# Why is Uranus able to support a regular satellite system?

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Uranus has an obliquity of 98° which means that the mutual inclination between a satellite orbiting in its equatorial plane and the orbit of Uranus around the Sun would exceed the critical angle for Kozai oscillations. This would drive the satellites to high eccentricities which would likely be extremely damaging to the stability of the system, yet Uranus does host a system of regular satellites on near-circular orbits in its equatorial plane.

This suggests something is suppressing the Kozai oscillations for the regular satellites, so what is doing this? I suspect it is linked either to the non-spherical shape of the planet or gravitational interactions between the moons, but I'm not sure which would be a more relevant factor.

The solar perturbations on most of the satellites of Uranus are on a very small scale indeed, which may explain the absence of the instabilities noted in the question.

A perturbational effect depends on the scale of the solar perturbing accelerations relative to the ordinary inverse-square attraction of the primary body. The scale factor (often designated $$m^2$$ in texts on the lunar theory such as Airy's 'Mathematical Tracts' and Godfray's 'Lunar Theory') increases with the separation of the satellite from the primary, it is also as the cube of the distance-ratio satellite-primary : primary-Sun (see detailed calculation below).

Taking as an example the most distant of the major moons of Uranus, Oberon at 583500 km:

The scale factor for the solar perturbing accelerations on Oberon in its orbit relative to Uranus is only about 1/5,000,000 of the gravitational acceleration towards Uranus felt by Oberon (calculation below).

Comparing the corresponding scale factor for Earth's moon and its solar perturbations, the factor is very much larger, close to 1/178, as is well-known. The Moon has a fairly strongly sun-perturbed orbit relative to the Earth, but the solar perturbations on Oberon are more than four orders of magnitude smaller, really very tiny.

It is possible that the two tiny outermost satellites XVI and XVII of Uranus may be experiencing perturbations large enough to drive growth of their eccentricities, their eccentricities at 0.18 and 0.52 are very large compared with the major satellites, all with eccentricity < 0.004 (source, Astronomical Almanac 2016).

Detail of the approximate calculation:

The 'sampled' solar perturbing acceleration on a satellite is taken for present purposes to be represented by the perturbing acceleration on the satellite when it is close to quadrature with the Sun (as seen from the planet). In this configuration, the solar perturbation on the satellite is directed towards the planet, adding here to the ordinary inverse-square attraction of the satellite towards the planet.

With mass-constants of the Sun, S, and of the planet, P ; planetary semi-axis a ; and planet-satellite separation d , plus an assumption that the mass of the satellite is very small relative to the other two:

1 ** the planet's accelerative attraction on the satellite is $$P/d^2$$ ;

2 ** the Sun's accelerative attraction on the planet is $$S/a^2$$ ;

3 ** and so also (to a quite close approximation) is the amplitude of the Sun's accelerative attraction on the satellite $$S/a^2$$ .

4 ** When the satellite is in quadrature, the resolved part of the Sun's vector attraction on it that does not cancel with the Sun's attraction on the planet, i.e. the net perturbation on the satellite at that point, is given very nearly by the proportions of the triangle satellite-planet-sun: the lengths of two of the sides are approximately a and the third d. In this configuration, the resolved part of acceleration #3 in the direction of the planet, to a close approximation, is thus --

$$(S/a^2) . (d/a)$$.

The ratio of perturbing acceleration 4 to ordinary planetary attraction 1 is thus

$$(S/P) . (d/a)^3$$.

For the Sun and Uranus, S/P ~= 22902 ,

for the Sun and Earth+Moon, S/P ~= 328901 .

Uranus is approximately 19 au from the Sun to the Earth's 1, the au is 149597871 km, the mean planetocentric distance of Oberon is 583500 km and of the Moon 385000 km.

Using these figures, the ratio

'solar perturbation on satellite : planetary attraction on satellite'

comes to ~ 1/178 for the Earth and Moon, and ~ 1/5,000,000 for Uranus and Oberon.

