Life's Building Blocks Created on Lab-Grown Comet
The chemicals necessary for the formation of life have been detected in lab-grown comet ice -- a discovery that could have huge implications for discovering how life as we know it was spawned.
Mix water, methanol and ammonia at low temperatures and low pressure, irradiate with ultraviolet light and what do you get?
A residue of organics, which when warmed to room temperature, contains ribose and other sugars that are believed to be building blocks for RNA and DNA, molecules essential for all known forms of life.
The experiment suggests that ribose and similarly structured sugars such as arabinose, xylose and lyxose could assemble under the chemical and temperature conditions of cosmic ices during the solar system's formation.
"The identification of ribose and related sugar molecules in the simulated cometary ice is new and entirely unexpected," astrochemist Cornelia Meinert, with the University of Nice Sophia Antipolis in Nice, France, wrote in an email to Discovery News.
The discovery, she added, "is relevant for many theories on the origin of life."
The experiment, reported in this week's Science, stems from work to develop an organics detector for the Philae comet lander, which was dispatched by Europe's Rosetta spacecraft to the surface of Comet 67P/Churyumov-Gerasimenko in November 2014.
Philae didn't find ribose on the comet, but it did detect three organic compounds that also turned up in the lab samples.
"The detection of ribose is really exciting and provides insight into the prebiotic origin of a critical compound needed for life," said University of Washington astronomer Donald Brownlee, who was not involved in the research.
"In the first few million years the outer regions of the solar system contained massive quantities of ice-coated dust grains and the proposed UV irradiation of these grains is surely an important source of organic materials. It seems like a wonderful gift from nature, that this process can produce ribose. We might not be here without it," Brownlee wrote in an email to Discovery News.
Scientists do not know how life began on Earth, but many theorize that key ingredients came from comets and asteroids crashing into the developing planet.
"I am sure that (ribose) can survive atmospheric entry," Brownlee added.
"Meteorites get hot on their surfaces but not in their interiors. If they are rocky materials, they are like Baked Alaskas. It is likely some cosmic dust particles from comets could also carry ribose through the atmosphere. A very interesting question is if Earth could make ribose or other critical molecules or whether it has to come from somewhere else. Irradiation of frozen volatiles is a natural process in space, but it does not easily occur on Earth," Brownlee said.
Meinert and colleagues do not yet know the exact mechanism that led to the formation of ribose and other sugar molecules in the simulated ices.
Previous attempts to find sugar molecules in simulated ices or meteorites failed due to analytical limitations, she added.
Follow-on studies are planned to look at the sugar molecules' structural asymmetry, or chirality, in hopes of learning more about the evolution of DNA.
Minert also would like to look for ribose in meteorites and in asteroid samples scheduled to be brought back to Earth by NASA's upcoming OSIRIS-REx and Japan's Hayabusa-2 missions.
This observation of Comet 67P/Churyumov-Gerasimenko was captured by the ESA Rosetta mission when it was 329 kilometers away on March 27. The comet it silhouetted by the sun, which is directly behind.
On Aug. 6, 2014, the European Space Agency's Rosetta spacecraft completed its decade-long journey to reach Comet 67P/Churyumov-Gerasimenko, becoming the first spacecraft to ever orbit a comet. The mission will reach its epic climax when it releases a small robotic lander, called Philae, onto the cometary surface in November. The lander will drill into the surface while Rosetta tags along with the comet's orbit as Churyumov-Gerasimenko makes close approach of the sun. Although Rosetta is unprecedented in that no other mission has achieved orbital insertion around a comet, it's certainly not the first robotic probe to make an intimate cometary encounter. So here's a rundown of 7 encounter of 6 comets by 5 spacecraft since the first close encounter with Halley's Comet in 1986.
Unquestionably the most famous comet in history, Halley's Comet was a prime target for space agencies in 1986 during its 75- to 76-year orbit through the inner solar system. Comet science is still a developing field, but in 1986, very little was known about the composition of these interplanetary vagabonds. In October of that year, the 15-kilometer-long Halley's Comet was visited by the European Space Agency's Giotto mission. The half-ton probe came within 600 kilometers (373 miles) of the comet's nucleus, taking the first photographs of the outgassing vapor from discrete areas of the surface producing its tail and coma (the gas surrounding the nucleus). It was this mission that confirmed the "dirty snowball" theory of cometary composition: a mix of volatile ices and dust. However, Giotto was only able to get so close to the famous comet with the help of the "Halley Armada," a number of international spacecraft all tasked with observing this rare event. Giotto captured the closest imagery, but two Russia/France probes (Vega 1 and 2) and two Japanese craft (Suisei and Sakigake) observed from afar.
