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The diameter of Neptune is approximately 49,500 km. This makes Neptune the 4th largest planet in the Solar System, after Jupiter, Saturn and Uranus.
I say approximately because the diameter of Neptune changes depending on where you measure it. Neptune is rotating on its axis, completing a full day once every 16 hours or so. This rapid rotation flattens Neptune out slightly so that the diameter measured from pole to pole is less than the equatorial diameter.
Neptune’s polar diameter is 48,682 km. While its equatorial diameter is 49,528 km. In other words, points on the equator are 423 km more distant from the center of Neptune than the poles.
Want some comparison? The diameter of Neptune is about 3.9 times the diameter of Earth.
We have written many stories about Neptune for Universe Today. Here’s an article about how Neptune’s south pole is the warmest part of the planet.
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A day on Neptune is 16 hours, 6 minutes and 36 seconds.
Wait, not so fast! Here’s the problem. Neptune isn’t a single solid object like the terrestrial planets, so different parts of the planet rotate at different speeds. This is a process that astronomers call differential rotation. Neptune’s equatorial zone takes about 18 hours to complete a rotation – that’s slower than the planet’s averate 16.1 hour rotation period. And the polar regions can take just 12 hours to rotate; much more quickly than the average.
This big difference in rotational rate between the equatorial regions and the planet’s poles means that Neptune has a strong latitudinal wind shear. This helps to generate the strongest winds in the Solar System. Astronomers have clocked winds on Neptune going as fast as 2,400 km/hour (1,500 miles/hour).
We have done several stories about Neptune on Universe Today. Here’s an article about movies of Neptune captured by Hubble. These show its rotation.
Neptune, captured by Voyager 2. Image credit: NASA
The color of Neptune is a bright azure blue. During its flyby in 1989, NASA’s Voyager 2 revealed the bright blue color, different from the pale blue color of Uranus. So why does Neptune have this color?
The answer to Neptune’s color comes from its cloud tops. The upper atmosphere of Neptune is made up of 80% hydrogen, 19% helium with a trace 1% amount of methane and other ices, like ammonia and water. Methane absorbs light at 600 nm, which is the red end of the spectrum of visible light.
Like all the planets in the Solar System, the light we see coming from Neptune is actually reflected light from the Sun. These methane clouds absorb the red end of the spectrum, and allow the blue end of the spectrum to bounce back out. So when you see the color of Neptune, you’re seeing reflected sunlight with the red light stripped out.
From a distance, Neptune looks just like a blue ball, but as you get closer you can see variations in its clouds. Lighter clouds of methane hang above the lower cloud deck. Powerful storms whip across the surface of Neptune; the fastest storms in the Solar System are on Neptune, with winds exceeding 2,400 km/hour. Neptune has a large dark storm, similar to the Great Red Spot on Jupiter.
Neptune, captured by Voyager. Image credit: NASA/JPL
The atmosphere of Neptune is similar to all the large planets in the Solar System; it mostly consists of hydrogen and helium, with trace amounts of methane, water, ammonia and other ices. But unlike the other gas planets in the Solar System, Neptune’s atmosphere has a larger proportion of the ices. It’s the methane in the planet’s upper atmosphere that give it its bright blue color.
At the highest altitudes, where the Neptune’s atmosphere touches space, it consists of about 80% hydrogen and 19% helium. There’s also a trace amount of methane. The light we see from Neptune is actually the reflected light from the Sun. Although the entire spectrum of light hits Neptune. This trace amount of methane absorbs light from the red end of the spectrum, while allowing the blue light to bounce back out. The color of Neptune’s atmosphere is brighter than Uranus, which has a similar atmosphere; astronomers aren’t sure why there’s such a dramatic color difference.
The upper level clouds on Neptune occur at the point where pressures are low enough for methane to condense. Astronomers have photographed these high altitude clouds forming shadows onto the lower cloud deck below. Deeper down inside Neptune, temperatures should get up to 0 C, where clouds of water might form.
As with the other planets, the atmosphere of Neptune is broken up into distinct bands of storms. In fact, the fastest moving winds in the Solar System occur at Neptune – winds have been clocked at 2,400 km/h (1,500 miles per hour). Some storms can grow large and remain for long periods of time. Neptune has its own Great Dark Spot, similar to the Great Red Spot on Jupiter.
