TOKYO — A Japanese space explorer took off today on a six-year journey to blow a crater in a remote asteroid and try to bring back rock samples.

The explorer, named Hayabusa2, is expected to reach the asteroid in mid-2018, spend about 18 months studying it and return in late 2020.

A small device will separate from the explorer and shoot a projectile to blast open a crater several feet in diameter. The explorer will then try to collect material from inside the crater.

Hayabusa2 will attempt to expand on the work of Hayabusa, which returned in 2010 after collecting material from the surface of another asteroid.

Asteroids can provide evidence not available on Earth about the birth of the solar system and its evolution. JAXA, Japan's space agency, said the research could help explain the origin of seawater and how the planet earth was formed.

LONDON — Visitors to Stonehenge will no longer have to shut out the sound of thundering traffic as they admire the ancient monument.The 1.8-mile tunnel, part of a $3.2 billion upgrade to the road, will eliminate motorists’ view of the stone circle. Helen Ghosh, director of heritage group the National Trust, said visitors to the site “will once again be able to hear the sounds of skylarks singing rather than the constant noise of traffic.”Stonehenge, built by Neolithic Britons between 3000 B.C. and 1600 B.C. is visited by a million people a year. A second road was closed last year as part of a makeover to de-clutter the surrounding landscape.