What will ‘cosmic detective’ OSIRIS-Rex bring back on September 24? | Explained

Come September 24, and debris from an alien world will land on the earth. NASA’s asteroid hunting spacecraft OSIRIS-Rex – short for Origins-Spectral Interpretation-Resource Identification-Security-Regolith Explorer – will drop a capsule containing pristine asteroid material in the Utah desert. OSIRIS-Rex, which is currently winging its way towards the earth after a close encounter with Bennu, a near-earth asteroid (NEA), “is a cosmic detective,” in the words of Dante Lauretta, the principal investigator of the mission.

“Asteroids are like cosmic treasure troves, containing a mix of raw materials like metals, water, and even organic compounds,” Dr. Lauretta told this writer in an email. The astro-material brought back by OSIRIS-Rex, he added, “may provide scientists with valuable insights into how planets formed, what materials were present in the early Solar System, and even how life on the earth might have originated.”

Celestial waltz

Many scientists believe that along with comets, carbon-rich asteroids like Bennu may have seeded the earth with primordial life as they smashed into the young planet more than four billion years ago.

Launched in 2016, the OSIRIS-Rex spacecraft completed a series of complex manoeuvres that included a return trip to the earth to use the planet’s gravitational pull for it to ‘slingshot’  itself back into space, with more speed. Scientists then injected the probe into orbit around Bennu in 2018 so that it whirled barely two kilometres above the space rock, even as both of them hurtled through space at 28 kilometres per second.

Mission controllers had to precisely choreograph this celestial waltz as Bennu’s frail gravity – so weak that it allows boulders to roll uphill on the asteroid! – could barely keep OSIRIS-Rex bound in orbit.

A Brian May riff

But even after achieving orbit, the mission almost ended in failure when the asteroid’s unexpectedly craggy surface rendered OSIRIS-Rex’s height-measuring instrument useless to attempt a landing. Controllers were forced to send the probe on an intricate holding pattern around Bennu for almost two and a half years as they tried to find a different landing spot.

Fortunately, they had an unlikely ally: the renowned lead guitarist of the rock band Queen, Brian May. A qualified astrophysicist, May used his expertise in stereoscopy to turn images taken by OSIRIS-Rex’s on-board cameras into detailed 3D maps of Bennu’s surface for locating potential landing sites.

Finally, on October 20, 2020, a comparatively boulder-free crater named ‘Nightingale’ was identified as a place where OSIRIS-Rex could land. To prevent the probe from sinking through the rubble-strewn surface, the probe’s touch-and-go Sample Acquisition Mechanism also used a blast of environmentally friendly nitrogen gas – instead of the conventional rocket thrusters – to avoid contaminating the debris flying everywhere, including into the spacecraft’s sample collection chamber. After its successful swoop on Bennu, OSIRIS-Rex took off and gradually pulled away from the asteroid’s gravity before setting course for the earth.

Earth in the crosshairs

After releasing its sample capsule above our planet’s atmosphere this Sunday, the doughty little spacecraft will fire its engines to shake free from the earth’s gravity and begin a new journey – to study another asteroid, Apophis, in 2029.

The asteroid belt between Mars and Jupiter is inhabited by thousands of space rocks, ranging in size from that of Ceres – the largest, with a width of more than 800 kilometres – to pint-sized stones. A part of the orbits of some of them bring them within 34 million kilometres of the sun, closer even than Mercury gets. Such eccentric orbits sometimes bring these quite close to the earth as well. This is what happened in 1937, when Hermes, a giant binary roid, zipped past the earth at less than twice the distance to the moon.

Planetary defence experts are keen to know more about such NEAs and how to approach them, because it is not improbable for the earth to be threatened someday by a runaway asteroid, or comet, with this fragile blue-green planet in its crosshairs.

Mining, not security

Indeed, while the chances of a serious earth-asteroid collision may be small, the odds averaged out over time of being killed by an earth-grazer roid are actually the same as being killed in an air crash. The problem is that even if these stragglers don’t pose a direct threat to the earth, planetary gravitation can cause their paths to change with each orbit.

Of greatest concern are asteroids wider than a kilometre across that stray into the Solar System’s ‘backyard’, which would put them on a collision course with the earth. If one of these hunks of stone and metal hits the planet, it will set off a million megaton explosions – that’s a million city-busting bombs going off at the same time. So it makes sense for space agencies to invest in plans to intercept these doomsday rocks, deflecting them from their trajectory or destroying them with nuclear explosions.

But spacefaring countries seem to have sidelined planet security for the mercantile goal of mining asteroids. Previous missions like NASA’s Galileo (launched in October 1989) and NEAR Shoemaker (February 1996) and Japan’s Hayabusa 1 (May 2003) and Hayabusa 2 (December 2014) tell us that asteroids are solidified debris from supernovae (exploding stars). They are made of the same stuff as the Solar System: dust, rocks, water ice, and an alloy of iron, nickel and cobalt – a sort of natural stainless steel.

That means huge lumps of high-quality steel can be extracted from asteroids, besides allowing enterprising engineers to tap the abundant water present in them,  in the form of permafrost or saturated minerals. This substance is not only essential for surviving in space but could also be a rocket propellant.

Windows into past and future

In fact, with asteroids hosting most of the raw materials needed to build a self-sufficient space colony, it is not surprising that many players are drawn to space mining. In fact, reaching NEAs and returning payloads to the earth might be easier compared to returning payloads from the moon.

“NEAs, being relatively closer to Earth, make the journey shorter and require less fuel,” Dr. Lauretta agreed. “The moon, although closer in some ways, has a stronger gravitational pull, which makes launching payloads from its surface more challenging and energy-intensive.”

But he added a caveat: “While it’s a fascinating idea, building a self-sufficient space colony using only asteroid resources is quite complex. Some asteroids could provide essential resources, but challenges like low gravity, lack of atmosphere, and radiation exposure need to be overcome. It’s like having all the ingredients to bake a cake but needing the right recipe and tools to make it work.”

Right now, however, all eyes are on the asteroidal regolith of rocks and dust that OSIRIS-Rex is bringing to the earth to help scientists peer back in time, to the violent birth of the Solar System. Maybe, just maybe, the astro-material will also reveal carbon-containing organic molecules – the building blocks of life – to tell the story of how life on our piece of rock began.

Prakash Chandra is a science writer.

• Come September 24, and debris from an alien world will land on the earth. NASA’s asteroid hunting spacecraft OSIRIS-Rex – short for Origins-Spectral Interpretation-Resource Identification-Security-Regolith Explorer – will drop a capsule containing pristine asteroid material in the Utah desert.
• OSIRIS-Rex, which is currently winging its way towards the earth after a close encounter with Bennu, a near-earth asteroid (NEA), “is a cosmic detective,” in the words of Dante Lauretta, the principal investigator of the mission.
• Launched in 2016, the OSIRIS-Rex spacecraft completed a series of complex manoeuvres that included a return trip to the earth to use the planet’s gravitational pull for it to ‘slingshot’ itself back into space, with more speed.