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The tiny moons of Mars are hard to explain. Scientists aren’t sure how they formed and how they wound up in their current orbits. But a Japanese mission that launched this month could settle the conundrum. The mission is MMX – Mars Moons Exploration. It will scan both Phobos and Deimos – chunks of rock the size of a small city. And it will land on Phobos, gathering samples for return to Earth. Both moons are dark, like a class of asteroids. In fact, astronomers long suspected they were captured asteroids. In this scenario, rocky “leftovers” from the birth of the planets flew close to Mars. The planet was surrounded by a cloud of gas and dust. As Phobos and Deimos passed through it, the cloud acted as a brake, slowing them enough for Mars to grab them. But it’s not easy for a planet to capture an asteroid. And the orbits of the moons aren’t like those of the captured asteroids of the giant outer planets. So scientists came up with another model: a giant impact. A massive space rock could have slammed into Mars, blasting out material that formed a ring around the equator. The debris coalesced to form several small moons. Phobos and Deimos are the only survivors. In yet another scenario, Mars captured a single large asteroid. It was sheared apart by Martian gravity, creating a ring that gave birth to Phobos and Deimos. MMX will arrive at Mars next year – a big step toward solving the mystery of the Martian moons.   Script by Damond Benningfield

In Gulliver’s Travels, which was published 300 years ago today, Jonathan Swift wrote that the people of Laputa had made an important discovery: “two lesser stars, or satellites, which revolve about Mars.” The fictional moons were small and close to the surface, orbiting the Red Planet in a matter of hours. Earthly astronomers took a little longer to find the real moons – they weren’t discovered until 1877. They were named Phobos and Deimos – fear and panic – after attendants of the god of war. Phobos is the larger moon. It’s lumpy, with an average diameter of about 14 miles. It orbits just 3700 miles from the surface of Mars. It rises in the west, then sets in the east less than four-and-a-half hours later. Deimos is about eight miles in diameter. It’s about three times farther from Mars, so it takes about two-and-a-half days to cross the sky, from east to west. It’s shaped a bit like a potato with a big dimple on one side. Several spacecraft have flown past the moons. But they’ve raised a lot of questions about them. Now, 300 years after Gulliver’s Travels, scientists may take a big step toward finding some answers. Japan launched the Mars Moons Exploration mission this month. The craft will study both moons from close range. And it will touch down on Phobos, hoovering up a few grams of pebbles and dust for return to Earth. More about that tomorrow. Script by Damond Benningfield

The Moon is crossing the constellation Taurus. Tonight, it’s quite close to the bull’s shoulder – the Pleiades star cluster. The bull’s bright eye, the star Aldebaran, is well below the Moon as they climb into view. It’ll be about the same distance to the right of the Moon tomorrow night. A dead “starship” is headed in Aldebaran’s direction. It won’t get there for more than two million years. But just in case anyone finds it, it carries a message. Pioneer 10 was launched in 1972. It was the first spacecraft to fly through the asteroid belt, and the first to explore Jupiter, the Sun’s largest planet. After that, it raced out of the solar system and into interstellar space. NASA last heard from it in early 2003. Today, it’s more than 13 billion miles away. The “message” is a plaque that’s made of aluminum and coated with gold. It measures nine by six inches. It includes the outlines of a naked man and woman. They’re standing in front of an outline of Pioneer to indicate their size. It also includes a chart of the solar system that shows Pioneer’s home planet. Other diagrams help pinpoint Earth’s location in the galaxy. No one expects Pioneer to ever be found. It won’t get all that close to Aldebaran, and the star’s only known planet isn’t a good home for life. After Aldebaran, Pioneer 10 will continue sailing through the cosmos – an extinct emissary from Planet Earth. Script by Damond Benningfield

