Volcanic activity on Io was discovered by Voyager 1 imaging scientist Linda Morabito. She spotted a little bump on Io’s limb while analyzing a Voyager image and thought at first it was an undiscovered moon. Moments later she realized that wasn’t possible — it would have been seen by earthbound telescopes long ago. Morabito and the Voyager team soon came to realize they were seeing a volcanic plume rising 190 miles (300 km) off the surface of Io. It was the first time in history that an active volcano had been detected beyond the Earth. For a wonderful account of the discovery, click here.
Today, we know that Io boasts more than 130 active volcanoes with an estimated 400 total, making it the most volcanically active place in the Solar System. Juno used its Jovian Infrared Aurora Mapper (JIRAM) to take spectacular photographs of Io during Perijove 7 last July, when we were all totally absorbed by close up images of Jupiter’s Great Red Spot.
Juno’s Io looks like it’s on fire. Because JIRAM sees in infrared, a form of light we sense as heat, it picked up the signatures of at least 60 hot spots on the little moon on both the sunlight side (right) and the shadowed half. Like all missions to the planets, Juno’s cameras take pictures in black and white through a variety of color filters. The filtered views are later combined later by computers on the ground to create color pictures. Our featured image of Io was created by amateur astronomer and image processor Roman Tkachenko, who stacked raw images from this data set to create the vibrant view.
Io’s hotter than heck with erupting volcano temperatures as high as 2,400° F (1,300° C). Most of its lavas are made of basalt, a common type of volcanic rock found on Earth, but some flows consist of sulfur and sulfur dioxide, which paints the scabby landscape in unique colors.
This five-frame sequence taken by NASA’s New Horizons spacecraft on March 1, 2007 captures the giant plume from Io’s Tvashtar volcano.
Located more than 400 million miles from the Sun, how does a little orb only a hundred miles larger than our Moon get so hot? Europa and Ganymede are partly to blame. They tug on Io, causing it to revolve around Jupiter in an eccentric orbit that alternates between close and far. Jupiter’s powerful gravity tugs harder on the moon when its closest and less so when it’s farther away. The “tug and release”creates friction inside the satellite, heating and melting its interior. Io releases the pent up heat in the form of volcanoes, hot spots and massive lava flows.
Forty years ago, the Voyager 1 and 2 missions began their journey from Earth to become the farthest-reaching missions in history. In the course of their missions, the two probes spent the next two decades sailing past the gas giants of Jupiter and Saturn. And while Voyager 1 then ventured into the outer Solar System, Voyager 2 swung by Uranus and Neptune, becoming the first and only probe in history to explore these worlds.
This summer, the probes will be marking the fortieth anniversary of their launch – on September 5th and August 20th, respectively. Despite having traveled for so long and reaching such considerable distances from Earth, the probes are still in contact with NASA and sending back valuable data. So in addition to being the most distant missions from Earth, they are the longest-running mission in history.
In addition to their distance and longevity, the Voyager spacecraft have also set numerous other records for robotic space missions. For example, in 2012, the Voyager 1 probe became the first and only spacecraft to have entered interstellar space. Voyage 2, meanwhile, is the only probe that has explored all four of the Solar System’s gas/ice giants – Jupiter, Saturn, Uranus and Neptune.
Their discoveries also include the first active volcanoes beyond Earth – on Jupiter’s moon Io – the first evidence of a possible subsurface ocean on Europa, the dense atmosphere around Titan (the only body beyond Earth with a dense, nitrogen-rich atmosphere), the craggy surface of Uranus’ “Frankenstein Moon” Miranda, and the ice plume geysers of Neptune’s largest moon, Triton.
These accomplishments have had immeasurable benefits for planetary science, astronomy and space exploration. They’ve also paved the way for future missions, such as the Galileo and Juno probes, the Cassini-Huygens mission, and the New Horizons spacecraft. As Thomas Zurbuchen, the associate administrator for NASA’s Science Mission Directorate (SMD), said in a recent press statement:
“I believe that few missions can ever match the achievements of the Voyager spacecraft during their four decades of exploration. They have educated us to the unknown wonders of the universe and truly inspired humanity to continue to explore our solar system and beyond.”
But what is perhaps most memorable about the Voyager missions is the special cargo they carry. Each spacecraft carries what is known as the Golden Record, a collection of sounds, pictures and messages that tell of Earth, human history and culture. These records were intended to serve as a sort of time capsule and/or message to any civilizations that retrieved them, should they ever be recovered.