The tiny outer satellites of Uranus are farther away from it than Oberon is, in a ratio of about 20.8 for the outer (XVII). Thus the perturbations on it, as a proportion of the ordinary attraction of Uranus at its distance, is $$(20.8)^3$$ times larger than for Oberon, making the relevant perturbation scale factor as large as about 1/550 , still smaller than for the one for our Moon, but perhaps enough for the disturbing effects to be reflected in its higher eccentricity of about 0.52.

{Update:} It turns out that the orbits of the outer Uranian moons have actually been studied: Brozovic, M.; Jacobson, R. A. (2009), "The Orbits of the Outer Uranian Satellites", The Astronomical Journal, 137 (4): 3834-42. Just one of the (high-eccentricity) outer satellites was found to be disturbed by a Kozai resonance and may be in unstable orbit. It appears that the conditions for the effect are not fulfilled for the others.

## How to locate planet Uranus

On January 31 and February 1, 2020, the waxing moon is near the seventh planet, Uranus, on our sky’s dome. At a distance of 20 astronomical units – or 20 Earth-sun units – from Earth, Uranus is faint. It was the first planet to be discovered in modern times, by William Herschel in the year 1781. He was using a telescope! Most people do use a telescope or binoculars to see it, but some have glimpsed it with the eye alone on a moonless night. Why are we showing you Uranus near the moon then? Just so you can get an idea of where it is in the sky after sunset, so that you can notice the stars around it, and then find Uranus when the moon has moved away.

On both January 31 and February 1, the moon is bright it’s at or near first quarter. Uranus, meanwhile, is located in front of the faint constellation Aries the Ram, close to the border of the constellation Pisces the Fishes. Now here’s the good news. Uranus moves only very slowly in front of the starry background. It’ll stay in front of Aries for several more years. So if you notice the stars near the moon tonight, you can use these stars to get oriented and, ultimately, to locate the seventh planet.

A good familiarity with Aries is your ticket to locating this faint world. For a detailed sky chart of Aries, click on The Sky Live and for a sky chart showing Uranus’ position from 2019 to 2032, click on Naked Eye Planets.

Or check out the chart below, which shows the constellation Aries.

This chart shows the approximate position for Uranus relative to the Aries stars 19 Aretis (abbreviated 19 Ari on chart) and HD 12479. Use these stars (which are about the same brightness as Uranus) to find Uranus, whose blue-green color may contrast to the reddish hue of the star HD 12479. Sky chart via IAU.

Of course, the moon and Uranus are only close together on the sky’s dome, not in space. The moon is nearly 250,000 miles (400,000 km) away from Earth, whereas Uranus lurks way out there, at well over 7,000 times the moon’s distance from us. Click on the Moon Tonight for the moon’s present distance in miles, kilometers or astronomical units (one astronomical unit = Earth/sun distance), and on Heavens-Above to know Uranus’ present distance from the sun and Earth in astronomical units.

Recently, the very bright planet Venus and the very faint planet Neptune were in conjunction. View photos of the Venus-Neptune conjunction here.

Venus will soon have another conjunction with another very faint planet (though not as faint as Neptune). Yep, it’ll be a conjunction of Venus with Uranus, and it’ll happen on March 9, 2020. Venus is now sitting rather low in the west at dusk and nightfall. It’ll be hard to miss this brilliant world, because Venus ranks as as the third-brightest celestial body in all the heavens, after the sun and moon. Day by day, as darkness falls, Venus will climb upward, toward Uranus, while Uranus will fall downward, toward Venus. The two will meet in March.

So know that these late January and early February evenings are not the best nights for seeing Uranus. You will have a tough time glimpsing it in the moon’s glare. But maybe bookmark some links, and then, when the moon leaves the evening sky, you’ll know where to look before Venus has its rendezvous with Uranus.

Steven Bellavia sent in this image of Uranus and 4 of its moons in December 2018. From upper left to lower right: Titania, Ariel, Umbriel, Oberon. Steve wrote: “Uranus has 27 moons, all of which are named after characters from the works of William Shakespeare and Alexander Pope … I find it amazing that William Herschel was able to see (and discover) Titania and Oberon, in 1787, only 6 years after he discovered the planet itself, using his home-built 18.8-inch telescope. Umbriel and Ariel were not discovered for another 64 years by William Lassell in 1851.” Voyager 2 is still the only spacecraft to have visited the outer planets Uranus and Neptune. Here is Uranus as seen by Voyager 2 in 1986. To the spacecraft, the planet appeared as a featureless blue ball. Image via NASA.