If you overlook the fact that you’d be instantly vaporized, there’d be one small advantage to standing at the surface of the Sun: You’d age more slowly than your friends and family back on Earth. The effect is called time dilation. It comes from Relativity – Albert Einstein’s theories of motion and gravity. They tell us that clocks at different locations tick at different rates. Keep in mind, though, that they tick at different rates as seen by observers moving at different speeds and in different gravitational fields. According to Special Relativity, as you go faster your clock slows down. General Relativity says your clock slows down as the pull of gravity gets stronger. On Earth, the effect has been confirmed by placing atomic clocks in high-flying jet aircraft. And GPS satellites are programmed to compensate for the effect. If they weren’t, the whole system would fail within days. Time dilation is more pronounced at the surface of the Sun because of the Sun’s great mass. A clock there would slow down by about 67 seconds per year compared to one on Earth. And when the Sun expires, its “corpse” will have even stronger gravity, slowing a clock by more than an hour per year. Time dilation is strongest just outside a black hole. An outside observer would see a clock at the cusp move almost infinitely slowly – never ticking off the final second before plunging into the black hole. Script by Damond Benningfield

Few of us have to hunt wild game to survive the long, cold winter these days. But that hasn’t always been the case. Native tribes and European settlers alike had to stock up as the weather grew cooler. And they relied on an autumn full Moon for help: the Hunter’s Moon. And that Moon is coming up tonight. It’s the full Moon after the Harvest Moon, which appeared in September. Like the Harvest Moon, the Hunter’s Moon helped people prepare for winter. Its light made it easier to see deer and other animals. And at high northern latitudes, the Moon rises only about a half-hour later each night around full Moon – a much smaller gap than average. So the big, bright Moon was in view by the time evening twilight faded – allowing hunters to stay in the fields long into the night. Despite what you might think, the Harvest and Hunter’s Moons aren’t any bigger and brighter than any other full Moons. The Moon’s orbit and its cycle of phases aren’t synchronized. So some years the Hunter’s Moon is closer than average. But in other years, it’s farther than average. This year we’re in luck, because it’s on the closer side. At the moment of full Moon, it’ll be about 230,000 miles away – a few thousand miles closer than average. That helps make this year’s Hunter’s Moon an especially beautiful sight, lighting the autumn fields for hunters – and everyone else, too. Tomorrow: stretching the year. Script by Damond Benningfield

Twenty-five years ago, NASA needed a hit. Its previous two missions to Mars had failed – both of them as they were arriving at the Red Planet. So it prepared the next mission with extra care, and sent it on its way on April 7th, 2001. The craft was named 2001 Mars Odyssey – a tribute to Arthur C. Clarke, the author of “2001: A Space Odyssey.” And like most of Clarke’s books, Mars Odyssey was a big hit. It entered orbit around Mars on October 23rd – 25 years ago this week. It’s the longest-operating spacecraft at any body in the solar system other than Earth. Among its many accomplishments, Odyssey has mapped the chemical and mineral composition of the entire Martian surface. It also discovered evidence of vast amounts of ice just below the surface. And it found places where liquid water once pooled on the surface. Those observations helped scientists pick interesting locations for landers and rovers. And it found the first caves ever seen on Mars – possible places for future missions to look for microscopic life. Odyssey also has served as a relay station for Mars landers and rovers. And it recorded radiation levels at the planet – critical information for planning human missions. As of late summer, the craft was still going. And barring any unexpected problems, it could add several more years to its record-breaking odyssey at the Red Planet. Script by Damond Benningfield

If you ignore the dark orange sky and the extreme cold, Saturn’s moon Titan might remind you of Earth. River channels empty into lakes and seas. Giant fields of dunes ripple across the surface. And clouds float through the sky, producing occasional rains. And if everything goes to plan, we should get some amazing views of that landscape in the next decade. A nuclear-powered “octocopter” will fly across the surface, covering several miles with each trip. It’ll monitor the weather and analyze the soil. Most important, it’ll search for elements of life – and evidence of life itself. Dragonfly is one of the most ambitious missions yet conceived. It’s scheduled for launch in 2028, and arrival at Titan six years later. Titan is about half-again the size of Earth’s moon. It has a cold, dense atmosphere that’s topped by “smog.” The atmosphere, surface, and lakes appear to contain lots of organic compounds – the building blocks of life. Except for the extreme cold, it may be a lot like Earth was about three-and-a-half billion years ago – at the dawn of life on our planet. So Dragonfly will help scientists determine if Titan is habitable – another home for life. Saturn is near our moon tonight. It’s close to the lower left of the Moon at nightfall, and even closer as they set, before dawn. It looks like a bright star. But you need a telescope to spot Titan – the target for a dragonfly.   Script by Damond Benningfield

