WAIKOLOA, Hawaii » Caltech astronomer Mike Brown, called the "planet killer" for his work that led to the demotion of Pluto, says the most fascinating object he has ever seen is the ball of rock and ice he named after a Hawaiian goddess.

"It might be safe to say it is the strangest object we have ever found in the solar system," he said in an interview Thursday.

Brown, in South Kohala for the 20th anniversary celebration of the Keck Observatory, says nothing has intrigued him more than Haumea, which he discovered in 2003. But discovering its true nature took additional years of research, much of it with the Keck.

"This is one of my favorite Keck detective stories," Brown said during a presentation Thursday at the Fairmont Orchid hotel.

After heated debate among scientists, Pluto, long the ninth planet of the solar system, was demoted to dwarf planet after Brown discovered another object, Eris, beyond the orbit of Neptune that was bigger than Pluto. Both exist in a region called the Kuiper Belt.

Today there are eight known major Kuiper Belt objects, including Eris, Pluto and two with Polynesian names: Haumea, named after the goddess of childbirth, and Makemake.

"Each one of the objects, they’re sort of like my kids," said Brown, whom Time last year named one of the 25 most influential people in space exploration. "I have stories I could tell you about each one."

Instead, he focused on Haumea in his presentation before about 140 scientists, academics, journalists and Keck donors.

"We named the object Haumea in honor of all the work that happened here at Keck on it," he said. "It’s a fantastic name. We chose the name very deliberately. In Hawaiian mythology, the children of Haumea are pieces of her that have broken off and populated the Hawaiian Islands."

Haumea is an oblong object with about the same radius as Pluto over its long axis and about a third of Pluto’s mass.

But it has other characteristics that make it unique in the solar system, Brown said.

» It’s rotating at breakneck speed.

"It’s a pretty massive object out there, and with its four-hour rotation period, it still is the fastest rotating large object anywhere in the solar system," Brown said. "It really sticks out as a quite strange object."

» It has a much greater density than Pluto or the other dwarf planets.

"Haumea is almost entirely made out of rock, which is something totally unexpected in the outer solar system," he said.

» It is coated with pristine ice.

"Haumea has the most pure water ice surface of anything we have been able to measure in the outer part of the solar system," he said, pointing to an analysis of its reflected light that showed a dramatic dip along a certain wavelength. "That dip right there occurs only if the water ice is in pure crystalline form."

He described it as "rocky on the inside, icy on the outside," adding, "It’s kind of like an M&M you don’t really want to eat."

Explanations for such oddities pointed to a collision with another body during the early stage of the solar system, Brown said, but theoreticians initially dismissed that possibility. Only after later findings, including the discovery at Keck of its tiny moons, Hi‘iaka and Namaka, did the naysayers come aboard, Brown said.

For instance, most moons in the Kuiper Belt, including Pluto’s moon Charon, result from a "mutual capture," essentially falling into each other’s gravitational arms.

But that happens only with objects roughly the same size.

By contrast, Hi‘iaka has only about 1 percent of Haumea’s mass, Brown said.

And there is a family resemblance: Hi‘iaka also has pristine ice.

"So if you wanted to somehow come up with a capture mechanism, you’d have to first capture it — which is impossible, and then you’d have to have accidentally captured the most unusual other Kuiper Belt object we have ever seen," he said.

"The most obvious answer seemed to me was that Haumea used to be a larger object and another object in the Kuiper Belt came and smacked it, sort of a glancing blow, started it spinning and broke off a lot of the ice that used to be there," Brown said. Some of the broken-off material clearly turned into its moons, he said.

"That fast spin would have elongated it and we’re left with the Haumea that we have today," he added. "It’s hard to imagine how you could have gotten Haumea otherwise."

But the future is equally intriguing, Brown said.

Haumea is in an oscillating orbit that will bring it close to Neptune in about 400 million years.

"When you cross the orbit of Neptune, two things can happen," Brown said in an interview. "You can get scattered outward, never to return. You can get scattered inward, and eventually if you get scattered inward, if you make it past Jupiter — Jupiter kind of plays goalkeeper for the inner solar system — Haumea would end up being the brightest comet probably ever in the history of the solar system.

"I calculated once that it would be brighter than the full moon for hundreds of years."