Mars is much more arid than even the driest deserts on Earth. But that hasn’t always been the case. Rivers once flowed there, filling lakes and perhaps even a giant ocean. And the Perseverance rover is tooling along inside one of those ancient water features. It’s in a crater that once held a large lake, fed by a river that poured through the crater’s rim.

Jezero Crater is about 30 miles wide. It formed when a giant asteroid slammed into Mars about four billion years ago.

Perseverance has found evidence of long wet periods, with long dry periods between. The rover has revealed layers of sediments deposited by water over hundreds of millions of years. It’s also found minerals that formed in a watery environment. And it’s found big boulders that were carried by a massive river.

The evidence shows that the first river flowed through Jezero a few hundred million years after the crater formed. Later, water filled the crater, forming a lake about 20 miles wide and maybe a hundred feet deep. And later still, a massive river punched through the crater’s rim. It deposited huge amounts of sediments, forming a large, thick delta. Eventually, though, the crater dried out – a dry remnant of a watery past.

Look for Mars below the Moon as they climb into good view, after midnight. The planet looks like a bright orange star. The true stars Pollux and Castor – the twins of Gemini – line up to the left of the Moon.

Script by Damond Benningfield

A couple of prominent astronomical bodies are meeting up in the early evening sky. One of them is pretty easy to spot, but the other will take a bit more work.

The easy one is Venus – the “evening star.” It’s the brightest body in the night sky other than the Moon. When it’s low in the sky, as it is now, it can easily be mistaken for the landing lights of an approaching airplane. And people sometimes report it as a UFO.

But there’s nothing unidentified about it. Venus is the second planet from the Sun. Since Earth is the third planet, our viewing angle on Venus is limited. At most, Venus can appear for a few hours after sunset or before sunrise. And right now, it’s not even around for that long – it drops from sight as the sky gets good and dark. Over the coming weeks, though, it’ll climb higher into the sky, and stay in view longer, as we head into winter.

Its fainter companion is the true star Antares – the heart of the scorpion. It’s one of the bigger, heavier stars in the galaxy – a supergiant.

Antares is among the brightest stars in the night sky. But it’s so low in the twilight now that finding it is a little tricky. Venus will point the way – and binoculars will enhance the view. Tonight, Antares is to the left of Venus. Over the next few nights, Venus will climb up and over Antares. They’ll stand closest on Thursday and Friday, before Venus pulls away – and Antares disappears in the sunset.

Script by Damond Benningfield

The gibbous Moon will get in the way early tomorrow. It’ll cover up a bright star – but only as seen from South Texas and points southward. And its light will all but wipe out a meteor shower.

The cover-up is an occultation. The Moon will pass directly in front of the star Elnath, which represents the tip of one of the horns of Taurus. That will block the star from view. From the United States, the only place to witness the vanishing act is south of San Antonio. The rest of the country will see a very close miss.

The view is limited because the Moon isn’t all that far away – less than a quarter of a million miles. So the viewing angle changes as you move farther north or south. Tonight, those north of the latitude of San Antonio will see Elnath pass above the Moon’s north pole.

Elnath will be close to the lower left of the Moon as they climb into good view by about 11 p.m. The brilliant planet Jupiter will be close by. The Moon will move closer to the star during the night. They’ll be at their closest in the wee hours of tomorrow morning, with the exact timing depending on your location.

The encounter is a bit of compensation for the fact that the Moon is a pest right now. The Orionid meteor shower is underway, and should be at its best late tonight – about the time of the Moon’s closest approach to Elnath. But the moonlight will overpower all the but the brightest meteors.

Tomorrow: a bright evening encounter.

Script by Damond Benningfield

The Moon barges through a region that’s packed with bright points of light the next couple of nights. All of them will lose a bit of their luster in the glare of the moonlight, but they’ll still form a beautiful ensemble. They’re all in good view by about 10 or 10:30, forming an arc around the Moon.

The pinpoint that’s closest to the Moon is the star Aldebaran. It represents the eye of Taurus, the bull. If you hold out your fist at arm’s length, it will neatly span the distance between the Moon and Aldebaran – about 10 degrees.

