Tag Archives: comets

Complex Organic Molecules Discovered in Infant Star System

The new discovery hints that the building blocks of the chemistry of life are universal.

For the first time, astronomers have detected the presence of complex organic molecules, the building blocks of life, in a protoplanetary disc surrounding a young star. The discovery, made with the Atacama Large Millimeter/submillimeter Array (ALMA), reaffirms that the conditions that spawned the Earth and Sun are not unique in the Universe. The results are published in the 9 April 2015 issue of the journal Nature.

Artist impression of the protoplanetary disc surrounding the young star MWC 480. ALMA has detected the complex organic molecule methyl cyanide in the outer reaches of the disc in the region where comets are believed to form. This is another indication that complex organic chemistry, and potentially the conditions necessary for life, is universal. Credit: B. Saxton (NRAO/AUI/NSF)
Artist impression of the protoplanetary disc surrounding the young star MWC 480. ALMA has detected the complex organic molecule methyl cyanide in the outer reaches of the disc in the region where comets are believed to form. This is another indication that complex organic chemistry, and potentially the conditions necessary for life, is universal.
B. Saxton (NRAO/AUI/NSF)

The new ALMA observations reveal that the protoplanetary disc surrounding the young star MWC 480 [1] contains large amounts of methyl cyanide (CH3CN), a complex carbon-based molecule. There is enough methyl cyanide around MWC 480 to fill all of Earth’s oceans.

Both this molecule and its simpler cousin hydrogen cyanide (HCN) were found in the cold outer reaches of the star’s newly formed disc, in a region that astronomers believe is analogous to the Kuiper Belt — the realm of icy planetesimals and comets in our own Solar System beyond Neptune.

Comets retain a pristine record of the early chemistry of the Solar System, from the period of planet formation. Comets and asteroids from the outer Solar System are thought to have seeded the young Earth with water and organic molecules, helping set the stage for the development of primordial life.

“Studies of comets and asteroids show that the solar nebula that spawned the Sun and planets was rich in water and complex organic compounds,” noted Karin Öberg, an astronomer with the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, USA, and lead author of the new paper.

“We now have even better evidence that this same chemistry exists elsewhere in the Universe, in regions that could form solar systems not unlike our own.” This is particularly intriguing, Öberg notes, since the molecules found in MWC 480 are also found in similar concentrations in the Solar System’s comets.

The star MWC 480, which is about twice the mass of the Sun, is located 455 light-years away in the Taurus star-forming region. Its surrounding disc is in the very early stages of development — having recently coalesced out of a cold, dark nebula of dust and gas. Studies with ALMA and other telescopes have yet to detect any obvious signs of planet formation in it, although higher resolution observations may reveal structures similar to HL Tauri, which is of a similar age.

Astronomers have known for some time that cold, dark interstellar clouds are very efficient factories for complex organic molecules — including a group of molecules known as cyanides. Cyanides, and most especially methyl cyanide, are important because they contain carbon–nitrogen bonds, which are essential for the formation of amino acids, the foundation of proteins and the building blocks of life.

Until now, it has remained unclear, however, if these same complex organic molecules commonly form and survive in the energetic environment of a newly forming solar system, where shocks and radiation can easily break chemical bonds.

By exploiting ALMA’s remarkable sensitivity [2] astronomers can see from the latest observations that these molecules not only survive, but flourish.

Importantly, the molecules ALMA detected are much more abundant than would be found in interstellar clouds. This tells astronomers that protoplanetary discs are very efficient at forming complex organic molecules and that they are able to form them on relatively short timescales [3].

As this system continues to evolve, astronomers speculate that it’s likely that the organic molecules safely locked away in comets and other icy bodies will be ferried to environments more nurturing to life.

“From the study of exoplanets, we know the Solar System isn’t unique in its number of planets or abundance of water,” concluded Öberg. “Now we know we’re not unique in organic chemistry. Once more, we have learnt that we’re not special. From a life in the Universe point of view, this is great news.”

[1] This star is only about one million years old. By comparison the Sun is more than four billion years old. The name MWC 480 refers to the Mount Wilson Catalog of B and A stars with bright hydrogen lines in their spectra.

[2] ALMA is able to detect the faint millimetre-wavelength radiation that is naturally emitted by molecules in space. For these most recent observations, the astronomers used only a portion of ALMA’s 66 antennas when the telescope was in its lower-resolution configuration. Further studies of this and other protoplanetary discs with ALMA’s full capabilities will reveal additional details about the chemical and structural evolution of stars and planets.

[3] This rapid formation is essential to outpace the forces that would otherwise break the molecules apart. Also, these molecules were detected in a relatively serene part of the disc, roughly 4.5 to 15 billion kilometres from the central star. Though very distant by Solar System standards, in MWC 480’s scaled-up dimensions, this would be squarely in the comet-forming zone.

Source: ESO


A second minor planet may possess Saturn-like rings

Researchers detect features around Chiron that may signal rings, jets, or a shell of dust.

By Jennifer Chu

CAMBRIDGE, Mass. – There are only five bodies in our solar system that are known to bear rings. The most obvious is the planet Saturn; to a lesser extent, rings of gas and dust also encircle Jupiter, Uranus, and Neptune. The fifth member of this haloed group is Chariklo, one of a class of minor planets called centaurs: small, rocky bodies that possess qualities of both asteroids and comets.