As noted, both ships are still in contact with NASA and sending back mission data. The Voyager 1 probe, as of the writing of this article, is about 20.9 billion km (13 billion mi; 140 AU) from Earth. As it travels northward out of the plane of the planets and into interstellar space, the probe continues to send back information about cosmic rays – which are about four times as abundant in interstellar space than around Earth.
From this, researchers have learned that the heliosphere – the region that contains the Solar System’s planets and solar wind – acts as a sort of radiation shield. Much in the say that Earth’s magnetic field protects us from solar wind (which would otherwise strip away our atmosphere), the heliopause protects the Solar planets from atomic nuclei that travel at close to the speed of light.
Voyager 2, meanwhile, is currently about 17.7 billion km (11 billion mi; 114.3 AU) from Earth. It is traveling south out of the plane of the planets, and is expected to enter interstellar space in a few years. And much like Voyager 1, it is also studying how the heliosphere interacts with the surroundings interstellar medium, using a suite of instruments that measure charged particles, magnetic fields, radio waves and solar wind plasma.
Once Voyager 2 crosses into interstellar space, both probes will be able to sample the medium from two different locations simultaneously. This is expected to tell us much about the magnetic environment that encapsulates our system, and will perhaps teach us more about the history and formation of the Solar System. On top of that, it will let us know what kinds of hazards a possible interstellar mission will have to contend with.
The fact that the two probes are still active after all this time is nothing short of amazing. As Edward Stone – the David Morrisroe Professor of Physics at Caltech, the former VP and Director of NASA’s Jet Propulsion Laboratory, and the Voyager project scientist – said:
“None of us knew, when we launched 40 years ago, that anything would still be working, and continuing on this pioneering journey. The most exciting thing they find in the next five years is likely to be something that we didn’t know was out there to be discovered.”
Keeping the probes going has also been a challenge since the amount of power they generate decreases at a rate of about four watts per year. This has required that engineers learn how to operate the twin spacecraft with ever-decreasing amounts of power, which has forced them to consult documents that are decades old in order to understand the probes’ software and command functions.
Luckily, it has also given former NASA engineers who worked on the Voyager probes the opportunity to offer their experience and expertise. At present, the team that is operating the spacecraft estimate that the probes will run out of power by 2030. However, they will continue to drift along their trajectories long after they do so, traveling at a speed of 48,280 km per hour (30,000 mph) and covering a single AU every 126 days.
At this rate, they will be within spitting distance of the nearest star in about 40,000 years, and will have completed an orbit of the Milky Way within 225 million years. So its entirely possible that someday, the Golden Records will find their way to a species capable of understanding what they represent. Then again, they might find their way back to Earth someday, informing our distant, distant relatives about life in the 20th century.
And if the craft avoid any catastrophic collisions and can survive in the interstellar medium of space, it is likely that they will continue to be emissaries for humanity long after humanity is dead. It’s good to leave something behind!
The twin Voyager spacecraft are now making their way through the interstellar medium. Even though they are going where none have gone before, the path ahead it is not completely unknown.
Astronomers are using the Hubble Space Telescope to observe the ‘road’ ahead for these pioneering spacecraft, to ascertain what various materials may lay along the Voyagers’ paths through space.
Combining Hubble data with the information the Voyagers are able to gather and send back to Earth, astronomers said a preliminary analysis reveals “a rich, complex interstellar ecology, containing multiple clouds of hydrogen laced with other elements.”
“This is a great opportunity to compare data from in situ measurements of the space environment by the Voyager spacecraft and telescopic measurements by Hubble,” said Seth Redfield of Wesleyan University, who led the study. “The Voyagers are sampling tiny regions as they plow through space at roughly 38,000 miles per hour. But we have no idea if these small areas are typical or rare. The Hubble observations give us a broader view because the telescope is looking along a longer and wider path. So Hubble gives context to what each Voyager is passing through.”
The combined data is also providing new insights into how our Sun travels through interstellar space, and astronomers hope that these combined observations will help them characterize the physical properties of the local interstellar medium.
“Ideally, synthesizing these insights with in situ measurements from Voyager would provide an unprecedented overview of the local interstellar environment,” said Hubble team member Julia Zachary of Wesleyan University.
