Discovering Uranus’s Rings (Sciency Words: Occultation)

October 24, 2015

Sciency Words MATH

Today’s post is part of a special series here on Planet Pailly called Sciency Words. Each week, we take a closer look at an interesting science or science-related term to help us all expand our scientific vocabularies together. Today’s word is:

OCCULTATION

You know that thing when the Moon passes in front of the Sun, completely blocking the Sun from our view here on Earth. That specific event, known as a solar eclipse, is an example of a more general phenomenon called an occultation.

The term is related to the more vernacular word “occult” in the sense that they both refer to things that are hidden. When a planet, moon, or other celestial body passes in front of a distant star, for example, the star is “occulted” in the sense that it is briefly hidden from sight.

Occultations are a rare and wonderful cosmic coincidence, and they also provide astronomers with an incredible opportunity. Whenever an occultation is predicted to occur, a great many powerful telescopes all across the globe swivel around to watch.

And sometimes amazing discoveries are made.

In 1977, the planet Uranus occulted a star with the unimaginative name of SAO 158687. After setting up their telescopes, astronomers presumably got their popcorn ready and waited to see what would happen. They were hoping some of the occulted starlight would pass through Uranus’s atmosphere, revealing the atmosphere’s structure and chemical composition.

Surprisingly, the show started early and ended late. SAO 158687 dimmed exactly five times before the occultation and exactly five times afterward. This provided the first evidence that Uranus has rings. At least five of them (we now know of thirteen Uranian rings).

And it’s a good thing we discovered those rings too. Given Uranus’s otherwise bland appearance, how else could I depict the planet’s sideways orientation without the help of those sideways oriented rings?

Oc09 Uranus Without Rings

P.S.: On a personal note, I’ve been feeling a little under the weather lately, which is why this edition of Sciency Words is a day late, and I want to apologize in advance if I don’t respond to comments as quickly as usual.


Is Uranus Boring?

October 21, 2015

Planetary scientists can say some pretty mean things abut planets, especially when they’re competing over limited funding and telescope time. That’s probably why Uranus has frequently been described as “boring.”

Oc08 Uranus Visible Light

Aside from the whole spinning sideways thing, Uranus doesn’t look particularly exciting. The entire planet is just a uniform cyan color with no distinguishing features. At least that’s how it appears to the unaided human eye.

Oc08 Uranus Ultraviolet Filter

Observations in non-visible wavelengths of light reveal a more complex and interesting world, with atmospheric belts and zones that look similar to what we’ve seen on Jupiter, Saturn, and Neptune.

And in 2014, the seventh planet from the Sun became a lot more interesting. Both professional and amateur astronomers began reporting anomalous bright spots in Uranus’s atmosphere. These bright spots were interesting enough to deserve observation time on the Hubble Space Telescope, which confirmed in October 2014 (one year ago this month!) that they were storm clouds.

It seems these storms are seasonal. Because of Uranus’s 98º tilt, the changing of the seasons are much more dramatic than would otherwise be expected, but since a Uranian year is over 84 Earth years long, we don’t get to see this happen very often.

As part of the 2015 Mission to the Solar System, I’ve spent almost a whole month studying Uranus (stop laughing). I kind of feel bad for this poor planet. Uranus is stuck with an embarrassing name, and it’s been too often neglected and misunderstood. But like many things in life, there’s a lot more to it than at first meets the eye.

Links

Uranus in True and False Color from NASA.

Giant Methane Storms on Uranus from Phys.org.

* * *

Today’s post is part of Uranus month for the 2015 Mission to the Solar System. Click here to find out more about this special series.


Sciency Words: Verona Rupes

October 16, 2015

Sciency Words PHYS copy

Sciency Words is a special series here on Planet Pailly celebrating the rich and colorful world of science and science-related vocabulary. Today, we’re looking at the term:

VERONA RUPES

In Wanderers, a short film by Erik Wernquist, we see ordinary humans of the future living, working, and having fun all across the Solar System. One of the fun parts is a cliff-jumping scene on Uranus’s moon Miranda, in a place called Verona Rupes.

The moons of Uranus are generally named after Shakespearean characters, or at least characters from classic literature. The Shakespeare theme also applies to features on those moons, so Verona Rupes is named after Verona, Italy, the setting of Romeo and Juliet. “Rupes” is the Latin word for cliff.

Estimated to be somewhere between 5 and 20 kilometers high (sources disagree wildly about the exact height), Verona Rupes is the tallest cliff in the Solar System, as far as we currently know. For comparison, commercial airliners here on Earth normally fly at an altitude of 9 kilometers.