Bottom line: As darkness falls on January 31, 2020, the moon shines rather close to Uranus on the sky’s dome.

## The Solar System at Ultraviolet Wavelengths

Amanda R. Hendrix , . Deborah L. Domingue , in Encyclopedia of the Solar System (Third Edition) , 2014

### 3.6 Uranus

Uranus presents a unique observational circumstance to the inner solar system observer because of the fact that its pole is inclined 89° to the ecliptic and that at the present position in its 84-year orbit about the Sun it presents its pole to the Earth. This unusual inclination, combined with its great distance from the Earth, makes it impossible to use an Earth-based instrument to undertake pole-to-pole comparisons as was done with Jupiter and Saturn. Uranus has a geometric albedo at NUV wavelengths of about 0.5, more than twice that of Jupiter and Saturn. This suggests that additional absorbers are present in the Jovian and Saturanian atmospheres that are not present in the atmosphere of Uranus. Both Uranus and Neptune possess hot thermospheres and stratospheres that are substantially clear of hydrocarbons and other heavy constituents, making the UV albedos higher than those of Jupiter and Saturn. A sharp increase in measured reflectance intensity at wavelengths longward of 150 nm is indicative of acetylene (C2H2) present in the atmosphere of Uranus.

Voyager 2 spacecraft observations of Uranus found a very small internal heat source compared to the large internal heat sources found in Jupiter and Saturn. This suggests that there is very little atmospheric mixing driven by heating and buoyancy in the Uranian atmosphere. Thus, UV observations are able to sense a deeper region of the atmosphere.

The UV emissions from Uranus' atmosphere have been measured by the IUE and the Voyager UVS. To increase the signal-to-noise ratio, the IUE observers used principally low-resolution observations and binned broad-wavelength regions together to search for broadband absorbers at UV wavelengths. Analysis of the IUE observations detected acetylene absorptions, which were also detected on Jupiter and Saturn. Based on these observations, the mixing ratio of acetylene is estimated to be 3 × 10 −8 . Analysis of the Voyager UVS observations of H2 band UV airglow emissions shows aurora at both magnetic poles, which are offset from the rotational poles by ∼60°. The auroral emissions on Uranus are very localized in magnetic longitude and do not form complete auroral ovals as are seen on Jupiter and Saturn.

## Could There Be Life on Uranus?

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The more we learn about life on Earth, the more we realize that it can live in some of the most inhospitable places on the planet: encased in ice, in boiling water, and even in places with high radiation. But could life exist elsewhere in the Solar System? Could there be life on Uranus?

There are a few problems. The first is the fact that Uranus has no solid surface. It’s mostly composed of ices: methane, water and ammonia. And then it’s enshrouded by an atmosphere of hydrogen and helium. The second is that Uranus is really cold. Its cloud tops measure 49 K (?224 °C), and then it gets warmer inside down to the core, which has a temperature of 5,000 K.

You could imagine some perfect place inside Uranus, where the temperature could support life. The problem is that the pressures inside Uranus are enormous at those temperatures, and would crush life. The other problem is that life on Earth requires sunlight to provide energy. There’s no process inside Uranus, like volcanism on Earth, that would give life inside the planet a form of energy.

Life on Uranus would have to be vastly different from anything we have here on Earth to be able to survive. Of course, it’ll be almost impossible to ever send a spacecraft down into the planet to look for ourselves.

We have written many articles about the search for life in the Solar System. Here’s an article about how life on Mars might have been killed off. And here’s an article about how the soil on Mars might have supported life.

Here’s a link to Hubblesite’s News Releases about Uranus, and here’s NASA’s Solar System Exploration guide.

We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.

## Is It Possible To Live On Uranus

i know this is a really stupid question but i really need help if you could type of like a paragraph on why humans can live on Uranus it would really help me!

