The Night Sky's Wanderers - Pluto, then Home

Well, I wish I had some lovely images of Pluto for you. But Pluto is so distant, even the Hubble space telescope has a hard time getting a clear image. Below is the highest-resolution picture of Pluto we have.

Credit: Eliot Young (SwRI) et al./NASA

No, Pluto's not pixelated, but the brown coloring is true color. I did find clearer images, but as far as I could tell, they were artists' renderings. NASA's New Horizons spacecraft, launched in 2006, is on schedule to reach Pluto in 2015, so we can hope for some better images then.

Maybe you've heard that Pluto was demoted awhile ago and is now considered a dwarf planet. The decision was made by a relatively small number of astronomers, so I'm skeptical that it will stick. It seems that many people are protective of the solar system's smallest planet.

It's been quite a tour we've been on to our neighboring planets, but it's time to come home. Earth is usually our point of observation, but with all the spacecraft zipping around, both manned and unmanned, it's not surprising that we now have beautiful images of our own world. First up is the iconic Earthrise:

Credit: Apollo 8/NASA

Taken in 1968 by the Apollo 8 crew, this is the first image of Earth from space and was described by photographer Galen Rowell as "the most influential environmental photograph ever taken."

Next is the Blue Marble:

Credit: Apollo 17 Crew/NASA

Blue Marble is possibly one of the most widely distributed photographs in the world, having been rescued from the NASA archives in the early 1980s by famine-relief and environmental groups.

And here's one more view of Earth, showing Antarctica and the tip of South America:

Credit: NEAR Spacecraft Team/JHUAPL/NASA

This image, taken in representative color, comes from the Near Earth Asteroid Rendezvous spacecraft. I like the swirling clouds, but that broad, white sheet of Antarctic ice doesn't make me want to visit there anytime soon.

And finally, one last thing: a nod to the star at the center of our solar system. The sun has no part of the night sky, in that its presence in the sky defines day. Even so, it participates in lunar eclipses and provides the solar winds for the auroras and generally keeps the solar system together with its gravitational pull. So here's a closing thought about our local star from Galileo:

"The Sun, with all the planets revolving around it, and depending on it, can still ripen a bunch of grapes as though it had nothing else in the Universe to do."

The Night Sky's Wanderers - Neptune

Credit: Voyager 2/NASA

Beautiful blue Neptune is, it seems, a shy planet, being very far out in the solar system. Discovered in 1846, its existence was deduced from mathematical prediction, not from being directly observed. Irregularities in the orbit of Uranus led astronomers to think that another planet must be gravitationally affecting Uranus. Their prediction turned out to be correct.

Credit: Voyager 2/NASA

The methane in Neptune's atmosphere absorbs red light, giving the planet its lovely blue hue. In 1989, Voyager 2, the only space craft to visit this distant world, recorded the Great Dark Spot in Neptune's atmosphere (upper left in the image above). But unlike Jupiter's persistent Great Red Spot, the dark spot was gone a few years later, based on Hubble observations, and a new spot had appeared elsewhere.

Credit: Voyager 2/NASA

Neptune in a gas giant planet and has the strongest winds in the solar system; they reach supersonic speeds of 1,300 mph. The image above shows light-colored clouds high in the atmosphere. Most of the atmosphere is hydrogen and helium, but scientists think that methane closer to the interior of the planet may condense out into diamonds, not only on Neptune but Uranus as well: "Once these diamonds form, they fall like raindrops or hailstones toward the center of the planet," says one of the researchers.

Credit: Voyager 2/NASA

Neptune has about a dozen moons, and pictured above are Neptune and Triton as crescents, a view never seen from Earth. The unusual angle of the photo yields a slightly reddish planet. What can't be seen are Neptune's rings, which were only discovered in the 1960s.

Credit: Voyager 2/NASA

Triton is Neptune's largest moon, and this color mosaic image shows its surface in great detail. Triton has the coldest surface temperature of any body in the solar system, minus 391 degrees Fahrenheit. It's so cold that nitrogen exists as frost.

