A team of UArizona-led researchers think that the near-Earth asteroid Kamo`oalewa might actually be a miniature moon.
A near-Earth asteroid named Kamo`oalewa could
be a fragment of our moon, according to a new paper published in Nature
Communications Earth and Environment by a team of astronomers led by the University
of Arizona.
Kamo`oalewa is a quasi-satellite – a subcategory
of near-Earth asteroids that orbit the sun but remain relatively close to Earth.
Little is known about these objects because they are faint and difficult to
observe. Kamo`oalewa was discovered by the PanSTARRS telescope in Hawaii
in 2016, and the name – found in a Hawaiian creation chant – alludes to an offspring
that travels on its own. The asteroid is roughly the size of a Ferris wheel –
between 150 and 190 feet in diameter – and gets as close as about 9 million
miles from Earth.
Due to its orbit, Kamo`oalewa can only be observed
from Earth for a few weeks every April. Its relatively small size means that it
can only be seen with one of the largest telescopes on Earth. Using the UArizona-managed
Large Binocular Telescope on Mount Graham in southern Arizona, a team of
astronomers led by planetary sciences graduate student Ben Sharkey found
that Kamo`oalewa's pattern of reflected light, called a spectrum, matches lunar
rocks from NASA's Apollo missions, suggesting it originated from the moon.
The team can't yet be sure how it may have broken
loose. The reason, in part, is because there are no other known asteroids with
lunar origins.
"I looked through every near-Earth asteroid
spectrum we had access to, and nothing matched," said Sharkey, the paper's
lead author.
The debate over Kamo`oalewa's origins between Sharkey
and his adviser, UArizona associate professor Vishnu Reddy, led to another
three years of hunting for a plausible explanation.
"We doubted ourselves to death," said Reddy,
a co-author who started the project in 2016. After missing the chance to
observe it in April 2020 due to a COVID-19 shutdown of the telescope, the team found
the final piece of the puzzle in 2021.
"This spring, we got much needed follow-up
observations and went, 'Wow it is real,'" Sharkey said. "It's easier
to explain with the moon than other ideas."
Kamo`oalewa's orbit is another clue to its lunar
origins. Its orbit is similar to the Earth's, but with the slightest tilt. Its orbit
is also not typical of near-Earth asteroids, according to study co-author Renu
Malhotra, a UArizona planetary sciences professor who led the orbit
analysis portion of the study.
"It is very unlikely that a garden-variety near-Earth asteroid would spontaneously move into a quasi-satellite orbit like Kamo`oalewa's," she said. "It will not remain in this particular orbit for very long, only about 300 years in the future, and we estimate that it arrived in this orbit about 500 years ago," Malhotra said. Her lab is working on a paper to further investigate the asteroid's origins.
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| An artist impression of Earth
quasi-satellite Kamo`oalewa near the Earth-Moon system. Astronomers
using the Large Binocular Telescope have shown that it might be a lost
fragment of the moon. Credit: Addy Graham/University of Arizona |
Kamo`oalewa is about 4 million times fainter than the faintest star the human eye can see in a dark sky.
"These challenging observations were enabled by
the immense light gathering power, of the twin 8.4-meter telescopes of the
Large Binocular Telescope," said study co-author Al Conrad, a staff
scientist with the telescope.
The study also included data from the Lowell Discovery
Telescope in Flagstaff, Arizona. Other co-authors on the paper include Olga
Kuhn, Christian Veillet, Barry Rothberg and David Thompson
from the Large Binocular Telescope; Audrey Thirouin from Lowell Observatory and
Juan Sanchez from the Planetary Science Institute in Tucson. The research was
funded by NASA's Near-Earth Object Observations Program.
