No! This is not earth’s second moon; it’s not even a “mini-moon”
By MUNGAI KIHANYA
The Sunday Nation
Nairobi,
13 October 2024
There are a lot of
stories in the mass media and on the Internet claiming that we have a
second moon that will stay with us until late November this year. As
exciting as that sounds, it is not altogether true: it is a half-truth.
Yes: on 29th September, the Earth captured a rogue space rock
and it will remain bound in the planet’s gravity until 25th
November 2024. But is this rock truly a moon?
Well, this event
brings back memories of the fate of Pluto. Pluto was demoted from being
classified as a planet after astronomers (not astrologers!) agreed on a
common definition of what a planet is – an object the, first, orbits a
star; secondly, is massive enough so that its gravity compresses its
shape into a spheroid; and, third, has swept the vicinity of its orbit
of nearly all other objects of comparable size.
Pluto does not
satisfy the last condition and so, it was removed from the list of
planets of the solar system. Though the definition of a moon is not as
clear as that of a planet, the space rock currently bound to earth’s
gravity (code named, 2024 PT5) is not in orbit around our planet, so it
definitely is not a moon! It just an ordinary asteroid.
Asteroid 2024 PT5 has
come so close to Earth that its trajectory will be bent by about 400
degrees. That is, it will make one swing around the Earth (360 degrees)
and then fly out at about 20 degrees off its original path. In other
words, it will not be captured in an orbit round our planet.
Furthermore, 2024 PT5
is too small to be designated as moon. It is only about 10m wide and
therefore, too small to see – it can only be viewed through a
professional telescope. In fact, by the time it was discovered in
August, it had already been captured by Earth’s gravity and was almost
half-way round its singular circuit around the planet. Our real Moon is
about 3,400km across.
With all the
excitement that this has created, it is now necessary for astronomers to
make an unequivocal definition of what qualifies to be called a moon –
the same way they did with planets. My suggestion would be that it is an
object that goes round a planet in a fixed orbit and is massive enough
for its gravity to compress its shape into a spheroid.
Some people are
calling it a “mini-moon”. I don’t think it qualifies as such; I would
call it a “micro-moon”.
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