Gravity Waves On Pluto?

The varying brightness in Pluto's atmosphere is caused by atmospheric gravity waves, or buoyancy waves. Image: NASA/New Horizons/Johns Hopkins APL/SWRI

New Horizons’ historic journey to Pluto and beyond continues to provide surprises. As data from the spacecraft’s close encounter with Pluto and its moons arrives at Earth, scientists are piecing together an increasingly intriguing picture of the dwarf planet. The latest discovery is centred around Pluto’s atmosphere, and what are called ‘atmospheric gravity waves.’

Atmospheric gravity waves are a different phenomenon than the gravity waves that were detected for the first time in February, 2016. Those gravity waves are ripples in the fabric of space time, first predicted by Albert Einstein back in 1916. After years of searching, the LIGO instrument detected gravity waves that resulted from two black holes colliding. The discovery of what you might call ‘Einsteinian Gravity Waves’ may end up revolutionizing astronomy.

New Horizons has revealed surprise after surprise in its study of Pluto. Its atmosphere has turned out to be much more complex than anybody expected. It’s composed of 90% nitrogen, with extensive haze layers. Scientists have discovered that Pluto’s atmosphere can vary in brightness depending on viewpoint and illumination, while the vertical structure of the layered haze remains unchanged.

Scientists studying the New Horizons’ data think that atmospheric gravity waves, also called buoyancy waves, are responsible. Atmospheric gravity waves are known to exist on only two other planets; Earth and Mars. They are typically caused by wind flowing over obstructions like mountain ranges.

The layers in Pluto’s atmosphere, and their varying brightness, are most easily seen when they are backlit by the Sun. This was the viewpoint New Horizons had when it captured these images on its departure from Pluto on July 14, 2015. The spacecraft’s Long Range Reconnaissance Imager (LORRI) captured them, using time intervals of 2 to 5 hours. What they show is the brightness of the layers changing by 30% without any change in their height above the surface of the planet.

LORRI, as its name suggests, is a long range image capture instrument. It also captures high resolution geologic data, and was used to map Pluto’s far side. The principal investigator for LORRI is Andy Cheng, from the Applied Physics Laboratory at Johns Hopkins University, in Maryland. “Pluto is simply amazing,” said Andy Cheng. “When I first saw these images and the haze structures that they reveal, I knew we had a new clue to the nature of Pluto’s hazes. The fact that we don’t see the haze layers moving up or down will be important to future modelling efforts.”

Overall, Pluto and its system of moons has turned out to be a much more dynamic place than previously thought. A geologically active landscape, possible ice volcanoes, eroding cliffs made of methane ice, and more, have woken us up to Pluto’s complexity. But its atmosphere has turned out to be just as complex and puzzling.

New Horizons has departed the Pluto system now, and is headed for the Kuiper Belt. The Kuiper Belt is considered a relic of the early Solar System. New Horizons will visit another icy world there, and hopefully continue on to the edge of the heliosphere, the same way the Voyage probes have. New Horizons has enough energy to last until approximately the mid-2030’s, if all goes well.

Are there Storms on the Moon?

Here on Earth, we’re always concerned with the weather.

“OK Google, am I going to need an umbrella tomorrow?”

[Google] No, rain is not expected tomorrow in Curtney. The forecast is 20 degrees and partly cloudy.

Uh, it’s pronounced “Courtenay”.

Fine, what if I lived on the Moon? OK Google, am I going to need an umbrella tomorrow on the Moon?

[Google] …

Let’s take Google’s silence for uncertainty.

The names of geological features on the Moon sure evoke mental images of weather. There’s the Ocean of Storms, also known as Oceanus Procellarum, or the Ocean of Clouds – aka Mare Nubium. In fact, most of the regions of the Moon are named after oceans. That’s got to count for something, right?

Many of the features on the moon are named as oceans. Credit: NASA
Many of the features of the moon were thought to be oceans. Credit: NASA

They got these names because the early astronomers thought they were seeing actual oceans on the Moon. They imagined vast seas, where heroic 6-legged creepy bug people plied the icy waves seeking fame, fortune and lunar plunder. I don’t know, like gold cheese or something. Seriously, they were making a lot of this stuff up until telescopes were invented.

But when the NASA astronauts finally set foot on the Moon, they knew they wouldn’t need to pack their snorkeling gear because there weren’t any oceans on the Moon, or really any atmosphere. The Moon is almost as dead and lifeless as space itself.

The storms we see battering the astronauts on every Mars science fiction story just can’t happen on the Moon because there’s no air there.

There’s an ongoing lethal radiation solar wind blowing from the Sun and deep space, but nothing that you’d be able to windsurf too.

So why isn’t there an atmosphere on the Moon? It all comes down to gravity. The Moon has about 1% of the mass of the Earth, which means that it doesn’t have enough gravity to hold onto any gas atmosphere. Anything that it did have would have been blown away by the solar wind billions of years ago.

We did a whole episode on what it would take to terraform the Moon, and it turns out you’d need to constantly replenish the atmosphere.

In fact, this is one of the reasons why the Martian atmosphere is so thin. It was probably thicker in the past, but the solar winds stripped off all the lighter atmosphere long ago. Now it’s just 1% the thickness of the Earth’s atmosphere.

Now, I’ve said that the Moon has almost no atmosphere. But almost no means partly yes. There is in fact an incredibly thin atmosphere surrounding the Moon which measures about a hundred trillionth the thickness of the Earth’s atmosphere.

There are a few sources of this atmosphere. First there’s volcanic outgassing that comes from the Moon. this contributes a little helium and radon. Then there’s the constant micrometeorite bombardment that kicks up pulverized lunar regolith.

