StarDate – Détails, épisodes et analyse

One popular sci-fi trope is invasion by alien “bugs” – microscopic organisms from other worlds that could harm life on Earth. But scientists also are concerned about things working the other way around: Earth bugs contaminating other planets. So landers are sterilized to prevent them from carrying any hitchhikers. And when the life of an orbiter ends, it’s targeted to crash into a place where it won’t cause any harm.

One world where that’s not a concern is Mercury. The Sun’s closest planet has no air – only a few atoms captured from the solar wind, or knocked off the surface of Mercury by the solar wind. And even that is a hard vacuum by Earth standards.

Mercury is zapped by solar energy. That heats the dayside to as high as 800 degrees Fahrenheit. And ultraviolet energy would destroy any Earth-like microbes.

So when the only Mercury orbiter to date wrapped up its mission, in 2015, it was allowed to crash into the planet.

The next Mercury mission is scheduled to fly past the planet next week, and enter orbit late next year. It may crash into Mercury when its mission is through as well – gouging a new crater, but leaving the planet uncontaminated.

Mercury is just creeping into the dawn sky. It looks like a fairly bright star. But it’s so low that you need a clear horizon to spot it. It’ll be a bit easier to see tomorrow because it’ll perch close to the right of the “fingernail” crescent Moon.

Script by Damond Benningfield

Star clusters are packed with stars, but not with planets. So far, only a few dozen of the more than 5600 confirmed exoplanets have been found in clusters. And two of those orbit a single star, in the Beehive Cluster.

The dearth of planets could simply mean that planets are hard to find. Only a small fraction of the stars in the Milky Way Galaxy reside in clusters, and not many clusters are close to us. And clusters can be tightly packed, making it hard to study their individual stars.

But because the stars are so tightly packed, it might be hard to make planets. As stars fly past each other, their gravity could stir up the raw materials for making planets, blocking their birth. And even when a planet is born, a close encounter could kick it away from its star. So maybe there really aren’t many planets in clusters.

The star in the two-planet system in the Beehive is a little smaller and cooler than the Sun, and four billion years younger. One of its planets is about twice the mass of Jupiter, the giant of our own solar system. And it’s so close to the star that it’s extremely hot. The other planet is even bigger, but much farther from the star, so it’s quite cold. So neither planet is a likely home for life.

The system is too faint to see without a telescope. But the Beehive is visible. Under dark skies, it looks like a hazy patch of light. At dawn tomorrow, it’s close to the right or upper right of the Moon.

Script by Damond Benningfield

No matter which system you go by, the names of the two brightest stars of Gemini aren’t quite right.

In mythology, the stars are named Pollux and Castor. They represent a pair of twin half-brothers. They had the same mother, but one had a mortal father, while the other was the son of Zeus, the king of the gods of Olympus. But the stars don’t look like twins. Pollux is almost twice as bright as Castor, and it looks orange, versus Castor’s pure white. They were called the twins mainly because they’re both bright, and they appear close together.

The stars themselves aren’t physically related. And they’re nothing alike. Pollux consists of a single giant star, while Castor is a system of six stars.

A second naming system is also off. In this system, Castor is Alpha Geminorum, while Pollux is Beta Geminorum.

The naming system was devised by Johann Bayer. In a star atlas published in 1603, he assigned each star to a constellation. And he named the stars using the letters of the Greek alphabet. “Alpha” usually was applied to a constellation’s brightest light, and “Beta” to the second-brightest. But in Gemini, they’re reversed. No one is quite sure why that’s the case. No matter the reason, though, the names of the bright “twins” of Gemini are a bit off.

The stars appear near the Moon early tomorrow. Pollux stands above the Moon at first light, with Castor a little farther to the upper left of the Moon.

Script by Damond Benningfield

When a delivery truck drops off its final package of the day, it isn’t abandoned – it’s prepped for more deliveries the next day. And it’s the same thing with several spacecraft. After delivering their main cargo, they’ve been given new missions – new addresses to check out.

