Phobos in 2008, as seen by the Mars Reconnaissance Orbiter. Photo: NASA/JPL-Caltech/University of Arizona
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Mars' unusual moons may have been created by collision with Pluto-sized object

Mars' moons are unusual in the Solar System - for their size, shape and colour from their parent planet. Where did they come from? We've got some clues to work with.

Of the four terrestrial planets in the inner Solar System, Mars has most of the moons. Phobos and Deimos are unusual, however, or at least unusual to us because of how different they are to our own Moon. (Residents of the moons of Jupiter and Saturn would probably be nonplussed.)

They're both a lot smaller relative to Mars than the Moon is to Earth, and - in the case of Phobos in particular - much closer. Both are less spherical and more potato-shaped, because they aren't large enough to be rounded under the force of their own gravity. Deimos (on average, roughly 12km across) orbits Mars at a distance of around 24,000km; Phobos, which is an average of 22km across, orbits at a height of only 6,000km. In astronomical terms, that's extraordinary - it's closer than many artificial satellites orbit Earth. Phobos is so close, in fact, that it orbits Mars faster than Mars rotates. To anyone watching from the planet's surface, the moon will appear to rise and set three times a day. Oh, and they both contain gateways to Hell.

This setup has puzzled astronomers for the more than a century since the moons were first discovered, and, this being Mars, some truly fantastical theories have been put forward over the year. (The best of these, undoubtedly, was Soviet astronomer Iosif Samuilovich Shklovsky's belief that Phobos was a kind of Martian space station, though better data soon ruled this out. Sadly.) As we've sent more and more landers and orbiting probes to Mars, astronomers have managed to gather a significant amount of data on these two moons as well, leading to two main schools of thought: one that says that they're captured asteroids, and another that says that they're made up of the debris from a large impact many millions of years ago.

Phobos passes in front of Deimos, as seen from the surface of Mars by the Curiosity rover in August 2013. Image: Nasa

This second hypothesis is currently seen as the best explanation for how our own Moon formed - the proto-Earth would have been struck by another object roughly the size of Mars, blasting both bodies into pieces which reassembled into the Earth-Moon system we know today. (Though there are some slight issues that are still proving tricky to resolve, such as the differences in chemical composition between the two bodies.) And, according to a new paper published in Icarus, that kind of scenario also works for explaining the Martian system.

Planetary scientists Robert Citron of UC Berkeley, and Hidenori Genda and Shigeru Ida of the Tokyo Institute of Technology, performed some simulations of the debris patterns that would be expected from large impact events, and what that debris would subsequently be expected to do. The authors stress that it's still a preliminary study, but the results show that the impact theory seems relatively plausible.

Mars has a huge depression covering most of its northern hemisphere, known as the Vastita Borealis. When Mars was younger, and warmer, it's possible that it formed the basin for the planet's largest ocean, and illustrations of a wet Mars tend to show the Borealis as a huge polar ocean. The researchers note that the shape and formation of the Borealis is consistent with what would be expected with a large, ancient collision event, as well as the thickness of the planetary crust, so they primarily look into whether something of that scale would be enough to form both Phobos and Deimos, while adjusting variables like the collision object's mass, its speed, its angle of impact and so on to see what happened.

"Our simulations show that for Borealis-scale impacts, enough material is ejected into orbit to form accretion disks that could produce Martian satellites," the researchers write. They estimate that an object of 1.68 x 1022kg - or something roughly the size of Pluto - once smashed into Mars' polar region, ejecting a debris disc of roughly 5 x 1020kg. An event like this would have actually caused the creation of possibly hundreds of "moonlets", less than 100m across each, which would have either rained back down onto the Martian surface over time, or have been forcefully ejected fast enough to reach escape velocity, and left the Martian system altogether. This would explain many of the craters we've seen on Mars, which look "stretched" compared to, say, the neat ones we see on our own Moon - they're the result of orbiting moonlets falling to the surface at angles close to horizontal, like pebbles skimming across a pond.

This is still only theoretical though, of course - this paper is just an exploration of whether such an impact was a) possible, and b) would provide enough debris so that whatever wasn't lost to space or back to the surface would match the real masses of Phobos and Deimos. The conclusion is that "at least one" could have been formed this way, or maybe both. "While a Borealis-scale impact may generate sufficient debris to form both Phobos and Deimos, further studies of the debris disk evolution are necessary," they write. "Our results can serve as inputs for future studies of martian debris disk evolution."

Ian Steadman is a staff science and technology writer at the New Statesman. He is on Twitter as @iansteadman.

Photo: Getty/New Statesman
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The mother lode: how mums became the ultimate viral fodder

The internet’s favourite joke used to be "your mum". Now it's "my mum".

“I was like: oh my.”

Terri Squires is describing her reaction to the news that she had gone viral. Last month, more than 213,000 people shared a tweet about Terri – but it wasn’t sent from her account. The 50-year-old Ohioan was propelled to internet stardom by her son, Jeff, who had tweeted about his mother.

