StarDate

Earth lies in the middle of the Sun’s habitable zone. That’s the distance from the Sun where conditions are most comfortable for life. And astronomers are concentrating their hunt for life in other star systems in their habitable zones.

There’s an idea that galaxies have habitable zones as well. The zones would have a good mix of chemical elements, not too much radiation, and a low risk of exploding stars.

Stars consist mainly of hydrogen and helium. But to make planets like Earth, you need a good supply of heavier elements — things like oxygen, silicon, and iron. Those elements are forged in the hearts of stars, then blown out into space when the stars die. So to have good conditions for life, you need a region where lots of dead stars have “seeded” the galaxy with heavy elements.

But you don’t want to be too close to stars that die in massive explosions. They can damage a planet’s atmosphere, exposing life to high levels of radiation. So you want to be away from a galaxy’s core, where stars are packed close together — including ones that might explode.

The cores of most galaxies also harbor supermassive black holes. As they pull in stars and gas they produce lots of radiation, saturating the space around them.

So in our home galaxy, the Milky Way, you want to be away from the core, but not too far away. And that’s just where Earth is — about half way from the center to the edge — in the galactic habitable zone.

Script by Damond Benningfield

A possible new space telescope probably won’t launch for a couple of decades, if at all. But astronomers are already looking for targets for it to study — star systems with planets that could host life.

Habitable Worlds Observatory will have several jobs. As the name suggests, one of those jobs will be to scan planets for signs of life. The telescope will screen out the light from a star, allowing it to take pictures of planets around the star.

Most important, the telescope will analyze the atmospheres of planets in the habitable zone — the region around a star that’s most comfortable for life. The telescope’s instruments will look for oxygen, ozone, methane, and other substances that are pretty good signs of life.

Early estimates say the telescope will cost more than 10 billion dollars, so scientists don’t want to waste any of its time. So they’re already compiling a list of star systems with candidate planets, using findings from many telescopes in space and on the ground.

And they’re trying to learn as much as possible about the systems. They want to know if the orbits of the habitable-zone planets are stable, for example; planets with unstable orbits might not have been in the zone long enough for life to develop.

The list of possible targets already has dozens of planetary systems. But the search continues — for planets that might tell us if there’s life elsewhere in the universe.

Script by Damond Benningfield

Many factors are involved in making a planet habitable: the size and composition of the planet, the stability of its orbit, its distance from its star. But scientists are still trying to figure out which factors are important.

An example is plate tectonics. Earth’s surface is divided into large “plates.” They glide along the rocks below the surface. They ram together, slide over each other, and recycle the crust. They allow heat to escape to the surface, and affect the chemistry of the atmosphere. So tectonics has been considered a key ingredient for the development of life.

But some recent studies have cast some doubt on that idea. One study found that the early Earth probably didn’t have tectonics. Instead, its crust was rigid — a “stagnant lid.” Instead, molten rock would have punched through the crust, building big volcanoes. That warmed the surface, allowing the development of the first life more than three and a half billion years ago. But the study also suggested that tectonics might be necessary to sustain life, and allow the development of more complex life.

But another study disputes even that. It says that life could last for billions of years on a stagnant-lid planet.

Some models show that plate tectonics could be rare on other planets. But if tectonics isn’t necessary for life, then the number of possibly habitable worlds goes way up — increasing the chances that we might find a “living” planet.

Script by Damond Benningfield

It’s pretty remarkable that scientists have figured out that some meteorites come from Mars. What’s even more remarkable is they may know just where on Mars one of them came from.

The meteorite is cataloged as Northwest Africa 7034. It was discovered in 2011, in the Sahara Desert. The rock weighs about 11 ounces. And because of its dark appearance, it’s nicknamed “black beauty.” An American bought the meteorite and donated it to the University of New Mexico.

Detailed analysis revealed that it came from Mars. And it contains the oldest bits of Mars yet seen: small crystals almost four and a half billion years old — almost as old as Mars itself.

Studying the meteorite can help scientists learn about the formation of Mars. But it helps to have more background about the meteorite. So geologists set about trying to find out where it came from. They used A-I to study millions of impact craters. They compared the types of craters, the composition of their rocks, and their magnetic fields. And they came up with a likely location: near a large crater in the southern hemisphere.

The rock likely was blasted from below the surface when an asteroid hit Mars one and a half billion years ago, gouging out a crater 25 miles across. The rock stayed on the surface until a smaller impact hurled it into space 5 to 10 million years ago. It then made its way to Earth — the oldest bits of Mars we’ve ever seen.

Script by Damond Benningfield

The landing sites of the two most recent American Mars rovers are about 2300 miles apart — roughly the distance from Los Angeles to Washington, D.C. Yet the sites are a lot alike. Both are inside impact craters that formed at least three and a half billion years ago. And both craters once held lakes — potential homes for microscopic life.

Curiosity landed in Gale Crater, in 2012. The crater is almost a hundred miles across, with a central mountain that’s three and a half miles high.

Curiosity has found that water could have filled the crater several times in its early history. Some of the lakes could have lasted for millions of years. Eventually, though, Mars lost most of its atmosphere, and the water on its surface disappeared.

Perseverance landed in Jezero Crater, in 2021. It’s a little less than 30 miles in diameter. But it, too, could have been filled up several times, with some of the lakes possibly hundreds of feet deep. At least one of the lakes formed when a massive flood ripped through the crater’s rim. It created a large river delta that Perseverance continues to explore.

Neither rover has found evidence of life. But they’ve revealed that both craters could’ve had the right conditions for life — billions of years ago.

Look for Mars well to the upper right of the Moon at dawn tomorrow. It looks like a bright orange star. More about Mars tomorrow.

