StarDate

To borrow from “Alice in Wonderland,” the case for life on Mars keeps getting curiouser and curiouser. Two rovers have discovered organic compounds there – the chemical building blocks of life – in locations that are thousands of miles apart. And some recent looks at results from the Viking landers of the 1970s suggests they, too, might have found organics. So it’s possible that microbes might have inhabited Mars in the past – and might do so even today. Some of the best evidence comes from the Perseverance rover. In 2024, it studied a formation known as Bright Angel – layers of sediment deposited at the bottom of a river perhaps three and a half billion years ago. A rock named Cheyava Falls contained a lot of organics. And a study earlier this year confirmed the finding. The compounds could have been produced by microscopic life. But there are several other possible explanations, including chemical reactions in the rocks themselves. Perseverance stored a sample of Cheyava Falls for return to Earth. Laboratory analysis could tell us for sure how the organics were formed. But NASA has nixed a planned sample-return mission. So we’re a long way from satisfying our curiosity about life on Mars. Look for Mars quite near the Moon early tomorrow. It looks like a bright star. They’re especially close as they climb into good view, around 2:30 or 3. We’ll talk about the Moon and another companion tomorrow. Script by Damond Benningfield

The Moon will run a gauntlet of bright stars and planets the next few mornings, from the twins of Gemini to the heart of the lion. The twins are up first. Pollux and Castor will perch to the upper left of the Moon at dawn tomorrow. Pollux is the brighter of the two, and it’ll be closer to the Moon. On the following mornings, the Moon will slide past Mars, Jupiter, and Regulus. These encounters are possible because all of these objects are near the ecliptic – the Sun’s path across the sky. The stars all maintain the same position relative to the ecliptic from month to month and year to year. Regulus, for example, is less than half a degree away from it – less than the width of a pencil held at arm’s length. The planets, on the other hand, can shift from one side of the ecliptic to the other. That’s because their orbits around the Sun are tilted a bit. The Moon’s orbit is tilted as well, by about five degrees. So the Moon can swing a little farther from the ecliptic. Tonight, it’s a few degrees north of it. By Wednesday, when it’s closest to Regulus, it’ll be just south of it. Despite that wiggle room, the Moon passes close to each of these bright pinpoints during every month-long cycle of phases. And when the geometry is just right, it can even cover them up – which it will do to Jupiter on Tuesday. We’ll have more about that later in the week, and more about the Moon and Mars tomorrow. Script by Damond Benningfield

Saturn is a “superior” planet. Among other things, it’s the second-largest and second-heaviest planet in the solar system. Technically, though, what makes it “superior” is its location. It’s the sixth planet from the Sun, so its orbit is outside Earth’s orbit. Superior planets can line up opposite the Sun in our sky – a point known as opposition. And that’s what Saturn is doing now. It’ll reach that point early Sunday. So for a while, it’ll be in the sky all night, and shine brightest for the year. Only a few planets and stars will outshine it. A planet looks especially bright at opposition for a couple of reasons. For one thing, it’s closest to Earth. Saturn, for example, will be about a hundred million miles closer than average. Another reason is the viewing angle. At opposition, a planet is reflecting more sunlight directly toward Earth than at any other time. In effect, the planet is a more efficient “mirror.” We see the same effect with the Moon. A full Moon – which also is in a “superior” position – is about six times brighter than a half Moon. The change in the Moon’s brightness is complicated by other factors, but the principle is the same – a superior Moon puts in a superior show – just like the superior planet Saturn. Saturn is low in the east at nightfall. It looks like a bright star. It climbs high across the south during the night, and is low in the west at dawn. Script by Damond Benningfield

