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How Big Is Neptune

Are There Oceans on Neptune

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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.

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We’ve also recorded an entire episode of Astronomy Cast all about Neptune. Listen here, Episode 63: Neptune.

Source: NASA

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Mysterious Ribbon at Edge of Solar System is Changing

A year ago, researchers from the IBEX mission – NASA’s Interstellar Boundary Explorer – announced the discovery of an unexpected bright band or ribbon of surprisingly high energy emissions at the boundary between our solar system and interstellar space. Now, after a year of observations, scientists have seen vast changes, including an unusual knot in the ribbon which appears to have ‘untied.’ Changes in the ribbon — a ‘disturbance in the force,’ so to speak, along with a shrunken heliosphere, may be allowing galactic cosmic rays to leak into our solar system.
Continue reading “Mysterious Ribbon at Edge of Solar System is Changing”

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What Galaxy Do We Live In?

If you are not an astronomy enthusiast you not have thought much about what galaxy do we live in. So depending on that the answer may surprise you. If you know anything about galaxies you know that they are groupings of stars that number in the hundreds of billions. The most famous is the Milky Way. It is from this galaxy that we even have the term. The simple point is that the Earth is part of the Milky Way even though if we see it in the sky it looks like we are observing it from the outside. Why is that? To understand you need to know exactly where we live in neighborhood of the Milky Way Galaxy.

As we are part of the solar system Earth pretty much follows the path of the sun as it goes through its own orbit around the galaxy. The Milky Way is a spiral galaxy type so it has arms sort of like an octopus. The Sun is located near the outward tip of the Sagittarius arm of the Milky Way. This makes Earth about 28,000 light years from the galactic core of our home galaxy.

The Solar System also has a galactic year that it follows. It takes around 200 million to 250 million years for the solar system to orbit the Sun. Another indicator of our position is where the galactic equator. While our star system is considered to be on the outskirts of the Milky Way this is only an estimate. It is believed that the Milky Way is larger than first estimated. There is also suspicion that our galaxy is in the process of absorbing other smaller galaxies. However, there is not enough empirical evidence available to support the claim.

So what would be so important about knowing what part of the galaxy we live in? One reason is space exploration. Some time in the future mankind may find a way to achieve faster than light space travel. This can provide a new set of challenges for engineers and astronomers to tackle. For example how would an astronaut keep from getting lost in space? Detailed mapping and computer programming in the future could help galactic wayfarers know where they are going and more importantly how to get home.

The other reason is that it never hurts to know our place in the scheme of things. Just thinking of the challenge of finding earth if we were so far way helps us to understand how truly vast the universe is.

We have written many articles about the Milky Way galaxy for Universe Today. Here are some facts about the Milky Way, and here’s an article about the closest galaxy to the Milky Way.

If you’d like more info on galaxies, check out Hubblesite’s News Releases on Galaxies, and here’s NASA’s Science Page on Galaxies.

We’ve also recorded an episode of Astronomy Cast about galaxies. Listen here, Episode 97: Galaxies.

Sources: SEDS, Daily Galaxy

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An Alien’s View of Our Solar System

We have just begun to try and image distant solar systems around other stars, and hopefully our techniques and technology will improve in the near future so that we can one day find — and take pictures of — planets as small as Earth. But what if another civilization from a distant star was looking at us? What would they see? A new supercomputer simulation tracking the interactions of thousands of dust grains show what our solar system might look like to alien astronomers searching for planets. It also provides a look back to how our planetary system may have changed and matured over time.

Continue reading “An Alien’s View of Our Solar System”

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Win ‘Star Walk’ and ‘Solar Walk’ Astronomy Apps

I’ve had a couple of people excitedly show me the Star Walk astronomy app on their iPhones and ipads, and it really is great. You can hold your device up to the sky and it will show you a sky map of your exact position. Move your device around the sky, and it moves with you. It is a very high quality, dynamic and realistic stargazing guide, which — if you are a beginning or experienced astronomer — makes skywatching easy for everybody! There is also a “Solar Walk” app — which has very cool 3D images, so grab your 3D glasses to fully enjoy. See more about this app below.
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Contest: Win “The Universe: Our Solar System” in Blu-ray


A new giveaway opportunity! This time it is the Blu-ray edition of The Universe: Our Solar System.

The Blu-ray edition of the History Channel’s The Universe consists of 10 episodes from the first season, and uses cutting-edge computer-generated imagery to bring distant planets and faraway stars up close. We’ve long been fascinated with the sky and outerspace, and in this series, history and science collide to investigate all we know about the Universe.

To win, send an email to [email protected] with “Solar System” in the subject line. Fraser will randomly pick one email as the winner. Deadline is Monday, August 30 at 12 pm PDT.

Find out about The Universe: Our Solar System at this link.

And by the way, the winner of the new book about the Sloan Digital Sky Survey, “The Grand and Bold Thing” by Ann Finkbeiner, was Irfaan Hamdulay from Cape Town, South Africa. Congrats!

