Asteroid Vesta - Images from the Dawn Spacecraft

With the New Horizons spacecraft hurtling toward its 2014 encounter with Pluto, and with the Dawn spacecraft now at its most up-close and personal encounter with Vesta, we are in the process of learning scads of information about two objects that are among the poorest understood and least explored bodies in the Solar System.

Before NASA's Dawn settled into orbit around the asteroid Vesta—the second largest object in the Main Asteroid Belt, after the Dwarf Planet Ceres—we knew very little about it. That it is mega-mountain of rock 330 miles across that rotates rather quickly in space and is slightly egg-shaped, these things we knew—but not much more.

What Dawn has revealed to us, however, is a tiny world with unexpected complexities, inside and out.

Inside, Vesta's anatomy may not be unlike Earth and the other Terrestrial planets, which all developed cores heavy with iron and mantles and crusts made of lighter silicate rocks when they were young and molten. This "differentiation" occurs for the same reason that gold particles sink to the bottom of a gold-pan as a prospector shakes the water-sand slurry back and forth: the gold is denser, the sand lighter, so the materials separate.

Outside, Vesta's surface offers amazing landscape vista opportunities for a future robot lander or astronaut: complex topography of valleys, cliffs, troughs, ridges, and a huge mountain, with elevation differences deviating above and below the global average elevation by as much as 15 miles—that's three Mount Everests, or two Marianas Trenches!

Parts of the surface resemble some of the basaltic formations of cooled lava in Hawaii, suggesting that, long ago, there may have been active volcanoes on Vesta, spewing out lava to shape the young surface.

What a sight it must have been—and it makes me smile when I think about the children's book "The Little Prince." My favorite part of that story was the description of how the Prince, on his little asteroid world (which was only twenty or thirty feet across, I'd guess), cooked his meals on a frying pan held over a miniature volcano, which he made sure to keep clean and functional with a periodic cleaning using a giant Q-tip….

All of these revelations—the core/mantle differentiation, complicated geography, possible tectonic features, and signs of past volcanism–have prompted some scientists to ask, should Vesta be reclassified as a Dwarf Planet, along with Ceres, Pluto, and the others thus dubbed?

I have on my desk at work a letter from a 3rd Grader. It starts, "I think Pluto should be a planet (not a Dwarf Planet)…." The letter continues in richer detail and quite a bit of passionate defense of Pluto, but I was struck by the fact that this 3rd Grader was, at the time Pluto was originally "demoted," three years old. (And some thought the Pluto controversy would end with the previous generation of kids….)

But it did get me wondering. If Dawn has changed our view of Vesta from a mere large asteroid to something maybe worthy of promotion to Dwarf Planet, what might New Horizons do to our current view of Pluto? I'm not suggesting the International Astronomical Union will reinstate Pluto as a planet when we get our first up-close images of its surface—after all, no matter what Pluto's surface may hold in store for us, this Dwarf Planet can't meet one of the three conditions for planethood: being massive enough to clear the region of space in which it revolves. Alas, Pluto shares its orbital space with other objects.

But I fully expect that New Horizons will change our perspective on Pluto, as Dawn is doing for Vesta. The more we learn of the rich details of mysterious places like these, the more, I think, we regard them as "worlds"—regardless of their classification as asteroid, dwarf planet, or planet.

Kepler 22B compared to the solar terrestrial planets

It's 600 light years from Earth, orbits a star very similar to our Sun in a period of about 290 days, and has a diameter about two and a half times that of Earth. What is it? It's the NASA Kepler mission's most recent exciting confirmed discovery, the extrasolar-planet (exoplanet) Kepler 22B.

Another real, Earth-sized planet to imagine? Cool! I'm on it….

It's fun to play around with the planetary possibilities, as science fiction writers have done for decades, but having a real find out there to pin our thoughts on is something more. On that blank ball-shaped canvass we can paint whatever atmosphere, hydrosphere, lithosphere–and who knows, biosphere?–we care to imagine, at least until scientific observation starts to fill in those details.

But, Kepler 22B offers something more to our fancy than a mere Earthoid dress-up doll. Being somewhat larger than our world, though still smaller than a Neptune or a Uranus, places it in the category of "super-Earth," a type of planet that we have very little experience with.