 Lunar sunrise sketches drawn by Commander E. A. Cernan during the Apollo 17 mission. Credit: NASA

Lunar sunrise sketches drawn by Commander E. A. Cernan during the Apollo 17 mission. Credit: NASA

But perhaps the strangest atmospheric feature is a storm that does rage across the surface of the Moon right at the terminator, the exact line between the Moon’s day side and its night side. It turns out the day side of the Moon is positively charged, and the night side is negatively charged.

As the terminator moves, the polarity of the dust flips and it drives it sideways. In fact, the astronauts who walked on the Moon actually reported seeing this. They saw bands or twilight rays in the sky around lunar sunrise/sunset.

Without a thick atmosphere, the surface of the Moon just doesn’t have any appreciable weather and definitely doesn’t have storms like we have on Earth. Mark Watney will need some other reason than weather to be stuck behind on the Moon.

How Do We Terraform The Moon?

Welcome back to our ongoing series, “The Definitive Guide To Terraforming”! We continue with a look at the Moon, discussing how it could one day be made suitable for human habitation.

Ever since the beginning of the Space Age, scientists and futurists have explored the idea of transforming other worlds to meet human needs. Known as terraforming, this process calls for the use of environmental engineering techniques to alter a planet or moon’s temperature, atmosphere, topography or ecology (or all of the above) in order to make it more “Earth-like”. As Earth’s closest celestial body, the Moon has long been considered a potential site.

All told, colonizing and/or terraforming the Moon would be comparatively easy compared to other bodies. Due to its proximity, the time it would take to transport people and equipment to and from the surface would be significantly reduced, as would the costs of doing so. In addition, it’s proximity means that extracted resources and products manufactured on the Moon could be shuttled to Earth in much less time, and a tourist industry would also be feasible.

Continue reading “How Do We Terraform The Moon?”

Hubble Directly Measures Rotation of Cloudy ‘Super-Jupiter’

Astronomers using the Hubble Space Telescope have measured the rotation rate of an extreme exoplanet 2M1207b by observing the varied brightness in its atmosphere. This is the first measurement of the rotation of a massive exoplanet using direct imaging.

This is a composite image of the brown dwarf object 2M1207 (centre) and the fainter object seen near it, at an angular distance of 778 milliarcsec. Designated "Giant Planet Candidate Companion" by the discoverers, it may represent the first image of an exoplanet. Further observations, in particular of its motion in the sky relative to 2M1207 are needed to ascertain its true nature. The photo is based on three near-infrared exposures (in the H, K and L' wavebands) with the NACO adaptive-optics facility at the 8.2-m VLT Yepun telescope at the ESO Paranal Observatory.
This is a composite image of the brown dwarf object 2M1207 (blue-white) and the planet 2M1207b, seen in red, located 170 light years from Earth in the constellation Centaurus. The photo is based on three near-infrared exposures with the taken with the 8.2-m VLT Yepun telescope at the ESO Paranal Observatory. Credit: ESO

Little by little we’re coming to know at least some of the 2,085 exoplanets discovered to date more intimately despite their great distances and proximity to the blinding light of their host stars. 2M1207b is about four times more massive than Jupiter and dubbed a “super-Jupiter”. Super-Jupiters fill the gap between Jupiter-mass planets and brown dwarf stars. They can be up to 80 times more massive than Jupiter yet remain nearly the same size as that planet because gravity compresses the material into an ever denser, more compact sphere.

2M1207b lies 170 light years from Earth and orbits a brown dwarf at a distance of 5 billion miles. By contrast, Jupiter is approximately 500 million miles from the sun. You’ll often hear brown dwarfs described as “failed stars” because they’re not massive enough for hydrogen fusion to fire up in their cores the way it does in our sun and all the rest of the main sequence stars.

Researchers used Hubble’s exquisite resolution to precisely measure the planet’s brightness changes as it spins and nailed the rotation rate at 10 hours, virtually identical to Jupiter’s. While it’s fascinating to know a planet’s spin, there’s more to this extraordinary exoplanet. Hubble data confirmed the rotation but also showed the presence of patchy, “colorless” (white presumably) cloud layers. While perhaps ordinary in appearance, the composition of the clouds is anything but.

 exoplanet 2M1207 b with the Solar System planet Jupiter. Although four times more massive than the Jovian planet, gravity compresses its matter to keep it relatively small. Credit: Wikipedia / Aldaron
Exoplanet 2M1207 b with the Solar System planet Jupiter for comparison. Although four times more massive than the Jovian planet, gravity compresses its matter to keep it relatively small. Credit: Wikipedia / Aldaron

The planet appears bright in infrared light because it’s young (about 10 million years old) and still contracting, releasing gravitational potential energy that heats it from the inside out. All that extra heat makes 2M1207b’s atmosphere hot enough to form “rain” clouds made of vaporized rock. The rock cools down to form tiny particles with sizes similar to those in cigarette smoke. Deeper into the atmosphere, iron droplets are forming and falling like rain, eventually evaporating as they enter the lower levels of the atmosphere.

“So at higher altitudes it rains glass, and at lower altitudes it rains iron,” said Yifan Zhou of the University of Arizona, lead author on the research paper in a recent Astrophysical Journal. “The atmospheric temperatures are between about 2,200 to 2,600 degrees Fahrenheit.” Every day’s a scorcher on 2M1207b.

Both Jupiter and Saturn also emit more heat than they receive from the sun because they too are still contracting despite being 450 times older. The bigger you are, the slower you chill.

Illustration of the extrasolar planet 2M1207b (foreground) orbiting a brown dwarf. Credits: NASA, ESA, and G. Bacon/STScI
Illustration of the extrasolar planet 2M1207b (foreground) orbiting a brown dwarf. Both shine brightly in infrared light. Credits: NASA, ESA, and G. Bacon/STScI

All the planets in our Solar System possess only a fraction of the mass of the Sun. Even mighty Jove is a thousand times less massive. But Mr. Super-Jupiter’s a heavyweight compared to its brown dwarf host, being just 5-7 times less massive. While Jupiter and the rest of the planets formed by the accretion of dust and rocks within a clumpy disk of material surrounding the early Sun, it’s thought 2M1207b and its companion may have formed throughout the gravitational collapse of a pair of separate disks.

