"Philae ... Headed for History"

Rosetta's Philae landed on a comet, 67P/Churyumov-Gerasimenko, this week: an historic 'first.'

Back on Earth, scientists at the ALMA radio telescope got the clearest picture yet of planets about to take shape around HL Tauri.

1. 'Any Landing You Walk Away From...'
   • Philae: Priorities, Science — and History
2. Philae on 67P/Churyumov-Gerasimenko: 'A Great Day'
3. The Rosetta Mission and Earth's Oceans
4. Planets Under Construction Around HL Tauri
   • Telescopes: "Dutch Perspective Glass" to the Arecebo Dish and Interferometry
   • HL Tauri's Protoplanetary Disk
   • Observations, Excitement, and Looking Ahead

---

Comet Firsts, 1985-2005

Robotic explorers started visiting comets in 1985, when The International Cometary Explorer (ICE) passed through Comet Giacobini-Zinner. The probe passed by Halley's Comet in 1986.

The Stardust spacecraft collected dust from Comet Wild 2's coma in 2004. The mission's Sample Return Capsule landed back on Earth in 2006.

In 2005, the Deep Impact spacecraft's instrumented impactor hit comet Temple 1.

Results of the impact surprised scientists. Debris kicked up from Tempel 1 had more dust and less ice than expected: and included clays, carbonates, sodium, and crystalline silicates. Clays and carbonates generally don't form without liquid water, and sodium is rare in space.

Maybe the Philae lander will find similar substances on Comet 67P/Churyumov-Gerasimenko.

First Soft Landing on a Comet: 2014

The Rosetta became the first spacecraft to orbit a comet in August of this year.

On Wednesday, Rosetta's Philae lander was the first spacecraft to make a soft landing on a comet, 67P/Churyumov–Gerasimenko.

The comet is several miles across, with a surface gravity very roughly 1/10,000^th what we experience on Earth. As I said last week, someone standing on the comet would weigh a fraction of an ounce. (November 7, 2014)

Someone did the math, and found that an astronaut standing on 67P could jump hard enough to escape the comet's weak gravitational field. Walking there would probably be impossible, although we could hop: carefully.

• "Could You Walk on the Surface of a Comet?"
  Rhett Allain, Dot Physics (August 6, 2014)

Since 67P/Churyumov–Gerasimenko's gravity is so weak, the Philae lander had harpoons and drills which were supposed to keep it from bouncing off, once it landed. The robot bounced, anyway.

Getting a Grip About Faith and Science

"...Scientists are hoping 67P's surface materials will hold fresh insights into the origins of our Solar System more than 4.5 billion years ago.

"One theory holds that comets were responsible for delivering water to the planets. Another idea is that they could have 'seeded' the Earth with the chemistry needed to help kick-start life. Philae will test some of this thinking...."
(BBC News (November 12, 2014))

If you're bracing for a screed about the evils of science: relax.

I'm a Catholic, so I don't have to decide which of the two creation accounts in Genesis is the 'right' one: or cling to the idea that Earth is flat.

I'm obliged to read and believe the Bible. (Catechism of the Catholic Church, 101-133)

But that doesn't mean I must believe that Job 9:6-7 is meant as a geography lesson: or that our Sun goes around Earth because Joshua 10:12-13 says so.

I've been over this before. (September 21, 2014)

I believe that God made the universe and the things of faith, so I must also believe that honest research cannot contradict faith. (Catechism, 159)

"...God can not deny himself, nor can truth ever contradict truth...."
(Dei Filius, Vatican Council I, 248 (1870) (quoted in Catechism, 159))

Faith and reason, religion and science, work together: or should. (Catechism, 39, 159, 282-286)

"The question about the origins of the world and of man has been the object of many scientific studies which have splendidly enriched our knowledge of the age and dimensions of the cosmos, the development of life-forms and the appearance of man. These discoveries invite us to even greater admiration for the greatness of the Creator, prompting us to give him thanks for all his works and for the understanding and wisdom he gives to scholars and researchers"
(Catechism, 283) [emphasis mine]

We're supposed to wonder how things began and where we're headed. It's part of being human. (Catechism, 282-289, 2293)

---

1. 'Any Landing You Walk Away From...'