The list has included three craft that delivered samples to Earth – bits of two asteroids, and some dust from a comet. The craft dropped capsules containing the samples into Earth’s atmosphere as they flew by. And another craft fired a cannonball into a comet.

After finishing their main missions, the spacecraft were still working. So they were given new missions. One of them is headed for a rendezvous with the asteroid Apophis, which will skim just above Earth in 2029. Another is headed for a comet.

Along the way, some of the missions have turned their cameras toward star systems with known planets. The craft can stare at a system for days or weeks. That allows them to measure tiny dips in a star’s light as a planet passes in front of it. Astronomers piece that together with information from other sources to refine a planet’s dossier – its size, mass, distance from its star, and more. One craft even found evidence of a second planet in a system, although it hasn’t been confirmed.

So even though some of these missions have long since dropped off their packages, they’re still delivering important discoveries about the universe.

Script by Damond Benningfield

Giant spiders crawl around the walls of an ancient city on Mars. And if that doesn’t sound like the plot of a bad movie, then what does? It turns out, though, that this plot is true – in a way. The “city” consists of walls of volcanic rock or hardened sand. And the “spiders” are explosions of dark dust from below the surface.

The region is called Inca City. It was discovered in 1972, in pictures from a Mars orbiter. It’s a grid of intersecting lines that resembles the outline of an ancient Incan city. The walls are miles long and hundreds of feet tall.

Scientists aren’t sure what created the lines. They could be hardened sand dunes. The most recent idea says they’re volcanic rock. Inca City may lie inside an old impact crater. Molten rock could have bubbled up through cracks in the crater floor. The floor was covered up, but the Martian winds have swept it clean, exposing the ridges.

Inca City is near the edge of the southern polar ice cap. Frozen carbon dioxide covers the region in winter. In spring, it vaporizes. Carbon dioxide a few feet below the surface can vaporize first, blowing holes in the ice above it. Dark dust in the plumes then settles to the surface – forming “spiders” around the walls of Inca City.

Look for Mars before and during dawn now. It looks like a bright orange star. Tomorrow, it’s to the upper right of the crescent Moon. The brilliant planet Jupiter stands above them.

Script by Damond Benningfield

The Moon and three other bright lights form a beautiful diamond in tomorrow’s dawn sky. Going clockwise from the Moon, the points of the diamond are the planet Jupiter, which is the brightest of the three; the planet Mars; and the star Elnath, the tip of one of the horns of Taurus.

The Sun illuminates about a third of the side of the Moon that’s facing our way. The most prominent feature in the sunlight is a giant dark patch known as the Ocean of Storms. It’s one of the largest features on the Moon. It covers one and a half million square miles – about one-tenth of the Moon’s entire surface.

A half dozen probes have landed in that vast region, including the Apollo 12 mission in 1969.

The most recent lander was Chang’e 5. The Chinese mission brought about four pounds of rocks and dirt back to Earth, in 2020. The samples indicated that the “ocean” formed about two billion years ago, when the Moon was about half of its current age. That makes the Ocean of Storms the youngest of the Moon’s big volcanic plains.

The feature may have formed when molten rock pushed its way to the surface through long, wide cracks. But the origin is still being debated. Some scientists say it formed after a massive asteroid slammed into the Moon. The impact gouged a wide crater that later filled with lava – forming a giant “ocean” on the Moon.

The Moon will stand close to Mars on Wednesday; more about that tomorrow.

Script by Damond Benningfield

The Sun has been feisty this year. It’s produced some monster storms that have pelted Earth with radiation and charged particles. That’s disrupted some communications, air travel, and other daily activities.

There’s evidence that the Sun has been much feistier in centuries past. If such major outbursts happened today, they could be really bad for modern technology. But the big ones in the past are good for archaeology. They’re helping scientists nail down the dates of some ancient human activities.

The Sun is especially active every 11 years or so. It blasts out giant clouds of charged particles. When the particles hit the atmosphere, they create cascades of other particles. That includes a radioactive form of carbon. Trees take up some of this carbon. The more active the Sun is, the more they absorb.

By analyzing the ratio of different forms of carbon in tree rings, scientists can determine which years were especially “stormy.” And that gives them a way to date human settlements.

