On Monday night's Late Show, David Letterman asked Donald Trump if he knows fellow rich guy Donald Sterling. The answer is yes, kind of. "I do know him, yes," Trump told Letterman, before backtracking a bit. "I mean, I've seen him.... I don't know him well. He's turned out to be... not so hot — what a total disaster." Yet Trump was impressed that Sterling is walking away from owning the Los Angeles Clippers with $2 billion, when the team, in Trump's estimate, is worth maybe $900 million, tops. And that's a good point: Sterling is a national disgrace, but who's laughing now? Sterling, maybe. Trump, definitely. --Peter Weber

The first baby has been born using technology that allows for the combination of DNA from three different people, CBS News reports. The procedure, which is illegal in the United States, was performed by a team led by Dr. John Zhang of the New Hope Fertility Center in New York at a facility in Mexico; the baby boy is now six months old.

The mother carried a genetic mutation for Leigh syndrome, a neurological disorder that is often fatal within a few years. Two of the mother's children had died from the syndrome, and she'd had four miscarriages. The new baby has so far been healthy and showed no signs of the disease thanks to the "revolutionary" technique, which "involved removing some of the mother's DNA from an egg, and leaving the disease-causing DNA behind," The Associated Press reports. "The healthy DNA was slipped into a donor's egg, which was then fertilized. As a result, the baby inherited DNA from both parents and the egg donor."

“This is the very first time at least in human reproduction that the offspring are produced with three parties — one sperm and different parts of two eggs ... So this is very revolutionary,” Zhang told CBS News. And while the procedure might not be allowed in the United States, Zhang insisted, "To save lives is the ethical thing to do." Jeva Lange

The mission to make humans "a multiplanetary species" just got a little bit closer to becoming a reality. Elon Musk's SpaceX program published a video Tuesday describing how the proposed Interplanetary Transport System would actually work — and it involves 28,730,000 pounds of thrust for lift-off, the support of a refueling pod, and winged solar panels to provide additional power to the ITS:

Musk is delivering a presentation on colonizing and building a city on Mars at the International Astronautical Conference in Guadalajara, Mexico (you can follow continual updates at The Verge, here). And for those dreaming of future travels to a terraformed Red Planet, you're in luck — the planet makes an unnaturally blue-and-green appearance at the end of the video.

Musk also said Tuesday that he believes in the future the cost of travel to Mars will be as inexpensive as buying a house. SpaceX plans to send its first ship of humans to the planet as early as 2024. Jeva Lange

Mother Earth isn't the only one suffering from rising levels of air pollution. A new report by the World Health Organization out Tuesday revealed that in 2014, 92 percent of the world's population was living with levels of air pollution that exceeded what WHO considers to be safe.

In particular, WHO is concerned about higher concentrations of pollution particles that are smaller than 2.5 micrometers, as these particles are tiny enough to "be inhaled, travel into the lungs, and enter the bloodstream," The Washington Post reported. "People think of air pollution as a respiratory disease," said Carlos Dora, head of WHO's air pollution team. "And in fact, it's heart disease, strokes and cardiovascular. Because there's very small particles that go into the blood. ... The damage air pollution does to the vessels is similar to the damage that cholesterol or high blood pressure do."

In 2012, an estimated 7.3 million people died from air pollution, produced both inside the home and outdoors. The problem is particularly acute in "low- and middle-income countries," which WHO reported accounted for 88 percent of the 3 million premature deaths caused by outdoor air pollution in 2012.

Still, wealthier countries certainly aren't in the clear. In Europe, cities including Paris and London failed to meet air quality standards, and in America, both Los Angeles and Manhattan fell short. Becca Stanek

While Monday night's first presidential debate had record-breaking viewership in the U.S., it also caught the attention of invested parties abroad. Russia state-sponsored media reportedly liked what they were seeing, but it was hardly the same scene in Mexico City:

"You want to go to Mexico or some other country? Good luck," Donald Trump told U.S. manufacturing companies during Monday night's presidential debate against Hillary Clinton.