What do we know of Kepler 22B beyond the barebone figures revealed by the Kepler spacecraft? In a word, not much. Kepler—a really big camera orbiting the Sun and staring at a patch of 150,000 or so stars in the constellation Cygnus—was designed to detect the presence of Earth-like exoplanets. Using the "transit" method of exoplanet detection, Kepler watches unblinkingly for the slight dimming of a star's light as one of its planets "transits," or moves across, its face.

That dimming can tell us exactly three things: the approximate diameter of the planet by how much of the star's light is blocked, the orbital period of the planet by how often it transits, and the distance between the planet and its star (because once you know the orbital period, you can calculate that distance–or visa versa–as long as you know the mass of the star the planet orbits…which we do).

Being relatively close to the size of the Earth makes Kepler 22B an important find, but maybe more important is the fact of the planet's distance from its star. Kepler's mission isn't merely to find Earth-sized planets, but ones that are within their stars' habitable zones: the right distance so that, given a sufficient atmosphere, liquid water could exist on their surfaces.

Kepler 22B is at that correct distance. Though it is closer to its star than Earth is from the Sun, that star is slightly cooler than the Sun, so its habitable zone is closer in. (Earth is obviously in the Sun's habitable zone; if you're not sure, go get yourself a glass of water.)

But back to what we know, and don't know, about Kepler 22B. Not having a super-Earth in our own Solar System, we don't have an up-close example to study. Is it like Earth, a rocky sphere from the core right up to the visible surface, with an apple-peel thin layer of gas and liquid on top? Or is it more like Uranus, with a solid core deep down with massive layers of fluid and gas upholstered around it? Or something between?

We don't know. Future observations may reveal more about this planet, and others. One day we might know more about Kepler 22B's atmosphere (if it has one) through spectroscopic measurements. If we can make a measurement of the planet's mass, we could calculate its average density and better place it on the spectrum between super-Earth and infra-Uranus.

Were we to travel there, could we land, step outside and breathe the air (as well as strain under a super-Earth's gravity)? Would we sink into the fluid envelope around the hidden core, falling to ever greater depths and atmospheric pressure? Would we find ourselves surrounded by human-sized chimpanzees?

That adventure is yet far in the future…but a lot of fun to imagine in the meantime….

NASA's Juno spacecraft is shown in orbit above Jupiter's colorful clouds in this artist's rendering. Image credit: NASA/JPL-Caltech.

Even though NASA is no longer in the business of deploying manned-missions to outer space, they continue to explore the cosmos in ways that have never before been possible.  Their next target is Earth's bigger, gassier neighbor: Jupiter.

On August 5, 2011 the National Aeronautics and Space Administration (NASA) in conjunction with the Southwest Research Institute launched the Juno mission,  which NASA says will, "improve our understanding of the solar system’s beginnings by revealing the origin and evolution of Jupiter."

This is a pretty big deal in the world of astrophysics.   NASA scientists theorize they will be able to determine the origin of The Giant Planet, "and thereby the solar system" by measuring the amount of water and ammonia in Jupiter's atmosphere.

Scott Bolton, Juno's principal investigator from the Southwest Research Institute in San Antonio explains the significance of the mission:

"Jupiter is the Rosetta Stone of our solar system.  It is by far the oldest planet, contains more material than all the other planets, asteroids and comets combined, and carries deep inside it the story of not only the solar system but of us. Juno is going there as our emissary — to interpret what Jupiter has to say."

But scientists will have to wait a few years to test their theories.  Even though Juno is traveling at a relative speed of over 13,000 miles an hour, it is not scheduled to reach its final destination until July 2016.

And the ride to Jupiter is not exactly a clear path.  Juno will face many obstacles – including large mentors – that can potentially derail the $1.1 billion project.

Thankfully, scientists can rely on old "maps," or astro-photographic images of the night sky to plan a flight path that will steer the spacecraft away from debris.

Dr. Bill Cooke, head of NASA's Meteoroid Environment Office, says the astro-photographic plates housed at the Pisgah Astronomical Research Institute (PARI) contributed directly to the success of the Juno mission;

"Juno, for example, in order for it to be successful they have to design it.  And one of the things they have to design it for is to protect it from meteoroids out in space.  Well we never measured meteoroids around Jupiter, because we don't go there very often, right?  So we have to take what             we've learned here at Earth to help us design that spacecraft to go to Jupiter and those negatives [at the Astronomical Photographic Data Archive] helped formulate the model we used to design that spacecraft to go to Jupiter.

