StarDate

Mars is a world of extreme geology. It has the tallest mountain in the solar system, one of the longest canyons, and one of the biggest holes in the ground. That hole is about 1400 miles wide and up to five miles deep. And its floor has been sculpted by everything from blowing sand to flowing water.

Hellas basin is in the southern hemisphere. It’s surrounded by jumbled terrain that’s a good bit higher than the planet’s average elevation.

And that’s no coincidence. Hellas basin was created about four billion years ago, when a giant asteroid slammed into the Martian surface. It blasted out a huge amount of rock — enough to cover the 48 contiguous United States in a layer more than two miles thick. Some of that rock fell back onto the surface, forming some of the higher terrain around Hellas.

The crater’s floor has been molded by wind-blown sand, glaciers, and flowing water. There’s even some evidence that it once was filled with water, forming a large sea.

Because Hellas is so deep, it has the densest atmosphere of any spot on Mars — twice the global average. So under the right conditions, liquid water could exist on the surface there for short periods. And during winter, the basin fills with frost and clouds, making it look pure white — a cold hole in the surface of Mars.

Look for Mars leading the Moon across the sky late tonight. It looks like a bright orange star, and rises to the upper right of the Moon.

Script by Damond Benningfield

Here on Earth, life inhabits just about every nook and cranny you can think of. That includes one of the driest spots on the planet — the Atacama Desert of Chile. Some parts of it receive an average of just a few millimeters of precipitation per year. And they can go many years without a drop. Even so, microbes live just below the desert surface. And that has implications for the possibility of life on Mars.

An international team studied the Atacama in 2015, ’16, and ’17. The scientists dug into the desert in several locations in search of microbes. The first expedition came not long after a rare rainfall. But little or no rain fell after that.

In the wetter 2015 samples, the team found abundant microscopic life not far below the surface. There was less activity the following years, but there was still some, even in the most arid locations. That suggests that some organisms have adapted to living in the Atacama, where it’s not only dry, but other conditions aren’t good for life, either.

Mars is even drier than the Atacama, and the surface chemistry isn’t very hospitable. Yet the Atacama study suggests that if microbes evolved on the young Mars, they might have adapted as the planet dried out. They could still exist today, living below the surface of this desert world.

And Mars is in great view late tonight. It’s just below the Moon as they climb into good view after midnight, and even closer to the Moon at first light.

Script by Damond Benningfield

A star that astronomers first thought was an infant still in the embrace of its nursery turns out to be a near twin to the Sun — although one that’s billions of years younger.

The star is known by a long catalog number. It’s in the constellation Monoceros, the unicorn. The star appears in front of one of the unicorn’s best-known residents, the Rosette Nebula. It’s a beautiful cloud that’s given birth to a cluster of young stars. That position in the sky led astronomers to conclude that the solar twin was associated with the Rosette.

But observations with a telescope in Australia revealed that the star is only 715 light-years away. That’s about 4500 light-years closer than the Rosette.

The observations also revealed that the star has the same color and surface temperature as the Sun. That means it’s a member of the same spectral class, G2. Although it’s a bit smaller and fainter than the Sun, it’s almost exactly the same mass. That makes it a close enough match for the astronomers who studied the star to classify it as a solar twin.

One major difference, though, is age. Based on how fast the star spins and other factors, the astronomers concluded that the star is just 180 million years old, compared to 4.6 billion years for the Sun.

Studying solar twins at different stages of evolution helps astronomers better understand the history and future of the Sun. And that helps them devise better models of how all stars evolve.

Script by Damond Benningfield

When it comes to space travel, if one thing doesn’t get you, another just might. When the Sun is quiet, for example, it lets in more radiation from outside the solar system. A recent study, in fact, said the level of cosmic rays could jump by as much as 30 percent in a few years, when the Sun is at its quietest.

Cosmic rays are energetic particles from exploding stars and other objects. They can damage a spacecraft’s electronics, perhaps even knocking the craft out. They also can harm any human occupants, increasing the risk of organ damage and cancer.

