Artist’s rendering.

An alien, visiting from another planet, would be forgiven for assuming that, if we did not showcase the sensational trial of a brunette every two years at minimum, the Earth Would Be Engulfed In Flames and Nancy Grace would resume her original form and go rampaging over the mountains, bellowing and devouring cattle raw.

It makes as much sense as the actual explanation.

The sensational trial of Jodi Arias is almost over — all but the sentence, and the shouting, which will continue to echo on cable for a few more days.

It’s reality TV before there was reality TV. It’s a time-honored format.

Every two years, the Old Ones rear up from the dormant volcano where they dwell. Their High Priestess, Nancy Grace, prostrates herself before their altar and promises to find a Sensational Trial on which to feed them. “Preferably a brunette who may have done something awful,” they add. “We digest those better.”

They need these sensational trials, or they will come rampaging over the earth and release another Honey Boo Boo Child. The Casey Anthony verdict had just made its way through the bowels of the Old Ones, and by January they were restless and hungry. Even the bizarre Chris Cuomo interview with Amanda Knox could not appease them. 

Where does the sensation come in? Is it the idea of “a young and beautiful girl who you just otherwise couldn’t imagine could perpetrate the kinds of crimes she was accused of” as Ashleigh Banford said on CNN, who provokes headlines like “Is This The Face of Evil?” Is it the sordid details? Is it the glasses? I understand that every trial is different, in the way the Worst Snowflake of the Century is different, but at a certain point all snowflakes look like snowflakes.

To the alien, this would seem a ritual: Like clockwork, every two years, we become obsessed with the Uniquely Evil Deeds of a Brown-Haired White Woman. We watch the courtroom. Nancy Grace denounces her. We learn the sordid details of her personal life. We stand outside the courthouse and cry and deliver breathless interviews into the camera. We get personally invested to the point that total strangers announce they are “elated” by the decision.

Why is this so riveting? Is it riveting? We didn’t want to know about the “sexcapades” (as Huffington Post describes them) of Jodi Arias before she was accused of murder. But somehow, now that she has been, this is relevant to our interests.

We have a deep craving for details of the lives of other people, but until they either sign up for it by hopping aboard the Reality TV train or doing something so awful that it makes their private lives fair public game, we have to avert our eyes. But the moment they do — we descend like vultures.

It’s like the universe, with its dark matter. There’s the News News, visible and bright on the major channels, and then there’s the Dark News, which accounts for a not-insignificant portion of the gravity of TV. Turn on any TV at any time and you can find a channel where someone is picking apart an ax murder. There are Dateline documentaries about What Really Happened That Fateful Night In July To The Unsuspecting [Name] Family. There is MSNBC’s “Lockup.” There’s the infamous “To Catch a Predator.” There’s regular celebrity and then there’s this weird echelon of criminal celebrity. It’s the headlines from which the ever-popular “Law & Order: SVU” is untimely ripped, and everyone watches that.

Every so often, something pops up from Dark News into News News. Casey Anthony made the jump. So did Amanda Knox and Jodi Arias. Enough people are paying furtive attention that we can admit to paying attention in public. This especially happens during Slow News Months, when no Big National Stories are nudging the Dark News back onto its side of the daytime cable line.

Perhaps Kander & Ebb, in the musical “Chicago,” did the best job of accounting for the strange appeal of these showy trials. Set before the days of cable and Nancy Grace and the News Beast that insisted on being fed hourly with sensational details and side-boob slideshows, they still knew what went into this.

 “Would you please tell the audience… err… the jury what happened?” So says defense lawyer Billy Flynn, to his client accused of murder.

He’s clear-eyed about what makes a sensational trial. When Roxie Hart, accused of killing her lover Fred Casely in a sensational manner, gets acquitted, he notes, You are a phony celebrity. You’re a flash in the pan.” 

“They love me!” Roxie exclaims.

Billy scoffs. “They’d love you a lot more if you were hanged. You know why? Because it would sell more papers!”

And that’s show biz, kid.

For the moment, the Old Ones are appeased and slink back into the earth.

Alexandra Petri writes the ComPost blog, offering a lighter take on the news and opinions of the day.