StarDate

Vast amounts of ice lie just below the surface of Mars — especially in the planet’s polar regions. A spacecraft that landed on Mars 10 years ago analyzed the ice with a chemical laboratory, confirming that it really was frozen water.

The Phoenix Mars lander touched down in the northern plains on May 25th, 2008, not far from the polar ice cap. The region was flat and featureless, with no mountains or valleys in sight.

Phoenix measured wind speeds of up to 35 miles per hour, and temperatures as low as 145 below. And it discovered that snow falls from thin clouds of frozen water high in the atmosphere.

Its main job, though, was to study the role of water in the region’s geology, and to determine whether the Martian surface could sustain microscopic life.

Using a robotic arm to dig into the orange dirt, it found a layer of almost pure ice just a few inches down. It dumped some of the dirt and ice into on-board laboratories. The analyses found that the chemistry of the dirt would not be friendly to microbes.

Phoenix operated until the Sun dipped too low in the sky to charge its batteries. Yet it’s still contributing to our understanding of the Red Planet. Earlier this year, a Mars orbiter snapped a picture of the lander and the shell that protected it during reentry. Dark streaks caused by the lander’s rocket engines had disappeared, and the shell was almost gone, too — covered up by wind-blown dust on the frigid plains of Mars.

Script by Damond Benningfield

If Mars colonists want to look for adventure, they’ll probably visit Tharsis Ridge. It’s a vast plateau of volcanic rock with some of the most spectacular features on the planet. Giant volcanoes loom at one side of the ridge, with canyons that dwarf the Grand Canyon on the other.

The ridge is several thousand miles across, and bulges several miles higher than the planet’s average elevation. It built up at least 3.7 billion years ago, when a massive pool of molten rock pushed upward from deep below the surface. “Hotspots” within the molten rock built giant volcanoes.

The most prominent of these volcanoes are known as Arsia Mons, Pavonis Mons, and Ascraeus Mons. They rise almost 10 miles high, and their bases are up to 300 miles across.

The biggest volcano on Earth is Mauna Loa, in Hawaii. It’s only 75 miles across and six miles tall. The difference is the way the crusts of the two planets are made. Earth’s crust consists of interlocking plates, which are in constant motion. They move across the pools of molten rock that build volcanoes. So over time, one volcano shuts down and another takes its place. Mars’s crust, on the other hand, is a solid sheet, so the volcanoes keep building in the same spot.

On the opposite side of the ridge is Valles Marineris. It’s a system of canyons that’s more than 2500 miles long, up to 375 miles wide, and six miles deep — another amazing landmark on Tharsis Ridge.

More about Mars tomorrow.

Script by Damond Benningfield

The shortest season on Mars arrives today — autumn in the northern hemisphere, and spring in the south. The season will last just 142 Mars days. That’s 52 days shorter than northern spring.

The difference is the result of Mars’s lopsided orbit. The distance between Mars and the Sun varies by about 25 million miles. When Mars is farthest from the Sun, it moves slower than when it’s closest to the Sun. That stretches one season, and compresses another.

The differing seasons would make it hard to create a Martian calendar that’s tied to the seasons. That hasn’t stopped people from trying, though. They’ve come up with several ideas.

Some schemes divide the year into 12 equal months, like those on Earth. Others use 18 months, or even 24. And still others have tried months of different lengths.

The concept of a “month” wouldn’t be as important on Mars as it is on Earth. A month here is based on the Moon’s cycle of phases, which lasts 29 and a half days. But the two Martian moons move across the sky much faster. The tiny outer moon, Deimos, completes its cycle of phases in just five and a half days. And the bigger inner moon, Phobos, crosses the sky twice every day. So the moons probably won’t be much help in designing a calendar for the Red Planet.

And Mars is climbing into better view by the day. Right now, it’s about a third of the way up the southern sky at first light, and looks like a bright orange star.

More tomorrow.

Script by Damond Benningfield

The first-quarter Moon snuggles especially close to a bright companion tonight. Regulus, the heart of Leo, the lion, will stand just a degree or so from the Moon as night falls — less than the width of your finger held at arm’s length. The Moon will pull away from the star later on, but they’ll still be quite close together as they set in the wee hours of the morning.

