Keck helps scientists identify orbit of asteroid’s moon


Scientists have, after eight years of study, been able to document an unusual orbit of a moon around an asteroid near Jupiter.

Franck Marchis, astronomer at the Carl Sagan center of the SETI Institute, and a team of astronomers first discovered the moon orbiting what is known as a Trojan asteroid, called Hektor, in 2006. Trojan asteroids are found 60 degrees in front of or 60 degrees behind Jupiter and are believed to be captured objects from the Kuyper belt, outside of our solar system, W.M. Keck Observatory officials said in an announcement about the moon’s orbit.

To determine the orbit, “we had to build a completely new software,” Marchis said Monday. “We had to do from scratch a way to estimate the orbit.”

Another challenge, Marchis said, was getting time with Keck II’s 10-meter telescope while it was fitted with the Near-Infrared Camera 2 instrument behind the adaptive optics and laser guide star system. The telescope’s time is “highly prized” and has limited availability, Marchis said.

What they found was a 12-kilometer diameter moon with a dense core, and layers of ice, Marchis said.

They are difficult to study because of their small size and distance from the sun, Keck officials said.

“This research could be a good start to think of a mission to an asteroid,” Marchis said, adding there have been no such discussions yet.

Going to look at the Trojan asteroids could give scientists a look about 4.5 billion years ago, he said.

Marchis offered an illustration to show what kind of information scientists might find if they could investigate the asteroids. If the solar system is a house, the asteroids could be the kind of dust, dirt and other detritus found inside a vacuum canister, the kind of items that can provide clues about things that previously happened in the house, he said.

The Trojan asteroids moved into place during a less stable time period and then became locked there, he added.

When there are planets orbiting a star, there are a few points, called Lagrangian points, at which an equilibrium exists, Keck Observing Science Manager Bob Goodrich said.

“They’re kind of dips in the gravity where stuff an accumulate,” he said. That’s where these Trojan asteroids are located.

Goodrich said it’s amazing how small of items a telescope like Keck is able to observe.

The findings were published late last month in the Astrophysical Journal Letters.

“The orbit of the moon is elliptical and tilted relative to the spin of Hektor, which is very different from other asteroids satellites have seen in the main-belt,” said Matija Cuk, paper coauthor and scientist at the Carl Sagan Center of the SETI Institute. “However, we did computer simulations, which include Hektor being a spinning football shape asteroid and orbiting the Sun, and we found that the moon’s orbit is stable over billions of years.”

Since the 1970s, scientists have had information about Hektor’s unusual shape, about 250-kilometers across and elongated with what scientists called a dual shape. An artist’s rendering showed a shaped that looked as though two balls had been shoved together.

Hektor’s ice and dense rock makeup indicate it could have come from the Kuyper belt. August Kopff discovered Hektor in 1907. Marchis and other scientists are still looking for a name for Hektor’s moon.