(From European Space Agency, via BBC News, used w/o permission.)
("Some radio data suggests the probe may be about 1km from the intended landing site"
(BBC News))

"Rosetta: concerns for comet lander after uneven landing"
Jonathan Amos, BBC News (November 13, 2014)

"After a historic but awkward comet landing, the robot probe Philae is now stable and sending pictures - but there are concerns about its battery life.

"The lander bounced twice, initially about 1km back out into space, before settling in the shadow of a cliff, 1km from its intended target site.

"It may now be problematic to get enough sunlight to charge its battery systems.

"Launched in 2004, the European Space Agency (Esa) mission hopes to learn about the origins of our Solar System.

"It has already sent back the first images ever taken from the crumbling, fractured terrain of a comet...."

One of Philae's three feet isn't touching 67P/Churyumov-Gerasimenko's surface, and the lander's harpoons and drills haven't anchored it to the comet's surface. The lander came to rest against some sort of hard 'vertical' surface, and may be on its side.

But, applying the 'any landing you walk away from is a good one' principle, I'd say this was a good landing. Philae is in one piece, and has been sending back data.

That's the good news.

The less-than-good news is that after bouncing along the comet's surface, Philae's third landing left its solar panels in partial shade.

Philae gets sunlight for only 90 minutes, roughly, during each 12-hour day. The probe left Rosetta, the orbiter, with its batteries fully charged: but was designed to recharge after landing, using its solar panels.

Depending on how much equipment gets used, Philae will run out of power between Friday and Saturday afternoon. Still, it could be worse.

Philae: Priorities, Science — and History

(From ESA/Rosetta/MPS for Osiris Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA, via BBC News, used w/o permission.)
("One remarkable image taken by the 'mothership' Rosetta shows Philae as a tiny speck, headed for history"
(BBC News))


(From ESA/Rosetta/Philae/CIVA, via BBC News, used w/o permission.)
("Another photo shows the craggy surface of the comet - looking over one of Philae's feet"
(BBC News))

"...The priority right now is to use Philae to acquire as much information as possible about the comet.

"In this regard, researchers are thrilled by the performance of the probe.

"However, they would dearly love to use the lander's drill. This was one of the key objectives of the mission - to pull up sub-surface material for chemical analysis in onboard labs...."
(Jonathan Amos, BBC News)

Philae's drill, the SD2: Sampling, Drilling and Distribution instrument, may never be used. Assuming the drill can reach the comet's surface, its rotational forces could "destabalize" Philae.

Drilling may be left for last: particularly if engineers can't shift Philae to a better position, where the lander can anchor itself, and get enough light on its solar pannels.

As ESA's operations head in Darmstadt, Germany, said: "You gather everything you can first, and then the risky things - you only do them at the end."

There's a lot of science for Philae to do without the drill. The lander carries 10 experiment packages:

• APXS Alpha Proton X-ray Spectrometer
• ÇIVA / ROLIS Rosetta Lander Imaging System
• CONSERT Comet Nucleus Sounding
• COSAC Cometary Sampling and Composition experiment
• MODULUS PTOLEMY Evolved Gas Analyser
• MUPUS Multi-Purpose Sensor for Surface and Subsurface Science
• ROMAP RoLand Magnetometer and Plasma Monitor
• SD2 Sample and Distribution Device
• SESAME Surface Electrical Sounding and Acoustic Monitoring Experiment
  (Rosetta fact sheet)

I know — that list only has nine items. ESA's fact sheet says there are 10 experiment packages on Philae, and that's the list of them.

My guess is that they count SESAME, the Surface Electrical Sounding and Acoustic Monitoring Experiment, as two experiment packages: one electrical sounding, the other an acoustic experiment.

I'm looking forward to seeing what we'll learn from the Rosetta mission's lander and orbiter: how closely its water matches Earth's, and what other substances it carried from the Solar System's borderlands.