Script by Damond Benningfield

The Perseverance Mars rover packs a laser gun. It’s not for defense against Martians. Instead, it’s a scientific instrument — a way to learn about Martian rocks without drilling into them. And the sound of the laser helps in that effort.

Perseverance zaps a target rock dozens of times in just a few seconds. That vaporizes some of the rock. The rover’s instruments analyze the composition of the vapor. That reveals the chemistry of the rock. Scientists use that information to infer something about how the rocks formed, and about the conditions on Mars when they formed.

A microphone on the rover records the sounds of the laser impact on the rocks. And the sound is different for different types of rocks. Scientists have used that difference to estimate the hardness of the rocks. And they combine the sounds with their analysis of the gas from the laser shots to measure the mineral composition of the rocks. So the eyes — and ears — of Perseverance are telling us a lot about the history of the rover’s location on Mars.

Look for Mars in the dawn sky. It looks like a fairly bright orange star, low in the east at first light. Tomorrow, the planet will stand close to the upper right of the Moon. Mars will climb a little higher into the morning sky as spring ends and we head into summer.

We’ll have more about Mars tomorrow.

Script by Damond Benningfield

There might be three ways to build a habitat on the Moon or Mars. You could bring along everything you need for the habitat from Earth. You could build it from local materials. Or, according to one NASA research team, you could grow it — using fungi.

The team has been working on the technique for years. It uses mycelia — the part of a fungus that grows out of sight. It’s tough, and it can form large networks of interlocking threads. And it can grow quickly.

Researchers have come up with several possible ways to use mycelia. One would be mixing it with the dirt on the Moon or Mars to make bricks. Another would be to make a layered structure, with water ice, the fungi, and a type of algae. And yet another would use an inflatable structure, with “baked” mycelia forming rigid walls and algae producing oxygen to inflate it.

For Mars, the mycelia would have to be engineered in a way that it couldn’t escape and take root on the Red Planet — potentially destroying evidence of any microscopic life there.

So there’s still a lot of work to be done before anyone can produce a “fungal growth” on the Moon or Mars.

The two worlds are close together in the early morning sky the next few days. Mars looks like a bright star. It will stand to the lower left of the Moon at dawn tomorrow, and about the same distance to the upper right of the Moon on Monday.

We’ll have more about Mars tomorrow.

Script by Damond Benningfield

At heart, just about every star is a potential cannibal. Stars that travel through space alone don’t get the chance to act on that instinct. But those with close companions sometimes do act on it. They can pull gas from the companion, eventually leaving the companion with no more than its hot core.

A recent study found a handful of such systems. Three of them are in Cygnus, the swan. One example is called 60 Cygni.

Its two stars are about as far apart as Mars and the Sun. The main star appears to be more than 10 times as massive as the Sun. It’s also much hotter and brighter than the Sun. The companion appears to be a stripped-down core — its outer layers have been cannibalized by the heavy star.

When the system was born, the stripped star probably was the more-massive member. As it reached the end of the prime phase of life, it puffed up. That allowed the companion to start pulling away some of the dying star’s outer layers of gas. Eventually, all of the material in the outer layers might have been transferred to the other star, making it the bigger member of the duo.

In time, that star will begin to expand as well. So the stripped-down companion may begin to pull away its outer layers — cannibalizing the cannibal.

Cygnus is low in the northeast not long after the sky gets good and dark. But you need binoculars or a telescope to find its possible cannibals.

Script by Damond Benningfield

Planetary scientists can hardly move these days without splashing into a new ocean — or at least a possible one. They’ve discovered that oceans of liquid water may be hidden below the icy crusts of many smaller bodies: several moons of the giant planets, the largest member of the asteroid belt, and even remote little Pluto.

One of the more recent “ocean worlds” may be Mimas, a moon of Saturn. It’s less than 250 miles in diameter. Its main feature is a giant impact crater. It’s so big that it makes Mimas look like a “death star” from Star Wars.

Mimas is pockmarked by a lot of craters. Many of them are so old that scientists had thought the little moon was dead, with nothing happening inside it. But precise measurements of Mimas’s orbit and its rotation on its axis revealed some odd “wobbles.”

Scientists proposed a liquid ocean as a possible explanation for those wobbles as early as 2014. A study released earlier this year solidified the case. It found that the ocean could lie 15 miles or so below the surface, and account for up to half of the moon’s volume. The ocean would have formed no more than 25 million years ago. That’s not enough time for evidence of it to show up on the surface. So the ocean remains hidden deep inside this “death-star” moon.

Look for Saturn especially close to our own moon in the wee hours of tomorrow morning. It looks like a bright star just above the Moon at dawn.

Script by Damond Benningfield

Most people keep their hands as far from snakes as possible. But handling a snake was the job for the mythological serpent bearer. He’s represented in the stars as the constellation Ophiuchus, which is in the east and southeast at nightfall. The head of the snake is above Ophiuchus, with its tail below.

In one story, the constellation represented a serpent god. In another, it was a god wrestling with a snake. And in still another, it was an ancient healer who learned the secret of life by watching snakes.

His left hand — the one holding the snake’s head — is represented by two stars: Yed Prior, which leads the way across the sky, and Yed Posterior.

In our sky, the stars are separated by less than the width of your finger held at arm’s length. But they’re not related. One is a little more than a hundred light-years away, while the other is about 160 light-years.

Both stars are more massive than the Sun. So even though they’re much younger than the Sun, they’ve already moved past the prime of life. They’ve burned through the hydrogen fuel in their cores. That’s caused their outer layers to expand to giant proportions. So they’re many times bigger and brighter than the Sun.

Yed Prior and Yed Posterior are about a quarter of the way up the east-southeastern sky at nightfall, with Yed Prior slightly higher. Under even moderately dark skies, they’re easy to see — outlining the hand of the serpent bearer.

Script by Damond Benningfield