(I have three culminating projects due on the same day and its Friday and they all want them by the monday coming up.)

Best Answer:  well for one thing, my anus has way too much of a gravitational pull. lol. jk.

1. seriously though. uranus does have a much greater gravitational pull and would probably be too much for us.

2. also the atmosphere is far to different from ours and we would not be able to breath the air.

3. the temperature is too cold and we would freeze to death

4. there is no liquid water so we would all die fo thirst in less than a week.

5. and there is nothing there for us to eat so if we didnt die of thirst, we would all still die of hungar.

one thing i would like to add that most of these people aparently do no know though. yes uranus is a gas planet. but after sending probs into space scientists have learned that far beneth the gassy exterior of the planet is a core either made of solid ground or liquid. so it is not souly gas.

Uranus is a gaseous planet, which means it lacks of solidity, no surface. Also, Uranus is extremely colder than Earth, as it is very farther from the Sun compare to Earth. Furthermore, Uranus has much more intense wind speeds which are far more severe than those of Earth. The Uranus atmosphere is very toxic, unstable, and inhospitable for sustainable life. Poisonous fumes/gases emit throughout Uranus. However, there maybe a possibility that Uranus could sustain life, once we develop the technology required to live on gaseous planets. But as of now, it's impossible to live on Uranus, or any other gas giants

1. uranus' composition --> it's made of gases not rock like the earth.

1) There is no surface. It is a gas giant.

2) There is no Oxygen in a breathable form.

3) The gravity of the planet would crush out skeletons.

4) There is no water in a usable form.

5) The radiation would kill us.

Uranus is a gas planet and we would have to float.

The gravity is too strong.

It is too far from the sun and thus very cold.

The winds on Uranus are insanely strong. (not trying to be silly)

Its really far from the sun - we need that. (living temperature zone, our dependence on plants etc.

atmosphere - hydrogen helium and methane. doesnt work for me.

eastacademic · 9 years ago

The atmosphere is inhospitable- temperature, pressure and composition.

The planet has no solid ground.

The gravity is too strong.

The terrible, terrible jet-lag.

Bullet Magnet · 9 years ago

Atmosphere (not enough oxygen, nitrogen, etc. etc. etc.)

Water (none liquid, I'm not sure if there even is any.)

Temperature (wwwaaayyy too cold.)

Land (I think Uranus is a gaseous planet, but I'm not sure.)

1. it's not big enough to accomodate the human race.

2. it has sporadic eruptions.

3. toxic fumes are expelled at times.

4. it is covered in darkness most of the time

5. I would not grant permission for them to inhabit my anus!

bettiewoeswoes · 9 years ago

usually answered in minutes!

Could a human live on uranus?

5 Reasons why I can't live in others planets?

Is anyone brave enough to let me know of 5 reasons why their life is worth living?

Can a planet with 30 percent water on its surface have an oxygen atmosphere if there were plants on it?

What percentage of Astrophysicists/Cosmologists are atheist/agnostic? I m specifically looking for Cosmic Origins scientists, hard to find.?

## Other Characteristics

Uranus is probably the coldest planet of the Solar System for reasons not yet understood. Something prevents the heat from Uranus’s core from reaching the surface.

Uranus is the only planet in the Solar System that spins on its side. It is believed that this was caused by a collision in the distant past. Like Venus, Uranus also spins in the opposite direction than the other planets of the Solar System.

The closest planets to Uranus, its neighbors, are Neptune and Saturn. Uranus has many moons, 27, and they were named after characters from fictional books.

Uranus was discovered in 1781 by William Herschel, a British astronomer. The planet was visited only once, by the spacecraft Voyager 2, in 1986.

Uranus is sometimes visible in the sky. You won’t need binoculars or a telescope to see it, but you can only view it on a very clear night sky. Even with binoculars, it would be easy to spot the planet.

## Mysteries of Uranus' oddities explained

The ice giant Uranus' unusual attributes have long puzzled scientists. All of the planets in our Solar System revolve around the Sun in the same direction and in the same plane, which astronomers believe is a vestige of how our Solar System formed from a spinning disc of gas and dust. Most of the planets in our Solar System also rotate in the same direction, with their poles orientated perpendicular to the plane the planets revolve in. However, uniquely among all the planets, Uranus' is tilted over about 98 degrees.

