StarDate

Astronomers are still trying to figure out whether one of the busiest planetary systems yet discovered could be a home for life. Some studies give it higher odds, while others give it lower odds.

Trappist-1 is 40 light-years away, in Aquarius, which is in the southwest at dusk, to the lower right of the Moon. The system contains at least seven planets. They’re all small and rocky, like the worlds of the inner solar system.

Part of the confusion about whether they could support life is that we have only one example of a life-bearing planet: Earth. So no one knows what conditions are needed for life to arise. Figuring it out is a matter of a lot of simulations, intuition, and plain-old guess work.

Another problem is the star itself. Trappist-1 is only a few percent the mass of the Sun, so it’s cool and faint. Yet such stars produce outbursts of radiation that are far more powerful than anything generated by the Sun.

A recent study says the outbursts are far more deadly than thought. But another says the outbursts might actually help — they could provide the jolt that life needs to get started.

And that’s a critical balance for the planets. They’re all within a few million miles of the star. Four of them could lie inside the “habitable zone” — the best location for life. But until we understand more about the star, the planets — and life itself — we won’t know whether anything can live in this busy star system.
 

Script by Damond Benningfield

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Jupiter is the beachball of the solar system: big, round, and painted with colorful stripes. It’s also the largest planet in the solar system, so each stripe is thousands of miles wide.

The stripes are created by Jupiter’s high-speed rotation — it spins on its axis once every 10 hours. They’re separated by jet streams that blow at hundreds of miles per hour and dip a couple of thousand miles into the atmosphere. And their borders can be turbulent, marked by ripples and waves as big as countries.

The bands alternate between light-colored zones and darker belts. The clouds in the zones are higher, while those in the belts are lower, allowing us to see deeper into Jupiter’s atmosphere. The clouds are made of ammonia and other compounds, with clouds of water below.

The bands are colored in shades of yellow, red, and brown, giving Jupiter its beachball appearance. The color may come from compounds of sulfur, phosphorus, and other elements dredged from deep below.

Giant storms float through the bands. The biggest is the Great Red Spot, which is the size of Earth — a colorful decoration for a colorful beachball.

Look for Jupiter to the upper left of the Moon this evening. It looks like a brilliant star — only the Moon and the planet Venus outshine it. And if you can’t catch them tonight, Jupiter and the Moon will be about the same distance apart tomorrow night, with Jupiter to the right of the Moon.
 

Script by Damond Benningfield

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The Sun’s two closest planets are snuggling close to each other. They’re quite low in the southwest at sunset. But they’re both bright, so if you time it right, you should be able to pick them out.

Venus is lower but brighter — the “evening star.” Fainter Mercury is a little above it. Mercury is the Sun’s closest and smallest planet, with Venus the next one out.

Mercury has no atmosphere to speak of. So with no wind or rain, any changes on its surface have to come from inside the little planet, or from impacts by objects beyond Mercury.

A recent study found that the surface changes much more often than expected. And most of the changes are driven from within.

Scientists compared more than 58,000 pairs of images from the Messenger spacecraft, which orbited Mercury from 2011 to 2015. It snapped pictures of the same regions of the planet at different times. By comparing those images, scientists found 20 changes to the surface.

One of them was an impact crater — a hole gouged by a collision with a space rock. But the others probably were caused by processes inside Mercury itself. They all appeared in regions that are associated with volcanic activity. So the features probably were created by quakes, the motions of molten rock, or other internal activities. The number of new features suggests that Mercury’s surface changes a lot — driven from inside the Sun’s smallest planet.
 

Script by Damond Benningfield

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Jean-Dominique Cassini probably taught us more about the planet Saturn than anyone else before or since. 350 years ago this month, he discovered its second-largest moon. It’s a giant “dirty snowball” — a mixture of ice and rock.

Cassini was a leading astronomer not only of his era, but of any era. He was born in Genoa, but later became a citizen of France, where he did most of his work. He studied Jupiter, the Moon, the speed of light, and much more. But he’s best known for his observations of Saturn.

