When observing with the GEMINI telescopes, two astronomers from Brazil and the United States discovered for the first time asteroids that are similar to “ordinary chondrites”, the most common meteorites found on Earth. Until now, astronomers have failed to identify their asteroidal sources because of the various geologic processes that occur after the meteorites are ejected from their asteroidal parent body.

Astronomy & Astrophysics is publishing the first discovery by T. Mothé-Diniz (Brazil) and D. Nesvorný (USA) of asteroids with a spectrum similar to that of ordinary chondrites, the meteoritic material that most resembles the composition of our Sun. Most of the meteorites that we collect on Earth come from the main belt of asteroids located between Mars and Jupiter ^[1]. They were ejected from their asteroidal “parent body” after a collision, were injected into a new orbit, and they finally felt onto the Earth. Meteorites are a major tool for knowing the history of the solar system because their composition is a record of past geologic processes that occurred while they were still incorporated in the parent asteroid.

One fundamental difficulty is that we do not know exactly where the majority of meteorite specimens come from within the asteroidal main belt. For many years, astronomers failed to discover the parent body of the most common meteorites, the ordinary chondrites that represent 75% of all the collected meteorites.

To find the source asteroid of a meteorite, astronomers must compare the spectra of the meteorite specimen to those of asteroids. This is a difficult task because meteorites and their parent bodies underwent different processes after the meteorite was ejected. In particular, asteroidal surfaces are known to be altered by a process called “space weathering”, which is probably caused by micrometeorite and solar wind action that progressively transforms the spectra of asteroidal surfaces. Hence, the spectral properties of asteroids become different from those of their associated meteorites, making the identification of asteroidal parent body more difficult.

Collisions are the main process to affect asteroids. As a consequence of a strong impact, an asteroid can be broken up, its fragments following the same orbit as the primary asteroid. These fragments constitute what astronomers call “asteroid families”. Until recently, most of the known asteroid families have been very old (they were formed 100 million to billions of years ago). Indeed, younger families are more difficult to detect because asteroids are closer to each other ^[2].

In 2006, four new, extremely young asteroid families were identified, with an age ranging from 50000 to 600000 years. These fragments should be less affected than older families by space weathering after the initial breakup. Mothé-Diniz and Nesvorný then observed these asteroids, using the GEMINI telescopes (one located in Hawaii, the other in Chile), and obtained visible spectra. They compared the asteroids spectra to the one of an ordinary chondrite (the Fayetteville meteorite ^[3]) and found good agreement.

This discovery is the first observational match between the most common meteorites and asteroids in the main belt. It also confirms the role of space weathering in altering asteroid surfaces. Identifying the asteroidal parent body of a meteorite is a unique tool when studying the history of our solar system because one can infer both the time of geological events (from the meteorite that can be analyzed through datation techniques) and their location in the solar system (from the location of the parent asteroid).

1. There are only a few exceptions, including the example of the famous meteorites coming from Mars.
2. After the primary asteroid is disrupted, the fragments move away from each other. The older the collision, the greater the distance between fragments.
3. Meteorites are named for the place they were collected. The Fayetteville meteorite fell near Fayetteville, Arkansas, on December 26, 1934.

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The prospects for life in the Universe just got sweeter, with the first discovery of a simple sugar molecule in space. The discovery of the sugar molecule glycolaldehyde in a giant cloud of gas and dust near the center of our own Milky Way Galaxy was made by scientists using the National Science Foundation’s 12 Meter Telescope, a radio telescope on Kitt Peak, Arizona.

“The discovery of this sugar molecule in a cloud from which new stars are forming means it is increasingly likely that the chemical precursors to life are formed in such clouds long before planets develop around the stars,” said Jan M. Hollis of the NASA Goddard Space Flight Center in Greenbelt, MD. Hollis worked with Frank J. Lovas of the University of Illinois and Philip R. Jewell of the National Radio Astronomy Observatory (NRAO) in Green Bank, WV, on the observations, made in May. The scientists have submitted their results to the Astrophysical Journal Letters.

“This discovery may be an important key to understanding the formation of life on the early Earth,” said Jewell. Conditions in interstellar clouds may, in some cases, mimic the conditions on the early Earth, so studying the chemistry of interstellar clouds may help scientists understand how bio-molecules formed early in our planet’s history. In addition, some scientists have suggested that Earth could have been “seeded” with complex molecules by passing comets, made of material from the interstellar cloud that condensed to form the Solar System.

Glycolaldehyde, an 8-atom molecule composed of carbon, oxygen and hydrogen, can combine with other molecules to form the more-complex sugars Ribose and Glucose. Ribose is a building block of nucleic acids such as RNA and DNA, which carry the genetic code of living organisms. Glucose is the sugar found in fruits. Glycolaldehyde contains exactly the same atoms, though in a different molecular structure, as methyl formate and acetic acid, both of which were detected previously in interstellar clouds. Glycolaldehyde is a simpler molecular cousin to table sugar, the scientists say.

The sugar molecule was detected in a large cloud of gas and dust some 26,000 light-years away, near the center of our Galaxy. Such clouds, often many light-years across, are the material from which new stars are formed. Though very rarified by Earth standards, these interstellar clouds are the sites of complex chemical reactions that occur over hundreds of thousands or millions of years. So far, about 120 different molecules have been discovered in these clouds. Most of these molecules contain a small number of atoms, and only a few molecules with eight or more atoms have been found in interstellar clouds.

“Finding glycolaldehyde in one of these interstellar clouds means that such molecules can be formed even in very rarified conditions,” said Hollis. “We don’t yet understand how it could be formed there,” he added. “A combination of more astronomical observations and theoretical chemistry work will be required to resolve the mystery of how this molecule is formed in space.”

