A minority student group at the University of California, Los Angeles, is accusing a professor of racism for correcting grammar and punctuation in minority students' assignments. The group, Students of Color, says "the grammar 'lessons'" are acts of "micro-aggression" that have created "a hostile class climate." Professor Val Rust said he was just trying to help students, but conceded they "don't feel that is appropriate."

About 4.3 billion years ago, up to 20 percent of Mars was covered by an ocean that reached about a mile in depth, according to scientists from NASA's Goddard Space Flight Center. The polar ice caps today contain the 13 percent of that ocean that didn't evaporate into space when Mars' atmosphere largely disappeared.

Geronimo Villanueva and his colleagues at Goddard reached this surprising conclusion by using infrared beams to make a map of water molecules in what's left of the Martian atmosphere, they report in Thursday's issue of the journal Science. "Our study provides a solid estimate of how much water Mars once had, by determining how much water was lost to space," Villanueva said in a statement.

Scientists already knew that Mars once had water, but this extends the red planet's wet period for much longer. "With Mars losing that much water, the planet was very likely wet for a longer period of time than was previously thought, suggesting it might have been habitable for longer," said Goddard's Michael Mumma, another author of the report. Mumma and Villanueva explain their research and its implications in greater detail in the NASA video below. —Peter Weber

The murder of Russian opposition figure Boris Nemtsov, right outside the Kremlin in the heart of Moscow, has prompted a lot of speculation about what role, if any, Vladimir Putin played in the killing. Jon Stewart didn't directly point the finger at Putin on Thursday night's Daily Show, but he did laugh at the Russian president's insistence that he will personally lead the investigation into Nemtsov's murder.

"Oh good, he's vowing to find the real killer," Stewart laughed, showing a photo of OJ Simpson. "That's a promise that always inspires confidence. The only thing that could be more OJ is if Putin started stealing sports memorabilia...." which, of course, he allegedly has. Not that Stewart was done with the comparisons: Putin started out as a fairly normal guy, like Draco Malfoy in the first Harry Potter novel, he said, but after spending too many nights "in the dungeon-y parts of Hogwarts" with the bad kids, Putin has become "Lord Vladimort." Hopefully there isn't a sequel. —Peter Weber

When Michael Brown, a black teenager, was shot by white police officer Darren Wilson in Ferguson, Missouri, last August, everyone was outraged — just not for the same reason, Jon Stewart said on Thursday night's Daily Show. Now, a new set of Justice Department reports suggests, "everybody was right!" The DOJ declined to press charges against Wilson and also found a troubling history of racism and de facto extortion by the Ferguson police. "According to our Justice Department," Stewart summarized, "everybody's anger was separate but equally justified."

Stewart largely left the "self-vindicating gloating" about Wilson to Fox News, while he and correspondent Jessica Williams tackled the Ferguson PD's habit of stopping black residents for things like "manner of walking along roadway," then funneling the resulting selective fines to city coffers — to the tune of $2.6 million in 2013. "What? $2.6 million?" Stewart said. "Maybe they don't hate blacks, they just love green." Williams played up the shake-down angle, but watch for Jason Jones' cameo at the end. —Peter Weber

About 20,000 Iraqi army troops, Shiite militia members, and Iranian advisers are advancing on Tikrit, in Iraq's largest effort to retake a city from Islamic State control. ISIS is staging counter-attacks and, sources tells Reuters, setting fire to oil fields about 20 miles northeast of Tikrit to slow the assault. Torching the Ajil oil field, ISIS apparently believes, will protect them from Iraq military helicopters.

Before ISIS conquered Tikrit last August, the Ajil field produced about 25,000 barrels of oil and 150 million cubic feet of gas a day. Under ISIS control, that amount has gone down significantly, but ISIS partly relies on its oil sales to fund its self-proclaimed caliphate.

Here's something you don't see every day (or night): A giant panda walking through the deserted streets of a town in southwest China. Closed-circuit television captured the bear as it ambled down the road late one night, seemingly enjoying having the streets all to herself. Experts who viewed the footage believe the animal is about 2 years old, and say that pandas are commonly found in this area. —Catherine Garcia

A long-term substitute Spanish teacher in Columbus, Ohio, was sentenced to 90 days in jail after showing students the explicit film The ABCs of Death, featuring graphic violence and sex.