He discovered a dark “gap” in Saturn’s rings. It’s named the Cassini Division in his honor. He also discovered four moons — one of them on December 23rd, 1672. Much later, it was named for the goddess Rhea, the wife of Kronos, the Greek equivalent of Saturn.

The moon is 950 miles in diameter — less than half the size of our own moon. It orbits Saturn once every four and a half days.

Most of what we know about Rhea came from the Cassini spacecraft — named for Jean-Dominique. It flew as close as about 40 miles from the moon. It showed that Rhea is about 75 percent ice and 25 percent rock. Its surface has two giant impact basins, plus some tall ice cliffs — the surface of a moon that was discovered 350 years ago.

Saturn is easy to find tonight because it’s quite close to our moon. It looks like a bright star to the right of the Moon at nightfall. But you need a telescope to see Rhea.
 

Script by Damond Benningfield

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One of the most remarkable scientific developments of the last couple of decades is the idea that life could exist elsewhere in our own solar system. Quite a few worlds are thought to have possible habitats: Mars, some of the moons of the giant outer planets, and the dwarf planets Pluto and Ceres. Even the planet Venus has been added to the list.

Venus would appear to be as unlikely a home for life as you could ever imagine. Its atmosphere is extremely hot, dense, and toxic. And it’s topped by clouds of sulfuric acid. Yet a few observations have hinted that microscopic life could inhabit those clouds.

Some observations have shown dark “mats” inside the clouds — a possible signature of bacteria. And a couple of years ago, a team reported evidence of phosphine in the clouds. Here on Earth, phosphine is a byproduct of life.

Follow-up work by other groups, though, discounts that possibility. The most recent is a study using SOFIA — an airborne observatory. It scanned Venus’s clouds in November of 2021. And it found no evidence of phosphine. In fact, scientists say there couldn’t be more than about one part per billion.

Even so, few are ready to give up on the possibility of life in the clouds of this inhospitable world.

Venus is the “evening star.” It’s quite low in the southwest at sunset, well to the lower right of the crescent Moon. The fainter planet Mercury is a little above Venus.
 

Script by Damond Benningfield

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The early evening sky serves up an amazing gift for this Christmas Eve: All five planets that are visible to the unaided eye are in view at the same time. And a thin crescent Moon adds a ribbon to the package.

Shortly after sunset, the Moon and the planets Venus and Mercury form a tight triangle quite low in the southwest. You’ll need a clear horizon to spot them, but it’s worth the effort. The view is a little better from locations that are farther south.

Venus is the “evening star” — the brightest object in the night sky after the Moon. Mercury is between the Moon and Venus and slightly higher. It’s fainter than Venus, but its proximity to the brighter objects will help it stand out.

Arc to the upper left and you’ll come to Saturn, the second-largest planet. It, too, looks like a bright star. And brighter Jupiter, the largest planet, stands due south, fairly high in the sky.

Continue the arc far to the lower left and you’ll come to planet number five, Mars. It’s beginning to fade from its peak early in the month, but it’s still unmistakable. It looks like a very bright orange star. A true star is close to its lower right: Aldebaran, the orange eye of the bull.

And Orion, one of the most beautiful of all constellations, is below them, quite low in the east. It will climb high across the south later on — more beauty in the night sky — a gift every single night of the year.

More about the evening sky tomorrow.
 

Script by Damond Benningfield

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A star that’s at the beginning of its final act is going out in style. It’s blowing hot gas off its surface, forming clouds on either side of the star. Powerful winds from the star are sculpting both clouds into cones, with the wide ends closer to the star.

The star doesn’t have a name — only a long list of numbers. But the entire complex is nicknamed Minkowski’s Footprint, after the astronomer who cataloged it, and its resemblance to a footprint in some images.

The star is bigger, brighter, and more massive than the Sun. But it’s burned through the nuclear fuel in its core, so the fusion reactions that power it are shutting down. That’s causing the star’s outer layers to surge out into space, creating a nebula around the star.

This process is in its early days, so it’s known as a protoplanetary nebula. The nebula is visible only because its gas and dust reflect light from the star. But in a few thousand years, the dying core will become much hotter. Its radiation will cause the clouds to glow on their own, creating a full-fledged planetary nebula.