This super-Jupiter will an ideal target for the James Webb Space Telescope, a space observatory optimized for the infrared scheduled to launch in 2018. With its much larger mirror — 21-feet (6.5-meters) — Webb will help astronomers better determine the exoplanet’s atmospheric composition and created more detailed maps from brightness changes.

Teasing out the details of 2M1207b’s atmosphere and rotation introduces us to a most alien world the likes of which never evolved in our own Solar System. I feel like I’m aboard the Starship Enterprise visiting far-flung worlds. Only this is better. It’s real.

Why Do We Sometimes See a Ring Around the Moon?

Moon halo by Rob Sparks

Have you ever looked up on a clear night and noticed there’s a complete ring around the Moon? In fact, if you look closely, the ring can have a rainbow appearance, with bright spots on either side, or above and below. What’s going on with the Moon and the atmosphere to cause this effect?

This ring surrounding the Moon is caused by the refraction of Moonlight (which is really reflected sunlight, of course) through ice crystals suspended in the upper atmosphere between 5-10 km in altitude. It doesn’t have to be winter, since the cold temperatures at high altitudes are below freezing any time of the year. Generally they’re seen with cirrus clouds; the thin, wispy clouds at high altitude.

The ice crystals themselves have a very consistent hexagonal shape, which means that any light passing through them will always refract light – or bend – at the same angle.

640px-Path_of_rays_in_a_hexagonal_prism
Path of rays in a hexagonal prism” by donalbein – Own work. Licensed under CC BY-SA 2.5 via Commons.
Moonlight passes through one facet of the ice crystal, and is then refracted back out at exactly the angle of 22-degrees.

Of course, the atmosphere is filled with an incomprehensible number of crystals, all refracting moonlight off in different directions. But at any moment, a huge number happen to be in just the right position to be refracting light towards your eyes. You just aren’t in a position to see all the other refracted light. In fact, everyone sees their own private halo, because you’re only seeing the crystals that happen to be aligning the light for your specific location. Someone a few meters beside you is seeing their own private version of the halo – just like a rainbow.

A halo rings the bright moon and planet Jupiter (left of moon) Credit: Bob King
A halo rings the bright moon and planet Jupiter (left of moon) Credit: Bob King

The size of the ring is most commonly 22-degrees. This is about the same size as your open hand on your outstretched arm. The Moon itself, for comparison, is the size of your smallest nail when you hold out your hand.

The 22-degree size corresponds to the refraction angle of moonlight.

We see a rainbow because the different colors are refracted at slightly different angles. This is exactly what happens with a rainbow. The moonlight is broken up into its separate colors because they all refract at different angles, and so you see the colors split up like a rainbow.

Lunar halo by Gustav Sanchez
Lunar halo with rainbow. Photo credit: Gustav Sanchez.
Moon dogs (or “mock moons”) are seen as bright spots that can appear on either side of the Moon, when the Moon is closer to the horizon, and at its fullest. These are located on either side of the lunar ring, parallel to the horizon.

In certain conditions, especially in the Arctic, where the ice crystals can be close to the surface, you can get a moon pillar. The light from the Moon reflects off the ice crystals near the surface, creating a glow near the horizon.

Sun pillar by Mary Spicer
This is a Sun pillar (not a moon pillar), but it’s the same general idea. Photo credit: Mary Spicer.

Want to see more? Here’s a great lunar halo photo from NASA’s APOD. And here’s more info from Earth and Sky.

What Is The Atmosphere Like On Other Planets?

Here on Earth, we tend to take our atmosphere for granted, and not without reason. Our atmosphere has a lovely mix of nitrogen and oxygen (78% and 21% respectively) with trace amounts of water vapor, carbon dioxide and other gaseous molecules. What’s more, we enjoy an atmospheric pressure of 101.325 kPa, which extends to an altitude of about 8.5 km.

In short, our atmosphere is plentiful and life-sustaining. But what about the other planets of the Solar System? How do they stack up in terms of atmospheric composition and pressure? We know for a fact that they are not breathable by humans and cannot support life. But just what is the difference between these balls of rock and gas and our own?

For starters, it should be noted that every planet in the Solar System has an atmosphere of one kind or another. And these range from incredibly thin and tenuous (such as Mercury’s “exosphere”) to the incredibly dense and powerful – which is the case for all of the gas giants. And depending on the composition of the planet, whether it is a terrestrial or a gas/ice giant, the gases that make up its atmosphere range from either the hydrogen and helium to more complex elements like oxygen, carbon dioxide, ammonia and methane.

Mercury’s Atmosphere:

Mercury is too hot and too small to retain an atmosphere. However, it does have a tenuous and variable exosphere that is made up of hydrogen, helium, oxygen, sodium, calcium, potassium and water vapor, with a combined pressure level of about 10-14 bar (one-quadrillionth of Earth’s atmospheric pressure). It is believed this exosphere was formed from particles captured from the Sun, volcanic outgassing and debris kicked into orbit by micrometeorite impacts.

Mercury's Horizon
A High-resolution Look over Mercury’s Northern Horizon. Credit: NASA/MESSENGER

Because it lacks a viable atmosphere, Mercury has no way to retain the heat from the Sun. As a result of this and its high eccentricity, the planet experiences considerable variations in temperature. Whereas the side that faces the Sun can reach temperatures of up to 700 K (427° C), while the side in shadow dips down to 100 K (-173° C).

Venus’ Atmosphere:

Surface observations of Venus have been difficult in the past, due to its extremely dense atmosphere, which is composed primarily of carbon dioxide with a small amount of nitrogen. At 92 bar (9.2 MPa), the atmospheric mass is 93 times that of Earth’s atmosphere and the pressure at the planet’s surface is about 92 times that at Earth’s surface.

