StarDate

On a spring evening in 1969, Eileen Brown was recording birds in her neighborhood in Bangor, Northern Ireland, not far from Belfast. The birds were interrupted by what sounded like thunder. The sky was clear, though. Instead of thunder, the rumbles were sonic booms. They were produced by a large meteor that was racing across the British Isles. Brown’s recording was the first ever made of a meteor — 50 years ago tonight.

As the meteor sped from southeast to northwest, it was seen by thousands of witnesses. They reported a blue-green or bright white fireball. Many reported that it split apart as it descended over Northern Ireland.

April 25th was a Friday that year. On Monday, a store owner found a hole in his roof and a chunk of rock on his floor — a part of the original space rock, now known as a meteorite. It weighed about 18 ounces.

The same day, a farm owner in County Londonderry found a crater in his field. It contained a meteorite weighing more than 10 pounds. The farm was in an area known as Bovedy. So that became the meteor’s official name.

Today, scientists know that the meteor was a chip off a much larger body. It contains tiny blobs of once-molten rock, known as chondrules. They tell us that the parent body formed at about the time of the birth of the solar system. A collision split it apart. One of its fragments eventually made its way to Earth — and into the history books.

Script by Damond Benningfield

Just days before its demise, the Cassini spacecraft recorded an odd chorus: radio waves produced by particles from the moon Enceladus that were zipping through Saturn’s magnetic field. Saturn’s magnetic field is strong but weird. It’s produced by the motions of different layers within the planet itself. These motions generate electric currents, which in turn create the magnetic field.

That’s pretty standard. In fact, it’s how Earth generates its magnetic field.

The weird thing about Saturn, though, is that its magnetic and geographic poles are almost perfectly aligned. Scientists had thought that to produce a magnetic field at all, the magnetic poles had to be tilted. Yet Saturn’s magnetic field is stronger than that of any other planet except Jupiter.

The magnetic field traps charged particles from the Sun and other sources, including Enceladus. The charged particles form radiation belts around Saturn.

The magnetic field funnels some particles toward Saturn’s poles, where they produce aurorae — like the northern and southern lights here on Earth. Cassini recorded their radio waves as well — the chorus of a giant planet’s giant magnetic field.

Saturn is in great view late tonight. It looks like a fairly bright star close to the Moon as they climb into sight in the wee hours of the morning.

Script by Damond Benningfield

The giants of the solar system will flank the gibbous Moon at dawn tomorrow. Jupiter — the king of the planets — will stand to the right of the Moon, with fainter Saturn the same distance to the left of the Moon.

After the Sun, Jupiter and Saturn make up most of the mass of the solar system. By comparison, all the other planets, moons, and smaller bodies are little more than the crumbs on the table after a big dinner.

The two planets grew so big in part because they were beyond the “snow line.” That was the distance from the embryonic Sun where temperatures were cold enough for water and other compounds to form solid grains. Those particles could stick together to form bigger and bigger bodies — helping Jupiter and Saturn form giant cores. The cores then pulled in huge amounts of hydrogen and helium gas that surrounded the Sun, boosting both worlds to immense proportions.

Planets that were inside the snow line couldn’t grow nearly as big. The Sun’s heat kept many compounds from forming solid particles. And solar radiation blew planet-making materials away from the inner solar system, toward the realm where Jupiter and Saturn were born. That left a thinner supply of planet-making materials, so the planets were thinner, too.

So Earth and the other three inner planets are small and dense — made of materials that the young Sun couldn’t easily vanquish.

We’ll have more about the Moon and Saturn tomorrow.

Script by Damond Benningfield

Anyone who likes to do a little ice fishing might consider Europa, one of the bigger moons of Jupiter. It has a global ocean that’s dozens of miles deep, capped by ice that’s miles thick. And there’s a chance the ocean could be inhabited — most likely by microscopic organisms, but perhaps by bigger ones.

Europa is a bit smaller than our own Moon. Its surface is made of blocks of ice that are criss-crossed by veins of a reddish material. That structure, along with several other lines of evidence, point to the hidden ocean.