The expelled material will continue to expand, forming a colorful bubble. After tens of thousands of years, it’ll fade from view, and only the hot but dead core will remain — the end of a star.

The nebula is near the beak of Cygnus, the swan, which is about a third of the way up the western sky at nightfall. But you need a telescope to see this dying star.
 

Script by Damond Benningfield

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The most-distant object that’s readily visible to the eye alone stands directly overhead at nightfall now, in the constellation Andromeda. Under dark skies, M31 looks like a tiny cloud. But it’s really a giant spiral galaxy much like our own — about two and a half million light-years away.

It’s the closest of all big galaxies, so it’s a popular target for astronomers. And one team recently found what may be a mid-sized black hole in its outskirts.

The black hole is in a star cluster that’s about six million times the mass of the Sun. It’s been classified as a globular cluster — a tightly packed ball of stars as old as the galaxy itself.

The new study used telescopes on the ground and in space. Their observations showed that the cluster’s light tapers off in an odd way. The stars at its center appear to be orbiting something that’s small but massive. And the cluster isn’t as old as the galaxy. From that, the astronomers concluded that a rare mid-sized black hole inhabits the cluster’s heart. It’s about a hundred thousand times the mass of the Sun.

The cluster probably began as the core of a smaller galaxy. As the galaxy passed near M31, its outer precincts were pulled away by M31’s more powerful gravity. The stars in those regions merged with M31. The core stuck together and entered orbit around the larger galaxy. And that’s where it is today — the remnant of a dead galaxy with a black hole in its heart.
 

Script by Damond Benningfield

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Today is the winter solstice — the shortest day and longest night of the year in the northern hemisphere. The Sun stands farthest south for the entire year, too, so it scoots low across the horizon.

For centuries, people in regions as far flung as China, Persia, and the Americas celebrated this astronomical event. It marked a turning point in the year — offering a future of longer, warmer days.

In ancient Rome, the solstice was celebrated with the most popular holiday of the year, Saturnalia. It honored Saturn, a god of agriculture. It grew out of older rituals that were tied to the winter planting season. Romans from all walks of life enjoyed a week-long festival. It featured music, feasting, gift giving, and decorating with greenery.

Early Christians celebrated the feast of Saint Lucy, who’s remembered for helping persecuted Christians who were in hiding. In legend, she wore a wreath of candles on her head to light the way while leaving her hands free.

If much of this sounds familiar, there’s good reason. Many of these ancient traditions live on in the modern celebration of Christmas — no longer linked to harvesting and planting, but still bringing light and festivity into the darkest season of the year.

And Julius Caesar added to the celebration when he reformed the calendar, in 46 BC. He placed the beginning of the year shortly after the solstice — on the first of January — where it remains today.
 

Script by Laura Tuma

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Shortly after noon the next couple of days, a dagger of sunlight will slide across a bluff on the banks of the Concho River at Paint Rock, Texas. As the Sun stands highest in the sky, the dagger will stab through the heart of a several-hundred-year-old pictograph.

The red painting depicts a shield — a possible symbol for the Sun. The dagger of sunlight crosses the shield only around the winter solstice, which is coming up tomorrow. It’s the shortest day of the year in the northern hemisphere, when the Sun stands farthest south in the sky.

The Paint Rock site contains hundreds of pictographs, which extend about half a mile along the bluff. Some of the pictures clearly depict the Sun.

A couple of decades ago, the site owners heard about other rock-art sites with alignments to the solstices or equinoxes. They contacted a University of Texas astronomer, who suggested they watch the site at local noon on these dates.

On the winter solstice of 1996, they discovered the dagger of sunlight crossing the shield. Later study confirmed that the alignment probably was intentional — the shaft of light shines through a crack in the rocks only at the solstice.

Native cultures may have painted the symbol to indicate the solstice. If so, then they probably held rituals on the solstice to confirm the power of the rulers, and to entice the Sun northward — bringing warmth back to the Texas hills.

More about the solstice tomorrow.
 

Script by Damond Benningfield

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