Is Earth technically a planet? The answer may actually be "no."
A lot of us took it quite personally when Pluto was demoted from a planet to a "dwarf planet." When the International Astronomical Union (IAU) decided to reclassify the ninth rock from the sun and revoke its planetary status, a little part of me died inside.
In order for a celestial body to be a planet, the IAU determined in 2006 that it must meet three criteria:
- It must orbit the sun.
- It must be large enough to be rounded by its own gravity.
- It must have cleared the neighborhood in its orbit.
The reason that Pluto was demoted to a dwarf planet is because the IAU determined Pluto hadn't fully "cleared its neighborhood." That means that Pluto was not gravitationally dominant because there were other bodies in its vicinity exerting gravitational influence.
What is shocking, however, is that by this same definition, Earth might also fail to qualify under the IAU's definition of a planet.
A year ago, the Pan-STARRS 1 asteroid survey telescope in Haleakala, Hawaii discovered something – other than the moon – that was orbiting earth. The discovery was named Asteroid 2016 HO3.
[caption id="attachment_842" align="aligncenter" width="343"]
Depiction of 2016 HO3's orbit around Earth.[/caption]
In the past years, astronomers have learned more about Asteroid 2016 HO3. Paul Chodas, the manager of NASA’s Center for Near-Earth Object (NEO) Studies, explains that “since 2016 HO3 loops around our planet, but never ventures very far away as we both go around the sun, we refer to it as a quasi-satellite of Earth."
Asteroid 2016 HO3 is formally considered a companion
of Earth, but it is technically too distant to be considered a true satellite. So, has Earth "cleared its neighborhood?" Is Earth even a planet?
The IAU's definition requires that in order for something to be a planet, there must be no other bodies of comparable size other than its satellites within its neighborhood. With Asteroid 2016 HO3 being a quasi-satellite, it calls into question whether the same arbitrary rules that doomed Pluto to dwarf planet status also apply to Earth. Definitionally, it seems they do.
Many in the space industry are angry that we're even having this conversation. They believe that Pluto never should have been relegated to dwarf planet status. "It's bull----," Alan Stern, the lead scientist on NASA's New Horizon mission, said in 2015 - nine years after the IAU's first announcement. Even the experts are still furious.
So what happens now? Your guess is as good as ours. It will be up to the International Astronomical Union to decide Earth's fate.
Will they realize that their rules are arbitrary and give both Earth and Pluto planetary status? Or will they double down on their decision and go after Earth next?
Our hearts were broken over Pluto's reclassification. We don't think we're strong enough to see Earth reclassified as well...