Geomagnetic storms occur when space weather hits and interacts with the Earth. Space weather is caused by fluctuations within the sun that blast electrons, protons and other particles into space. I study the hazards space weather poses to space-based assets and how scientists can improve the models and prediction of space weather to protect against these hazards.
When space weather reaches Earth, it triggers many complicated processes that can cause a lot of trouble for anything in orbit. And engineers like me are working to better understand these risks and defend satellites against them.
The sun occasionally blasts huge amounts of particles into space during active events like solar flares and coronal mass ejections.
What causes space weather?
The sun is always releasing a steady amount of charged particles into space. This is called the solar wind. Solar wind also carries with it the solar magnetic field. Sometimes, localized fluctuations on the sun will hurl unusually strong bursts of particles in a particular direction. If Earth happens to be in the path of the enhanced solar wind generated by one of these events and gets hit, you get a geomagnetic storm.
The speed at which the ejected plasma or solar wind arrives at Earth is an important factor — the faster the speed, the stronger the geomagnetic storm. Normally, solar wind travels at roughly 900,000 mph (1.4 million kph). But strong solar events can release winds up to five times as fast.
Emissions from the sun, including the solar wind, would be incredibly dangerous to any life form unlucky enough to be directly exposed to them. Thankfully, Earth’s magnetic field does a lot to protect humanity.
The first thing solar wind hits as it approaches Earth is the magnetosphere. This region surrounding the Earth’s atmosphere is filled with plasma made of electrons and ions. It’s dominated by the planet’s strong magnetic field. When solar wind hits the magnetosphere, it transfers mass, energy and momentum into this layer.
The magnetosphere can absorb most of the energy from the everyday level of solar wind. But during strong storms, it can get overloaded and transfer excess energy to the upper layers of Earth’s atmosphere near the poles. This redirection of energy to the poles is what results in fantastic aurora events, but it also causes changes in the upper atmosphere that can harm space assets.
Dangers to what’s in orbit
There are a few different ways geomagnetic storms threaten orbiting satellites that serve people on the ground daily.
This situation is exactly what led to the demise of the the SpaceX Starlink satellites in February. Starlink satellites are dropped off by Falcon 9 rockets into a low-altitude orbit, typically somewhere between 60 and 120 miles (100 and 200 km) above the Earth’s surface. The satellites then use onboard engines to slowly overcome the force of drag and raise themselves to their final altitude of approximately 350 miles (550 km).
The latest batch of Starlink satellites encountered a geomagnetic storm while still in very low-Earth orbit. Their engines could not overcome the significantly increased drag, and the satellites began slowly falling toward Earth and eventually burned up in the atmosphere.
Drag is just one hazard that space weather poses to space-based assets. The significant increase in high-energy electrons within the magnetosphere during strong geomagnetic storms means more electrons will penetrate the shielding on a spacecraft and accumulate within its electronics. This buildup of electrons can discharge in what is basically a small lightning strike and damage electronics.
Finally, geomagnetic storms can disrupt the ability of satellites to communicate with Earth using radio waves. Many communications technologies, like GPS, for example, rely on radio waves. The atmosphere always distorts radio waves by some amount , so engineers correct for this distortion when building communication systems. But during geomagnetic storms, changes in the ionosphere — the charged equivalent of the thermosphere that spans roughly the same altitude range — will change how radio waves travel through it. The calibrations in place for a quiet atmosphere become wrong during geomagnetic storms.
This, for example, makes it difficult to lock onto GPS signals and can throw off the positioning by a few meters. For many industries — aviation, maritime, robotics, transportation, farming, military and others — GPS positioning errors of a few meters are simply not tenable. Autonomous driving systems will require accurate positioning as well.
How to protect against space weather
Satellites are critically important for much of the modern world to function, and protecting space assets from space weather is an important area of research.
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The ability to accurately forecast storms would make it possible to preemptively safeguard satellites and other assets to a certain extent by shutting down sensitive electronics or reorienting the satellites to be better protected. But while the modeling and forecasting of geomagnetic storms has significantly improved over the past few years, the projections are often wrong. The National Oceanic and Atmospheric Administration had warned that, following a coronal mass ejection, a geomagnetic storm was “likely” to occur the day before or the day of the February Starlink launch. The mission went ahead anyway.
