Friday, July 10, 2015

Pluto's 'Whale,' Comet 67P's Sinkholes

New Horizons is closer to Pluto than it was when I started writing this post, and should send back about 5,000 times as much data as Mariner did in its Mars flyby, 50 years ago. (BBC News)

The ESA's Philae lander 'woke up' last month, but the big news from the Rosetta mission are Comet 67P/Churyumov–Gerasimenko's sinkholes: and the jets of gas and dust coming from at least some of them.
  1. Mapping Pluto
  2. Pluto Probe Hiccups
  3. Alien Life on a Comet??
  4. Comet 67P/Churyumov–Gerasimenko's Sinkholes

Pulp Science Fiction and Pluto


(From Frank R. Paul, via Fabio Feminò and David S. Zondy, used w/o permission.)
(Frank R. Paul's very-imaginary people on Pluto, 1930s.)

I think these Frank R. Paul illustrations are from Fantastic Adventures, around 1939. (Robbie Gonzalez, io9.com)

This series of pictures is long on imagination — and humor — with a cheerful disregard for what scientists knew about the planets around the time of the Second Sino-Japanese War.

Pluto had been discovered by Clyde Tombaugh in 1930. At the time, the discovery of "Planet X" may have been as exciting as as the growing roster of exoplanets is today.

Turns out that Pluto isn't "Planet X;" it had been observed but not identified as early as 1909; and it isn't, quite, a planet. I'll get back to that.

Science Goes "Gra-"


In comics and movies, a mad scientist whose hubris leads him — odd, how the mad scientist was "he" — to commit crimes against man and nature, can be entertaining. His real-life counterparts, not so much. (December 12, 2014)

Thinking is not — I say this a lot, so feel free to click down to Mapping Pluto, go get a cup of coffee, take a walk, whatever — a sin.

My faith doesn't demand an interest in what we're discovering about this universe: but it's not threatened by knowledge, either. Scientific discoveries are invitations "...to even greater admiration for the greatness of the Creator...." (Catechism of the Catholic Church, 283)

I've encountered fervently religious folks who seem dedicated to the notion that faith and reason are at war, but I'm a Catholic — so I'm expected to think. For one thing, "Conscience is a judgment of reason ... a law of the mind...." (Catechism, 1778)

It isn't faith or reason: it's faith and reason. ("Fides et Ratio," John Paul II (September 14, 1998); Catechism of the Catholic Church, 35)

We are rational creatures, and expected to think. (Catechism, 32, 154-159, 299)

Then there's the question of life in the universe. That came up in recent news, when some journalists got hold of speculation about life on comets. And I'm getting ahead of myself.

Enough of this. The New Horizons spacecraft has been sending back increasingly-clear images of Pluto. I'm looking forward to seeing what we learn about that cold world.


1. Mapping Pluto



(From NASA/JHU-APL/Southwest Research Institute, via BBC News, used w/o permission.)
("The map combines images takes between 27 June and 3 July"
(BBC News))
"New Horizons: Pluto map shows 'whale' of a feature"
Jonathan Amos, BBC News (July 8, 2015)

"Scientists have released their latest map of Pluto, using images from the inbound New Horizons spacecraft.

"It unwraps the visible parts of the sphere on to a flat projection, giving another view of the features that have started to emerge in recent days.

"Evident are the light and dark patches at the equator, including one long dark band being dubbed 'the whale'...."
Pluto was discovered in 1930, and called the Solar System's ninth planet until about 10 years ago. Astronomers had started wondering about Pluto back in 1977, when Charles T. Kowal discovered 2060 Chiron: or identified, more accurately.

Chiron started showing up in observations as far back as 1895, at least, but wasn't tagged as a planet/minor planet/dwarf planet/whatever until 1977.

Astronomers call Chiron 2060 when they think it's an asteroid minor planet, 95P/Chiron when they think it's a comet. I figure Pluto, Chiron, Eris, and other assorted stuff that orbits will get satisfactorily labeled — eventually.

Meanwhile, I keep reading the occasionally-heated debate about the differences between dwarf planets, minor planets, comets, and asteroids. Which reminds me of Planetoid comics, and that's another topic.

One more thing: Pluto is also a trans-Neptunian object, AKA TNO, transneptunian object; and a Kuiper belt object. (December 29, 2013)

Until very recently, we didn't know much about Pluto: mainly because it's so far away. It's cold, with a very thin atmosphere: mostly nitrogen (N2), methane (CH4), and carbon monoxide (CO).

