Left: Pioneer 10’s view of Jupiter in March 1973. Right: Webb Telescope’s view of Jupiter in July 2022. Image: NASA, ESA, CSA, Jupiter ERS Team; image processing by Judy Schmidt
For centuries, astronomers were limited to ground-based observations of the planets, but now we use spacecraft to capture close-up views of our neighboring worlds. Excitingly, our views of solar system planets have been getting progressively better over the decades, as these images attest.
The dawn of the Space Age finally made it possible for humankind to capture close-up views of astronomical objects. We haven’t wasted this opportunity, sending probes to every planet in our solar system and even to Pluto, a dwarf planet located over 5 billion miles (8 billion kilometers) away.
The first missions to the planets began in the 1960s, and it’s something we still get excited about. We’ve assembled a series of photos showing some of our earliest images of the planets compared to similar portraits captured during recent missions. Regardless of the era or the quality, each one has a story to tell, and each continues to stir the imagination.
In 1983, astronomer Michael Rowan-Robinson conducted a search for a proposed 10th planet (Pluto still being a planet at the time) using data from the Infrared Astronomical Satellite, the first infrared space telescope. Rowan-Robinson didn’t turn up a new planet, and by 1991, he was pretty sure that such a planet did not exist, at least not in the area of the sky he looked in.
But since then, new regions of the sky have been proposed as potential homes of a hidden planet, now called Planet Nine. Some astrophysicists suspect that a planet—or at least, something with a lot of gravity—exists out there due to the movements of objects in the Kuiper Belt, a distant disc of comets, asteroids, and icy things beyond the orbit of Neptune.
On the heels of recent research that suggested new potential hiding spots for Planet Nine, Rowan-Robinson revisited the 38-year-old data and found three infrared sources that he says could be the theorized world. His paper is set to be published in the Monthly Notices of the Royal Astronomical Society and is currently hosted on the preprint server arXiv.
Planet Nine (formerly Planet X, said like the letter) has long been considered a possibility. The discovery of Neptune in 1846 came after astronomers found Uranus’s orbit was slightly different than math predicted. They realized that something was perturbing Uranus gravitationally; that object turned out to be an eighth planet.
Observations of Neptune then led astronomers to believe there may be yet another planet out there, messing with the newly discovered world’s orbit. Pluto was found in 1930 by looking at objects on photographic plates, but it couldn’t account for the movement of Neptune.
Scientists who search for Planet Nine estimate that its mass is several times bigger than Earth’s, with an orbit lasting thousands of years. Of course, Planet Nine is just one answer to the quandary of why some objects’ orbits are wonky. One alternative theory is that instead of Planet Nine is actually a ring of debris. Others have suggested the “planet” could be a bowling ball-sized black hole.
For the recent work, Rowan-Robinson redid his search from nearly 40 years ago and found three points in the data from late summer 1983 that indicate some object moving across the sky. The data sources sit low on the galactic plane, though, meaning that the satellite was taking the data through plenty of dusty, cloudy material that can emit infrared light.
In other words, the work is something of a long shot. And Rowan-Robinson is well aware of that. “Given the poor quality of the IRAS detections, at the very limit of the survey, and in a very difficult part of the sky for far infrared detections, the probability of the candidate being real is not overwhelming,” he wrote in his paper.
But that’s no reason not to dig further. It’s not cryptoastronomy; people looking for a ninth planet are investigating a real mathematical problem. It is a particularly “shiny solution,” though, as planetary astronomer Michele Bannister told Gizmodo in 2017.
We may have new answers fairly soon. The Vera Rubin Observatory in Chile is under construction and will image the entire sky every week using the largest digital camera ever built. Compared to when astronomers had to use just their eyes to search for changes in the cosmos, we now have artificial intelligence that can detect intriguing signals in data far beyond the abilities of the naked eye. It’s fair to say we’re closer to finding out the truth than we were before. Good things come to those who wait… but hopefully we won’t have to wait much longer.
More: Is the Elusive ‘Planet Nine’ Actually a Massive Ring of Debris in the Outer Solar System?
NASA’s Hubble Space Telescope keeps an eye on Jupiter’s Great Red Spot, a 10,000-mile-wide storm system that has been swirling for at least 190 years and possibly much longer. Recent data from the telescope indicates that the spot’s outer winds have picked up speed in the past decade.