Instead of thinking about the reality of stars spread in all directions and at various distances from the Earth, it is easier to understand by envisioning the celestial sphere. To picture what the celestial sphere is, look up at the night sky and imagine that all of the stars you see are painted on the inside of a sphere surrounding the Solar System. Stars then seem to rise and set as the Earth moves relative to this 'sphere'. As Uranus rotates and orbits the Sun, it keeps its poles aimed at fixed points with relation to this sphere, so it appears to roll around and wobble from an Earth observer's perspective. Uranus also has a ring system, like Saturn's, and a slew of 27 moons which orbit the planet around its equator, so they too are tipped over. How Uranus' unusual set of properties came to be has now been explained by a research team led by Professor Shigeru Ida from the Earth-Life Science Institute (ELSI) at Tokyo Institute of Technology. Their study suggests that early in the history of our Solar System, Uranus was struck by a small icy planet -- roughly 1-3 times the mass of the Earth -- which tipped the young planet over, and left behind its idiosyncratic moon and ring system as a 'smoking gun'.

The team came to this conclusion while they were constructing a novel computer simulation of moon formation around icy planets. Most of the planets in the Solar System have moons, and these display a menagerie of different sizes, orbits, compositions and other properties, which scientists believe can help explain how they formed. There is strong evidence Earth's own single moon formed when a rocky Mars-sized body hit the early Earth almost 4.5 billion years ago. This idea explains a great deal about the Earth and its Moon's composition, and the way the Moon orbits Earth.

Scientists expect such massive collisions were more common in the early Solar System, indeed they are part of the story of how all planets are thought to form. But Uranus must have experienced impacts that were very different from Earth simply because Uranus formed so much farther from the Sun. Since the Earth formed closer to the Sun where the environment was hotter, it is mostly made of what scientists call 'non-volatile' elements, meaning they don't form gases at normal Earth-surface pressures and temperatures they are made of rock. In contrast, the outermost planets are largely composed of 'volatile' elements, for example things like water and ammonia. Even though these would be gases or liquids under Earth-surface like temperatures and pressures, at the huge distances from the Sun the outer planets orbit, they are frozen into solid ice.

According to professor Ida and his colleagues' study, giant impacts on distant icy planets would be completely different from those involving rocky planets, such as the impact scientists believe formed Earth's Moon. Because the temperature at which water ice forms is low, the impact debris from Uranus and its icy impactor would have mostly vapourised during the collision. This may have also been true for the rocky material involved in Earth's Moon-forming impact, but in contrast this rocky material had a very high condensation temperature, meaning it solidified quickly, and thus Earth's Moon was able to collect a significant amount of the debris created by the collision due to its own gravity. In the case of Uranus, a large icy impactor was able to tilt the planet, give it a rapid rotation period (Uranus' 'day' is presently

17 hours, even faster than Earth's), and the leftover material from the collision remained gaseous longer. The largest mass body, what would become Uranus, then collected most of the leftovers, and thus Uranus' present moons are small. To be precise, the ratio of Uranus' mass to Uranus' moons' masses is greater than the ratio of Earth's mass to its moon by a factor of more than a hundred. Ida and colleagues' model beautifully reproduces the current configuration of Uranus' satellites.

As Professor Ida explains, 'This model is the first to explain the configuration of Uranus' moon system, and it may help explain the configurations of other icy planets in our Solar System such as Neptune. Beyond this, astronomers have now discovered thousands of planets around other stars, so-called exoplanets, and observations suggest that many of the newly discovered planets known as super-Earths in exoplanetary systems may consist largely of water ice and this model can also be applied to these planets.'

## What Does Uranus Sound Like?

Farewell shot of Uranus as Voyager II departs. January 25, 1986. Range 600,000 miles. Image credit: NASA. Click for more information.

Sometimes kids ask really simple questions – and parents have no idea what the answers are. When one of our colleagues was asked what it sounds like on the planet Uranus, she was stumped. And so were we! So we asked an expert. (And, yes, we know this subject lends itself to jokes about flatulence, but we’ll let you come up with your own jokes – this is a pun-free post.)