The sun is like a child that often throws tantrums. It’s essential for life to go on, but its ever-changing disposition make things challenging.
Piyush Mehta receives funding from the National Science Foundation and the National Aeronautics and Space Administration. He is affiliated with the National Aeronautics and Space Administration as a Special Government Employee and is a member of the NASA Space Weather Council.
This article is republished from The Conversation under a Creative Commons license.
NASA, Hubble Heritage Team
On April 24, 1990, the Space Shuttle Discovery launched, carrying the Hubble Space Telescope (HST, or just "Hubble"). This orbiting telescope was the first of NASA's Great Observatories. For more than 30 years, HST has provided astronomers with incredible scientific data on everything from solar system objects to some of the most distant galaxies in the cosmos. Hubble was named for American astronomer Edwin Hubble, who in the early 20th century helped establish that the universe is much bigger than the Milky Way and showed the cosmos is expanding.
Stacker collected 50 Hubble images, taken between 1990 and 2020, that express both the beauty of the universe and important scientific knowledge. HST is a bus-sized satellite containing a 2.4-meter-diameter mirror for focusing light from distant objects, along with a suite of instruments for photography, measuring light intensity, and taking the spectrum of various astronomical sources. Hubble is primarily an optical telescope, viewing the cosmos in the same type of light we can see, and it also has the ability to see into the infrared and ultraviolet parts of the spectrum of light. The size of the telescope and its location above Earth's atmosphere (with its pesky weather and distortions from air currents) make HST one of the best optical telescopes still in operation.
HST is jointly operated by NASA and the European Space Agency and was designed to be serviced by astronauts. Unfortunately, the Hubble needed to be repaired immediately after launch, when it turned out its mirror was slightly flawed. NASA astronauts installed additional mirrors to compensate for the flaws in 1993 and upgraded other scientific instruments on five different occasions, with the last upgrade being in 2009. Meanwhile, no plans are in the works to build an equivalent space telescope, so astronomers and nonscientists alike hope Hubble will continue to work indefinitely.
Click on for 50 images of the universe as seen from the Hubble Space Telescope.
NASA, J. Hester, P. Scowen (Arizona State University)
Perhaps Hubble's most popular image involves part of the Eagle Nebula known as the "Pillars of Creation." The Eagle Nebula is a star-forming region of the Milky Way, which means a cold cloud of gas and dust dense enough for gravity to take hold and collapse material into new stars. Ultraviolet light from these newborn stars erodes the nebula away, leaving the beautifully sculpted pillars in the image.
NASA, ESA, Hubble Heritage Team
The dense gas and dust of the Eagle Nebula are opaque in visible light but transparent to infrared. Hubble's infrared vision of the Pillars of Creation reveals they are harboring additional baby stars swaddled in gas.
NASA, Jon Morse (University of Colorado)
In the early 1800s, the unremarkable star Eta Carinae in the southern constellation Carina grew suddenly brighter, briefly becoming the second-brightest star in the entire sky before fading. Later observations, including the one that produced this famous Hubble image, showed that Eta Carinae is actually two very massive stars shedding matter in two huge lobes of gas. Astronomers think these stars are unstable and will eventually explode in a supernova.
NASA, ESA, University of Washington, PHAT team
Andromeda Galaxy (also known as M31) is the closest large galaxy to our Milky Way, near enough for astronomers to distinguish individual stars. This Hubble mosaic of a portion of Andromeda is the biggest image the telescope has made (constructed of 7,398 individual exposures!), containing over 100 million visible stars. Like the Milky Way, M31 is a spiral galaxy, with many of its brightest stars clustered in arms winding out from the galactic center.
NASA, ESA, A Simon (GSFC)
While much of Hubble's greatest work involves distant stars and galaxies, the observatory has also provided a wealth of information about our solar system. This 2017 image of Jupiter is part of an HST program to chart changes in the atmospheres of the giant outer planets. In particular, astronomers are watching the way Jupiter's famous Great Red Spot (known since the time of Galileo) is shrinking.
Auroras are caused when electrically charged particles cascade into a planet's atmosphere. On Earth, these are the northern and southern lights visible at high latitudes; Jupiter, being a much bigger planet with a huge magnetic field, has proportionally larger auroras. Hubble captured Jupiter's auroras using its ultraviolet instrument, and this picture was constructed by overlaying the UV image over a visible-light photo.
