“Potentially dangerous asteroid” to pass safely through Earth on March 21

The interplanetary intruder will not come closer than 1.25 million kilometers from Earth, but it will present a valuable scientific opportunity for astronomers.

The largest asteroid expected to pass through our planet in 2021 will be at its closest on March 21, offering astronomers a rare opportunity to take a good look at a rocky relic that formed at the dawn of our solar system.

Called 2001 FO32, the near-Earth asteroid will make its closest approach at a distance of about 1.25 million miles (2 million kilometers) – or 5 1/4 times the distance from Earth to the Moon. There is no threat of collision with our planet now or for centuries to come.

“We know very precisely the orbital trajectory of the 2001 FO32 around the Sun, because it was discovered 20 years ago and has been followed since,” said Paul Chodas, director of the Center for Near Earth Object Studies (CNEOS), which is managed by NASAJet Propulsion Laboratory in Southern California. “There is no chance that the asteroid will approach Earth within 1.25 million kilometers.”

However, this distance is close in astronomical terms, which is why 2001 FO32 has been designated a “potentially dangerous asteroid”. CNEOS calculates high-precision orbits for near-Earth objects (NEOs) in support of NASA’s Planetary Defense Coordination Office, relying on ground-based telescopes and radars to help accurately characterize l orbit of each NEO to improve long-term hazard assessments.

During this approach, the FO32 2001 will go at around 124,000 km / h, faster than the speed at which most asteroids encounter Earth. The reason for the asteroid’s unusually fast close approach is its sharply tilted and elongated (or eccentric) orbit around the Sun, an orbit tilted 39 degrees from the Earth’s orbital plane. This orbit brings the asteroid closer to the Sun than Mercury and twice as far from the Sun as March.

As 2001 FO32 makes its journey through the inner solar system, the asteroid picks up speed like a skateboarder rolling on a half moon, then slows down after being sent back into deep space and flipped toward the Sun. It orbits every 810 days (about 2 1/4 years).

After its brief visit, 2001 FO32 will continue its solitary journey, not approaching Earth again until 2052, when it will pass approximately seven lunar distances, or 2.8 million kilometers.

Astronomical geology

Asteroid 2001 FO32 was discovered in March 2001 by the Lincoln Near-Earth Asteroid Research (LINEAR) program in Socorro, New Mexico, and was estimated, based on optical measurements, to be approximately 3,000 feet (1 kilometer) wide. In more recent follow-up observations from NEOWISE, 2001 FO32 appears faint when observed in infrared wavelengths, suggesting that the object is likely less than a kilometer in diameter. Analysis by the NEOWISE team shows that it measures between 1,300 and 2,230 feet (440 to 680 meters) in width.

Even though it is at the smaller end of the scale, 2001 FO32 will still be the largest asteroid to pass this close to our planet in 2021. The last close approach to a particularly large asteroid was that of 1998 OR2 April 29, 2020. While 2001 FO32 is a bit smaller than 1998 OR2, it will be three times closer to Earth.

The March 21 meeting will provide astronomers with the opportunity to better understand the size and albedo of the asteroid (that is, how shiny or reflective its surface is) and a rough idea of ​​its makeup.

This will be achieved, in part, through the use of NASA’s Infrared Telescope Facility (IRTF), a 3.2-meter (10.5-foot) telescope atop Hawaii’s Mauna Kea that will observe the asteroid in the days leading up to the close approach using its workhorse. infrared spectrograph, SpeX. “We’re trying to do geology with a telescope,” said Vishnu Reddy, associate professor at the Lunar and Planetary Laboratory at the University of Arizona in Tucson.

When sunlight hits the surface of an asteroid, minerals in the rock absorb certain wavelengths while reflecting others. By studying the spectrum of light reflected off the surface, astronomers can measure the chemical “fingerprints” of minerals on the asteroid’s surface. “We’re going to use the IRTF to get the infrared spectrum to see its chemical makeup,” Reddy explained. “Once we know this, we can do comparisons with meteorites on Earth to find out what the 2001 FO32 minerals contain.”

For example, if 2001 FO32 were identified as rich in iron, it would mean that it is denser and therefore more massive than a stony asteroid of similar size; observations showing a low albedo surface (meaning it’s dark) may indicate that the asteroid contains a lot of carbon, suggesting that it could be the nucleus of a long-dead comet.

To look closer

In addition, radar observations by the Deep Space Network (DSN) can be made to get a detailed view of the asteroid. An operation of NASA’s Space Communications and Navigation (SCaN) program, the DSN comprises three ground stations – one in California (Goldstone), one in Spain (Madrid) and one in Australia (Canberra). Their satellite dishes can be used to bounce radio signals off 2001 FO32 so that other radio antennas can receive them. Such radar observations can provide additional insight into the asteroid’s orbit, provide a better estimate of its dimensions and rotational speed, and help glimpse surface features (such as large boulders or craters). . They could even reveal any small satellites that could be towed.

“Observations dating back 20 years have revealed that about 15% of near-Earth asteroids comparable in size to 2001 FO32 have a small moon,” said Lance Benner, senior scientist at JPL. “Currently, little is known about this object, so the very close encounter offers an exceptional opportunity to learn a lot about this asteroid.”

Over 95% of near-Earth asteroids the size of 2001 FO32 or larger have been discovered, tracked and cataloged. None of the large asteroids in the catalog stand a chance of impacting Earth in the next century, and it is extremely unlikely that any of the remaining undiscovered asteroids of this size could impact Earth. Still, efforts continue to uncover any asteroids that could pose a risk of impact. The more information there is about these objects, the better prepared mission designers will be to hijack them should any of them threaten Earth in the future.

Meanwhile, amateur astronomers can gather their own information on 2001 FO32. “The asteroid will be the brightest as it moves across the southern sky,” JPL’s Chodas said. “Amateur astronomers in the southern hemisphere and at lower northern latitudes should be able to see this asteroid using medium-sized telescopes with apertures of at least 8 inches at night leading to the closest approach. , but they’ll probably need star maps to find it. “

JPL hosts CNEOS for the NASA Near-Earth Object Observation Program at the NASA Planetary Defense Coordination Office. The University of Hawaii operates the IRTF under contract to NASA. The SpeX instrument was built at the University of Hawaii.