The storm has an “outer lane” and an “inner lane” of winds, both of which rotate counterclockwise. While the outer lane has sped up recently, the winds closer to the center of the spot were actually moving much slower in 2020 than they were back in 2009. The research exploring these wind trends was published last month in the Astrophysical Journal Letters.
“Since we don’t have a storm chaser plane at Jupiter, we can’t continuously measure the winds on site,” said Amy Simon, a planetary scientist at NASA’s Goddard Space Flight Center, in a NASA press release. “Hubble is the only telescope that has the kind of temporal coverage and spatial resolution that can capture Jupiter’s winds in this detail.”
The pickup in wind speed was steady: less than a 2-mile-per-hour change per Earth year from 2009 to 2020. It’s only because the team had 11 years of Hubble data, and that Hubble can see Jupiter with such precision, that they could pick out the trend. The winds are blowing at around 400 miles per hour, slightly slower than the cruising speed of a commercial airliner.
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Though Jupiter appears serene in images—a big marble in space—the planet is a turbid ball of gas that is constantly moving. Just last year, an entire new spot popped up on the planet. And for all its fame, even the Great Red Spot is something of an enigma; our modern instruments can’t probe much of the storm besides what happens on the surface.
“Hubble can’t see the bottom of the storm very well. Anything below the cloud tops is invisible in the data,” said Michael Wong, a planetary scientist specializing in atmospheres at the University of California at Berkeley, and the paper’s lead author, in the same release. Wong added that the recent trend is “an interesting piece of data that can help us understand what’s fueling the Great Red Spot and how it’s maintaining energy.”
Planetary scientists do know some things about the spot. It has a tiered structure in which the storm’s higher clouds are toward the center, and the outer edges of the storm are deeper in the planet. The storm is slowly becoming more circular compared to the oval it’s long been.
The storm has been observed for nearly 200 years—maybe even 350 years, as it’s hard to say whether spots described by earlier astronomers were one and the same as the Great Red Spot—but it’ll likely take more time and better instruments to dig deeper into the tempestuous mystery at Jupiter’s heart.
More: Jupiter’s Great Red Spot Is About to Reveal Its Mysteries
A team of astrophysicists looking at data from the Cassini spacecraft’s tour of Saturn have estimated a new size for the planet’s core. Studying gravitational effects on the icy rings, the team determined that Saturn’s core is a combination of ice, rock, hydrogen, and helium about 50 times as massive as Earth, making it much more diffuse than previously thought.
“The conventional picture has it that Saturn’s interior has a neat division between a compact core of rocks and ices and an envelope of mostly hydrogen and helium. We found that contrary to this conventional picture, the core is actually ‘fuzzy’: all those same rocks and ices are there, but they are effectively blurred out over a huge fraction of the planet,” said Christopher Mankovich, a researcher at the California Institute of Technology and lead author of a paper on the findings, published today in Nature Astronomy.
The rocks and ice inside Saturn slowly give way to the more gassy parts of the planet as you move away from the core, he said. The team found that the core didn’t have a clear-cut end point; rather, it had a transition region that made up about 60% of Saturn’s entire diameter, making the core a huge part of the planet’s total size and much larger part than the 10% to 20% of a planet’s diameter that a more compact core would be.
Previously, Saturn was thought to have a rocky, metallic core under all that frigid, fluid gas. “When the observations were limited to the traditional gravity field data, the compact core model did a fine job,” Mankovich said, but the newer data from Cassini has given us a different, better picture of the planet’s insides. As National Geographic reported in 2015, the idea of studying Saturn’s interior using its rings has been floating around for the past few decades. But Cassini, in its 13 years of flying through Saturn’s rings (before it ran out of fuel in 2017) offered up the actual data on those dazzling structures and the processes within them.
An illustration of how researchers think Saturn’s core is organized.Illustration: Caltech/R. Hurt (IPAC)
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Saturn can be thought of as a giant space blender, spinning its constituent elements of ice, rock, and gases that are in some places so cold they behave like fluids. The planet’s surface moves a little bit in all the hubbub—about 3 feet every couple hours, placid for an object its size—and that wobble causes fluctuations in the planet’s gravitational field, which stretches outwards in spirals to the planet’s rings, distorting them. The icy particles that make up Saturn’s rings move in response to those gravitational changes from the planet’s sloshing insides, tantamount to seismic activity for a planet that is not rocky.
