Mount Kilimanjaro.

How many of us will ever stand at its peak?

Jessica Biel will.

Jess has joined with singer Lupe Fiasco, creator of the hot debut CD Lupe Fiasco's Food & Liquor, and Aussie thesp Isabel Lucas, on an expedition to climb Mt. K., which at 19,000 feet is the highest point in all of Africa.

The Summit on the Summit adventure, scheduled for January, was organized by singer-producer Kenna ("Say Goodbye to Love") to raise awareness of the need for clean water worldwide. Kenna says his dad suffered from waterborne diseases as a child in Ethiopia.

Jess, 27, said she was "astonished" to learn that more than a billion people across the globe have no access to clean water. "This is a basic human necessity that needs to be addressed now," she said.

Nuclear bombshell, part deux

Mackenzie Phillips, who this week dropped a nuclear bombshell when she told Oprah she had a decade-long incestuous affair with her pops, "Papa" John Phillips of The Mamas & the Papas, yesterday defended Papa as a "good man."

The 49-year-old American Graffiti star writes in her new memoir, High on Arrival, that the affair began in '79 when she was 19. It ended, she writes, 10 years later when she had an abortion after becoming pregnant with her dad's child. (Her dad died in '01.)

The actress, who has been outspoken about her lifelong struggles with drugs, also writes that she regularly did drugs with dad.

Yesterday on NBC's Today, Mackenzie defended Papa, saying they lived in "a very permissive time and a very rock-and-roll world, and pretty much anything went." Her dad "did the best he could," she said.

Mackenzie's account is contested by her stepmother - and former Mamas and Papas member - Michelle Phillips. "I have every reason to believe it's untrue," she tells the Hollywood Reporter. She says Mackenzie is using tall tales to sell her book. Meanwhile, Mackenzie's half-sister, Chynna Phillips, tells US Weekly Mackenzie told her about the incest in '97. Chynna says she believes it happened.

Travolta testifies in extortion trial

John Travolta took the stand in a Nassau, Bahamas, court Wednesday to describe how he helped a nanny perform CPR on his 16-year-old son Jett, who died Jan. 2 after suffering a seizure while the family was on holiday.

"Jeff [Kathrein], the other nanny, was doing some compressions. I was doing the breathing," Travolta said. He publicly admitted for the first time that Jett "was autistic . . . [and] suffered from a seizure disorder."

Pleasant Bridgewater, a former senator, and Tarino Lightbourne, an ambulance driver, are on trial for attempted extortion. They allegedly threatened to release Jett's medical records unless John paid them $25 mil.

An 'Anatomy' baby

Ellen Pompeo, 39, who embodies the very heart and soul of ABC's heartful and soulful drama, Grey's Anatomy, has been delivered of a girl, her rep tells Usmagazine.com. It's the first baby for Ellen and husband Chris Ivery. "Her name is Stella Luna Pompeo Ivery," her rep says. "She was born Sept. 15." Wonder why it took Ellen a week to announce it? Consider this: Grey's season debut was set for . . . last night.

New babe for Jude's brood

Brit smoothie Jude Law, 36, isn't only the charmingest man in Hollywood - he's also one of the most fecund: The All the King's Men star is a father for the fourth time.

The lucky vessel for Jude's prolificity?

Why, it's Samantha Burke, 24, the would-be actress Jude dated last year while filming Sherlock Holmes in New York. Burke's rep, Eileen Koch, tells People that the model-actress on Tuesday gave birth to a 5-pound-12-ounce baby girl. "Samantha Burke is overwhelmed with joy at the arrival of her beautiful and healthy baby girl, Sophia," Koch says. "The baby and mom are doing wonderful."

Jude, who previously sired three kids with ex-wife Sadie Frost, acknowledged that Burke was carrying his baby less than two months ago. He is currently playing Hamlet at New York's Broadhurst Theater. (To make more babies, or not. That is the question. . . .)

A new 'View' for Heidi

Heidi Montag, 23, who symbolizes all that is good, clean, pure, and sacred about America, will be a guest host on The View Thursday, filling in for the show's moral compass, Elisabeth Hasselbeck, who is on maternity leave. Cohost Whoopi Goldberg once chided Heidi and hubby Spencer Pratt for being p.r.-crazy, narcissistic jerks who staged ludicrous photo ops, fake weddings and the like.

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Contact "SideShow" at sideshow@phillynews.com. This column contains information from Inquirer wire services.