2007: The year in the solar system

2019-02-26 02:09:01

By David Shiga Surprises abounded in the solar system in 2007. A meteorite crashed to Earth in Peru and left some unsolved mysteries, a massive dust storm erupted on Mars and threatened NASA’s robotic rovers, and an obscure comet suddenly brightened by a factor of a million and became visible to the naked eye. It was an exciting year for comets and asteroids. Scientists discovered a new family of asteroids to which the asteroid that killed off the dinosaurs appears to belong. The Baptistina asteroids are fragments of a huge 170-kilometre-wide asteroid that shattered into pieces in a collision 160 million years ago, with one of the fragments later slamming into Earth and wiping out T. rex. Speculation about the cause of a crater that appeared in the countryside of Peru on 15 September ended when an expedition of scientists found fragments of a stony meteorite at the site. But experts were still puzzled over some aspects of the crash, including how the meteorite had remained in one piece without breaking apart in the atmosphere. A normally very dim comet called Comet Holmes unexpectedly brightened by a factor of a million in a period of just 36 hours in October. The outburst made it temporarily visible to the naked eye and may have been due to a crack opening up in the comet’s nucleus and expelling clouds of gas and dust. A rare meteor shower called the alpha Aurigids, which had previously been seen only three times in history, returned to wow skygazers in September 2007. Unlike most meteor showers, which are due to comets with short periods, the alpha Aurigids are due to debris from a long-period comet that takes 2000 years to orbit the Sun. Japan’s Hayabusa spacecraft began limping back to Earth. Scientists still hope that it might contain a sample of material from asteroid Itokawa, despite serious problems during the collection process. NASA’s Dawn spacecraft launched in September. It will reach the asteroids Vesta in 2011 and Ceres in 2015. The newly launched STEREO spacecraft allowed scientists to witness a comet getting its tail ripped off by a solar outburst, something inferred from previous observations, but never seen directly. Mars continued to be the most intensely studied planet aside from Earth, with rovers crawling over its surface and spacecraft analysing it from orbit. NASA’s Spirit rover accidentally revealed an important clue to Mars’s past when one of its wheels, which has been unable to turn since 2006, ploughed up a patch of soil while being dragged along during a drive, revealing silicate-rich soil. Silicates form in the presence of hot water, and rover scientists pointed to the soil as evidence that volcanic activity once sent hot water or steam percolating through the soil at the site, making it a potential habitat for life at the time. Severe dust storms erupted on Mars in mid-2007, threatening to reduce the rovers’ solar power enough that one of them might freeze to death. By September, however, skies were clear enough for Opportunity to start its long-awaited drive into the giant crater Victoria. Meanwhile, analysis of Martian clays from orbit suggested that Mars was not as warm and wet in its past as previously believed, though radar observations hinted at vast stores of water ice on the planet’s equator. And NASA’s Phoenix Mars lander blasted off in August. Phoenix is expected to touch down in May 2008 to determine whether the soil has thawed in the recent past and to look for organic molecules that could signal past or present life. At Saturn, the Cassini spacecraft again returned a wealth of results on the ringed planet and its moons. Scientists struggled to explain a bizarre hexagon-shaped clearing in the clouds of Saturn’s north pole. It also found what appears to be a lake of liquid methane or ethane the size of Earth’s Caspian sea on Saturn’s moon, Titan, the largest lake found there so far. And a new analysis of radio data from the Huygens lander that touched down on Titan in 2005 revealed tentative signs that there could be an ocean of liquid water beneath the moon’s surface. Cassini’s close flyby of Saturn’s walnut-shaped moon, Iapetus, revealed that it is spotted like a Dalmatian, apparently because dark material that splattered onto its face from other moons got warmer than lighter material, creating a feedback loop of ice sublimation. Finally, scientists proposed that the bizarre spongy appearance of Saturn’s moon Hyperion is due to the moon’s high porosity, with 42% of its volume being empty space. The Moon was a hot target in 2007, with both Japan and China sending robotic orbiters there. Japan’s Kaguya spacecraft launched towards the Moon in September. After reaching orbit in October, it beamed back high-definition videos of the Moon’s surface and Earthrise, and released two smaller probes to help measure the Moon’s lumpy gravity field. China launched its first spacecraft beyond Earth orbit, hurling its Chang’e 1 probe towards the Moon in October. The spacecraft reached lunar orbit in November. Internet gossip suggested the spacecraft’s first publicly released image of the Moon was a fake, but a careful analysis confirmed it to be genuine. NASA announced it would also send another robotic spacecraft called GRAIL to the Moon in 2011 to obtain better gravity field measurements than Kaguya, in addition to its Lunar Reconnaissance Orbiter already set for launch in 2008. Jupiter had a visit in February by the New Horizons spacecraft for a gravity boost en route to Pluto. New Horizons obtained a movie of a volcanic plume spurting from Jupiter’s moon, Io. A curious lack of moons smaller than 16 kilometres across hinted that Jupiter’s smallest satellites may have eroded away. The Hubble Space Telescope, making its own observations of Jupiter from Earth orbit, observed mysterious and dramatic changes to Jupiter’s stripes. Finally, the Voyager 2 spacecraft reached a solar system boundary called the termination shock 30 years after being launched,