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As part of her trip to England, Pamela had a chance to sit down with Oxford astrophysicist Chris Lintott and record an episode of Astronomy Cast. From the first stars to the newest planets, molecules and the chemistry that allows them to form affects all aspects of astronomy. While most astronomers group molecules into three bins of hydrogen, helium and everything else, there are a few who do proper chemistry by studying the sometimes complex molecules that form between the stars.
Moon imagery from two different cameras on Chandrayaan-1. Credit: ISRO
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India’s Chandrayaan-1 spacecraft has successfully sent back some of its first science data and images from the moon, but the spacecraft is also experiencing rising temperatures, and mission managers have decided to use the instruments sparingly to avoid overheating. Chandrayaan-1 is currently orbiting over the sunlit side of the moon, and a rise in temperatures inside the spacecraft was expected, but still is a cause for concern. “This rise and fall in temperature inside a satellite is a normal cyclical process,” Mylswamy Annadurai, project director of Chandrayaan-I, told a newspaper in India, The Indian Express. “There is nothing unusual about it. But since this is the first cycle being faced by Chandrayaan, we are being extra cautious. We have decided to wait till the temperatures dip to bring the mission into the operational phase.” As of now, all but two of the instruments onboard have been switched on and tested. But only one instrument at a time is being used, and the two inactive instruments won’t be turned on until engineers know spacecraft is cool enough.
But scientists released a very nice video from the Terrain Mapping Camera…
Here’s a link to the movie of images stitched together for a view of flying over the Moon. The videos at ISRO only works in Internet Explorer. Find the science images at ISRO’s site here.
During the current orbital phase the spacecraft is almost continually in the sun and experiencing ‘summer.’ The Moon also radiates heat as it receives energy from the sun. The spacecraft’s temperature is expected to stabilize by the end of December. Until then, scientists will use one instrument at a time, but hope to operate all instruments simultaneously by mid-January.
Chandrayaan-1 has a heater, which is capable of increasing the temperature during the ‘winter’ but there is no cooling mechanism. If temperatures start reaching the upper limit, there would be no option but to switch off all the instruments. Image from the TMC of the Moon's polar region. Credit: ISRO
The two instruments that haven’t been turned on yet are not only more sensitive to heat but also to high voltage. One is the Swedish sub-atomic reflecting analyzer (SARA), which will image the Moon’s permanently shadowed polar regions. The other is the Indian X-ray spectrometer, HEX, which will study radioactive emissions from the lunar surface.
“We thought it would be wise to wait for the temperature to go down before testing them,” Annadurai said. The extra-cautiousness on the part of mission scientists is only because this is Chandrayaan’s first experience with such phenomenon. “We are well within the upper limit of the spacecraft’s temperature bracket. But we want to remain in this comfort zone as it is our first experience,” Annadurai added.
Chandrayaan-1 carries 11 payloads, including a Terrain Mapping Camera (TMC), Hyper Spectral Imager (HySI), Lunar Laser Ranging Instrument (LLRI), High Energy X-ray Spectrometer (HEX), Moon Impact Probe (MIP), Chandrayaan-1 X-ray Spectrometer (C1XS), Smart Near-IR Spectrometer (SIR-2), Radiation Dose Monitor Experiment (RADOM), Sub Kev Atom reflecting Analyser (SARA), Miniature Synthetic Aperture Radar (MiniSAR) and Moon Mineralogy Mapper (M3).
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When we look at the Moon, we see a landscape shaped by impact craters. But scientists only discovered the true cause of crater in the last hundred years. Before that, they believed that there were many volcanoes on the Moon, and this is what caused the craters we see today.
Now we know that craters come from meteorite impacts, that still doesn’t answer the question: are there volcanoes on the Moon?
There used to be volcanoes on the Moon. The Moon is much smaller than the Earth. Although it was molten after its formation, it cooled down relatively rapidly. Scientists think that the Moon’s interior remained hot enough to produce magma for about a billion years after the Moon formed. The lava that came out of the Moon cooled quickly, and formed fine-grain, dark rocks called basalt. The Apollo astronauts sampled this material when they landed on the Moon.