The initial look at the clouds’ composition shows very small variations in the abundances of the chemical elements contained in the structures.
“These variations could mean the clouds formed in different ways, or from different areas, and then came together,” Redfield said.
Astronomers are also seeing that the region that we and our solar system are passing through right now contains “clumpier” material, which may affect the heliosphere, the large bubble that is produced by our Sun’s powerful solar wind. At its boundary, called the heliopause, the solar wind pushes outward against the interstellar medium. Hubble and Voyager 1 made measurements of the interstellar environment beyond this boundary, where the wind comes from stars other than our sun.
“I’m really intrigued by the interaction between stars and the interstellar environment,” Redfield said. “These kinds of interactions are happening around most stars, and it is a dynamic process.”
Both Voyagers 1 and 2 launched in 1977 and both explored Jupiter and Saturn. Voyager 2 went on to visit Uranus and Neptune.
Voyager 1 is now 13 billion miles (20 billion km) from Earth, and entered interstellar space in 2012, the region between the stars that is filled with gas, dust, and material recycled from dying stars. It is the farthest a human-made spacecraft has even traveled. Next big ‘landmark’ for Voyager 2 is in about 40,000 years when it will come within 1.6 light-years of the star Gliese 445, in the constellation Camelopardalis.
Voyager 2, is 10.5 billion miles (16.9 billion km) from Earth, and will pass 1.7 light-years from the star Ross 248 in about 40,000 years.
Of course, neither spacecraft will be operational by then.
But scientists hope that for at least the next 10 years, the Voyagers will be making measurements of interstellar material, magnetic fields, and cosmic rays along their trajectories. The complimentary Hubble observations will help to map interstellar structure along the routes. Each sight line stretches several light-years to nearby stars. Sampling the light from those stars, Hubble’s Space Telescope Imaging Spectrograph measured how interstellar material absorbed some of the starlight, leaving telltale spectral fingerprints.
When the Voyagers run out of power and are no longer able to communicate with Earth, astronomers still hope to use observations from Hubble and subsequent space telescopes to characterize the environment where our robotic emissaries to the cosmos will travel.
Jupiter global map created from still images from the Hubble Space Telescope
It’s been widely reported, including at Universe Today, that the apple of Jupiter’s eye, the iconic Great Red Spot (GRS), has been shrinking for decades. Even the rate of shrinkage has been steadily increasing.
Back in the late 1800s you could squeeze three Earths inside the GRS. Those were the days. Last May it measured just 10,250 miles (16,496 km) across, big enough for only 1.3 of us.
And while new photos from the Hubble Space Telescope show that Jupiter’s swollen red eye has shrunk an additional 150 miles (240 km) since 2014, the good news is that the rate of shrinkage appears to be well, shrinking. The contraction of the GRS has been studied closely since the 1930s; even as recently as 1979, the Voyager spacecraft measured it at 14,500 miles (23,335 km) across. But the alarm sounded in 2012, when amateur astronomers discovered sudden increase in the rate of 580 miles (933 km) a year along with a shift in shape from oval to roughly circular.
For the moment, it appears that the GRS is holding steady, making for an even more interesting Jupiter observing season than usual. Already, the big planet dominates the eastern sky along with Venus on October mornings. Consider looking for changes in the Spot yourself in the coming months. A 6-inch or larger scope and determination are all you need.
New imagery from the Hubble OPAL program also shows a curious wisp at the center of the Great Red Spot spanning almost the entire width of the hurricane-like vortex. This filamentary streamer rotates and twists throughout the 10-hour span of the Great Red Spot image sequence, drawn out by winds that are blowing at 335 mph (540 km/hr). Color-wise, the GRS remains orange, not red. Currently, the reddest features on the planet are the North Equatorial Belt and the occasional dark, oval “barges” (cyclonic storms) in the northern hemisphere.
That’s not all. The photos uncovered a rare wave structure just north of Jupiter’s equator that’s only been seen once before and with difficulty by the Voyager 2 spacecraft in 1979. The scientists, whose findings are described in this just-published Astrophysical Journal paper, say it resembles an earthly atmospheric feature called a baroclinic wave,a large-scale meandering of the jet stream associated with developing storms.