Many of these facts about Neptune and Triton were new to me, but maybe you remember a PBS special from 1989, Neptune All Night. It was a live, seven-hour show featuring data and images from Voyager's fly-by as they were coming back to Earth. It's up on YouTube (that's where the link goes), although the video quality isn't great. Still, I love the idea of staying up all night to watch brand-new images from the very edge of the solar system. Slowly the planets are giving up their secrets, even the shy one.

The Night Sky's Wanderers - Uranus

Credit: Voyager 2 Team/NASA

As we move outward in the solar system, we come to Uranus, a planet that was unknown to the ancients, having been discovered in relatively modern times (1781). Another gas giant, its atmosphere is mostly hydrogen and helium, but also includes different kinds of ice - methane, water and ammonia.

Credit: E. Karkoschka et al. (University of Arizona)/NICMOS/HST/NASA

Unlike the other gas giant planets, Uranus doesn't have a lot of features visible in its atmosphere. The image above, from the Hubble space telescope, was taken in infrared light. Cloud bands and formations become prominent, and the Uranian rings can be seen as well.

Credit: NASA/ESA/L. Sromovsky (Univ. of Wis., Madison)/H. Hammel (Space Science Inst.)/K. Rages (SETI)

Another beautiful Hubble image shows Uranus's moon, Ariel, in transit across the planet's surface. This is actually an unusual alignment because the orbits of the Uranian moons are such that the moons rarely cross in front of the planet to cast a shadow.

Credit: The Voyager Project/NASA

Rocky, icy Titania, another of the Uranian satellites, was imaged by Voyager 2, the only space craft to visit the planet. Titania is the largest moon in the system and is named, like many of its neighboring moons, for a character from a Shakespearean play.

Credit: Astrogeology Team (USGS)/The Voyager Project

Voyager's image of the moon Oberon features a curious crater, just right of center - a mysterious face dubbed Hamlet (no kidding).

Speaking of names ... can we even begin to count the number of schoolchildren who have laughed themselves silly over Uranus? It actually was originally named the Georgium Sidus, after King George III of England. But in keeping with the convention of naming the planets after gods, "Uranus" was proposed, that being the name of the Greek god of the sky. So laugh if you must, get in touch with your inner middle school self, and enjoy these pictures of Uranus.

The Night Sky's Wanderers - Saturn

Credit: CICLOPS/JPL/ESA/NASA

When I first learned about the planets in school, I remember deciding that Saturn was my favorite, because it had rings. We now know that Jupiter, Neptune and Uranus also have rings, but Saturn's are the most spectacular.

Humans have known about the rings of Saturn since the 17th century, but in the last few years, we've been able to see them from a new perspective. The image above was taken by the Cassini spacecraft from Saturn's orbit. It shows Saturn eclipsing the sun and seems to reveal that Saturn's night side receives some reflected light from its rings.

Credit: Cassini Imaging Team/SSI/JPL/ESA/NASA

In another perspective not visible from Earth, this Cassini image shows Saturn as a crescent. The light and shadow interplay here is impressive, with the rings casting shadows onto the planet surface, and the planet casting its own shadow onto the rings. Saturn, like Jupiter, is a gas giant, and subtle banding in its cloud tops can be seen here as well.

Credit: Cassini Imaging Team/SSI/JPL/ESA/NASA

This final "beauty shot" shows Saturn from below. The resolution of these images is spectacular, but Cassini had more in store for scientists - confirmation of a very strange formation at Saturn's north pole.

Credit: NASA/JPL/VIMS Team/University of Arizona

This Cassini infrared image confirms the hexagonal cloud system originally spotted by Voyager in the 1980s. It's not just a chance arrangement of clouds: this movie shows the rotation of the entire hexagon. Scientists are working on explanations for this phenomenon, but let's face it - this is beyond mysterious. It's more like, who could even conceive that something like this existed? How can clouds possibly form this shape?

As the late Carl Sagan said, "Somewhere, something incredible is waiting to be known."

The Night Sky's Wanderers - Jupiter

Credit: NASA/JPL/Space Science Institute

Spectacular Jupiter, largest planet in the solar system, is as mysterious as it is beautiful. Classified as a gas giant, all we can see of it are its cloudtops. These swirling, exotic clouds are made up of ammonia, hydrogen sulfide and water and are capable of generating lightning.