The brightest member of the group is the planet Jupiter. It looks like a brilliant star – the brightest object in the sky at that hour other than the Moon. It’s about 17 degrees to the lower left of the Moon.

Elnath, the star at the tip of one of the bull’s horns, is about the same distance from the Moon, to the upper left of Jupiter. It’s the faintest member of the group, but still pretty easy to see. The Moon will huddle especially close to Elnath tomorrow night.

Finally, the point that’s farthest from the Moon is Capella, the brightest star of Auriga, the charioteer. It’s to the left of the Moon by about 25 degrees. That’s two and a half times the width of your fist. The star is quite bright, so you won’t have any trouble picking it out – a member of a quartet of bright pinpoints near the gibbous Moon.

We’ll have more about this beautiful lineup tomorrow.

Script by Damond Benningfield

More than 1.3 million chunks of ice and rock have been discovered in the asteroid belt – a wide zone between the orbits of Mars and Jupiter. But asteroids don’t always stay there. They can be kicked out of the belt by collisions, or by the gravity of Jupiter. Some of these outcasts come close to Earth’s orbit, so they’re called near-Earth asteroids.

Astronomers group these objects based on their orbits. The largest group is the Apollos. They account for more than half of all near-Earth asteroids – more than 20,000 have been discovered so far. Their orbits cut across Earth’s orbit.

Apollos are named for the first member of the group ever discovered, which was first seen in 1932. Apollo probably is about a mile in diameter, and it appears to have a moon that’s about the length of a football field.

The largest Apollo is called Sisyphus. It’s perhaps five miles in diameter. That’s about the size of the asteroid that wiped out the dinosaurs when it hit Earth 66 million years ago.

Many other Apollos have also hit us. An asteroid just 60 feet in diameter exploded above Russia in 2013, for example. It shattered windows across a wide area, injuring about 1500 people. And most of the meteorites found on Earth are fragments of Apollo asteroids. So astronomers are keeping their eyes on these potentially dangerous outcasts from the asteroid belt.

Script by Damond Benningfield

The space around our planet feels a lot more crowded these days. Over the past few decades, astronomers have discovered more than 35,000 asteroids whose orbits come close to Earth’s orbit around the Sun. And the total keeps going up – they find a couple of hundred more every month.

Asteroids are chunks of rock and ice. Most are tiny, but the largest are hundreds of miles in diameter. Most of them inhabit the asteroid belt – a wide zone between the orbits of Mars and Jupiter – more than 1.3 million of them so far.

But near-Earth asteroids come much closer to the Sun – and Earth. Their orbits bring them within 120 million miles of the Sun, which is not far outside Earth’s orbit. And quite a few of them actually cross our orbit.

Some of these asteroids could someday hit Earth. They’re known as potentially hazardous asteroids. Astronomers have cataloged more than 2700 of them. None is on a known collision course. But a few will come close. In 2029, for example, the asteroid Apophis will pass less than 20,000 miles from our planet.

Several search projects are scanning the heavens for other near-Earth asteroids. They’re trying to find everything that’s big enough to present a major threat. Early detection might allow us to deflect an asteroid on a collision course – keeping us safe in our crowded region of the solar system.

More about near-Earth asteroids tomorrow.

Script by Damond Benningfield

The full Moon lights up the sky the next couple of nights. It’s full early tomorrow, when the Moon and Sun line up on opposite sides of Earth. And the Moon is especially close to us tonight – the second-closest passage of the year – so it’s especially bright.

Because this is the first full Moon after the Harvest Moon, which we saw in September, it’s known as the Hunter’s Moon.

The Hunter’s Moon follows the Harvest Moon because long ago, when the full Moons were named, the hunt always followed the harvest. After farmers reaped their crops in September or early October, the fields were bare and open. There was no place for game to hide, so hunters took advantage of the next full Moon – the Hunter’s Moon – to track their quarry.