It’s possible that hot, mineral-rich water could percolate into the bottom of the ocean, providing the ingredients for life: water, chemistry, and energy.

Two missions are scheduled to head for Europa soon. A European craft will launch in 2022, with an American one following as little as a year later. The American craft will swoop as low as 15 miles above the surface.

Landing on Europa might be tricky. A recent study said that spikes of ice several stories tall could ring the moon’s equator. Yet scientists are already pondering missions that would peek into the ocean. One concept — a “tunnelbot” — would use nuclear power to melt through the ice — allowing it to “fish” for life on this amazing moon.

Look for Jupiter quite close to our own Moon late tonight. Jupiter is just below the Moon as they rise, after midnight, and looks like a brilliant star. They’ll be even closer at first light.

Script by Damond Benningfield

The Sun is really big — more than a hundred times the diameter of Earth. Yet it’s a mere dot compared to a star that huddles close to the Moon tonight. That star is almost a thousand times the diameter of the Sun — one of the giants of the galaxy. If it took the Sun’s place, it would extend most of the way out to Jupiter, engulfing Earth and the other inner planets.

Antares is the leading light of Scorpius. It’s to the lower right of the Moon as they climb into view, after midnight. The brilliant planet Jupiter rises to their lower left; more about that tomorrow.

Antares consists of two stars. The lesser one is still a monster — many times the size and mass of the Sun. Yet it’s hidden by the glow of the main star, known as Antares A.

Estimates of the size and mass of Antares A vary. But it’s probably about 15 times the mass of the Sun. That great weight squeezes its core, revving up the nuclear reactions that power the star and making the core especially hot. Radiation from the hot core pushes on the surrounding gas, inflating Antares to supergiant proportions.

That size makes it especially bright — about 10,000 times brighter than the Sun at visible wavelengths. But the surface of Antares is cooler than the Sun. Cooler stars emit much of their energy in the infrared. When you add that to the visible light, Antares is at least 60,000 times the Sun's brilliance — a giant display from a giant star.

Script by Damond Benningfield

A thin but reliable meteor shower is building up this weekend. It should hit its peak in the wee hours of Monday or Tuesday. Unfortunately, though, the gibbous Moon will get in the way. Its glare will overpower all but the brightest meteors.

The Lyrids are one of the most reliable of all meteor showers. The earliest record comes from 2700 years ago, in ancient China, where a scribe reported that meteors fell like rain.

Most years, the Lyrids produce no more than 20 or so meteors per hour. But the shower has produced a few outbursts.

The most intense was recorded in 1803, along the East Coast. A group of skywatchers in Albany, New York, said that “stars seemed to fall from every point in the Heavens, as far as our sight could extend.” Another observer, in Portsmouth, New Hampshire, counted 167 meteors in 10 or 15 minutes. After that, he gave up counting and just enjoyed the show.

One of the most extensive reports came from Richmond, Virginia. Much of the town had been roused by a fire alarm in the wee hours of the morning. The blaze was quickly extinguished. But the sky stayed ablaze for a couple of hours. The local paper said it looked like “a show of skyrockets.” It “alarmed many, and astonished every person who beheld it.”

Alas, there won’t be nearly as much to behold this year. Even so, if you can find a dark, safe skywatching spot, you might see a few bright Lyrids through the moonlight.

Script by Damond Benningfield

Every year or two, we see a scenario play out like this: A web site, book, or other source says that some cosmic catastrophe is about to befall Earth: an impact by a comet or asteroid, a close encounter with a rogue planet, or disasters caused by an alignment of planets and stars. NASA and others say the story isn’t true. People attack the denials, claiming that scientists are lying. The date passes — with no catastrophe. The cycle starts all over again.

Such rumors are nothing new. In 1910, people were scared that gases in the tail of Comet Halley would be lethal. They bought gas masks and “comet pills” to protect themselves.

But the Internet and social media have made the problem worse. In 2011 and 2013, for example, campaigns predicted that comets headed toward the Sun would smash into Earth. And just this year, a headline in a British tabloid warned of danger from an “apocalypse” asteroid.