Dr. Cooke is referring to a collection of nearly 150,000 old astro-photographic plates and film known as APDA, or the Astronomical Photographic Data Archive.  The APDA collection is stored at PARI's secure facility in Western North Carolina.

Dr. Cooke became aware of the collection a few years ago and has quickly become on of its biggest advocates:

"The photo archive which contains a lot of the photographs that form the basis of modern meteor science are housed … at ADPA.  They collected them from around the country, but those old photographs, that data, formed the basis for everything we know now in regards to meteors.  So it's kind of like visiting a treasure trove of ancient data.  The great hieroglyphic inscriptions out there in APDA."

Brendan Fallon of the American Meteor Society examines film in the APDA collection.

The connection between APDA and the Juno mission came full orbit during this year's annual NASA Fireball Workshop, which took place at PARI's Rosman, North Carolina campus.  Attendees were able to watch the Juno launch and then walk into the archives to hold the original pieces of film that helped Juno's engineers develop a safe flight path.

By relying on old astronomical plates and film – some of which date over 100 years old – today's astronomers can safely stand on the shoulders of their predecessors and reach for the stars, without fear of being knocked down by meteors.

For more info check out NASA's website for the JUNO mission:

twitter: @NASAJuno

http://missionjuno.swri.edu/

NASA's Stratospheric Observatory for Infrared Astronomy, also known as SOFIA. (Photo: NASA)

The new SOFIA observatory isn't your average NASA project. Engineers took a 30-year old 747 airplane, cut a hole in the side and installed a 17-ton telescope. Most telescopes are either on the ground or somewhere in orbit, but SOFIA falls somewhere in the middle, flying around at about 40,000 feet.

I got the chance to hitch a ride on one of its recent research flights as the plane left Moffett Field at the NASA Ames Research Center. It's definitely not the kind of flight where you get a bag of peanuts and movie.

The researchers take advantage of the nighttime sky, so we left at dusk for 10-hour tour flying zigzags across the Pacific Ocean. Each leg of the journey is carefully calculated so the telescope can pinpoint a far away star. The plane interior is packed with computers and equipment. It also lacks insulation since much of it was removed to install the telescope, so it's both cold and loud inside.

At four in the morning, the astronomers are still hard at work. If they're as tired as I am, they certainly aren't showing it.

"For me, this is very exciting," says Ian McLean, a professor at the University of California-Los Angeles. He usually works on the ground. "All my career has been ground-based astronomy. So, it's only my second flight."

McLean says there's a good reason to do astronomy in the stratosphere. The atmosphere is thinner, which means it's easier for the telescope to see the stars. "It's almost as good as space," says McLean. "Not quite, but almost."

And unlike the Hubble Space Telescope, this telescope lands everyday, which means the scientists can update and fix the equipment. "By the time you get a mission into orbit, the technology you're using is relatively old. Here we can stay state of the art all the time," says McLean. NASA began developing SOFIA in 1997 and almost cancelled the project at one point. It flew its first science mission in November 2010 and now costs about $80 million a year to operate.

Searching for a "Holy Grail"

McLean says the SOFIA telescope could show astronomers something that's considered a Holy Grail in their field: seeing a star being born. It happens in huge, dusty clouds – stellar nurseries, as Mclean calls them. "The cloud is huge, light years across and it's gradually contracting to form a whole nursery of stars."

Inside NASA's SOFIA Observatory, somewhere over the Pacific Ocean.

But there's a problem. Astronomers can't see what's happening inside the clouds because, once again, they're made of dust and it's hard to see through.

"We don't mean dust bunnies, but we mean little, tiny little grains of solid material. Doesn't matter how big a telescope you have, you can't see inside it," McLean says.

That's why SOFIA looks at a special kind of light called infrared light. If you look through a telescope on the ground, you're looking at the visible light from space – the light our eyes can see. Infrared light is invisible to us, but it penetrates space dust, which means the telescope can see through the dust too.

"You get to see what you can't see with your eye. It's like a window has been opened," says McLean. They're looking for exactly how stellar nurseries give birth to young stars. McLean says catching a star as it's forming can reveal clues about how own solar system formed.

But star birth isn't the only thing these researchers want to see. They're also looking at the way stars die.

