Number 1: The Descent of Man
When I first wrote about this picture, I called it the Best. Image. Ever.
And it still is. It's my #1 Astronomy Picture of 2008.
This is the Phoenix lander as it descends underneath its parachute… to the surface of Mars. The picture was taken by the phenomenal HiRISE camera on board the Mars Reconnaissance Orbiter. I first saw it on The Planetary Society blog written by my friend Emily Lakdawalla.
Why did I pick this one? Because it is direct evidence of humans reaching out to another planet. Not only that, it's taken by another spacecraft we had sent there, a robotic emissary that was already in orbit taking high resolution images of the Red Planet. Showing incredible skill and foresight, the engineers here on Earth told HiRISE where to point, and at the right moment they snapped this proof that our grasp sometimes equals our reach.
I love this picture. It's simple enough, just a few pixels showing the fuzzy shape of the lander and its drogue. If you look carefully, you can see the shroud lines, too, and make out the shape of the parachute. I think that's why this image speaks to me so profoundly: it's not grand, it's not gloriously colored, it's not presupposing, yet the depth of its meaning is colossal.
A more visually interesting shot was taken as Phoenix descended past a crater, and it's a remarkable image as well... but I like the other one better. It's simple, straightforward, and drives the point home that we are no longer a single-planet species.
Viking, Sojourner, Spirit, Opportunity, Phoenix. MRO, MGS, Mariner 8 and 9, Odyssey, Express. We send our emissaries to Mars because we want to learn, we want to explore. We want to know more about Mars so we can know more about Earth, but we also just want to know more. That’s the nature of humanity, and it’s something we should praise. It’s kept us alive for hundreds of millennia, and it may yet ensure the survival of our species as well.
Number 2: The Mote in Sauron's Eye
For hundreds of years, it was a rare event to discover a new planet. Herschel found Uranus, Adams and Leverrier uncovered Neptune, Tombaugh stumbled on Pluto (only to have its status reduced decades later). Are there more planets in the solar system? Maybe, but they’ll be forbidding and remote. Still, there are worlds to be found orbiting other stars. The first were detected in 1992, orbiting the burned-out cinder of a massive star. Then in 1995, the first planet orbiting a sun-like star was found, and the floodgates opened. To date, over 300 have been found… but none seen directly in visible light. They have all been inferred by their affect on their parent star (either through the Doppler effect or by dimming its light during a transit). One was seen directly in infrared light, but that’s still somehow not satisfying. We’re humans; we want something we can see with our eyes!
That wish came true in November of this year. Using the Hubble Space Telescope, and aiming toward the bright southern star Fomalhaut in 2004, astronomer Paul Kalas took visible light images which turned out to contain a small blip of light. He waited two years, and took more images. The blip of light moved, and moreover moved with the star… almost. The overall motion with the star indicated it was gravitationally bound to Fomalhaut, but the excess motion betrayed that orbital motion itself.
Kalas had discovered a planet.
The image itself is incredibly dramatic; Fomalhaut is a young star, barely 200 million years old. It is still surrounded by a ring of dust, circling it at a distance of 17 billion kilometers. The ring is off-center and has a sharp edge, both indicating the presence of a planet, probably in an elliptical orbit.
And there it is, just where it should be. A planet with about three times the mass of Jupiter, taking 870 years to orbit Folmalhaut. Its gravity sculpts the ring, and its distance from Fomalhaut allows us to see it against the fierce background glare of the star.
For all of history we’ve wanted to be able to gaze upon an alien world, and there it is.
Number 3: Marsalanche!
I’ll admit it. I’m prejudiced. When I think of Mars, I think of an arid, cold, dead planet. If Mars ever had a heyday, it was a billion years ago when it may have been warmer, wetter, and possibly even harboring microbial life.
But those days are long dead, and since then Mars has remained entombed by time, changeless and dull.
Cripes, I can be an idiot sometimes.
That, me droogs, is a Martian landslide caught in the act!
It was taken by the incredible HiRISE camera on board the Mars Reconnaissance Orbiter, an instrument that has half-meter resolution of the surface of the Red Planet. This was a routine picture that just so happened to actually snag the dust cloud from an avalanche.
The cliff on the left is 700 meters high (!) with a 60 degree slope; the dust cloud is about 180 meters across. If the slide started at the very top of the cliff, it would take a rock about 20 seconds to freefall all the way down (probably in reality it would take longer due to momentum and such), and hit the ground at 70 meters per second (150 mph). The higher-res image is spectacular.
