StarDate

There’s no liquid water on the surface of Mars. But if you could squeeze the planet like a damp sponge, a lot of water might ooze out. Observations by a Mars lander suggest that huge amounts of water might lurk below the surface – enough to cover the entire planet with an ocean a mile deep.

Mars was much warmer and wetter in the distant past. Rivers flowed across the surface, feeding into lakes and perhaps a giant ocean. Most of that water has vanished. There’s some frozen water in the polar ice caps and in slabs below the surface, but no liquid water.

Scientists have been trying to figure out what happened to the rest of the water. Some of it was lost to space. But some could have trickled below the surface, in either liquid or frozen form.

The InSight lander listened for “marsquakes” for four years. The way sound rumbles through the planet reveals details about what’s below the surface.

A recent look at those observations suggested there could be a lot of water more than seven miles down. It would be contained in cracks and pores in volcanic rock – not as underground reservoirs. Still, it’s more than enough water to account for the ancient lakes and ocean – now hidden far below the Martian dunes.

Look for Mars close to the upper right of the Moon as they climb into good view in late evening. The planet looks like a bright orange star.

Script by Damond Benningfield

When astronomers compare the brightness of different stars, they use a scale known as absolute magnitude. That’s how bright the stars would look if they were lined up at the same distance: 10 parsecs, which is 32.6 light-years.

One star they’d barely have to nudge is Pollux, the brightest star of Gemini. It’s only one light-year farther than that distance. So if it moved to exactly 10 parsecs, you’d have a hard time telling any difference in its appearance.

That includes its color. Its orange glow tells us that its surface is thousands of degrees cooler than the surface of the Sun.

Originally, Pollux would have shined almost pure white – an indication that its surface was much hotter than it is today. But the star used up the hydrogen fuel in its core. That triggered a series of changes that caused its outer layers to puff up to giant proportions. As the gas expanded, it cooled, making the star orange. Today, Pollux is the closest giant star to the Sun – a bit more than 10 parsecs away.

Pollux is close to the Moon as they climb into good view by about 10 o’clock tonight. The moonlight will wash out some of the star’s color. Gemini’s other twin, the star Castor, will stand farther to the upper left of the Moon. They’ll be high in the sky at first light. By then, the Moon will line up half way between Pollux and an even brighter orange light: the planet Mars. We’ll have more about Mars and the Moon tomorrow.

Script by Damond Benningfield

This has been a busy year for the Sun. It’s near the peak of its 11-year magnetic cycle, so it’s produced some big eruptions of energy and charged particles. Some of those outbursts have caused troubles here on Earth. And future storms could cause even bigger troubles, with some cities facing a greater threat than others.

Solar outbursts are triggered by storms on the surface of the Sun. Lines of magnetic force become tangled and twisted. Eventually, they snap, then reconnect. That blasts energy and particles throughout the solar system.

When these waves hit Earth, they can create brilliant auroras that appear much farther south than usual. On the downside, they can damage or destroy orbiting satellites, knock out some radio communications, and force airlines to reroute flights. And they can knock out power grids on the surface. An especially powerful storm could disrupt a grid for weeks.

Scientists in Britain have been looking at the likelihood of such outages. They’ve considered many factors: the layout of power grids, how well the ground in a region conducts electricity, and how close to the surface auroras might come, among others. In the United States, the cities at greatest risk appear to be Milwaukee and Washington, D.C.

The researchers are looking at those and other cities in more detail. That should allow them to come up with a better understanding of the risks we all face from our “stormy” star.

Script by Damond Benningfield

Jupiter is the “big brother” of the solar system in more ways than one. It’s more than twice as massive as all the other planets and moons combined. That makes its gravity especially strong, so it can push around the little guys. What’s more, Jupiter likely is the oldest of the Sun’s planets.

Like all the planets, Jupiter probably was born from a disk of gas and dust around the young Sun. It began to grow in the cold outer regions of the solar system. Bits of ice, rock, and metal stuck together. By the time the Sun was perhaps one or two million years old, Jupiter had already grown to about 20 times the mass of the present-day Earth.