Paul Byrne is a planetary geologist and an assistant professor in NC State’s Department of Marine, Earth, and Atmospheric Sciences. Because Byrne studies how (and why) planets look the way they do, we figured that he’d be a great person to talk to about what Uranus might sound like. And we were right!

What Would It Sound Like If You Were On Uranus?

Basically, it would sound windy. (Again, you will have to supply your own puns here.)

“This answer depends on where on Uranus you are,” Byrne says. “Uranus is what we call an ‘ice giant,’ and is composed almost entirely of gases and fluids, so there’s no real ground to stand on. From a distance – in other words, in space – there’s no sound at all (space is a vacuum, and sound doesn’t travel in a vacuum – or, at least, not very well), so you won’t be able to hear Uranus. But within the atmosphere itself, there’s plenty of sound there’s wind, which you could hear if you were able to fly through the atmosphere in a helicopter, say, or in a balloon.

“It’s extremely difficult and expensive to get any kind of vehicle to Uranus, so it’ll be a long time before we really do hear the planet’s weather, but it’s certainly possible.”

This made us think of another question. We know that there are radio telescopes that collect radio waves from radio sources in space, but …

Do Planets Emit Radio Waves?

“All the giant planets in our solar system – Jupiter and Saturn (together called ‘gas giants’), as well as Neptune and Uranus – emit radio signals,” Byrne says. “So pointing a radio telescope at these worlds means that we’re able to ‘hear’ them this way, too. But the difference is that we’re ‘hearing’ them at radio frequencies, instead of what we normally consider as ‘sound’ (which is caused by minor vibrations in air, water or some other medium).

“In fact, Jupiter is the second-noisiest body in the solar system, in terms of radio emissions, after the sun,” Byrne says. “Uranus and Neptune are the least noisy of these four giant planets. Jupiter’s radio noisiness is due, in part, to the fact that it’s closer to Earth than those other worlds. But mainly, it seems, Jupiter is so noisy because it is just much bigger – Jupiter is about three times more massive than Saturn, and more than 20 times more massive than Uranus and Neptune.”

What Can We Learn About Planets From Radio Waves?

“Listening to giant planets at radio frequencies can tell us a great deal about their composition and interior structure, and even their weather systems,” Byrne says. “We can learn about their magnetic fields (all giant planets have internally powered magnetic fields, just as Earth does, although the mechanisms creating these fields are probably different between the giants and our rocky world). And it’s also possible to determine the rate at which the giant planets are rotating.

“Of course, doing so is much easier with a spacecraft near a planet, rather than from Earth – which is exactly what NASA’s Voyager 2 spacecraft did when it flew past Uranus in 1986.”

What Do Radio Waves Tell Us About Uranus?

“A lot of what we know about Uranus comes from the Voyager 2 probe, which carried a variety of instruments including a radio experiment,” Byrne says. “Voyager 2 was able to help measure the rotation rate of Uranus, and was even able to hear bursts of radio waves that could have been lightning!”

## An Additional Planet Between Saturn and Uranus Was Kicked Out of the Solar System

New work led by Carnegie’s Matt Clement reveals the likely original locations of Saturn and Jupiter. These findings refine our understanding of the forces that determined our Solar System’s unusual architecture, including the ejection of an additional planet between Saturn and Uranus, ensuring that only small, rocky planets, like Earth, formed inward of Jupiter.

In its youth, our Sun was surrounded by a rotating disk of gas and dust from which the planets were born. The orbits of early formed planets were thought to be initially close-packed and circular, but gravitational interactions between the larger objects perturbed the arrangement and caused the baby giant planets to rapidly reshuffle, creating the configuration we see today.

“We now know that there are thousands of planetary systems in our Milky Way galaxy alone,” Clement said. “But it turns out that the arrangement of planets in our own Solar System is highly unusual, so we are using models to reverse engineer and replicate its formative processes. This is a bit like trying to figure out what happened in a car crash after the fact — how fast were the cars going, in what directions, and so on.”

