Exiting Defense Secretary Jim Mattis has been replaced by his deputy, Patrick Shanahan, a former Boeing executive who will assume the role Jan. 1. Last week, Mattis said he’d remain in his post until February. The notoriously fractured relationship between President Donald Trump and the former Marine general split permanently in the wake of Trump’s shock announcements that he’d withdraw U.S. troops from Syria and Afghanistan — moves that blindsided key allies. Given the tension between the two, it’s unlikely Mattis will be given a celebratory send-off.

At least 281 people are dead and 1,000 hurt as rescue workers continue to comb through debris in coastal towns on Java and Sumatra after a tsunami tore ashore without warning Saturday night. Local residents have been warned that ongoing eruptions by the Anak Krakatau volcano — which is believed to have caused the disaster by setting off undersea landslides — could trigger another tsunami in the Sunda Strait. Indonesian President Joko Widodo ordered a speedy cleanup effort on the affected islands, saying, “Hopefully, those who are left have patience.”

Ahead of a President’s Working Group meeting today to discuss the outlook of financial markets — and after the S&P 500’s 7.1 percent drop last week — Steven Mnuchin tweeted that he called executives from America’s six largest banks to ensure they could weather any sudden dips. The CEOs reportedly told Mnuchin they had “ample liquidity” for lending and other market operations. Meanwhile, White House aides reportedly discussed arranging a meeting between President Trump and Fed chief Jerome Powell amid Trump’s anger over the central bank’s rising interest rates.

Following President Trump’s recent decision to withdraw U.S. troops from Syria, and despite Ankara’s pledge to delay an offensive against U.S.-backed Kurdish forces, the Turkish military has reportedly massed troops near a Kurdish-held town in northern Syria. The convoy is said to include scores of armored vehicles and weaponry. Yesterday Trump tweeted that he had a “long and productive” call with Turkish President Recep Tayyip Erdogan, who welcomed Trump’s decision. Meanwhile, a Kurdish military official said his forces were “taking necessary measures” in case they’re attacked.

Know This: Acting White House chief of staff Mick Mulvaney has said the federal government shutdown could last into the new year. British authorities have released two people previously suspected of illegal drone activity over Gatwick Airport. And Supreme Court Justice Ruth Bader Ginsburg is reportedly back to work after undergoing cancer surgery.

To our readers: OZY wishes you a happy, healthy holiday! We’ll be back to catching you up — and vaulting you ahead — on Dec. 26.

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For the 63rd straight Christmas Eve, the North American Aerospace Defense Command will track Santa Claus’ sleigh despite the U.S. Congress failing to pass spending legislation. Around 1,500 volunteers will respond to calls and emails from around the world, NORAD said. The tradition started in 1955, when a typo in a Sears ad urged children to dial Santa at a number that was really a private Air Force line. Military staff and volunteers have handled inquiries ever since as their “tracking” technology has become more sophisticated.

Yesterday the American space tech company launched its first national security space mission as the Falcon 9 rocket carried the $500 million GPS III SV01 satellite, the first of several upgrades to the U.S. Air Force GPS network. Since the 1990s, the Air Force has launched two iterations of GPS satellites, and Sunday’s launch is the first of a new generation. GPS III SV01, nicknamed Vespucci after Italian cartographer and explorer Amerigo Vespucci, will provide three times more accurate information, helping everyone from soldiers to travelers finding their way on the road.

Archaeologists uncovered the petrified remains of a harnessed, saddled horse tied to a stable in the Italian village destroyed by Mount Vesuvius in A.D. 79. The find, announced Sunday, was made at a villa — excavated in the early 1900s, but later reburied — and was thought to have been owned by a high-ranking military officer. Several other fossilized horses were also found. They were likely killed by volcanic ash or boiling vapors before they could outrace the eruption, said researchers, who hope to open the villa to the public.

Dec. 23 is Festivus, the alternative holiday “for the rest of us” made popular by the hit TV series — during which an aluminum pole is put up instead of a tree, and featuring traditions like an “Airing of Grievances” and “Feats of Strength.” In Google’s own tradition, there’s now a special graphic to acknowledge the holiday: A desktop search of “Festivus” renders a pole down the left side of the results page. Republican Sen. Paul Rand is a notable Festivus observer, and used the “Airing of Grievances” to highlight government waste.

Both the league and the NFL Players Association have requested an inquiry into Carolina Panthers safety Eric Reid’s claim he was targeted with “random” drug tests as punishment for participating in a collusion lawsuit against the NFL. In the suit, Reid asserts the league kept him off the field due to his national anthem protests. Since filing the grievance, the six-year pro said he was drug tested seven times in 11 weeks. “If my name came up that many times I’d buy a lottery ticket,” said Panthers head coach Ron Rivera.