Comet 67P (The Guardian)

Catching up on some old stuff which I had saved to post on the blog.


Loved this picture, from an aesthetic and scientific point of view.  In addition, text described well the picture to a non-science audience.

Philae poses comet chemistry conundrum (Chemistry World 30th July)

As the Philae lander bounced across comet 67P/Churyumov–Gerasimenko’s surface in November last year, two chemical instruments were able to take tentative – but intriguingly contradictory – sniffs of its environment. Those mass spectrometry measurements provide compositional details important for deciphering the origins of life on Earth, a key aim of the Rosetta mission that carried Philae. But while the cometary sampling and composition (COSAC) instrument detected 16 organic molecules¹, half of which contain nitrogen atoms, Ptolemy reports very low concentrations of nitrogen-containing compounds².

Nevertheless, Jen Blank, a senior scientist at the Nasa Ames Research Center in California, US, highlights the historic achievement of syncing orbit with a comet and sending a lander down to the surface. ‘The Philae data are amazing,’ enthuses Blank, who’s studied how comets may have supplied Earth with molecules needed for life, but wasn’t involved in Rosetta or Philae. ‘These are the first measurements of organic compounds collected directly on a comet or asteroid.’
Philae was programmed to take sniffs shortly after touching down on 67P as an ‘insurance policy’, explains Ian Wright from the Open University in Milton Keynes, UK, and principal investigator for Ptolemy. That was well planned, because the touchdown became a rebound that sent Philae out of communication range, preventing further measurements to date.
The lander was also therefore in motion in the minutes between the instruments doing their respective basic analyses, or sniffs, of whatever material happened to have entered them. One potential explanation for the distinct results is therefore that they reflect differences between locations on the comet, Wright suggests. The fact that COSAC’s sample port is on Philae’s underside, and Ptolemy’s is on its top is another. ‘Have we analysed separate grains?’ Wright asks. ‘We’ve no reason to expect that the surface would be homogenous.’

Exhausting serendipity

COSAC’s best sniff happened automatically 25 minutes after Philae’s first contact, while the lander was around 150 metres above the surface. The instrument consists of a gas chromatograph and a time-of-flight mass spectrometer intended to analyse organic compounds in samples drilled from the comet’s surface. Though Philae couldn’t drill, the impact threw up some solid material, part of which apparently entered COSAC’s two exhaust pipes. The COSAC team, headed by Fred Goesmann from the Max Planck Institute for Solar System Research in Göttingen, Germany, thinks the exhaust’s warmth evaporated volatile compounds, allowing their detection.

The compounds COSAC identified included methyl isocyanate, acetone, propionaldehyde and acetamide, which have not previously been reported in comets. Acetamide is also one of four compounds detected that can produce important biological molecules like amino acids, sugars and DNA bases. Blank is especially excited by acetamide’s presence. ‘It's easy to imagine a pathway to an amino acid,’ she says. However, Goesmann is cautious not to read too much into their presence. ‘Comets with such a composition do not work against life,’ he tells Chemistry World. ‘In the right environment, emerging life could make use of it.’

However, the small amount of material COSAC was looking at meant it couldn’t detect anything but the smallest compounds. That means it wouldn’t have seen any ‘molecules of life’, such as amino acids, even if they were present. And although it could have, it didn’t see much ammonia, formaldehyde or carbon dioxide, which are common components of cometary ice, or any sulfur compounds. The COSAC scientists link the lack of ice to measurements previously made by Rosetta showing 67P’s surface is covered in a carbon-based coat rather than frozen.

Icy isolation

To determine isotope ratios of chemicals on 67P and establish their origins, Ptolemy’s gas chromatograph and ion trap mass spectrometer were also supposed to be fed drilled samples. However, it was reduced to making six sniffs at 14 second intervals about 20 minutes after Philae hit 67P. Like COSAC, it failed to find any signs of sulfur. Ptolemy saw mostly water and carbon dioxide, ice components expected on comets, but no significant indication of ammonia, and very low levels of nitrogen compounds overall. The COSAC scientists suggest that the absence of this key source of nitrogen could be because it has evaporated or been used up in reactions.

