The "surface" of Neptune, its uppermost layer, is one of the most turbulent and active places in the Solar System. Credit: NASA/JPL
How did Neptune get its name? Shortly after its discovery, Neptune was only referred to as “the planet exterior to Uranus” or as “Le Verrier’s planet”. The first suggestion for a name came from Johann Galle, who proposed the name Janus. Another proposal was Oceanus. Urbain Le Verrier, who discovered the planet, claimed the right to name his discovery: Neptune. Soon Neptune became the internationally accepted name.
In roman mythology, Neptune was the god of the sea. The demand for a mythological name seemed to be in keeping with the nomenclature of the other planets, all of which, except for Earth, were named for Greek and Roman mythology. Most languages today use some variant of the name “Neptune” for the planet.
Now that you know how the planet was named, how about some facts about the planet itself. Size wise, the planet has an equatorial radius 24,764 km, a polar radius of 24,341 km, and a surface area of 7.6408×10,sup>9km2. It has a volume of 6.254×1013km3, a mass of 1.0243×1026kg, and a mean density of 1.638 g/cm3.
Its atmosphere is composed primarily of hydrogen and helium along with traces of hydrocarbons and nitrogen. It also contains a high proportion of ices like: water, ammonia, and methane. Astronomers occasionally categorize Neptune as an ice giant. The interior of Neptune is primarily composed of ices and rock. Traces of methane in the outermost regions account for the planet’s blue appearance. Neptune’s atmosphere is notable for its active and visible weather patterns. These weather patterns are driven by the strongest sustained winds of any planet in the Solar System, with recorded wind speeds as high as 2,100 km/h.Because of its great distance from the Sun, Neptune’s outer atmosphere is one of the coldest places in the Solar System, with temperatures at its cloud tops approaching ?218°C. Temperatures at the planet’s center are approximately 5,000°C. Neptune is one of the most interesting planets in our solar system. There are plenty of other articles about the planet here on Universe Today.
We have written many articles about Neptune for Universe Today. Here’s an article about the size of Neptune, and here’s an article about the atmosphere of Neptune.
Infrared image of Neptune from Keck Observatory in Hawaii. Credit: Mike Brown/CalTech
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The confessed (and remorseless) “Pluto Killer” Mike Brown has turned his gaze – and the 10-meter telescope at the Keck Observatory in Hawaii – on Neptune, our solar system’s furthest “official” planet. But no worries for Neptune – Mike isn’t after its planetary status… he’s taken some beautiful infrared images instead!
Normally only visible as a featureless blue speck in telescopes, Brown’s image of Neptune — along with its largest moon Triton — shows the icy gas giant in infrared light, glowing bright red and orange.
Neptune and Triton in infrared. Credit: Mike Brown/CalTech.
Brown’s initial intention was not just to get some pretty pictures of planets. The target of the imaging mission was Triton and to learn more about the placement of its methane, nitrogen and seasonal frosts, and this sort of research required infrared imaging. Of course, Neptune turned out to be quite photogenic itself.
“The big difference is doing the imaging in the infrared where methane absorbs most of the photons,” said Brown. “So the bright places are high clouds where the sunlight reflects off of them before it had a chance to pass through much of the atmosphere. Dark is clear atmosphere full of methane absorption.
“I just thought it was so spectacular that I should post it.”
No argument here, Mike!
Neptune, now officially the outermost planet in our solar system, is the fourth largest planet and boasts the highest wind speeds yet discovered — 1,250 mph winds scream around its frigid skies! Like the other gas giants Neptune has a system of rings, although nowhere near as extravagant as Saturn’s. It has 13 known moons, of which Triton is the largest.
With its retrograde orbit, Triton is believed to be a captured Kuiper Belt Object now in orbit around Neptune. Kuiper Belt Objects are Mike Brown’s specialty, as he is the astronomer most well-known for beginning the whole process that got Pluto demoted from the official planet list back in 2006.
Jason Major is a graphic designer, photo enthusiast and space blogger. Visit his website Lights in the Dark and follow him on Twitter @JPMajor or on Facebook for the most up-to-date astronomy awesomeness!