That extreme height may sound crazy, but it makes sense in the context of Miranda’s landscape. Miranda is sometimes called the Frankenstein’s monster of moons because it has a bizarre, patchwork-like appearance. It looks as though someone took bits and pieces of different planets and moons and haphazardly stitched them together.

Only the southern hemisphere of Miranda has been photographed, so it’s entirely possible more Verona Rupes-like cliffs may be discovered one day in the northern hemisphere.

Jumping off Verona Rupes might not be as terrifying as it seems. Yes, it’s a long drop, but Miranda only has 0.8% of Earth’s surface gravity. So rather than plummeting to your death, you’d drift lazily to… actually, you’d still plummet to your death, or at least serious injury.

Acceleration due to gravity may be low, but after falling 5 to 20 kilometers, you’ll still smack the ground at a velocity of several hundred kilometers per hour. Fortunately, according to Erik Wernquist’s website, those thrill-seekers on Miranda have small rockets to brake their falls.

Links

Miranda High Resolution of Large Fault from JPL Photojournal.

Verona Rupes: Tallest Known Cliff in the Solar System from Astronomy Picture of the Day.

Bizarre Shape of Uranus’ “Frankenstein” Moon Explained from Space.com.


Uranus: How to Get There

October 15, 2015

We know next to nothing about Uranus. Telescopic observations can only tell us so much, and the only other data we have comes from a flyby mission (Voyager 2) back in the 80’s. To learn more about the 7th planet from the Sun, we need to put a spacecraft in orbit.

Oc06 Uranus Asks a Question

Setting Course for Uranus

First of all, you can’t just point your rocket at Uranus and go. You have to aim for where Uranus will be, not where it currently is.

Secondly, there are no straight lines in space. Your course will be a curved trajectory, heavily influenced by the Sun’s gravity and the gravities of any planets you happen to pass near. If you time things right, this can work to your advantage and help you conserve fuel.

Thirdly, once you reach Uranus, you’ll have to slow down enough to be captured by Uranus’s gravity. None of these issues are unique to Uranus, but this third point… this is where Uranus makes things extra challenging.

Slamming on the Brakes

The farther you want to travel into the Outer Solar System, the faster you need to go. Otherwise, the Sun’s gravity will start pulling you back. By the time you get into the general vicinity of Uranus, you’re approaching the kind of velocity needed to leave the Solar System entirely. Then at a critical moment, you have to decelerate rapidly in order to enter orbit.

It’s sort of like flooring it down the highway and then, just as you’re about to zoom right past your exit, slamming on the brakes. I won’t go into the role the rocket equation plays in a maneuver like that. Let’s just say your spacecraft will need a tremendous, stupendous amount of fuel to pull this off.

This is one of the reasons why Voyager 2 was a flyby mission. Even if NASA wanted to enter Uranian orbit, passing up the opportunity to flyby Neptune later, the spacecraft simply couldn’t do it.

Oc06 Uranus Flyby

A better option for a Uranus orbiter might be to accelerate at a slower pace, taking a much longer, more spirally course away from the Sun, like the MESSENGER mission in reverse. The only problem is that the journey would take many decades to complete, so most of the researchers involved would likely die of old age before the spacecraft reached its destination.

Could We Still Do It?

According to a JPL paper entitled “The Case for a Uranus Orbiter,” we could place a spacecraft in Uranian orbit within a reasonable time span and without breaking NASA’s budget. Such a mission would truly test the limits of current technology, but we could do it.

In some distant Sci-Fi future, full of anti-gravity and warp drive technology, a quick trip to Uranus or Neptune would sound a lot more feasible. But my guess is that even then, hotshot space pilots might find that rapid deceleration to be a bit of a challenge.

* * *

Today’s post is part of Uranus month for the 2015 Mission to the Solar System. Click here for more about this series.


Sciency Words: Ice Giant

October 9, 2015

Sciency Words BIO copy

Sciency Words is a special series here on Planet Pailly celebrating the rich and colorful world of science and science-related vocabulary. Today, we’re looking at the term:

ICE GIANT

Depending on whom you ask, our Solar System has either four gas giants or only two. Uranus and Neptune are sometimes classified as ice giants instead.

Oc04 Vanilla Ice Giant

Why do we have to make this distinction? Because in the 1990’s (around the time that annoying Vanilla Ice song came out), astronomers began to realize that Uranus and Neptune are fundamentally different from Jupiter and Saturn.