A Star on the Way Out

As the plane makes as sharp right turn, the telescope focuses on an object called NGC 7027. It's a planetary nebula – also known as a dying star. Mclean and his team are capturing an infrared image of the nebula, which is about 3,000 light years away. They can also see what it's made of.

"It has a distinctive shape. It's oval. There's a hole in the middle and that's because it literally is a shell of gas that came off the star," says McLean.

7027 is dying because the star has run out of fuel – the same fate that our sun will face in about five billion years. As it dies, the star casts off its outer layers, shedding huge amounts of material to form a cloud around it. But it's not entirely a sad story.

"It won't be wasted," says McLean. "The material that was thrown off by that star in its dying phase, somewhere, millions, perhaps billions of years from now, will find its way into a new star and the planets that form around it."

From dead stars come new stars – and planets like our own. The oxygen and nitrogen in our bodies were once formed inside a star. "The cosmos is within us," as astronomer Carl Sagan once said. "We're made of star stuff."

As sky begins to lighten, we descend towards the Dryden Aircraft Operations Facility in the Mojave Desert, where the plane is based. The SOFIA telescope is now flying twice a week. Astronomers from around the world are lining up to get onboard.

Gale Crater, the destination for NASA's new rover Curiosity. Credit: NASA, Google Earth

Ready for yet another great Martian adventure? Another prestigious interplanetary mission to that fabled world? The next technological ambassadorship of space-age robots and exotic landscapes? Or, how about an inglorious romp to go dumpster diving to sift through a pile of geological garbage…?

In any case, get set; on November 25th the launch window opens for NASA’s next Mars rover, “Curiosity,” which will arrive over yonder next August.

Inglorious dumpster diving? What’s NASA got planned this time, anyway?

Answer: Gale Crater, a large impact blast about 1400 miles to the west of Gusev Crater, where the rover Spirit now sits motionless—and incommunicado—in its last rusting place.

When I heard that Curiosity was bound for Gale Crater, my first impulse was to start up Google Earth, switch to Mars mode, and zoom in on Gale Crater for a landing to see, at least superficially, what might be of interest there to an explorer. (You can do this too; download Google Earth at www.google.com/earth, select Mars, and search for Gale Crater.)

My first Google-vista of Gale, which included several overlaid strips of high-resolution imagery from the Mars Reconnaissance Orbiter (MRO), hinted that there may be a LOT of interest here.

Gale Crater, about 90 miles across, sports a really large mountain right in the middle—mostly filling the bowl, in fact. The mountain, whose peak rises around 2700 feet above average Martian surface level (can’t say sea level there…not in the present day, at least), towers 3 miles above the deepest part of the crater surrounding it.

I zoomed in on an MRO overlay of a canyon high on the mountain, finding what looks like layered deposits exposed by whatever cutting action had carved the canyon in the past. The landscape I find there is stunning, the details rich. I almost feel as though I’ve stood where Curiosity is soon to tread.

The rover will be set down by a sort of rocket-propelled winch, lowered gently to the base of the mountain where an alluvial fan promises potential riches. Not wind-worn pebbles of solid gold, not fist-sized chunks of diamond—well, probably not—but rather the riches of dirt that may have been deposited there by the action of water. A dumpster of chemical, geological, and potentially biological history.

One of the reasons Gale Crater was chosen as Curiosity’s destination is that it is a deep, low-altitude impact crater, situated at a “downhill” destination where water, if indeed it did flow on Mars long ago, is very likely to have converged, dumping all sorts of soil, rock, and whatever else might have come along for the ride.

Curiosity carries ten instruments designed to conduct a range of measurements, including chemical analysis of soil and rock samples in search of organic compounds that may have been preserved. Where Curiosity’s predecessors, Spirit and Opportunity, have looked for the chemical signs of past water to help tell us whether Mars was ever hospital to life, Curiosity will look for the leftovers of life itself. And in the bottom-lands of Gale Crater, at the foot of a huge mountain from which the rubble of layer upon layer of history has been scoured, it will be in a really good place to do it.

Endeavour Crater; Credit: NASA, Google Earth

Who would have imagined three years ago, when the already veteran Opportunity set forth from its two-year prospecting site at Victoria Crater on a long march to the much larger Endeavour Crater, that the Fates would actually NOT stop this Energizer-Bunny dead in its tracks?