Four images of Neptune taken a few hours apart by the Hubble Space Telescope on June 25-26, 2011. Credit: NASA, ESA and the Hubble Heritage Team (STScI/AURA)
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To celebrate the first complete orbit of the planet Neptue since its discovery in 1846, the Hubble Space Telescope took a series of images with the Wide Field Camera 3, showing the different faces of the planet as it rotates on its axis. The images were take on June 25-26, 2011.
Even with a telescope as powerful as Hubble, the planet still appears fairly small, but some details are visible. While its blue color is the most distinctive feature, the turbulent conditions in the planet’s atmosphere also show up. Neptune’s thick atmosphere is largely made up of hydrogen and helium and is thought to host the Solar System’s most furious storms, with winds of up to 2000 km/h.
See more about Neptune and these images from ESA’s Hubble page (including access to wallpaper-sized images) and tead more about Neptune’s discovery and anniversary in our article by Tammy Plotner.
Editor’s note: We all want to explore other worlds in our solar system, but perhaps you haven’t considered the bizarre weather you’d encounter — from the blistering hurricane-force winds of Venus to the gentle methane rain showers of Saturn’s giant moon Titan. Science journalist Michael Carroll has written a guest post for Universe Today which provides peek at the subject matter for his new book, “Drifting on Alien Winds: Exploring the Skies and Weather of Other Worlds.”
It’s been a dramatic year for weather on Earth. Blizzards have blanketed the east coast, crippling traffic and power grids. Cyclone Tasha drenched Queensland, Australia as rainfall swelled the mighty Mississippi, flooding the southern US. Eastern Europe and Asia broke high temperature records. But despite these meteorological theatrics, the Earth’s conditions are a calm echo of the weather on other worlds in our solar system.
Take our nearest planetary neighbor, Venus. Nearly a twin of Earth in size, Venus displays truly alien weather. The hurricane-force Venusian winds are ruled not by water (as on Earth), but by battery acid. Sunlight tears carbon dioxide molecules (CO2) apart in a process called photodissociation. Leftover bits of molecules frantically try to combine with sulfur and water to become chemically stable, resulting acid hazes. Temperatures soar to 900ºF at the surface, where air is as dense as the Earthly oceans at a depth of X feet.
Venus is the poster child of comparative planetology, the study of other planets to help us understand our own. Earth’s simmering sibling has taught us about greenhouse gases, and gave us an even more immediate cautionary tale in 1978. The Pioneer Venus orbiter discovered that Venus naturally generates chlorofluorocarbons (CFCs) in its atmosphere. These CFCs were tearing holes in the planet’s ozone. At the same time, a wide variety of industries were preparing to use CFCs in insecticides, spray paints, and other aerosol products. Venus presented us with a warning that may have averted a planet-wide crisis.
In the same way, Mars has provided insights into long-term climate change. Its weather is a simplified version of our own. Locked within its rocks and polar caps lie records of changing climate over eons.
But fans of really extreme weather must venture further out, to the outer planets. Jupiter and Saturn are giant balls of gas with no solid surface, and are known as the “gas giants.” They are truly gigantic: over a thousand Earths could fit within Jupiter itself.
The skies of Jupiter and Saturn are dominated by hydrogen and helium, the ancient building blocks of the solar system. Ammonia mixes in to produce a rich brew of complex chemistry, painting the clouds of Jupiter and Saturn in tans and grays. Lightning bolts sizzle through the clouds, powerful enough to electrify a small city for weeks. Ammonia forms rain and snow in the frigid skies. Jupiter’s Great Red Spot is a centuries-old cyclone large enough to swallow three Earths. Saturn has its own bizarre storms: a vast hexagon-shaped trough of clouds races across the northern hemisphere. Over the south pole, a vast whirlpool gazes from concentric clouds like a Cyclops.
Beyond Jupiter and Saturn lie the “ice giants”, Uranus and Neptune. These behemoths host atmospheres of poisonous brews chilled to cryogenic temperatures. Methane tints Uranus and Neptune blue. Neptune’s clear air reveals a teal cloud deck. Hydrocarbon hazes tinge Uranus to a paler shade of blue-green. Neptune’s clear air is somewhat of a mystery to scientists. This may be because cloud-forming particles can’t stay airborne long enough to become visible clouds. Some scientists propose that Neptune’s abundant methane rains may condense so rapidly that within a few seconds tiny methane raindrops swell to something the size of a beachball. There are no clouds adrift, because methane rains out of the atmosphere too quickly.
