From New Scientist: “Far-off asteroid caught cohabiting with Uranus around the sun”

NewScientist

New Scientist

16 February 2017
Ken Croswell

1
Now with added Trojans. NASA/Erich Karkoschka (Univ. Arizona)

A rare Trojan asteroid of Uranus has been found, following the same orbit as the planet. Its existence implies there could be many more of these companion asteroids, and that they are more common than we thought.

A Trojan asteroid orbits the sun 60 degrees ahead of or behind a planet. Jupiter and Neptune have numerous Trojans, many of which have been in place for billions of years. These primordial rocks hold information about the solar system’s birth, and NASA has just announced plans to visit several of them in the 2020s and 2030s.

But Saturn and Uranus live in a rougher neighbourhood: the giant planets on either side of them yank Trojans away through their gravitational pull. So Saturn has no known Trojan, and Uranus had only one.

In July, though, astronomers reported a new asteroid, named 2014 YX49, that shares Uranus’s orbital period of 84 years. Now computer simulations of the solar system by brothers Carlos and Raul de la Fuente Marcos at the Complutense University of Madrid, Spain, indicate the asteroid is a Uranus Trojan. The simulations show that the asteroid has maintained its position ahead of Uranus for thousands of years.

“It is bigger, probably twice as big as the first one,” says Carlos. The new asteroid is brighter than the first, but its exact size depends on how much light its surface reflects. If it reflects half the sunlight striking it, it’s 40 kilometres across; if it reflects 5 per cent, its diameter is 120 kilometres.

Accidental find

The new asteroid was found by accident, which Carlos says implies there should be more waiting to be discovered. He thinks its Trojans could number in the hundreds.

Unlike the Trojans of Jupiter and Neptune, the simulations suggest that the two known Uranus Trojans are transient rather than permanent. Carlos suspects Uranus lacks primordial Trojans because the other giant planets kicked them away.

The simulations indicate that the new asteroid was once a centaur, an object that skirts between the orbits of the giant planets. About 60,000 years ago, buffeted by their gravitational tugs, it was caught ahead of Uranus in its orbit around the sun and became a Trojan; it is likely to remain so for another 80,000 years, before eventually becoming a centaur again.

Although Carlos thinks Uranus has no permanent Trojans, David Jewitt at the University of California at Los Angeles is willing to wait and see. “In the end the answer will come — as always — from observations,” he says. “People will either find permanent Uranus Trojans or not.”

And Saturn? “The neighbourhood of Saturn is even more chaotic than that of Uranus,” Carlos says, due to Jupiter’s proximity. Still, he thinks Trojans of Saturn could exist.

Journal references: Monthly Notices of the Royal Astronomical Society and ArXiv, arxiv.org/abs/1701.05541

See the full article here .

Please help promote STEM in your local schools.

STEM Icon

Stem Education Coalition

#accidental-find, #basic-research, #new-scientist, #trojan-asteroids, #uranus

From The Atlantic: “The Many Mysteries of Uranus”

Atlantic Magazine

The Atlantic Magazine

Feb 2, 2016 [Just found this in social media.]
David Moscato

1
NASA / JPL-Caltech

An ode to the oddball of our solar system.

The best planet in our solar system is not, as Adrienne LaFrance claimed several months ago, Jupiter. Nor is it Saturn, as Ross Andersen argued in a rebuttal last month. I teach science for a living, which means I have a hard time allowing misinformation to pass by uncorrected—and after reading those articles, I knew I had to step in before any more intellectual damage was done.

The best planet is Uranus—Uranus the bizarre. Uranus the unique. Saturn may be flashy and pretty, and Jupiter may be huge and dramatic, but they can’t hold a candle to Uranus’s intrigue. While all the other planets spin like tops around the sun, Uranus lies on its side. It isn’t the farthest planet from the sun, yet it manages to be the coldest. Its magnetic field is nowhere near where it’s supposed to be, and its ghoulish blue-green atmosphere seems to alternate between dull stagnation and fits of activity.

Even its name is unusual. Uranus is the only planet with a name derived from a Greek deity, rather than a Roman one. Correctly pronounced “YOOR-uh-nus,” it’s an homage to the Greek god Ouranos, Father Sky—who, it bears noting, is the father of Cronus (Saturn), and the grandfather of Zeus (Jupiter).

In fact, Uranus has been breaking the mold as long as we’ve known about it. Mercury, Venus, Mars, Jupiter, and Saturn are all easily visible to the naked eye; humans have been gazing at those planets for millennia, but Uranus was the first planet discovered by modern astronomy. It’s so far away, and its movement so slow, that it was originally thought to be a star until Sir William Herschel revealed its planetary nature in 1781. Less than a decade later, it received a namesake chemical element: uranium, discovered in 1789. (Meanwhile, Neptune and Pluto didn’t make it into the periodic table for another 150 years.)