Their closeness is just an illusion — they just happen to line up in the same direction in the sky. In reality, they’re an extraordinary distance apart.

The Moon is a quarter of a million miles away. That’s a vast distance on the human scale, but the tiniest baby step by astronomical standards.

Regulus, on the other hand, is a bit more than 79 light-years away. In other words, traveling at the speed of light — about 670 million miles per hour — it takes light a bit more than 79 years to reach Earth. So a beam of light that leaves the surface of Regulus tonight won’t arrive at Earth until the year 2097. To put that in perspective, it’s just a few months longer than the life expectancy of a baby born in the United States. So we can truly say that Regulus is a lifetime away.

There’s a bit of uncertainty in the distance to any star. In the case of Regulus, it’s about seven-tenths of a light-year. That doesn’t sound like much until you consider this: That slight margin of error is equal to about 17 million times the distance to the Moon.

Script by Damond Benningfield

A pair of eyes stares down from the northeast as night falls right now — the eyes of Draco, the dragon. They’re above brilliant Vega, one of the night sky’s most prominent stars.

The brighter of the eyes is the star Eltanin, the dragon’s leading light. The name means “the serpent,” because the star once represented the entire dragon.

Eltanin is an orange giant. It’s a good bit bigger, heavier, and brighter than the Sun. That makes it easy to see even though it’s more than 150 light-years away.

It should get a lot easier to see in the coming millennia. That’s because Eltanin and the Sun are moving closer together. In about one and a half million years they’ll be at their closest — just 28 light-years apart. Assuming Eltanin hasn’t changed much by then, it’ll be the brightest star in the night sky — about as bright as the current champ, Sirius.

The other eye, Rastaban, is just above Eltanin. Its name means “head of the serpent.” It’s more than twice as far as Eltanin. It’s also a giant, but a much bigger and brighter one — a thousand times as bright as the Sun. So it’s only a little fainter than Eltanin despite the extra distance. It’s about the same color as the Sun, though — yellow-white.

The rest of Draco curves to the left and above the dragon’s eyes, and curls around Polaris, the North Star. The eyes stare in the opposite direction — toward Hercules, who killed the dragon before both of them were placed in the heavens.

Script by Damond Benningfield

Many stars are binaries — two separate stars in orbit around each other. In some cases, though, the two stars are so close to each other that they’re actually stuck together. These contact binaries are surprisingly common. And with a pair of binoculars, you can see one tonight, in the constellation Cepheus, the king.

In 1926, astronomer Jan Schilt observed the star after another astronomer told him its spectrum resembled that of the best-known contact binary. Schilt found that the star’s brightness varied as the two stars went around each other. The variation in brightness occurred across the entire orbit. That meant the stars were so close together that one or the other was always blocking some of its companion’s light.

Today, the system is known as VW Cephei. It’s 90 light-years from Earth. No telescope in existence can see it as two stars instead of one. But the constant change in brightness means the stars are so close that they are indeed stuck together. If you lived on an orbiting planet, your sun would look like a glowing peanut, with the two lobes whirling around each other every 6 hours and 41 minutes.

If you have binoculars and a good star map, you can see VW Cephei for yourself. It’s so far north that for anyone in the United States it never sets. Over just a few hours, the system’s brightness rises 60 percent from minimum to maximum, as the two stuck-together stars race around each other in the far northern sky.

Script by Ken Croswell

Seen from above, storms here on Earth are bright white. On the Sun, though, the storms look dark.

Sunspots are produced by the Sun’s magnetic field. Because the Sun is a ball of gas, different latitudes spin at different rates. That causes the Sun’s lines of magnetic force to get twisted and tangled. They poke through the surface, where they “push” against the hot gas. That reduces the flow of gas from deep within the Sun, producing blotches that can be several thousand degrees cooler than the rest of the surface.

A cooler gas emits less light than a hotter one, so the sunspots look dark. But they’re not as dark as they appear. If you could pull one out and look at it on its own, it would glow reddish-orange. It’s dark only when compared to the brighter surface around it.