One of the strangest cases of bizarre weather comes to us from Neptune’s moon Triton. Triton’s meager nitrogen air is tied to the freezing and thawing of polar ices, also composed of nitrogen. Triton’s entire atmosphere collapses twice a year, when it’s winter on one of the poles. At that time of year, all of Triton’s air migrates to the winter pole, where it freezes to the ground. The moon only has “weather” during the spring and fall; its atmosphere exists only during those seasons.
So, the next time you contemplate complaining about the heat, think of Venus. And if it’s blizzards you worry about, find comfort in Triton: at least our atmosphere doesn’t disappear in winter!
An 'overhead' view of New Horizons' location. Credit: NASA
The Pluto-bound New Horizons spacecraft will fly by another planet today (March 18, 2011). However, the robotic craft won’t be taking any images as it zooms past Uranus’ orbit at about 6 p.m. EDT, 3.8 billion kilometers (2.4 billion miles) away from the gas giant (and 2.0 billion km (1.8 billion miles) from Earth). New Horizons is currently in hibernation mode, and the great distance from Uranus means any observations wouldn’t provide much as far as data and images. But, even so, this event is a ‘landmark’ so to speak in New Horizon’s gauntlet across the solar system.
“New Horizons is all about delayed gratification, and our 9 1/2-year cruise to the Pluto system illustrates that,” said Principal Investigator Alan Stern, of the Southwest Research Institute. “Crossing the orbit of Uranus is another milepost along our long journey to the very frontier of exploration.”
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New Horizons is now well over halfway through its journey to Pluto. Motoring along at 57,900 km/hr (36,000 mph), it will travel more than 4.8 billion km (3 billion miles) to fly past Pluto and its moons Nix, Hydra and Charon in July 2015.
But the journey doesn’t end there. After that, New Horizons will head off to a post-Pluto encounter with other objects within the Kuiper Belt, some event(s) which might take place even into the 2020’s. The planetary science community is working on the selection of potential targets.
The mission still has more than 4 years to go to get to Pluto; it will take 9 nine months to send all the data back to Earth.
The next planetary milestone for New Horizons will be the orbit of Neptune, which it crosses on Aug. 25, 2014, exactly 25 years after Voyager 2 made its historic exploration of that giant planet.
“This mission is a marathon,” says Project Manager Glen Fountain, of the Johns Hopkins University Applied Physics Laboratory. “The New Horizons team has been focused on keeping the spacecraft on course and preparing for Pluto. So far, so good, and we are working to keep it that way.”
Neptune is more than just the 8th planet in our solar system; it is a celestial reminder of the power that mathematics grants us.
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There are many ways to determine ‘how big is Neptune’. It has an equatorial radius 24,764 km, a polar radius of 24,341 km, and a surface area of 7.6408×10,sup>9km2. It has a volume of 6.254×1013km3, a mass of 1.0243×1026kg, and a mean density of 1.638 g/cm3. Now that you know most of the planet’s critical digits, here is a little information about its make up.
Neptune is the eighth and farthest planet from the Sun. It is the fourth-largest planet by diameter and the third-largest by mass. Neptune’s mass is 17 times that of the Earth. On average, Neptune orbits the Sun at a distance of 30.1 astronomical units. It was discovered on September 23, 1846. Neptune was the first planet found by mathematical prediction rather than direct observation. Alexis Bouvard deduced its existence from gravitational perturbations in the orbit of Uranus. The planet was later observed by Johann Galle. Its largest moon, Triton, was observed a short time later.
Neptune’s atmosphere is composed primarily of hydrogen and helium along with traces of hydrocarbons and nitrogen. It also contains a high proportion of ices like: water, ammonia, and methane. Astronomers occasionally categorize Neptune as an ice giant. The interior of Neptune, like that of Uranus, is primarily composed of ices and rock. Traces of methane in the outermost regions in part account for the planet’s blue appearance. Neptune’s atmosphere is notable for its active and visible weather patterns. When Voyager 2 flew by the planet’s southern hemisphere possessed a Great Dark Spot. These weather patterns are driven by the strongest sustained winds of any planet in the Solar System, with recorded wind speeds as high as 2,100 km/h.Because of its great distance from the Sun, Neptune’s outer atmosphere is one of the coldest places in the Solar System, with temperatures at its cloud tops approaching ?218°C. Temperatures at the planet’s center are approximately 5,000°C.