Jupiter’s “current wave” riffles across a region rich with cyclonic and anticyclonic storms. The wave may originate in a clear layer beneath Jupiter’s clouds, only becoming visible when it propagates up into the cloud deck, according to the researchers. While it’s thought to be connected to storm formation in the Jovian atmosphere, it’s a mystery why the wave hasn’t been observed more often.
The OPAL program focuses on long-term observation of the atmospheres of Jupiter, Uranus and Neptune until the end of the Saturn Cassini Mission and all four planets afterwords. We have to keep watch from Earth as no missions to Saturn and beyond are expected for quite some time. To date, Neptune and Uranus have already been observed with photos to appear (hopefully) soon in a public archive.
Hey, Mars, you’ve got company. Looks like there’s a second “red planet” in the Solar System — Pluto. Color images returned from NASA’s New Horizons spacecraft, now just 10 days from its encounter with the dwarf planet, show a distinctly ruddy surface with patchy markings that strongly resemble Mars’ appearance in a small telescope.
On Mars, iron oxide or rust colors the planet’s soil, while Pluto’s coloration is likely caused by hydrocarbon molecules called tholins that are formed when cosmic rays and solar ultraviolet light interact with methane in Pluto’s atmosphere and on its surface. Airborne tholins fall out of the atmosphere and coat the surface with a reddish gunk.
A particular color or wavelength of UV light called Lyman-alpha is most effective at stimulating the chemical reactions that build hydrocarbons at Pluto. Recent measurements with New Horizons’ Alice instrument reveal the diffuse glow of Lyman-alpha light all around the dwarf planet coming from all directions of space, not just the Sun.
Since one of the main sources of Lyman-alpha light besides the Sun are regions of vigorous star formation in young galaxies, Pluto’s cosmetic rouge may originate in events happening millions of light years away.
“Pluto’s reddish color has been known for decades, but New Horizons is now allowing us to correlate the color of different places on the surface with their geology and soon, with their compositions,” said New Horizons principal investigator Alan Stern of the Southwest Research Institute, Boulder, Colorado.
Tholins have been found on other bodies in the outer Solar System, including Titan and Triton, the largest moons of Saturn and Neptune, respectively, and made in laboratory experiments that simulate the atmospheres of those bodies.
As you study the photos and animation, you’ll notice that Pluto’s largest dark spot is redder than the most of the surface; you also can’ help but wonder what’s going on with those four evenly-spaced dark streaks in the equatorial zone. When I first saw them, my reaction was “no way!” They look so neatly lined up I assumed it was an image artifact, but after seeing the rotating movie, maybe not. It’s more likely that low resolution enhances the appearance of alignment.
But what are they? Located as they are on the Charon-facing side of Pluto, they may be related to long-ago tidal stresses induced by each body on the other as they slowly settled into their current tidally-locked embrace or something as current as seasonal change.
Voyager 2 photographed cyrovolcanos at Triton during its 1989 flyby of the Neptune system. Nitrogen geysers and plumes of gas and ice as high as 5 miles (8 km) were seen erupting from active volcanoes, leaving dark streaks on its icy surface.
Seasonal heating from the Sun is the most likely cause for Triton’s eruptions; Pluto’s dark streaks may have a similar origin.
Today, New Horizons lies just 7.4 million miles (11.9 million km) from its target. Sharpness and detail visible will rapidly improve in just a few days.
“Even at this resolution, Pluto looks like no other world in our Solar System,” said mission scientist Marc Buie of the Southwest Research Institute, Boulder in a recent press release.
A quarter of a century has passed since NASA’s Voyager 1 spacecraft snapped the iconic image of Earth known as the “Pale Blue Dot” that shows all of humanity as merely a tiny point of light.
The outward bound Voyager 1 space probe took the ‘pale blue dot’ image of Earth 25 years ago on Valentine’s Day, on Feb. 14, 1990 when it looked back from its unique perch beyond the orbit of Neptune to capture the first ever “portrait” of the solar system from its outer realms.
Voyager 1 was 4 billion miles from Earth, 40 astronomical units (AU) from the sun and about 32 degrees above the ecliptic at that moment.
The idea for the images came from the world famous astronomer Carl Sagan, who was a member of the Voyager imaging team at the time.
He head the idea of pointing the spacecraft back toward its home for a last look as a way to inspire humanity. And to do so before the imaging system was shut down permanently thereafter to repurpose the computer controlling it, save on energy consumption and extend the probes lifetime, because it was so far away from any celestial objects.