Credit: Cassini Imaging Team/Cassini Project/NASA

One of Jupiter's most distinctive features, the Great Red Spot, is a giant storm that has been raging since at least the 17th century, when it was first observed by humans.

Credit: Voyager 2/NASA

Jupiter may have a rocky core; we don't know for sure. But most of its bulk comes from liquid metallic hydrogen - a form of hydrogen that only exists under extreme pressure.

Jupiter's rings were discovered during the Voyager 1 flyby in 1979. Apparently, two of the scientists on the Voyager team insisted that they look for rings, even though no one thought they would find any. And there they were. (The image below was taken by the Galileo spacecraft.)

Credit: NOAO/J. Burns (Cornell) et al./Galileo Project/JPL/NASA

I could go on with more facts about Jupiter, but let's face it - these planetary posts are really about the images. It can be hard to keep track of the news about the various spacecraft and each new set of dazzling images. By the time we finish with this tour of the solar system, you should be all caught up (at least for a little while!).

The Night Sky's Wanderers - Mars

Credit: J. Bell (Cornell U.), M. Wolff (SSI) et al., STScI, NASA

Mars, the angry red planet named for the Roman god of war, has long been a planetary candidate to shelter extraterrestrial life. From the 19th century observation of canals (which turned out to be an optical illusion) to the mid-20th century War of the Worlds radio broadcast of invading Martians to recent images of faces and creatures in the rocky landscape, there is something about Mars that has given humans hope that we are not the sole occupants of our solar system.

Credit: Mars Exploration Rover Mission, Cornell, JPL, NASA

Images of the Martian surface are coming back from NASA's Exploration Rovers and the European Space Agency's Mars Express. What's interesting about these images is that it's not at all hard to imagine walking around in this landscape. Dusty and rocky, it brings to mind a desert - not so different from Earth.

Credit: Mars Exploration Rover Mission, Cornell, JPL, NASA

The image above not only shows sandy dunes, but clouds in the Martian sky. It might be easy to imagine walking around, but you better bring your own air. The atmosphere is almost all carbon dioxide. Clouds can be composed of carbon dioxide ice or water ice.

Credit: G. Neukum (FU Berlin) et al., Mars Express, DLR, ESA

While there is no liquid water on Mars, there is water ice near the poles. This Mars Express image of a region near the north pole, taken from orbit, shows white areas of ice and steep cliffs almost 2 km (1.2 miles) high.

Back in August 2003, Mars passed as closely as it had to Earth in 60,000 years. I grabbed my binoculars to get a look. There it was, red and strangely large. It gave me an odd feeling to see it, something I've also felt when viewing a lunar eclipse. There was an uneasiness, almost a primal reaction to something unusual going on in the night sky. It was some vestige of an ancient response to natural phenomena that were uncommon and not well understood, the kind of response that no doubt led to some action to appease the gods.

To see more images of Mars, go to the Astronomy Picture of the Day link and search for Mars. You'll find pictures of a dust devil, a two-toned rock and other unusual features of the Martian surface.

"Mars is there, waiting to be reached." - Buzz Aldrin

The Night Sky's Wanderers - Venus

Credit: NASA/Johns Hopkins APL/Carnegie Institution

Beautiful Venus, the brightest object in the night sky after the moon, has been shrouded in mystery for millenia and has only recently begun to give up some of its secrets to science.

The atmosphere of Venus is filled with thick clouds that had kept scientists from viewing its surface. The image above from the Messenger spacecraft is typical of images of the planet taken using only visible light.

To overcome this problem, Venus has been imaged using radar and ultraviolet light. The image below, from the Magellan spacecraft, was created using radar and shows a false-color map of the planet surface, with red representing mountains and blue, valleys.