The more astronomers studied this new planet, the clearer it became that it was an odd one. Consider the seasons on a world turned sideways: Summer on Uranus is two decades of non-stop sunlight, and winter is an equal amount of time spent in total darkness, facing the cold void of distant space. Day and night only exist during spring and fall, where they cycle every 17 hours. Some have suggested that the planet was knocked askew by a gravitational tug-of-war with a large moon that has since been lost; others have proposed that it was the result of a collision with a massive object (much larger than Earth), or even multiple collisions.

This strange posture is just one on Uranus’s list of mysteries, a list that also includes its temperature. While the other gas planets are still slowly radiating out the heat of their formation, Uranus generates hardly any internal heat at all. No one is sure why, but that lack of heat may be the underlying cause of the planet’s extreme atmospheric temperatures: Deeper cloud layers get as low as 360 degrees below zero, colder than any other planet in the solar system, and yet the outer-most layer can reach more than 500 degrees, far higher than any other gas giant.

Like Jupiter and Saturn, Uranus’s atmosphere is full of hydrogen and helium, but unlike its larger cousins, Uranus also holds an abundance of methane, ammonia, water, and hydrogen sulfide. Methane gas absorbs light on the red end of the spectrum, giving Uranus its blue-green hue. If you were to fly down through the layers of the atmosphere, the surrounding clouds would grow denser and denser, colder and colder, bluer and bluer as the gases absorbed more of the visible spectrum. And deep below the atmosphere you may find the answer to yet another one of Uranus’s big puzzles: Its unruly magnetic field is tilted 60 degrees from its rotational axis, much stronger on one pole than the other, and shifted a few thousand miles off-center. Some astronomers believe the warped field may be the result of vast oceans of ionic liquids hidden beneath the greenish clouds, full of water, ammonia, or even liquefied diamond.

Perhaps Uranus wouldn’t be quite so mysterious if more spacecraft stopped by—but while Mars, Jupiter, and Saturn seem to receive a constant stream of high-tech fan-mail from Earth, Uranus has only been visited once. In 1986, Voyager 2 swung by on its way into deep space.

NASA Voyager 2
NASA Voyager 2

It was the first and so far the only mission to get an up-close view of Uranus, and what the probe saw was, at first glance, dull. Voyager 2 observed little atmospheric activity, and few cloud formations. For a moment, it seemed the icy clouds held little of interest. But it’s been 30 years since the Voyager fly-by, and we’re wiser now.

When Voyager visited, Uranus was just about at its solstice—the South Pole was almost directly facing the sun, and its North Pole was turned away. But as Uranus continued along its slow orbit, the seasons changed, and the northern hemisphere slowly came back into the light. In 2007, Uranus reached its equinox, the time when the equator faces the sun and the hemispheres receive equal sunlight. According to Imke de Pater, a professor of astronomy at the University of California, Berkeley, the earlier observations of Uranus were “nothing like what we’ve seen during the Equinox.” Over the past several years, astronomers have witnessed winds that blow hundreds of miles an hour, massive storm systems persisting for hours to years, bright cloud patches that migrate across the planet, and “dark spot” storms similar to the famous Neptunian version.

Uranus’s trips around the sun take just over eight decades, but it doesn’t travel alone. It is joined in its orbit by 27 known moons and 13 known rings, altogether every bit as bizarre as the planet itself. The rings of Uranus aren’t made of bright ice like Saturn’s—they’re more reserved, mostly rock and dust, and so dark they can be hard to spot (even Voyager 2 overlooked Uranus’s two outermost rings). But when Saturn’s rings have dissipated, as astronomers suspect will happen millions of years from now, Uranus’s surprisingly stable rings—which come in all sorts of strange flavors—will remain long into the future. One appears to be made entirely of dust knocked off the moon Mab by asteroid impacts; another dusty ring seems to have disappeared sometime in the last few decades, while a different ring appeared elsewhere; and perhaps most incredibly, one of the rings “breathes,” expanding and contracting around five kilometers once every several hours. According to Mark Showalter of the SETI Institute, these rings are “totally unlike anything else we’ve seen.”

And then there are the moons, which, like Uranus itself, bear unusual names—most moons in our solar system inherit their names from Greek mythology, but Uranus’s moons come from English literature. There’s Umbriel, strangely dark except for a mysterious bright band; Oberon, covered in craters and one very large mountain; Miranda, scarred by cracks and fissures so extreme they put the Grand Canyon to shame; and two dozen more.

When describing the motion of Uranus’ moons, Showalter uses words like “random” and “unstable.” The moons are constantly pushing and pulling each other gravitationally, which makes their long-term orbits unpredictable, and over millions of years some are expected to crash into each other. In fact, at least one of Uranus’s rings is thought to be the result of such a collision.