“We hope this discovery inspires renewed efforts to find even more kinds of molecules, so that, with a better idea of the total picture, we may be able to deduce the details of the prebiotic chemistry taking place in interstellar clouds,” Hollis said.

The discovery was made by detecting faint radio emission from the sugar molecules in the interstellar cloud. Molecules rotate end-for-end, and as they change from one rotational energy state to another, they emit radio waves at precise frequencies. The “family” of radio frequencies emitted by a particular molecule forms a unique “fingerprint” that scientists can use to identify that molecule. The scientists identified glycolaldehyde by detecting six frequencies of radio emission in what is termed the millimeter-wavelength region of the electromagnetic spectrum — a region between more-familiar microwaves and infrared radiation.

The NRAO 12 Meter Telescope used to detect the sugar molecule has been a pioneer instrument in the detection of molecules in space. Built in 1967, it made the first detections of dozens of the molecules now known to exist in space, including the important first discovery of carbon monoxide, now widely used by astronomers as a signpost showing regions where stars are being formed. The 12 Meter Telescope is scheduled to be closed at the end of July, in preparation for the Atacama Large Millimeter Array, an advanced system of 64 radio-telescope antennas in northern Chile now being developed by an international partnership.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

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A new pathway for methane production has been uncovered in the oceans, and this has a significant potential impact for the study of greenhouse gas production on our planet. The article, published in the journal Nature Geoscience, reveals that aerobic decomposition of an organic, phosphorus-containing compound, methylphosphonate, may be responsible for the supersaturation of methane in ocean surface waters.

Methane is a more potent greenhouse gas than CO₂ on a per weight basis. Although the volume of methane in the atmosphere is considerably less than CO₂, methane is much more efficient at trapping the long wavelength radiation that keeps our planet habitable but is also responsible for enhanced greenhouse warming. Today, between 20-30% of the total radiative forcing of the atmosphere is due to methane. Terrestrial sources of methane production are well known and studied (including extraction from natural gas deposits and fermentation of organic matter), but those known sources did not account for the levels of methane observed in the atmosphere.

David Karl, an Oceanographer in the School of Ocean and Earth Science and Technology at the University of Hawai’i at Mânoa and lead author of this paper, was interested in this “methane enigma” and why the surface ocean was loaded with methane, over and above levels found in the atmosphere. When looking at the literature, Karl found a possible solution to the enigma, in the compound methylphosphonates, a very unusual organic compound only discovered in the 1960s. In the laboratory, the aerobic growth of certain bacteria on methylphosphonate can lead to the production of methane, but until now this process of methylphosphonate degradation in the ocean had not been suggested as a possible pathway for the aerobic production of methane in the sea.

“When people began measuring methane in the ocean, they found that methane concentrations varied with geographical location and with water depth”, says Karl. “If methane was inert in the ocean, its concentration should be constant and nearly equal to the concentration in the atmosphere. What the scientists found was that methane was lower than expected in deep waters, implying net consumption by microbes. However the big surprise was that near surface concentrations were higher than in the overlying atmosphere which indicated a local production of methane in the sea. Because methane is produced only in regions devoid of oxygen and since the surface ocean contains high oxygen levels this was very perplexing.”

Karl was able to combine a long term interest in methane, 20 years of ocean observing data at the Hawaii Ocean Timeseries site Station Aloha, and new technology that Massachusetts Institute of Technology co-author Edward DeLong and colleagues have developed to produce methane in aerobic marine environments. “I think this work nicely demonstrates the complementarity of different methods and approaches, which include oceanography, microbial ecology, and genomics techniques,” says DeLong. “In the case of genomics, the growing databases of marine microbial genomic and metagenomic data have great potential to help us link which organisms, and which genes, are responsible for driving important nutrient and elemental cycles in the sea, like aerobic methane generation.

With our colleagues at the Center for Microbial Oceanography: Research and Education (C-MORE, of which Karl is the Director, and DeLong the Co-Director), we plan next to learn how and when microbial communities turn on and off their methane production genes, in response to the methane precursors, like methylphosphonate, in their natural environment. This should provide new insights about the ‘who’ and the ‘how’ of this newly discovered methane generating process in the sea.”

Although the implications for global climate change are still being studied, the warming and further stratification of the ocean seem likely to affect marine methane production. “This is a newly recognized pathway of methane formation that needs to be incorporated into our thinking of global climate,” says Karl. “Since our oceans cover ¾ of the planet, you just need to stimulate this pathway a little bit and you’re going to create more methane. And one way you can tweak it is to stratify the oceans, which we know will happen. All of the climate models show that the ocean will become more nutrient limited over time.”

Phil Taylor, Acting Head of the Ocean Section, Division of Ocean Sciences at the National Science Foundation (NSF) agrees. “This remarkable discovery about methane production where we thought there would be none is a harbinger of many new insights on the ocean’s changing biogeochemical nature, and the intricate microbiological reasons for those changes.”

Interest in this research crosses many specialties. Oceanographers will be excited because it offers a solution to the long standing methane paradox. Microbiologists will be excited because it shows an aerobic production pathway of methane, which goes against everything that is currently known about methane, and Climatologists will be interested because it’s a potent greenhouse gas that we don’t have constraints on, and this new pathway is very exciting.

“NSF funded C-MORE with the hope that its scientists would make new discoveries about the vast genomic diversity and complexity in the microbial world, and its impacts from cellular to global scales,” says Matt Kane, Program Director for the NSF Division of Environmental Biology. “These findings are an example of the payoffs that come from an interdisciplinary and integrative approach to microbial oceanography.”

This research was supported by the Gordon and Betty Moore Foundation and the National Science Foundation.

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