OSIRIS-REx prepares to deliver Bennu asteroid samples — and start its next mission

Think about arriving again at Earth after touring by means of space for seven years, tirelessly transmitting photographs and hauling again rock samples from the diamond-shaped asteroid 101955 Bennu. Time for trip, proper? Hardly for intrepid OSIRIS-REx.

This Sunday, Sept. 24, the craft’s major mission will culminate when it swings by Earth and drops off the biggest set of samples to ever be returned from an asteroid. The pristine rocks will likely be a scientific boon, a window into the early solar system that might present key clues to the origins of water and life on Earth.

However as quickly because the spacecraft leaves Earth’s neighborhood, it would start an prolonged mission to look at a second asteroid, 99942 Apophis. The brand new mission guarantees to be a blockbuster follow-up that sheds gentle on one of the menacing asteroids close to Earth’s orbit. In truth, Apophis will go solely 20,000 miles (32,000 kilometers) from Earth’s floor on April 13, 2029 — nearer than most geosynchronous satellites, practically 10 occasions nearer than the Moon, and visual to the bare eye for observers within the Jap Hemisphere.

Though the OSIRIS craft won’t be able to return any samples from Apophis, it would nonetheless have the ability to deploy its full arsenal of observational devices throughout this shut encounter, giving scientists key data on what could also be mandatory to 1 day spare Earth from an incoming asteroid.

Mission to Bennu

The OSIRIS-REx mission launched from Cape Canaveral on Sept. 8, 2016 in the direction of Bennu. The probe carried out an Earth flyby in September 2017, which is a key maneuver that permits it to succeed in close by asteroids whereas preserving propellant. Lastly, on Dec. 3, 2018, the explorer reached Bennu, revealing the darkish asteroid to be a dusty and rock-covered world with a diameter practically 1,600 ft (490 m), virtually as large because the Empire State Constructing is tall.

OSIRIS-REx spent the following 20 months characterizing Bennu. The asteroid didn’t disappoint and turned out to be a captivating world.

For one, it’s a carbon wealthy surroundings with water and potential amino acids — the constructing blocks for all times on Earth. Lab evaluation will verify whether or not amino acids exist on Bennu after samples are delivered.

ORISIS-REx additionally discovering that Bennu is ejecting particles into space, expelling pebbles and dust from its floor. It is a hazard to close by spacecraft. Sensors can turn out to be smudged, resulting in poor photographs; solar arrays might be pitted and clouded, failing to generate energy; and navigational star-sensors might be tainted, disorienting the probe.

As for the construction of Bennu itself, it’s a porous orb, representing a set of small rocks and boulders thrown along with dust tossed in. Whereas astronomical photographs taken from afar might counsel Bennu is a stable rock, in actual fact it’s loosely packed, with 20 to 40 p.c of its quantity being empty space. If an individual stepped onto Bennu, they could sink into the floor as if moving into a baby’s play pit of plastic balls, the team reported in analysis revealed in July 2022.

OSIRIS-REx additionally found that Bennu’s orbit is altering. A “day” on Bennu lasts a brief 4 hours and 17.8 minutes. However that’s sufficient to warmth up the asteroid’s dayside. When that heat facet rotates into the thing’s nightside, it cools, giving off radiation, which acts a small thruster propelling Bennu in the direction of the Solar by practically 0.18 miles (0.29 km) per yr.

This power known as the Yarkovsky impact, after Polish-Russian civil engineer Ivan Yarkovsky, who documented the idea within the early 1900s. This impact could cause rotating asteroids to float over the a long time, making their long-term trajectories tough for astronomers to pin down — and in addition the chance of them impacting Earth. That makes measuring the Yarkovsky impact a key remark for robotic explorers with up-close views of PHAs. Per Dante Lauretta of LPL, “OSIRIS-REx performed an important position in exactly characterizing Bennu’s orbit,” ruling out future impacts for the following 200 years.

Returning samples to Earth

From Earth-based telescopes, astronomers had believed the asteroid’s floor to be easy, lined by dust and some rocks. However when OSIRIS-REx arrived at Bennu, the workforce was in for a shock: The world was practically fully strewn with huge boulders — a problem for accumulating samples.

A number of months of shut mapping highlighted only some boulder-free zones that additionally introduced the multitude of small stones — a number of inches (a number of centimeters) in size — that the mission was in search of to pattern. With patience and a daring approach, OSIRIS-REx efficiently touched down on the floor and collected nearly 10.5 ounces (300 grams) of pebbles and dust, exceeding the mission’s acknowledged objective of two ounces (60 grams).

OSIRIS-REx wrapped up observations in Could 2021 and departed Bennu to return the samples to Earth. The trek required 2½ years orbiting the Solar twice within Venus’ orbit. On Sunday, the spacecraft will launch the pattern return capsule for an atmospheric reentry, parachute descent, and a touchdown on the Utah Check and Coaching Vary.

OSIRIS’ subsequent chapter

OSIRIS-REx will then change names to OSIRIS Apophis Explorer, or OSIRIS-APEX, with LPL’s Dani Della-Giustina taking up for Lauretta as principal investigator. The retiring Lauretta is elated that Della-Giustina, one among his former college students, will lead OSIRIS’ subsequent chapter, defining the asteroids geared toward our house.