This isn’t a sound effect from a sci-fi movie. Instead, it’s the “voice” of the auroras on the planet Saturn – radio waves that have been shifted to wavelengths we can hear. They were recorded by the Cassini spacecraft as it closed in on Saturn two decades ago. The radio waves are produced by the complex interplay between Saturn’s magnetic field and the solar wind – a steady flow of charged particles from the Sun. Motions deep inside the planet generate the magnetic field, which is about as strong as Earth’s. But because Saturn is much bigger than Earth, its magnetic field is much bigger as well – it fills a huge volume of space. The magnetic field forms a teardrop-shaped “bubble” around Saturn. That bubble deflects much of the solar wind. But some of the particles make it through. The lines of magnetic force guide some of them toward the magnetic poles. They spiral in, emitting radio waves as they do so. And when the particles hit the upper atmosphere, they create auroras – shimmering curtains powered by the Sun. Saturn is putting in its best appearance of the year. It’s at opposition – it lines up opposite the Sun. It’s closest to Earth, so it shines brightest. And it’s in view all night. The giant planet looks like a bright golden star. It’s low in the east at nightfall, and climbs high across the south later on. Script by Damond Benningfield

Saturn puts in its best appearance of the year over the next few nights. On Sunday, it’ll reach opposition – it will line up opposite the Sun. It’s closest to Earth at opposition, so it shines brightest. And it’s in view all night. It looks like a bright golden star. It’s low in the east at nightfall, and climbs high across the south later on. Saturn reaches opposition every 12 and a half months – the result of the combined motions of Saturn and Earth. Earth orbits the Sun at an average speed of about 67,000 miles per hour. Saturn is more than nine times farther from the Sun. And thanks to the laws of orbital motion, it moves only a third as fast as Earth. Johannes Kepler formulated those laws four centuries ago. He determined that the planets follow elliptical orbits; instead of perfect circles, the orbits are stretched out. There’s a relationship between the planet’s distance and its orbital period – the time it takes to make one full turn around the Sun. And a planet moves fastest when it’s closest to the Sun, and slowest when it’s farthest. Earth’s distance varies by only about three percent, so there’s not much change in its orbital speed. But Saturn’s distance varies by more than 10 percent, so there’s a bigger change in its speed. All of this works together to bring Saturn into alignment every 12 and a half months – shining at its best. More about Saturn tomorrow. Script by Damond Benningfield

To modern eyes, the stars of Sagittarius form the outline of a teapot. But in Greek mythology, the constellation was far more extensive. It represented a centaur – half-man, half-horse – holding a bow and arrow. And the brightest star in the constellation plays a role in both of those pictures. Kaus Australis is at the lower right corner of the teapot. It also represents the southern end of the bow – in fact, that’s the meaning of its name. It’s actually a binary – two stars in a wide orbit around one another. One of the stars is like the Sun. But from the system’s distance of about 145 light-years, it’s much too faint to see with the eye alone. The star we can see is much bigger and heavier than the Sun, and about 500 times brighter. And it spins in a hurry – once every 1.6 days, compared to almost four weeks for the Sun. If it were spinning just a little faster, it would rip itself apart. In fact, it’s closer to that self-destruct point than any other star yet seen. As a result of its rotation, the star is squashed – it’s about a third wider through the equator than the poles. And because they’re closer to the star’s core, the poles are thousands of degrees hotter than the equator. Astronomers can’t explain the star’s high-speed rotation. The star could be siphoning gas from a much-closer companion that’s hidden from view – spinning up the tip of the archer’s bow. Script by Damond Benningfield

Galaxies aren’t good neighbors. They can stretch and pull the galaxies around them, rip them apart, and even gobble them up. A case in point is the Magellanic Clouds – the largest satellite galaxies of the Milky Way. The Large Magellanic Cloud is about 165,000 light-years away. It’s about a third as wide as the Milky Way, and perhaps one-tenth as massive. The small cloud is a little smaller and farther away. Both of them are being distorted by the Milky Way’s gravity. And both may be incorporated into the Milky Way billions of years from now. But they’re also interacting with each other. In fact, a recent study says the gravity of the large cloud may be ripping the smaller one apart. Researchers have studied the system for more than a decade from an observatory in Chile. They’ve measured the motions of millions of stars. And they found that the stars in the Small Magellanic Cloud aren’t moving the way they expected. Most models say the galaxy forms a rotating disk, like the Milky Way. But the observations revealed that most of the stars are moving outward – away from the center of the galaxy. And that applied even to the stars in the center itself. The most likely cause is the pull of the Large Magellanic Cloud. Its gravity is dragging the stars away from their galactic home. That could eventually rip the smaller galaxy apart – leaving only some shredded remnants for the Milky Way. Script by Damond Benningfield