There’s no practical reason to keep these names today. Still, the names of the full Moons add a bit of romance or mystery to what might otherwise sound mundane. “Hunter’s Moon” has a lot more appeal than simply “the full Moon of October.”

The full Moon always rises around sunset and sets at sunrise. It’s easy to forget that the Moon rises later every day, so sometimes it appears in daylight. But it’s so pale compared to the Sun that we seldom even notice it.

You won’t have any trouble noticing the Moon tonight, though. Look for it beginning around sundown, lighting the way for hunters – and the rest of us, too.

We’ll talk about some other nearby celestial neighbors tomorrow.

Script by Damond Benningfield

If you have sharp eyes or good binoculars, you can sometimes see double in the night sky – two stars that are quite close together. In some cases, the stars really are close – they can be bound to each other by gravity, forming a binary.

In other cases, though, it’s just a coincidence. The stars are unrelated, but they just happen to line up in the same direction. These stars are known as optical doubles. And some of them are beautiful sights – especially when viewed through a telescope. The two members can show different colors, providing a nice contrast.

One of the best-known examples is Albireo. It marks the head of Cygnus, the swan, and it’s high overhead at nightfall. A small telescope reveals one blue star and one gold star. The best measurements to date indicate that the stars are about 30 light-years apart.

An example that’s visible to the eye alone is Algedi, in Capricornus. It’s due south at nightfall. The eye can just make it out as two separate points of light. The stars are hundreds of light-years apart.

Sometimes, it’s hard to tell if a double star is a binary or not. The best example is Mizar and Alcor, in the handle of the Big Dipper. It’s fairly easy to see the stars as two points of light. They actually move through space together, so they probably were born together. But astronomers aren’t sure if they’re a true binary – or just two related stars moving through space on their own.

Script by Damond Benningfield

Stars aren’t always good neighbors. They can drag away planets from other stars. In some cases, they grab the planets for themselves. In others, they fling the planets away, to wander through space alone. And they might even fling away two or more planets, which then move through space together as “Jumbos” – Jupiter-Mass Binary Objects.

Astronomers first reported these odd pairings a year ago. Webb Space Telescope found them in the Trapezium – a cluster of young stars in the Orion Nebula.

The nebula has given birth to a couple of thousand stars, all of which are no more than a couple of million years old. And the stars are tightly packed, so close encounters between them are common. During those encounters, one star can pull planets away from another. In fact, Webb revealed more than 500 giant planets that aren’t orbiting any star.

About one-tenth of the planets are in binaries – the Jumbos. A study a few months ago said that, if two planets in a star system are aligned in just the right way, a passing star could pull away both of them. But the planets would stay together – zipping through a cluster of young stars and stolen planets.

The Orion Nebula is visible to the unaided eye. It looks like a faint, fuzzy star – energized by the light of several brilliant stars in the Trapezium. The nebula climbs into good view after midnight. It stands high in the south-southwest at dawn, below the stars of Orion’s Belt.

Script by Damond Benningfield

This has been a big year for exploring the Moon. The highlight came in June, when a Chinese mission landed on the lunar farside – the side we never see from Earth. Chang’e 6 then scooped up some samples and brought them to Earth for study – the first samples ever collected from the farside.

A couple of less-ambitious missions touched down earlier in the year. Both landers tipped over, but they managed to transmit some pictures.

More lunar missions had been scheduled for later this year.

The headliner was a rover called Viper. It was designed to hunt for ice near the south pole, along with other materials that might help support future human bases on the Moon. Viper was scheduled to spend 100 days trundling across the surface, including some areas that receive little or no direct sunlight.

This summer, though, NASA canceled the mission. Viper had already cost $450 million during several years of development and testing. But it wasn’t ready for flight, and neither was its ride to the Moon. NASA decided it would be too expensive to finish out. Instead, it’ll use the rover’s instruments for other projects – possible highlights for lunar exploration in future years.

Look for the gibbous Moon rolling across the southern sky tonight. The planet Saturn is to the left of the Moon at nightfall, and looks like a bright star. Saturn will be a little closer to the upper right of the Moon tomorrow night.

Script by Damond Benningfield