Okay, enough jaw-dropping incredulity. Some things CAN be built to last….

About three weeks ago, Opportunity reached the rim of the 14-mile wide Endeavour Crater, after clocking nearly 21 miles since its landing seven and a half years ago. By Earth-rover standards, that’s about one round trip to work and home again for me, and about 25 minutes of my time—but Opportunity’s commute is a far greater feat, alone on another world, long minutes away even by radio waves, no service garages for maintenance, no fuel stations other than the daily dose of energy doled out by the Sun.

One of the first things Opportunity did upon reaching the rim of the giant crater, after taking some pictures to give us the lay of the land, was to examine some rocks. After all, more than anything else, the Mars Exploration Rovers are geologists, or rock hounds, sent to tell us about the Martian environment, today and in the past, through the chemical makeup and stratigraphy of the rocks and soil.

Data from orbital spacecraft have shown that the materials at the rim of Endeavour may date back to early in Martian history, making for fertile ground in Opportunity’s quest to uncover clues to the planet’s past. Evidence for the presence of clay minerals, possibly formed under wet conditions favorable to life, has been brought to light—which really adds some excitement to the rover’s rock hounding exploits to come.

On Opportunity’s approach to the crater rim, it spotted in the distance unusual outcroppings, and a “shelf” of what looks like sedimentary rock with inclusions of material that may have been deposited by water action.

Water water water, the watch-words of Martian exploration for many years. Where there is, or was, water, perhaps there is, or was, some form of life. And while the Mars Exploration Rovers weren’t designed to look for signs of life directly, their larger, better equipped descendant, Curiosity, to be launched in November, is. Curiosity, do tell….

As a child I liked to imagine what it would be like to land on and walk about the surface of Mars. Mind you, back then we had no images from Mars’ surface—not until 1976 when Viking landed. We had low-res images taken from space, and plenty of science fiction sound stage backdrops and sets from various TV shows and films (and a Mars stand-in, Death Valley, in Robinson Crusoe on Mars).

Opportunity still appears to be in good shape, so the odyssey of its exploration seems to have a good chance of delivering yet another episode of the Life (?) and Times of Mars….

From hosting tweetups with space enthusiasts, to sharing space amazing videos on YouTube, NASA has embraced social media as a way to spread its message and further popularize astronomy.

Social media has broadened our access to astronomy and life off Earth. If you've dreamed of owning your own telescope and seeing distant lands, there are more resources than ever to help make your dreams a reality. Here are just a few options for budding armchair astronomers:

Astronomy.net

Photography enthusiasts can share their Flickr photos with Astronomy.net, contributing to astronomers' knowledge base. Using photos from telescopes, cameras and even camera phones, astronomers can build a map of the sky to search for new discoveries, such as the birth or death of a star.

Planet Quest

Part of the Kepler Mission and NASA's Jet Propulsion Laboratory, Planet Quest gives visitors a detailed look at our galaxy. Beautiful videos and interactive games detail the process of searching for habitable exoplanets.

LightBuckets

Rent time on telescopes around the world and collect images of your favorite astronomical sights from the comfort of your home computer. If you're looking to majorly up your nerd cred, this is an excellent option.

Slooh

If space had a cable channel, Slooh might be it. The site broadcasts major astronomical events over the Web. If you can't make it to that eclipse all the way around the world, Slooh is probably broadcasting it.

What other astronomy resources do you like? Share them with us in the comments.

Artist concept of a Y Dwarf star

In the ongoing hunt for things in space that are more and more difficult to find (because scientists love a good challenge), NASA’s WISE spacecraft has revealed something new lurking in the dark: Y Dwarfs.

The newly discovered, though long anticipated, “Y Dwarf” is an even smaller, cooler version of the sub-stellar object called a brown dwarf, with surface temperatures hovering around that of a human body, or even “room temperature.”

Y Dwarf stars are so cool that even the infrared radiation they emit is faint, and it took the new, state of the art instruments on NASA’s WISE (Wide-field Infrared Survey Explorer) spacecraft to detect them. With its highly sensitive IR cameras, WISE has discovered about 100 new brown dwarf stars, with six among them being Y Dwarfs ranging in distance from 9 to 40 light years away.