If you’re searching for life on another world, you don’t want to find life that’s hitchhiked from Earth. But preventing contamination isn’t easy. Over the past few decades, we’ve identified quite a few worlds in the outer solar system that could be habitable. These worlds are coated with frozen water. But they could have oceans of liquid water below the crust. Those oceans could supply the minerals and the energy needed for life. So scientists are especially interested in them. But they want to make sure that any life they find really is native. So every mission to these worlds goes through a careful process of sterilization. But building and launching a spacecraft requires hands-on contact by hundreds of people. They build the instruments, assemble the spacecraft, test it, and attach it to its booster. Much of the work is done in high-level cleanrooms. Along the way, the spacecraft and its components may be cleaned with chemicals, baked at high temperatures, or zapped with radiation – all to prevent Earthly “bugs” from catching a ride. One especially interesting target is Enceladus, a moon of Saturn. It has a buried ocean, but some of its water shoots into space. Some of it falls back onto the surface – perhaps making it easier to find native life on this icy world. Saturn is close to the right of our own moon in early evening. It looks like a bright star. It’ll stay close to the Moon all night. Script by Damond Benningfield

The Moon is full today. But it’s not just any old full Moon. It’s the best-known of them all: the Harvest Moon – the subject of books, music, and lots of fall festivals. In centuries past, the Harvest Moon was much more than a pop-culture event. It provided enough light for farmers to harvest their crops well into the night. And at high northern latitudes, it helped out for several nights in a row. Officially, the Harvest Moon is the full Moon that’s closest to the fall equinox. That put it around harvest time – especially at higher latitudes, where autumn frosts soon would blanket the night. Without artificial lights to help them out, farmers relied on the Moon to add hours to their work time. The Moon is bright enough to help for several nights before and after it’s full. And thanks to the angle at which it climbs into the sky, for latitudes north of about Milwaukee or Minneapolis it rises only a few minutes later each night. So farmers in such high northerly climes didn’t have to wait around for the Moon to rise – they could keep on harvesting through the twilight and into the night. Tonight, the planet Saturn is quite close below the Moon at nightfall, and stays close throughout the night. It looks like a bright star. Like the full Moon, it’s about to line up opposite the Sun – setting up its own prime viewing time. We’ll have more about Saturn and the Moon tomorrow. Script by Damond Benningfield

Neptune has lost its vibrancy. The planet itself hasn’t changed – only our perception of it – the result of a bit of creative license exercised 37 years ago. Neptune is the Sun’s fourth-largest planet – four times the diameter of Earth. But it’s also the most-distant major planet – 30 times farther from the Sun than Earth is. Our only close look at Neptune came in August 1989, when Voyager 2 flew just 3,000 miles above its cloudtops. It transmitted hundreds of pictures of the planet. They revealed white bands of clouds racing through Neptune’s atmosphere, and a massive storm – the Great Dark Spot. In most of the pictures, Neptune has a deep cerulean palette. But a couple of years ago, a team reprocessed the images. The original project team had enhanced the planet’s color and contrast. That revealed details in the atmosphere that otherwise wouldn’t show up. But it also concealed Neptune’s true appearance: a pale blue-green. So Neptune isn’t as vibrant as it seemed – but it’s still an amazing world far from the Sun. Neptune is closest to Earth today for the entire year. It shines at its brightest, and it’s in the sky all night. You still need help to see it. But its location is easy to spot. As night falls, it’s about half way between the full Moon – the Harvest Moon – and the planet Saturn, which looks like a bright star to the lower left of the Moon. Script by Damond Benningfield