Sheila Kearns, 58, was found guilty of four counts of disseminating matter harmful to juveniles. Kearns — who doesn't even speak Spanish — showed The ABCs of Death to students on April 11, 2013, and two classmates testified that they found it extremely disturbing. "This is what happens when you put a teacher in a class that she cannot teach," Judge Charles A. Schneider said, according to The Columbus Dispatch.

The excuse Kearns came up with further infuriated Schneider: Kearns claimed that she didn't watch the movie before putting it on, and had no idea what it was about. (The title didn't give her a clue?) She said that the entire day, her back was turned to the television, and she never once turned around to see what was on the screen. Schneider didn't fall for it, calling her claim "unconscionable. There's no way you'll persuade me that's what happened."

On Thursday night's Late Night, Jada Pinkett Smith talked about working with hot topless men on Magic Mike XXL, and told Seth Meyers that the film finally made her understand that thing about men having two separate, competing command centers. "For the first time in my life, that other head below started talking to me: Procreate, procreate, procreate, procreate," she said. "My top head was, like, 'Jada, there is not a Will Smith on this set, you can't procreate with nobody!'" That whole day of filming, she added, "I felt really bad for guys."

That led to Pinkett Smith talking about how she enjoys watching her husband's on-screen sex scenes. As with her use of "procreate," she got the message across using family-safe language. "When I'm with Will, I get to experience him physically," Pinkett Smith explained, "but very rarely do I get to see what he looks like when he's in the game." Meyers kept his head, but at the end he conceded that "this is the hottest interview I've ever done." And yet, somehow, it's safe for work. —Peter Weber

It's been 20 years since the U.N. women's conference in Beijing, where 189 countries adopted a platform for action to achieve equality for women, but Phumzile Mlambo-Ngcuka says that no country on earth has reached gender equality.

The executive director of UN Women said that while there has been some progress — mostly in women’s health and girls’ education — violence against women and a lack of women in decision-making roles are "global phenomena" that make equality difficult. "The sheer scale of the use of rape that we've seen post-Beijing, I think that tells us that the women's bodies are viewed not as something to respect, but as something that men have the right to control and to abuse," she told The Associated Press. Leaders across the world need to start speaking out "very strongly and very openly" against sexual violence and the denial of women's rights, she added.

The platform for action from the Beijing conference called for the end of discrimination against women and the closing of the gender gap in health, human rights, employment, education, and other areas. Today, there are less than 20 female heads of state and government and the percentage of women lawmakers has only increased by 11 percent over the past two decades. "We just don't have critical mass to say that post-Beijing women have reached a tipping point in their representation," Mlambo-Ngcuka told AP. Next week, the Commission on the Status of Women will meet to revisit the Beijing platform.

Whoever takes over for Jon Stewart at The Daily Show — and now we know it won't be Samantha Bee — will have plenty of opportunity to hire new talent. On Thursday, TBS announced that it has signed Bee for her own topical comedy show, as yet unnamed, that will allow her to "apply her smart and satirical point of view to current and relevant issues." TBS also recently poached Bee's husband, Jason Jones, for a scripted comedy series.

Jones and Bee will be executive producers on both shows, and TBS is talking up the "family affair" angle. "We actually have their kids coming in next week to pitch us animation," said Brett Weitz, TBS executive vice president of original programming, in a statement. Presumably TBS will leave the comedy writing to the pros.

The notoriously press-shy Harper Lee isn't one to mince words, and she let a pesky reporter know that his efforts to get her to talk were all in vain.

Over on AL.com, Connor Sheets admits that he basically stalked Lee for several days, trying to reach the author through her lawyer and publisher before actually going to her nursing home in Monroeville, Alabama. Despite the fact that she has been known to tell reporters asking for an interview "not just no, but hell no," Sheets said he finally decided to send her a two page letter on Feb. 5. He let her know that while he didn't expect a response, he was hoping she would "confirm that she is in fact lucid and fully in control of the destiny of Go Set a Watchman," her soon-to-be-released book.

Instead of answering this insulting question — did he seriously expect her to write back, "Why yes, I am completely lucid! Thanks so much for your concern about my mental faculties, random stranger!" — she returned the now-crumpled letter with a brief message scrawled on the bottom: "Go away! Harper Lee." Sounds like a fitting response to someone who just can't take a hint.