"Cold" is a relative term. Minnesota's winter is "cold," compared to our summer. Average monthly temperature in Minneapolis runs from January's −11 °C (13 °F) to July's 23 °C (73 °F). Pluto's average surface temperature runs from about 33 K 44 Kelvin (−229 °C) to 55 K (-218.15 °C).

That's really cold. At Earth's sea level pressure, and those temperatures, methane is a solid. Even if Pluto had an atmosphere as thick as ours, though, hydrogen would be a has. That stuff starts boiling at 20.28 K (−423.17 °F/−252.87°C).

I doubt that anybody seriously thinks there's life on Pluto; but a larger, colder, planet might support 'life as we don't know it.' (March 7, 2014)

New Horizons: Science, Technology, and Fear



(From NASA/APL/Southwest Research Institute, used w/o permission.)
(New Horizons position at 1700 UTC/1200 Central Daylight Time. (CDT) (July 8, 2015) )

New Horizons was 7,479,894 kilometers/4,647,790 miles away from Pluto at noon Wednesday, July 8, 2015. At that distance, light — and radio signals — take nearly nine hours to travel from the spacecraft to Earth.

It's scheduled to send the last pre-flyby data to Earth Sunday and Monday, and send the first post-flyby data on Wednesday. Tuesday, July 14, 2015, New Horizon will be passing Pluto: about nine and a half years after its January 19, 2006, launch.

Like most real spaceships, New Horizons doesn't look much like its science fiction counterparts. Patrick Moore, in "The Sky at Night," described it as being about the size and shape of a cocktail table glued to a grand piano. (Wikipedia)

That dark bit, sticking out from New Horizons' main body, is a radioisotope thermoelectric generator: a sort of atomic battery that's providing about 200 watts now.

As usual, some folks protested before the launch. They've got a point.

The generator holds about 24 pounds of plutonium: radioactive stuff you wouldn't want to be around. Not without shielding. The Cassini-Huygens got protested for the same reason.

I'm glad that NASA has the U.S. DOE do a risk assessment before launching dangerous stuff. There was a low (1 in 350) chance that some radioactive material might get loose during launch. Then there's the worst-case scenario, where every ounce of on-board plutonium got spread as far as possible.

If that had happened, everyone up to 105 kilometers of the release would be exposed: to 80% above the North America's average background radiation.

More:

Fukushima Daiichi, Chernobyl, and the Manure Crisis of 1894


Before you run to that 1950s fallout shelter in the back yard: remember that radioactive stuff permeates the universe, including Earth. The stuff's responsible for background radiation coming from air, water, food, soil, rocks, and the depths of space.

Now that I think about it, that fallout shelter might a low-level radiation hazard. Remember those 'radon' headlines, several years back?

There's a little bit of radioactive stuff in rocks. As it breaks down, it releases radon gas. Normally, it's not a problem: unless you're living in a cave.

During the 1970s 'energy crisis,' folks started insulating their homes: a lot. Good news: we're using energy much more efficiently now.

Not-so-good news: we discovered that toxic stuff had been getting ventilated away, and now was trapped inside our efficiently-heated homes, like formaldehyde.

Radon, too. Some parts of the United States — including Minnesota — have more radon underfoot than others. And that's yet another topic. ("Radon in the Home," Radiation and Your Health, Centers for Disease Control and Prevention)

Worldwide, the natural background radiation is about four times more than what we get from our tech. A lot of that's from medical imaging: also stuff like radioactive building materials, coal-powered generating stations, and cigarettes. (Wikipedia)

Then there are nuclear accidents, like the Chernobyl and Fukushima Daiichi disasters.

I'm not upset that we use dangerous technologies; like nuclear power, steam engines, and fire.

We've learned to safely use fire and flint tools, and developed an alternative to horse-drawn wagons before burying London in manure. (May 9, 2014; July 9, 2011)

- - - and we still sometimes get careless with fire.

But I have yet to run into a 'NO MORE FIRES/BAN FIRES' protest.

Studying this world and developing new tools is part of being human. What we do with them is where ethics comes in. (Catechism, 2293, 2493-2499)

Also using our brains, and that's yet again another topic. (March 29, 2015; June 15, 2014)


2. Pluto Probe Hiccups



(From NASA/JHU-APL/SWRI, via BBC News, used w/o permission.)
("The spots are part of a dark band that wraps around much of Pluto's equatorial region"
(BBC News))
"New Horizons: Pluto probe 'on course' for flyby"
Jonathan Amos, BBC News (July 6, 2015)

"New Horizons lost very little science data when it went into 'safe mode' at the weekend, the mission team says.

