Just days after its InSight lander touched down safely on Mars after a long, uncertain journey, NASA is getting set for another nail-biter: the arrival of the space agency’s OSIRIS-REx spacecraft at its target, a skyscraper-size asteroid known as Bennu.

Bennu is a small solar-system body with big scientific potential: Astronomers suspect the asteroid’s rocky composition has remained more or less unchanged since it formed some 4.5 billion years ago. The sample from Bennu, a near-Earth asteroid, could help scientists understand not only more about asteroids that could impact Earth but about how planets formed and life began.

NASA said the estimated 2.1-ounce sample size equates to about 30 sugar packets worth of dirt and rocks.

OSIRIS-REx — the name is an acronym for Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer — launched into space in September 2016 and has been making its way toward Bennu since.

After arriving at Bennu, OSIRIS-REx will spend several weeks maneuvering around the asteroid, collecting data on its mass, topography, and composition. The spacecraft will begin its survey at a remove of roughly 12 miles, and culminate in a series of low-pass flyovers some 800 feet above the asteroid’s surface before entering the asteroid’s orbit on New Years’ Eve. If NASA is successful, Bennu will become the smallest object the agency has ever orbited.

OSIRIS-REx will depart Bennu in the spring of 2021 to begin its two-and-a-half-year journey back to Earth.

Japan’s Hayabusa mission returned a small sample of an asteroid known as 25143 Itokawa in 2010; a successor craft, Hayabusa-2, arrived at an asteroid called Ryugu last year and is expected to return a sample in 2020.

OSIRIS-REx and Hayabusa 2 are companion missions,” Dante Lauretta, a planetary scientist at the University of Arizona and the principal investigator for the OSIRIS-REx mission, said in September. “We work together to understand the history of the solar system.”

Bennu is as wide as five football fields and weighs around 79 billion kilograms, which is 1,664 times heavier than the Titanic. It has a 1 in 2,700-chance of striking Earth between 2175 and 2199.

It is estimated that the energy unleashed in this impact would be equivalent to 1,200 megatons, which is 80,000 times the energy released by the Hiroshima bomb.

Will Asteroid Bennu hit Earth and wipe out humanity?

“We’re not talking about an asteroid that could destroy the Earth,” OSIRIS-REx principal investigator Dante Lauretta, of the Lunar and Planetary Laboratory at the University of Arizona, told Space.com. “We’re not anywhere near that kind of energy for an impact.”