This is a two-disc set:

DISC 1: Secrets of the Sun / Mars: The Red Planet / The End of the Earth: Deep Space Threats To Our Planet / Jupiter: The Giant Planet / The Moon

DISC 2: Spaceship Earth / The Inner Planets: Mercury & Venus / Saturn: Lord of the Rings / Alien Galaxies / Life and Death of a Star

In this series you can witness the sun’s birth at the dawn of our solar system, and its death, billions of years in the future; explore the possibility of a human settlement on Mars; and learn about the devastating threats posed by the meteorites, comets, and asteroids that routinely collide with Earth.

Each of the 44-minute episodes begins with a general introduction of subjects ranging from the sun to individual planets. Each topic is then broken down into a series of segments that detail specific ideas, theories, or components integral to the understanding of the main topic as well as historical material, current studies and theories, and projections of potential future events and scientific advances.

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Our Solar System: Now 2 Million Years Older

Why Do Planets Orbit the Sun

Our solar system is beautiful and aging gracefully, but it might be even older than we originally thought, by as much as 2 million years. A group of scientists analyzed lead isotopes within a 1.49-kilo (3.2-pound) meteorite found in the Moroccan desert in 2004 and found evidence that suggests the mineral was formed 4.56 billion years ago, making the meteorite the oldest object ever found. This finding is between 300,000 and 1.9 million years older than previous estimates.

Marking the age of the Solar System has been defined as the time of formation of the first solid grains in the nebular disc surrounding the proto-Sun, and this has been done previously dating calcium–aluminium-rich inclusions in meteorites.

The team, led by Audrey Bouvier and Meenakshi Wadhwa of Arizona State University’s the Center for Meteorite Studies, looked at the extent to which uranium-238 and uranium-235 isotopes had decayed into their daughter isotopes lead-207 and lead-206.

Previous studies that dated the solar system looked at the Efremovka and Allende meteorites found in Kazakhstan in 1962 and Mexico in 1969, respectively.

While the timing may not seem like a big difference for something that is billions of years old, Bouvier said in New Scientist that it could make a difference when pinning down the conditions that led to the solar system’s formation, and those needed for other life-friendly planetary systems to form.

Their study was published by the journal Nature Geoscience.

Nature paper: Bouvier, A. & Wadhwa, M. Nature Geosci. advance online publication doi:10.1038/NGEO941 (2010).

Sources: New Scientist, PhysOrg

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Clockwork Planets

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While the Perseid meteor shower has been putting on quite a show, there’s an awesome “no telescope needed” eye-catching apparition that only requires a clear western skyline. If you haven’t been watching the planets – Mercury, Saturn, Venus and Mars – line up like clockwork, then don’t despair. You have a few more days yet!

While the uniformed all-too-often see “signs of bad portent” in a planetary alignment, the rest of us know this is a perfectly normal function of our solar system called a conjunction. This is a simple positional alignment as seen (usually from Earth’s viewpoint) from any given vantage point. The world isn’t going to end, the oceans aren’t going to rise… and Mars is darn-sure not going to be the size of the Moon. All alignments of at least two celestial bodies are merely coincidental and we even have a grand name for what’s happening – an appulse.

When planets are involved, their near appearance usually happens in the same right ascension. They really aren’t any closer to each other than what their orbital path dictates – it just appears that way. In the same respect, there is also conjunction in ecliptical longitude. But, if the planet nearer the Earth should happen to pass in front of another planet during a conjunction it’s called a syzygy!

One thing is for sure… You don’t have to be a syzy-genius to simply enjoy the show and the predictable movements of our solar system. Just find an open western skyline and watch as twilight deepens. Tonight the Moon will be directly south of Venus and over the next couple of days the planetary alignment will gradually separate as brilliant Venus seems to hold its position, while Mars, Saturn and Mercury drift north. Enjoy the show! Because just like the yearly Mars/Moon Myth?

It happens like clockwork…

Many, many thanks to the incredible Shevill Mathers for providing us with this breathtaking photo. (Do you know just how hard it is to get a shot like that without over or under exposing? I dare you to try it…) Every fox has a silver lining!

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The Earth and Moon May Have Formed Later Than Previously Thought

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The Earth and Moon were created as the result of a giant collision between two planets the size of Mars and Venus. Until now it was thought to have happened when the solar system was 30 million years old or approximately 4.5 billion years ago. But new research shows that the Earth and Moon may have formed much later – perhaps up to 150 million years after the formation of the solar system.

“We have determined the ages of the Earth and the Moon using tungsten isotopes, which can reveal whether the iron cores and their stone surfaces have been mixed together during the collision,” said Tais W. Dahl, from the Niels Bohr Institute at the University of Copenhagen in collaboration with professor David J. Stevenson from the California Institute of Technology (Caltech).