NASA, CXC/SAO/J. DePasquale
The Antennae Galaxies are a pair of galaxies in the process of colliding, a slow process taking hundreds of millions of years. This picture combines images from NASA's Great Observatories—Hubble (visible light), the Spitzer Infrared Observatory (infrared), and the Chandra X-ray Observatory (X-rays)—highlighting how these premiere space telescopes work together. The collision between the galaxies is producing new stars at a fast rate.
NASA, ESA, Robert Williams, Hubble Deep Field Team (STScI)
In 1996, astronomers pointed HST at a small unremarkable spot on the sky nearly empty of stars and took pictures for 10 days to get a clear view deep into the cosmos. The 342 photos assembled from the project make up the Hubble Deep Field Survey and contain roughly 3,000 individual galaxies, some billions of light-years away. In fact, nearly everything you see in this image is a galaxy, revealing the diversity and evolution of galaxies over the history of the universe.
NASA, ESA, K. France (University of Colordo, Boulder)
In early 1987, astronomers spotted a new bright point of light in the nearby galaxy in the Large Magellanic Cloud: Supernova 1987A, the explosion of a massive star. Because it is the closest supernova in modern times, astronomers have been able to track the aftereffects of the explosion. This 2010 Hubble image shows expanding bubbles of matter blasted away from the dying star, producing beads of light where the material slammed into clumps of gas in the surrounding region.
NASA, ESA, Andrea Dupree (Harvard-Smithsonian CfA), Ronald Gilliland (STScI)
Despite the power of modern telescopes like HST, most stars other than the sun are too far away to be anything but points of light. However, Hubble captured the first details on another star in 1996: the red giant Betelgeuse, which is part of the constellation Orion. As the diagram shows, Betelgeuse is so huge it's no longer spherical; in 2020, material ejected from the star blocked enough of its light that it dimmed visibly.
Galaxy clusters are the largest objects in the universe held together by gravity and can consist of thousands of individual galaxies. Abel 370 has so much mass (mostly in the form of mysterious invisible dark matter) that its gravity focuses light from more distant galaxies, producing magnified and distorted images of objects too far to be seen ordinarily. You can see some of those magnified galaxies in this HST image, appearing as smeared arcs of light.
NASA, ESA, M. Showalter (SETI Institute)
Before the New Horizons probe arrived on Pluto in 2015, astronomers turned HST to the dwarf planet to look for any potential hazards. This 2012 image shows Pluto's five moons, including a fifth previously unknown moon, now known as Styx. Hubble was also used to discover the moons Nix, Hydra, and Kerberos, which are too small to be seen with less powerful telescopes.
NASA, Raghvendra Sahai and John Trauger (JPL), WFPC2 science team
Smaller stars like our sun don't explode as supernovas but shed material as they die. Some of these form "planetary nebulas" like the Hourglass Nebula, which forms two interlinked bubbles of gas. The eerie effect here is because Hubble doesn't "see" color the way people do, so the image colors (and many other images in this slideshow) correspond to the presence of particular types of atoms or molecules: green for hydrogen, red for nitrogen, and blue for ionized oxygen.
NASA, ESA, Hubble Heritage Team
The Horsehead Nebula in the constellation of Orion is one of the most popular objects to look at through backyard telescopes, where it looks like a horse-shaped shadow against background stars. This HST infrared image shows newborn stars hiding inside the billowing nebula gas. Like the Eagle Nebula, the Horsehead is being eroded by ultraviolet light from nearby young, hot stars.
NASA, ESA, D. Batcheldor and E. Perlman (Florida Institute of Technology), Hubble Heritage Team
M87 is a giant elliptical galaxy (meaning: it has mostly old stars and no spiral arms) in the Virgo Cluster of galaxies. Like nearly every galaxy we know of, M87 harbors a huge black hole near its center, which was imaged by the Event Horizon Telescope in 2019. This set of HST pictures shows a jet of matter blasted out by that black hole, stretching out farther than the visible edges of M87.
NASA, ESA, J. DePasquale (STScI), R. Hurt (Caltech/IPAC)
The Crab Nebula is the remains of a star that went supernova and which was observed across the world in 1054 C.E. This image combines optical light from Hubble (in yellow), infrared light from Spitzer (in red), and X-ray light from Chandra (in blue), revealing the complex internal structure of this centuries-old supernova remnant. Matter continues to collide inside the nebula even after all this time, explaining the tendrils and bubbles you see in the picture.