Venus is also the hottest planet in our Solar System, with a mean surface temperature of 735 K (462 °C/863.6 °F). This is due to the CO²-rich atmosphere which, along with thick clouds of sulfur dioxide, generates the strongest greenhouse effect in the Solar System. Above the dense CO² layer, thick clouds consisting mainly of sulfur dioxide and sulfuric acid droplets scatter about 90% of the sunlight back into space.

Another common phenomena is Venus’ strong winds, which reach speeds of up to 85 m/s (300 km/h; 186.4 mph) at the cloud tops and circle the planet every four to five Earth days. At this speed, these winds move up to 60 times the speed of the planet’s rotation, whereas Earth’s fastest winds are only 10-20% of the planet’s rotational speed.

Venus flybys have also indicated that its dense clouds are capable of producing lightning, much like the clouds on Earth. Their intermittent appearance indicates a pattern associated with weather activity, and the lightning rate is at least half of that on Earth.

Earth’s Atmosphere:

Earth’s atmosphere, which is composed of nitrogen, oxygen, water vapor, carbon dioxide and other trace gases, also consists of five layers. These consists of the Troposphere, the Stratosphere, the Mesosphere, the Thermosphere, and the Exosphere. As a rule, air pressure and density decrease the higher one goes into the atmosphere and the farther one is from the surface.

Closest to the Earth is the Troposphere, which extends from the 0 to between 12 km and 17 km (0 to 7 and 10.56 mi) above the surface. This layer contains roughly 80% of the mass of Earth’s atmosphere, and nearly all atmospheric water vapor or moisture is found in here as well. As a result, it is the layer where most of Earth’s weather takes place.

The Stratosphere extends from the Troposphere to an altitude of 50 km (31 mi). This layer extends from the top of the troposphere to the stratopause, which is at an altitude of about 50 to 55 km (31 to 34 mi). This layer of the atmosphere is home to the ozone layer, which is the part of Earth’s atmosphere that contains relatively high concentrations of ozone gas.

Space Shuttle Endeavour sillouetted against the atmosphere. The orange layer is the troposphere, the white layer is the stratosphere and the blue layer the mesosphere.[1] (The shuttle is actually orbiting at an altitude of more than 320 km (200 mi), far above all three layers.) Credit: NASA
Space Shuttle Endeavour sillouetted against the atmosphere. The orange layer is the troposphere, the white layer is the stratosphere and the blue layer the mesosphere. Credit: NASA
Next is the Mesosphere, which extends from a distance of 50 to 80 km (31 to 50 mi) above sea level. It is the coldest place on Earth and has an average temperature of around -85 °C (-120 °F; 190 K). The Thermosphere, the second highest layer of the atmosphere, extends from an altitude of about 80 km (50 mi) up to the thermopause, which is at an altitude of 500–1000 km (310–620 mi).

The lower part of the thermosphere, from 80 to 550 kilometers (50 to 342 mi), contains the ionosphere – which is so named because it is here in the atmosphere that particles are ionized by solar radiation.  This layer is completely cloudless and free of water vapor. It is also at this altitude that the phenomena known as Aurora Borealis and Aurara Australis are known to take place.

The Exosphere, which is outermost layer of the Earth’s atmosphere, extends from the exobase – located at the top of the thermosphere at an altitude of about 700 km above sea level – to about 10,000 km (6,200 mi). The exosphere merges with the emptiness of outer space, and is mainly composed of extremely low densities of hydrogen, helium and several heavier molecules including nitrogen, oxygen and carbon dioxide

The exosphere is located too far above Earth for any meteorological phenomena to be possible. However, the Aurora Borealis and Aurora Australis sometimes occur in the lower part of the exosphere, where they overlap into the thermosphere.

This photo of the aurora was taken by astronaut Doug Wheelock from the International Space Station on July 25, 2010. Credit: Image Science & Analysis Laboratory, NASA Johnson Space Center
Photo of the aurora taken by astronaut Doug Wheelock from the International Space Station on July 25, 2010. Credit: NASA/Johnson Space Center

The average surface temperature on Earth is approximately 14°C; but as already noted, this varies. For instance, the hottest temperature ever recorded on Earth was 70.7°C (159°F), which was taken in the Lut Desert of Iran. Meanwhile, the coldest temperature ever recorded on Earth was measured at the Soviet Vostok Station on the Antarctic Plateau, reaching an historic low of -89.2°C (-129°F).

Mars’ Atmosphere:

Planet Mars has a very thin atmosphere which is composed of 96% carbon dioxide, 1.93% argon and 1.89% nitrogen along with traces of oxygen and water. The atmosphere is quite dusty, containing particulates that measure 1.5 micrometers in diameter, which is what gives the Martian sky a tawny color when seen from the surface. Mars’ atmospheric pressure ranges from 0.4 – 0.87 kPa, which is equivalent to about 1% of Earth’s at sea level.

Because of its thin atmosphere, and its greater distance from the Sun, the surface temperature of Mars is much colder than what we experience here on Earth. The planet’s average temperature is -46 °C (51 °F), with a low of -143 °C (-225.4 °F) during the winter at the poles, and a high of 35 °C (95 °F) during summer and midday at the equator.

The planet also experiences dust storms, which can turn into what resembles small tornadoes. Larger dust storms occur when the dust is blown into the atmosphere and heats up from the Sun. The warmer dust filled air rises and the winds get stronger, creating storms that can measure up to thousands of kilometers in width and last for months at a time. When they get this large, they can actually block most of the surface from view.

Mars, as it appears today, Credit: NASA
Mars, as it appears today, with a very thin and tenuous atmosphere. Credit: NASA

Trace amounts of methane have also been detected in the Martian atmosphere, with an estimated concentration of about 30 parts per billion (ppb). It occurs in extended plumes, and the profiles imply that the methane was released from specific regions – the first of which is located between Isidis and Utopia Planitia (30°N 260°W) and the second in Arabia Terra (0°N 310°W).