When you look at the Moon, you see lighter and darker regions. The lighter regions are the mountainous highlands. The darker regions are vast “seas” of basalt lava that erupted out of the Moon billions of years ago.
Are there volcanoes on the Moon today?
There is recent evidence that there were volcanoes on the far side of the Moon much longer than on the near side. While the near side of the Moon shut down more than 3 billion years ago, there seems to be evidence that there were volcanoes on the surface of the Moon as recent as about a billion years ago.
Some researchers believe there are still vents that blast out volcanic gasses, but there are no longer active volcanoes on the Moon.
In an effort to bring the space news efforts from the Internet to the radio, I have my own little radio show every Wednesday!
I’ve been a regular guest on Paranormal Radio with Captain Jack (his awesome show will start immediately after mine, so stay tuned) for a few months now and it looks like they enjoy what I have to say and gave me this two hour slot each week!
I’m really excited about the possibilities this opens up as it is a great way to promote not only articles on the Universe Today and my space science blog Astroengine.com, but the whole space blogosphere. Key to this will be a regular slot for the Carnival of Space where a superb collection space news can be found on the finest space blogs. So, I hope to give the CoS good coverage each week, starting with the 80th week of the Carnival (I’m looking at you Ethan!)…
Keep up to date with the Astroengine Live schedule and how to listen in »
Astroengine Live actually started last week, but due to technical teething problems I was unable to archive the episode. If you did listen in, you would have heard me getting all excited about the possibilities for the International Space Station and the future of manned space flight, but I’ll be sure to give a quick run-down of last week’s show today.
I’m still trying to find my way with doing a live show and as the set-up is pretty basic at the moment (I can’t interview guests or have phone-ins), but this will change in the not-so-distant future.
So, if you fancy listening in today, the show starts at 4pm PST (7pm EST/midnight GMT).
To Listen Live:
Use your standard streaming audio player » Or visit WPRT Radio for more information »
Contact Me:
Send any emails about any space/science related news to: [email protected] and I’ll try to give it a mention!
Note: I also have my own theme tune! It’s based on Crystal Method’s “High Roller” that rocked anyway, but it’s now the foundation of Astroengine Live! So if anything, tune into the first 5 minutes to hear what the excellent WPRT team have created for me!
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Saturn’s moon Enceladus may indeed hide an underground reservoir of water. Scientists analyzed the plumes seen spewing from the moon with the Cassini spacecraft, and found water vapor and ice. “There are only three places in the solar system we know or suspect to have liquid water near the surface,” said Joshua Colwell Cassini team scientist from the University of Central Florida. “Earth, Jupiter’s moon Europa and now Saturn’s Enceladus. Water is a basic ingredient for life, and there are certainly implications there. If we find that the tidal heating that we believe causes these geysers is a common planetary systems phenomenon, then it gets really interesting.”
Using data from Cassini’s Ultraviolet Imaging Spectrograph (UVIS), the team’s findings support a theory that the plumes observed are caused by a water source deep inside Enceladus. An Earth analog is Lake Vostok in Antarctica, where liquid water exists beneath thick ice.
Scientists suggest that in Enceladus’s case, the ice grains would condense from the vapor escaping from the water source and stream through the cracks in the ice crust before heading into space. That’s likely what Cassini’s instruments detected in 2005 and 2007, the basis for the team’s investigation.
The team’s work also suggests that another hypothesis is unlikely. That theory predicts that the plumes of gas and dust observed are caused by evaporation of volatile ice freshly exposed to space when Saturn’s tidal forces open vents in the south pole. But the team found more water vapor coming from the vents in 2007 at a time when the theory predicted there should have been less.
Instead, their results suggest that the behavior of the geysers supports a mathematical model that treats the vents as nozzles that channel water vapor from a liquid reservoir to the surface of the moon. By observing the flickering light of a star as the geysers blocked it out, the team found that the water vapor forms narrow jets. The authors theorize that only high temperatures close to the melting point of water ice could account for the high speed of the water vapor jets.