Ptolemy also found hints of polyoxymethylene, a polymer thought to be produced from formaldehyde by cosmic radiation, previously detected on Halley’s Comet. This source of formaldehyde is another important potential resource for origin-of-life chemistry, Wright underlines. ‘It can produce simple sugars like ribose,’ he says. ‘These are things that we hope will be picked up by astrobiologists in refining their ideas.’

John Plane from the atmospheric and planetary chemistry group at the University of Leeds calls these measurements ‘technically incredible’. ‘It’s a wonderful achievement to get any data,’ he says. Plane is especially pleased because COSAC’s findings support lab experiments showing cometary ice can produce small organic molecules. ‘It’s nice to have them confirmed, and get a first idea of relative abundance,’ he says. ‘That’s useful if you want to simulate the next step, how these molecules could react together to make peptides and DNA.’
Meanwhile, Rosetta has recently regained tenuous contact with Philae, enough for scientific commands to be sent to Ptolemy last week, Wright reveals. ‘We haven’t got any data back,’ he admits. ‘When we get a communication window it might come back, but it’s a fingers crossed job. As time goes on we’re becoming less convinced that’s going to happen.’

Rosetta's lander Philae wakes up from hibernation (14 June)

Rosetta's lander Philae has woken up after seven months in hibernation on the surface of Comet 67P/Churyumov-Gerasimenko.
The signals were received at ESA's European Space Operations Centre in Darmstadt at 22:28 CEST on 13 June. More than 300 data packets have been analysed by the teams at the Lander Control Center at the German Aerospace Center (DLR).
"Philae is doing very well: It has an operating temperature of -35ºC and has 24 Watts available," explains DLR Philae Project Manager Dr. Stephan Ulamec. "The lander is ready for operations."
For 85 seconds Philae "spoke" with its team on ground, via Rosetta, in the first contact since going into hibernation in November.
When analysing the status data it became clear that Philae also must have been awake earlier: "We have also received historical data – so far, however, the lander had not been able to contact us earlier."
Now the scientists are waiting for the next contact. There are still more than 8000 data packets in Philae’s mass memory which will give the DLR team information on what happened to the lander in the past few days on Comet 67P/Churyumov-Gerasimenko.
Philae shut down on 15 November 2014 at 1:15 CET after being in operation on the comet for about 60 hours. Since 12 March 2015 the communication unit on orbiter Rosetta was turned on to listen out for the lander.

Most of Earth's Water Came from Asteroids, Not Comets

Asteroids, not comets, may have delivered most of Earth's water to the planet when the solar system was young, new data from a probe orbiting a comet suggests.
Comets are some of the solar system's most primitive building blocks, with many dating to soon after its formation. Scientists think that these dirty snowballs probably helped seed Earth with key ingredients for life, such as organic compounds.
The European Space Agency's (ESA) Rosetta spacecraft is helping scientists learn more about the role these icy nomads have played in the evolution of the solar system and life on Earth by analyzing the composition of Comet 67P/Churyumov–Gerasimenko. In August, Rosetta became the first spacecraft to orbit a comet, and in November, its Philae lander became the first probe to make a soft touchdown on a comet's surface. Rosetta is also the first mission to escort a comet as it travels around the sun. [See images from ESA's Rosetta mission]

Now, Rosetta has helped solve a mystery about how Earth became the watery world it is today. Before Rosetta began orbiting Comet 67P/C-G in August, it was using an instrument known as ROSINA (short for Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) to analyze the chemical fingerprint of gases in the comet's fuzzy envelope. Scientists focused on data from the instrument regarding water to help uncover whether asteroids or comets delivered the water in Earth's oceans.

Heavy water on Earth and in comets

Models of Earth's birth suggestthat the planet was quite hot after its formation about 4.6 billion years ago, so scientists think it's unlikely that any water currently on Earth's surface dates back to the time of the planet's creation. However, prior studies have hinted that cosmic impacts could have easily brought water later, during a violent era known as the Late Heavy Bombardment, about 800 million years after Earth's formation.

To uncover the source of Earth's water, scientists look for bodies elsewhere in the solar system with similar water. Out of every 10,000 water molecules on Earth, three are not normal water molecules, but instead are so-called heavy water molecules.