The largest moon of Neptune was an agent of chaos. It wasn’t born with Neptune itself. Instead, it was captured by the giant planet. As it spiraled in, it might have hit one of Neptune’s existing moons. And it scattered the others – knocking some of them out of orbit. Only one of them might have survived. There’s a lot of evidence of that idea. Triton is about the same size and composition as Pluto. It contains more than 99 percent of the total mass of Neptune’s moons and rings. And it orbits in the opposite direction from Neptune’s rotation. There’s no way for a moon to form in that kind of orbit, so Triton must have formed elsewhere in the solar system. It was captured when Neptune was young. It might have caromed off an existing moon. Or it might have had a companion. When the duo passed close to Neptune, it was ripped apart – Triton entered orbit, while its sibling was kicked off on its own. Triton then bludgeoned its way through the system. A recent study says the only surviving moon is Nereid, Neptune’s third-largest moon. Researchers looked at it with Webb Space Telescope. They found that it’s made of the same materials as the moons of Uranus – not the other moons of Neptune. That suggests it was born with the planet, and survived Triton’s chaotic arrival. Neptune is at its brightest this week. It’s in the east at nightfall, to the upper right of the bright planet Saturn. But you need a telescope to see it. More tomorrow. Script by Damond Benningfield

It’s not often that someone hands an astronomer a major discovery. But that’s what happened 180 years ago today. German astronomer Johann Galle, the director of Berlin Observatory, received a letter from Urbain Le Verrier. The French astronomer had calculated the likely position of a planet beyond Uranus, which at the time was the Sun’s most-distant known planet. Galle looked for the new planet that night – and found it: the planet Neptune. Le Verrier had calculated that Uranus wasn’t orbiting the Sun as expected. He decided that it was being nudged out of position by the gravity of another planet, farther from the Sun. He calculated the planet’s location, then sent his results to Berlin. British astronomer John Couch Adams had made similar calculations. He passed his results to his own colleagues. One of them searched for the planet, and saw it, in 1845 – but he didn’t realize it. So Adams usually is credited as a co-discoverer. But some research in recent years has suggested that his calculations were off, so there’s a debate about who discovered the Sun’s eighth planet. Appropriately enough, Neptune is at its best this week. It lines up opposite the Sun, so it’s closest to Earth, and shining at its brightest. But it’s so far away that you need a telescope to pick it out. It’s not far to the upper right of the bright planet Saturn, which is low in the east at nightfall. More tomorrow. Script by Damond Benningfield

The Sun speaks to us. It tells us about conditions deep inside it, far below its surface. That helps scientists understand how the Sun is put together, how it works, and how it changes. Listening to the Sun is called helioseismology. It works in the same way that seismology works on Earth. Motions inside the Sun generate sound waves. Those waves can travel all the way around the Sun. And they can travel deep inside it. They cause the surface to vibrate. And scientists can measure the vibrations – the Sun’s voice. The voice is complicated. It’s producing many frequencies of sound – like a diva singing many octaves of notes all at the same time. Some of the waves penetrate all the way to the core, where the Sun generates energy. Others stay close to the surface. Scientists have to unscramble this cacophony to understand what the waves are telling us. One thing that scientists have learned recently is that an important region in its magnetic field has changed over the past four decades. Today, that region is much closer to the surface than it was 40 years ago, suggesting that our star is undergoing some changes. The magnetic field is especially important to Earth. Magnetic storms can knock out satellites and power grids, disrupt radio waves, and cause other problems. So we may be able to better protect our technology by listening to the voice of the Sun. Script by Damond Benningfield

