Rosetta Mission Crashes Into Comet Theories
The historic Rosetta mission has ended with a crash landing. How has it changed ideas about comets?
We’ve followed the Rosetta mission with great interest since we announced in January 2003 that it would carry the story of Genesis to a comet. It seemed too ambitious to actually land a craft on a comet, but mission engineers succeeded in building, launching and flying the craft and its Philae lander all the way to a landing on the surface of a comet for the first time (compare the 2001 landing of Eros on an asteroid, 2/13/01). Only a few mishaps, like a launch delay that required a target change to Comet 67P (1/13/03) and then Philae’s premature silence after it landed (11/12/14, 11/13/14), marred an otherwise magnificent achievement. Rosetta passes into the history books now that engineers sent it to the surface last Friday (Sept 30), but its data will be analyzed for years to come. Here are reports with video clips about the end of mission:
- Rosetta’s descent towards region of active pits (PhysOrg, Sept 9 preview of the descent plan)
- Rosetta mission ends in comet collision (BBC News)
- Mission accomplished: Rosetta crashes into comet (Nature)
NASA posted a sharp image of the surface of the comet from 10 miles up, and then a close-up just before it crash landed (NASA-JPL participated in some instruments, but the mission was designed and operated by the European Space Agency, ESA).
As the back-slaps and nostalgia begin to fade, what will the legacy of Rosetta be? We reported on 1/26/15 that the first results were surprising: the dumbbell shape, the surprising diversity of surfaces, and the meringue-like low density. A year later (1/26/16), scientists who had been surprised not to find water were surprised to find water. This past June, astronomers were proposing the strange idea that bi-lobed comets bust up and reform continuously (6/17/16).
Now, reporters are beginning to sum up the major findings of the mission. Nature says that mission scientists have only analyzed about 5% of the data so far after its two years in orbit.
Rosetta has already made striking findings, including the discovery of water from comet 67P with a different isotopic composition to that on Earth, as well as molecular oxygen and nitrogen, which points to the comet being as old as the Solar System itself. Scientists also determined how 67P got its strange rubber-duck shape, deducing that the head and body were formed separately.
But many questions remain. A big challenge will be to figure out how the pebbles visible in Rosetta’s final shots were created, says Lowry.
Rebecca Boyle at New Scientist summarized “Rosetta’s Biggest Hits,” the top seven findings to date:
- Comets are more than meets the eye: This one had a curious duck-like shape, two lobes with a narrow neck. Scientists had expected a potato-shaped body. “At first, no one was sure how this was possible,” Boyle says. Later, scientists concluded it was a binary body that became joined at the neck.
- Comets have complex topography: so much for boring, homogeneous dirty snowballs. “Comet 67P has cliffs and canyons, boulders and weird bumps, inky pits and fine fractures – and regions as hard as asphalt, with others soft as sand.“
- Comets contain the building blocks of life (if you can call miscellaneous organic compounds “building blocks of life”). Scientists detected phosphorus, and glycine, the simplest amino acid among ethanol and other compounds.
- Comets can be bone dry: scientists expected lots of water ice on the surface, but they found Comet 67P to be parched at first. Water-ice jets started forming when it got closer to the sun. “Comet 67P has water, but its chemical signature is nothing like that on Earth,” Boyle says. “This may go against the theory that comets supplied Earth with its water in the solar system’s youth.”
- Comets sing: a low-frequency hum was detected, apparently from charged particles in the jets.
- Comets stink: if Philae had carried an astronaut, he would have to hold his nose. Philae found smelly stuff down on the surface: “These included hydrogen sulphide, ammonia and hydrogen cyanide – compounds that respectively call to mind rotten eggs, cat urine and bitter almonds.” Hydrogen cyanide is also extremely toxic to life.
- Landing on a comet is hard, but we did it: Philae unexpectedly bounced a couple of times, ending up miles away from its target point. Too bad the harpoons didn’t fire to grip the surface. It did land, though, sending some data and photos before its shadowed location made it lose power.
On July 28, PhysOrg posted an article about the birth of comets based on Rosetta’s findings. Are they primordial, as has long been thought, or do they show processing from collisions with other bodies? For decades, planetary scientists thought comets formed from pristine material in the outer solar system, combining ices with various molecules to form “dirty snowballs.”
The unusually high porosity of the interior of the nucleus provides the first indication that this growth cannot have been via violent collisions, as these would have compacted the fragile material….
Earlier work showed that the head and body were originally separate objects, but the collision that merged them must have been at low speed in order not to destroy both of them….
The article favors the pristine accretion model, but one must keep in mind that only 5% of Rosetta’s data has been analyzed. And Comet 67P might not be representative of all comets. Other comet missions, especially Stardust and Deep Impact, startled astronomers by revealing evidence of compounds that required high temperatures for their formation.
One thing is certain: we don’t see comets accreting today. We see them disintegrating. The Hubble Space Telescope just found another one, named Comet 332P, disrupting into fragments. Science Daily says:
“In the past, astronomers thought that comets die when they are warmed by sunlight, causing their ices to simply vaporize away,” Jewitt said. “But it’s starting to look like fragmentation may be more important. In comet 332P we may be seeing a comet fragmenting itself into oblivion.”
The researchers estimate that comet 332P contains enough mass for 25 more outbursts. “If the comet has an episode every six years, the equivalent of one orbit around the sun, then it will be gone in 150 years,” Jewitt said. “It’s just the blink of an eye, astronomically speaking. The trip to the inner solar system has doomed it.”
PhysOrg’s comet theory article claimed that small “goosebump” objects on Rosetta’s comet indicate slow accretion of small cometesimals. Yet small particles lack the gravity to accrete. If comets cannot accrete slowly, yet disintegrate rapidly, what does that say about their formation? What does it say about their lifetimes? Can these delicate cotton-candy rubble piles really exist for billions of years?
We’ve already seen the demise of the theory that comets delivered water to Earth. That leaves our planet in a theory drought, waiting for an explanation how a wet world 70% covered with water emerged from a hellish inferno of volcanoes and impacts. We’ve already seen, furthermore, surprising discoveries from other comet missions in addition to Comet 67P. While we celebrate the engineering success of Rosetta (good examples of intelligent design), we must be wary of assumption-laden theories based in a materialistic worldview. The ubiquitous “surprise effect” observed at each first-time encounter with solar system bodies reveals deep conflict between those assumptions and the truth. Maybe it’s time for ESA to actually read a replica of the Rosetta Stone they placed on the spacecraft: i.e., the words of Genesis 1-3 inscribed on a disc in 1,000 languages.