How the Sun creates asteroids

Posted by Alison Klesman
on Thursday, October 19, 2017

This enhanced color image of Ernutet Crater on Ceres shows organic material as a reddish glaze. Researchers suspect the organics were native to the dwarf planet and brought to the surface by an impact. // NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

By Richard Talcott

From its position at the center of the solar system, the Sun spews harsh radiation and energetic particles whose effects are felt well beyond the realm of the planets. In most cases, these emissions are forces of destruction, but not always. On Wednesday at the 49th annual meeting of the Division for Planetary Sciences in Provo, Utah, Apostolos Christou of the Armagh Observatory and Planetarium in Northern Ireland showed how sunlight can be creative.

Christou and his team studies Martian Trojans — asteroids trapped in gravitational safe havens known as Lagrangian points. These points lie 60 degrees ahead of and behind Mars in its orbit around the Sun. Nine of the Trojans reside near the trailing point while only one orbits ahead of Mars. Of the nine trailers, eight form a tight-knit family headed by the 1.2-mile-wide (2 kilometers) Eureka. Christou’s team thinks the family arose from the YORP effect, a process in which sunlight slowly but steadily increases Eureka’s spin rate. Eventually, a piece of the object breaks off into an independent asteroid — what Christou calls a “YORPlet” — in a closely related orbit. Supporting the idea is the fact that Eureka rotates once every 2.5 hours, about as fast as an asteroid of this type can spin without breaking up. Eureka’s offspring can survive for more than a billion years.

Another intriguing development comes from the Dawn spacecraft’s ongoing reconnaissance of Ceres. The probe has discovered organic material on the dwarf planet’s surface, with the highest concentrations near the 32-mile-wide (52 kilometers) crater Ernutet. Simone Marchi of the Southwest Research Institute examined whether the organics were brought to Ceres by asteroid and comet impacts, or whether it is native to the dwarf planet. Because heat destroys the hydrocarbon bonds in organics, he was able to rule out high-speed collisions of comets as their source. And an asteroid impact would allow organics to survive only if it were a relatively slow, glancing blow. But Marchi did find that an impact could dredge up pre-existing organics from below Ceres’ surface, and he believes this is how Ernutet got its organic material.

Saturn’s largest moon, haze-shrouded Titan, appears here in one of the last images Cassini returned. In 2015, the spacecraft discovered a toxic cloud of benzene and hydrogen cyanide above the moon’s south pole. // NASA/JPL-Caltech/Space Science Institute

Finally, Carrie Anderson of NASA’s Goddard Space Flight Center reported on the chemical composition of a cloud that the Cassini spacecraft discovered in 2015 near the south pole of Saturn’s largest moon, Titan. The cloud lies in Titan’s stratosphere roughly 115 miles (185 km) high, far above the tropospheric clouds that rain methane. Anderson’s team conducted laboratory experiments that simulated conditions in Titan’s stratosphere to try to match the cloud’s spectral fingerprint. They found the best match with a mixture containing 79 percent benzene and 21 percent hydrogen cyanide. The cloud was discovered two years before winter began in the moon’s southern hemisphere, and has a different chemical composition than a northern hemisphere cloud seen a decade ago two years after the onset of northern winter. Anderson attributes the difference to slight seasonal variations at the two poles.

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