FIVE THINGS ABOUT ASTEROID BENNU

1 BIG BLACK ROCK

Asteroid Bennu, a black rock taller than the Empire State Building, is the intended target of a NASA spacecraft set to blast off Thursday night. Not only will the robotic probe named Osiris- Rex fly to this ancient asteroid, it will scout it out for two years before scooping up some gravel and dust, and deliver the samples back to Earth. The mission will take seven years, from launch to sample return.

2 BIG SPACE BALL

Bennu is shaped like a ball, with a fat middle. Scientists believe the equatorial girth is loose rubble or gravel, the ideal size for collecting a sample. The asteroid rotates every four hours. This rotation is slow enough for a spacecraft to reach out and suck in samples, using nitrogen gas to stir up the surface. Bennu is believed to be 1,600 feet across.

3 COSMIC NEIGHBOURS

Bennu’s orbit around the sun is only a little bigger than Earth’s; it circles the sun about every 14 months and swings by Earth every six years. That cuts down on the travel time for Osiris- Rex, below, and, via its proximity to the sun, keeps its solar wings energized.

4 NOT A PLANET KILLER

Bennu is potentially hazardous, but no Earth- ender. There’s a slight chance it could strike our planet 150 years or so from now — just one- tenth of one per cent. It would be a major natural disaster, carving out a huge crater, but not a knockout punch for life on Earth.

5 CARBON, PLEASE

Bennu is the colour of coal. That’s a sign the asteroid is rich in carbon dating back to the origin of the solar system 4.5 billion years ago. If so, Bennu is a time capsule that could help explain how life sprouted on Earth.