Ammonia was also tentatively detected on Mars by the Mars Express satellite, but with a relatively short lifetime. It is not clear what produced it, but volcanic activity has been suggested as a possible source.

Jupiter’s Atmosphere:

Much like Earth, Jupiter experiences auroras near its northern and southern poles. But on Jupiter, the auroral activity is much more intense and rarely ever stops. The intense radiation, Jupiter’s magnetic field, and the abundance of material from Io’s volcanoes that react with Jupiter’s ionosphere create a light show that is truly spectacular.

Jupiter also experiences violent weather patterns. Wind speeds of 100 m/s (360 km/h) are common in zonal jets, and can reach as high as 620 kph (385 mph). Storms form within hours and can become thousands of km in diameter overnight. One storm, the Great Red Spot, has been raging since at least the late 1600s. The storm has been shrinking and expanding throughout its history; but in 2012, it was suggested that the Giant Red Spot might eventually disappear.

Jupiter is perpetually covered with clouds composed of ammonia crystals and possibly ammonium hydrosulfide. These clouds are located in the tropopause and are arranged into bands of different latitudes, known as “tropical regions”. The cloud layer is only about 50 km (31 mi) deep, and consists of at least two decks of clouds: a thick lower deck and a thin clearer region.

There may also be a thin layer of water clouds underlying the ammonia layer, as evidenced by flashes of lightning detected in the atmosphere of Jupiter, which would be caused by the water’s polarity creating the charge separation needed for lightning. Observations of these electrical discharges indicate that they can be up to a thousand times as powerful as those observed here on the Earth.

Saturn’s Atmosphere:

The outer atmosphere of Saturn contains 96.3% molecular hydrogen and 3.25% helium by volume. The gas giant is also known to contain heavier elements, though the proportions of these relative to hydrogen and helium is not known. It is assumed that they would match the primordial abundance from the formation of the Solar System.

Trace amounts of ammonia, acetylene, ethane, propane, phosphine and methane have been also detected in Saturn’s atmosphere. The upper clouds are composed of ammonia crystals, while the lower level clouds appear to consist of either ammonium hydrosulfide (NH4SH) or water. Ultraviolet radiation from the Sun causes methane photolysis in the upper atmosphere, leading to a series of hydrocarbon chemical reactions with the resulting products being carried downward by eddies and diffusion.

Saturn’s atmosphere exhibits a banded pattern similar to Jupiter’s, but Saturn’s bands are much fainter and wider near the equator. As with Jupiter’s cloud layers, they are divided into the upper and lower layers, which vary in composition based on depth and pressure. In the upper cloud layers, with temperatures in range of 100–160 K and pressures between 0.5–2 bar, the clouds consist of ammonia ice.

Water ice clouds begin at a level where the pressure is about 2.5 bar and extend down to 9.5 bar, where temperatures range from 185–270 K. Intermixed in this layer is a band of ammonium hydrosulfide ice, lying in the pressure range 3–6 bar with temperatures of 290–235 K. Finally, the lower layers, where pressures are between 10–20 bar and temperatures are 270–330 K, contains a region of water droplets with ammonia in an aqueous solution.

On occasion, Saturn’s atmosphere exhibits long-lived ovals, similar to what is commonly observed on Jupiter. Whereas Jupiter has the Great Red Spot, Saturn periodically has what’s known as the Great White Spot (aka. Great White Oval). This unique but short-lived phenomenon occurs once every Saturnian year, roughly every 30 Earth years, around the time of the northern hemisphere’s summer solstice.

These spots can be several thousands of kilometers wide, and have been observed in 1876, 1903, 1933, 1960, and 1990. Since 2010, a large band of white clouds called the Northern Electrostatic Disturbance have been observed enveloping Saturn, which was spotted by the Cassini space probe. If the periodic nature of these storms is maintained, another one will occur in about 2020.

The winds on Saturn are the second fastest among the Solar System’s planets, after Neptune’s. Voyager data indicate peak easterly winds of 500 m/s (1800 km/h). Saturn’s northern and southern poles have also shown evidence of stormy weather. At the north pole, this takes the form of a hexagonal wave pattern, whereas the south shows evidence of a massive jet stream.

The persisting hexagonal wave pattern around the north pole was first noted in the Voyager images. The sides of the hexagon are each about 13,800 km (8,600 mi) long (which is longer than the diameter of the Earth) and the structure rotates with a period of 10h 39m 24s, which is assumed to be equal to the period of rotation of Saturn’s interior.

The south pole vortex, meanwhile, was first observed using the Hubble Space Telescope. These images indicated the presence of a jet stream, but not a hexagonal standing wave. These storms are estimated to be generating winds of 550 km/h, are comparable in size to Earth, and believed to have been going on for billions of years. In 2006, the Cassini space probe observed a hurricane-like storm that had a clearly defined eye. Such storms had not been observed on any planet other than Earth – even on Jupiter.

Uranus’ Atmosphere:

As with Earth, the atmosphere of Uranus is broken into layers, depending upon temperature and pressure. Like the other gas giants, the planet doesn’t have a firm surface, and scientists define the surface as the region where the atmospheric pressure exceeds one bar (the pressure found on Earth at sea level). Anything accessible to remote-sensing capability – which extends down to roughly 300 km below the 1 bar level – is also considered to be the atmosphere.

Diagram of the interior of Uranus. Credit: Public Domain
Diagram of the interior of Uranus. Credit: Public Domain

Using these references points, Uranus’  atmosphere can be divided into three layers. The first is the troposphere, between altitudes of -300 km below the surface and 50 km above it, where pressures range from 100 to 0.1 bar (10 MPa to 10 kPa). The second layer is the stratosphere, which reaches between 50 and 4000 km and experiences pressures between 0.1 and 10-10 bar (10 kPa to 10 µPa).