Earlier this year, for example, a team studied rings in logs that were used to make houses and other structures at a site in Greece. The scientists found rings that recorded a busy year for solar activity. It corresponded to a previously discovered peak, in 5259 BC. Counting all of the tree rings showed the site had been inhabited for at least a couple of hundred years – including a time with an especially feisty Sun.

Script by Damond Benningfield

Stars aren’t always what they seem. Consider the two brightest stars of Lyra. The constellation’s leading light is Vega. It looks 20 times brighter than the second-ranked star, Sulafat. But that’s only because Vega’s much closer. If you lined them up at the same distance, Sulafat would look 60 times brighter than Vega.

The difference is caused by their stage in life. Vega’s in the prime of life. It’s “fusing” the hydrogen atoms in its core to make helium, releasing energy in the process. Vega is more massive than the Sun, so those reactions happen at a much faster rate – making Vega about 40 times brighter than the Sun.

Sulafat has moved into the next stage of life. It’s converted the hydrogen in its core to helium. Now, it’s fusing hydrogen in a thin layer around the core. That’s caused its outer layers to puff up, helping the star shine about 2400 times brighter than the Sun.

Eventually, Sulafat will start fusing the helium in its core. That’ll make it even bigger and brighter. Then it’ll shed its outer layers, leaving only its dead core. Vega will experience the same fate – more than a billion years from now.

Lyra is high overhead at nightfall. It’s easy to spot because Vega’s one of the brighter stars in the night sky. Four stars outline a tilted, flat box to the lower right of Vega. Sulafat is at the corner of the box that’s farthest from Vega.

Script by Damond Benningfield

In the early 20th century, much of the world had “Mars fever.” Percival Lowell had mapped what he called “canals” on Mars, built by a dying civilization. H.G. Wells published “War of the Worlds,” about a Martian invasion. Inventor Nicola Tesla reported hearing possible signals from Mars. So there was a lot of interest in the Red Planet. In 1901, Richard Taylor wrote this march to capture the enthusiasm – “A Signal From Mars.”

People listened for signals 100 years ago this week. Mars was passing especially close to Earth. Astronomer David Todd thought Martians might try to contact us. So he organized a campaign to listen for radio transmissions.

Among others, he worked with Charles F. Jenkins, who’d built a device that could transmit photographs via radio. Jenkins later developed early forms of television.

Starting on August 21st, 1924, Jenkins recorded radio waves on a roll of photographic paper whenever Mars was in the sky – more than 20 hours in all. Todd said he saw faces in the squiggles on the paper. But Jenkins thought it was nothing but noise.

Technicians at some radio stations reported hearing odd sounds during the hunt. Most of the sounds came from Earth, although some might have been natural radio waves from astronomical objects.

But none of them came from the Red Planet. There were no signals from Mars.

Script by Damond Benningfield

Army and Navy radio stations around the world had something extra to listen for 100 years ago this week: Mars. The Red Planet was passing closer to Earth than it had in centuries. A retired astronomer thought that Martians might take advantage of the encounter to beam greetings to the neighbors. So he organized an effort to hear the transmissions.

David Todd had led the astronomy program at Amherst College in Massachusetts. Most scientists of the day said there was no chance of a Martian civilization, but Todd disagreed.

Radio pioneers Nicola Tesla and Guglielmo Marconi had reported hearing odd signals from space several years earlier. Some interpreted the signals as broadcasts from Mars. And Percival Lowell had created maps of Martian “canals” – built to bring water from the polar ice caps to a dying civilization. All of that convinced Todd that it was worth listening for Martian broadcasts.

Todd asked radio stations to go silent for five minutes of every hour for several nights. Only one complied – station WRC, in Washington, D.C. But technicians at other stations listened for odd signals. The military instructed its radio operators to listen as well, but only if it didn’t interfere with normal operations. And it made its leading cryptographer available to decode any Martian messages.

Todd also enlisted the help of a television pioneer, and we’ll have more about that tomorrow.

Script by Damond Benningfield