Obviously, this was an incredible find, which is why it’s Number 3 on my list. Had HiRISE snapped this a minute earlier there would have been nothing to see, and if it had been a minute or two later it would have seen a dissipating dust cloud that wouldn’t be nearly so dramatic. That implies these events are somewhat common on Mars, and that the longer we stay there and the more we look, the more amazing things we’ll find.
Number 4: Spiral Art
Sigh. Spiral galaxies. Sigh.
This beauty is NGC 7331, and it’s about 50 million light years away. The incredible spiral pattern is caused by gravitational traffic jams in the disk; gas and dust pile up where the gravity into those arms, forming new stars. In a sense, the arms are an illusion, they don’t have that many more stars in them than in the between-arm space, it’s just that that’s where all the massive, bright, short-lived stars are, making the arms easier to see. Those barn-burner stars don’t live long enough to leave the arms, so between the arms it looks darker… but plenty of more modest stars (like the Sun) live there.
This image was taken by Vicent Peris using the 3.5 meter telescope at the Calar Alto Observatory in southern Spain. In full resolution it is beautiful beyond words.
Number 5: Sic (Luna) Transit Gloria Mundi
Once a month, the Moon makes one complete orbit around the Earth. Stuck here on the surface as we are, we see the Moon moving across the sky as it orbits. Sometimes, rarely, its path intersects that of the Sun, and we see a solar eclipse. A little more common is a lunar eclipse, when the Moon enters the Earth’s shadow, and again we’re stuck on the ground, so we see the Moon darken and sometimes turn blood red.
But we never see the moon pass in front of the Earth, because we’re on the Earth. However, our spacecraft are not so disadvantaged.
The Deep Impact mission was launched in 2005, and later that year successfully slammed a copper block into a comet. The spacecraft itself sailed on, and the mission was retooled (and renamed to EPOXI) to observe other scientific events. Some smart person at NASA realized that if they turned the probe’s telescopes around they could see some drama unfolding back home. They did so, and what they got totally blew me away: the Moon transiting the Earth.
There has never been a generation of humans in all of history who could see such an event. If you ever get a little depressed, or lonely, or think like there’s nothing going on that’s interesting any more, think on that for a moment or two. A thousand generations of people could only imagine such a thing, but we can actually do it.
Number 6: kaBLAM!
Regular readers know how much I loves me my gamma-ray bursts (GRBs). These are the most titanic blasts in the known Universe, second in bangs only to the Big one. They can occur in two ways, as far as we know. One is when the core of a supermassive star collapses, forming a black hole. Within milliseconds, a flat dense disk of material begins to swirl around the hole, and there is a vast and mighty brew of forces that focuses twin beams of energy and matter which blast out of the star’s heart. They tear through the star and scream across the Universe, and for thousands of light years, anything they touch, they kill.
The other way to get a GRB is when two orbiting superdense neutron stars merge. The end result is similar to that of a massive star collapse; a black hole forms, the beams are focused, and death ensues.
If one were to form less than about 7000 light years from the Earth, and were aimed at us, it would be lights out. If one were 100 light years away, it would almost literally set the planet on fire.
Happily, GRBs form a long, long way away. Still, their power is unbelievable, and that’s why I picked two GRBs for the Number 6 slot. Pictured above, on the left, is GRB080319B which was 7.5 billion light years away and yet was bright enough to be seen with the unaided eye. It lasted only seconds, but had you been looking in the right spot at the right time, you would have seen an explosion that took place halfway across the Universe!
On the right is GRB080913, which is the most distant GRB ever detected, at a numbing 12.8 billion light years away. In other words, when the star died to create this explosion, the Universe was less than a billion years old… and when it reached Earth, the light from this ancient detonation had been crossing the reaches of space almost 13 billion years, since before the Earth was born, before the Sun formed, before there was even a Milky Way Galaxy.
Both images are from NASA’s Swift satellite. GRB080309B is an X-ray image, and GRB080913 is a combination of X-ray and ultraviolet imaging. These are examples of images that are not much to look at, until you truly comprehend what you are seeing. Both these objects are so far away that our brains cannot comprehend the numbers, and the energy released in a few seconds by either explosion was comparable to the Sun’s entire ten-billion year lifespan output.