Jupiter then began to gobble up vast amounts of gas. After another two or three million years, it was several dozen times Earth’s mass. It pulled in so much material that it cleared a wide gap in the disk around the Sun. And it blocked the stuff that was outside its orbit from drifting inward. That may have prevented the birth of anything more massive than Earth closer to the Sun.

Earth, by the way, wasn’t born until the Sun was about 50 million years old – a younger brother to giant Jupiter.

Look for Jupiter to the upper right of the Moon as they climb into view this evening. It looks like a brilliant star. The true star Aldebaran – the eye of the bull – is farther along that line. And fainter Elnath – the tip of the bull’s horn – is quite close above the Moon.

Script by Damond Benningfield

The bright Moon has some bright companions tonight: the planet Jupiter and the stars Aldebaran and Elnath. But the Moon washes out some fainter lights: the Leonid meteor shower.

The shower is expected to reach its peak late tonight – perhaps 15 or 20 meteors per hour. But only the brightest of them will shine through the glare of the just-past-full Moon.

The nearby planet and stars will be much easier to see – especially Jupiter, which will stand below the Moon as they climb into good view. It’s the brightest pinpoint of light in the sky for most of the night.

Jupiter is so bright for several reasons. For one, it’s the largest planet in the solar system – 11 times the diameter of Earth. For another, it’s blanketed by clouds that reflect most of the sunlight that strikes them. And finally, the planet is especially close now – less than 400 million miles away. It’ll be at its closest early next month.

Aldebaran is to the lower right of the Moon. It’s Taurus’s brightest star. It represents the bull’s eye. It shines bright orange, but the color might be muted by the nearby Moon.

Elnath is the second-brightest star of Taurus. It’s at the tip of one of the bull’s horns. It, too, is washed out by the moonlight. Even so, it should still be pretty easy to pick out – part of a beautiful arc around the gibbous Moon.

Jupiter and Elnath will be even closer to the Moon tomorrow night. More about that tomorrow.

Script by Damond Benningfield

The first intentional message to other civilizations was beamed into the galaxy 50 years ago tomorrow. There wasn’t much to it – just 1,679 bits of data. When properly decoded, the message yields a picture – stick-figure outlines of a person and the message’s planet of origin, for example. The image also features the facility that beamed it into space: the giant Arecibo radio telescope, which collapsed a few years ago.

The Arecibo message was conceived by Frank Drake. He was a pioneer in SETI – the search for extraterrestrial intelligence. He’d conducted the first search for radio signals just 15 years earlier. One of his collaborators was celebrity astronomer Carl Sagan.

The message was intended primarily as a publicity stunt. Arecibo had just received a major upgrade, and astronomers wanted to show it off. So the message was transmitted just once – it wasn’t repeated.

Other messages have followed, from radio telescopes around the world. Today, though, scientists and others are debating the wisdom of alerting the rest of the galaxy to our presence. They wonder whether messages to the stars might bring an unpleasant response.

The target for the Arecibo message was M13, a giant star cluster in Hercules. It’s in the west-northwest at nightfall, and it’s an easy target for binoculars or a small telescope. But it’s so far away that the message won’t get there for another 25,000 years.

Script by Damond Benningfield

Half of the planets discovered in other star systems are about the same size and mass as Uranus and Neptune, two of the giants of our own solar system. But we don’t know much about these exoplanets – in part because we don’t know much about Uranus and Neptune themselves. They’re billions of miles away, and only one mission has visited either planet.

But scientists hope to learn more around the middle of the century. A panel of scientists recommended a “flagship” mission to Uranus as NASA’s next big project for planetary exploration. An orbiter would loop around Uranus and its moons for years, while a probe would parachute into the planet’s atmosphere.

Uranus is an oddball. It lies on its side – probably the result of a collision with another planet when it was young. Scientists would like to know more about the impact and how it affected the planet’s interior. The sideways orientation also gives Uranus a cycle of seasons unlike that of any other planet. And some of the planet’s moons could have oceans of liquid water below their icy crusts.

