Antares, the bright star at the heart of Scorpius, huddles quite close to the Moon early this evening. They set not long after the sky gets dark, so there’s not a lot of time to look for them.

The Moon is a thin crescent now, so it’s night across most of the lunar disk. But on the bright sliver that’s in daylight, you can still make out some of the dark lunar “seas” – vast plains of volcanic rock. They formed long ago, when giant asteroids slammed into the Moon. Molten rock bubbled up from below, then cooled and hardened.

A recent study found evidence of an especially big impact three-and-a-half billion years ago. The hit would have been powerful enough to melt the surface across a wide area.

Researchers discovered the evidence in a meteorite known as Northwest Africa 12593. It was found in Mali, in 2017. It contained some tiny crystals that form only under extreme heat. The chemistry of the meteorite suggested the impact happened three-and-a-half billion years ago.

A later impact shattered the lava plain, jumbling up the rocks. And a third impact blasted some of the fragments into space, including the one that fell to Earth. The initial impact happened at about the time of similar events on Earth and the asteroid Vesta. That suggests that the inner solar system was littered with many giant space rocks at the time – cosmic “missiles” that sometimes smashed into Earth and the other large worlds.

More tomorrow.

Script by Damond Benningfield

Cassiopeia is an easy constellation to pick out. The stars of the queen form a prominent letter M or W, which is visible even through moderate light pollution. And under dark skies, binoculars reveal several star clusters around that pattern, all immersed in the glow of the Milky Way.

One of the highlights is NGC 7789. It was discovered in 1783 by Caroline Herschel – the first woman to be paid for her work as an astronomer. Through a telescope, the contours of the cluster and nearby clouds of dust resemble a rose. So NGC 7789 also is known as Caroline’s Rose.

The cluster is about 6800 light-years away, in the opposite direction from the center of the galaxy. And it’s packed with stars. It has 1300 confirmed members, with an estimated total of 3,000 stars or more.

The cluster’s age has been tough to pin down. A recent study says it’s one-and-a-quarter billion years old. Previous estimates are a little higher. Regardless of the exact age, the cluster has made several orbits around the center of the galaxy. By the time many other clusters have made that many orbits, they’ve been pulled apart by the gravity of the rest of the galaxy. The stars survive, but they head their separate ways. Caroline’s Rose is in the northeast at nightfall, just above Cassiopeia’s outline. It climbs high across the north during the night.

Script by Damond Benningfield

A pair of big, young star clusters is one of the skywatching highlights of autumn evenings. Each cluster contains thousands of stars. And hundreds of those stars are especially impressive – supergiants that are many times the size and mass of the Sun, and many thousands of times brighter.

The clusters are NGC 869 and 884. Together, they’re known as the Double Cluster. They’re in the northeast at nightfall, in the constellation Perseus the hero. Under dark skies, they’re visible to the eye alone as a single smudge of light. Binoculars split them apart, revealing two sparkling collections of stars.

The clusters are more than 7,000 light-years away. They form the core of the Perseus OB1 Association – a huge complex of stars and clouds of gas and dust. The region has given birth to perhaps tens of thousands of stars.

All of the stars were born in the recent past, as measured on the astronomical time scale. The Double Cluster is only about 14 million years old, compared to four-and-a-half billion years for the Sun. One way astronomers determine that age is through the types of stars found in the clusters. The most-massive stars burn out in a hurry. But the clusters still contain many such stars.

Some of those monsters won’t last much longer, though – they’ll blast themselves to bits as supernovas – brilliant light shows in the Double Cluster.

Script by Damond Benningfield

The stars in a binary system can be quite intimate. One star can pull gas off the surface of its companion, for example. And in extreme cases, the stars can merge to form a single star. Both types of interactions can make the stars look a lot younger than they really are.

Many examples of this are found in Messier 10. It’s a globular cluster – hundreds of thousands of stars all packed into a ball a few dozen light-years across.

The cluster includes an especially large number of blue stragglers – stars that look a lot younger and bluer than the cluster should contain. M10 itself is billions of years older than the Sun. It probably was born with many hot, blue stars. But such stars burn out quickly. So there’s no way that any of the cluster’s original blue stars could still be around.