One popular subject is Nibiru, a supposed planet or brown dwarf in the outer solar system. Stories frequently predict that it will hurtle into the inner solar system. The stories say that it’ll either hit Earth, or pass so close that it’ll cause monster earthquakes, volcanic eruptions, and other problems.

All of the rumors are just that. Nibiru doesn’t exist. No known asteroid or comet is on a collision course. And planetary alignments happen all the time — beautiful displays that are no threat at all.

Script by Damond Benningfield

A bright star system with a complicated future keeps company with the full Moon tonight. Spica stands to the right or lower right of the Moon at nightfall.

Spica consists of two big, heavy stars. One is more than 10 times as massive as the Sun, while the other is about seven times the Sun’s mass.

Such heavy stars burn through their nuclear fuel in a hurry. As a result, they live much shorter lives than stars like the Sun. In fact, the heavier of Spica’s stars is already nearing the end of its “normal” lifetime. It’s beginning a series of changes that will cause its outer layers to puff up to hundreds of times the size of the Sun.

And that’s where things get complicated. The two stars are only a few million miles apart. As the heavier star gets bigger, it will dump some of its gas onto its companion. And soon after that, it’ll engulf the companion.

Under normal circumstances, the heavier star eventually would explode as a supernova. But the companion may complicate things. As the bigger star engulfs the companion, the cores of the two stars will spiral closer together. The cores may merge, hastening the explosion of the heavier one. Or they may collide more violently, setting off an even bigger blast. Or perhaps there won’t be enough time for a collision, so the heavier star will explode on its own, perhaps disrupting the smaller star.

No matter how it plays out, there’s no doubt that Spica faces an interesting future.

Script by Damond Benningfield

Scientists are still working out their models of Earth’s atmosphere — models that become more important as our planet’s climate changes. Even as they work out the details, though, they’re already thinking about applying those models to exoplanets — worlds that orbit stars other than the Sun.

Modeling the workings of another planet isn’t easy, though. That’s because we know very little about the planets — and even their stars.

For most of the planets discovered so far, scientists know how big the planet is, how heavy it is, and how far it is from its star. They’ve measured some of the chemistry of the atmospheres of a few planets. And they know the brightness and temperature of the parent stars.

But that still leaves a lot of unknowns. Scientists don’t know how a planet is tilted on its axis, for example — the key factor in creating the seasons here on Earth. They don’t know how much of a planet’s surface is covered by land or water. And they don’t know if a planet has moons, which can generate tides and help keep a planet from wobbling too wildly.

They also don’t know much about the stars that host planets. In particular, they need to know how the light from a star varies — and whether the star produces big explosions of particles and energy.

Still, scientists are beginning to generate their first models of individual planets — models that may tell us whether any of these alien worlds could be possible homes for life.

Script by Damond Benningfield

We don’t have a single picture that shows us the surface of an exoplanet — a planet in a star system other than our own. Yet astronomers already know what we’d see if we could get a good look at one class of exoplanet: clouds on the night side, and clear skies on the day side.

These planets are known as hot Jupiters. They’re as big as Jupiter, the giant of our own solar system, and many are much heavier than Jupiter. They’re hundreds of millions of miles closer to their stars than Jupiter is to the Sun, so they’re extremely hot.

Astronomers have learned about the planets in several ways. They’ve watched as a planet passes in front of its star, allowing starlight to filter through the planet’s atmosphere. And they’ve used infrared telescopes to measure changes in heat coming from a system as the planet orbits its star.

These observations reveal that nighttime temperatures on hot Jupiters hover around a thousand degrees. Daytime temperatures are much hotter. That suggests that clouds form on the night side of such a planet, trapping some of its heat. But it’s just too hot on the day side, so the clouds vaporize as they rotate into the light.

The clouds aren’t like anything on Earth, though. Instead of water, they’re made of silicates — like grains of sand. Some even contain the minerals that make up rubies and sapphires — hot jewels on some sizzling-hot planets.

More about exoplanets tomorrow.

Script by Damond Benningfield