When I show people astronomical sights through my telescope, the one view that elicits the most comments is Saturn with its rings. Many times I’ve heard people say “Wow! That’s amazing.” Or, “Oh, that’s not real. You have a picture in there.” Saturn, more than any other common backyard telescope target, looks like the pictures you’ve seen in books.
Saturn
isn’t the only planet with a ring system. Jupiter, Uranus, and Neptune also
have rings but are only visible with very powerful telescopes or spacecraft passing
nearby.
Imagine
the sense of awe if we lived on a planet with rings, something we sometimes see
in science fiction movies. Had you been around on Earth 466 million years ago,
you might have been able to enjoy that very experience. A recent study suggests
that Earth may very well have sported a ring like Saturn.
Planetary
rings are ephemeral. They don’t last forever, although they do exist for
millions of years. The evidence for Earth’s possible ring is circumstantial but
quite intriguing. Starting about 466 million years ago, Earth experienced a
period of enhanced meteor cratering, a period known as the Ordovician impact
spike. During that cratering period, virtually all of the impacts on Earth, centered on a narrow band along the equator. Typically, impacts should occur
randomly over the Earth’s surface.
This
narrow cratering band implies that the objects striking Earth all came from that
area of the sky over the equator. The easiest explanation for such a narrow band of cratering
events along the equator is a ring of debris encircling our planet. If a ring
forms around a planet, it will always settle over the equator.
During the same time frame, sedimentary rocks show a large increase in L chondrite material. L chondrite-type asteroids are common in the asteroid belt. Denizens in the asteroid belt occasionally collide, scattering debris around the solar system.
The researchers, led by Andrew G. Tomkins, a geologist at Monash
University in Australia, suggest that one large fragment came close to Earth,
passing so closely that Earth’s gravity shattered it and the debris formed a
ring.
Based
on the cratering record, the study participants claimed the ring lasted
approximately 40 million years, a typical lifetime for a planetary ring. During
that same period of time, Earth experienced one of its most intense glaciation
events and mass extinctions known as the Hirnantian global icehouse period. The
researchers suggest that shading from the ring decreased solar radiation
reaching the planet’s surface, triggering the short but intense glaciation
period. “The existence of such a ring, forming around 466 million years ago and
persisting for a few tens of millions of years could explain several puzzles in
our planet’s past,” Tomkins wrote.
None
of this evidence is absolute proof that we once had a ring like Saturn’s, but
it is strongly suggestive. More work needs to be done to help corroborate their
conclusion.
Each month, I write an astronomy-related column piece for
the Oklahoman newspaper. After publishing it there, I post that column on my blog page.