Scientists only recently detected Chariklo’s ring system — a surprising finding, as it had been thought that centaurs are relatively dormant. Now scientists at MIT and elsewhere have detected a possible ring system around a second centaur, Chiron.

In November 2011, the group observed a stellar occultation in which Chiron passed in front of a bright star, briefly blocking its light. The researchers analyzed the star’s light emissions, and the momentary shadow created by Chiron, and identified optical features that suggest the centaur may possess a circulating disk of debris. The team believes the features may signify a ring system, a circular shell of gas and dust, or symmetric jets of material shooting out from the centaur’s surface.

“It’s interesting, because Chiron is a centaur — part of that middle section of the solar system, between Jupiter and Pluto, where we originally weren’t thinking things would be active, but it’s turning out things are quite active,” says Amanda Bosh, a lecturer in MIT’s Department of Earth, Atmospheric and Planetary Sciences.

Bosh and her colleagues at MIT — Jessica Ruprecht, Michael Person, and Amanda Gulbis — have published their results in the journal Icarus.

Catching a shadow

Chiron, discovered in 1977, was the first planetary body categorized as a centaur, after the mythological Greek creature — a hybrid of man and beast. Like their mythological counterparts, centaurs are hybrids, embodying traits of both asteroids and comets. Today, scientists estimate there are more than 44,000 centaurs in the solar system, concentrated mainly in a band between the orbits of Jupiter and Pluto.

While most centaurs are thought to be dormant, scientists have seen glimmers of activity from Chiron. Starting in the late 1980s, astronomers observed patterns of brightening from the centaur, as well as activity similar to that of a streaking comet.

In 1993 and 1994, James Elliot, then a professor of planetary astronomy and physics at MIT, observed a stellar occultation of Chiron and made the first estimates of its size. Elliot also observed features in the optical data that looked like jets of water and dust spewing from the centaur’s surface.

Now MIT researchers — some of them former members of Elliot’s group — have obtained more precise observations of Chiron, using two large telescopes in Hawaii: NASA’s Infrared Telescope Facility, on Mauna Kea, and the Las Cumbres Observatory Global Telescope Network, at Haleakala.

In 2010, the team started to chart the orbits of Chiron and nearby stars in order to pinpoint exactly when the centaur might pass across a star bright enough to detect. The researchers determined that such a stellar occultation would occur on Nov. 29, 2011, and reserved time on the two large telescopes in hopes of catching Chiron’s shadow.

“There’s an aspect of serendipity to these observations,” Bosh says. “We need a certain amount of luck, waiting for Chiron to pass in front of a star that is bright enough. Chiron itself is small enough that the event is very short; if you blink, you might miss it.”

The team observed the stellar occultation remotely, from MIT’s Building 54. The entire event lasted just a few minutes, and the telescopes recorded the fading light as Chiron cast its shadow over the telescopes.

Rings around a theory

The group analyzed the resulting light, and detected something unexpected. A simple body, with no surrounding material, would create a straightforward pattern, blocking the star’s light entirely. But the researchers observed symmetrical, sharp features near the start and end of the stellar occultation — a sign that material such as dust might be blocking a fraction of the starlight.

The researchers observed two such features, each about 300 kilometers from the center of the centaur. Judging from the optical data, the features are 3 and 7 kilometers wide, respectively.  The features are similar to what Elliot observed in the 1990s.

In light of these new observations, the researchers say that Chiron may still possess symmetrical jets of gas and dust, as Elliot first proposed. However, other interpretations may be equally valid, including the “intriguing possibility,” Bosh says, of a shell or ring of gas and dust.

Ruprecht, who is a researcher at MIT’s Lincoln Laboratory, says it is possible to imagine a scenario in which centaurs may form rings: For example, when a body breaks up, the resulting debris can be captured gravitationally around another body, such as Chiron. Rings can also be leftover material from the formation of Chiron itself.

“Another possibility involves the history of Chiron’s distance from the sun,” Ruprecht says. “Centaurs may have started further out in the solar system and, through gravitational interactions with giant planets, have had their orbits perturbed closer in to the sun. The frozen material that would have been stable out past Pluto is becoming less stable closer in, and can turn into gases that spray dust and material off the surface of a body. ”

An independent group has since combined the MIT group’s occultation data with other light data, and has concluded that the features around Chiron most likely represent a ring system. However, Ruprecht says that researchers will have to observe more stellar occultations of Chiron to truly determine which interpretation — rings, shell, or jets — is the correct one.

“If we want to make a strong case for rings around Chiron, we’ll need observations by multiple observers, distributed over a few hundred kilometers, so that we can map the ring geometry,” Ruprecht says. “But that alone doesn’t tell us if the rings are a temporary feature of Chiron, or a more permanent one. There’s a lot of work that needs to be done.”

Nevertheless, Bosh says the possibility of a second ringed centaur in the solar system is an enticing one.

“Until Chariklo’s rings were found, it was commonly believed that these smaller bodies don’t have ring systems,” Bosh says. “If Chiron has a ring system, it will show it’s more common than previously thought.”

This research was funded in part by NASA and the National Research Foundation of South Africa.

Source: MIT News Office