Sagan later published a well known and regarded book in 1994 titled “Pale Blue Dot,” that refers to the image of Earth in Voyagers series.
“Twenty-five years ago, Voyager 1 looked back toward Earth and saw a ‘pale blue dot,’ ” an image that continues to inspire wonderment about the spot we call home,” said Ed Stone, project scientist for the Voyager mission, based at the California Institute of Technology, Pasadena, in a statement.
Six of the Solar System’s nine known planets at the time were imaged, including Venus, Earth, Jupiter, and Saturn, Uranus, Neptune. The other three didn’t make it in. Mercury was too close to the sun, Mars had too little sunlight and little Pluto was too dim.
Voyager snapped a series of images with its wide angle and narrow angle cameras. Altogether 60 images from the wide angle camera were compiled into the first “solar system mosaic.”
Voyager 1 was launched in 1977 from Cape Canaveral Air Force Station in Florida as part of a twin probe series with Voyager 2. They successfully conducted up close flyby observations of the gas giant outer planets including Jupiter, Saturn, Uranus and Neptune in the 1970s and 1980s.
Both probes still operate today as part of the Voyager Interstellar Mission.
“After taking these images in 1990, we began our interstellar mission. We had no idea how long the spacecraft would last,” Stone said.
Hurtling along at a distance of 130 astronomical units from the sun, Voyager 1 is the farthest human-made object from Earth.
Voyager 1 still operates today as the first human made instrument to reach interstellar space and continues to forge new frontiers outwards to the unexplored cosmos where no human or robotic emissary as gone before.
Here’s what Sagan wrote in his “Pale Blue Dot” book:
“That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. … There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world.”
Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.
Sometimes first impressions are poor ones. When the Voyager 2 spacecraft whizzed by Uranus in 1986, the close-up view of the gas giant revealed what appeared to a be a relatively featureless ball. By that point, scientists were used to seeing bright colors and bands on Jupiter and Saturn. Uranus wasn’t quite deemed uninteresting, but the lack of activity was something that was usually remarked upon when describing the planet.
Fast-forward 28 years and we are learning that Uranus is a more complex world than imagined at the time. Two new studies, discussed at an American Astronomical Society meeting today, show that Uranus is a stormy place and also that the images from Voyager 2 had more interesting information than previously believed.
Showing the value of going over old data, University of Arizona astronomer Erich Karkoschka reprocessed old images of Voyager 2 data — including stacking 1,600 pictures on top of each other.
He found elements of Uranus’ atmosphere that reveals the southern hemisphere moves differently than other regions in fellow gas giants. Since only the top 1% of the atmosphere is easily observable from orbit, scientists try to make inferences about the 99% that lie underneath by looking at how the upper atmosphere behaves.
“Some of these features probably are convective clouds caused by updraft and condensation. Some of the brighter features look like clouds that extend over hundreds of kilometers,” he stated in a press release.
“The unusual rotation of high southern latitudes of Uranus is probably due to an unusual feature in the interior of Uranus,” he added. “While the nature of the feature and its interaction with the atmosphere are not yet known, the fact that I found this unusual rotation offers new possibilities to learn about the interior of a giant planet.”
It’s difficult to get more information about the inner atmosphere without sending down a probe, but other methods of getting a bit of information include using radio (which shows magnetic field rotation) or gravitational fields. The university stated that Karkoschka’s work could help improve models of Uranus’ interior.
So that was Uranus three decades ago. What about today? Turns out that storms are popping up on Uranus that are so large that for the first time, amateur astronomers can track them from Earth. A separate study on Uranus shows the planet is “incredibly active”, and what’s more, it took place at an unexpected time.
Summer happened in 2007 when the Sun shone on its equator, which should have produced more heat and stormy weather at the time. (Uranus has no internal heat source, so the Sun is believed to be the primary driver of energy on the planet.) However, a team led by Imke de Pater, chair of astronomy at the University of California, Berkeley, spotted eight big storms in the northern hemisphere while looking at the planet with the Keck Telescope on Aug. 5 and 6.
Keck’s eye revealed a big, bright storm that represented 30% of light reflected by the planet at a wavelength of 2.2 microns, which provides information about clouds below the tropopause. Amateurs, meanwhile, spotted a storm of a different sort. Between September and October, several observations were reported of a storm at 1.6 microns, deeper in the atmosphere.
