The Lunar Reconnaissance Orbiter has been circling the Moon since 2009, taking thousands of images in amazing resolution unseen since Apollo. Many of these pictures have been simply astonishing, including the one above taken in March 2011: an unnamed crater a few kilometers across (the image is 2.2 km or about 1.4 miles wide). Whatever smacked into the Moon all those eons ago blew out a lot of dust and other material that fell back to the surface, spreading out like the broad petals of a flower. In the crater floor you can barely see some boulders and other debris that must have gone straight up and back down after the impact. The Moon has no air, but formations like this erode after time anyway: countless meteorite impacts, the solar wind, and even thermal flexing during the Moon's day/night cycle take their toll. So we know that such craters must be young, but that's a relative term: this impact may have occurred when dinosaurs still walked the Earth.

Image credit: NASA/GSFC/Arizona State University

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Solar eclipses are relatively rare events on the Earth's surface. The Moon's orbit around the Earth is tilted a bit with respect to the Earth's orbit around the Sun, so the Moon has to be at the right place at the right time to block the Sun.

But what if you're in orbit around the Earth? In that case, the Earth itself blocks the Sun all the time (of course, if you want to be pedantic, it happens to us on the surface every time the Sun sets). NASA's Solar Dynamics Observatory stares at the Sun 24/7/365, and was placed in an orbit to minimize the amount of time the Earth blocks its view. But it does happen twice a year, when the orbits all align.

The picture above is from late March 2011, during one of these eclipse seasons. The edge of the Earth cut right across the disk of the Sun, creating this odd view. This particular shot is in the ultraviolet, where Earth's atmosphere is almost opaque, completely cutting off the Sun's light... except for that one little curlicue on the left. That's an extremely bright filament of material, luminous enough to have some of its light get through, despite our atmosphere.

This is a weird and wonderful picture, accessible only from space, which is why I picked it for this year's list.

Image credit: NASA/GSFC/SDO

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We might like to think of the Sun as a steady, calm source of light and heat, but in reality it undergoes a cycle of violent activity driven by magnetic fields. This cycle peaks every 11 years or so, and we're due for the next maximum in 2013 or 2014. The previous minimum lasted an unusually long time, but things started ramping up again in 2011. Sunspots marring the Sun's face started appearing in greater numbers, and many of them were the source of incredible outbursts of energy called solar flares.

This picture shows a flare from August 2011, as seen in the ultraviolet by NASA's Solar Dynamics Observatory. When the subatomic particles spurted out by such flares interact with our own magnetic field, the result can be spectacular aurorae, which are also becoming a common sight. They can also cause blackouts (as a particularly large event did to Quebec in March 1989) and damage our satellites - including GPS and communication satellites. Studying the Sun is more than just science: our economy can literally depend on it.

Image credit: NASA/SDO/AIA

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The MESSENGER spacecraft was launched in 2004 and spent seven years getting to Mercury; it's not all that easy dropping a probe down into the inner solar system. It swung by Mercury twice (not to mention the Earth once and Venus twice!) before finally settling into orbit in March 2011, and then beginning its scientific mission of analyzing the overheated world. Among the first pictures it took was this one, showing the crater named Debussy (after the composer). The crater is 80 km (50 miles) wide, but reaching much farther are those streaks called rays; collapsed plumes of ejected material when whatever hit Mercury hit Mercury. Many craters on the Moon show rays, and in some cases pictures of the two objects look very similar.

Since March, MESSENGER has taken huge amounts of data of the planet, increasing our knowledge of what makes it tick - and it's returned not just images but also laser altimetry data, spectroscopy, and mineralogical maps. Mercury isn't much like Earth at all, but sometimes it's the contrasts that aid our understanding. The planets in the solar system are a diverse lot, and it's only by studying all of them that we can come to understand the one we live on.

Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

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In March of 2011, the spacecraft MESSENGER became the first ever moon of Mercury, taking unprecedented high-resolution images of the solar system's smallest official planet. But while it was on its tortuous path to Mercury, engineers back home programmed the spacecraft to take a series of snapshots, pointing the cameras painstakingly across the solar system. The result is what you see above: every planet in the solar system, a sort of cosmic family portrait.


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Saturn and its rings are a continuously-playing show of beauty and grace, but the giant planet also has a vast retinue of moons, each as different from each other as any family of siblings (which make it very hard to pick my favorite from ones like this or this). The biggest, the aptly-named Titan, is a monster, bigger than the planet Mercury and possessing an atmosphere of nitrogen that's twice as thick as Earth's! The atmosphere is so thick and opaque that it blocks our view of the ground in visible light. Infrared light can penetrate that gloom, though, and it's not by coincidence that the Cassini spacecraft is equipped with filters and detectors designed to look in those wavelengths.

Using that equipment, astronomers created the first-ever multicolor map of the surface of Titan (a map using a single color was created in 2009). This false-color map shows elevated regions (white areas), lakes of liquid methane and ethane near the north pole of the moon, and what's most amazing to me, vast areas of wind-blown dunes (shown in brown)! Those aren't grains of sand in the dunes, but grains of frozen hydrocarbons, blown across the plains by Titan's thick air. Detailed radar observations by Cassini show them to be much like dunes on Earth, but a bit chillier: the temperature on the surface of Titan is a numbing (or perhaps I should say "shattering") -180°C (-300°F).

And yet, it's a world not so different than ours: atmosphere, liquid lakes, wind... and at those temperatures, the chemistry of methane is similar to that of water at room temperature on Earth. It's not crazy to wonder if there's life on Titan...

Image credit: NASA/JPL/University of Arizona/CNRS/LPGNant

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Of all these pictures of our planetary neighbors, I think I might love this one the most. That's us: it's home. Blue, with feathered white, the only planet to really look this way (Uranus and Neptune are both blue, but for different reasons; we have water, they have methane). This picture is from Terra, a NASA Earth-observing satellite, designed to look down and investigate our environment.

But that's not why this picture really amazes me. Look at it more carefully: almost all you see is water! If you look to the upper right you'll see the west coast of the US, Baja California, and Mexico. Everything else you see is ocean. The satellite was over the Pacific when this was taken, and that expanse of water is vast, covering nearly an entire hemisphere of the planet. It's a coincidence that this is the way things are right now; continental drift changes the sizes of the oceans over geologic time scales. But still, it's a sharp reminder of just how much water we have here on Earth, and why we look for it so steadfastly on other worlds, and why we need to take our job as planetary caretakers more seriously.

Image credit: NASA

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