November 1, 2000

C.U. Researchers Detect Saturn Moons

Print More

Two Cornell professors were among an international team of astronomers that may have discovered four moons orbiting Saturn, last Thursday.

The celestial bodies were discovered more than nine million miles from Saturn’s surface, and according to their orbital calculations, the objects are almost certainly new satellites of the large planet.

The discovery was announced at the annual meeting of the Division for Planetary Sciences of the American Astronomical Society in Pasadena, Ca. Profs. Joseph Burns, theoretical and applied mechanics, and Philip Nicholson, astronomy, are members of the team, and Brett Gladman Ph.D. ’96 — responsible for planning observations of the moons — led the expedition.

The astronomers detected four faint bodies using several telescopes around the world during the past two months.

Gladman spotted the first two moons on Aug. 7 in La Silla, Chile, using the European Southern Observatory’s 2.2-meter telescope. He confirmed the sightings with J. J. Kavelaars, research associate, McMaster University on Sept. 23 and 24 in Mauna Kea, Hawaii.

Until the finding, the sixth planet from the sun was known to have only one irregular, outer satellite. That moon, Phoebe, was discovered 102 years ago at a Peruvian observatory by W. Pickering, an American astronomer.

Upon this latest discovery, Saturn took the lead in the solar system with a total of 22 moons. Uranus has 21.

So far, very little is known about the moons, according to the Cornell astronomers. Estimates of their size — between six and 30 miles in diameter — are based on hypotheses of their reflectivity.

The discovery of two Uranian satellites in 1997 prompted the team of scientists to begin research on Saturn.

“That motivated us to use the Canada-France-Hawaii telescope, with its larger CCD array camera, to conduct a more systematic search for irregular moons of the outer planets,” said Matthew Holman, astrophysicist, Harvard-Smithsonian Center for Astrophysics, one member of the team.

“We started with Uranus and Neptune and found three additional Uranian moons but no Neptunian moons,” he said. Then, “after that success we decided to move next to Saturn.”

The four irregular moons have elliptical orbits, and their enormous distance from Saturn indicates that they were captured into orbit after the planet was formed. This is unlike larger regular satellites that are closer to the planet with nearly circular orbits and are thought to have formed as Saturn was created.

For the past four years, the team of astronomers discovered nine irregular satellites around Uranus and Saturn.

While studying at Cornell, Gladman developed the technique that was used to find the moons from Saturn.

The process for discovery involved attaching light-sensitive semiconductors — called charge-coupled devices — to telescopes in order to identify the distant points of light. About three digital images of a particular field are taken each hour every night.

Nicholson said, “The same piece of sky is imaged for about three to four different nights to notice where objects have moved.”

The team warned that the findings are only in the beginning stages. The researchers have found other specks of light that may turn out to be Saturnian moons as well.

“Of course, we have announced candidate satellites that will need further observation to prove that they are indeed satellites,” Holman said. “But our experience with the Uranian moons gives us confidence that they are likely to be satellites.”

Nicholson said that the vast majority of satellites located in Saturn’s vicinity are orbiting the planet.

“It would be rare for them to be orbiting the Sun,” he said.

However, “there is also about a five percent chance of these objects being comets in the outer solar system,” he added.

According to Nicholson, the discovery is just the beginning for the astronomers. Much more work lies ahead.

“The next work is to confirm the orbits of these satellites by observing them as often as possible before Saturn goes behind the sun in March, 2001,” said Jean-Marc Petit, astronomer, Observatoire de la Cote d’Azur in France, a member of the team. “We want also to extend the search to larger distances from the planet, [because] we have only looked up to less than one degree away.”

Nicholson said that the team will determine the objects’ orbits by next August.

Casini, a National Aeronautic and Space Administration probe, is on its way to Saturn for a 2004 arrival that may be able to explore the four satellites, according to Kavelaars.

After fully investigating Saturn’s moons, the team will move on to explore Jupiter.

Archived article by Ritu Gupta