Found in 2004, Apophis is classed as a doubtlessly hazardous asteroid (PHA) — which means it approaches inside 4.65 million miles (7.5 million km) of Earth’s orbit and is larger than 500 ft (140 meters) in diameter. It’s a stony-type asteroid with some iron and nickel blended in, although much less carbon and water in comparison with Bennu. At practically 1,100 ft (340 meters) in size, its form could also be like a peanut, its two lobes maybe solely loosely linked.

OSIRIS-APEX will rendezvous with and examine Apophis, turning into the one mission to trace the asteroid on-orbit because it approaches and flies by Earth in 2029. Its objectives embody observing any shifting floor options and alterations to its spin, in addition to measuring Apophis’ inner construction — essential data for a PHA.

OSIRIS’ operator, the College of Arizona’s Lunar and Planetary Laboratory (LPL), designed and constructed the spacecraft with the objective to characterize multiple asteroid. At present, OSIRIS’ devices are all operational, aside from one laser altimeter.

Sadly, there is just one pattern return capsule — the one stuffed with rocks from Bennu that may depart for the Utah desert. Nevertheless, the sampling arm on OSIRIS can poke Apophis for solutions. Particularly, this could take a look at the idea that some asteroids have an outer layer, or crust, shaped by the Solar’s harsh radiation. As Mike Nolan, LPL’s deputy principal investigator for APEX, places it, Apophis has been “baked by the Solar, frozen within the darkness, and [it will be] shaken by Earth’s 2029 shut encounter.”

Lengthy-term monitoring

Apophis is a very essential PHA as one of the hazardous asteroids that might affect Earth, crossing our plaent’s path as soon as each 324 days. Latest ground-based radar observations published in March 2021 have clarified Earth is secure for the following 100 years. However asteroids’ orbits shift over the a long time because of the Yarkovsky impact. In 2020, a workforce of researchers led by David Tholen of the University of Hawai‘i reported that Apophis’ orbit is slowly shrinking across the Solar, most definitely because of the Yarkovsky impact. Thus, Apophis and different PHAs with altering orbits are a continuing risk. OSIRIS-APEX’s monitoring of Apophis won’t solely refine its orbit, but additionally higher measure the Yarkovsky impact.

To be able to catch Apophis, OSIRIS-APEX must zip by the Earth 4 occasions, adjusting the probe’s orbit every go whereas saving valuable remark propellant. The September 2023 Bennu pattern drop-off and flyby will likely be coupled with 2025 and 2027 flybys. OSIRIS-APEX will start observations of Apophis on April 8, 2029, 5 days earlier than its close approach of Earth.

When Apophis reaches its closest level to Earth of the flyby on April 13, 2029, OSIRIS-APEX can have the very best seat in the home, trailing the asteroid from a distance of about 19,000 miles (30,000 km). Monitoring and imaging will reveal the asteroid’s form, mass, and rotation and determine any streams of pebbles strewn into space.

The probe’s objectives are to research how Apophis reacts to Earth’s gravitational and tidal forces. The asteroid spins about its brief axis about as soon as each 30 hours, however this might change drastically underneath Earth’s gravitational affect. Floor options might alter as effectively. There could be landslides or boulder migration. Mud might levitate and pool in low factors on the floor. Maybe indicators of stress fractures might seem.

Roughly two months later, OSIRIS-APEX will rendezvous with Apophis, characterizing mineral and floor particulars right down to 2 inches (5 cm), in addition to estimating the inner construction.

The APEX mission will likely be extra daring than Bennu in a technique: With the propellant saved zooming by Earth, scientists plan to make use of the probe’s thrusters to actively disturb Apophis’s floor with a view to look at and examine the subsurface.

Understanding the inner construction of a PHA influences how greatest to change an asteroid’s orbit — a mission which may be essential to divert future threats. NASA’s Double Asteroid Redirection Check (DART) mission in 2022 tested kinetic impact procedures by slamming into the moonlet Dimorphos, shortening its orbital period round its host asteroid Didymos by 32 minutes. This was a shock to scientists, who had estimated a mere 5- to 10-second change. Dimorphos’ construction should be extra like a heap of unfastened boulders, versus a stable rock; when DART created a crater, tons of dust and unfastened rock streamed into space, creating a further kick that modified the asteroid’s movement greater than the affect alone may have accomplished.

Preventative measures

It isn’t a matter of whether or not we are going to discover an asteroid with Earth’s title it, it’s a matter of when — and what we are able to do to forestall it from putting us. Every asteroid is a world of its personal. However what we be taught from OSIRIS’ samples of Bennu and its observations of Apophis will assist form how we reply to a possible Earth-impactor. These and future missions can defend the Earth whereas shedding gentle on PHAs’ traits and orbits. Moreover, these close by worlds might turn out to be key depots for humanity to broaden outward from our house.

Doug Kapua is a space evaluation and train planner at US STRATCOM. The views introduced on this article are these of the writer and don’t essentially characterize the views of US STRATCOM, the U.S. Air Power, DoD, or the U.S. Authorities.