NASA: ESA, Hubble Heritage Team
RS Puppis is a star known as a Cepheid variable: aging stars that pulsate, with predictable fluctuations in their light. This southern hemisphere star pulsates roughly every six weeks, creating "light echoes" in the surrounding gas. Early 20th-century astronomer Henrietta Swan Leavitt discovered that Cepheid variables have a connection between the frequency of fluctuations and their brightness, which allowed Edwin Hubble to make the first measurement of the distance to Andromeda Galaxy.
NASA, ESA, A. Simon, M.H. Wong, OPAL Team
As part of the giant planet monitoring program, HST captured this beautiful image of Saturn. Not only are the planet's famous rings shown clearly, but you can also see the hexagonal storm at Saturn's north pole, a feature not identified before the Cassini spacecraft mission.
NASA, ESA, Jonathan Nichols (University of Leicester)
Earth's seasons are caused by the fact that our axis is tilted, so the north pole points toward the sun in the summer and away in winter. Saturn has an even stronger axial tilt, but Hubble captured this ultraviolet image near the planet's equinox so that both poles were nearly in view at once. That allows us to see the auroras—northern and southern lights—in a single image, a rare occurrence.
NASA, ESA, Hubble Key Project Team, High-Z Supernova Search Team
The bright star-light object toward the lower-left corner of this image is Supernova 1994D, on the outskirts of the galaxy NGC 4526. It's a Type Ia supernova, which is the explosion of a white dwarf (the remnant of the core of a star like our sun). Astronomers use Type Ia supernovas to measure the expansion of the universe because they're bright enough to be seen from billions of light-years away.
NASA, ESA, S. Beckwith (STScI), Hubble Heritage Team
The Whirlpool Galaxy (M51) is a favorite galaxy for many people, and this Hubble image shows why. As a "grand design" spiral galaxy, the spiral arms are clearly defined, dotted with bright young blue stars and pink clouds where new stars are forming. Gravitational interactions with the smaller galaxy likely drive this star formation at the right side of the image.
NASA, ESA, Hubble Heritage Team
The Ring Nebula is a planetary nebula, the shedded material from a dying sun-like star. We see this system from an angle that shows the ring structure, but this 2013 HST image reveals the blue part of the nebula is an oblong bubble that passes through the ring. At the Ring Nebula's very center, you can make out a white dot that is a white dwarf, the remnant of the original star's core.
NASA, ESA, C. Kiss, J. Stansberry
The two largest known objects beyond Neptune in our solar system are Eris and Pluto; the third-largest is Gonggong, discovered in 2007 and finally named in 2019. These HST images show how astronomers discovered its moon Xiangliu by comparing archival pictures and looking for how things changed. Gonggong, like other distant solar system worlds, is too small to be anything but a pinpoint of light in most telescopes, requiring observatories of Hubble's caliber.
NASA, ESA, N. Pirzkal, HUDF Team (STScI)
Following up on the earlier Hubble Deep Field Survey, astronomers upped the ante and conducted the Hubble Ultra Deep Field Survey, looking at one relatively empty patch of the sky for roughly 1 million seconds (nearly 12 full days). This longer exposure revealed 10,000 galaxies, including some of the most distant yet discovered.
The Bullet Cluster is actually two galaxy clusters caught in the act of collision, where the "bullet" is a shockwave in X-ray emitting hot gas (from Chandra, shown in red). The visible light Hubble data allowed astronomers to measure where the mass from each cluster was concentrated (shown in blue). They found most of that mass was separated from the hot gas, meaning it's made up of invisible matter; this is one of the best direct measurements of the mysterious dark matter that makes up most of the matter in the cosmos.
The Voyager 2 spacecraft provided us with our first images of Neptune with its 1989 flyby, showing, in particular, a large dark-colored storm on the planet's blue disk. Later Hubble pictures didn't show this Great Dark Spot, meaning the storm had dissipated. However, a new Great Dark Spot formed in a different place on Neptune, as seen in this image; this behavior shows how huge storms form and break up on giant worlds.
