I'm Caitlin Hofmeister, and welcome to SciShow Space News!
 
Let’s start on Mars, where last week the Curiosity rover took its third sample, hopefully scooping up more evidence that there was once abundant liquid water on the planet. Pausing on what looked like sandstone, Curiosity came upon a dark, bumpy, fine-grained rock formation that mission scientists named Windjana. Wondering what chemical process would create such a texture, the scientists had the rover drill a two-centimeter hole into the rock. They’re now examining the powdered sample with Curiosity’s suite of chemical analysis instruments, called the Sample Analysis at Mars, or SAM, to gain insight into how Martian sand deposits apparently turned into sandstone, because that process usually involves water. And pinpointing the chemistry of the water that created the sandstone might help scientists learn more about the processes that created other landmarks, like Curiosity's ultimate destination – the strange layered mountain known as Mount Sharp. Curiosity has roved over four kilometers on its way to Mount Sharp and collected three samples. The first two were of mudstone, also created by watery conditions. So if this sample indeed turns out to be sandstone, that'll make three pretty solid pieces of evidence that Mars once had abundant liquid water.
 
Now, you might’ve heard buzz recently about a secret space plane that's been circling Earth. Aaaand it’s not really a secret. The fact that the thing exists definitely isn’t a secret. But the precise details of its mission remain unclear. It’s called the X-37B Orbital Test Vehicle and -- having been launched in December of 2012 -- it’s now been orbiting Earth for more than 500 days, which is nearly twice as long as the engineers thought it would last. The vehicle is a project of the U.S. Air Force, which has taken over the initiative from NASA to develop a new generation of reusable spacecraft. In fact, earlier this year, the X 37 program moved into the same hangar at the Kennedy Space Center where the space shuttle program used to operate. Kind of like the shuttle, X-37b launches vertically with the aid of an Atlas V rocket and lands horizontally, like a plane. But otherwise it bears only a superficial resemblance to our beloved shuttles. First of all, X 37b has no crew, and it’s less than 9 meters long, with a payload bay about the size of a pickup truck. It has a single engine for propulsion, but otherwise it runs on solar power, so it can recharge during flight. And satellite images suggest it has made very few maneuvers on its current mission, so it seems to be running very efficiently. X-37b can also orbit at a lower altitude than the space shuttle did -- around 175 kilometers, about half of the shuttle’s cruising altitude. 
 
Soooo, what is it doing up there? While there has been debate about whether it could be used as a spy satellite, the official line from the Air Force is that it’s flying to prove that it can fly. We have a lot of experience with reusable craft, thanks to the shuttle program, but X-37 can show us how we can pilot craft remotely, and also how long we can keep spacecraft up there. Once the testing phase is over, the Air Force says X 37 orbiters will have lots of applications, like rendezvousing with satellites and fixing solar arrays. What the military purposes of this vehicle might be, we can only speculate, and we don’t like to do that.
 
Finally, I want you to squint real hard at the Segue-1, the faintest galaxy ever detected. It’s being described as a “fossil” from the early universe, but it might be more accurate to say it’s a galaxy that just never grew up. Segue-1 isn't all that far away — it’s actually orbiting our own Milky Way galaxy — but it's so dim we can barely see it. It only has about 1,000 stars in it, and just seven that we can actually see. In 2013 astronomers from the Carnegie Institution for Science analyzed five of the Segue-1's stars, red dwarfs that are much older and dimmer than our Sun. And they found something kind of strange: Segue-1 has fewer metals than any known galaxy. Heavy elements, like iron, are more than 3,000 times less abundant there than they are in our own galaxy. That's because galaxies build heavy elements as they form more and more generations of stars. 
 
Stars form from clouds of gas, and when they reach ignition, the elements from those gases fuse into heavier elements, just as the Sun fuses hydrogen into helium. Eventually stars become so massive that they explode in supernovae, leaving behind clouds of heavier elements than the first clouds had. And the generation that forms after that fuses elements that are heavier still. But because Segue-1 lacks these heavy elements, it suggests that it formed only one generation of stars 13 billion years ago, and then stopped. Astronomers think the galaxy was just so small, the elements released from the first supernovae didn't create clouds massive enough to form new stars. So Segue-1 is essentially an entire galaxy composed of simple, light elements — a window into what all galaxies once looked like, when the universe was young.
 
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