Is the asteroid Psyche really a hunk of mostly metal? Is the object, which is nearly as wide as Massachusetts, the core of a baby planet whose rocky outer layers were knocked off during a cataclysmic collision in the early days of the solar system?
Right now, all that astronomers can say is maybe, maybe not.
NASA launched a spacecraft on Friday morning, also named Psyche, on a journey to the asteroid belt between Mars and Jupiter to find out.
“We’re really going to see a kind of new object, which means that a lot of our ideas are going to be proven wrong,” said Lindy Elkins-Tanton, a professor of earth and space exploration at Arizona State University who serves as the mission’s principal investigator.
Being proven wrong, she added, “is, I think, the most exciting thing in science.”
That voyage in search of answers kicked off Friday at 10:19 a.m. Eastern time. Falcon Heavy, the largest of SpaceX’s operational rockets, lifted off from Kennedy Space Center in Florida, sending the massive spacecraft on a journey that will last about six years and travel billions of miles.
Friday’s flight overcame early, unfavorable weather forecasts for what appeared to be a flawless liftoff. About eight minutes into the flight, the rocket’s upper stage entered a 45-minute coasting period during which it will prepare to deploy the spacecraft on its flight away from Earth. You can watch the ongoing flight in the video player above or on NASA’s YouTube channel.
The asteroid named Psyche has long been a curious enigma. Spotted in 1852 by Annibale de Gasparis, an Italian astronomer, it is named for the Greek goddess of the soul, and it was just the 16th asteroid to be discovered. In the early observations, it was, like the other asteroids, a starlike point of light that moved in an orbit around the sun, and not much more.
Beginning in the 1960s, astronomers found in telescope observations that the color of Psyche was similar to iron meteorites that have fallen on Earth, said Jim Bell, a professor of earth and space exploration also at Arizona State University who will lead studies of the asteroid with the spacecraft’s camera instrument. Astronomers bounced pulses of radar off Psyche, and the reflections coming back to Earth were brighter than those that came from other small objects in the asteroid belt.
“It became pretty clear that there’s some component of the surface that’s very radar reflective,” Dr. Bell said. “And the simplest way to do that is with metallic fragments.”
And then when scientists observed Psyche passing relatively close to larger worlds, its orbit was deflected in a way that suggested something quite massive, and potentially much denser than rock.
Most rocks like granite have a density of two to three grams per cubic centimeter. Water, whether liquid or ice, is about one gram per cubic centimeter. Metals like iron are much denser, between six and nine grams per cubic centimeter.
“Some of those early estimates were like, wow, this is really quite unusual,” Dr. Bell said.
Psyche appeared to be almost pure metal. Earth’s core is made of iron and nickel, and the measurements of Psyche gave rise to the thought that it could be the remnant of a similar core that belonged to a baby planet. Such worlds are known as planetesimals, where temperatures are high enough that denser metals melt and fall to the center.
It is impossible to explore the core of a planet like Earth 1,800 miles below the surface, but going to Psyche could provide more information about what is at the center of our planet.
Or that hypothesis could be completely wrong.
“Psyche could be something entirely different than that,” Dr. Elkins-Tanton said. “I would love to be totally surprised.”
More recent measurements have led to lower estimates of the asteroid’s density, a bit less than four grams per cubic centimeter: still denser than rock and ice, but not as dense as metal. That suggests Psyche is made of metal plus something else: perhaps rock, perhaps empty space.
“My best guess is that it’s more than half metal based on the data that we’ve got,” Dr. Elkins-Tanton said.
If Psyche turns out to be full of valuable metals, it is too far away for anyone to mine using current technologies. Dr. Elkins-Tanton notes that even at its closest, Psyche is some 150 million miles from Earth, which is about five times as far as Earth is from Mars at the two planets’ closest possible approach.
The Psyche mission was scheduled to launch a year ago. The spacecraft had already been shipped to the Kennedy Space Center. But engineers ran out of time to test all of the navigation software before the launch window closed.
Once it launches, the Psyche spacecraft will head toward Mars, swinging by the red planet in May 2026 and using its gravity as a slingshot toward Psyche the asteroid, arriving in August 2029 after traveling 2.2 billion miles.
The spacecraft will spend at least 26 months in orbit around the asteroid studying the body with instruments that include a magnetometer to measure the magnetic fields, a camera to take pictures of the surface and an gamma-ray spectrometer to identify what the asteroid is made of.
In addition, the spacecraft’s radio will be used to measure the asteroid’s gravity by measuring slight shifts in the frequency of the Doppler shift of signal, rising as it moves toward Earth, falling when it is moving away. That could give further insights to its composition and internal arrangement.
