StarDate

With the end of winter still weeks away, people in colder climates may be dreaming of dips in a warm ocean under a steamy sky. And we know a couple of places where they wouldn’t have to wait for the change of seasons — a pair of “twin” planets orbiting a star in Lyra.

Kepler-138 is more than 200 light-years away. It consists of a star that’s much smaller, fainter, and cooler than the Sun, and perhaps four planets. Two of the planets are a little bigger and heavier than Earth. Such worlds typically are balls of rock and metal, just as Earth is. But these planets — Kepler-138 c and d — are different.

Studies with telescopes in space and on the ground showed that both planets are much less dense than Earth. But they’re too dense to be made of gas. Instead, they probably have dense centers surrounded by a layer of water more than a thousand miles deep.

The planets are so close to the star, though, that not all of the water is liquid. Each may have a thick atmosphere made of water vapor — like a giant steam bath. The atmosphere pushes down on the layer of water below, forming a deep ocean. But there’s probably not a sharp boundary between them. Instead, there may be a deep transition zone — part liquid and part gas — creating hot, wet worlds in a distant star system.

Lyra is high in the east at dawn, marked by its brightest star, Vega. But you need a telescope to see Kepler-138.
 

Script by Damond Benningfield

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Families of stars almost always break up. Usually, members drift away gradually. Sometimes, though, some of them run away from the family group in a big hurry.

An example is Mu Columbae. It’s in the constellation Columba, the dove, which is low in the south as night falls. The star is about 1300 light-years away. But it’s so brilliant that, under dark skies, it’s visible to the eye alone — but just barely.

Mu Columbae is one of the more impressive stars in our part of the galaxy. It’s about 16 times the mass of the Sun, and perhaps 45,000 times brighter. And it’s moving at about 260,000 miles per hour relative to the Sun. That’s far zippier than all but a handful of other stars.

Astronomers have discovered that Mu Columbae is moving in exactly the opposite direction from another runaway star, in Auriga the charioteer. Tracing their paths backward shows that they converge at a pair of massive stars in Orion.

The leading idea says the runaways began their high-speed journeys about 2.6 million years ago. Two pairs of massive stars passed quite close to each other. They staged a fast, violent gravitational dance. The heaviest members of the two pairs changed partners, forming a new binary. The less-massive members of the original systems were kicked out. So instead of run-aways, the stars are actually kick-aways — stars kicked out of the family by their weightier siblings.
 

Script by Damond Benningfield

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A faint dove sails low across the sky on February evenings. It’s due south as night falls now. But it’s so low that you need to be pretty far south to see it.

Columba is a recent constellation. Dutch mapmaker Petrus Plancius created it in the late 16th century. He carved it from a region with almost no bright stars. He called it Columba Noachis — Noah’s Dove. It represented the dove released from Noah’s Ark at the end of the biblical flood.

The dove’s brightest star is Alpha Columbae. It’s bright enough to see with the unaided eye, even though it’s about 260 light-years away. That means it really is bright — more than a thousand times brighter than the Sun.

The star is also much bigger and heavier than the Sun. And it’s spinning much faster than the Sun does. As a result, it’s flinging hot gas from its surface out into space. As that material cools, atoms link up to form solid particles, encircling the star in a cloud of dust.

Models of how stars evolve suggest Alpha Columbae is less than a hundred million years old — just a couple of percent the age of the Sun. Because of its great mass, though, it’s aging much faster than the Sun. That means it’s almost half way through the prime of life, when it steadily “fuses” hydrogen in its core to make helium. At the end of that phase, it’ll puff up to giant proportions and shine much brighter than it does now — making the dove much more prominent.

More about Columba tomorrow.
 

Script by Damond Benningfield

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For New Horizons, the big moment of glory came in 2015, when it flew past Pluto. Yet its work isn’t done. The spacecraft is traveling through the Kuiper Belt — a zone of icy bodies beyond the orbit of Neptune, the Sun’s most remote major planet. It flew close to one of those bodies in 2019. Now, it’s scanning other members of the belt from long range. It’s also studying the outer regions of the Sun’s magnetic “bubble,” and looking into deep space.