Sunspots appear in cycles that last about 11 years.

When a cycle begins, the Sun’s magnetic field is well organized. As the field lines begin to twist, though, sunspots begin to pop up, and always at high latitudes — not far from the poles. Over time, the number of spots goes up, and the spots move closer to the equator. At the cycle’s peak, there can be scores of sunspots. After that, the magnetic field begins to reorganize itself, so the number of spots goes down.

The current cycle has been one of the quietest ever seen. And it’s on the way down, with a period of minimum activity in a year or two — a time where we might go days with no sunspots at all.

Script by Damond Benningfield

It’s been a quarter-century since the end of the last American mission to the planet Venus. And there probably won’t be a new one for at least a decade or so — NASA has turned down several proposals for new craft to study our neighboring world.

But there’s still a lot to learn about Venus. And one of the most interesting questions is what the planet was like when it was young.

Today, Venus is a volcanic wasteland. Its atmosphere is dense and toxic, with temperatures soaring close to 900 degrees Fahrenheit. And the atmosphere is topped by clouds of sulfuric acid.

The early Venus, though, might have been much more hospitable. In fact, there’s evidence that it might once have been covered by liquid water — perhaps enough to form a global ocean. That wetter, cooler era could have lasted as long as two billion years.

After that, though, the water vanished. Venus got hotter, so the oceans boiled into the atmosphere. That trapped more heat, eventually helping to create the hellish environment on the present-day planet.

Finding out more about Venus’s history will require more trips to the planet, with landers that are capable of operating for months or years — something that’s extremely tough to do on this intriguing world.

For now, look for Venus in the west beginning shortly after sunset this evening, to the right of the crescent Moon. Venus is the brilliant “evening star,” so you can’t miss it.

Script by Damond Benningfield

The aliens that invade Earth in many Hollywood blockbusters aren’t that bright. Some of them come here to take our natural resources — particularly water and metals. But Earth is a terrible place to grab those things. That’s because it takes a lot of energy to lift them away from Earth’s gravity.

If you wanted to get those same resources for cheap, the place to go would be the asteroid belt.

Astronomers have cataloged more than a half million asteroids in the belt, which lies between the orbits of Mars and Jupiter. The biggest of them is about 600 miles in diameter. And estimates say there could be a million or more that are at least a kilometer across.

Some asteroids are big chunks of iron and nickel. Others contain lots of carbon compounds. And still others are packed with silicon, magnesium, oxygen, and many other useful elements.

And many asteroids, if not most of them, contain a lot of frozen water. In fact, the largest object in the belt, Ceres, may hold more water than Earth does, hidden just below the surface. And its gravity is tiny compared to Earth’s, so it would take much less energy to carry the water away.

For a civilization capable of interstellar travel, then, it should be pretty easy to slide up next to an asteroid and start carving it apart. Even a fairly small one could provide millions of tons of raw materials, all for the taking — and without having to swat away those pesky Earthlings.

Script by Damond Benningfield

The senior citizens of the Milky Way galaxy are its globular clusters. Most of these giant balls of stars are more than 10 billion years old. And one of the oldest of them all measures out at about 14 billion years — as old as the universe.

That cluster is known as M92. It’s in Hercules, which is in the east and northeast as night falls. It’s an easy target for binoculars, to the left of the Keystone, a lopsided square of stars that outlines the strongman’s body.

M92 isn’t as prominent as another globular cluster in Hercules, M13. Even so, it’s one of the brightest globulars in the night sky. It spans several dozen light-years, and it contains several hundred thousand stars.

Astronomers have measured its age by measuring the composition of those stars. They’re made almost entirely of hydrogen and helium, the simplest chemical elements. They have only a tiny smattering of heavier elements.

Hydrogen and helium were forged in the Big Bang. Almost all the other elements were made by stars. When stars die, they expel some of their material into space, where it can be incorporated into new stars. So each generation of stars has a higher proportion of the heavier elements.

That means that stars with almost none of these elements were born when the universe was young. In the case of M92, they were born not long after the universe itself was — making the cluster one of the oldest members of the Milky Way galaxy.

Script by Damond Benningfield