As Jonathan Amos wrote:

"...Whatever happens in the hours ahead, the mission is already assured of its place in history...."
(Jonathan Amos, BBC News)

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2. Philae on 67P/Churyumov-Gerasimenko: 'A Great Day'

(From European Space Agency, used w/o permission.)
(ESA's European Space Operations Centre (ESOC) in Darmstadt, as Philae lander touched down on 67P/Churyumov-Gerasimenko. (November 12, 2014))

"Rosetta: Scientists await news of 'bouncing' comet probe"
(November 12, 2014)

"Scientists are facing a tense wait to learn the fate of a robot probe that made a historic landing on a comet - but did not stay in place as planned.

"Data from the Philae craft indicates it landed at least three times on the comet, after harpoons failed to attach it to the surface on the first attempt....

"...The chief of the European Space Agency said the landing - after a decade-long journey - was a 'big step' for humans.

"Esa Director-General Jean-Jacques Dordain described it as 'a great great day, not only for Esa, but... I think for the world'...."

The good news is that Philae touched down and promptly started sending data from Comet 67P/Churyumov-Gerasimenko's surface.

The not-so-good news was that the lander apparently bounced, and probably hasn't anchored itself to the comet.

Still: I think this is "a great great day ... for the world," as the ESA Director-General said.

Humanity's scientific knowledge has expanded a great deal since my youth: and I'm sure we have much left to learn. I like living in an era where we're taking our first steps into the universe, and that's another topic.

---

3. The Rosetta Mission and Earth's Oceans

(From ESA/Rosetta/Philae/Civa, via BBC News, used w/o permission.)
("In September, Rosetta snapped this 'selfie' of its solar panels and the comet 67P"
(BBC News))

"The past, the present, and the challenges ahead for Europe's comet chaser"
BBC News (November 11, 2014)

"After a precisely orchestrated 10-year chase across the solar system, the European Space Agency's Rosetta probe finally caught Comet 67P/Churyumov-Gerasimenko on 6 August 2014. Since that historic rendezvous, Rosetta has been in a powered orbit around the comet: the first of its kind. The mission is now set to become the first to land on a comet, and the first to follow a comet around the Sun....

"...Rosetta was originally due to launch in 2003 aimed at a different, much smaller comet called 46P/Wirtanen.

"However, the failure of an Ariane 5 rocket attempting to put a communications satellite into orbit in 2002 meant that the Rosetta mission was delayed until the fault was found. Instead of the tiny 46P/Wirtanen, the mission was re-focussed on the larger 67P/Churyumov-Gerasimenko....

"...The carbon-fibre lander, about the size of fridge, will be dropped to the rocky surface from about 1km. It will use harpoons to attach itself. Philae is designed to be able to land on a slope of up to 30 degrees. Esa says the feet of the lander are equipped with large pads to allow it to touch down on a soft surface, but these feet will also try to place screws into the icy surface...."

Comets like 67P/Churyumov-Gerasimenko are as old as the Solar System. They've spent most of the last 4,568,000,000 years far from our star, in cold storage.

Planets have changed since the Solar System's early days. Comets are very nearly the same as they were when the planets formed. Studying a comet gives scientists a look at the material which became planets: including Earth.

One of the puzzles which the Rosetta mission may help solve is where Earth's oceans came from. Scientists are pretty sure that when our planet formed, it was a bit too warm to keep its water. (September 6, 2013)

But about three quarters of our planet is covered by water: it must have come from somewhere. Comets, or stuff very much like today's comets, is one possible source for the water in Earth's oceans, rivers, and lakes.

Earth's water has a particular ratio of deuterium, an isotope of hydrogen, to normal hydrogen. This ratio is not the same water on other planets.

So far, the ratio scientists have found in comets is about the same as in Earth's oceans: which suggests that at least some of our water came from comets after Earth cooled down. (Wikipedia.org, Deuterium; European Space Agency, Rosetta's frequently asked questions)

Rosetta and the Philae lander will also look for complex organic molecules on and in 67P/Churyumov-Gerasimenko.