Neptune has a planetary ring system. The rings may consist of ice particles coated with silicates or carbon-based material, which gives them a reddish hue. The three main rings are the narrow Adams Ring, 63,000 km from the center of Neptune, the Le Verrier Ring, at 53,000 km, and the broader, fainter Galle Ring, at 42,000 km. A faint outward extension to the Le Verrier Ring has been named Lassell; it is bounded at its outer edge by the Arago Ring at 57,000 km. Not only is the planet large, but it has many interesting features as well.
We have written many articles about Neptune for Universe Today. Here’s an article about the color of Neptune, and here are some pictures of Neptune.
Illustration of a primordial Kuiper Belt binary during a close approach with the planet Neptune, similar to the encounters studied by Parker and Kavelaars. Credit: University of Victoria
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A very popular explanation for the dynamical evolution of our solar system is being challenged by a new model that takes the blame away from Neptune for knocking a collection of planetoids known as the Cold Classical Kuiper Belt out to their current, distant home. PhD student Alex Parker from the University of Victoria in British Columbia, Canada presented evidence showing that the large population of binary objects in the Kuiper Belt gives witness to a different series of events than the Nice Model – which says Neptune’s migrations were responsible for a sending KBO’s into chaotic orbits. “Kuiper binaries paint a different picture,” Parker said during a press briefing at the American Astronomical Society’s Division of Planetary Sciences meeting this week. “I should title my talk as ‘Neptune not guilty of harassment’ or perhaps more accurately, “Planet Neptune acquitted of one count of harassment.’”
The Nice Model holds that the objects in the scattered Kuiper Belt were placed in their current positions by interactions with Neptune’s migrating resonances. Originally, the Model says, the Kuiper belt was much denser and closer to the Sun, with an outer edge at approximately 30 AU. Its inner edge would have been just beyond the orbits of Uranus and Neptune, which were in turn far closer to the Sun when they formed. As Neptune migrated outward, it approached the objects in the proto-Kuiper belt, capturing some of them into resonances and sending others into chaotic orbits.
But the survey of the Kuiper Belt being done by Parker and his thesis supervisor Dr. J. J Kavelaars (Herzberg Institute of Astrophysics), which has been running for a decade, tells a different story. “Thirty per cent of Kuiper Belt Objects are binaries, some in very wide orbits around each other in a slow waltz, weakly bound to their partners,” Parker said. “These binaries should have been destroyed if the Kuiper Belt Objects were thrown out of solar system.”
Since binaries are extremely common in the Kuiper Belt, they are useful tools for astronomers, said Parker. “Pluto and Charon are the most famous of these binaries and since their orbits can be affected by their environment, we can use them to test what the interplanetary environment is like and what it was like in the past.”
Diagram illustrating the process that destroys binaries during close encounters. Credit: University of Victoria
Using computer simulations, the researchers determined that many binary systems in part of the Belt would have been destroyed by the manhandling they would have experienced if Neptune did indeed move the Kuiper Belt to its current location.
The survey characterizes the orbits of these binaries and found that many are extremely wide – the widest one is about 100,000 km – and they are very delicate. “Because they are so weakly bound they can be upset by collisions from small objects peppering the KBOs,” said Parker, “and they would not be there today if the members of this part of the Kuiper Belt were ever hassled by Neptune in the past.”
Additionally, the current environment of the Kuiper Belt does not lend itself to the creation of these binaries, so they have been interacting with each other for a very long time. The research done by Parker and his colleagues suggest that the Kuiper Belt formed near its present location and has remained undisturbed over the age of the solar system.
The new model also solves the missing mass problem for the Kuiper Belt, Parker said. “The Nice Model – as well as all the other models of the formation of the Kuiper Belt — suggests its density was much higher so the binaries could be generated, but we don’t see that density today.”