New Horizons is expected to keep going into the next decade. So scientists are taking advantage of its position, more than five billion miles away. It’s near the edge of the Sun’s region of magnetic influence. It’s only the fifth spacecraft to journey that far. It’s headed in a different direction from the others, so it’s giving scientists a 3-D look at that zone.

The view of deep space from the Kuiper Belt is especially dark, so New Horizons’ instruments have a good view of it. They’ve discovered that the space between galaxies is brighter than expected. A recent study suggests that glow could be produced by particles of dark matter interacting with each other.

Astronomers are looking for new members of the Kuiper Belt for New Horizons to study. That’s resulted in the discovery of hundreds of objects. If things work out, they might even find one that New Horizons could fly close to — one last moment of glory for a hard-working spacecraft.
 

Script by Damond Benningfield

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The three brightest objects in the night sky line up as night falls. The planets Jupiter and Venus are below the Moon, in that order. Nothing else is anywhere close to their brightness, so you can’t miss them.

The Moon is the last of the three bodies to set, about 9:30 or 10. We won’t see it again until sunset tomorrow. If you just can’t wait that long, though, you can see bits of the Moon at more than 40 locations across the United States.

Those bits are from the Apollo missions. Astronauts collected almost 850 pounds of lunar samples. Hundreds of scientists around the world have studied the collection of rocks and dirt. Most of the remaining samples are stored in a lab at Johnson Space Center in Houston, where they’re still shipped out for study — and probably will be for decades to come.

But NASA has sent out many samples for public display. Most of them came from the final three Apollo missions. Most of the display samples are tiny — not more than a few grams.

They’re on display at NASA visitor centers, presidential libraries, and Smithsonian museums. Others are at state science and history museums, or at big aviation museums. According to NASA, they can be found in 23 states — from Massachusetts to California, Florida to Hawaii, plus Washington, D.C.

And if you’re outside the U.S., you’re not shut out: Lunar samples are on display in almost a dozen other countries.
 

Script by Damond Benningfield

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The Moon and the planet Jupiter stage a spectacular encounter this evening. Jupiter looks like a brilliant star next to the Moon. Venus, the “evening star,” is close below them, completing an impressive tableau.

Jupiter has four big moons of its own. And a spacecraft that’s been orbiting Jupiter since 2016 has recently turned its instruments toward three of them.

The biggest is Ganymede — the largest moon in the entire solar system. The Juno spacecraft flew just 650 miles from it in June of 2021 — the closest encounter with Ganymede in almost two decades.

Juno confirmed the moon has a deep ocean buried far below its icy surface. It also provided new details on Ganymede’s innards, and on the composition and temperature of some of its surface features.

Juno made a close pass by the moon Europa early last year. Europa has a buried ocean, too. But it’s much closer to the surface, and it’s considered a possible habitat for life. Scientists are still analyzing those observations.

And in December, Juno made the first of nine encounters with Io. It’s the smallest of the four big moons. Instead of ice and water, it’s a world of volcanoes — more than any other body in the solar system. Juno will pass less than a thousand miles from Io a couple of times.

The craft will continue its reconnaissance of Jupiter as well — telling us more about the solar system’s largest planet.

More about the Moon and its companions tomorrow.
 

Script by Damond Benningfield

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The last time the United States sent a mission to Venus, the first George Bush was president, and cell phones were as big as your head. Today, we’re getting ready to go back. NASA’s preparing two missions — one to orbit the planet, and the other to drop a probe into its atmosphere.

Venus is the second planet from the Sun. It’s a bit smaller than Earth. Its atmosphere is hot, dense, and toxic, and topped by clouds of sulfuric acid. Those clouds make it impossible to see the surface. But the last American mission, Magellan, which was launched in 1989, used radar to peer through the clouds. It mapped a surface covered by rugged volcanic features.

The new missions are Veritas and Davinci. Like Magellan, Veritas will use radar to map the surface. But its radar will be more powerful, so it’ll provide much better maps. Veritas also will map the composition of the rocks.

