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ESA/Rosetta/NAVCAM, CC BY-SA IGO 3.0

Scientists have wondered for decades where xenon (the heaviest stable noble gas on Earth) came from. Now they have a partial answer: at least one-fifth of it in Earth's atmosphere may have originated in comets, a new study finds.

Eight of the nine different isotopes of xenon on Earth have been traced to different parts of the cosmos that came together as the planet and our solar system formed. But the source of the remaining xenon isotope was a mystery.

How they solved the mystery: Data collected by the Rosetta spacecraft, whose mission is to study a comet known as 67P, showed that xenon leaking from it had been trapped in the comet's icy surface from a time before our solar system was formed. It matched one of the isotopes of xenon on Earth that scientists had been unable to source – strongly suggesting it came from comets just like 67P.

What it means: If such a significant portion of xenon found in Earth's atmosphere came from comets, then it's also possible that comets raining down on our planet for millions of years also delivered other important materials, like water and the building blocks of life.

Go deeper

The dark new reality in Congress

National Guard troops keep watch at security fencing. Photo: Kent Nishimura/Los Angeles Times via Getty Images

This is how bad things are for elected officials and others working in a post-insurrection Congress:

  • Rep. Norma Torres (D-Calif.) said she had a panic attack while grocery shopping back home.
  • Rep. Jim McGovern (D-Mass.) said police may also have to be at his constituent meetings.
  • Rep. Adam Kinzinger (R-Ill.) told a podcaster he brought a gun to his office on Capitol Hill on Jan. 6 because he anticipated trouble with the proceedings that day.
Off the Rails

Episode 3: Descent into madness ... Trump: "Sometimes you need a little crazy"

Photo illustration: Sarah Grillo/Axios. Photos: Tom Williams/CQ-Roll Call, Chip Somodevilla/Getty Images

Beginning on election night 2020 and continuing through his final days in office, Donald Trump unraveled and dragged America with him, to the point that his followers sacked the U.S. Capitol with two weeks left in his term. This Axios series takes you inside the collapse of a president.

Episode 3: The conspiracy goes too far. Trump's outside lawyers plot to seize voting machines and spin theories about communists, spies and computer software.

President Trump was sitting in the Oval Office one day in late November when a call came in from lawyer Sidney Powell. "Ugh, Sidney," he told the staff in the room before he picked up. "She's getting a little crazy, isn't she? She's really gotta tone it down. No one believes this stuff. It's just too much."

Convicts turn to D.C. fixers for Trump pardons

Trump confidante Matt Schlapp interviews Jared Kushner last February. Schlapp is seeking a pardon for a biotech executive. Photo: Samuel Corum/Getty Images

A flood of convicted criminals has retained lobbyists since November’s presidential election to press President Trump for pardons or commutations before he leaves office.

What we're hearing: Among them is Nickie Lum Davis, a Hawaii woman who pleaded guilty last year to abetting an illicit foreign lobbying campaign on behalf of fugitive Malaysian businessman Jho Low. Trump confidante Matt Schlapp also is seeking a pardon for a former biopharmaceutical executive convicted of fraud less than two months ago.