Credit: Magellan Spacecraft/Arecibo Radio Telescope/NASA

The only probes that have landed on Venus to date are the Soviet Venera 9 and 10 space crafts. They landed on Venus in October 1975 and sent back images, including these:


The Russian-made Venera probes were created to withstand the extraordinary atmospheric pressure on Venus (equal to 90 Earth atmospheres), extreme temperatures (around 850 degrees F) and a descent through the thick clouds in the upper atmosphere, which are made up of sulfuric acid.

Does that somehow sound familiar to you? A Russian-made probe designed for extreme conditions? It certainly sounded familiar to me, as a long-forgotten pop culture memory slowly made its way back to the light of day.

It was, in fact, the basis of a two-part episode of the The Six Million Dollar Man. "Death Probe" first aired in 1977 and featured a Russian probe that had been launched into space to study the surface of Venus. But somehow it returned to Earth and landed in the western U.S. Thinking it was on Venus, it began carrying out its mission, but when it encountered human resistance, it turned deadly. If it could withstand extreme pressures and temperature, how could it be stopped?


If you remember this episode, you also remember its strange yellow eye that zeroed in on any human standing in its way.


Creepy! But fortunately, Colonel Steve Austin was on the case and was finally able to destroy the formidable probe.

Portions of "Death Probe" are up on YouTube. People leaving comments vividly remember this episode, with some actually reporting nightmares. I had no idea it was based on actual space craft, but I also remember this episode very well. In many ways, it's emblematic of 1970s television - Russian bad guys, polyester clothing. But what really made it stand out was the idea of technology run amok. What humans had created could not be controlled and was now a deadly threat. Colonel Austin and his friends had to use both technology (his bionics) and their brainpower to bring an end to the rampage.

It was exciting viewing back then. To be honest, more than a few of my childhood evenings were spent in front of the television. But there were also trips to the planetarium and local observatory to get a first-hand look at the planets, unfiltered by thoughts of scary space probes.

If memories of action shows aren't enough of a planetary encounter for you, you're in luck. Check out the pre-dawn sky this weekend, where Venus and Jupiter will be in close proximity. You'll find them rising out of the east-southeast horizon a couple of hours before sunrise. Sunday morning, the crescent moon will join them to create a lovely show.

The Night Sky's Wanderers - Mercury

Credit: NASA/Johns Hopkins APL/Carnegie Institution

Let's turn our attention once again to the night sky by considering its wandering points of light, the planets. We begin this tour of the solar system with Mercury, the planet closest to the sun.

Named for the messenger to the Roman gods, Mercury moves quickly in its orbit around the sun, but spins very slowly on its axis. As a result, a Mercurian year is equal to 88 Earth days, while a Mercurian day is 58 Earth days. With days that last so long, Mercury has extreme temperatures, with high temperatures up to 752 degrees F (400 C) and lows down to -292 F (-180 C).

Because of its proximity to the sun, Mercury has always been difficult to observe. The Hubble space telescope is unable to take images of Mercury due to safety precautions that prevent it from pointing too close to the sun. Humans got their first close-up look of Mercury in 1974, when the spacecraft Mariner 10 sent back images surveying about half of the planet's surface. The image below is a composite of data from its fly-bys:

Credit: Mariner 10/US Geological Survey

When I first saw this image, I thought, wow, Mercury is one beat-up little planet, all pock-marked with craters. But scientists are looking to Mercury for help in understanding how the solar system formed and changed over time. The surface of Mercury is less changeable than Earth's, and so might be able to reveal information on early planetary formation.

To further explore Mercury's secrets, the space probe Messenger was launched in August 2004. Its first fly-by produced this image, of the "hidden" side of Mercury that Mariner 10 missed:

Credit: NASA/Johns Hopkins APL/Carnegie Institution

This image was sent back to Earth just last week, along with the image at the top of this post. It doesn't get more current than that.

Swift in its orbit, both fiery and frigid, Mercury keeps close company with the sun while potentially holding the key to understanding the young solar system. Messenger is scheduled to enter its orbit in 2011, while the European Space Agency and Japan plan to jointly launch of pair of probes to Mercury in 2013.

If you want to take a look at Mercury yourself, it's best viewed at dusk or dawn. Check out this link for the best viewing dates for Mercury (and all the planets) in 2008.