Davinci will orbit as well. But it’ll also drop a probe into the atmosphere. It’ll parachute through the clouds and go all the way to the surface. It should tell us more about how the atmosphere formed and evolved, and why it’s so different from Earth’s atmosphere.

Veritas is scheduled to launch no earlier than 2027, with Davinci following two years later.

Venus is the “evening star.” It’s in the southwest at nightfall. The planet Jupiter looms to its upper left. And tonight, the Moon is directly below Venus in the early twilight.

More tomorrow.

Script by Damond Benningfield

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Iron is all around us. By mass, it’s the most common element in our entire planet. It makes up most of the core and a good bit of the crust. It even gives our blood its red color. And every bit of it was created inside stars.

All stars “fuse” together lightweight elements to make heavier ones. Right now, the Sun is fusing hydrogen, the lightest element of all, to make helium.

Stars like the Sun eventually make a few other elements, such as carbon and oxygen. But most of the elements beyond those are made inside much more massive stars, where temperatures are hundreds of millions of degrees higher. The fusion reactions produce energy, which makes the star shine and keeps it from collapsing under its own gravitational pull.

At the end of this chain of reactions is nickel-56, a radioactive element that decays to make iron. The iron can’t fuse to create heavier elements, so fusion stops. Without those reactions, the star’s core collapses. The layers around the core fall inward, then rebound in a titanic explosion — a supernova.

The explosion blasts many of the elements created inside the star into space. Over time, some of these elements — along with some even heavier ones created in the fury of the supernova — are incorporated into new stars and planets. So the iron that’s such a vital ingredient in our world and in our bodies was forged billions of years ago — in the hearts of stars.
 

Script by Damond Benningfield

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There’s more than one way to gauge the brightness of a star. And the difference reveals important details about the star itself.

An example is Alpheratz — a binary star system that’s almost a hundred light-years away. Officially, it’s one of the brighter stars of the constellation Andromeda. But it’s also the brightest corner of the Great Square of Pegasus. Right now, it’s at the top of the square, which is low in the west and northwest at nightfall. It’s to the right of the brilliant planets Venus and Jupiter, so it’s easy to find.

One way to measure a star’s brightness is by its absolute magnitude. That tells us how bright a star would look to the eye from a distance of 10 parsecs — about 33 light-years. And on that scale, the brighter star of Alpheratz — star A — would look almost exactly 100 times brighter than the Sun.

But that’s only part of the story. On a scale known as luminosity, Alpheratz is 240 times the Sun’s brightness.

The difference is the result of surface temperature. Alpheratz A is many thousands of degrees hotter than the Sun. At that temperature, it shines a lot bluer than the Sun, which is yellow. More important, hot stars produce a lot more ultraviolet light than the Sun does. So when you add up all wavelengths, Alpheratz A shines even brighter — a brilliant corner of the Great Square of Pegasus.

Tomorrow: Even hotter stars whip up something heavy.
 

Script by Damond Benningfield

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Extra weight can make a big difference in lifespan — whether it’s a person or a star.

Consider Procyon, the Little Dog Star. It’s actually a binary — two stars locked in orbit around each other. They were born together, a couple of billion years ago. But one of the stars was more massive than the other. As a result, it’s been “dead” for more than a billion years, while its companion has lived on.

Procyon is in the east-southeast at nightfall. It’s only 11 and a half light-years away, and it stands not far to the upper left of Sirius, the brightest star in the night sky. The combination makes Procyon easy to spot.

The system’s main star is Procyon A. It’s bigger, brighter, and heavier than the Sun. Procyon B is a dead stellar core — a white dwarf. It’s about 60 percent as massive as the Sun, but only about the size of Earth.

Procyon B was much heavier when it was born. Because of that, its core was much hotter than Procyon A, which revved up its nuclear reactions. That caused Procyon B to age much faster. After only about 700 million years, the reactions ended, the core collapsed, and the star’s outer layers were kicked off into space.

Procyon A was less massive, so it kept going. But today, it, too, is nearing the end. It’s making the transition to the next stage of life, which will end with the formation of a white dwarf as well. So Procyon will end as a pair of dead stars whirling through the darkness.
 

Script by Damond Benningfield

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