5 things to know for your new day -- Monday, September 28

(CNN)World leaders gather at the U.N. NASA makes a big announcement. And the Pope returns home.

It's Monday, and here are five things to know for your new day.

UNITED NATIONS GENERAL ASSEMBLY

    Pow wow: President Obama will mix speeches with meetings today, as he gives his annual address at the U.N. General Assembly and meets with world leaders, most notably Russian President Vladimir Putin. Yesterday Obama promised today's address would have a more blunt tone -- "Along with the grey hair, I'm becoming more likely to speak my mind" -- but it remains to be seen if that bluntness will extend to his meeting with Putin. Other world leaders -- Chinese President Xi Jinping, Iranian President Hassan Rouhani and Cuban leader Raul Castro -- will also address the U.N.
    President Obama and Russian President Vladimir Putin will cross paths again in New York.

    NASA

    Big reveal: So what's the big announcement that NASA will make today about Mars? Evidence of aliens? Too obvious. Or maybe they've found Mark Watney, Matt Damon's fictional astronaut from "The Martian" movie? No, that's too promotional. The best bet? CNN's Michael Pearson says it could be a confirmation of water flowing periodically on the Red Planet's surface. Not as sexy as aliens, but still pretty important (if it happens).

    POPE FRANCIS

    Homeward bound: The White House. Madison Square Garden. Independence Hall. It was quite the itinerary for Pope Francis during his first trip to the United States. He's returned home to Rome, just hours after celebrating Mass in Philadelphia, where he praised America's tradition of religious freedom and immigration, but warned that injustice can tear a society down. Francis said he left the U.S. with "a heart full of gratitude and hope."
    Pope Francis meets with victims of sexual abuse
    Pope Francis meets with victims of sexual abuse

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    ISIS

    Strange bedfellows: Has Iraq made a deal with the devil (or devils)? Over the weekend Iraq said it's struck an agreement with Russia, Iran and Syria to share intelligence in the fight against ISIS. This follows recent news that Russia is building up its military presence in Syria. And add to this the fact that the U.S.-led coalition's bombing campaign hasn't exactly yielded fruit, it's further evidence the fight against ISIS isn't going so well.

    GEORGIA EXECUTION

    Set: 7 p.m. Tuesday. That's when Kelly Gissendaner is scheduled to die. Unless a hearing this morning in Atlanta stops it, she'll be the first woman executed in Georgia in 70 years. Gissendaner was convicted of arranging the 1997 murder of her husband. Her execution has been postponed twice this year: once for a winter storm and a second time because of controversy over the types of drugs Georgia uses in executions. Her children and others want Gissendaner's death sentence commuted, saying that she's a changed person and has been rehabilitated.
    Kelly Gissendaner