Can We Call the Bright Spot in Ceres’ Occator Crater a Cryovolcano Yet?

Evidence is mounting around the cryovolcanic history of the solar system’s innermost dwarf planet — and its most recent eruptions may have happened within the last four million years.

NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Since NASA’s Dawn mission arrived at dwarf planet Ceres in 2015, we’ve been treated to some wonderfully detailed images of the small world’s pockmarked terrain. Understanding the underlying processes of what is believed to be an ice-filled celestial body, however, is taking some time to decipher. But with more observations comes more understanding and planetary scientists are getting close to realizing what lies beneath those craters and, possibly, unlocking the secrets behind a very icy and very alien phenomenon we have no experience of in our terrestrial lives.

That phenomenon is cryovolcanoes. And Ceres seems to have them.

The most startling feature on Ceres is Occator Crater. This 57 mile-wide feature is the result of a massive impact tens of millions of years ago. Large craters on small worlds isn’t necessarily a strange thing in our battered solar system, but what is strange about Occator is the very bright feature (and small bright patches surrounding it) in the crater’s center. Even before Dawn arrived in orbit and only fuzzy images of Ceres were available, hopes were high that this bright anomaly in the otherwise gray Cererian landscape could be indicative of ices or some mineral compound that was formed by the presence of water.

There have been many studies into Occator’s icy center, but new research into the crater’s age compared to the bright spot’s age appears to, once again, point to a cryovolcanic origin.

Cryovolcanoes — or, simply, ice volcanoes — are hypothetical features that are believed to be common throughout the outer solar system. These ice volcanoes are thought to erupt in a similar fashion to the volcanoes we have on Earth, but instead of molten rock, these volcanoes erupt ice-cold volatiles — like water, methane or ammonia. Dwarf planet Pluto, for example, has features that look like cryovolcanoes, as does Saturn’s moon Titan and Jupiter’s moon Ganymede. These locations are extremely cold and known to contain large quantities of methane and water, so internal heating (caused by radioactive decay or tidal processes) melt the ices and force them to the surface. When they vent through the crust, gases are released and the liquids quickly freeze and sublimate.

Around these vents, cryovolcanoes will grow, and if Ceres really does have its own ice volcanoes, this will be the closest planetary body to the sun (and Earth) known to have them.

Now, in research headed by the Max Planck Institute for Solar System Research (MPS) in Göttingen, Germany, scientists using Dawn data have, for the first time, taken a stab at dating the age of the bright material in the center of Occator Crater and realized that the location has likely been the site of many cryovolcanic eruptions in the recent past.

Occator Crater as observed by NASA’s Dawn spacecraft (NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

In the center of Occator, a pit measuring around 7 miles wide can be found, likely formed during the massive impact approximately 30 million years ago. But around the edges of that pit are mountains, some 750 meters high, and in the center is a cracked dome measuring 400 meters high and nearly 2 miles wide. This bright dome is called Cerealia Facula and surrounding it appears to be material that was spewed from a cryovolcanic vent. Analysis has shown that this material contains salts that were formed in the presence of water from Ceres’ interior and then deposited onto the surface. The minerals around Cerealia Facula has been dated to only four million years, meaning that there has been cryovolcanic eruptions long after the Occator impact punctured Ceres’ crust.

“The age and appearance of the material surrounding the bright dome indicate that Cerealia Facula was formed by a recurring, eruptive process, which also hurled material into more outward regions of the central pit,” said Andreas Nathues, lead investigator of Dawn’s Framing Camera. “A single eruptive event is rather unlikely.” As noted in an MPS news release, Jupiter moons Callisto and Ganymede have similar features that are also believed to be related to cryovolcanic eruptions.

“The large impact that tore the giant Occator crater into the surface of the dwarf planet must have originally started everything and triggered the later cryovolcanic activity,” added Nathues.

Previous imagery of haze inside Occator Crater has led to the suspicion that ices remain on the surface today; the haze could be vapor from sublimating water ice exposed on the surface having been forced to the surface from Ceres’ interior. Evidence for this haze has been supported by other studies and appears to vary throughout the day as one would expect — increased sunlight would accelerate sublimation (ice turning from a solid to a vapor without passing through the liquid phase).

If volatiles are still being extruded through this vent today, this would seem to indicate that, in addition to the cryovolcanic eruptions in the last four million years, some form of activity continues to this day. Add this to the recent discovery of organic material on Ceres’ surface, this small world has become a very big asset for planetary science.

For more on Ceres’ icy eruptions, check out one of my last DNews videos:

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What Will It Take To Blow Up Pluto?

“25 billion of your biggest bombs please. I’ll pay credit, thanks!”

"I love the smell of venting volatiles in the morning..."
"I love the smell of venting volatiles in the morning..."

The Pluto debate frustrates me, as you may have noticed. It’s not that I have particularly strong views about whether it should be called a planet or a dwarf planet or a plutoid or pygmy planetoid, it’s that I really don’t care; I actually see Pluto’s “demotion” as exciting progress in the field of Solar System science rather than any derogatory gesture aimed at Pluto. Pluto is still Pluto; it hasn’t been knocked out of orbit, it hasn’t even been “bombed” (unlike our poor old Moon), it’s just being filed under a different category.

