North Korean leader Kim Jong Un arrived in China on Tuesday for a two-day visit, his third trip since March. Kim is expected to brief Chinese President Xi Jinping on his recent summit with President Trump. Kim and Trump agreed to work together toward the denuclearization of the Korean Peninsula. Trump also offered to guarantee the security of the North Korean regime and promised to end "war games" with South Korea, which both North Korea and China have criticized as provocative. The long-reclusive Kim also is expected to use the clout he gained from his meeting with Trump to push for relief from tough international economic sanctions. Harold Maass

If you're already planning your summer vacation at the shore, maybe it's time to reconsider.

Scientists have traveled all around the world, taking more than 100 samples from the ocean along the way, and discovered nearly 200,000 new species — of viruses. Separated into five different subgroups, these 195,728 viral populations expand our knowledge of marine viruses by a factor of 12.

While the sheer number of invisible viruses in the oceans might make you cringe, it's actually valuable information, Gizmodo explained. This giant catalog of viruses is essential to understanding how marine ecosystems function, especially with regards to microbes, which are tiny cellular organisms that make up over half of the life in the ocean, pound by pound.

The exciting new find was published on Thursday in the journal Cell, by a team of researchers led by Ann Gregory, a postdoctoral researcher at VIB, a life science research institute in Belgium. The new research "expands our knowledge of what the biological entities on our planet are," Gregory told Gizmodo.

Despite the huge set of data provided, this is still far from a complete list of every virus in the oceans, the study authors noted. But it will certainly prove useful to all sorts of scientific inquiry, from examining marine life to discovering new antibiotics. Learn more at Gizmodo. Shivani Ishwar

North Korea presented the United States with a $2 million bill for Otto Warmbier's hospital care — and the U.S. agreed to pay it, The Washington Post reports.

When a U.S. envoy, Joseph Yun, went to Pyongyang in 2017 to bring the detained American student home, the Post reports he was issued a $2 million bill. Warmbier had fallen into a coma after he was detained in 2016 and remained unconscious for 15 months, dying six days after he finally returned to the U.S.

Yun signed a pledge agreeing the U.S. would pay this $2 million bill under orders from Secretary of State Rex Tillerson and President Trump, the report says. Otto Warmbier's father, Fred Warmbier, told Post he hadn't heard about the hospital bill but that it sounds like a "ransom" for his son.

Trump had previously touted the fact that "we got our hostages back" from North Korea and "I paid nothing." CNN reports that the U.S. has not paid the bill, with a Trump administration official saying, "We made clear that they never going to get anything." Another source said that the bill did not come up during Trump's summits with Kim Jong Un but noted that it could come up in the future. Brendan Morrow

It's not former Vice President Joe Biden's first time on the presidential train. But seeing as he's safely boarded — albeit a bit late — for 2020, let's take a look back at his past journeys.

Biden's first bid was for the 1988 presidential race and, in no surprise given his Amtrak obsession, he revealed it in a June 1987 speech in Wilmington, Delaware's train station.

Yet Biden failed to keep his run on the rails, and hopped out of the contenders' car just a few months later.

As promised in that 1988 speech, there were "other presidential campaigns," namely 2008's. Biden formally revealed his run in a Jan. 31, 2007 Meet the Press appearance, and followed it up with a video on his website.

Biden's withdrawal from the race didn't come until nearly a year later after rolling into fifth place in the Iowa caucus, and he made that choice in a small speech to supporters and staffers. Of course, Biden still ended up in the White House, becoming former President Barack Obama's running mate at this Aug. 23, 2008 event in Illinois.

Compare these past announcements to Biden's 2020 video here. Kathryn Krawczyk

Former Vice President Joe Biden says he didn't even want former President Barack Obama's endorsement, anyway.

After Biden officially announced his presidential campaign on Thursday, an Obama spokesperson released a statement praising his "knowledge, insight, and judgment." But it stopped short of an endorsement, and CNN's Jeff Zeleny reported Obama is unlikely to endorse because he would prefer "to let the candidates make their cases directly to the voters."

Obama last election cycle endorsed Hillary Clinton in June 2016, one month ahead of the Democratic National Convention. In February, The New York Times reported that Biden and his allies don't expect Obama to endorse him or any other candidate in the 2020 Democratic primary, and that former first lady Michelle Obama is also unlikely to do so.

Asked about this lack of endorsement, Biden said on Thursday that he actually asked Obama not to do so. "I asked President Obama not to endorse," he said, CNN reports. "Whoever wins this nomination should win on their own merits." Brendan Morrow

Did you know Joe Biden takes the Amtrak?

Just a few hours after the former vice president announced his candidacy for president, he was already spotted back aboard his favorite mode of transportation. America's top train line has been as constant in Biden's life as presidential campaigns, and, unsurprisingly, it's already a big part of his 2020 one.

Biden got his public transportation reputation back in his senatorial days, riding the train back and forth between his family in Delaware and Capitol Hill every day. He even took the Amtrak home after President Trump's inauguration in 2017. Now, the train has yet again pulled back into Biden's station, both in reality and in a very prominent place on Biden's campaign website. Kathryn Krawczyk

Fox News legal analyst Andrew Napolitano is blasting President Trump over Special Counsel Robert Mueller's report, suggesting it proves he obstructed justice numerous times.

In an op-ed for Fox News, Napolitano wrote that Mueller's report includes "at least a half-dozen crimes of obstruction committed by Trump," including Trump allegedly asking his White House counsel to fire Mueller, something Trump has denied doing. "That's obstruction of justice," Napolitano definitively and repeatedly states in a video after running through a number of incidents described in the Mueller report.

The Fox News analyst ripped into the president for this behavior, writing, "ordering obstruction to save himself from the consequences of his own behavior is unlawful, defenseless and condemnable."

Napolitano also takes issue with Attorney General William Barr, saying he's "wrong" to say a person can't be guilty of obstruction if they aren't guilty of the underlying crime being investigated. Instead, Napolitano says, the "nearly universal view of law enforcement" is that any attempted interference with an investigation is obstruction, and the obstruction doesn't have to be successful to be unlawful.

Napolitano summarized the situation in a video, saying the report concludes that Trump "probably committed the crimes of obstruction of justice but probably should not be charged for them," which he calls a "head-scratcher." The question now, Napolitano writes in his op-ed, is whether Democrats will "utilize Mueller's evidence of obstruction for impeachment." Brendan Morrow