The spacecraft swept within 4,609 kilometres of the Martian surface on 15 May, executing a precisely planned gravity assist manoeuvre designed to dramatically boost its speed and alter its trajectory without consuming onboard fuel.
Mission controllers later confirmed the fly-by delivered exactly what was needed, accelerating the spacecraft by around 1,600km/h and subtly shifting its orbital plane to line up for its rendezvous with asteroid Psyche in 2029.
According to NASA’s Jet Propulsion Laboratory navigation lead Don Han, the fly-by was both technically flawless and emotionally rewarding for the team monitoring the mission in real time.
“Although we were confident in our calculations and flight plan, monitoring the Deep Space Network’s Doppler signal during the fly-by was still incredibly exciting,” Han said.
“We’ve confirmed Mars gave the spacecraft the boost it needed, and Psyche is now firmly on course for arrival at the asteroid in mid-2029.”
The fly-by also served as a full-scale rehearsal for the mission’s eventual operations around asteroid Psyche, with all scientific instruments powered up and undergoing calibration throughout the encounter.
Among the systems tested were the spacecraft’s multispectral imagers, magnetometers, and gamma-ray and neutron spectrometer – instruments that will eventually help scientists determine whether Psyche is the exposed metallic core of an ancient, failed planet.
As the spacecraft approached Mars, it captured striking imagery of the planet from an unusual perspective. Because Psyche arrived at a steep angle relative to the sun, Mars appeared as a thin crescent illuminated through its dusty atmosphere, creating brighter-than-expected visual effects.
During closest approach, the spacecraft rapidly photographed the Martian surface and atmosphere, collecting thousands of images that researchers said will prove invaluable both scientifically and operationally.
Arizona State University scientist Jim Bell, who leads the Psyche imaging instrument team, said the Mars observations were providing a rare opportunity to refine imaging systems before the spacecraft reaches its final destination.
“We’ve captured thousands of images of Mars during approach and close fly-by operations,” Bell said.
“The dataset is giving us an excellent opportunity to calibrate the cameras, validate our image-processing tools and better prepare for operations at asteroid Psyche itself.”
Several other Mars missions also assisted with the fly-by campaign, including NASA’s Perseverance rover, Curiosity rover, Mars Reconnaissance Orbiter, 2001 Mars Odyssey, along with the European Space Agency spacecraft Mars Express and ExoMars Trace Gas Orbiter.
Early readings from Psyche’s magnetometers may even have detected Mars’ bow shock – the region where solar wind interacts with the planet’s atmosphere and magnetic environment.
With Mars now fading behind it, the spacecraft will soon restart its solar-electric propulsion system for the long cruise towards the main asteroid belt between Mars and Jupiter.
The mission’s target, 16 Psyche, is unlike almost any asteroid previously studied. Roughly 280 kilometres wide, it is believed to potentially represent the exposed metallic core of a primordial planetesimal – one of the building blocks from which rocky planets such as Earth formed billions of years ago.
If confirmed, scientists said, that the asteroid could provide humanity’s first direct glimpse into the interior structure of an early planet.
Once Psyche arrives in August 2029, the spacecraft will progressively shift through a series of orbital altitudes around the asteroid, mapping its surface, analysing its composition and searching for clues about the violent processes that shaped the early solar system.
Mission principal investigator Lindy Elkins-Tanton said the successful Mars fly-by marked a major milestone after years of planning.
“We can thank the Red Planet for giving our spacecraft a critical gravitational slingshot farther into the solar system,” she said.
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