StarDate Billy Henry

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