The night sky is disappearing. Growing cities and towns pump more artificial light into the sky all the time. That creates a glowing dome that blots out the view of the Milky Way, meteors, and other beautiful but faint sights. Light pollution does more than make it impossible to appreciate the beauty of the night sky. It can interfere with the migrations of many animals, and it can harm human health. And it wastes energy by shining light into the sky instead of onto the ground, where it’s needed. In recent decades, though, some places have tried to limit the light pollution. They’ve passed laws that restrict outdoor lighting, keeping the sky as dark as possible. An international organization certifies the most successful ones. And number one on the list was Flagstaff, Arizona. It was declared the first International Dark-Sky City 25 years ago this week. Flagstaff began protecting the night in 1958. Lowell Observatory was adding a big new telescope, and it needed dark skies to get the best results. So the city placed restrictions on outdoor lighting. As the city grew over the following years, it beefed up those regulations, winning certification in 2001. Today, there are more than 60 dark-sky communities, plus dozens of dark-sky parks, reserves, and other sites. That includes a wide swath of West Texas, which is home to McDonald Observatory. These locations help keep the night sky from disappearing.   Script by Damond Benningfield

William Lassell made a fortune selling beer to factory workers in Liverpool. He used that money to set up his own astronomical observatory, called Starfield, outside Liverpool. And he equipped it with telescopes he built himself – some of the best in the world. Using one of those instruments, Lassell made a major discovery 175 years ago this week. Make that two discoveries: two large moons of the planet Uranus. They were named Ariel and Umbriel, after characters from the works of William Shakespeare and Alexander Pope. The moons are almost exactly the same size – about 720 miles in diameter. And they have a similar makeup – mixtures of rock and frozen water and methane. But they look different. Umbriel is dark, and it’s covered by many large impact craters. That suggests the moon is quiet and still – not much happens there. Ariel is brighter, and it’s much more interesting. It’s crossed by giant canyons and cliffs, with few craters. Liquid water may bubble to the surface from an underground ocean. At the surface, it freezes. That may push the surrounding crust, causing it to crack. So Ariel may be an active world orbiting a giant planet. Uranus is an easy target for binoculars. It’s halfway between Aldebaran – the bright eye of the bull – and the Pleiades star cluster. They climb into good view in late evening. But the view will be better before dawn, after the Moon has dropped from sight. Script by Damond Benningfield

The modern constellations offer a convenient way to appreciate the beauty of the night sky. Using the outline of a scorpion or a lion as a landmark makes it easier to find your way around. It’s also a good way to exercise your imagination. Our imaginations don’t all show us the same pictures, though. The western constellations were passed down from ancient Greece and Rome. And many of them are even older – they came from ancient Babylon and Sumeria. But just about every culture had its own star pictures – its own map of the night sky. An example is Capricornus. In western mythology, it represents a sea-goat – half goat and half fish – perhaps a story about the god Pan. But records from ancient China describe something different. Six of the stars in that region formed an ox, known as Niu – a sacrifice for mid-winter. Three others formed dams to hold water for the emperor’s fields, which were also in Capricornus. And other stars formed parts of different pictures – different stories in the night sky. Capricornus is low in the south at nightfall. The constellation isn’t especially bright, so it’s invisible from light-polluted cities. Under darker skies, you can see the outline of a wide triangle. Tonight, the gibbous Moon is near the triangle’s eastern point. That makes it easier to find where the sea-goat is, but harder to see its faint outline. Script by Damond Benningfield