Jupiter in its infancy was thought to orbit the Sun three times for every two orbits that Saturn completed. But this arrangement is not able to satisfactorily explain the configuration of the giant planets that we see today. Matt Clement and his co-authors showed that a ratio of two Jupiter orbits to one Saturnian orbit more consistently produced results that look like our familiar planetary architecture. Credits: NASA/JPL Caltech/SwRI/MSSS/Gerald Eichstädt/Seán Doran

Clement and his co-authors — Carnegie’s John Chambers, Sean Raymond of the University of Bordeaux, Nathan Kaib of University of Oklahoma, Rogerio Deienno of the Southwest Research Institute, and André Izidoro of Rice University — conducted 6,000 simulations of our Solar System’s evolution, revealing an unexpected detail about Jupiter and Saturn’s original relationship.

Jupiter in its infancy was thought to orbit the Sun three times for every two orbits that Saturn completed. But this arrangement is not able to satisfactorily explain the configuration of the giant planets that we see today. The team’s models showed that a ratio of two Jupiter orbits to one Saturnian orbit more consistently produced results that look like our familiar planetary architecture.

“This indicates that while our Solar System is a bit of an oddball, it wasn’t always the case,” explained Clement, who is presenting the team’s work at the American Astronomical Society’s Division for Planetary Sciences virtual meeting today. “What’s more, now that we’ve established the effectiveness of this model, we can use it to help us look at the formation of the terrestrial planets, including our own, and to perhaps inform our ability to look for similar systems elsewhere that could have the potential to host life.”

The model also showed that the positions of Uranus and Neptune were shaped by the mass of the Kuiper belt — an icy region on the Solar System’s edges composed of dwarf planets and planetoids of which Pluto is the largest member — and by an ice giant planet that was kicked out in the Solar System’s infancy.

Reference: “Born eccentric: Constraints on Jupiter and Saturn’s pre-instability orbits” by Matthew S. Clement, Sean N. Raymond, Nathan A. Kai, Rogerio Deienno, John E. Chambers and André Izidoro, 6 October 2020, ICARUS.
DOI: 10.1016/j.icarus.2020.114122

This work was supported by the U.S. National Science Foundation, the NSF’s CAREER award, CNRSs PNP program, NASA Astrobiology Institute’s Virtual Planetary Laboratory Lead Team, the NASA SSW program, and NASA.

The majority of computing for this project was performed at the OU Supercomputing Center for Education and Research at the University of Oklahoma. Some of the computing for this project was performed on Carnegie’s Memex cluster. The authors thank Carnegie Institution for Science and the Carnegie Sci-Comp Committee for providing computational resources and support that contributed to these research results. The authors acknowledge the Texas Advanced Computing Center at The University of Texas at Austin for providing HPC, visualization, database, or grid resources that have contributed to the research results reported within this paper.

## Video l Uranus – A Planet Tilted And It’s Emitting X-rays

Right, I know this post is going to be a butt of a lot of giggles but here goes anyway.

When you look at images of planets in our solar system, they all seem to follow a certain design. The rocky ones are round with a few moons, while the gas giants and the ice giants have rings. But one of them is different. It seems to be tilted on its side, with its rings nearly at right angles to its equator. That planet is Uranus.

Until 1781, we all thought that there were only six planets in our solar system. But on March 13 of that year, exactly 240 years ago, the astronomer William Herschel identified a seventh planet, when he observed a faint object in the constellation Gemini. At first, he thought it was a comet but then later decided that this was a new planet – the first one ever observed through a telescope. It would be two years before it was accepted as a planet, in part because of observations made by another astronomer Johann Elert Bode.

Although Herschel wanted to name it after the monarch of the United Kingdom, the tradition was to name planets after mythological figures and this is why it became Uranus – Greek god of the sky, grandfather of Zeus (or Jupiter) and father of Cronos (or Saturn).

Like all the other planets in our solar system, Uranus was formed 4.5 billion years ago, as a result of swirling gas and dust collapsing due to gravity. Like the other giant planets, it was also probably formed closer to the Sun and then moved to the outer solar system. Uranus’ composition is similar to Neptune. Most of its mass is a hot dense, fluid of icy water, methane, and ammonia above a small rocky core, that’s why both planets are known as ice-giants. It also has a magnetosphere, several moons, and a ring system.

