PASADENA, Calif. - Between feedings and diaper changes of his newborn daughter, Michael E. Brown may yet find an 11th planet.
Once conducted almost exclusively on cold, lonely nights, observational astronomy these days is often done under bright California sunshine.
When he has a few spare minutes, Dr. Brown, a professor of planetary astronomy at the California Institute of Technology, downloads images taken during a previous night by a robotically driven telescope at Palomar Observatory 100 miles away. Each night, the telescope scans a different swath of sky, photographing each patch three times, spaced an hour and a half apart.
In any one of the photographs, a planet or some other icy body at the edge of the solar system looks just like a star. Unlike a star it moves between the exposures.
Dr. Brown's computer programs flag potential discovery candidates for him to inspect. He quickly dismisses almost all of them - double images caused by a bumping of the telescope, blurriness from whirls in the atmosphere or random noise.
Sometimes, like last Jan. 5, he spots a moving dot.
Dr. Brown had rewritten his software to look for slower-moving and more distant objects.
On that morning, he was sitting in his Caltech office - unremarkable university turf sparsely decorated with a not-full bottle of Jack Daniel's, a dragon mobile, a dinosaur toothbrush, a Mr. Potato Head and other toys and knickknacks that long predated parenthood - and re-examining images from nearly a year and a half earlier, Oct. 21, 2003.
The first several candidates offered by the computer were the usual garbled images.
Then he saw it: a bright, unmistakably round dot moving across the star field.
He did a quick calculation. Even if this new object reflected 100 percent of the sunlight that hit it - and nothing is perfectly reflective - it would still be almost as large as Pluto.
That meant, without any additional data, Dr. Brown knew he had discovered what could be the 10th planet.
He noted the time: 11:20 a.m. Dr. Brown knew that astrologers would ask because they had asked after earlier discoveries of smaller Kuiper Belt objects.
He thought about a bet he had made with a friend, for five bottles of Champagne, that he would discover something larger than Pluto by Jan. 1, 2005, five days earlier. He sent her an e-mail message asking for a five-day extension.
Dr. Brown seems destined for future astronomy textbooks, either as the discoverer of the first new planet in 75 years or as the man who pushed Pluto out of the planetary pantheon. Astronomers have long argued over whether Pluto should be a planet and speculated that ice balls larger than Pluto might be hiding in the Kuiper Belt, a ring of debris beyond the orbit of Neptune. Several objects approaching the size of Pluto have been discovered in recent years.
Dr. Brown and two colleagues, David Rabinowitz of Yale and Chad Trujillo of the Gemini Observatory in Hawaii, are the first to point to something that is almost certainly larger than Pluto.
"If people want to get rid of Pluto, I'm more than happy to get rid of Pluto and say this one isn't a planet, either," Dr. Brown said.
"If culturally we would be willing to accept a scientific definition, that would be great," he continued. "The only thing that would make me unhappy is if Pluto remained a planet, and this one was not one."
So far, little is known about the new planet, which carries the temporary designation of 2003 UB313. It is currently nine billion miles from Sun, at the farthest point of its 560-year orbit.
A couple of centuries from now, its elliptical trajectory will take it within 3.3 billion miles of the Sun, closer than some of Pluto's orbit. And the orbit is surprisingly askew.
While most of the solar system circles the Sun in a flat disc, the new planet's orbit is tilted about 45 degrees from the disc.
Planet finding was not a career goal for Dr. Brown. Until recently, he was among those who argued that nothing in the Kuiper Belt deserved to be called a planet, not even Pluto.
Dr. Brown, 40, grew up in Alabama, a child of the 1970's, which left a mark in his speech patterns. For things he likes, he inevitably calls them "cool."
His father, an engineer at I.B.M., had moved to Huntsville to work on the giant Saturn rockets, which were being designed at NASA's Marshall Space Flight Center to carry astronauts to the Moon.
When he was finishing up his undergraduate degree in physics at Princeton, he thought he would pursue theoretical work in cosmology, devising ideas about how the universe came together.
Then James Peebles, a physics professor at Princeton, mentioned to him how astronomy needed more observers actually looking at the sky.
"That was it," Dr. Brown recalled. "As soon as he said it, I was like, O.K."
In graduate school at the University of California, Berkeley, he still planned to work on the far, far away - distant galaxies that blast out loud radio signals. His thesis adviser, Hyron Spinrad, made his graduate students also work on comets, because he was interested in them and could not get help otherwise. Dr. Brown was captivated as well. "I thought, This stuff is cool," he said.
That brought his interests inside the solar system. Later Dr. Brown came across a tiny, little-used 24-inch telescope at the Lick Observatory outside San Jose. "You find the telescope first and then find your thesis program," he said.
His thesis topic turned out to be the volcanoes on Io, one of the moons of Jupiter, and how the gases from the volcanoes are swept up into Jupiter's magnetic fields, accelerated into orbit around Jupiter and then slammed back into Io at 125,000 miles per hour.