The rings are a plane for astrophysical research that makes Saturn unique among the other gas giants, like Jupiter, which lack such a useful access point to the interior. Mankovich said the new findings about Saturn add credence to the idea that gas giant evolution is a gradual process, beginning with the building of a core from the coagulation of bits of space rock and then proceeding to accreting gas to form the rest of the planet.
This is only the latest in what has been a stringofinsights from Cassini on the Saturnian interior and the processes that could be induced by it. More Cassini data on other oscillations has yet to be looked at, and mysterious accelerations felt by the spacecraft in the later stages of its operation have yet to be explained. It may be a while before we return to Saturn with another spacecraft (the limelight is currently on Venus and Mars), but thankfully Cassini left astrophysicists with their hands full.
More: Cassini Dropped Its Most Mind-Blowing Look at Saturn’s Rings Yet
Composite image of Uranus, composed of an X-ray image taken by Chandra (shown in pink) and an optical image taken by the Keck-I Telescope. Image: X-ray: NASA/CXO/University College London/W. Dunn et al; Optical: W.M. Keck Observatory
Using NASA’s Chandra X-ray Observatory, astronomers have detected X-rays coming from Uranus, revealing a previously unknown dimension of this majestic ice giant.
The new finding, published in JGR: Physics, means that X-ray emissions have been detected on every planet in the solar system except Neptune. What’s more, the discovery could yield new insights into more distant X-ray-emitting objects, including black holes, supernovae, quasars, and neutron stars. The new paper was led by astronomer William Dunn from University College London.
Composed primarily of hydrogen and helium, Uranus exhibits two sets of rings, both in orbit above its equator. The planet is somewhat of an oddball, as it rotates on its side relative to the plane of the solar system (no other planet does this). NASA’s Voyager 2 spacecraft visited Uranus very briefly in 1986, so aside from that, astronomers have been depending on telescopes, such as Chandra and Hubble, to study the seventh planet from the Sun.
Dunn, along with physicist Affelia Wibisono, a PhD student at UCL and a co-author of the study, uncovered the evidence of Uranus’s X-ray emissions in Chandra data gathered in 2002 and 2017. The data from 2002 was gathered by the Chandra Advanced CCD Imaging Spectrometer, while the 2017 data came from Chandra’s High Resolution Camera, in addition to optical observations. The observed signals are very weak, but they’re there.
With X-rays confirmed on Uranus, the challenge now is to determine the cause.
“There are three main ways that a planet can produce X-rays: fluorescence, scattering of solar X-rays, and auroral emissions,” explained Wibisono in an article she wrote for the Chandra website.
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Uranus, like many other objects in the solar system—including comets, moons, and even the dwarf planet Pluto—is likely scattering X-rays received by the Sun. But this doesn’t appear to be the exclusive source of X-rays on Uranus. As Wibisono points out, “our calculations suggest that Uranus was producing more X-rays than it should if the planet was only scattering the Sun’s X-rays.”
The authors proposed two different theories to explain the emissions. One possibility is that Uranus’s rings are churning out X-rays, similar to what’s happening with the rings around Saturn. This process, known as fluorescence, happens when energetic charged particles, such as electrons and protons, collide with the rings, causing them to glow in X-rays.
Another possibility is that the X-rays are being produced by Uranus’s auroras, as NASA explains in a statement.
On Earth, we can see colorful light shows in the sky called auroras, which happen when high-energy particles interact with the atmosphere. X-rays are emitted in Earth’s auroras, produced by energetic electrons after they travel down the planet’s magnetic field lines to its poles and are slowed down by the atmosphere. Jupiter has auroras, too. The X-rays from auroras on Jupiter come from two sources: electrons traveling down magnetic field lines, as on Earth, and positively charged atoms and molecules raining down at Jupiter’s polar regions.
Trouble is, the cause of auroras on Uranus is still poorly understood, so much of this remains guesswork. Further “observations of Uranus by Chandra and other X-ray telescopes are needed before we can give a definitive answer,” admits Wibisono.
Uranus presents a fascinating object for studying various aspects of the distant planets, and that’s on account of its unusual spin axis and wonky magnetic field. With its odd tilt, astronomers can see Uranus at an irregular angle, and due to its magnetic field, which is also weirdly tilted, astronomers could eventually find a connection with the planet’s complex and variable auroras. There’s still plenty to learn about this strange and wonderful ice giant.