Thousands of miles away, the 200 people packed into Pinche Gringo, a Texas-style barbecue restaurant in Mexico City, broke into cheers and clinked their glasses frothed with beer.

It was just one of Trump's six references to Mexico last night, and a signal to drink for U.S. expats watching in Mexico.

The patio, filled with wooden tables, a bar pouring draft beers, and a kitchen designed to look like an Airstream trailer, was packed with Democrats and Hillary Clinton supporters who would raise their glasses and yell Salud! every time Trump mentioned "Mexico." Predictably, there weren't any/many Trump fans in the bar — or anywhere else in Mexico, for that matter. [Fusion]

Up to a million American citizens live in Mexico; the event at Pinche Gringo, organized by Democrats Abroad, also helped expats register to vote. "Trump is having a huge effect. His comments have really helped gin up interest," Doug Hall, an American citizen who now lives in Mexico, told Fusion. "There is a lot of momentum this year. We are registering a lot of people." Jeva Lange

Senate Democrats blocked a proposed government spending bill Tuesday, downing the proposal with a 55-45 vote that threatens to shut down the government if an agreement is not reached by the Oct. 1 deadline. The resolution, backed by Republican leadership, would have funded the government through Dec. 9 but was rejected on the grounds that it did not give aid to Flint, Michigan, but did provide for flood victims in Louisiana, Maryland, and West Virginia. Democrats have said they don't oppose the flood aid, but that it should not be included in the funding bill unless aid also goes toward Flint's ongoing water crisis.

"Why do you feel you have to punish people in Louisiana ... for Flint when there's a pathway forward on Flint through the WRDA bill?" Sen. Bill Cassidy (R-La.) said, naming a bill the Senate approved to give Flint $220 million for water infrastructure. The House version of the WRDA bill — fully named the Water Resources Development Act — did not include the provision for aid to Flint, however, meaning the two chambers would need to re-negotiate it after returning from the election hiatus.

"The Republicans are essentially saying, 'The disasters in our states are more important than the disasters in your state,'" Senate Minority Leader Harry Reid (D-Nev.) said. "It is unfair, and it is wrong.” Jeva Lange

The first presidential debate of the 2016 election cycle was the most-watched debate ever, with 80.9 million people tuning in to see Donald Trump and Hillary Clinton go head to head. Clinton and Trump's first presidential showdown topped the second-most viewed debate in U.S. history, between Jimmy Carter and Ronald Reagan in 1980, by 300,000 viewers.

The debate was especially accessible for viewers this year as it was shown on every major news network, in addition to being streamed on Facebook and YouTube. By comparison, the first debate between Mitt Romney and President Obama in 2012 garnered only 67 million viewers on average. And while some analysts had expected viewership to drop after the first hour of the debate, Nielsen data showed early signs of viewers sticking around to watch the whole thing.

The official Nielsen number tallies only traditional TV viewers, disregarding online streaming or group-watching events, so likely many more than 80.9 million people actually watched the debate. Still, Monday's record falls short of some early expectations the debate would attract 100 million or more viewers, which would have been comparable to Super Bowl 50. Jeva Lange

Former New York City Mayor Rudy Giuliani said in a Monday night interview that Hillary Clinton might be "too stupid to be president," if she really believed her husband Bill Clinton over then-White House intern Monica Lewinsky when he denied early allegations of their affair in the 1990s. "She didn't just stand by him, she attacked Monica Lewinksy," Giuliani said. "After being married to Bill Clinton for 20 years, if you didn't know the moment Monica Lewinsky said that Bill Clinton violated her that she was telling the truth, then you're too stupid to be president."

While Donald Trump was too "gentlemanly" and "reserved" to bring up the subject at the presidential debate Monday night, Giuliani suggested he would not have hesitated to mention Bill's past indiscretions. Giuliani also said the fact that Trump didn't broach the topic is evidence he's a feminist.

You can hear the rest of Giuliani's evidence in his full interview, below. Becca Stanek