A normal water molecule is made of two hydrogen atoms and one oxygen atom. In heavy water, a normal hydrogen atom is replaced with deuterium, which is like hydrogen except that it has an extra neutron in its nucleus. (A regular hydrogen atom has only one proton in its nucleus.)
To see if comets might be the source of Earth's water, in 1986, the ESA probe Giotto flew by Halley's Comet, becoming the first spacecraft to make close observations of a comet. It discovered that Halley's Comet had twice the amount of heavy water compared to normal water as Earth does.
Halley's Comet comes from the Oort Cloud, a giant spherical cloud of trillions of icy bodies that extends from 5,000 to 100,000 times the distance of Earth to the sun. The data from Halley's Comet and from other Oort Cloud comets "ruled out Oort Cloud comets as being the source of terrestrial water," said lead study author Kathrin Altwegg,of the University of Bern in Switzerland, principal investigator for the ROSINA mass spectrometer on Rosetta. [

But the Oort Cloud is not the only source of comets in the solar system. Another home to the dirty snowballs is the disc-shaped Kuiper Belt, which extends from about 30 to 55 times the distance of Earth to the sun. In 2011, data from ESA's Herschel Space Observatory revealed that Kuiper Belt comet 103P/Hartley 2 had a deuterium-to-hydrogen ratio "that matched terrestrial water's perfectly," Altwegg said during a news conference Tuesday (Dec. 9). "The Hartley 2 measurement — that was a real big surprise."

Not all comets are alike

Now, Rosetta has provided data from Comet 67P/C-G, another Kuiper Belt comet. However, Rosetta has discovered that this comet possesses an even higher deuterium-to-hydrogen ratio than seen in Oort Cloud comets — three times the amount of heavy water compared to normal water as Earth has.

This probably rules out Kuiper Belt comets from bringing water to Earth," Altwegg said. Instead, most of Earth's water was probably delivered by asteroids, Altwegg said.

"Today's asteroids have very little water — that's clear," Altwegg added. "But that was probably not always the case. During the Late Heavy Bombardment 3.8 billion years ago, at that time, asteroids could have had much more water than they could now."

The asteroids seen now "have stayed in the vicinity of the sun for 4.6 billion years," Altwegg said. "They've lost water due to the sun, due to heat. But to start with, they might have had much more water than they have now." Future analysis of ice-rich bodies in the asteroid belt could shed light on whether Earth's water really did come from there, Altwegg said.

The differences seen between Comet 103P/Hartley 2 and Comet 67P/C-G suggest that Kuiper Belt comets are much more diverse than previously thought. This could mean that "they were probably not all assembled in the same location in the solar system," Altwegg said. Kuiper Belt comets with relatively low deuterium-to-hydrogen ratios might have formed close to the sun, where solar warmth may have helped them lose deuterium, while those with relatively high deuterium-to-hydrogen ratios might have originated farther away.

In the future, when Comet 67P/C-G flies closer to the sun, the scientists hope to fly Rosetta through a jet of gas that the comet will give off as it gets warmer and more active. This will help reveal if the deuterium-to-hydrogen ratio seen from the water near the comet's surface is the same as that from near its core.

"Hopefully, we'll get to fly directly through a jet [in the] summertime [of] next year," said Matt Taylor, ESA Rosetta project scientist.

Where could Philae be?

Scientists are also still on the lookout for Philae, which made a bouncy landing on Comet 67P/C-G's surface in mid-November. The refrigerator-size probe's anchoring harpoons did not fire as planned during touchdown, and it bounced off the comet twice before settling down on its surface.
It broadcasted scientific data for about 57 hours on the comet's surface before its primary batteries ran out.
ESA officials aren't sure where Philae is now. Panoramic images from the probe reveal "one side of the lander appears to be in a hole," Taylor said during the news conference. "I see an overhanging clifflike structure."
A radio instrument known as CONSERT, short for Comet Nucleus Sounding Experiment by Radiowave Transmission, on both Rosetta and Philae has narrowed the lander's position to a strip a few hundred feet long by a few dozen feet wide.
"We're using that to kind of nail down where we think we should be looking harder," Taylor said. "Once we get identification of where the lander is, that will give us a better fix on what we believe the illumination conditions are and a better idea of when we should expect the lander to have sufficient illumination to start charging its batteries and come back online."
A "back-of-a-beer-mat calculation" suggests Philae might come back online around May, Taylor added.
The new comet findings are detailed in this week's issue of the journal Science