NASA, ESA, S.H. Suyu, K.C. Wong
Quasars are supermassive black holes that heat up matter until it glows brightly. In these HST pictures, gravity from a foreground galaxy focuses and splits light from more distant quasars, making one quasar look like four. This effect is known as strong gravitational lensing, and astronomers use it to measure how far those quasars are from Earth by timing when each image flickers.
NASA, ESA, Hubble Heritage Team
The Southern Pinwheel Galaxy (M83) is a "flocculent" spiral galaxy, meaning its spiral arms look fleecy thanks to the copious amounts of gas and dust they contain. This high-resolution image of M83 reveals the processes of star formation and cavities where stars exploded in supernovas.
NASA, Hubble Heritage Team
The Great Nebula of Orion is a star-forming nebula that can be seen on a dark night without a telescope in Orion's "sword." A young hot star in that nebula, LL Ori, is pumping out streams of charged particles known as stellar wind at speeds high enough to produce a shockwave in the surrounding gas. Though we can't see the whole thing, this shockwave surrounds the star, though not in a spherical shape.
NASA, Hubble Heritage Team
The two galaxies making up the object Arp 142 collided, their mutual gravity pulling one of the galaxies into a shape resembling a galactic penguin. This penguin was once a spiral galaxy like ours, but the encounter has disrupted its shape and driven the production of new stars. The second object is an elliptical galaxy, which consists of older stars and little gas, which may be why its shape hasn't been roughed up as much by the collision.
NASA, ESA, P. Kalas (University of California, Berkeley)
These two images show disks of dust and ice around newborn stars, which are thought to resemble the Kuiper Belt in the outer part of our own solar system. These protoplanetary disks, as they are called, form from the leftovers of the host star's birth. In these cases, there might be planets orbiting closer in, but even Hubble's capabilities aren't good enough to see something so relatively tiny.
NASA, ESA, Hubble Heritage Team
Globular clusters are roughly spherical collections of tens of thousands of stars, including some of the oldest stars we know of. The cluster 47 Tucanae (located in the southern constellation Tucan) is part of the Milky Way but is older than our galaxy by several billion years.
NASA, ESA, E. Sabbi
The Large Magellanic Cloud is the largest satellite galaxy of the Milky Way, and home to Supernova 1987A. It's also home to the huge star-forming region known as the Tarantula Nebula. Hubble's infrared camera revealed a staggering 800,000 stars and protostars inside the Tarantula, of which you can see more than a few in this image.
NASA, ESA, and D. Jewitt (UCLA)
The comet C/2017 K2 PANSTARRS (or more simply K2) was first seen by Hubble in 2017 when it was past the orbit of Saturn. Comets are made of rock and ices (including water ice, carbon dioxide ice, and others) that form the distinctive tails when heated by the Sun. Even at that distance, sunlight was enough to melt the outer layers of K2, making it the most distant active comet ever seen.
NASA, ESA, M. Durbin, J. Dalcanton, B.F. Williams (University of Washington)
The Milky Way is one of three large galaxies in the small cluster known as the Local Group. The other two are Andromeda (the biggest of the group) and Triangulum (M33), a small spiral. Despite the fact that it's probably as old as its larger neighbors, Triangulum is producing new stars at a fairly high rate, which intrigues astronomers.
Galaxy collisions may seem violent, but they're one major way small galaxies grow into bigger ones, as they merge together. And undoubtedly galactic collisions are beautiful, as in with the galaxies of Arp 273, which HST captured to commemorate its 21st anniversary. As with other examples of interacting galaxies we've seen, Arp 273 shows star formation spurred on by each galaxy's gravitational tug on the other.
NASA, ESA, A. Simon, M. Wong, A. Hsu
When Voyager 2 visited Uranus in 1986, the pictures it returned to Earth showed a green-blue planet nearly unblemished by clouds. By contrast, this recent Hubble image shows a stormy cap of clouds over Uranus' pole. Since Uranus has the most extreme axial tilt of all planets—essentially tipped on its side—it also experiences the most extreme seasons, which may drive weather in ways we don't fully understand yet.
Supernovas, by definition, only happen once, since when a star blows up, there's nothing left to explode again. However, using strong gravitational lensing, astronomers were able to witness Supernova Refsdal four times when light from the explosion passed near a foreground galaxy. This effectively quadrupled the data from the supernova, providing both extra information about the explosion and a way to test the modern theory of gravity in new ways.