The troposphere is the densest layer in Uranus’ atmosphere. Here, the temperature ranges from 320 K (46.85 °C/116 °F) at the base (-300 km) to 53 K (-220 °C/-364 °F) at 50 km, with the upper region being the coldest in the solar system. The tropopause region is responsible for the vast majority of Uranus’s thermal infrared emissions, thus determining its effective temperature of 59.1 ± 0.3 K.

Within the troposphere are layers of clouds – water clouds at the lowest pressures, with ammonium hydrosulfide clouds above them. Ammonia and hydrogen sulfide clouds come next. Finally, thin methane clouds lay on the top.

In the stratosphere, temperatures range from 53 K (-220 °C/-364 °F) at the upper level to between 800 and 850 K (527 – 577 °C/980 – 1070 °F) at the base of the thermosphere, thanks largely to heating caused by solar radiation. The stratosphere contains ethane smog, which may contribute to the planet’s dull appearance. Acetylene and methane are also present, and these hazes help warm the stratosphere.

Uranus. Image credit: Hubble
Uranus, as imaged by the Hubble Space Telescope. Image credit: NASA/Hubble

The outermost layer, the thermosphere and corona, extend from 4,000 km to as high as 50,000 km from the surface. This region has a uniform temperature of 800-850 (577 °C/1,070 °F), although scientists are unsure as to the reason. Because the distance to Uranus from the Sun is so great, the amount of sunlight absorbed cannot be the primary cause.

Like Jupiter and Saturn, Uranus’s weather follows a similar pattern where systems are broken up into bands that rotate around the planet, which are driven by internal heat rising to the upper atmosphere. As a result, winds on Uranus can reach up to 900 km/h (560 mph), creating massive storms like the one spotted by the Hubble Space Telescope in 2012. Similar to Jupiter’s Great Red Spot, this “Dark Spot” was a giant cloud vortex that measured 1,700 kilometers by 3,000 kilometers (1,100 miles by 1,900 miles).

Neptune’s Atmosphere:

At high altitudes, Neptune’s atmosphere is 80% hydrogen and 19% helium, with a trace amount of methane. As with Uranus, this absorption of red light by the atmospheric methane is part of what gives Neptune its blue hue, although Neptune’s is darker and more vivid. Because Neptune’s atmospheric methane content is similar to that of Uranus, some unknown constituent is thought to contribute to Neptune’s more intense coloring.

Neptune’s atmosphere is subdivided into two main regions: the lower troposphere (where temperature decreases with altitude), and the stratosphere (where temperature increases with altitude). The boundary between the two, the tropopause, lies at a pressure of 0.1 bars (10 kPa). The stratosphere then gives way to the thermosphere at a pressure lower than 10-5 to 10-4 microbars (1 to 10 Pa), which gradually transitions to the exosphere.

Neptune’s spectra suggest that its lower stratosphere is hazy due to condensation of products caused by the interaction of ultraviolet radiation and methane (i.e. photolysis), which produces compounds such as ethane and ethyne. The stratosphere is also home to trace amounts of carbon monoxide and hydrogen cyanide, which are responsible for Neptune’s stratosphere being warmer than that of Uranus.

In this image, the colors and contrasts were modified to emphasize the planet’s atmospheric features. The winds in Neptune’s atmosphere can reach the speed of sound or more. Neptune’s Great Dark Spot stands out as the most prominent feature on the left. Several features, including the fainter Dark Spot 2 and the South Polar Feature, are locked to the planet’s rotation, which allowed Karkoschka to precisely determine how long a day lasts on Neptune. (Image: Erich Karkoschka)
A modified color/contrast image emphasizing Neptune’s atmospheric features, including wind speed. Credit Erich Karkoschka)

For reasons that remain obscure, the planet’s thermosphere experiences unusually high temperatures of about 750 K (476.85 °C/890 °F). The planet is too far from the Sun for this heat to be generated by ultraviolet radiation, which means another heating mechanism is involved – which could be the atmosphere’s interaction with ion’s in the planet’s magnetic field, or gravity waves from the planet’s interior that dissipate in the atmosphere.

Because Neptune is not a solid body, its atmosphere undergoes differential rotation. The wide equatorial zone rotates with a period of about 18 hours, which is slower than the 16.1-hour rotation of the planet’s magnetic field. By contrast, the reverse is true for the polar regions where the rotation period is 12 hours.

This differential rotation is the most pronounced of any planet in the Solar System, and results in strong latitudinal wind shear and violent storms. The three most impressive were all spotted in 1989 by the Voyager 2 space probe, and then named based on their appearances.

The first to be spotted was a massive anticyclonic storm measuring 13,000 x 6,600 km and resembling the Great Red Spot of Jupiter. Known as the Great Dark Spot, this storm was not spotted five later (Nov. 2nd, 1994) when the Hubble Space Telescope looked for it. Instead, a new storm that was very similar in appearance was found in the planet’s northern hemisphere, suggesting that these storms have a shorter life span than Jupiter’s.

Reconstruction of Voyager 2 images showing the Great Black spot (top left), Scooter (middle), and the Small Black Spot (lower right). Credit: NASA/JPL
Reconstruction of Voyager 2 images showing the Great Black spot (top left), Scooter (middle), and the Small Black Spot (lower right). Credit: NASA/JPL

The Scooter is another storm, a white cloud group located farther south than the Great Dark Spot – a nickname that first arose during the months leading up to the Voyager 2 encounter in 1989. The Small Dark Spot, a southern cyclonic storm, was the second-most-intense storm observed during the 1989 encounter. It was initially completely dark; but as Voyager 2 approached the planet, a bright core developed and could be seen in most of the highest-resolution images.

