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Adapted from an article in the LA Times (July 15, 2016):

A layer of soot deposited after the K/T extinction event may explain why dinosaurs but not everything else died. (See The Cosmos, A Closer Look 8.5, p. 220.)

Researchers from Japan argue that the 6-mile-wide asteroid slammed into an oil field in the present day Yucatán Peninsula and triggered an inferno that launched a massive cloud of smoke into the sky. The resulting layer of soot that enveloped the globe would have been just the right thing to kill the dinosaurs and most other land-dwelling creatures.

Previous theories have postulated that the asteroid sparked the mass extinction by releasing high levels of sulfuric acid particles in the atmosphere. The particles would have caused complete darkness, near-freezing temperatures and acid rain. However, sulfuric acid particles don’t hang around for very long — and if they did, the results would have been catastrophic for many species besides dinosaurs. Instead, soot from the immense fire caused by the Chicxulub impact was a prime candidate.

The scientists collected soot samples from the thin band of rock that marks the timing of the extinction of dinosaurs and found the same composition from locations around the world. They hypothesize that soot was slowly deposited on land in the five years following the massive collision. The powdery substance is primarily made of black carbon that results from incineration of organic matter.

The tiny particles are about a million times more light-absorbing than carbon dioxide. They would have blocked about 85% of sunlight from reaching Earth and cut rainfall by nearly 80%, creating near-drought conditions, as well as causing temperatures to plummet. In this post-asteroid wasteland, plants began to die off, cutting off the food supply to creatures higher up the food chain — such as the dinosaurs — while allowing smaller mammals, birds and aquatic creatures to survive.

Link: the LA Times article

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NASA’s MESSENGER orbiter of Mercury ran out of fuel and crashed into Mercury on May 1, 2015, ending a very successful mission. The craft slammed into Mercury’s surface at about 8,750 mph and created a new crater on the planet’s surface.

MESSENGER’s demise went unobserved because the probe hit the side of the planet facing away from Earth, so ground-based telescopes were not able to capture the moment of impact. Space-based telescopes also were unable to view the impact, as Mercury’s proximity to the Sun would damage their optics.

MESSENGER had been in orbit more than four years and completed 4105 orbits around Mercury. Among its many accomplishments, the MESSENGER mission determined Mercury’s surface composition, revealed its geological history, discovered its internal magnetic field is offset from the planet’s center, and verified its polar deposits are dominantly water ice.

The movie below shows a NASA simulation of the spacecraft’s epic voyage.

Links: MESSENGER home, Sky & Telescope’s report, NY Times article, high-resolution image of the crash-site, map of gravity anomoalies measured by deviations of MESSENGER from its predicted orbit.

In an article in the New York Times, January 31, 2015, Peter Brannen reports on the ongoing debate about what caused the extinction of the non-bird dinosaurs at the end of the Cretaceous period (see A Closer Look 8.5, p. 220).

01DINOSAUR-articleLarge

Credit: Emiliano Ponzi/NY Times

While to many, the NEO impact theory and the discovery of the Chicxulub impact crater is compelling evidence, some geologists point to enormous floods of lava in India, called the Deccan Traps, as an alternate explanation.

Read more about the debate here.

From a NASA press release, April 18, 2014:

Ground controllers at NASA’s Ames Research Center in Moffett Field, California, have confirmed that NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft impacted the surface of the Moon, as planned, on Thursday, April 17. LADEE lacked fuel to maintain a long-term lunar orbit or continue science operations and was intentionally sent into the lunar surface. The spacecraft’s orbit naturally decayed following the mission’s final low-altitude science phase. (See p. 135.)

Credit: NASA

During impact, engineers believe the LADEE spacecraft, the size of a vending machine, broke apart, with most of the spacecraft’s material heating up several hundred degrees – or even vaporizing – at the surface. Any material that remained is likely buried in shallow craters. At the time of impact, LADEE was traveling at a speed of 3,600 miles per hour.

In early April, the spacecraft was commanded to carry out maneuvers that would lower its closest approach to the lunar surface. The new orbit brought LADEE to altitudes below one mile (two kilometers) above the lunar surface. This is lower than most commercial airliners fly above Earth, enabling scientists to gather unprecedented science measurements.

In the coming months, mission controllers will determine the exact time and location of LADEE’s impact and work with the agency’s Lunar Reconnaissance Orbiter (LRO) team to possibly capture an image of the impact site. A thorough understanding of the characteristics of our nearest celestial neighbor will help researchers understand other bodies in the solar system, such as large asteroids, Mercury and the moons of outer planets.

Links: full NASA press release; NY Times article; LADEE mission homepage.