The planets in the solar system were created by collisions between planetary embryos orbiting the newborn sun. In the collisions the small planets congealed together and formed larger and larger planets. When the gigantic collision occurred that ultimately formed the Earth and Moon, it happened at a time when both planetary bodies had a core of metal (iron) and a surrounding mantle of silicates (rock). But when did it happen and how did it happen? The collision took place in less than 24 hours and the temperature of the Earth was so high (7000º C), that both rock and metal must have melted in the turbulent collision. But were the stone mass and iron mass also mixed together?

The age of the Earth and Moon can be dated by examining the presence of certain elements in the Earth’s mantle. Hafnium-182 is a radioactive substance, which decays and is converted into the isotope tungsten-182. The two elements have markedly different chemical properties and while the tungsten isotopes prefer to bond with metal, hafnium prefers to bond to silicates, i.e. rock.

It takes 50-60 million years for all hafnium to decay and be converted into tungsten, and during the Moon forming collision nearly all the metal sank into the Earth’s core. But did all the tungsten go into the core?

“We have studied to what degree metal and rock mix together during the planet forming collisions. Using dynamic model calculations of the turbulent mixing of the liquid rock and iron masses we have found that tungsten isotopes from the Earth’s early formation remain in the rocky mantle,” said Tahl.

The new studies imply that the moon forming collision occurred after all of the hafnium had decayed completely into tungsten.

“Our results show that metal core and rock are unable to emulsify in these collisions between planets that are greater than 10 kilometers in diameter and therefore that most of the Earth’s iron core (80-99 %) did not remove tungsten from the rocky material in the mantle during formation” said Dahl.

The result of the research means that collision that created the Earth and the Moon may have occurred as much as 150 million years after the formation of the solar system, much later than the 30 million years that was previously thought.

The research results have been published in the scientific journal, Earth and Planetary Science Letters.

From a University of Copenhagen press release.

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Astronomy Without A Telescope – The Nice Way To Build A Solar System

When considering how the solar system formed, there are a number of problems with the idea of planets just blobbing together out of a rotating accretion disk. The Nice model (and OK, it’s pronounced ‘niece’ – as in the French city) offers a better solution.

In the traditional Kant/Laplace solar nebula model you have a rotating protoplanetary disk within which loosely associated objects build up into planetesimals, which then become gravitationally powerful centres of mass capable of clearing their orbit and voila planet!

It’s generally agreed now that this just can’t work since a growing planetesimal, in the process of constantly interacting with protoplanetary disk material, will have its orbit progressively decayed so that it will spiral inwards, potentially crashing into the Sun unless it can clear an orbit before it has lost too much angular momentum.

The Nice solution is to accept that most planets probably did form in different regions to where they orbit now. It’s likely that the current rocky planets of our solar system formed somewhat further out and have moved inwards due to interactions with protoplanetary disk material in the very early stages of the solar system’s formation.

It is likely that within 100 million years of the Sun’s ignition, a large number of rocky protoplanets, in eccentric and chaotic orbits, engaged in collisions – followed by the inward migration of the last four planets left standing as they lost angular momentum to the persisting gas and dust of the inner disk. This last phase may have stabilised them into the almost circular, and only marginally eccentric, orbits we see today.

The hypothesized collision between 'Earth Mk 1' and Theia may have occurred late in rocky planet formation creating the Earth as we know it with its huge Moon of accreted impact debris

Meanwhile, the gas giants were forming out beyond the ‘frost line’ where it was cool enough for ices to form. Since water, methane and CO2 were a lot more abundant than iron, nickel or silicon – icy planetary cores grew fast and grew big, reaching a scale where their gravity was powerful enough to hold onto the hydrogen and helium that was also present in abundance in the protoplanetary disk. This allowed these planets to grow to an enormous size.

Jupiter probably began forming within only 3 million years of solar ignition, rapidly clearing its orbit, which stopped it from migrating further inward. Saturn’s ice core grabbed whatever gases Jupiter didn’t – and Uranus and Neptune soaked up the dregs. Uranus and Neptune are thought to have formed much closer to the Sun than they are now – and in reverse order, with Neptune closer in than Uranus.

And then, around 500 million years after solar ignition, something remarkable happened. Jupiter and Saturn settled into a 2:1 orbital resonance – meaning that they lined up at the same points twice for every orbit of Saturn. This created a gravitational pulse that kicked Neptune out past Uranus, so that it ploughed in to what was then a closer and denser Kuiper Belt.

The result was a chaotic flurry of Kuiper Belt Objects, many being either flung outwards towards the Oort cloud or flung inwards towards the inner solar system. These, along with a rain of asteroids from a gravitationally disrupted asteroid belt, delivered the Late Heavy Bombardment which pummelled the inner solar system for several hundred million years – the devastation of which is still apparent on the surfaces of the Moon and Mercury today.

Then, as the dust finally settled around 3.8 billion years ago and as a new day dawned on the third rock from the Sun – voila life!