In sum, the planet’s of our Solar System all have atmospheres of sorts. And compared to Earth’s relatively balmy and thick atmosphere, they run the gamut between very very thin to very very dense. They also range in temperatures from the extremely hot (like on Venus) to the extreme freezing cold.

And when it comes to weather systems, things can equally extreme, with planet’s boasting either weather at all, or intense cyclonic and dust storms that put storms here n Earth to shame. And whereas some are entirely hostile to life as we know it, others we might be able to work with.

We have many interesting articles about planetary atmosphere’s here at Universe Today. For instance, he’s What is the Atmosphere?, and articles about the atmosphere of Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune,

For more information on atmospheres, check out NASA’s pages on Earth’s Atmospheric Layers, The Carbon Cycle, and how Earth’s atmosphere differs from space.

Astronomy Cast has an episode on the source of the atmosphere.

How Does The Sun Produce Energy?

There is a reason life that Earth is the only place in the Solar System where life is known to be able to live and thrive. Granted, scientists believe that there may be microbial or even aquatic life forms living beneath the icy surfaces of Europa and Enceladus, or in the methane lakes on Titan. But for the time being, Earth remains the only place that we know of that has all the right conditions for life to exist.

One of the reasons for this is because the Earth lies within our Sun’s Habitable Zone (aka. “Goldilocks Zone”). This means that it is in right spot (neither too close nor too far) to receive the Sun’s abundant energy, which includes the light and heat that is essential for chemical reactions. But how exactly does our Sun go about producing this energy? What steps are involved, and how does it get to us here on planet Earth?

Continue reading “How Does The Sun Produce Energy?”

Could We Terraform a Black Hole?

Is there any possible way to take a black hole and terraform it to be a place we could actually live?

In the challenge of terraforming the Sun, we all learned that outside of buying a Dyson Spaceshell 2000 made out of a solar system’s worth of planetbutter, it’s a terrible idea.

Making a star into a habitable world, means first destroying the stellar furnace. Which isn’t good for anyone, “Hey, free energy! vs. Let’s wreck this thing and build houses!”

Doubling down on this idea, a group of brilliant Guidensians wanted to crank the absurdity knob all the way up. You wanted to know if it would be possible to terraform a black hole.

In order to terraform something, we convert it from being Britney Spears’ level of toxic into something that humans can comfortably live on. We want reasonable temperatures, breathable atmosphere, low levels of radiation, and Earthish gravity.

With temperatures inversely proportional to their mass, a solar mass black hole is about 60 billionths of a Kelvin. This is just a smidge over absolute zero. Otherwise known as “pretty damn” cold. Actively feeding black holes can be surrounded by an accretion disk of material that’s more than 10 million degrees Kelvin, which would also kill you. Make a note, fix the temperature.

There’s no atmosphere, and it’s either the empty vacuum of space, or the superheated plasma surrounding an actively feeding black hole. Can you breathe plasma? If the answer is yes, this could work for you. If not, we’ll need to fix that.

You’d be hard pressed to find a more lethal radiation source in the entire Universe.

Black holes can spin at close to the speed of light, generating massive magnetic fields. These magnetic fields whip high energy particles around them, creating lethal doses of radiation. There are high energy particle jets pouring out of some supermassive black holes, moving at nearly the speed of light. You don’t want any part of that. We’ll add that to the list.

Black holes are known for being an excellent source of vitamin gravity. Out in orbit, it’s not so bad. Replace our Sun with a black hole of the same mass, and you wouldn’t be able to tell the difference.

So, problem solved? Not quite. If you tried to walk on the surface, you’d get shredded into a one-atom juicy stream of extruded tubemanity before you got anywhere near the time traveling alien library at the caramel center.

Reduce the gravity. Got it.

Artist rendering of a supermassive black hole. Credit: NASA / JPL-Caltech.
Artist rendering of a supermassive black hole. Credit: NASA / JPL-Caltech.

As we learned in a previous episode on how to kill black holes, there’s nothing you can do to affect them. You couldn’t smash comets into it to give it an atmosphere, it would just turn them into more black hole. You couldn’t fire a laser to extract material and reduce the mass, it would just turn your puny laser into more black hole.

Antimatter, explosives, stars, rocks, paper, scissors…black hole beats them all.

Repeat after me. “Om, nom, nom”.

All we can do is wait for it to evaporate over incomprehensible lengths of time. There are a few snags with this strategy, such as it will remain as a black hole until the last two particles evaporate away. There’s no point where it would magically become a regular planetoid.

That’s a full list of renovations for the cast and crew of “Pimp my Black Hole”.

Let’s look at our options. You can move it, just like we can move the Earth. Throw stuff really close to a black hole, and you get it moving with gravity. You could make it spin faster by dropping stuff into it, right up until it’s rotating at the edge of the speed of light, and you can make it more massive.

With that as our set of tools, there’s no way we’re ever going to live on a black hole.

It could be possible to surround a black hole with a Dyson Sphere, like a star.

Freemon Dyson theorized that eventually, a civilization would be able to build a megastructure around its star to capture all its energy. Credit: SentientDevelopments.com
Freemon Dyson theorized that eventually, a civilization would be able to build a megastructure around its star to capture all its energy. Credit: SentientDevelopments.com

It turns out there’s a way to have a pet black hole pay dividends aside from eating all your table scraps, shameful magazines and radioactive waste. By dropping matter into a black hole that’s spinning at close to the speed of light, you can actually extract energy from it.

Imagine you had an asteroid that was formed by two large rocks. As they get closer and closer to the black hole, tidal forces tear them apart. One chunk falls into the black hole, the smaller remaining rock has less collective mass, which allows it to escape. This remaining rock steals rotational energy from the black hole, which then slows down the rotation just a little bit.

This is the Penrose Process, named after the physicist who developed the idea. Astronomers calculated you can extract 20% of pure energy from matter that you drop in.