Instead, the blue stragglers probably were rejuvenated. Some appear to have stolen gas from a companion. The extra material “revs up” the nuclear reactions in the recipient, making it look much younger.

Other blue stragglers may be the results of mergers – the stars spiral together. That would increase the rate of nuclear reactions as well – turning two old stars into what looks like a brand new one.

Messier 10 is in Ophiuchus, the serpent bearer. The cluster is in the southwest as night falls, to the upper right of the teapot of Sagittarius. Through binoculars, the cluster looks like a hazy smudge of light.

Script by Damond Benningfield

The second-largest asteroid in the solar system is a puzzler. Most studies say it has the same layers as a planet, but that it’s not massive enough to pull itself into a fully rounded shape like a planet. But one study found that it’s not layered at all.

Vesta accounts for almost a tenth of all the mass in the asteroid belt. Its average diameter is about 325 miles. But it’s flattened and a bit stretched out.

The surface of Vesta is covered with volcanic rock. Combined with other observations, that suggests that Vesta is layered, with a distinct core, mantle, and crust. If so, then it formed very early in solar-system history, allowing it to incorporate a lot of radioactive material. Heat from radioactive decay partially melted it, allowing heavier materials to sink to the center and lighter ones to float to the surface.

But a study last year contradicted that. Using delicate measurements of Vesta’s gravity field, scientists determined that the asteroid isn’t fully layered. It might have started to develop layers, but never got hot enough to finish the job. Or it might have formed from debris blasted off a larger body by a giant impact – creating a massive space rock that’s all jumbled up.

Vesta lines up opposite the Sun in our sky tonight. It’s brightest for the year, and it’s in view all night. Even so, you need binoculars to spot it. It’s not far below the bright planet Saturn, which is low in the east at nightfall.

Script by Damond Benningfield

The solar system is big. Really big. It’s almost three billion miles from the Sun to Neptune, the most distant major planet. It’s more than three billion miles to Pluto. And it’s more than twice that far to the edge of the Sun’s magnetic “bubble” – the boundary with interstellar space.

It’s almost impossible to comprehend those distances – they’re just too far beyond anything we ever experience. But we can get an idea of the scale from models of the solar system – the bigger, the better. And there are some king-size models around the planet.

The largest is in Sweden – it spans most of the country. It includes all the major planets, plus many dwarf planets, asteroids, and comets. The Sun is represented by a ball-shaped arena in Stockholm that’s about 350 feet across. At that scale, Earth is bigger than a beachball, and is almost five miles away. Neptune is about 140 miles out, while the edge of the magnetic bubble is several times farther.

The biggest model in the United States is in Maine. It spans almost a hundred miles, along U.S. 1. It extends to the dwarf-planet Eris, which is more than twice as far as Pluto.

Other large models are found in New Mexico, Illinois, Michigan, and several other states. Some of them are small enough that you can walk them, while you need a car or bike for the others. But all of them can help you understand the scale of our big neighborhood.

Script by Damond Benningfield

A meteorite found in the Sahara Desert could be a fragment of a destroyed sibling of Earth. The small planet might have been blasted to rubble when the solar system was young. Some of the planet’s remains could have been incorporated into the other rocky worlds, including Earth.

NWA 12774 is a one-pound meteorite that was found in northwestern Africa in 2019. It belongs to a rare class known as angrites. They account for less than one-tenth of one percent of all known meteorites. They’re also among the oldest meteorites – they formed more than four and a half billion years ago, when Earth and the other planets were still taking shape.

Based on the composition of the meteorite alone, a team of researchers concluded that it was a fragment of a larger body that was disrupted during the early solar system. When the scientists included the structure of the meteorite, they determined that it came from near the surface of the parent body. That world would have been at least 2200 miles in diameter – as big as the Moon – and perhaps as big as Mars.

The parent world probably was destroyed in a collision with another large body. Such collisions probably were common in the early solar system. Earth probably smacked into a Mars-sized planet, for example. The impact blasted huge amounts of material into space, which eventually came together to form the Moon.

Script by Damond Benningfield