2
An image from the Hubble Space Telescope of the planet and its rings (NASA)

Learn enough, and it’s impossible to not be entranced by the beautiful chaotic dance of Uranus’s ring and moon system. Hidden among those strange movements may be the keys to understanding the unusual gravitational interactions of bodies across the cosmos.

So why not take a closer look?

Astronomers have considered sending an orbiter to Uranus, but there are complications. For one, Uranus is incredibly far away, between 1.5 and 2 billion miles from Earth. Besides that, Uranus is hard to predict. We don’t know what to expect from the fluctuating temperatures of the planet’s upper atmosphere, and while the chaotic motion of the moons is too slow to threaten a spacecraft, there’s reason to suspect we haven’t yet spotted all of the moons and debris orbiting the planet.

“What I’d really like to do,” says Glenn Orton of NASA’s Jet Propulsion Laboratory, “is get a probe into the atmosphere.” There, astronomers might be able to start unraveling some of Uranus’ most enduring puzzles: the deep structure of its atmosphere, the cause of its off-kilter magnetic field, and perhaps the reason for its frigid internal temperatures.

Until then, we can only gaze at the planet across 2 billion miles of space, guessing at its secrets. The best questions in science are the unanswered ones, and the best planet in the solar system is seventh from the sun, shrouded in methane and in mystery.

See the full article here .

Please help promote STEM in your local schools.

STEM Icon

Stem Education Coalition

#s-joined-in-its-orbit-by-27-known-moons-and-13-known-rings-altogether-every-bit-as-bizarre-as-the-planet-itself, #the-atlantic, #uranus, #uranus-is-incredibly-far-away-between-1-5-and-2-billion-miles-from-earth

From Smithsonian: “Uranus May Have Been Hiding Two Moons”

smithsonian
Smithsonian.com

October 18, 2016
Jason Daley

1
NASA

2
A recent Hubble Space Telescope view reveals Uranus surrounded by its four major rings and by 10 of its known satellites. The new moons would be between 2.5 and 8.6 miles (4 and 14 kilometres) in diameter, if they did exist

In 1986, when the Voyager 2 probe flew past Uranus, it detected ten previously undiscovered moons orbiting the blue-green gas giant.

NASA Voyager 2
NASA Voyager 2

Uranus’ moon total currently stands at 27, but if analysis by planetary scientists at the University of Idaho, Moscow, is correct, Voyager missed two moons during its historic fly-by, reports Ken Croswell at New Scientist.

Reexamining the Voyager data, planetary scientists Rob Chancia and Matthew Hedman noticed that two of Uranus’ rings, Alpha and Beta, had a wavy pattern. Previously scientists observed similar ripples with the rings caused by two of the planet’s other moons, Cordelia and Ophelia. The gravity of these two moons and the couple other dozen orbs zipping around the planet, force the space dust and particles into narrow rings.

Researchers believe these latest wobbly rings have a similar source: another two moons around Uranus. Their research will appear in the Astronomical Journal.

“These moons are pretty tiny,” Chancia tells Croswell. In fact, if they exist they are between 2.5 and 8.5 miles across. The moons are so small that even if Voyager 2’s cameras did pick them up, they were probably just considered background noise, reports Charlotte England at The Independent. Even so, as Croswell points out, two of Saturn’s moons are even smaller.

Based on the colors of Uranus’s other moons, the new satellites are probably also dark in color. “Not only are Uranus’s rings dark, so are most of the little satellites that are in that region,” Hedman tells Croswell.

Confirming the moons would require using the Hubble Space Telescope to survey the area. In fact, in 2005, Mark Showalter of the SETI Institute discovered several rings and two new moons around Uranus, which were named Mab and Cupid, using Voyager data and Hubble images.

“The new discoveries demonstrate that Uranus has a youthful and dynamic system of rings and moons,” Showalter said at the time. Showalter tells Croswell that he and his colleagues will be examining Hubble data looking at Uranus in the coming months, which may help confirm the new moons.

If the moons don’t show up during that survey, the final option is waiting for a probe to visit the distant planets. While there are no firm plans to send an orbiter to explore the area, last year NASA asked the science community to think about the types of robotic orbiters needed to visit Neptune and Uranus—the only two planets in the solar system that have not been orbited by probes. If NASA does green light a mission, it likely won’t get off the ground until the late 2020s or early 2030s.

See the full article here .

Please help promote STEM in your local schools.

STEM Icon

Stem Education Coalition

Smithsonian magazine and Smithsonian.com place a Smithsonian lens on the world, looking at the topics and subject matters researched, studied and exhibited by the Smithsonian Institution — science, history, art, popular culture and innovation — and chronicling them every day for our diverse readership.

#astronomy, #basic-research, #smithsonian, #uranus, #uranus-may-have-been-hiding-two-moons