The Cold Classical Kuiper Belt lies in a very flat ring between 6 and 7 billion kilometers from the Sun, and contains thousands of bodies larger than 100 kilometers across. The Kuiper Belt is of special interest to astrophysicists because it is a fossil remnant of the primordial debris that formed the planets, said Parker. “Understanding the structure and history of the Kuiper Belt helps us better understand how the planets in our solar system formed, and how planets around other stars may be forming today.”
It would be an interesting survey to catalog the initial reactions readers have to “Trojans”. Do you think first of wooden horses, or do asteroids spring to mind? Given the context of this website, I’d hope it’s the latter. If so, you’re thinking along the right lines. But how much do you really know about astronomical Trojans?
While most frequently used to discuss the set of objects in Jupiter’s orbital path that lie 60º ahead and behind the planet, orbiting the L4 and L5 Lagrange points, the term can be expanded to include any family of objects orbiting these points of relative stability around any other object. While Jupiter’s Trojan family is known to include over 3,000 objects, other solar system objects have been discovered with families of their own. Even one of Saturn’s moons, Tethys, has objects in its Lagrange points (although in this case, the objects are full moons in their own right: Calypso and Telesto).
In the past decade Neptunian Trojans have been discovered. By the end of this summer, six have been confirmed. Yet despite this small sample, these objects have some unexpected properties and may outnumber the number of asteroids in the main belt by an order of magnitude. However, they aren’t permanent and a paper published in the July issue of the International Journal of Astrobiology suggests that these reservoirs may produce many of the short period comets we see and “contribute a significant fraction of the impact hazard to the Earth.”
The origin of short period comets is an unusual one. While the sources of near Earth asteroids and long period comets have been well established, short period comets parent locations have been harder to pin down. Many have orbits with aphelions in the outer solar system, well past Neptune. This led to the independent prediction of a source of bodies in the far reaches by Edgeworth (1943) and Kuiper (1951). Yet others have aphelions well within the solar system. While some of this could be attributed to loss of energy from close passes to planets, it did not sufficiently account for the full number and astronomers began searching for other sources.
In 2006, J. Horner and N. Evans demonstrated the potential for objects from the outer solar system to be captured by the Jovian planets. In that paper, Horner and Evans considered the longevity of the stability of such captures for Jupiter Trojans. The two found that these objects were stable for billions of years but could eventually leak out. This would provide a storing of potential comets to help account for some of the oddities.
However, the Jupiter population is dynamically “cold” and does not contain a large distribution of velocities that would lead to more rapid shedding. Similarly, Saturn’s Trojan family was not found to be excited and was estimated to have a half life of ~2.5 billion years. One of the oddities of the Neptunian Trojans is that those few discovered thus far have tended to have high inclinations. This indicates that this family may be more dynamically excited, or “hotter” than that of other families, leading to a faster rate of shedding. Even with this realization, the full picture may not yet be clear given that searches for Trojans concentrate on the ecliptic and would likely miss additional members at higher inclinations, thus biasing surveys towards lower inclinations.
To assess the dangers of this excited population, Horner teamed with Patryk Lykawka to simulate the Neptunian Trojan system. From it, they estimated the family had a half life of ~550 million years. Objects leaving this population would then undergo several possible fates. In many cases, they resembled the Centaur class of objects with low eccentricities and with perihelion near Jupiter and aphelion near Neptune. Others picked up energy from other gas giants and were ejected from the solar system, and yet others became short period comets with aphelions near Jupiter.
Given the ability for this the Neptunian Trojans to eject members frequently, the two examined how many of the of short period comets we see may be from these reservoirs. Given the unknown nature of how large these stores are, the authors estimated that they could contribute as little as 3%. But if the populations are as large as some estimates have indicated, they would be sufficient to supply the entire collection of short period comets. Undoubtedly, the truth lies somewhere in between, but should it lie towards the upper end, the Neptunian Trojans could supply us with a new comet every 100 years on average.