There’s isn’t much out there that would give you better return on your investment.

Also, it’s got to have a similar satisfying feeling as dropping pebbles off a bridge and watching them disappear from existence.

Terraforming a black hole is a terrible idea that will totally get us all killed. Don’t do it.

If you have to get close to that freakish hellscape I do recommend surrounding your pet with a Dyson Sphere and then feeding it matter and enjoying the energy you get in return.

A futuristic energy hungry civilization bent on evil couldn’t hope for a better place to live.

Have you got any more questions about black holes? Give us your suggestions in the comments below.

Planet Earth

In addition to being the birthplace of humanity and the cradle of human civilization, Earth is the only known planet in our Solar System that is capable of sustaining life. As a terrestrial planet, Earth is located within the Inner Solar System between between Venus and Mars (which are also terrestrial planets). This place Earth in a prime location with regards to our Sun’s Habitable Zone.

Earth has a number of nicknames, including the Blue Planet, Gaia, Terra, and “the world” – which reflects its centrality to the creation stories of every single human culture that has ever existed. But the most remarkable thing about our planet is its diversity. Not only are there an endless array of plants, animals, avians, insects and mammals, but they exist in every terrestrial environment. So how exactly did Earth come to be the fertile, life-giving place we all know and love?

Continue reading “Planet Earth”

Are Martian Dust Storms Dangerous?

Just how dangerous are the terrifying dust storms that swarm Mars?

Brave explorers trek across the red dunes of Mars when a dangerous dust storm blows in. In moments, our astronauts are blasted by gale force winds and driving sand, reducing visibility to zero. The brave heroes stumble desperately through the driving onslaught, searching in vain for shelter from the catastrophic conditions. One is blown into a ravine, or right to the edge of the cliff, requiring a dramatic rescue and likely a terrible terrible sacrifice and important parting words showing the true mettle of our heroes.

“Tell my Asuka… printed body pillow… I loved her…”

Will they make it? Why the heck would anyone land on that dusty irradiated death trap? Actually, a better question might be “Why do writers lean so hard on this trope?”. I’m looking at you Andy Weir.

Martian dust storms don’t just come from the fevered imagination of the same sci-fi writer who gave us a lush Venusian jungle, Saturnalian lava flats and Moon floor cheese. These dust storms are all too real and they drive at serious windspeeds.

NASA’s Viking landers clocked them at 100 km/h during dust storm season. Which is a thing on Mars. The landers sheltered enough from the big storms that they probably didn’t experience the greatest winds they’re capable of.

Scientists have seen evidence that sand is shifted around on the surface of Mars, and the regolith requires high wind speeds to pick it up and shove it around. Dust devils spin up across the surface, and rotate at hurricane speeds.

When the wind is above 65 km/h, it’s fast enough to pick up dust particles and carry them into the atmosphere encasing the planet in a huge, swirling, shroud. Freaked out yet? Is this dangerous? It sure sounds dangerous.

Apologies to all the fearmongering sci-fi writers, but actually, it’s not that dangerous. Here’s why.

First off, you’re not on Mars. It’s a book. Second, it’s a totally different experience on Earth. Here when you feel the wind blasting you in the face, or watch it dismantle a house during a tornado, it’s the momentum of the air particles hammering into it.

An illustration of a dust storm on Mars. Credit: Brian Grimm and Nilton Renno
An illustration of a dust storm on Mars. Credit: Brian Grimm and Nilton Renno

That momentum comes from air particle density and their velocity. Sadly, the density of the atmosphere on Mars is a delicate 1% of what we’re used to. It’s got the velocity, but it just doesn’t have the density.

It’s the difference between getting hit by a garden hose and a firehose with the same nozzle speed. One would gets you soaked, the other can push you down the street and give you bruises.

To feel a slight breeze on Mars similar to Earth, you multiply the wind speed by 10. So, if the wind was going about 15 km/h here, you’d need to be hit by winds going about 150 km/h there to have the same experience.

It’s not impossible for winds to go that fast on Mars, but that’s still not enough wind to fly a kite. To get it off the ground your mission buddy holds the kite, and you run around in the dumb Martian sand like a try-hard ass.

It would fly for a second and then crash down. You’d wonder why you even brought a kite to Mars in the first place because it’s NEVER windy enough.

Boo hoo. Your Mars kite doesn’t work. Good news! You’re on Mars!
Bad news. It was a one way trip. Good news! A wizard has made you immortal!
Bad news. The wizard has brought to life the entire fictional cast of the Twilight series and they’re also there and immortal. Have fun brooding with your new dorky friends, FOR ETERNITY.

What I’m saying is you could stand on the red planet restaurant patio and laugh at anything the weather system could throw at you. That is unless, you’re solar powered.

Opportunity Rover. Credit: NASA
Opportunity Rover. Credit: NASA

Mars gets regular dust storms. From time to time, they can get truly global. In 2001, a storm picked up enough dust to shroud the entire planet in a red haze. Temperatures went up as dust helped trap heat in the atmosphere. This storm lasted for 3 months before temperatures cooled, and the dust settled back down again.

During a storm in 2007, dust blocked 99% of the light reaching the solar panels of the Opportunity rover. This severely decreased the energy it had to power its instruments, and most importantly, the heaters. Ultimately, it was possible that the cold could kill the rover, if the dust hadn’t subsided quickly enough.

If you happen to see a movie or read a book about an astronaut on Mars dealing with a dangerous dust storm, don’t worry. They’ll be fine, the wind won’t shred them to pieces. Instead, focus on unbreathably thin atmosphere, the bone chilling cold, or the constant deadly radiation.

That and where’s their food come from again? Well, now you know dust storms aren’t a big issue. Want to travel to Mars? Tell us in the comments below.

If you haven’t checked it out yet, go read “The Martian”. Jay and I loved the pants off it and we can’t wait to see the film version.