NASA, ESA, Hubble Heritage Team
All stars—our sun included—produce "wind" in the form of electrically charged particles blowing off the surface. The star at the center of the Bubble Nebula is 45 times more massive than the sun, and its wind has carved out a cavity in the surrounding gas seven light-years across. The nebula itself is the beautifully illuminated shape made where the wind collides with that gas.
NASA, ESA, A. Riess
Spiral galaxy NGC 1015 has a striking appearance, in large part, because we see it almost perfectly "face on." The central part of the galaxy is marked by a bar of stars and gas, surrounded by a ring of matter. But this Hubble image also fortuitously includes Supernova 2009ig, a Type Ia supernova caused by the explosion of a white dwarf.
Most shapes in space are round or blobby, but the planetary nebula HD 44179 is boxy, giving it the popular name the Red Rectangle. This 2004 Hubble image shows that the fundamental shape of the matter being shed by a dying star is more like an X, which explains why the material looks rectangular from a distance.
NASA, ESA, A. Parker
Makemake is one of the dwarf planets in the outer solar system discovered within the past 20 years. Until 2015, astronomers couldn't tell if it had a satellite or not, but this Hubble image revealed a faint moon that might have been hiding in Makemake's glow previously. Named "S/2015 (136472) 1" and nicknamed "MK 2," the moon's presence helps astronomers measure important properties about Makemake, such as its mass.
NASA, ESA, O. Gnedin, W. Brown
This picture of a star looks downright mundane until you realize it's speeding out of our galaxy at a breakneck 1.6 million miles per hour. HE 0437-5439 is known as a "hypervelocity" star, and it was likely part of a multiple-star system that drifted too close to the Milky Way's supermassive black hole. The dance of gravity stripped HE 0437-5439 from its companions and kicked it out of the galaxy entirely.
NASA, ESA, Hubble Heritage Team
The Sombrero Galaxy (M104) is another of Hubble's greatest hits, thanks to its very bright disk surrounded by a ring of dust. Because we see the galaxy nearly edge-on, it's hard to distinguish a lot of its features. However, astronomers have used this Hubble image to identify 2,000 globular clusters of stars in and around the galaxy.
NASA, ESA, STScI
Mars can feel downright mundane compared to many of the other cosmic objects in Hubble's catalog, but astronomers have turned the telescope to look at our planetary neighbor many times in the past 30 years. This 2018 image shows the Red Planet with a winter cap of clouds over the north pole. You can also see Mars' two small potato-like moons, Phobos and Deimos, in the right and lower side of the photo, respectively.
At first look, Stephan's Quintet seems to be five galaxies in collision. However, it turns out only three are actually interacting, and the bright galaxy in the upper left corner is seven times closer to Earth than the others. This optical illusion highlights the fact that occasionally things can look close together when they're actually very far apart, despite space being very big and mostly empty.
NASA, ESA, HEIC, Hubble Heritage Team
The Cat's-Eye Nebula may be another planetary nebula, but each star like our sun seems to die in its own beautiful and spectacular fashion. This nebula, in particular, is strikingly complex, with concentric layers of shed material overlapping bubbles and an almost spiral-arm structure.
NASA, ESA, P. Oesch (Yale University)
Galaxy GN-z11 just looks like a red blob in this HST image, but that's because it's a breathtaking 13.4 billion light-years away. Since the universe is only about 13.8 billion years old, this means GN-z11 formed about as early as any galaxy can exist. In fact, it was very bright blue 13.4 billion years ago, but as the light from it traveled, it got stretched into the red part of the spectrum, a phenomenon known as cosmic redshifting.
NASA, Hubble Heritage Team
The star V838 Monocerotis (in the constellation Monoceros, or the Unicorn) brightened suddenly in 2002, then faded. Astronomers turned to HST to look at it and found an expanding shell of gas around the star. This image shows a Firefox-like swirl of material shed by the star, which was probably left over from an earlier outburst.
NASA, ESA, Hubble Legacy Field Team
In 2019, Hubble astronomers collected 7,500 images taken over 16 years of observations to make the Hubble Legacy Survey. This mosaic includes infrared, optical, and ultraviolet data to provide a view of the cosmos, both deep and wide. With 265,000 galaxies in the field, you could spend your life looking at it and still find new things to discover, a worthy summation of Hubble's 30-year career so far.