At roughly half the size of Halley's comet, Comet Borrelly was found to have similar attributes to its famous cousin. The nucleus was also potato-shaped and blackened. Outgassing vapor was also observed coming from cracks in the nucleus crust where volatiles were exposed to sunlight, sublimating ices into space. NASA's Deep Space 1 probe flew past the comet with a close approach of 3,417 kilometers on Sept. 22, 2001.
Comet Wild 2 -- pronounced "Vilt" after its Swiss discoverer Paul Wild who spotted it in 1978 -- underwent a dramatic alteration in 1974. It is calculated that due to a close pass of Jupiter in 1974, the 5 kilometer-wide comet now orbits the sun every 6 years as opposed to its leisurely 43 years before the gas giant bullied it. The orbital modification meant that Wild 2 was an ideal target for NASA's Stardust mission to lock onto. On Jan. 4, 2004, the Stardust probe gave chase, getting so close to the comet that it was able to collect particles from Wild 2's coma. This image was taken at a distance of less than 240 kilometers (149 miles). The Stardust sample return canister came back to Earth safely, landing in Utah on Jan. 15, 2006. The microscopic particles captured from the comet continue to provide a valuable insight into the organic compounds comets contain. Interestingly, the Stardust spacecraft was granted a mission extension (dubbed New Exploration of Tempel 1 -- NExT). In 2011 it rendezvoused with its second comet, Tempel 1 -- the scene of NASA's 2005 Deep Impact mission -- to analyze the crater that Deep Impact's impactor left behind on the cometary surface.
NASA's Deep Impact mission reached the eight-kilometer-wide (five-mile-wide) comet Tempel 1 in 2005. On July 4, the probe deliberately smashed its impactor into the comet's nucleus, producing a cloud of fine material. A crater -- 100 meters wide (328 feet) by 30 meters (98 feet) deep -- was left behind. A treasure trove of compounds were spotted by the Deep Impact spacecraft and the explosion could be observed from Earth. In 2011, the recycled Stardust-NExT mission visited comet Tempel 1 for the second time.
The fifth space probe encounter with a comet happened on Nov. 4, 2010. NASA's recycled Deep Impact probe -- now the EPOXI mission -- visited comet Hartley 2, examining its strange-shaped nucleus. Described as a "peanut" or "chicken drumstick," this comet is an oddity. During its close approach of under 700 kilometers (435 miles), EPOXI photographed the comet's irregular topography: two rough lobes connected by a smooth center. Jets of gas could be seen being ejected from discrete locations. During the Hartley 2 flyby press conference at NASA's Jet Propulsion Laboratory (JPL), mission scientists expressed their surprise that these jets of vapor are being emitted from sun-facing and shaded regions on the comet surface. Needless to say, analysis of the Hartley 2 flyby data will keep scientists busy for some time to come. "This is an exploration moment," remarked Ed Weiler, NASA's Associate Administrator for the Science Mission Directorate, during the conference.
On Feb. 14, 2011, the veteran Stardust-NExT (New Exploration of Tempel) mission made history by visiting a comet for the second time. Comet Tempel 1 was first encountered by NASA's Deep Impact mission in 2005 after smashing the cometary nucleus with an impactor. This second encounter provided scientists with an unprecedented opportunity to study the same comet after six years of orbiting the sun. Preliminary findings suggested Tempel 1 has undergone some erosion during those six years in deep space. Also, the impact crater left behind by Deep Impact was imaged during the Stardust-NExT flyby and it appeared to match the size and shape predicted after the 2005 impact. However, the crater appeared smoother than expected, so work is ongoing to analyze the 72 photographs taken by the flyby to understand the processes shaping the comet's nucleus.
At 5:29 a.m. EDT (9:29 a.m. GMT) on Aug. 6, 2014, the European Rosetta spacecraft completed a 6.5 minute-long engine burn to insert itself into orbit around Comet 67P/Churyumov-Gerasimenko. Once under the influence of the comet's weak gravity, the spacecraft began to carry out a series of triangular loops, taking several days to complete. The long-duration mission is the first of its kind, where the spacecraft will study the comet from orbit, watching for surface changes as it approaches the sun, making perihelion (the point of closest solar approach). In November, a small lander called Philae will touch down on the surface to drill into the comet's material, revealing its small-scale composition. This photograph from Rosetta was captured on Aug. 3 when the probe was fast approaching the comet at a distance of less than 300 kilometers.