When the Sun is active, its winds and magnetic field act as a shield against cosmic rays — they keep most of them from reaching the inner solar system. But the Sun’s activity changes over a period of 11 years. At its peak, it produces a lot of dark sunspots and big outbursts of energy and particles. These activities also can endanger electronics and people, but they keep the cosmic rays at bay. At its lowest point, though, the Sun is quiet, so many more cosmic rays get through.

The last couple of cycles have been unusually quiet, with the low points especially so. At the same time, observations from an instrument on a Moon-orbiting satellite have shown that the number of cosmic rays has been jumping faster than expected. As a result, the level of cosmic rays could jump by up to 30 percent at the next solar minimum — another hazard for the dangerous business of spaceflight.

Script by Damond Benningfield

The biggest moons of the biggest planets are some of the most remarkable worlds in the solar system. One of the moons of Jupiter, for example, is covered with giant volcanoes. And another Jovian moon may have a global ocean of liquid water beneath its icy crust.

The most remarkable moon of all, though, has to be Titan, the largest moon of Saturn. And what makes it remarkable is not that it looks exotic, but that it looks familiar. Riverbeds flow across its surface, emptying into lakes and seas. Clouds waft through the sky, occasionally dropping rain. And giant dunes undulate across its mid-section. In other words, it looks a lot like Earth.

And in some ways it may resemble the Earth of billions of years ago. The main thing they have in common is that Titan has a thick atmosphere that’s rich in organic compounds — the building blocks for life.

There’s one big difference between Earth and Titan, though: temperature. Titan is so cold that water is frozen as hard as granite. So the liquids that form the clouds, carve the rivers, and fill the lakes are ethane and methane. Even so, in many ways Titan is the most Earth-like world in the solar system — a familiar landscape that makes it a remarkable world.

Saturn is in good view the next couple of nights. The planet looks like a bright star, and stands to the lower left of the Moon as they climb into view late tonight. It will stand closer to the right of the Moon tomorrow night.

Script by Damond Benningfield

Stars follow a life-long weight-loss program. They blow charged particles off their surfaces. Over time, the amount of material in these “winds” can add up. Some of the heavier stars, in fact, can expel enough material to make several stars as massive as the Sun.

An example is Antares, the leading light of the celestial scorpion. It’s in good view tonight, to the right of the full Moon as darkness falls.

Antares is a supergiant — one of the biggest and brightest stars in the galaxy. It’s about 12 times the Sun’s mass, and big enough that if you placed it at the center of the solar system, it would extend past the orbit of Mars.

But when Antares was born, about 11 million years ago, it was even heavier. Studies in recent years have placed its initial mass at about 15 to 17 times the mass of the Sun. The difference has been blown out into space on the star’s winds.

Antares has lost so much of its original weight because it was heavy to begin with. Massive stars “burn” through their nuclear fuel quickly, making their cores extremely hot. Radiation from the core of such a star causes its outer layers to puff outward. That far from the core, the surface gravity is relatively low, so it’s easy for radiation to push hot gas out into space.

Antares is fated to expel even more of its mass. At the end of its life, its core will collapse, causing its outer layers to explode as a supernova — blasting most of its remaining gas out into the galaxy.

Script by Damond Benningfield

A trio of bright lights lines up parallel to the western horizon this evening. The lights are low in the sky at sunset, and set by 11 o’clock or so.

The center light is also the brightest: Venus, the evening star. It’s the brightest object in the night sky other than the Moon.

Despite its nickname, Venus isn’t a star at all. Instead, it’s a planet. It shines so prominently because it’s close by, and because it’s close to the Sun, so it receives a lot of sunlight. It’s also covered by bright clouds that reflect most of that sunlight back into space.

The second-brightest member of the trio is Capella. It’s to the right of Venus, by about two and a half times the width of your fist held at arm’s length.

Capella is a true star. Or to be more precise, it’s four stars, all bound by gravity. The stars form two pairs. One pair is faint. But the other consists of two giant stars, both of which are quite bright. So even from a distance of 43 light-years, the system forms the sixth-brightest star in the night sky.