New Horizons image of Neptune and its largest moon, Triton. June 23, 2010. Credit: NASA
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This summer, the New Horizons spacecraft was awoken for its annual systems checkout, and took the opportunity to exercise the long range camera by snapping pictures of Neptune, which at the time, was 3.5 billion km (2.15 billion miles) away. The Long Range Reconnaissance Imager (LORRI) snapped several photos of the gas giant, but Neptune was not alone! The moon Triton made a cameo appearance. And the New Horizons team said that since Triton is often called Pluto’s “twin” it was perfect target practice for imaging its ultimate target, Pluto.
This image gets us excited for 2015 when New Horizons will approach and make the closest flyby ever of Pluto.
“That we were able to see Triton so close to Neptune, which is approximately 100 times brighter, shows us that the camera is working exactly as designed,” said New Horizons Project Scientist Hal Weaver, of the Johns Hopkins Applied Physics Laboratory. “This was a good test for LORRI.”
Weaver pointed out that the solar phase angle (the spacecraft-planet-Sun angle) was 34 degrees and the solar elongation angle (planet-spacecraft-Sun angle) was 95 degrees. Only New Horizons can observe Neptune at such large solar phase angles, which he says is key to studying the light-scattering properties of Neptune’s and Triton’s atmospheres.
“As New Horizons has traveled outward across the solar system, we’ve been using our imagers to make just such special-purpose studies of the giant planets and their moons because this is a small but completely unique contribution that New Horizons can make — because of our position out among the giant planets,” said New Horizons Principal Investigator Alan Stern.
Triton is slightly larger than Pluto, 2,700 kilometers (1,700 miles) in diameter compared to Pluto’s 2,400 kilometers (1,500 miles). Both objects have atmospheres composed mostly of nitrogen gas with a surface pressure only 1/70,000th of Earth’s, and comparably cold surface temperatures approaching minus-400 degrees Fahrenheit. Triton is widely believed to have been a member of the Kuiper Belt (as Pluto still is) that was captured into orbit around Neptune, probably during a collision early in the solar system’s history.
This week Neptune will return to the spot where it was discovered in 1846, in the constellation Capricornus. The planet will complete its first orbit, since being discovered, in 2011. Credit: Starry Night Software, via Space.com
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Last week, Space.com had a great article about how on August 20, 2010, Neptune finally completed one orbit around the Sun since its discovery in 1846, and was now back to its original discovery position in the night sky . The original article was widely quoted, and created a lot of buzz on Twitter, Facebook and other websites. But then, later in the day some contradictory info came out, culminating with Bill Folkner, a technologist at JPL declaring via Twitter: “Neptune will reach the same ecliptic longitude it had on Sep. 23, 1846, on July 12, 2011.” Space.com ended up amending their article, but why the confusion? And could both statements be true? Depending on your perspective, perhaps yes.
“These apparently contradictory statements highlight the problems of defining planetary orbits,” astronomer Brian Sheen from the Roseland Observatory in the UK told Universe Today. “There are two ways of following the progress of a planet around the Sun/night sky.”
The first is from the perspective of being on planet Earth (specifically at the center of our planet) – called geocentric longitude, Sheen said, also known as right ascension.
The second is from the perspective of being on the Sun (specifically at the center of the Sun and indeed our solar system) which is called heliocentric longitude, and also ecliptic longitude.
“The orbital period of a planet is measured with reference to the heliocentric longitude, in the case of Neptune this is 164.8 years,” Sheen explained. “The problem of referencing via geocentric longitude is that the Earth itself is orbiting the Sun and therefore changing its relative position to the other planet, this case, Neptune.”
Neptune was discovered Sept 23, 1846. Adding 164.8 years to that date brings us to July 2011, and specifically 12th July. However taking the Earth’s motion into account we have a number of close approaches. Confusion about this situation is exacerbated by the fact that Neptune retrogrades at opposition.
And so, in April and July of this year (2010), Neptune came very close to returning to its apparent position in the sky at the time of its discovery (in geocentric right ascension and declination), actually much closer than it will be next year when it returns to its 1846 heliocentric longitude. It’s location at discovery and currently is in the constellation Capricornus.
But still, Neptune will not complete its first orbit since being discovered until in 2011.
“Given a discovery date of 23rd Sept 1846 and an orbital period of 164.8 years gives a return date of well into 2011 and a rough check gives 9-13 July,” Sheen said. “This accords well with the given date of 12th July.”
This gives us a celebration to look forward to in 2011!