Scientists found adenine and guanine, nucleobases used in DNA and RNA, in a meteorite. I think it's likely that 67P/Churyumov-Gerasimenko includes some of life's chemical components, too. Either way, studying this comet will help us understand how life started on Earth: and maybe elsewhere. (February 21, 2014)

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4. Planets Under Construction Around HL Tauri

(From ALMA, C. Brogan, B. Saxton; via BBC News; used w/o permission.)
("A protoplanetary disc has formed around the young star HL Tau"
(BBC News))

"Planet formation captured in photo"
Jonathan Webb, BBC News (November 6, 2014)

"The clearest ever image of planets forming around an infant star has been taken by the Alma radio telescope.

"In a vast disc of dust and gas, dark rings are clearly visible: gaps in the cloud, swept clear by brand new planets in orbit.

"The sun-like star at the centre, HL Tau, is less than a million years old and is 450 light years from Earth in the constellation Taurus.

"The image was made possible by Alma's new high-resolution capabilities.

"Because the process of planet formation takes place in the midst of such a huge dust cloud, it can't be observed using visible light.

"Alma, the Atacama Large Millimeter/submillimeter Array, has snapped the impressive new image using much longer wavelengths, which it detects by comparing the signal from multiple antennas up to 15km apart...."

HL Tauri is a name so short it hardly needs an abbreviation, but it has one: HL Tau, which is what Jonathan Webb's article uses. HL Tauri is, or will be, "sun-like," but right now it's distinctly cooler than our star.

HL Tauri is very young. The BBC article says "less than a million years old." For a star like our sun, that's "young:" the Solar System is 4,568,000,000 years old, give or take fifty million years.

The BBC article calls that image a "photo," but it's not your usual photograph.

HL Tauri is inside a huge cloud of dust and gas that blocks visible light: electromagnetic radiation with wavelengths from about 390 to 700 nanometers. To 'see' inside the cloud, astronomers used longer wavelengths — measured in millimeters, not nanometers.

The ALMA observatory's radio telescopes use interferometry to get high-resolution images in radio wavelengths.

Telescopes: "Dutch Perspective Glass" to the Arecebo Dish and Interferometry

A large telescope can generally show more details than a small one, which is why telescopes got bigger over the centuries, from the early 17th-century "Dutch perspective glass" to the Hale and BTA-6 reflectors of the mid-20th century.

Radio telescopes get better resolution with greater size, too. The Arecibo Observatory's dish antenna is about a thousand feet across, and still the largest on Earth.

My guess is that it may be the largest dish antenna ever built, since astronomers started using interferometry in the early 20th century. Maybe, after we start building large structures in space - - - and that's yet another topic.

Combining light, or radio waves, from two or more separate telescopes gives images with resolution nearly as high as what they'd get with a single huge telescope. The down side is that whatever they're 'looking' at has to be fairly bright, since the array has less surface are than a single large lens or reflector of equivalent size.

HL Tauri's Protoplanetary Disk

(From ALMA (ESO/NAOJ/NRAO), used w/o permission.)
("This image compares the size of the Solar System with HL Tauri and its surrounding protoplanetary disc. Although the star is much smaller than the Sun, the disc around HL Tauri stretches out to almost three times as far from the star as Neptune is from the Sun."
(ALMA (ESO/NAOJ/NRAO)))

HL Tauri's protoplanetary disk isn't red-hot. Astronomers often assign colors to wavelengths outside our visual range, partly because it's easier to pick out features when they're different colors: partly, I suspect, because it looks cool.

The protoplanetary disk is warmer than the surrounding dust and gas, but not by much. It's probably a few tens of Kelvins above absolute zero. At those temperatures, hydrogen can be a liquid.

Some of the dark patches in the disk may become planets. Scientists think the process takes millions of years, but HL Tauri's protoplanetary disk is much closer to being set of planets than astrophysicists expected in such a young star.

As I've said before, there's a great deal left to learn.

Observations, Excitement, and Looking Ahead

(From NSF, A. Khan; via BBC News; used w/o permission.)
("The image matches predictions from computer simulations and illustrations like this one"
(BBC News))

"...'When we first saw this image we were astounded at the spectacular level of detail,' said Dr Catherine Vlahakis, a senior member of the Alma team.