Although there is no solid conclusion yet, there may be one soon. Enceladus is a prime target of Cassini during its extended Equinox Mission, underway now through September 2010. Cassini launched from the Kennedy Space Center in 1997 and has been orbiting Saturn since July 2004.
The team’s findings are reported in the Nov. 27 issue of the journal Nature.
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Seemingly, the current space shuttle mission, STS-126, has been all about two things: recycling and restoring. The crew has been working almost nonstop to get a new system that turns urine into drinking water to work correctly; and spacewalkers spent a majority of four grueling EVAs cleaning and lubricating a jammed solar-wing joint on the station’s right side. And now there’s good news to report on both fronts. The urine recycling system now seems to be working perfectly. “Not to spoil anything, but I think up here the appropriate words are ‘Yippee!'” space station commander Mike Fincke told ground controllers. Mission Control replied, “There will be dancing later.” The recycling system will be a necessity for supporting the International Space Station’s crew, which will increase from three to six in early 2009. Also essential will be enough power to support the larger crew, so having the SARJ working correctly, the Solar Alpha Rotary Joint which allows the solar arrays to track the sun, is more good news. After Endeavour astronauts worked on the giant gears and replaced bearing assemblies, initial tests found the starboard SARJ working well, with no power spikes or excessive vibrations. So, with the major hurdles on the mission being cleared, the astronauts will be able to enjoy an irradiated, freeze-dried, vacuum-packed Thanksgiving holiday meal on Thursday. And UT readers can now enjoy some of the great images from this mission in the gallery below.
Endeavour approaching ISS. Credit: NASA
The space station crew had this view of space shuttle Endeavour as it approached the ISS for docking. Visible in the payload bay is the Italian-built Leonardo Multipurpose Logistics Module, or cargo carrier. Playing with food. Credit: NASA
Fresh fruit is a rarity and a delicacy in space, and is one of the things the ISS crew enjoys the most during a shuttle visit. Here astronauts Shane Kimbrough and Sandra Magnus are pictured with fresh fruit floating freely on the middeck of Space Shuttle Endeavour. STS-126 EVA. Credit: NASA
Heidemarie Stefanyshyn-Piper and Steve Bowen work in tandem near a truss structure during one of four spacewalks conducted during the STS-126 mission. Astronauts install a new component. Credit: NASA
The shuttle crew brought up “home improvements” for the ISS and here, Greg Chamitoff and Sandy Magnus move a crew quarters rack in the Harmony node of the International Space Station. This will be a future crew member’s personal space and sleep station. Inside of Leonardo. Credit: NASA
A view inside the Leonardo Multipurpose Logistics Module, which carried up 14,000 lbs of supplies and new facilities for the space station including two water recovery systems racks for recycling urine into potable water, a second toilet system, new gallery components, two new food warmers, a food refrigerator, an experiment freezer, combustion science experiment rack, two separate sleeping quarters and a resistance exercise device. View of the ISS and solar arrays. Credit: NASA
Can you find the astronaut in this image? Spacewalker Steve Bowen is dwarfed by the station components and solar arrays in this view. Shuttle and station crews. Credit: NASA
Following a space-to-Earth press conference, members of the International Space Station and Space Shuttle Endeavour crews posed for a group portrait on the orbital outpost. Astronaut Donald Pettit appears at photo center. Just below Pettit is astronaut Heidemarie Stefanyshin-Piper. Clockwise from her position are astronauts Shane Kimbrough, Steve Bowen, Eric Boe, Chris Ferguson and Michael Fincke, along with cosmonaut Yury Lonchakov, and astronauts Sandra Magnus and Gregory Chamitoff. Another EVA view. Credit: NASA
One more EVA picture for you. Here Steve Bowen works during the mission’s fourth and final EVA as maintenance continueson the International Space Station. During the six-hour spacewalk, Bowen and astronaut Shane Kimbrough (not visible), completed the lubrication of the port Solar Alpha Rotary Joints (SARJ) as well as other station assembly tasks. Bowen returned to the starboard SARJ to install the final trundle bearing assembly, retracted a berthing mechanism latch on the Japanese Kibo Laboratory and reinstalled its thermal cover. Bowen also installed a video camera on the Port 1 truss and attached a Global Positioning System antenna on the Japanese Experiment Module Pressurized Section.
