One of the largest known comets is about to pass through our planet in the only journey through the inner solar system that will make during our lifetime.
Five years ago, the Hubble Space Telescope detected a large comet at the farthest distance ever made, as it approached the sun from the distance between the orbits of Saturn and Uranus. Now, this giant space snowball is reaching its closest passage through Earth this Thursday.
Comet C / 2017 K2 will be at the closest point to us in its current swing through the inner solar system on July 14th. However, even at its closest point, it will still be farther away from us than the average distance between Earth and Mars. This will probably make it difficult to see the comet without at least a small telescope, despite its substantial height.
There is a significant amount of uncertainty at this point about the comet’s core size, according to NASA solar system ambassador Eddie Irrizarry and Kelly Kizer Whitt on EarthSky, with different observations suggesting a range of 11 to 100 miles (18 and 161 kilometers). ample. This means that C / 2017 is among the legitimately large comets and among the handful of largest comets discovered so far, such as Hale-Bopp and Bernardinelli-Bernstein.
The size of the comet’s tail, or coma, is equally massive and unclear. Early observations suggest that the dust and gas trail behind C / 2017 K2 is between 81,000 and 500,000 miles (130,000 and 800,000 kilometers) wide. So between the width of one and six Jupiters, this is a completely epic path.
To see the comet for yourself, you can check out online public observatories like the Virtual Telescope Project that will host review parties this week. You can also put your hands on a telescope and start practicing now to detect objects with an app like Stellarium, which will also be able to point your lenses in the right direction as the comet approaches.
After passing us, the C / 2017 K2 will continue towards the perihelion on December 19, which is its closest step through the sun, before heading back out into deep space. Comets tend to behave unpredictably the closer they get to the sun. This could suddenly become more active and bright, or it could break and disappear from view.
Whatever happens, this visit will probably be our only chance to get to know this comet. Its orbit is so long that it will not return in a few million years.