“I didn’t really realise what it meant at first until he was like: ‘Mum, you do realise that millions of people have looked at this?’ … When I started seeing those numbers I was like: ‘Oh boy’.”

It’s a funny story – and Terri laughs heartily all she tells it. After coming out of a meeting, she checked her phone and noticed a picture of a missing – white – dog on Facebook. She quickly texted 17-year-old Jeff to check that the family dog, Duey, was safe. “That’s not Duey… Duey’s face is brown,” replied her son. “OK – just checking,” replied Terri.

More than 600,000 people “liked” Terri’s mistake after Jeff shared screenshots of the text message exchange on Twitter. But Terri is just one of hundreds of mums who have gone viral via their sons and daughters. Texts mums send, mistakes they make, things they fail to notice – these have all become the ultimate viral fodder.

In the last three months alone, Gerald’s mum went viral for a microphone mishap, Adam’s mum shot to Twitter fame for failing to understand WhatsApp, Lois’ mum got tricked by her daughter, Harry’s mum was hit in the head with a football, Hanna’s mum misunderstood a hairstyle, and Jake’s mum failed to notice her son had swapped a photo in her home for a portrait of Kim Jong-un.

But how do the mothers behind these viral tweets feel?

“I'm pretty much a mum that everybody wants to talk to these days,” says Terri, with another warm laugh. The mum of three says going viral “is not that big of a deal” to her, but she is happy that her son can enjoy being a “local superstar”. But is she embarrassed at being the punchline of Jeff’s joke?

“Believe me, I have thick skin,” she says. “I kinda look at what it is, and it’s actually him and his fame. I’m just the mum behind it, the butt of the joke, but I don't mind.”

Not all mums feel the same. A handful of similar viral tweets have since been deleted, indicating the mothers featured in them weren’t best pleased. A few people I reach out to haven’t actually told their mums that they’re the subject of viral tweets, and other mums simply don’t want any more attention.

“I think I’ve put my mum through enough with that tweet already,” says Jacko, when I ask if his mum would be willing to be interviewed. In 2014, Jacko tweeted out a picture of his family writing the word “cock” in the air with sparklers. “This is still my favourite ever family photo,” he captioned the tweet, “My mum did the ‘O’. We told her we were going to write ‘Love’.”

“No one ever expects to call home and say ‘Mum, have you heard of something called LADbible? No, you shouldn’t have, it’s just that a quarter of a million of its fans have just liked a photo of you writing the word ‘cock’ with a sparkler’,” Jacko explains.

Although Jacko feels his mum’s been through enough with the tweet, he does say she was “ace” about her new found fame. “She’s probably cooler about it all than I am”. Apart from the odd deletion, then, it seems most mums are happy to become viral Twitter stars.

Yet why are mums so mocked and maligned in this way? Although dads are often the subject of viral tweets, this is usually because of jokes the dads themselves make (here’s the most notable example from this week). Mums, on the other hand, tend to be mocked for doing something “wrong” (though there are obviously a few examples of them going viral for their clever and cunning). On the whole: dads make jokes, mums are the butt of them.

“We all think our mums are so clueless, you know. They don’t know what’s going on. And the fun thing is, one day we come to realise that they knew way more of what was going on than we thought,” says Patricia Wood, a 56-year-old mum from Texas. “People always kind of make fun of their mums, but love them.”

Last year, Patricia went viral when her daughter Christina tweeted out screenshots of her mum’s Facebook posts. In them, Patricia had forgotten the names of Christina’s friends and had candidly written Facebook captions like: “My gorgeous daughter and her date for formal, sorry I forgot his name”. Christina captioned her tweet “I really can't with my mom” and went on to get more than 1,000 likes.

“I felt, like, wow, it was like we’re famous, you know. I thought it was really cool,” says Patricia, of going viral. Her experiences have been largely positive, and as a part-time Uber driver she enjoys telling her customers about the tweet. “But I did have one bad experience,” she explains. A drunken passenger in her car saw the tweet and called Patricia an “asshole”.

Another aspect of viral fame also worried Patricia. She and her daughter were invited on a reality show, TD Jakes, with the production company offering to pay for flights and hotels for the pair. “I have too many skeletons in my closet and I didn't want them to come dancing out,” says Patricia, of her decision not to go. “By the time I got off it, it would be the Jerry Springer show, you know. I’m kind of a strange bird.”

On the whole, then, mothers are often amused by going viral via their offspring – and perhaps this is the real beauty of tweeting about our mums. Since the moment they earn the title, mums can’t afford to be fragile. There is a joy and relatability in “my mum” tweets – because really, the mum in question could be anyone’s. Still, from now on, mums might be more careful about what they tell their sons and daughters.

“When I send Jeff a text now I make sure I’m like: ‘Is my spelling correct? Is what I’m saying grammatically correct?’,” says Terri, “Because who knows where the words are gonna end up?”

Amelia Tait is a technology and digital culture writer at the New Statesman.