The imaginative side of me likes the idea: a cool, dark, quiescent “star,” like a large, lone Jupiter, floating in the dark interstices between the showier “main sequence” stars, warmly casting its low-energy heat rays into the stellar community. And perhaps it has planets, too, this dark star; worlds of icy darkness, day and night. By night, the clearest, darkest, starriest skies you can see anywhere; by day, the same, except with a softly glowing magenta “sun” embedded in the glittering blackness….
…but this is not what comes to mind when I think of a star! Stars are supposed to be blindingly bright, incredibly hot, and violently eruptive! Right?

Stars, like planets, belong to a wide, continuous spectrum of physical stature, from the giant “O” class stars with 60 solar masses, 50,000 degree C surface temperatures, and 800,000 times the brightness of our Sun down the scale though the B, A, F, G (our Sun), and K classes, to the small M class stars. M stars possess less than a tenth the mass of our Sun and as little as a thousandth the brightness, being only two to three thousand degrees at the surface.

But below the classical “Oh Be A Fine (Girl or Guy—pick one!), Kiss Me” scale, astronomers have added letters to the scale as they theorized, and eventually observed, even lesser balls of gas that were still too massive to be classified as big planets: L, T, and sometimes Y. Well, not sometimes—not now that WISE has seen six of them, pulling them out of theory into scientific fact.

Beside temperature and mass, one of the attributes astronomers use to help classify these objects is by the abundances, or lack, of certain chemical compounds, like titanium oxide, methane, water vapor—which got me to thinking. It is too hot on our Sun for chemical compounds (molecules) to exist; they would quickly be broken into simple chemical elements (atoms) if they ever appeared there. But Y Dwarfs have surface temperatures not unlike that of the air surrounding you right now, and so more complex molecules can dwell there.

It occurs to me (following a short string of ifs) that, if Y Dwarfs have these Earth-like surface temperatures, and if the heat energy from inside the star is sufficient, and if sufficiently complex molecules could develop, over time, under those conditions—if, if, if—then might it be possible for life to exist on such an object?

Life, on a star? That’s my own musing, nothing more, but how cool would that be?

Vesta, image from NASA's Dawn spacecraft

Ion thrusters full! Set us into a standard orbit, Mr. Sulu….

Well, I don't know if any of the helms-persons at NASA are named Sulu, but we have indeed achieved orbit—that is, NASA's Dawn spacecraft around the large asteroid Vesta.

I wrote about Dawn and Vesta not long ago, before the spunky little ion-driven robot arrived there. Since then, Dawn has reached its first destination, 117 million miles from Earth, entering a 9,900 mile orbit around Vesta on July 15th. Science observations are expected to begin in early August, but already Dawn has sent back wonderful preliminary images showing details never before seen.

Vesta's surface may bear features and materials among the oldest in the Solar System. Already we can see that Vesta is pock-marked and scared by impacts incurred over the eons. Similar to how a forensic scientist may determine the sequence of events that occurred at a crime scene by studying the physical evidence left behind, the scars and residues on Vesta will help paint a picture of conditions throughout the Solar System's history.

Almost as cool as its science mission is Dawn's propulsion system. To use a term from a certain Smith and Jones movie, it's "the New Hotness." Technology first demonstrated on NASA's Deep Space 1 spacecraft, Dawn's engine is the first solar electric ion propulsion system used on a purely scientific spacecraft. Using electrical power generated by solar panels, Dawn's engine ionizes xenon atoms and accelerates them with an electric field, squirting them out the back of the engine to produce thrust–similar to a balloon-powered car or rocket toy propelled by spurting air. And though a conventional chemical rocket can produce much stronger thrust, Dawn's ion drive, operating with high efficiency and over longer periods of time, achieves up to 10 times the velocity change for an equivalent amount of propellant.

(As a sign of the technological times, in one episode of the original Star Trek series, Scotty was awe-stricken by an advanced alien spacecraft that used ion propulsion. Ironic; what today's space explorers wouldn't give for warp drive….)

Dawn will spend a year orbiting and studying Vesta before it moves onto its second target, Ceres, to harvest its secrets.

Vesta is now the largest known asteroid in our Solar System. It was second fiddle to Ceres for a long time, but back in 2006 when Pluto got "demoted" to dwarf planet status, Ceres' status also changed—promoted or demoted, take your pick. Sure, Ceres is now in the more exclusive club of the dwarf planets, but it's the smallest of that group, whereas when it was an asteroid, it was the largest, going from big fish in big pond to junior member of the upstairs office team….