A King Amongst Dwarfs

In my opinion, calling Pluto a “planet” was unworkable, especially after a bigger dwarf planet was discovered in 2005 by a team of astronomers led by Dr. Mike Brown. This dwarf planet was named Eris (or 136199 Eris) and at first it seemed like we had gained a tenth planet.

The “ten planets” thing was short lived, however. In recognition that Eris probably represented the beginning of a spate of discoveries of welterweight worlds, the International Astronomical Union (IAU) took a vote in 2006 and decided to redefine what constitutes a planet. Pluto was in the firing line, became a rounding error and was dropped from the planetary club.

Kicked out and nowhere to go.
Kicked out and nowhere to go.

But it wasn’t all bad for the little guy. Pluto was designated king of all “plutoids” (trans-Neptunian dwarf planets) in 2008, meaning another three dwarf planets now orbited the Sun with this designation (Eris, Haumea, and Makemake in addition to Pluto).

In a previous Astroengine article, I made the point (and I’m going to quote myself because I can):

Just so my opinion is known, I don’t care what Pluto is called. If NASA decided to explode Pluto as part of a Kuiper belt clearing project, then yes, I might be a bit annoyed; I’d even start a blog titled “Save Pluto.” But calling Pluto a dwarf planet (or the rather cute plutino) really doesn’t bother me.

I haven’t really thought much about this statement until, today, @PlutoKiller himself (Mike Brown) tweeted, “Seriously, what just happened? The entire discussion is on placing explosives in the solar system. Pluto has not even been mentioned.” I then fired off a reply saying something about building a New Horizons 2 and packing it with plutonium to which @PlutoKiller said, Evil Santa-style: “Just in time for Xmas.”

And then the penny dropped.

Kuiper Belt Cruelness

To be honest, I’m astonished I haven’t thought of this before. Looking at Mike’s Twitter feed should have been enough inspiration, but until I wondered down the bombing Pluto => plutonium enrichment => lets fly a shedload of plutonium to Pluto path, that I asked the question: How much energy is needed to completely destroy Pluto?

Now we’re talking! Time for some Kuiper belt mayhem!

It might seem quiet now...
It might seem quiet now...

I’m not talking about simply bombing Pluto and making a big crater, I’m not even talking about fire bombing all the volatiles out of its frozen surface, I want to remove Pluto from existence. Why do I want to do this? Well, for fun, and because @PlutoKiller himself said so. And it’s Halloween, so why not?

So how much energy is required to do this?

For this gargantuan task, I cheated and looked up the method used by Matt Springer over at Built on Facts to derive how much energy was required by the Star Wars Death Star to shred Earth. In that case, 2.2 × 1032 Joules was needed to totally erase our planet (that’s a week’s-worth of solar output). That’s a lot, right?

Plutoid Killing Equation

Now, energy is energy and mass is mass, let’s give Pluto the same treatment. Using the following equation (known henceforth as the “Plutoid Killing Equation”, or simply PluKE), we can find out how much energy we need to erase Pluto:

The equation that can turn a dwarf planet into dust, as derived by Matt Springer.

This equation is the total gravitational binding energy of a sphere of mass, M and radius, R. G is the Gravitational Constant. For Pluto, a sphere, its vital statistics are:

MPluto = 1.305 × 1022 kg

RPluto = 1.153 × 106 m

and

G = 6.673 × 10-11 m3 kg-1 s-2

Plugging the numbers into PluKE, we can derive the total energy required to kill Pluto, literally:

EPluto(dead) = 5.914×1027 Joules

Oops, who put those WMDs there?
Oops, who put those WMDs there?

But what does this number mean? This is the bare minimum energy required to match the gravitational binding energy of Pluto. If you want to rip the dwarf planet apart (plus pyrotechnics and speeding debris), you’ll need a lot more energy. However, nearly 6×1027 Joules (that’s a 6 followed by 27 zeros) delivered into Pluto in one second should give the little world a very bad day.

Tsar Very Much

But how can we “deliver” this vast quantity of energy in one second? I suspect that any super-advanced civilization hell-bent of wiping out planets will have a better idea of this than me, but using weapons that are available to modern man might be a good place to start. Forget the uber-powerful death ray emitted by the Death Star, that’s sci-fi. It may not be sci-fact, but how about sending some nuclear bombs to the Kuiper belt?

How many bombs will we need? Ten? Ten dozen? A thousand?

The most powerful nuclear weapon tested was the Soviet 58 MT Tsar Bomba in 1961. So if we know how much energy is released by one of those beasts, we should be able to work out how many we’ll need to send to the unsuspecting Pluto.

1 MT = 1 megaton of TNT = 4.184×1015 Joules

therefore, a single Tsar Bomba has the potential to release an energy of:

58 MT = 58 × 4.184×1015 Joules = 2.427×1017 Joules

We needed 6×1027 Joules to wipe out Pluto, obviously the 2.4×1017 Joules a single bomb can deliver is woefully short of our goal. So how many Tsar Bomba weapons do we need?

