflective areas that stumped astronomers for almost a year and are now presumed to contain salt.
In keeping with Piazzi’s theme, features on Ceres are being named for deities and festivals related to agriculture.
Dawn is currently in its lowest orbit, 240 miles (385 km) from the dwarf planet’s surface.
The animation just released is composed of images that were taken from a higher orbit, about 900 miles (1,450 km) above Ceres’ surface, between August and October 2015.
“The simulated overflight shows the wide range of crater shapes that we have encountered on Ceres. The viewer can observe the sheer walls of the crater Occator, and also Dantu and Yalode, where the craters are a lot flatter,” said Dawn mission specialist Ralf Jaumann of the German Aerospace Center, DLR.
“Our knowledge, our capabilities, our reach and even our ambition all are far beyond what Piazzi could have imagined, and yet it is because of his discovery that we can apply them to learn more, not only about Ceres itself but also about the dawn of the Solar System,” Rayman said.
Video Courtesy of NASA Jet Propulsion Laboratory
Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.