" 'HL Tau is no more than a million years old, yet already its disc appears to be full of forming planets.'

"Prof Tim de Zeeuw is director general of the European Southern Observatory, one of several organisations involved in Alma. He said: 'Most of what we know about planet formation today is based on theory. Images with this level of detail have up to now been relegated to computer simulations or artist's impressions.'..."
(Jonathan Webb, BBC News)

Johathan Webb quotes Oxford astrophysicist Dr. Aprajita Verma: "...phenomenal ... This shows how exciting Alma is going to be - it's going to be an incredible instrument."

I did a little checking, and Dr. Verma's Twitter account (@aprajitaverma) includes this ReTweet, from ESO: "...ALMA's taking us from artist's impressions & computer simulations to real images of planet formation!..."

Looks like the excitement's genuine: and understandable. Up to now, as the ESO's Tim de Zeeuw said: "Most of what we know about planet formation today is based on theory...." The ALMA image shows details that theory says should be there — and it's nice to get confirmation.

I think it's exciting when observation doesn't back up theory, too. That tells scientists that there's more to the universe than we thought.

The recent ALMA observations seem confirm existing theories, to an extent. This detailed image of HL Tauri's protoplanetary disk shows features that theory said should be there; and a planetary system that's further along in its development that scientists expected.

HL Tauri's planets may take another few million years to settle into a semi-permanent arrangement. Even so, that protoplanetary disk is a transient phenomenon on a cosmic time scale: and that's yet again another topic.

More of my take on science and God's creation:

• "Harpooning the 'Rubber Duck' Comet; Public Safety — and Space Aliens"
  (November 7, 2014)
  Particularly
  • 67P/Churyumov-Gerasimenko: 4,500,000,000 years in cold storage
• "Sagittarius B2, Water, and Asteroid Mining"
  (October 3, 2014)
  Particularly
  • Pillars Beneath Earth and NASA
  • God Thinks Big
  • Organic Molecules in Sagittarius B2
• "Kapteyn b, Habitable Zones, and Using Our Brains"
  (July 18, 2014)
  Particularly
  • Copernicus and Newfangled Ideas
  • Poetry isn't Science
• "Ceres, a Comet, and Venusian Water "
  (January 24, 2014)
  Particularly
  • Rosetta Wakes Up
    • Destination: 67P/Churyumov-Gerasimenko
    • Thar's Water in Them Thar Comets
• "Dust and Fomalhaut: Learning that There's More to Learn"
  (December 27, 2013)

Background:

• 67P/Churyumov–Gerasimenko
  • European Space Agency
    • Rosetta | Rendezvous with a comet
    • Rosetta fact sheet
    • Rosetta's frequently asked questions
    • Rosetta's target: comet 67P/Churyumov-Gerasimenko
  • JPL/NASA
    • "MIRO Overview"
    • "The Singing Comet"
  • Wikipedia
    • 67P/Churyumov–Gerasimenko
      • Orbital history
      • Rosetta mission
    • Comet
      • Physical characteristics
      • Comets and impact on life
    • Kuiper belt
    • Formation and evolution of the Solar System
    • Oort cloud
    • Scattered disc
• New image of HL Tauri
  • Atacama Large Millimeter/submillimeter Array (ALMA)
    Home page, English
    • "Revolutionary ALMA Image Reveals Planetary Genesis"
      Press release (November 5, 2014)
  • Altacama Large Millimeter/submillimeter Array
    ESO, ALMA Science
    • Basics
  • "Imaging polarimetry of HL Tauri and GG Tauri: A geometrically thin disk around GG Tauri"
    T. Yamashita, K. Hodapp, T. Moore; Astrophysical Journal, Part 2 - Letters (February 10, 1994)
  • Interferometry
    Ask an Astrophysicist, Imagine, Goddard Spaceflight Center
  • Wikipedia
    • Astronomical interferometer
    • Atacama Large Millimeter Array
      • Overview
    • HL Tauri
    • Interferometry