StarDate

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

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

The surface of the Moon seems eternal. There’s no air or water to reshape it, and no plate tectonics to jiggle things around. But the Moon does change – sometimes in a hurry. Scientists recently discovered an impact crater that’s almost 750 feet in diameter. It had been gouged during the spring of 2024.

The crater was found in images snapped by L-R-O – Lunar Reconnaissance Orbiter. The craft’s been mapping the lunar surface for years. It’s photographed almost all of the surface many times. Scientists compare images taken at different times to see how things have changed.

The new impact crater was the biggest change seen so far. The crater is three times wider than any other crater gouged during LRO’s time in orbit. It’s about 150 feet deep, and its rim rises more than 25 feet above the surrounding landscape. The impact blasted out boulders as big as houses. And bright “rays” of smaller bits of debris were splashed far from the crater’s edge. Such a powerful impact on Earth could level a city, and kill everything within miles of the impact site.

Some good-sized pieces of debris from the crater’s formation could have traveled dozens of miles – something for designers of lunar habitats to keep in mind.
The scientists who reported the discovery say that such a large crater should form about once every 140 years. So LRO recorded a rare major change on our satellite world.

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