Now look at the pictures again. You are gazing upon death writ large, energies vast and titanic, almost beyond our ken.
Almost. Remember, while there are mysteries abounding with GRBs, we do have a decent understanding of how they work. We’re clever, we humans.
Number 7: The galaxy that ate too much and got gas
It’s been known for a long time that galaxies are not picky eaters. In fact, they’re cannibals.
Yes, they eat each other. If a little galaxy gets too close to a big one, the gravity of the beefier of the pair will rip the littler one apart, and the contents of the loser get absorbed into the winner. Most big galaxies show evidence of this, and our own Milky Way is eating at least one galaxy right now, and has probably swallowed down dozens before it.
But we’re pikers compared to NGC 1132, a monster elliptical galaxy over 300 million light years away. In visible light it’s 20% bigger in diameter than the Milky Way, and may outmass our galaxy by a factor of ten! It’s truly gargantuan. This Hubble image reveals the enormous extent of the galaxy, but even that’s only a part of the picture; most of the mass of this galaxy is in hot X-ray emitting gas and invisible dark matter.
Still, there is beauty in this overwhelming visible-light picture. Besides the obvious and pleasing smooth profile of the galaxy itself, there are also thousands of galaxies in the background, making the high-res original image well worth your time to download and peruse.
Number 8: Spitzer spies the heart of a nebula
Most stars in the galaxy are born in vast gas clouds, stellar nurseries that bear stars of all masses. In the center, the most massive, hottest, and brightest stars flood the gas with ionizing ultraviolet radiation. This causes the gas to glow (similar to the way a neon sign does). This radiation, together with the massive winds of subatomic particles blown off the stars, carve out monster cavities in the clouds light years across.
The results can be incredibly beautiful objects like the nebula W5. It’s easy to tell which stars are doing the work: look to where the "fingers" are pointing. Around the edge of the cavity are light-years long fingers of material caused by the erosive winds, a bit like sandbars in stream. They point directly upstream to the source of the winds.
W5 is one of my picks because it’s beautiful, it’s interesting, and c’mon, it’s heart shaped! The gas is even reddish, and since this image was taken with the Spitzer Space Telescope, we’re seeing it in the infrared… because it’s warm. I wish I could have originally posted this on Valentine’s Day, but you take what you can get. The original image is even larger, and boasts more detail of this vast creche as well.
Number 9: Methuselah Moon
We’re mostly used to seeing the Moon as a fat crescent in the sky, because it’s up right after sunset, a time when people might notice it. Or maybe when it’s full, since it’s bright and obvious.
But a thin crescent Moon is a sight to see! It can be a challenge to spot, in fact, struggling against the brightness of the early evening or morning sky. The closer it is to the Sun, the harder it is to spot: it’s thinner, of course, and the bright Sun washes it out.
Which is why this next image is so incredible: it was taken just 10 minutes before the Moon was closest to the Sun in the sky, when it was a mere five degrees away. It was taken by Martin Elsässer, a gifted astrophotographer. It’s hard to imagine this record will be broken… and no one will be able to shave more than 10 minutes off it anyway!
Number 10: Watermelon Planet
Mercury is a tough planet to observe. It orbits so close to the Sun that in our sky it never seems to get very far from our nearest star, meaning you can only get clear views of it when it’s near the horizon, before the Sun rises or after it sets. Our own murky atmosphere distorts the image, so to study it, we really need to send probes.
Mariner 10 mapped some of Mercury in the 1970s, but due to the vagaries of orbital mechanics only got to see half the planet. And while it was ground breaking at the time, the images it returned were not very high-resolution.
Enter MESSENGER. This new spacecraft has to swing by the tiny planet three times before it can settle into an orbit, but in the two passes it’s done so far it’s already transformed out knowledge of Mercury. There were so many images to choose from; I considered this detailed overview showing tons of features, or this incredibly feature-laden crater rim segment, or this oblique view of a triply-concentric-crater, or these phenomenal rays blasting out of a young impact feature, or this beautiful view of sunset at a double crater where you can see the mountain shadows on the crater floor.
But in the end, it was the overview of Mercury showing the rays from impact craters blanketing the entire planet that made me sit back in wonder. It was taken as MESSENGER departed the planet for the second time, when it was nearly 28,000 km out. There is something about a large-scale yet detailed image that is truly pleasing to the eye; there is beauty and science together here (and in my mind, the two are nearly indistinguishable).