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Sunday, March 3, 2024
March 3, 2024

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Welcome to NASA’s hot asteroid autumn

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An unusual disc-shaped object from space landed last month on the barren sands of a U.S. military testing ground.

Scorched from its fiery journey through the atmosphere, the capsule was lifted by helicopter and taken to a custom-built clean room at the Utah Test and Training Range, where it sat unopened under a continuous flow of nitrogen to avoid contamination by the germs of its new home planet.

It was flown the next day to NASA’s Johnson Space Center in Houston. There, a hazmat-suited team carefully pried open the capsule to reveal the extraterrestrial treasure inside.

NASA will announce its initial findings on Wednesday. What we already know is that the capsule contains a sample from the asteroid Bennu, a roughly 4.6 billion-year-old relic of the earliest days of our planetary neighborhood.

The completion of the sample’s 1.2-billion-mile trip to Earth is part of a trio of missions in a season that Lori Glaze, NASA’s chief of planetary science, has called “asteroid autumn.”

Long famous for killing the dinosaurs and starring in apocalypse movies, asteroids are essentially construction debris from the building of the solar system. The same collapsed cloud of gas and dust that condensed in places to create the planets also produced smaller rocks that never achieved planet size or status.

This fall, NASA marks milestones in three different missions that explore unanswered questions about the process that made Earth, the stuff that makes the solar system and how we might save ourselves should a much larger space rock come hurtling our way.

Mission 1: OSIRIS-REx/OSIRIS-APEX

The Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer spacecraft (helpfully nicknamed OSIRIS-REx ) launched in 2016 and headed to Bennu with the goal of collecting NASA’s first asteroid sample and delivering it back to Earth.

The best proxies for asteroids we have on Earth are meteorites, small rocks from space that survived the fiery trip through Earth’s atmosphere. (Those that burn up upon entry, as an estimated 95% of such objects do, are called meteors.)

Some meteorites start out as asteroid fragments, though there’s no way to know what larger body they used to be part of. Regardless, a lot of key information about them gets lost during the long trip to Earth.

By the time one lands on the surface, friction from barreling through the atmosphere has seared its outer surface. All meteorites are coated in what’s known as “ fusion crust,” a hard rind of glassy material left behind when the exterior melted upon entry. They’re also contaminated with germs from Earth’s air and soil and may have spent years exposed to the elements before being found.

With OSIRIS-REx, “the objective is to bring back an ancient piece of the early solar system that is pristine,” said astrobiologist Jason Dworkin, the mission’s project scientist at NASA’s Goddard Space Flight Center in Maryland. “You can use these leftovers of the formation of the solar system to construct what happened in that formation.”

The spacecraft collected nearly 9 ounces (250g) of rocks, dust and other debris during its touch-and-go visit to Bennu’s Hokioi crater in October 2020. The precious cargo was stowed in the capsule that landed in the Utah desert.

NASA scientists will analyze the sample’s chemistry to help them figure out how the compounds necessary for life evolved from these early materials. But most of the payload will be frozen and archived so that future scientists — some of whom may not yet have been born — will be able to study it using technologies more advanced than what’s available today.

“That’s what excites me the most,” Dworkin said. “I have my own science, but the future is what is thrilling.”

The craft that traveled to Bennu has already moved on to its next assignment. Now named OSIRIS-APophis EXplorer, or OSIRIS-APEX, the craft is headed to Apophis, a peanut-shaped asteroid that, for a little while, seemed more likely to smash disastrously into Earth than any known object in the solar system.

Though that possibility has been decisively ruled out, Apophis is still on track to come closer to Earth than has any object of its size in recorded history. Scientists are taking advantage of the April 2029 flyby to grab a sample of that rock as well. Apophis is a stony asteroid, the most common type of potentially hazardous asteroid. Studying its composition could prove very helpful in understanding how to defend the planet from extraterrestrial threats.

Mission 2: Psyche

On Thursday, a SpaceX rocket will lift off from Kennedy Space Center to begin a 2.2-billion-mile journey to 16 Psyche, a metallic asteroid that orbits between Mars and Jupiter. It’s worth the long voyage: Psyche, the largest known metallic object in the solar system, is probably made of the same metals that form the cores of the rocky planets.

Though Earth’s core is certainly closer — a little less than 4,000 miles beneath the surface — it’s actually harder to access. Heat and pressure would obliterate any probe well before it reached the molten rock, which is hotter than the surface of the sun.