“The colors and morphology of this [latter] cloud complex suggests that the storm may be tied to a vortex in the deeper atmosphere similar to two large cloud complexes seen during the equinox,” stated Larry Sromovsky, a planetary scientist at the University of Wisconsin, Madison.
What is causing the storms now is still unknown, but the team continues to watch the Uranian weather to see what will happen next. Results from both studies were presented at the Division for Planetary Sciences meeting of the American Astronomical Society in Tucson, Arizona today. Plans for publication and whether the research was peer-reviewed were not disclosed in press releases concerning the findings.
Nothing stands still. Everything evolves. So why shouldn’t Saturn’s kookie, clumpy F ring put on a new face from time to time?
A recent NASA-funded study compared the F ring’s appearance in six years of observations by the Cassini mission to its appearance during the Saturn flybys of NASA’s Voyager mission, 30 years earlier.
While the F ring has always displayed clumps of icy matter, the study team found that the number of bright clumps has nose-dived since the Voyager space probes saw them routinely during their brief flybys 30 years ago. Cassini spied only two of the features during a six-year period.
Scientists have long suspected that moonlets up to 3 miles (5 km) wide hiding in the F ring are responsible for its uneven texture. Kinks and knots appear and disappear within months compared to the years of observation needed changes in many of the other rings.
“Saturn’s F ring looks fundamentally different from the time of Voyager to the Cassini era,” said Robert French of the SETI Institute in Mountain View, California, who led the study along with SETI Principal Investigator Mark Showalter. “It makes for an irresistible mystery for us to investigate.”
Because the moonlets lie close to the ring and cross through it every orbit, the research team hypothesizes that the clumps are created when they crash into and pulverize smaller ring particles during each pass. They suspect that the decline in the number of exceptionally bright kinks and the clumps echoes a decline in the number of moonlets available to do the job.
So what happened between Voyager and Cassini? Blame it on Prometheus. The F ring circles Saturn at a delicate point called the Roche Limit. Any moons orbiting closer than the limit would be torn apart by Saturn’s gravitational force.
“Material at this distance from Saturn can’t decide whether it wants to remain as a ring or coalesce to form a moon,” said French. “Prometheus orbits just inside the F ring, and adds to the pandemonium by stirring up the ring particles, sometimes leading to the creation of moonlets, and sometimes leading to their destruction.”
Every 17 years the orbit of Prometheus aligns with the orbit of the F ring in a way that enhances its gravitational influence. The researchers think the alignment spurs the creation of lots of extra moonlets which then go crashing into the ring, creating bright clumps of material as they smash themselves to bits against other ring material.
Sounds like a terrifying version of carnival bumper cars. In this scenario, the number of moonlets would gradually drop off until another favorable Prometheus alignment.
The Voyagers encounters with Saturn occurred a few years after the 1975 alignment between Prometheus and the F ring, and Cassini was present for the 2009 alignment. Assuming Prometheus has been “working” to build new moons since 2009, we should see the F ring light up once again with bright clumps in the next couple years.
Never seen Neptune? Now is a good time to try, as the outermost ice giant world reaches opposition this weekend at 14:00 Universal Time (UT) or 10:00 AM EDT on Friday, August 29th. This means that the distant world lies “opposite” to the Sun as seen from our Earthly perspective and rises to the east as the Sun sets to the west, riding high in the sky across the local meridian near midnight.
2014 finds Neptune shining at magnitude +7.6 in the constellation of Aquarius. Unfortunately, the planet is too faint to be seen with the naked eye, but can be sighted using a good pair of binoculars if know exactly where to look for it. Though the telescope, Neptune exhibits a tiny blue-gray disk 2.4” across — 750 “Neptunes” would fit across the apparent diameter of the Full Moon — that’s barely discernible. Don’t be afraid to crank up the magnification in your quest. We’ve found Neptune on years previous by patently examining suspect stars one by one, looking for the one in the field that stubbornly refuses to focus to a star-like point. Make sure your optics are well collimated to attempt this trick. Neptune will exhibit a tiny fuzzy disk, much like a second-rate planetary nebula. In fact, this is where “planetaries” get their moniker, as the pesky deep sky objects resembled planets in those telescopes of yore…
The 1846 discovery of Neptune stood as a vindication of the (then) new-fangled theory of Newtonian gravitational dynamics. Uranus was discovered just decades before by Sir William Hershel in 1781, and it stubbornly refused to follow predictions concerning its position. French astronomer Urbain Le Verrier correctly assumed that an unseen body was tugging on Uranus, predicted the position of the suspect object in the sky, and the race was on. On the night of September 24th, Heinrich Louis d’Arrest and Johann Gottfried Galle observing from the Berlin observatory became the first humans to gaze upon the new world referring to it as such. Did you know: Galileo actually sketched Neptune near Jupiter in 1612? And those early 18th century astronomers got a lucky break… had Neptune happened to have been opposite to Uranus in its orbit, it might’ve eluded discovery for decades to come!