Day and night will be just about equal the next few days for the entire world. That’s because fall arrives in the northern hemisphere tomorrow. It’s the September equinox – the moment the Sun crosses the equator from north to south. At that moment, the Sun stands directly above the equator. So no matter where you are, the Sun rises due east and sets due west. Equinox means “equal nights.” That tells us that day and night should be the same length. But that’s not quite the case. In the northern hemisphere, daytime – the interval from sunrise to sunset – lasts a few minutes longer than nighttime. They won’t balance out until a few days after the equinox. One reason for the difference is the way we figure the moments of sunrise and sunset. For day and night to be equal, we’d have to think of them as the time the Sun is bisected by the horizon – when half is in view, and half is hidden. Instead, of course, we consider sunrise as the moment the top of the Sun first peeks into view. And sunset is the moment when the Sun fully disappears. That adds a minute or so to the “daytime” side of the equation. And we don’t actually see the Sun rise and set – at least not live. Earth’s atmosphere bends the Sun’s rays around the planet. So by the time you see the setting Sun touch the horizon, it’s actually already set. You’re seeing an extended version of things – stretching the daylight for a few extra minutes. Script by Damond Benningfield

In Shakespeare’s play “Julius Caesar,” Caesar makes a bold proclamation: But I am constant as the northern star, / Of whose true-fix’d and resting quality / There is no fellow in the firmament. Caesar turned out to be not so constant, of course. And neither is the northern star. In fact, Earth sees a cycle of North Stars – a cycle that lasts for 26,000 years. The current North Star is Polaris. It stands almost due north. So from the northern hemisphere, all the other stars appear to wheel around it as Earth turns on its axis. But Polaris will slide away from that honored spot over the coming centuries. And about 1200 years from now, it’ll be replaced by Errai, in the constellation Cepheus the king. We go through a sequence of north stars because of a slow wobble in Earth’s axis – the result of the gravitational pull of the Sun and Moon. When you combine a star’s brightness and its proximity to true north, Polaris may be the best of them all. Errai appears only about a third as bright as Polaris, and it won’t get quite as close to due north. Even so, it will reign as the North Star for about 2,000 years, before passing the crown to another star in Cepheus. The king is high in the north at nightfall, to the upper right of Polaris. It looks like a child’s drawing of a house, although it’s upside down during the evening hours. Errai is the peak of the house’s roof – a future inconstant North Star. Script by Damond Benningfield

Two well-known star patterns highlight the northern sky this evening. The Big Dipper is low in the north-northwest at nightfall, and in the northeast at first light tomorrow. And W-shaped Cassiopeia is just the opposite – in the northeast at nightfall, and the north-northwest at dawn. As that sequence tells us, both star patterns make a big circle around the sky during the night. They circle the North Star, Polaris – the hub of the sky. All the stars in the northern sky appear to move around Polaris – the result of Earth turning on its axis. For much of the United States, the stars of the Big Dipper and Cassiopeia never set – they’re close enough to Polaris that they never drop below the horizon. So they’re in the sky every day and night of the year, endlessly circling the North Star. Such stars are called circumpolar. The number of such stars from any given location depends on your latitude. From 30 degrees north, anything within 30 degrees of Polaris always remains above the horizon. From 50 degrees north, it’s anything within 50 degrees of Polaris. So as you go farther north, more stars are circumpolar. And if you go all the way to the north pole, all the stars are circumpolar – nothing ever rises or sets. Each star follows the same path across the sky night after night – circling Polaris, the hub of the northern sky. Polaris won’t keep that position; we’ll talk about its successor tomorrow. Script by Damond Benningfield

A thousand spacecraft could head for our closest neighboring planetary system in just a few decades. Don’t book your ticket just yet, though – each craft would weigh about as much as a penny. But working together, they could provide a few sharp pictures of the system, and even look for signs of life. A team of scientists and engineers published the idea earlier this year. The team proposed sending the probes to Proxima Centauri. It’s the closest star outside the solar system – four-and-a-quarter light-years away. And it has two confirmed planets. One of them is about the size and mass of Earth, and it’s in the region that’s most comfortable for life. The probes would be equipped with tough but thin “sails” 13 feet wide. A powerful laser would fire at each probe for eight minutes. The pressure of the light would boost the probes to 20 percent of the speed of light. It would take them 21 years to reach their target. The probes would use lasers to stay in touch with each other, and with Earth. About 300 probes could survive the trip. Their instruments could hunt for evidence of life in the planets’ atmospheres. There’s a lot of work to make it happen – advances in materials, lasers, computers, and even our knowledge of the distance to Proxima Centauri. But the researchers said the current rate of advancement should make such a trip feasible in the decades ahead. Script by Damond Benningfield