Depiction of stratospheric winds near Jupiter’s south pole.Image: ESO
For the first time ever, astronomers have measured winds inside Jupiter’s middle atmosphere, revealing unexpectedly fast jet streams within the planet’s deeper layers.
A paper published in Astronomy & Astrophysics is giving new meaning to the term “polar vortex.”
Using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, astronomers have clocked the speed of polar jets located far below the cloud tops, and, wow, is it ever gusty down there. The fastest of these jets is moving at 895 miles per hour (1,440 km/h), which is nearly five times faster than winds produced by the strongest hurricanes on Earth.
Thibault Cavalié, the lead author of the study and a planetary scientist at the Laboratoire d’Astrophysique de Bordeaux in France, said these jets, found under Jupiter’s main auroras (yes, Jupiter has auroras, and they’re quite stunning), seem to be the “lower tail of the supersonic jets seen 900 km [560 miles] above,” as he explained in an email. These currents could form a “huge anticyclone with a diameter of 3 to 4 Earth diameters and a vertical extent of 900 km,” said Cavalié, to which he added: “This is unique in the solar system.”
In a statement put out by the European Southern Observatory, Cavalié described the newly detected feature as a “unique meteorological beast.”
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Measuring wind speed below the top atmospheric layer of Jupiter is not easy. The iconic red and white bands that streak across Jupiter are typically used to measure winds at the top layer, and the planet’s auroras, which are linked to strong winds in the upper atmosphere, are also used as reference points. But to be fair, scientists haven’t really been able to measure winds in the middle atmosphere of Jupiter—the stratosphere—until now.
Two things made these measurements possible: a famous comet and a very powerful telescope.
Comet Shoemaker-Levy 9 impacting Jupiter in 1994.Image: ESO
The comet in question is Shoemaker–Levy 9, which smashed into Jupiter in 1994. The impact left distinctive molecules in the atmosphere, and they’ve been blowing around the gas giant for the past 27 years. The presence of these molecules—namely hydrogen cyanide—made it possible for Cavalié and his colleagues to peer below the cloud tops and measure the speed of stratospheric jet streams.
To detect these molecules, the team used 42 of ALMA’s 66 high-precision antennas, marking the first time that scientists have obtained such measurements in Jupiter’s middle atmosphere.
Specifically, the ALMA data allowed the scientists to measure tiny frequency changes in the radiation emissions of molecules as they’re blown by winds in this part of the planet. In other words, they measured the Doppler shift. By doing so, “we were able to deduce the speed of the winds much like one could deduce the speed of a passing train by the change in the frequency of the train whistle,” explained Vincent Hue, a planetary scientist at the Southwest Research Institute and a co-author of the new study, in the ESO statement.
These measurements showed that winds under the auroras near the poles were moving at 895 mph, which is more than twice the speed of winds swirling within the planet’s Great Red Spot. Toward the equator, stratospheric winds were clocked at an average speed of 373 mph (600 km/h).
High-speed winds had previously been detected at the upper atmospheric layer, but scientists figured that the deeper you go the slower you go, as far as wind speeds are concerned. The new research suggests otherwise, a finding that came as a complete surprise to the team.
The newly detected winds are fast, but they’re not the fastest in the solar system, nor are they even the fastest on Jupiter. The winds observed under the aurora of Jupiter are “twice as fast as the fastest winds measured at the cloud-top of Jupiter,” said Cavalié. “Higher up,” however, and “still under the aurora in a layer called the ionosphere,” there are “winds with supersonic speeds of 1 to 2 kilometers per second [0.62 to 1.24 miles per second],” or 2,240 to 4,475 mph (3,600 to 7,200 km/h). Neptune, he added, “has the strongest winds in the solar system at cloud level and they are 25% faster than the winds we have measured under the aurora.”
This research, in addition to measuring winds in Jupiter’s stratosphere, was done as a proof-of-concept for similar investigations to be carried out by the Submillimetre Wave Instrument (SWI) aboard the upcoming Jupiter Icy Moons Explorer (JUICE). Launch is scheduled for next year, and it’ll be the first European mission to Jupiter, with arrival expected in around 10 years time.