So what's Vesta like—what we know about it at the moment, anyway? Vesta is a mega-mountain of rock and dust, somewhat lumpy and potato-shaped, but approximating a spherical object with a mean diameter of about 330 miles–roughly the distance from Oakland to Los Angeles as the ion-driven robot flies. In terms of surface area, Vesta has about twice the real estate as the entire state of California!

Sounds pretty big—and it is—but you'd still need over 20,000 Vestas to make one planet with the mass of the Earth. And if you stood on the surface of Vesta, you'd weigh little more than 2% what you weigh on Earth. Myself, I'd weigh in at a tad under 5 pounds. Presumably that means I could jump a hundred feet into the sky and land again safely.

I don't know about the science, but Vesta sounds like a fun place to me!

The "Ice Giant" Neptune. Credit: NASA/Voyager 2

Would you believe we discovered the planet Neptune only one year ago? Weird; I seem to have heard about this planet all my life—it was even my favorite planet at one point, back in childhood. What's this paradox?

Well, not a paradox—just semantics. It has been one year since Neptune's discovery. One Neptunian year. It takes Neptune, the most distant known (official) planet, about 165 years to orbit the Sun one time.

Doing the math backward, 2011 – 165 = 1846. Neptune was officially discovered on September 23rd of that year in a sort of virtual team effort-slash-international-rivalry extravaganza by at least three people. (To be nit-picky, it was actually July 12th when Neptune completed one Neptunian year since its discovery, since the Neptunian year is a couple of months short of exactly 165 Earth years….)

Usually, the discovery of a celestial object is credited to one individual: the first to spot it through a telescope. Sometimes there is battle over the credit because two people may have spotted the object around the same time, and documented proof of who found it first is needed to settle the debate, or lack thereof to let the controversy go on.

But Neptune was the first planet to be discovered mathematically, based on observed perturbations in the motion of Uranus (Uranus, incidentally, was the first planet to actually be discovered; it's difficult to say that any of the other planets were "discovered" in the conventional sense, as all of them—Mercury, Venus, Mars, Jupiter, and Saturn—are naked-eye objects, and so have been available to human eyesight since human eyesight was invented).

In Neptune's case, in France and in England, Alexis Bouvard and John Couch Adams, respectively, each deduced that Uranus' orbital perturbation was caused by the influence of another as yet undiscovered planet. Another Frenchman, Urbain Le Verrier, mathematically predicted the position of this unseen lurker, and German astronomer Johann Galle turned a telescope to the predicted position, finding Neptune less than a degree away. Eventually, credit for Neptune's discovery—or at least the process of discovery–was divvied up among the group.

Why was Neptune once my favorite planet in childhood? Well…because it's blue, of course! Just as good a reason as any, and blue was my favorite color. Like its slightly larger near-twin, Uranus, Neptune's upper atmosphere is made mostly of hydrogen and helium gas, but the presence of methane tints it blue. The thick atmospheric shell is believed to extend downward 10 to 20 percent the distance to the planet's center.

Deeper down is thought to exist a mantle containing significant amounts of volatile materials, like methane, ammonia, and water. This hot, dense, high-pressure fluid shell might be thought of as an "ocean" more than an atmosphere—although the distinction between gas and liquid is blurred by the extraordinary temperature and pressure of the material (taking an extreme example of what I mean, even the Sun's core, with a density a hundred times greater than liquid water on Earth, is considered a gas–or plasma–by virtue of its great temperature).

Nevertheless, sometimes Neptune, and Uranus, are referred to as "liquid giants"—or even "ice giants", though it's difficult for me to reconcile the term "ice" with the multi-thousand degree temperatures deep down inside these worlds….

Under all that stuff, Neptune's solid core, made of rock and nickel iron primarily, has a mass not much greater than planet Earth—as if, at the center of this giant piece of liquid confection, there exists a crunchy center, a shrouded planet Earth. What a gem! And maybe literally, as it is speculated that deep inside the planet's mantle, carbon atoms coming from methane may be squeezed by the pressure into diamond crystals, which "rain" down upon the rocky core. Neptune, planet of riches…if only….

At Chabot, we'll be having a Neptune's First Anniversary since Discovery celebration on that date, September 23rd. Hope you can join us!