"Nasa's Pluto probe experienced a fault on Saturday that put it temporarily out of contact with the Earth, as it speeds towards a flyby next week.

"Principal investigator Alan Stern said that about 30 observations of the dwarf planet were missed as a consequence of the hiccup.

"This represents 'far less than 1%' of the top science about to come back...."
This "hiccup" happened after engineers sent the command sequence for New Horizons' Pluto flyby. The onboard computer was trying to write the instructions to its flash memory while compressing data from its observations.

That was too much data moving around at the same time. The computer couldn't handle both tasks, dropped both, and did what it's programmed to do: shifted to a safe mode. A backup computer took over, and the main computer 'woke up' just over an hour later.

There isn't another 'burn to flash' process scheduled for the next few days, or the Pluto flyby: so that particular issue won't keep scientists from getting New Horizons' reports.


3. Alien Life on a Comet??

"Rosetta comet 'may be home to alien life' "
The Week (July 6, 2015)

"Astronomers say data sent back by Rosetta point to the presence of microbial life on Comet 67P

"he Rosetta spacecraft's Philae lander has sent back information that could point to the existence of microbial alien life on Comet 67P, astronomers from the University of Cardiff have said....

"...According to astronomer and astrobiologist Professor Chandra Wickramasinghe, the comet's black hydrocarbon crust could be home to microbes not dissimilar to the 'extremophiles' found in some of the most inhospitable places on Earth, such as those that live deep in Antarctic ice or in the Mariana Trench....

"...He and colleague Dr Max Wallis from the University of Cardiff argue that comets could have helped bring life to Earth, and to other planets in our solar system, including Mars...."
I've glanced over a few slightly-snarky responses to this bit of news. I'll agree that some of the reporting has been a bit on the silly side: and exaggerated the "scientists say" angle.

Granted, University of Buckingham's Chandra Wickramasinghe and University of Cardiff's Max Wallis add up to more than one scientist. But they're by no means an overwhelming majority, or even a significant minority, of the Anglo-European science community.

On the other hand, they just might be right. Over the last few decades, we've been finding critters living in very unexpected places: like alkali lakes, hot springs, and radioactive waste. (December 5, 2014; March 7, 2014)

My guess is that comets like Comet 67P/Churyumov–Gerasimenko don't support life. The things are probably too small, and nowhere near stable enough, for critters to live. That didn't keep me from enjoying Lifeforce, a yarn about vampires hiding in Halley's Comet.

Finally, a quick quot from the Wikipedia page about The Week. "...This weekly news magazine is known for a wide focus that incorporates current events, news, health, media, science, arts, and more into an easily digestible format...."


4. Comet 67P/Churyumov–Gerasimenko's Sinkholes



(From ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA, used w/o permission.)
("Pits on the surface of Comet 67P/Churyumov–Gerasimenko's northern hemisphere...."
(Reuters))
"Rosetta spacecraft finds massive sinkholes on comet's surface"
Irene Klotz, Reuters (July 1, 2015)

"The comet being studied by Europe's Rosetta spacecraft has massive sinkholes in its surface that are nearly wide enough to swallow Egypt's Great Pyramid of Giza, research published on Wednesday shows.

"Scientists suspect the pits formed when material on the comet's surface collapsed, similar to sinkholes on Earth, a study published in the journal Nature said.

"The cavities on comet 67P/Churyumov-Gerasimenko, which Rosetta has been orbiting since August, are enormous, stretching some 656 feet (200 meters) in diameter and 590 feet (180 meters) in depth.

"In comparison, the Great Pyramid is 756 feet (230 meters) across and currently 455 feet (139 meters) tall...."
Three centuries back, Isaac Newton observed vapors coming from comets.

Around the mid-20th century, scientists realized that comets released so much gas and dust that they must be mostly ice or other volatile stuff. Robot spacecraft sent to Halley's Comet in the mid-1980s gave us our first look at comet jets.

ESA's Rosetta orbiter is much closer, 10 to 30 kilometers, roughly six to 18 miles, from comet 67P/Churyumov-Gerasimenko. The Philae lander 'woke up' June 13, and that's still another topic.