It’s also sobering to think that Neptune has only recently completed a single orbit of the Sun in 2011 since its discovery. Opposition of Neptune occurs once every 368 days, meaning that opposition is slowly moving forward by about three days a year on our Gregorian calendar and will soon start occurring in northern hemisphere Fall.
Now for the “wow factor” of what you’re actually seeing. Though tiny, Neptune is actually 24,622 kilometres in radius, and is 58 times as big as the Earth in volume and over 17 times as massive. Neptune is 29 A.U.s or 4.3 billion kilometres from Earth at opposition, meaning the light we see took almost four hours to transit from Neptune to your backyard.
Neptune is currently south of the equator, and won’t be north of it again until 2027.
Next month, keep an eye on Neptune as it passes less than half a degree north of the +4.8 magnitude star Sigma Aquarii through mid-September, making a great guide to find the planet…
Still not enough of a challenge? Try tracking down Neptune’s large moon, Triton. Orbiting the planet in a retrograde path once every 5.9 days, Triton is within reach of a large backyard scope at magnitude +14. Triton never strays more than 15” from the disk of Neptune, but opposition is a great time to cross this curious moon off of your observing life list. Neptune has 14 moons at last count.
And speaking of Triton, NASA recently released a new map of the moon. We’ve only gotten one good look at Triton, Neptune, and its retinue of moons back in 1989 when Voyager 2 conducted the only flyby of the planet to date. Will Pluto turn out to be Triton’s twin when New Horizons completes its historic flyby next summer?
The Moon also passes 4.3 degrees north of Neptune on September 8th on its way to “Supermoon 3 of 3” for 2014 on the night of September 8th/9th. Fun fact: a cycle of occultations of Neptune by the Moon commences on June 2016.
When will we explore Neptune once more? Will a dedicated “Neptune orbiter” ever make its way to the planet in our lifetimes? All fun things to ponder as you check out the first planet discovered using scientific reasoning this weekend.
Talk about recycling! Twenty-five years after Voyager 2 zinged past Neptune’s moon Triton, scientists have put together a new map of the icy moon’s surface using the old data. The information has special relevance right now because the New Horizons spacecraft is approaching Pluto fast, getting to the dwarf planet in less than a year. And it’s quite possible that Pluto and Triton will look similar.
Triton has an exciting history. Scientists believed it used to be a lone wanderer until Neptune captured it, causing tidal heating that in turn created fractures, volcanoes and other features on the surface. While Triton and Pluto aren’t twins — this certainly didn’t happen to Pluto — Pluto also has frozen volatiles on its surface such as carbon monoxide, methane and nitrogen.
What you see in the map is a slightly enhanced version of Triton’s natural colors, bearing in mind that Voyager’s sensors are a little different from the human eye. Voyager 2 only did a brief flyby, so only about half the planet has been imaged. Nonetheless, the encounter was an exciting time for Paul Schenk, a planetary scientist at the Lunar and Planetary Institute in Houston. He led the creation of the new Triton map, and wrote about the experience of Voyager 2 in a blog post.
“Triton is a near twin of Pluto,” wrote Schenk. “Triton and Pluto are both slightly smaller than Earth’s Moon, have very thin nitrogen atmospheres, frozen ices on the surface (carbon monoxide, carbon dioxide, methane and nitrogen), and similar bulk composition (a mixture of ices, including water ice, and rock. Triton however was captured by Neptune long time ago and has been wracked by intense heating ever since. This has remade its surface into a tortured landscape of overturned layers, volcanism, and erupting geysers.”
He also added speculation about what will be seen at Pluto. Will it be a dead planet, or will geology still be affecting its surface? How close will Triton be to Pluto, particularly regarding its volcanoes? Only a year until we know for sure.