(6×1027 Joules) / (2.4×1017 Joules) = 2.5×1010

We need to build 25,000,000,000 nuclear bombs. 25 billion. Ouch.

Obviously, looking at this estimation, it is impossible to destroy a dwarf planet as puny as Pluto using the most powerful weapon known to man. Also, it’s worth keeping in mind that this is the bare minimum of energy that needs to be applied to Pluto to match its gravitational binding energy, so to destroy it, you’ll need a lot more bombs.

There’s also the question of how to distribute the weapons. Would you put them all in one place? Distribute them all around the globe? Perhaps burrow into the centre of the body? I suppose putting all the bombs in one place might be impressive, kicking a chunk of plutoid into space.

Now I must report these findings to @PlutoKiller himself, I fear he won’t be happy with the outcome of my calculations

Pluto Could Still Be A Planet! (Who Cares?)

pluto_alone1

All right, that title was a little harsh, but I think you get the point. It’s not that I don’t love Pluto, Pluto is a fine little planet… dwarf planet… hold on, plutoid. It holds a certain charm and mystique, plus we have the mother of all NASA missions (New Horizons) gliding its way to the outer icy reaches of the Solar System — the Kuiper Belt to be precise — to take a look at Pluto, up close, for the first time. I can’t wait for 2015 when the spacecraft starts taking snapshots, it will be awesome.

But what of the small planety-thingy’s status? Is it still a planetary outcast, destined for a life on Cosmic Skid Row? Or is Pluto about to get the mother of all reprieves and be re-classified as a planet? Does it really matter?

The reason why I ask is that the whole “demotion” thing was seen as bad news. I actually saw it as an exciting development in Solar System exploration (but hoped it wouldn’t tarnish the little rock’s popularity all the same). In actuality, Pluto is 27% less massive than the recently discovered dwarf planet Eris, so how could Pluto still be called a planet? Should Eris be classified as a planet, then? In light of new dwarf planet discoveries, Pluto became a rounding error and had to be re-classified. The International Astronomical Union drew up some planetary rules and found that Pluto didn’t have the gravitational clout to clear its own orbit and so was re-classified as a dwarf planet in 2006.

Suddenly, Pluto had “fans” that took the re-classification personally and got angry at the IAU for throwing Pluto out of the planetary club. Their reason? Only 4% of IAU members were present for the re-classification vote, they saw it as a personal slight against the “9th planet.” Even the nutty state of Illinois was FURIOUS and reinstated Pluto as a planet… (just in the state of Illinois).

We’ve heard this emotional story of planetary bullying over and over, so I won’t go over the details again. The whole Pluto story has been widely covered, many people pointing the finger at the evil IAU 4%, some have even gone as far as saying this is evidence that there is a growing rift between the public and scientists (let’s take national votes on scientific decisions! That would be fun). But what does it really matter? Really.

Is the Pluto re-classification a breech of our human rights? How about planetary rights? Is it indicative of the number of idiot scientists who voted in the 2006 IAU poll? Is this an indicator of poor scientific thinking? Could a war be sparked over this atrocity? Was it really a ‘bad’ decision?

Just so my opinion is known, I don’t care what Pluto is called. If NASA decided to explode Pluto as part of a Kuiper belt clearing project, then yes, I might be a bit annoyed; I’d even start a blog titled “Save Pluto.” But calling Pluto a dwarf planet (or the rather cute plutino) really doesn’t bother me. It’s a consequence of scientific endeavour, despite the perceived “controversy.” As the legendary astronomer Patrick Moore said, “…you can call it whatever you like!” Pluto is still Pluto.

However, it looks like Pluto might be re-classified again… big yawn.

This time, heavy hitter Alan Stern, Principal Investigator for the New Horizons mission, weighed in with his opinion on the matter. “Any definition that allows a planet in one location but not another is unworkable. Take Earth. Move it to Pluto’s orbit, and it will be instantly disqualified as a planet,” Stern said.

This implies that if Earth was moved to the Kuiper belt, as things move a lot more sluggishly out there, a planet with the gravitational pull of the Earth couldn’t clear its orbit, therefore the “must clear its own orbit” criteria is a bad location-based definition for a planet. (I would argue that there’s every possibility that Earth could clear it’s own orbit at that distance given enough time, but what would I know, I’m no planetary physicist, but everyone seems to have an opinion about Pluto, so there’s mine.)

This analogy is a bit like saying a car driven down a country lane is a car. But a car driven on a freeway is a bike.

There is the counter argument to this case; if there was something as big as Mars, or even Earth, it may have tunnelled out a path through the Kuiper belt, thereby clearing its orbit. Alas, there appears to be no solid consensus as to the nature of this littered volume of space (at least until 2015), hence all the fuss.

Now there’s some big noise that the IAU will reconvene and discuss the Pluto hoopla again, giving a vague glimmer of hope to pro-planet plutonites that the 2006 decision will be overthrown. Alas, I very much doubt that as, quite frankly, there are more pressing (and more interesting) matters to discuss such as: what the hell hit Jupiter?! We should re-classify Jupiter as ‘the inner Solar System’s gaseous protector’!

Source: New Scientist