The third member of the trio is Procyon, about the same distance to the left of Venus. It’s also known as the Little Dog Star because it’s the leading light of Canis Minor, the Little Dog. It looks bright mainly because it’s close — less than 12 light-years away.

And if those bright objects aren’t enough, two others stand above Venus: Castor and Pollux, the twins of Gemini — adding to the light show in the western evening sky.

Script by Damond Benningfield

The Atlantic hurricane season opens on June 1st. Its giant storms can span hundreds of miles and last for days.

But a Jupiter-orbiting spacecraft has discovered regions where it’s always hurricane season, the storms can span thousands of miles, and they don’t seem to have an expiration date.

Juno arrived at Jupiter almost two years ago. It orbits the giant planet once every 53 days, from pole to pole. That allows it to see regions of Jupiter that haven’t been seen before: the north and south poles. And the view is amazing — a giant cyclone sits atop each pole, with other big cyclones all around them.

The central storm at the north pole is boxed in by eight other storms, all of which are at least 2500 miles across. The storms actually form two boxes. They’re offset by 45 degrees, with one box a little smaller than the other.

The storm at the south pole is surrounded by five other cyclones, which are a bit more randomly distributed. They’re also bigger than their northern kin: up to about 4300 miles across.

Juno has watched the storms for months, and seen little change. No one is sure why the storms around the central ones are there at all, or why they don’t merge — mysteries for Juno to continue exploring as it looks down on the stormy poles of Jupiter.

And Jupiter looks like a brilliant star close to the right or upper right of the Moon at nightfall, and staying close to the Moon throughout the night.

Script by Damond Benningfield

The Moon slides between a couple of bright points of light tonight. The planet Jupiter is close to the lower left of the Moon as night falls. It’s brighter than anything else in the night sky except the Moon and Venus, so you can’t miss it. And the star Spica is a little farther to the right of the Moon.

Jupiter is the biggest, heaviest planet in the solar system. It’s about 11 times Earth’s diameter, and more than 300 times its mass. In fact, it’s heavier than all the other planets and moons in the solar system combined.

Yet Jupiter is insignificant compared to many planets found in other star systems. Some of those planets are up to a few dozen times heavier than Jupiter. And many of them orbit much closer to their parent stars than Jupiter is to the Sun.

But conditions close to a star are just too hot to allow the formation of big balls of gas like Jupiter and the giant exoplanets. So those other worlds probably formed much farther out, where conditions were much colder. Gravitational interactions with other planets then caused them to spiral closer in. That might have caused planets that were born even closer to fall into their suns.

Something similar could have happened in the solar system. Jupiter might have migrated inward, clearing out the close-in planets. It then moved out to its current position, allowing new planets to form closer to the Sun — including our own Earth.

More about Jupiter tomorrow.

Script by Damond Benningfield

A star with an important history huddles close to the Moon tonight. Spica, the leading light of Virgo, is to the lower right of the Moon at nightfall. It’s one of the brighter stars in the sky, and it’s not close to any other bright stars, so it stands out.

Many cultures have used Spica as a calendar marker. Partly that was because of its brightness and isolation. But it was also because the times of year at which it appeared and disappeared coincided with important agricultural events. And that connection led to its name — Spica means a “spike” or ear of grain.

A study a few years ago suggested that Spica guided wheat farming in the Fertile Crescent — the area of the Middle East where wheat was first domesticated.

The study said that, more than 10,000 years ago, Spica disappeared in the west just after sunset when it was time to harvest the wheat crop. And it returned to view in the east just before sunrise almost six weeks later, when it was time to thresh the grain. It was the only star that could have served as a calendar marker for both events.

Another study looked at a calendar of ancient Armenia. It found that the year began with Spica’s first appearance in the dawn sky, a few days before the summer solstice. That places the birth of the calendar at about the same time that agriculture was beginning in the region.

Spica has played a role in many other cultures as well — helping them track the changing seasons.

Script by Damond Benningfield