Uranus is about 1.8 billion miles (or 2.9 billion km) from the Sun, which is about 19 times the distance of the Earth from the Sun. Due to this massive distance, astronomers knew little about this ice-giant other than five of its moons for 200 years. In 1977, scientists at the Kuiper Airborne Observatory and the Perth Observatory in Australia made a major discovery: Uranus, like Saturn, had rings! These rings differed from Saturn though – circling the planet at almost 90 degrees from its plane of orbit. The planet is orbiting on its side and is also known as the “sideways planet”. It is thought that another Earth-sized object crashed into it at some point and tilted it. Uranus is also one of just two planets, the other being Venus, that rotate in the opposite direction than the other planets i.e from east to west.

A year on Uranus is 84 Earth years, its day is about 17 Earth hours, and it has a diameter of about 31,500 miles (or over 50,000 km), making it four times wider than Earth. Its unique tilt is the reason for some of the most extreme seasons in the solar system. Uranus’ north pole experiences 21 years of night in winter and 21 years of daytime in summer and 42 years of day and night in the spring and fall (autumn). Its temperature can reach -357F (or -180C) and its atmosphere comprises of hydrogen, helium and methane. However, it has more methane than Jupiter and Saturn, which is why it has the lovely blue colour we can see in images. Uranus has 13 known rings, the inner ones being narrow and dark and the outer ones brightly coloured. In total it has 27 known moons, named after characters from the works of Shakespeare and Alexander Pope.

Voyager 2 is the only spacecraft that flew by Uranus in 1986, greatly increasing our knowledge of this icy world, its moons, and rings in just six hours, making its closest approach of 50,700 miles above the planet’s top clouds. Other than that, no spacecraft has orbited it. Voyager 2 imaged its large moons, revealing each to be unique with more geological activity than was expected. More than 7,000 images returned by Voyager 2 revealed 11 new moons and two new rings.

The Hubble Space Telescope, launched in 1990, has been observing it and the other outer planets. In 2019, it revealed a vast bright stormy cloud cap across the north pole – providing a fresh look at a long-lived storm circling the planet’s north polar region. Keck Observatory and Hubble Telescope observations show that its outer rings are blue and the inner new ring are reddish in colour. In March 2020, scientists at NASA’s Goddard Space Flight Center, reanalysed Voyager 2 data, finding a giant magnetic bubble known as a plasmoid that may have been slowly throwing the planet’s atmosphere out to space. And Voyager 2 data still keeps on giving. An image it took 13 years ago recorded a moon that went unnoticed until Erich Karkoschka from the University of Arizona noticed Uranus’ 18th moon when he compared the 1986 photo with a recent one taken by Hubble in 1999.

Then this year, on March 31, 2021, astronomers detected X-rays being emitted from Uranus for the first time, using NASA’s Chandra X-ray Observatory observations, taken in 2002 and 2017. While X-rays have been detected on most of the planets in our solar system, they had not been detected on the ice-giants Neptune and Uranus, till this latest study.

The X-rays are probably caused by the Sun’s X-ray light being scattered by the planet, similar to Jupiter and Saturn. However, there is also evidence that at least one other source of X-rays is present on Uranus. This could be the planet’s rings producing the X-rays, like the rings of Saturn do. The charged electrons and protons that surround Uranus space environment could be colliding with the rings, which could cause them to glow in X-rays. Auroras were also observed on Uranus in other wavelengths in 2011. Because Uranus’ magnetic field is inclined 59 degrees to its spin axis, the auroral spots appear far from the planet’s north and south poles – offset from its centre, making them complex and variable. These auroras could also be the reason for the X-rays.

NASA astronomers think that determining the sources of the X-rays from Uranus could help increase understanding of X-ray emissions from other objects in space, such as black holes and neutron stars.

Fun fact: Just eight years after the discovery of Uranus, a radioactive element was discovered in 1789. This element, Uranium, was named after the ice giant.