Pictured above are the orbits of the over 1,000 known Potentially Hazardous Asteroids (PHAs). These documented tumbling boulders of rock and ice are over 140 meters across and will pass within 7.5 million kilometers of Earth -- about 20 times the distance to the Moon. Although none of them will strike the Earth in the next 100 years -- not all PHAs have been discovered, and past 100 years, many orbits become hard to predict.
At 72, he said, he feels a moral obligation to step up his activism in his remaining years.
"If we burn even a substantial fraction of the fossil fuels, we guarantee there's going to be unstoppable changes" in the climate of the earth, he said. "We're going to leave a situation for young people and future generations that they may have no way to deal with."
GROVER, which stands for both Greenland Rover and Goddard Remotely Operated Vehicle for Exploration and Research, is an autonomous, solar-operated robot that carries a ground-penetrating radar to examine the layers of Greenland's ice sheet. Its findings will help scientists understand how the massive ice sheet gains and loses ice.