“We can learn more about Earth’s core and the core of the other rocky planets by going to space, which is weirdly easier than going to visit them in person,” said Lindy Elkins-Tanton, the mission’s principal investigator.

The spacecraft — also called Psyche — was originally scheduled to launch Thursday, but its departure was delayed after engineers spotted an issue with its thrusters. The craft is expected to reach the asteroid’s orbit in August 2029 and will then spend more than two years circling the object. Engineers from NASA’s Jet Propulsion Laboratory in La Cañada Flintridge will manage the mission, which is led by Arizona State University.

There’s no landing or sampling planned. That’s in part due to the exorbitant expense of hauling a sample across so much space. But it’s also because no one is quite sure what Psyche’s surface looks like.

Our only glimpses of the asteroid thus far are a few blurry telescope images. Based on its movements, scientists think that it’s big (173 miles across at its broadest point, about the width of Massachusetts) and potato-shaped. Analysis of the light reflecting off the asteroid and density estimates based on its shape and presumed mass suggest it’s highly metallic. Beyond that, it’s a mystery.

“It’s a primary exploration of a new kind of world, something that we really are going to be surprised by,” said Elkins-Tanton, a planetary scientist at Arizona State.

The craft is equipped with a pair of cameras that can photograph light in both the visible spectrum and in near-infrared wavelengths the human eye can’t see on its own. Those high-resolution pictures will reveal the asteroid’s topography and mineral makeup. Probes on the craft will collect data on its magnetic field, chemistry and gravity, all of which provide clues to its origins, interior structure and exterior composition.

Scientists believe Psyche could be the metallic core of a planetesimal, an early version of a rocky planet that came together in the chaos of the solar system’s formation only to have its outer crust battered away in collisions with other objects. Or it could be something entirely different.

Psyche “is a very unusual object. It must come from an unusual process,” Elkins-Tanton said. “And my favorite thing would be if it turned out not to be part of a core, and instead taught us something completely surprising about solar system formation.”

Mission 3: Lucy

Why visit a single asteroid when you can visit a bunch? That’s the goal of Lucy, a spacecraft that makes the first of 10 planned stops on its space rock tour next month.

Named for the fossilized remains of an early human ancestor discovered in Ethiopia in 1974, the mission is “trying to unlock the early history of the solar system, like Lucy unlocked the early history of humanity,” said Thomas Statler, a program scientist in NASA’s Planetary Science Division.

The space agency launched Lucy in 2021 with a plan to visit eight asteroids over a 12-year period and has added two more space rocks to the itinerary since. The mission is managed by NASA Goddard.

After traveling through the main asteroid belt that lies between Mars and Jupiter, the craft will become the first to explore two groups of rocks known as the Jupiter Trojan asteroids.

Although objects in the main belt are primarily detritus from the making of the rocky planets closer to the sun, scientists believe the Trojans are relics left over from the construction of Jupiter and the other gas giants.

“The Trojans are the last major population of things in the solar system that we have not seen,” Statler said.

The clusters of asteroids move roughly in tandem with Jupiter, bracketing the planet as it moves along its orbit. (If Jupiter were at the 12 on a clock face, the Trojans would be concentrated around the 10 and 2.) They come within roughly 365 million miles of Earth at their closest point and and are 601 million miles away at the farthest.

Visiting objects that far requires creative navigation, which explains the craft’s circuitous 4-billion-mile route. It will skim the inner edge of the main asteroid belt before looping back toward Earth for a gravity assist that will fling it out toward the Trojans.

Lucy wasn’t scheduled to have its first asteroid encounter until 2025. But this year, scientists identified a good candidate in the inner asteroid belt for an early flyby.

On Nov. 1, Lucy will make its closest approach to Dinkinesh, which is barely 0.4 miles across. Though Dinkinesh itself isn’t a terribly interesting asteroid, the flyby will serve as a dress rehearsal to test Lucy’s systems before it encounters more attractive scientific targets.

At each of its 10 stops, Lucy will map the asteroid’s size, color and surface geology; assess its mass and density; and check for any rings. Astronomers are hopeful that the variety of data will help fill in some missing parts of the solar system’s story.

“It’s not just the number of asteroids that we’re visiting, it’s the number of comparisons you can make between them,” Statler said. “That’s where the science is.”

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