Images from the orbiter show 18 roughly-circular pits on Churyumov-Gerasimenko's northern hemisphere. Stuff is visibly jetting out of some of them.
"... The pits are a few tens to a few hundreds of metres in diameter and extend up to 210 m below the surface to a smooth dust-covered floor. Material is seen to be streaming from the most active pits.

" 'We see jets arising from the fractured areas of the walls inside the pits. These fractures mean that volatiles trapped under the surface can be warmed more easily and subsequently escape into space,' says Jean-Baptiste Vincent from the Max Planck Institute for Solar System Research, lead author of the study. ..."
(ESA)
These scientists think the pits are like sinkholes on Earth: previously-underground cavities with collapsed roofs. Water and limestone getting together make many of earth's sinkholes, like Mammoth Cave National Park's Cedar Sink.

We may eventually find karst landscapes on other planets: but comets aren't made of limestone. Something else forms them.

The scientists figure the comet's interior voids might be left over from when the comet formed: results of very low-speed collisions between building-size chunks of cometary stuff.

Or maybe frozen carbon dioxide, carbon monoxide, and other 'ices,' sublimated — evaporated directly from solid to gas. That could be triggered when sunlight heats the comet's surface, which in turn warm up deeper layers.

Or it could happen when water ice changes from an amorphous to a crystaline state, releasing heat and starting sublimation in carbon monoxide and dioxide ice.

Either way, the second two processes would happen when the comet comes closer to our sun.

Meanwhile, Somewhere on the Surface - - -


The Roestta mission's Philae lander detached from Rosetta at 08:35 UTC, November 12, 2014. At 15:34:04 UTC,1 it touched down on 67P/Churyumov-Gerasimenko: and bounced. Back on Earth, 28 minutes later, engineers and scientists got the 'I have landed' signal: and started wondering what had gone wrong.

Data sent back from Philae looked — odd — because the lander was slowly rising from the comet's surface. After reaching an altitude of about one kilometer, it fell back; bounced again, at 17:25:26 UTC; and finally came to rest after a third impact at 17:31:17 UTC.

Philae's 'brain,' the Central data management system, weighs about 2.9 kilograms/6.4 pounds. That's more that twice as heavy as an adult human's brain, but we're still not making computers as compact as biological neurocircuitry: and certainly weren't over a decade back, when Philae was built. (August 15, 2014)

A 6.4-pound early-21st-century computer can only do so much: and certainly wasn't up to dealing with an unexpectedly gentle landing — and failure of the mooring harpoons.

Philae's onboard computer did what it was programed to do at touchdown: turned off the lander's reaction wheel, which transferred momentum to the now-'airborn' lander, which started rotating every 13 seconds.

Something — probably hitting something jutting out from the comet's surface, slowed the spin to once every 24 seconds — and sent the craft tumbling.

In a way, it's remarkable that Philae was still working when it finally fetched up against a cliff or crater wall — and kept sending data for about 60 hours before using up its reserve power and switching to hibernation mode.

67P/Churyumov-Gerasimenko is closer to the sun now, and Philae 'woke up.' The probe has been sending back data it stored during its first active period: slowly, since the orbiter isn't 'overhead' all that often. And that's — what else? — another topic.

More:
Asteroids, planets, a comet, and life in the universe, from my viewpoint:

1 "UTC" stands for Coordinated Universal Time, temps universel coordonné in French. It's abbreviated as UTC, instead of TUC or CUT, because English speakers originally proposed CUT, while French speakers said it should be TUC. Folks finally settled on UTC, an acronym which would be equally acceptable — or disliked — by both parties.

My opinion is that we should call it "ET," for Earth Time, but it's probably too early for that. Quite a few folks probably still remember that movie and there's that long-running television show.

Astronomers use Terrestrial Time, which I think is a step in the right direction.

UTC is based on International Atomic Time: a time standard set by the weighted average of over 400 atomic clocks in more than 50 laboratories at various spots at or near Earth's surface — coordinated by GPS and two-way satellite time and frequency transfer.

The International Telecommunication Union, a United Nations agency involved with information and communication technologies, recommended today's UTC setup.

We're still using leap seconds to keep UT1, the most commonly-used version of UTC, within 0.9 seconds of Solar time at a virtual point on Earth's surface.

Eventually, Earth Time may be defined as something other than where the sun is, relative to a spot on an island off the European coast — or maybe not. Our current setup puts the International Date Line near the middle of this planet's largest body of water: which is convenient.

2 comments:

John Launder said...

Another enjoyable and perceptive article.

Brian Gill said...

Thank you, John Launder.

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