The winds on a giant planet more than 200 light-years from Earth are like the Big Bad Wolf: they’ll huff and puff and blow your house down. And if that’s not enough of a problem, the temperature can jump by 500 degrees in just a few hours. The planet orbits the star HD 80606. The star is a lot like the Sun. And it has a distant companion star that’s a near twin. They’re in Ursa Major, the great bear. At dawn, the system stands to the upper right of the Big Dipper, although you need a telescope to see it. The planet is HD 80606 b. It’s about four times the mass of Jupiter, the giant of our own solar system. But it’s about the same size as Jupiter, so it’s much denser. Its orbit is one of the most elongated of any known planet – its distance ranges from just three million miles to 85 million. As the planet approaches the star, it’s like being popped into an oven: The amount of energy it receives when it’s closest to the star is 800 times greater than when it’s farthest. So the planet heats up in a hurry. The approach also stirs up the winds. They blow outward from the point that’s in the middle of the hemisphere that faces the star. They may top out at 11,000 miles per hour – huffin’ and puffin’ all the way around this turbulent planet. Script by Damond Benningfield

The Moon huddles close to the heart of the scorpion this evening – the star Antares. It’s among the 15 brightest star systems in the night sky. If our eyes could see all forms of light, Antares would look perhaps 10 times brighter still. That’s because it emits most of its energy in the infrared – wavelengths that are too long for the human eye to perceive. All stars emit radiation across the electromagnetic spectrum – from radio waves to X-rays. That includes the Sun. But the mix of wavelengths depends on the star’s surface temperature, which we see as its color. Stars like the Sun are yellow-white. Their energy peaks at visible wavelengths – the type of energy our eyes have evolved to see. Stars that are hotter than the Sun look white or blue. But their light peaks beyond those colors – mainly in the ultraviolet – wavelengths that are much too short for us to see. Antares, on the other hand, is thousands of degrees cooler than the Sun, so it looks orange. But it emits most of its light in the infrared. And it produces a lot of it. The star is a supergiant – far bigger than the Sun. At visible wavelengths, it shines about 10,000 times brighter than the Sun. Throw in the infrared and all the other wavelengths, and it could be a hundred thousand times the Sun’s total brightness – one of the true stunners in our part of the galaxy. Tomorrow: A planetary Big Bad Wolf. Script by Damond Benningfield

The first planet ever discovered orbiting a Sun-like star is nothing like anything in our own solar system. But it helped astronomers learn more about the history of the solar system. The planet orbits 51 Pegasi. The star is a little bigger, heavier, and brighter than the Sun. The planet is 51 Pegasi b. It’s about half as heavy as Jupiter, the giant of the solar system. But it’s much closer in – just a few million miles from the star. The planet’s gravity causes the star’s light to “wobble” a bit. Precise measurements of that wobble revealed the planet’s details. Astronomers have since discovered hundreds more planets with the same technique, including many planets that are “hot Jupiters” like 51 Pegasi b. There’s no way for such a massive planet to form so close to its star. So it must have been born much farther out, then migrated to its current location. That realization led to theories that the Sun’s giant planets shifted around when the solar system was young. And that could have nudged the small inner planets, including Earth. It might even have pushed closer planets into the Sun – destroying some of Earth’s planetary siblings. Pegasus is in the east at nightfall. Look for four moderately bright stars that form the Great Square, which is tilted on its side. 51 Pegasi is along the top right side of the tilted square. Under dark skies, it’s barely visible to the eye alone. Script by Damond Benningfield