A team of UArizona-led researchers think that the near-Earth asteroid Kamo`oalewa might actually be a miniature moon.
By Mikayla Mace Kelley, University
Communications
November
11, 2021 -- A near-Earth asteroid named Kamo`oalewa could be a fragment of our
moon, according to a paper published today
in 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 UArizona 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.
Researchers aren't yet be sure how the
asteroid may have broken loose from the moon. That's partly 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.
A debate over Kamo`oalewa's origins
between Sharkey and his adviser, UArizona associate professor of lunar and
planetary sciences 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 the asteroid in April 2020 due to a COVID-19
shutdown of the Large Binocular 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," said Malhotra, whose lab
is working on a paper to further investigate the asteroid's origins. "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."
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 for 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.
https://news.arizona.edu/story/near-earth-asteroid-might-be-lost-fragment-moon
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