NASA will attempt to snag an asteroid sample today

NASA will attempt to grab a sample from an asteroid tonight.

The big picture: Scientists hope the sample from the asteroid Bennu will allow them to learn more about the early days of the solar system and how it has evolved over billions of years.

How it works: NASA's OSIRIS-REx spacecraft arrived at Bennu about two years ago equipped with an arm designed to touch the surface of the asteroid and collect a sample.

• The sampling tool will kick up some dust by firing nitrogen gas as it comes in contact with the surface, hopefully allowing it to take a relatively large sample of the asteroid before moving away and eventually heading back to Earth.
• The spacecraft should collect at least 60 grams of material from the asteroid, far more than any asteroid sample nabbed directly from its source before.

But, but, but: This sampling attempt won't be easy. The asteroid is strewn with boulders and obstacles that make grabbing material from its surface more complicated.

• Initially, scientists expected to find an asteroid with a relatively smooth, sandy surface. Instead, Bennu is a rocky jumble of boulders that could spell troubling during the sampling attempt — also called the touch and go, or TAG, maneuver.
• "Even within our Nightingale landing site, there still were some obstacles that we would really like to avoid during a TAG attempt," Mark Fisher of Lockheed Martin, which built the spacecraft for NASA, told me. "We actually changed the design of our flight software while it was up there, and we have basically a patch in place that can tell it to miss particular rocks."

What's next: It takes about 20 minutes for OSIRIS-REx to get commands from Earth, so the spacecraft will need to perform its TAG maneuver without input from people back on the planet.

• "I'm not thinking of this as seven minutes of terror. That's much more like a Mars EDL — entry, descent and landing. This is much more of a four and a half hours of mild anxiousness," Beth Buck, OSIRIS-REx mission operations program manager for Lockheed Martin said during a press briefing.
• NASA will know whether the spacecraft was able to touch Bennu's surface this evening, but mission managers likely won't know whether a sample was successfully taken until next week when they're able to properly check for any extra mass onboard.

Go deeper: NASA will air live coverage of the sampling attempt tonight starting at 5pm ET.