He entered the planet-searching business through a chance opportunity. When he arrived at Caltech a decade ago, the 48-inch Samuel Oschin Telescope at Palomar was just finishing up a large sky survey. While many astronomers clamor for use of Palomar's main 200-inch telescope, Dr. Brown realized he could easily get ample time on the smaller one.
So, just as he did at Lick, he looked for a project to fit the telescope.
The first Kuiper Belt object had been discovered a few years earlier, and Dr. Brown thought it would be useful to do a systematic sweep of the sky to look for them. In past centuries, the trick to discovering a planet was knowing exactly where to look. Now, computers and automated telescopes have allowed a new strategy: look everywhere.
Dr. Brown has a love of code names, so he and his colleagues decided if they ever found something larger than Pluto, they would give it the code name Xena, after the television series starring Lucy Lawless as an ancient Greek warrior.
It was also partly a nod to Planet X, a long-hypothesized massive planet in the outer solar system.
In 2002, Dr. Brown and Dr. Trujillo turned up their first big find: a Kuiper Belt object about 775 miles wide, or about as large as Pluto's moon, Charon. They named it Quaoar, after a god in Native American mythology, and learned their first lesson in astronomical discovery: find a pronounceable name. (Quaoar is pronounced KWAH-o-wahr.)
A year later, Dr. Brown, Dr. Trujillo and Dr. Rabinowitz of Yale found something stranger, an object larger than Quaoar and much father out, eight billion miles. And stranger yet, its 11,000-year orbit carries it out as far as 84 billion miles, far beyond anything else known in the solar system.
Initially, they excitedly thought it might be larger than Pluto and called it Xena for a few days. But further measurements and calculations indicated it was probably, at most, three-quarters the diameter of Pluto. When they announced the discovery last year, they gave it the name of Sedna, after an Inuit goddess.
The name was easily pronounceable, but it peeved some astronomers, especially amateur asteroid searchers, who felt Dr. Brown had again flouted the International Astronomical Union's naming rules. The rules prohibit discoverers from publicly announcing any name, even a tentative one, before the union approves it, a process that takes months to years. The critics wanted the union to rebuke Dr. Brown and reject the name.
One amateur astronomer, Reiner M. Stoss, even proposed Sedna as a name for a small, earlier discovered asteroid, to thwart Dr. Brown.
Dr. Brown admitted, "I consciously broke the rules," but he felt that the preliminary designation, 2003 VB12, was too obscure and confusing for a noteworthy addition to the solar system. "I thought, This is stupid," he said. "This object needs to have a name before it goes public."
After Sedna, the astronomers also realized that there could be more discoveries lurking in their photographs.
Dr. Brown finds that betting is an effective way to spur scientific progress. He would have found the planet sooner or later, but late last year he realized that his best hope for winning the Champagne bet was to sift through thousands of candidates in the old images.
On Dec. 20, going through the images from the previous May, he discovered a new bright Kuiper Belt object.
It was big, but not big enough. He gave that one the code name of Santa.
When he later discovered a moon around Santa, he gave the moon the code name Rudolph. (When he discovered yet another Kuiper Belt object in April, he continued in the holiday vein and code named that one Easter Bunny. He even had a code name for his daughter before she was born and he and his wife had not yet settled on a name. The whiteboard in his office had a list of tasks labeled "TDBP" - To Do Before Petunia.)
He spent Christmas through New Year's examining old images.
Nothing turned up.
Then on Jan. 5 - not Jan. 8 as he had said at his news conference - he finally found one he could call Xena. "What if it's the size of Mercury?" he mused in his notes.
This time, Dr. Brown decided to play by the International Astronomical Union's rules and did not announce his real intended name for 2003 UB313, leading to rumors that he had officially proposed Xena.
Meanwhile, Dr. Brown, on family leave until the end of year, found a new set of data to work with: his daughter Lilah's sleeping and eating patterns.
In the hospital, he and his wife had, like many new parents, written down a record of feeding and sleeping times.
Dr. Brown wrote a computer program to generate colorful charts from the information and put them online at lilahbrown.com.
"Who wouldn't be fascinated?" Dr. Brown asked. "Well, I guess, most people."
Black bars indicate the times that his wife, Diane Binney, is breast-feeding Lilah. Blue bars indicate when Dr. Brown is feeding a bottle to her. Green bars indicate the hours Lilah is awake and content; red bars indicate the fussy times.
Dr. Brown said he hoped to find a pattern in Lilah's sleep cycle - she has been waking up, on average, every 2.5 hours. If one nap lasted only 1.5 hours, would that mean the next nap would last 3.5 hours, giving her parents a chance to rest?
A chart with cloudlike splatter of data points gave the unfortunate answer. "There is absolutely no correlation," Dr. Brown said.