While Jupiter and Saturn are composed of over 90% hydrogen, Uranus and Neptune have a more interesting mix of chemicals: methane, ammonia, water… They have hydrogen too, but the ratio of hydrogen to other stuff is much lower.

It’s believed that during the formation of the Solar System, Uranus and Neptune accumulated vast quantities of ice (hence the name ice giant). By ice, I mean any volatile substance in a solid state, not just water ice.

In describing modern Uranus and Neptune, astronomers continue to call substances like methane, ammonia, and water “ice” even though these substances aren’t necessarily in a solid form anymore. Also, don’t let any of this terminology mislead you into thinking these planets are cold. Their interiors are extremely hot, regardless of their so-called “icy” composition.

Perhaps the biggest difference between gas and ice giants relates to us humans. We don’t honestly know much about the gas giants, but we know even less about their icy cousins. Jupiter and Saturn have been visited by a handful of space probes. Uranus and Neptune have only been visited once each, and that was back in the 80’s.

Oc04 Uranus Spins Right Round

NASA is currently considering a flyby mission to Uranus or Neptune (or both) similar to the recent flyby of Pluto by New Horizons. Approval for that may come in the next year or so.

Of course, if we really want to understand what ice giants are like and why they’re so different, we should send an orbiter, not just a flyby mission. Unfortunately, entering orbit around Uranus or Neptune is much easier said than done. More on that next week.

Links

NASA’s Next Big Spacecraft Could Visit an Ice Giant from Astronomy Magazine.

The Atmospheres of the Ice Giants, Uranus and Neptune from NASA’s Jet Propulsion Laboratory.

Are There Oceans on Neptune? from Universe Today.


Uranus: Why’s It Sideways?

October 5, 2015

Something’s odd about Uranus. It spins sideways. In more technical lingo, the planet’s axis of rotation is titled approximately 98º in relation to the orbital plane of the Solar System. I feel like I say this a lot on this blog, but there are currently several competing theories to explain why.

One Big Collision: Maybe one large object, more massive than Earth, collided with Uranus, knocking Uranus sideways.

 

Oc02 Uranus Struck Once

Many Little Collisions: Or maybe a group of smaller objects collided with Uranus, knocking Uranus sideways.

Oc02 Uranus Struck Many Times

Computer simulations seem to favor this idea, mainly because it does a better job accounting for the sideways orientation of not only Uranus but also its rings and moons.

A Lost Moon: Or perhaps long ago, Uranus had an additional moon: an especially massive moon with a large gravitational pull, enough to cause Uranus to tip on its side. Later, this hypothetical moon would have been yanked out of orbit by gravitational interactions with one of the other gas giants.

I’m skeptical of this lost moon idea, mainly because Earth’s large moon supposedly prevents our own planet from wobbling or tipping over in its orbit.  I much prefer the collision or multiple collisions hypotheses.

Is Uranus really as odd as we think?

Consider the fact that Venus’s rotation is also out of whack with the rest of the Solar System. Venus rotates backwards (possibly because of a collision, by the way). That means two out of eight planets rotate out of alignment with the rest of the Solar System. That’s 25%!

We still don’t know much about planets in other star systems, but if this 25% statistic holds true (and given how common collisions are in space, I see no reason why it wouldn’t), then Uranus may not be all that unusual after all.

Links

Series of Bumps Sent Uranus into Its Sideways Spin from Europlanet.

A Collisionless Scenario for Uranus Tilting from arxiv.org.

* * *

Today’s post is part of Uranus month for the 2015 Mission to the Solar System. Click here for more about this series.


Sciencey Words: Uranus

October 2, 2015

As we continue our voyage through the Solar System, we now reach a planet that has become the butt of far too many childish jokes.

Oc01 Presenting Uranus

I’ve sort of been dreading this. Uranus is the first planet discovered in modern times. It’s only been visited by a spacecraft once. It’s colder than it should be, the atmosphere is oddly featureless (at least in visible light), and some of its moons are pretty strange. Also, Uranus is spinning sideways for some reason.

But it’s hard to take any of that seriously because… well… you know why.

In fact, I rarely if ever hear about new discoveries on or concerning Uranus. Part of the reason is that Uranus is so far away and so difficult to observe; however, Neptune is even farther, and I do occasionally hear about new discoveries there.

I sometimes wonder if astronomers are deliberately avoiding this area of research. I mean, nobody wants to be the guy who probes Uranus for a living.

So how did the seventh planet from the Sun get this embarrassing name? The story, as it turns out, is really interesting.


So what do you think of Uranus’s name? Would you have preferred Herschel or Georgium Sidus or some other possibility?