NASA hasn’t yet started on the mission – in part because it’s working on a lot of other big-ticket items. So it’ll be a while before we get a close look at this common type of giant planet.

Right now, Uranus is low in the east as darkness falls. Tonight, it’s not too far to the lower left of the Moon. But it’s so faint that you need binoculars or a telescope to see it.

Script by Damond Benningfield

It’s cold in the outer solar system. The planet Uranus, for example, is 20 times farther from the Sun than Earth is. As a result, its 28 known moons all shiver at hundreds of degrees below zero. Yet several of the planet’s bigger moons might have active volcanoes. Instead of molten rock, they’d belch out molten ice – a slushy brew from buried oceans of liquid water.

We don’t know for sure if any of the moons have ice volcanoes, but there’s evidence that they do. The surfaces of the moons are fairly young, for example. That suggests that something is renewing them – like material from the interior. And a couple of the moons appear to be pumping material into the space around Uranus.

Recent observations by Webb Space Telescope found additional evidence for an ocean on the moon Ariel. It’s coated with frozen carbon dioxide. Webb found the layer of C-O-2 is especially thick. And it’s mixed with carbon monoxide. Both compounds should quickly vaporize and drift off into space. Their presence suggests the supply is being renewed – perhaps by volcanoes belching ice from a hidden ocean.

Uranus is putting in its best appearance of the year. The giant planet rises around sunset and is in view all night. It’s brightest for the year, too, although you still need binoculars to pick it out. Tonight, it lines up about half way between the almost-full Moon and the bright planet Jupiter.

We’ll have more about Uranus tomorrow.

Script by Damond Benningfield

Polar vortex has entered the American lexicon with a fury in recent years. It’s used to describe especially bitter outbreaks of winter weather. The northern hemisphere actually has two polar vortexes. The one that gives us the extreme cold is fairly low in the atmosphere. It’s formed by jet streams that encircle the pole that sometimes plunge southward. The other is much higher in the atmosphere.

The higher vortexes are seen on every planet and moon in the solar system with much of an atmosphere. That includes Uranus, the third-largest planet. Scientists found evidence to confirm the vortex last year.

Hints of a vortex around the north pole were seen in 2015. More recently, scientists looked at the pole with a giant radio telescope in New Mexico. They saw an especially bright area at the pole itself, with a dark ring around it. The bright region was warmer than the surrounding atmosphere. The combination provides strong evidence of a polar vortex.

Air in the upper atmosphere moves toward the poles. It’s deflected by the planet’s high-speed rotation – forming a “vortex” around the north pole.

Uranus is putting in its best appearance of the year. It’s lining up opposite the Sun, so it rises around sunset and is in view all night. It’s brightest for the year as well. But you still need binoculars or a telescope to see it, along the border between Taurus and Aries.

We’ll have more about Uranus tomorrow.

Script by Damond Benningfield

It’s springtime – on Mars, anyway – because today is the spring equinox for the Red Planet’s northern hemisphere.

Like the seasons on Earth, the seasons on Mars are the result of the planet’s tilt on its axis. In fact, the two planets are tilted at almost the same angle. So the north pole dips toward the Sun at the start of northern summer, while the south pole dips sunward at the start of northern winter. The equinoxes are half way between those points.

But there are some differences between the seasons on Earth and Mars. Mars’s orbit is more stretched out than Earth’s orbit, so there’s a bigger difference in the planet’s distance from the Sun. Mars’s distance varies by about 26 million miles.

That has a couple of effects. For one thing, it creates a big disparity between the seasons in the northern and southern hemispheres. Mars is farthest from the Sun during southern winter, and closest during summer. That means southern winters are colder than northern winters, while summers are warmer.

And second, Mars moves fastest when it’s close to the Sun, and slowest when it’s far away. That causes a big difference in the length of the seasons. Northern spring is the longest – it lasts 194 Mars days. Northern fall is the shortest – just 142 days.

Look for bright orange Mars climbing into good view in late evening, and high in the southwest at first light – a world that’s springing into a new season.

Script by Damond Benningfield